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Atmospheric Effects (1995-2001)

The enormous aerosol cloud from the March-April 1982 eruption of Mexico's El Chichón persisted for years in the stratosphere, and led to the Atmospheric Effects section becoming a regular feature of the Bulletin thorugh 1989. Lidar data and other atmospheric observations were again published intermittently between 1995 and 2001; those reports are included below.



Bulletin Reports - Index

Reports are organized chronologically and indexed below by Month/Year (Publication Volume:Number), and include a one-line summary. Click on the index link or scroll down to read the reports.

02/1995 (BGVN 20:02) Lidar data from Russia and Germany

04/1995 (BGVN 20:04) Lidar data from Cuba

07/1995 (BGVN 20:07) Lidar data from Cuba and Germany

10/1995 (BGVN 20:10) Lidar data from Germany and Virginia

02/1996 (BGVN 21:02) Lidar data from Cuba, Germany, and Hawaii; aerosol layer with unknown source

05/1996 (BGVN 21:05) Lidar data from Virginia, Germany, and Cuba

10/1996 (BGVN 21:10) Lidar data from Hampton, Virginia

12/1996 (BGVN 21:12) Lidar data from Germany may suggest an aerosol layer centered at about 19 km

01/1997 (BGVN 22:01) Lidar data from Hampton, Virginia, USA

03/1997 (BGVN 22:03) Lidar data from Cuba, Hawaii, and Virginia

05/1997 (BGVN 22:05) German lidar data from early 1991 through mid-1997

10/1997 (BGVN 22:10) Lidar data from Germany

11/1997 (BGVN 22:11) Volcanic aerosol optical thicknesses since 1960

03/1998 (BGVN 23:03) Lidar data from Germany and Virginia

06/1998 (BGVN 23:06) Lidar data from Hawaii and Germany

11/1998 (BGVN 23:11) Lidar data from Hampton, Virginia, USA

12/1998 (BGVN 23:12) Lidar data from Garmisch-Partenkirchen, Germany

04/1999 (BGVN 24:04) Tracing recent ash by satellite-borne sensors and ground-based lidar

05/2001 (BGVN 26:05) Volcanic aerosol optical thicknesses derived from lunar eclipse observations

12/2001 (BGVN 26:12) Multi-year lidar from Hampton, VA, USA shows peaks and current low



Information is preliminary and subject to change. All times are local (unless otherwise noted)


February 1995 (BGVN 20:02) Citation IconCite this Report

Lidar data from Russia and Germany

Lidar data from Russia during April through December 1994 (table 1) continued to show a volcanic aerosol layer over Obninsk, generally between 14 and 21 km altitude. Throughout most of 1994 (see Bulletin v. 19, no. 4 for January-March 1994 data), backscattering ratios and integrated backscatter for the Nd-YAG wavelength generally remained stable at 1.2-1.4 and 0.18-0.34 x 10-3, respectively. However, after 4 November the backscattering ratio was consistently-3.

Table 1. Lidar data from Russia and Germany showing altitudes of aerosol layers; some layers have multiple peaks. Backscattering ratios are for the Nd-YAG wavelength of 0.53 microns, with equivalent ruby values (0.69 microns) in parentheses for data from Germany. The integrated value shows total backscatter, expressed in steradians^-1, integrated over 150-m intervals from 15-30 km at Obninsk, and over 300-m intervals from the tropopause to 30 km at Garmisch-Partenkirchen.

DATE LAYER ALTITUDE (km) (peak) BACKSCATTERING RATIO BACKSCATTERING INTEGRATED
Obninsk, Russia (55°N, 38°E)
12 Apr 1994 11.3-23.9 (18.7) 1.23 0.22 x 10-3
17 Apr 1994 13.9-16.4 (15.7) 1.32 0.33 x 10-3
17 Apr 1994 16.4-19.3 (18.5) 1.35 --
17 Apr 1994 19.3-24.8 (20.3) 1.33 --
21 Apr 1994 11.8-20.5 (18.4) 1.37 0.33 x 10-3
21 Apr 1994 20.5-23.1 (21.6) 1.34 --
28 Apr 1994 12.1-21.1 (17.5) 1.28 0.23 x 10-3
13 May 1994 13.9-21.2 (19.9) 1.20 0.18 x 10-3
15 May 1994 13.5-17.9 (11.0) 1.26 0.22 x 10-3
15 May 1994 17.9-21.5 (19.7) 1.23 --
16 May 1994 11.6-17.6 (16.6) 1.24 0.22 x 10-3
16 May 1994 17.6-21.4 (19.1) 1.23 --
08 Jun 1994 14.9-21.8 (19.9) 1.24 0.22 x 10-3
28 Jun 1994 15.1-24.5 (18.7) 1.23 0.22 x 10-3
08 Jul 1994 12.4-14.2 (14.0) 1.12 0.23 x 10-3
08 Jul 1994 14.2-25.1 (18.8) 1.24 --
10 Jul 1994 12.0-14.0 (13.7) 1.12 0.23 x 10-3
10 Jul 1994 14.0-25.1 (18.4) 1.24 --
11 Jul 1994 13.0-14.1 (13.7) 1.12 0.24 x 10-3
11 Jul 1994 14.1-26.8 (18.8) 1.25 --
28 Jul 1994 10.5-14.0 (13.1) 1.09 0.23 x 10-3
28 Jul 1994 14.0-24.5 (19.0) 1.26 --
19 Aug 1994 11.5-25.4 (17.2) 1.21 0.21 x 10-3
06 Sep 1994 12.7-25.1 (17.6) 1.33 0.29 x 10-3
15 Sep 1994 12.6-15.5 (14.8) 1.24 0.27 x 10-3
15 Sep 1994 15.5-25.3 (17.6) 1.28 --
07 Oct 1994 13.1-24.8 (15.1) 1.44 0.35 x 10-3
08 Oct 1994 13.0-25.1 (18.8) 1.26 0.25 x 10-3
09 Oct 1994 13.3-25.1 (18.8) 1.25 0.23 x 10-3
10 Oct 1994 10.7-16.1 (14.9) 1.25 0.24 x 10-3
10 Oct 1994 16.1-20.3 (17.6) 1.27 --
24 Oct 1994 13.3-22.7 (19.7) 1.23 0.21 x 10-3
04 Nov 1994 13.1-20.2 (19.6) 1.27 0.25 x 10-3
11 Nov 1994 16.0-30.0 (20.5) 1.14 0.11 x 10-3
05 Dec 1994 16.6-20.6 (19.4) 1.10 0.08 x 10-3
05 Dec 1994 20.6-24.8 (24.1) 1.15 --
10 Dec 1994 17.0-22.1 (19.3) 1.14 0.08 x 10-3
11 Dec 1994 13.3-21.7 (19.0) 1.16 0.12 x 10-3
Garmisch-Partenkirchen, Germany (47.5°N, 11.0°E)
01 Dec 1994 12-31 (17.9) 1.17 (1.4) --
01 Dec 1994 11-30 (22.0) 1.20 (1.5) --
06 Dec 1994 11-30 (18.4) 1.19 (1.5) --
15 Dec 1994 11-30 (18.2) 1.25 (1.6) --
17 Dec 1994 12-29 (16.2) 1.23 (1.6) --
06 Jan 1994 10-30 (21.3) 1.25 (1.6) --
16 Jan 1994 11-29 (21.3) 1.28 (1.6) --
19 Jan 1994 8-28 (18.0) 1.29 (1.7) --
27 Jan 1994 9-26 (19.0) 1.25 (1.6) --
07 Feb 1994 11-27 (18.1) 1.24 (1.6) --

During December through early February 1995, lidar data from Germany revealed the continued presence of an aerosol layer over Garmisch-Partenkirchen. Peak altitude during this period was usually 16-19 km. The backscattering ratio for the Nd-YAG wavelength, 1.2-1.3, has been unchanged since June 1994 (see Bulletin v. 19, nos. 10-11).

In Germany, a secondary peak on 1 December and the above-20-km peaks on 6 and 16 January may have been fresh volcanic aerosols caused by the 19 September eruption of Rabaul or the 1 October eruption of Kliuchevskoi (Bulletin v. 19, nos. 8-9). A secondary peak at ~24 km altitude was also detected on 5 December at Obninsk, Russia.

Information Contacts: Sergey Khmelevtsov, Institute of Experimental Meteorology, Lenin Str. 82, Obninsk, Russia; Horst Jager, Fraunhofer -- Institut fur Atmospharische Umweltforschung, Kreuzeckbahnstrasse 19, D-8100 Garmisch-Partenkirchen, Germany.


April 1995 (BGVN 20:04) Citation IconCite this Report

Lidar data from Cuba

At Camaguey, Cuba, a volcanic aerosol layer was detected at 19-23 km altitude from 18 November through 28 December 1994 (table 2). Backscatter ratios (0.53 µm) were in the 1.26-1.40 range, with integrated backscatter values of 0.18-0.29 x 10-3. These data are similar to those acquired in Cuba during July-October 1994 (Bulletin v. 19, v. 10).

Table 2. Lidar data from Cuba showing altitudes of aerosol layers (bases only). Backscattering ratios are for the Nd-YAG wavelength of 0.53 µm. The integrated value shows total backscatter, expressed in steradians^-1, integrated over 300-m intervals from 16-33 km.

DATE LAYER ALTITUDE (km) (peak) BACKSCATTERING RATIO BACKSCATTERING INTEGRATED
Camaguey, Cuba (21.2°N, 77.5°W)
05 Nov 1994 18.1 (23.2) 1.38 0.22 x 10-3
09 Nov 1994 16.3 (25.0) 1.41 0.28 x 10-3
18 Nov 1994 18.4 (23.8) 1.40 0.25 x 10-3
24 Nov 1994 18.1 (22.6) 1.40 0.29 x 10-3
29 Nov 1994 17.5 (21.6) 1.42 0.29 x 10-3
03 Dec 1994 18.1 (22.0) 1.33 0.23 x 10-3
07 Dec 1994 18.4 (22.0) 1.33 0.18 x 10-3
17 Dec 1994 18.4 (22.6) 1.26 0.19 x 10-3
24 Dec 1994 17.8 (21.1) 1.39 0.22 x 10-3
28 Dec 1994 17.8 (19.0) 1.28 0.20 x 10-3

Information Contacts: Juan Carlos Antuna, Centro Meteorologico de Camaguey, Apartado 134, Camaguey 70100, Cuba.


July 1995 (BGVN 20:07) Citation IconCite this Report

Lidar data from Cuba and Germany

Lidar data from Germany during April-June (table 3) continued to reveal a volcanic aerosol layer centered at 18-20 km altitude. Backscattering ratios again showed a decline from earlier in the year (Bulletin v. 20, no. 2). In Cuba, a volcanic aerosol layer was detected at 20-22 km altitude between 20 May and 28 June. Lidar data (0.53 µm) showed a noticeable decline in both integrated backscattering and backscatter ratios from November-December values (Bulletin v. 20, no. 4).

Table 3. Lidar data from Germany and Cuba, showing altitudes of aerosol layers. Only bases of the layers are shown for Cuba. Backscattering ratios are for the Nd-YAG wavelength of 0.53 µm, with equivalent ruby values (0.69 µm) in parentheses. Integrated values show total backscatter, expressed in steradians^-1, integrated over 300-m intervals from the tropopause to 30 km at Garmisch-Partenkirchen and 16-33 km at Camaguey.

DATE LAYER ALTITUDE (km) (peak) BACKSCATTERING RATIO BACKSCATTERING INTEGRATED
Garmisch-Partenkirchen, Germany (47.5°N, 11.0°E)
03 Apr 1995 10-31 (18.9) 1.26 (1.6) --
24 Apr 1995 cirrus-27 (19.0) 1.20 (1.5) --
02 May 1995 10-24 (18.4) 1.17 (1.4) --
07 May 1995 11-27 (19.1) 1.14 (1.3) --
17 May 1995 cirrus-27 (17.6) 1.26 (1.6) --
22 May 1995 10-30 (18.2) 1.18 (1.4) --
28 May 1995 10-27 (19.7) 1.15 (1.4) --
20 Jun 1995 10-29 (19.4) 1.16 (1.4) --
27 Jun 1995 12-27 (18.1) 1.13 (1.3) --
29 Jun 1995 cirrus-26 (18.3) 1.12 (1.3) --
Camaguey, Cuba (21.2°N, 77.5°W)
20 May 1995 16.0 (20.8) 1.17 1.10 x 10-4
27 May 1995 16.0 (21.7) 1.20 1.39 x 10-4
28 Jun 1995 16.6 (21.1) 1.15 0.99 x 10-4

Information Contacts: Horst Jager, Fraunhofer -- Institut fur Atmospharische Umweltforschung, Kreuzeckbahnstrasse 19, D-8100 Garmisch-Partenkirchen, Germany; Juan Carlos Antuna, Centro Meteorologico de Camaguey, Apartado 134, Camaguey 70100, Cuba.


October 1995 (BGVN 20:10) Citation IconCite this Report

Lidar data from Germany and Virginia

Lidar data from Germany for July and August (table 4) again revealed the presence of a volcanic aerosol layer centered at 17-19 km altitude. Backscattering ratios have decreased since the last reports (Bulletin v. 20, nos. 2 and 7). October lidar data from Hampton, Virginia, showed an aerosol layer at 18-19 km altitude; these values are similar to the previous report (Bulletin v. 19, no. 11). Backscatter data declined to the range of 1.22-1.25 from 1.38-1.50.

Table 4. Lidar data from Germany and Virginia, USA, showing altitudes of aerosol layers. Backscattering ratios are for the ruby wavelength of 0.69 microns. The integrated value shows total backscatter, expressed in steradians^-1, integrated over 300-m intervals from the tropopause to 30 km.

DATE LAYER ALTITUDE (km) (peak) BACKSCATTERING RATIO BACKSCATTERING INTEGRATED
Garmisch-Partenkirchen, Germany (47.5°N, 11.0°E)
07 Jul 1995 11-27 (19.7) 1.12 (1.3) --
19 Jul 1995 12-26 (19.8) 1.13 (1.3) --
21 Jul 1995 13-29 (18.0) 1.12 (1.3) --
26 Jul 1995 11-28 (19.1) 1.13 (1.3) --
31 Jul 1995 13-24 (18.8) 1.09 (1.2) --
03 Aug 1995 12-27 (17.5) 1.12 (1.3) --
Hampton, Virginia (37.1°N, 76.3°W)
23 Mar 1995 12-25 (17.8) 1.36 0.135 x 10-3
04 May 1995 12-25 (18.7) 1.3 0.104 x 10-3
19 Oct 1995 15-30 (18.1) 1.22 0.059 x 10-3
23 Oct 1995 15-30 (18.8) 1.25 0.065 x 10-3

Information Contacts: Horst Jager, Fraunhofer -- Institut fur Atmospharische Umweltforschung, Kreuzeckbahnstrasse 19, D-8100 Garmisch-Partenkirchen, Germany; Mary Osborn, NASA Langley Research Center (LaRC), Hampton VA 23665, USA.


February 1996 (BGVN 21:02) Citation IconCite this Report

Lidar data from Cuba, Germany, and Hawaii; aerosol layer with unknown source

Colorful twilights of long duration have been reported since late September 1995 by observers in England and across the United States in Florida, Maryland, Kentucky, Arkansas, Texas, New Mexico, Colorado, California and Hawaii (F. M. Mims III and others, 1996). This report describes information compiled by Mims and co-authors and includes lidar backscatter data from sites in Cuba, Germany, and Hawaii (figure 1 and table 5). Lidar values are similar to those from earlier in 1995 (Bulletin v. 20, nos. 7 and 10).

Figure with caption Figure 1. Lidar backscattering in 1994 and 1995 for Camagüey, Cuba and Garmisch-Partenkirchen, Germany (see table 1 for details). Data courtesy of Rene Estevan and Horst Jäger; plot courtesy of Forrest Mims III.

Table 5. Lidar data from Cuba and Germany showing altitudes of aerosol layers; some layers have multiple peaks. Backscattering ratios are for the Nd-YAG wavelength of 0.53 microns, with equivalent ruby values (0.69 microns) in parentheses for data from Germany. The integrated value shows total backscatter, expressed in steradians^-1, integrated over 300-m intervals from 16-33 km for Cuba and from the tropopause to 30 km at Garmisch-Partenkirchen. Courtesy of Rene Estevan and Horst Jäger.

DATE LAYER ALTITUDE (km) (peak) BACKSCATTERING RATIO BACKSCATTERING INTEGRATED
Camaguey, Cuba (21.2°N, 77.5°W)
28 Jul 1995 15.1 (21.4) 1.23 1.75 x 10-4
28 Jul 1995 15.1 (22.0) 1.21 --
13 Aug 1995 15.4 (23.8) 1.24 1.79 x 10-4
18 Aug 1995 16.0 (20.5) 1.18 1.04 x 10-4
26 Aug 1995 13.9 (19.9) 1.24 1.58 x 10-4
26 Aug 1995 13.9 (20.0) 1.31 --
30 Aug 1995 14.5 (22.6) 1.26 1.69 x 10-4
15 Sep 1995 16.6 (18.4) 1.20 1.10 x 10-4
15 Sep 1995 16.6 (21.1) 1.17 --
Garmisch-Partenkirchen, Germany (47.5°N, 11.0°E)
10 Aug 1995 10-28 (19.8) 1.13 (1.3) --
04 Sep 1995 11-26 (17.9) 1.11 (1.2) --
09 Sep 1995 10-27 (18.2) 1.14 (1.3) --
18 Sep 1995 11-33 (18.4) 1.14 (1.3) --
26 Sep 1995 13-27 (18.4) 1.17 (1.3) --
09 Oct 1995 14-32 (18.5) 1.13 (1.3) --
15 Oct 1995 11-27 (19.0) 1.10 (1.2) --
23 Oct 1995 13-29 (17.5) 1.13 (1.3) --
05 Nov 1995 9-32 (16.3) 1.14 (1.3) --
11 Nov 1995 11-31 (18.1) 1.11 (1.2) --
20 Nov 1995 11-29 (17.3) 1.16 (1.3) --
01 Dec 1995 8-32 (17.4) 1.13 (1.3) --
09 Dec 1995 11-31 (14.9) 1.14 (1.3) --
28 Dec 1995 10-27 (16.5) 1.11 (1.2) --
Mauna Loa, Hawaii (19.5°N, 155.6°W)
01 Aug 1995 16-27 (22.0) 1.38 0.93 x 10-4
08 Aug 1995 16-27 (22.0) 1.31 0.61 x 10-4
16 Aug 1995 16-27 (22.0) 1.35 0.71 x 10-4
23 Aug 1995 16-27 (22.3) 1.27 0.59 x 10-4
31 Aug 1995 16-27 (22.0) 1.32 0.67 x 10-4
12 Sep 1995 16-26 (21.7) 1.31 0.53 x 10-4
12 Oct 1995 16-26 (23.2) 1.28 0.74 x 10-4

Visual observations from both the ground and commercial aircraft of colorful twilights and a prominent solar aureole suggest a stratospheric cloud now extends from about 20 to 37°N. The origin of the scattering aerosols is presently unknown. Many of the twilights last fall and winter had a duration of 45-60 minutes, which implies an altitude for the aerosols of ~23-35 km. Photographs of the twilights closely resemble images of El Chichón and Pinatubo twilights.

Increased aerosol optical thickness (AOT) has been measured at two sites (Seguin, Texas, and San Diego, California) where extended twilights have been reported. (The optical thickness is equal to the negative natural logarithm of the attenuation of incident light, or Tau = -ln(I/Io), where I and Io are the initial and final light intensity, respectively.) The lowest AOT (1.003 µm) at Seguin, Texas, during winter 1995-96 was 0.03 higher, double the smallest AOT during the previous two winters (figure 2).

Figure with caption Figure 2. Aerosol optical thickness (AOT) at 1.003 microns from 23 September 1989 to 27 March 1996 measured at Seguin, Texas USA. The data show both the seasonal cycle (greatest optical clarity in winter, least in summer) and the volcanic perturbation from Pinatubo. Courtesy of Forrest M. Mims III.

Visual and AOT observations of the aerosol cloud have been corroborated by lidar measurements in Cuba from September-December 1995 (figure 1 and table 5). Several episodes of unusually high total integrated backscatter at 16-33 km occurred during this period. Finally, backscatter data from Germany confirm visual and Sun photometer observations that the new aerosol has not reached 47.5°N.

Reference. Mims, F.M., III, Meinel, C., Roosen, R.G., Russell, R.T., Hawkins, G.P., and Easton, H., 1996, Stratospheric aerosol cloud of unknown origin: unpublished manuscript.

Information Contacts: Horst Jäger, Fraunhofer -- Institut für Atmosphärische Umweltforschung, Kreuzeckbahnstrasse 19, D-8100 Garmisch-Partenkirchen, Germany; Forrest M. Mims III, Sun Photometer Atmospheric Network (SPAN), 433 Twin Oak Rd., Seguin, TX 78155 USA; Rene Estevan and Juan Carlos Antuña, Centro Meteorologico de Camagüey, Apartado 134, Camagüey 70100, Cuba [J.C.A is presently at Univ. Maryland, Dept. of Meteorology, College Park, MD 20742 USA]; John Barnes, Mauna Loa Observatory, P.O. Box 275, Hilo, HI 96720 USA.


May 1996 (BGVN 21:05) Citation IconCite this Report

Lidar data from Virginia, Germany, and Cuba

Lidar data from Virginia, USA, again revealed the presence of a volcanic aerosol layer centered at about 22 km altitude in April and May 1996 (table 6), somewhat higher than the 18-19 km measured during August-December 1995 (Bulletin v. 20, no. 10, and table 6). Over Germany, the aerosol layer was concentrated around 15-20 km altitude during January-April 1996, consistent with measurements made during late 1995 (Bulletin v. 21, no. 2). Backscattering ratios continued to show a decreasing trend at Hampton, and remained stable at Garmisch-Partenkirchen. Data from Cuba during January-April 1996 were highly variable, but still comparable to late-1995 data (Bulletin v. 21, no. 2). The base of the aerosol layer was consistently around 15-17.5 km (dropping to 12.7-13.3 km in April), but the layer peak ranged from 18.1 up to 27.1 km. Backscattering ratios were also variable, with seven measurements showing the expected slow decrease to the 1.11-1.17 range, but with the other six being anomalously high in the 1.35-1.51 range.

Table 6. Lidar data from Virginia, Cuba, and Germany showing altitudes of aerosol layers; some layers have multiple peaks. Backscattering ratios from Virginia are for the ruby wavelength of 0.69 µm; those from Germany and Cuba are for the Nd-YAG wavelength of 0.53 µm, with equivalent ruby values in parentheses for data from Germany. The integrated value shows total backscatter, expressed in steradians-1, integrated over 300-m intervals from 16-33 km for Cuba and from the tropopause to 30 km at Hampton and Garmisch-Partenkirchen. Courtesy of Mary Osborn, Horst Jäger, and Rene Estevan.

DATE LAYER ALTITUDE (km) (peak) BACKSCATTERING RATIO BACKSCATTERING INTEGRATED
Hampton, Virginia (37.1°N, 76.3°W)
04 Dec 1995 13-25 (18.7) 1.22 1.05 x 10-4
25 Apr 1996 15-26 (22.4) 1.14 0.61 x 10-4
21 May 1996 15-28 (22.4) 1.18 0.64 x 10-4
31 May 1996 16-26 (22.0) 1.13 0.32 x 10-4
Garmisch-Partenkirchen, Germany (47.5°N, 11.0°E)
04 Jan 1996 10-32 (19.1) 1.15 (1.30) --
11 Jan 1996 09-31 (19.2) 1.14 (1.28) --
17 Jan 1996 10-30 (16.4) 1.13 (1.25) --
31 Jan 1996 10-28 (19.8) 1.12 (1.23) --
06 Feb 1996 09-28 (15.7) 1.11 (1.21) --
23 Feb 1996 10-27 (14.7) 1.13 (1.25) --
27 Feb 1996 10-27 (18.2) 1.10 (1.20) --
05 Mar 1996 09-31 (17.9) 1.13 (1.25) --
05 Mar 1996 PSC peak at 19.8 -- --
07 Mar 1996 09-28 (17.9) 1.14 (1.27) --
14 Mar 1996 10-31 (15.8) 1.15 (1.29) --
23 Mar 1996 12-28 (18.0) 1.13 (1.25) --
15 Apr 1996 10-27 (17.2) 1.12 (1.24) --
Camaguey, Cuba (21.2°N, 77.5°W)
19 Jan 1996 14.8 (19.9) 1.17 0.55 x 10-4
24 Jan 1996 15.1 (21.7) 1.08 0.12 x 10-4
29 Jan 1996 15.1 (18.7) 1.58 4.90 x 10-4
04 Feb 1996 15.4 (23.5) 1.35 1.40 x 10-4
09 Feb 1996 17.2 (27.1) 1.11 0.26 x 10-4
15 Feb 1996 17.5 (22.3) 1.51 1.00 x 10-4
15 Feb 1996 17.5 (23.8) 1.48 --
24 Feb 1996 17.2 (25.6) 1.11 0.27 x 10-4
02 Mar 1996 16.9 (23.8) 1.16 0.13 x 10-4
18 Mar 1996 15.1 (18.1) 1.17 0.66 x 10-4
31 Mar 1996 15.7 (21.4) 1.16 0.69 x 10-4
05 Apr 1996 12.7 (23.8) 1.36 3.20 x 10-4
12 Apr 1996 13.3 (19.4) 1.27 0.66 x 10-4

Information Contacts: Mary Osborn, NASA Langley Research Center (LaRC), Hampton VA 23665, USA; Horst Jäger, Fraunhofer -- Institut für Atmosphärische Umweltforschung, Kreuzeckbahnstrasse 19, D-8100 Garmisch-Partenkirchen, Germany; Rene Estevan and Juan Carlos Antuña, Centro Meteorologico de Camagüey, Apartado 134, Camagüey 70100, Cuba [J.C.A is presently at Univ. Maryland, Dept. of Meteorology, College Park, MD 20742 USA];


October 1996 (BGVN 21:10) Citation IconCite this Report

Lidar data from Hampton, Virginia

Table 7 lists the 48-inch lidar measurements at 0.69 µm taken with ruby laser in Hampton, Virginia (37.1°N, 76.3°W). An aerosol layer peak was located at 19.3-25.3 km during early October; lidar backscatter ratios were consistent at 1.11-1.16 (table 7).

Table 7. Lidar data from Virginia, USA, showing altitudes of aerosol layers. Backscattering ratios are for the ruby wavelength of 0.69 µm. Integrated values show total backscatter, expressed in steradians-1, integrated over 300-m intervals from the tropopause to 30 km.

DATE LAYER ALTITUDE (km) (peak) BACKSCATTERING RATIO BACKSCATTERING INTEGRATED
Hampton, Virginia (37.1°N, 76.3°W)
04 Oct 1996 15-30 (21.4) 1.13 5.84 x 10-5
11 Oct 1996 14-30 (25.3) 1.16 4.55 x 10-5
16 Oct 1996 15-29 (19.3) 1.11 4.26 x 10-5

Information Contacts: Mary Osborn, NASA Langley Research Center (LaRC), Hampton VA 23665, USA.


December 1996 (BGVN 21:12) Citation IconCite this Report

Lidar data from Germany may suggest an aerosol layer centered at about 19 km

Lidar data for part of 1996 (mid-May through the month of September) over Germany (table 8) indicated a possible aerosol layer centered between 14.7 and 21.6 km altitude. The possible layer's center often resided at ~19 km. The "ci" in Table 9 stands for cirrus. Cirrus in the tropopause region usually obscures the lower boundary of the aerosol layer.

Table 8. Backscattering ratios from German lidar data for the Nd-YAG wavelength of 0.53 µm, 16 May-30 September 1996. The equivalent backscattering ratios for ruby are in parentheses (ruby wavelength, 0.69 µm). Courtesy of Horst Jäger.

DATE LAYER ALTITUDE (km) (peak) BACKSCATTERING RATIO BACKSCATTERING INTEGRATED
Garmisch-Partenkirchen, Germany (47.5°N, 11.0°E)
16 May 1996 11-30 (19.8) 1.11 (1.20) --
22 May 1996 ci-29 (14.7) 1.09 (1.20) --
24 May 1996 12-31 (17.9) 1.11 (1.20) --
31 May 1996 14-38 (20.1) 1.09 (1.20) --
08 Jun 1996 14-27 (19.6) 1.09 (1.20) --
19 Jun 1996 9-27 (18.8) 1.10 (1.20) --
03 Jul 1996 13-28 (19.7) 1.07 (1.20) --
31 Jul 1996 11-30 (19.4) 1.09 (1.20) --
06 Aug 1996 ci-26 (19.5) 1.07 (1.20) --
08 Aug 1996 ci-27 (18.5) 1.06 (1.10) --
18 Aug 1996 12-27 (21.6) 1.06 (1.10) --
23 Aug 1996 11-26 (16.4) 1.06 (1.10) --
26 Sep 1996 12-26 (19.1) 1.06 (1.10) --
30 Sep 1996 12-25 (15.6) 1.07 (1.20) --

Information Contacts: Horst Jäger, Fraunhofer -- Institut für Atmosphärische Umweltforschung, Kreuzeckbahnstrasse 19, D-8100 Garmisch-Partenkirchen, Germany.


January 1997 (BGVN 22:01) Citation IconCite this Report

Lidar data from Hampton, Virginia, USA

Table 9 lists the 48-inch lidar measurements at 0.69 µm taken with a ruby laser in Hampton, Virginia (37.1°N, 76.3°W). An aerosol layer peak was located in the range 13-31 km altitude during early October; lidar backscatter ratios varied between 1.13 and 1.21.

Table 9. Lidar data from Virginia, USA, showing altitudes of aerosol layers. Backscattering ratio are for the ruby wavelength of 0.69 µm. Integrated values show total backscatter, expressed in steradians-1, integrated over 300-m intervals from the tropopause to 30 km.

DATE LAYER ALTITUDE (km) (peak) BACKSCATTERING RATIO BACKSCATTERING INTEGRATED
Hampton, Virginia (37.1°N, 76.3°W)
10 Oct 1996 14-29 (15.5) 1.15 4.94 x 10-5
31 Oct 1996 15-31 (27.5) 1.13 4.45 x 10-5
03 Dec 1996 12-30 (22.3) 1.16 5.58 x 10-5
01 Jan 1997 14-28 (21.1) 1.21 7.34 x 10-5
22 Jan 1997 13-28 (21.2) 1.19 6.41 x 10-5

Information Contacts: Mary Osborn, NASA Langley Research Center (LaRC), Hampton VA 23665, USA.


March 1997 (BGVN 22:03) Citation IconCite this Report

Lidar data from Cuba, Hawaii, and Virginia

Table 10 lists atmospheric data from Cuba, Hawaii, and Virginia. Lidar data from Cuba for 27 September through 19 December 1996 indicated a possible atmospheric layer centered between 13.6 and 20.5 km altitude. Lidar data from Hawaii for 3 July through 18 December indicated a possible atmospheric layer centered between 21.7 and 28.0 km altitude. Lidar data from Virginia (USA) for 26 February through 3 April indicated a possible atmospheric layer centered between 15.5 and 20.5 km altitude.

Table 10. Lidar data collected for Cuba (1996), Hawaii (1996) and Virginia (1997), showing altitudes of aerosol layers. Backscattering ratios from Camagüey are for the Nd-YAG wavelength of 0.53 µm; those from Mauna Loa and Hampton are for the ruby wavelength of 0.69 µm. Integrated values show total backscatter, expressed in steradians-1, integrated over 300-m intervals from 16-33 km for Cuba, 15.8-33 km for Hawaii, and from the tropopause to 30 km for Virginia. For Cuba, only bases of the layers are shown. Courtesy of Rene Estevan Arredenta, John Barnes, and Mary Osborne.

DATE LAYER ALTITUDE (km) (peak) BACKSCATTERING RATIO BACKSCATTERING INTEGRATED
Camaguey, Cuba (21.2°N, 77.5°W)
27 Sep 1996 9.1 (16.3) 1.37 2.28 x 10-4
25 Oct 1996 15.1 (20.5) 1.21 1.00 x 10-4
30 Oct 1996 8.8 (19.0) 1.52 5.40 x 10-4
08 Nov 1996 9.4 (18.7) 1.45 3.54 x 10-4
01 Dec 1996 10.0 (18.1) 1.39 1.05 x 10-4
05 Dec 1996 9.4 (16.0) 1.31 2.14 x 10-4
11 Dec 1996 10.0 (18.1) 1.25 1.91 x 10-4
Mauna Loa, Hawaii (19.5°N, 155.6°W)
03 Jul 1996 16-28 (24.7) 1.22 0.48 x 10-4
10 Jul 1996 16-33 (24.1) 1.34 0.99 x 10-4
17 Jul 1996 6-34 (22.0) 1.29 0.83 x 10-4
01 Aug 1996 16-27 (25.3) 1.18 0.51 x 10-4
07 Aug 1996 16-32 (24.7) 1.36 0.88 x 10-4
20 Aug 1996 17-31 (24.4) 1.34 0.91 x 10-4
28 Aug 1996 16-31 (25.9) 1.28 0.67 x 10-4
04 Sep 1996 17-29 (23.5) 1.24 0.76 x 10-4
11 Sep 1996 17-30 (28.0) 1.40 0.88 x 10-4
18 Sep 1996 17-32 (24.1) 1.29 0.78 x 10-4
27 Sep 1996 17-32 (24.4) 1.28 0.73 x 10-4
02 Oct 1996 17-34 (25.3) 1.36 0.84 x 10-4
10 Oct 1996 16-34 (28.0) 1.38 0.97 x 10-4
17 Oct 1996 16-33 (25.0) 1.38 0.93 x 10-4
31 Oct 1996 16-32 (22.1) 1.30 0.95 x 10-4
27 Nov 1996 15-30 (24.4) 1.40 1.19 x 10-4
04 Dec 1996 17-34 (23.8) 1.28 0.63 x 10-4
10 Dec 1996 16-34 (25.0) 1.37 1.00 x 10-4
18 Dec 1996 16-34 (21.7) 1.45 1.20 x 10-4
Hampton, Virginia (37.1°N, 76.3°W)
26 Feb 1997 11-25 (19.6) 1.18 0.818 x 10-4
13 Mar 1997 11-25 (15.5) 1.15 0.562 x 10-4
21 Mar 1997 11-25 (16.1) 1.15 0.536 x 10-4
25 Mar 1997 13-25 (17.3) 1.16 0.508 x 10-4
03 Apr 1997 10-25 (20.5) 1.17 0.645 x 10-4

Information Contacts: Rene Estevan Arredondo, Centro Meterorologico de Camagüey, Apartado 134, Camaguey 70100, Cuba; John Barnes, Mauna Loa Observatory, P.O. Box 275, Hilo, HI 96720 USA; Mary Osborn, NASA Langley Research Center (LaRC), Hampton, VA 23665 USA.


May 1997 (BGVN 22:05) Citation IconCite this Report

German lidar data from early 1991 through mid-1997

The Pinatubo aerosol layer at Garmisch-Partenkirchen declined to a minimum in the summer of 1996 (figure 3 and table 11). Since then no further decay was observed. The January-June 1997 average value of the integrated backscatter represents ~70% of 1991 pre-Pinatubo value. It is too early, however, to establish the aerosol load observed since mid-1996 as a new stratospheric background.

Figure with caption Figure 3. Graph showing the log of the lidar backscatter versus time at Garmisch-Partenkirchen, Germany for the latter two-thirds of 1991 through mid-1997. The plotted data are preliminary 532 nm integral values of stratospheric aerosol backscatter (integrated from the tropopause or cirrus to the top of the aerosol layer) versus time. Labeled arrows indicate the eruptions of Pinatubo and Kliuchevskoi. Courtesy of Horst Jager.

Table 11. Lidar data from Germany (October 1996-June 1997) and Hawaii (July-December 1996) showing altitudes of aerosol layers. Backscattering rations are for the Nd-YAG wavelength of 0.53 um, with equivalent ruby values in parentheses for data from Germany; those from Mauna Loa are for the ruby wavelength of 0.69 um. The integrated value shows total backscatter, expressed in steradians-1, integrated over 300-m intervals from the tropopause to 30 km at Garmisch-Partenkirchen and 15.8-33 km at Hawaii. The "ci" stands for cirrus clouds; their presence in the tropopause region usually obscures the lower boundary of the aerosol layer. Courtesy of Horst Jager and John Barnes.

DATE LAYER ALTITUDE (km) (peak) BACKSCATTERING RATIO BACKSCATTERING INTEGRATED
Garmisch-Partenkirchen, Germany (47.5°N, 11.0°E)
03 Oct 1996 13-28 (16.3) 1.08 (1.15) --
24 Oct 1996 9-27 (19.8) 1.08 (1.16) --
31 Oct 1996 Ci-26 (15.2) 1.06 (1.12) --
03 Nov 1996 Ci-30 (14.4) 1.06 (1.12) --
09 Nov 1996 12-27 (15.1) 1.08 (1.15) --
22 Nov 1996 9-32 (15.2) 1.08 (1.15) --
04 Dec 1996 Ci-30 (16.7) 1.08 (1.16) --
26 Dec 1996 10-30 (23.3) 1.07 (1.14) --
29 Dec 1996 9-26 (22.5) 1.07 (1.13) --
12 Jan 1997 12-29 (17.5) 1.09 (1.17) --
15 Jan 1997 12-29 (22.1) 1.09 (1.17) --
17 Jan 1997 10-28 (19.8) 1.08 (1.15) --
30 Jan 1997 10-27 (18.7) 1.09 (1.17) --
06 Feb 1997 14-28 (22.5) 1.09 (1.17) --
10 Feb 1997 11-29 (20.3) 1.07 (1.13) --
22 Feb 1997 13-27 (19.8) 1.08 (1.15) --
01 Mar 1997 12-26 (20.9) 1.08 (1.16) --
09 Mar 1997 11-28 (20.1) 1.10 (1.20) --
12 Mar 1997 16-26 (20.6) 1.07 (1.15) --
02 Apr 1997 13-26 (22.7) 1.07 (1.14) --
07 Apr 1997 12-27 (18.7) 1.10 (1.20) --
17 Apr 1997 12-26 (15.9) 1.06 (1.13) --
24 Apr 1997 13-30 (18.5) 1.10 (1.20) --
14 May 1997 Ci-28 (19.7) 1.08 (1.16) --
06 Jun 1997 Ci-25 (19.9) 1.08 (1.16) --
Mauna Loa, Hawaii (19.5°N, 155.6°W) (corrected data)
03 Jul 1996 16-28 (24.7) 1.22 0.48 x 10-4
10 Jul 1996 16-33 (24.1) 1.34 0.99 x 10-4
17 Jul 1996 16-34 (22.0) 1.29 0.83 x 10-4
01 Aug 1996 16-27 (25.3) 1.18 0.51 x 10-4
07 Aug 1996 16-32 (24.7) 1.36 0.88 x 10-4
20 Aug 1996 17-31 (24.4) 1.34 0.91 x 10-4
28 Aug 1996 16-31 (25.9) 1.28 0.67 x 10-4
04 Sep 1996 17-29 (23.5) 1.24 0.76 x 10-4
11 Sep 1996 17-30 (28.0) 1.40 0.88 x 10-4
18 Sep 1996 17-32 (24.1) 1.29 0.78 x 10-4
27 Sep 1996 17-32 (24.4) 1.28 0.73 x 10-4
02 Oct 1996 17-34 (25.3) 1.36 0.84 x 10-4
10 Oct 1996 16-34 (28.0) 1.38 0.97 x 10-4
17 Oct 1996 16-33 (25.0) 1.38 0.93 x 10-4
31 Oct 1996 16-32 (22.1) 1.30 0.95 x 10-4
27 Nov 1996 15-30 (24.4) 1.40 1.19 x 10-4
04 Dec 1996 17-34 (23.8) 1.28 0.63 x 10-4
10 Dec 1996 16-34 (25.0) 1.37 1.00 x 110-4
18 Dec 1996 16-34 (21.7) 1.45 1.20 x 10-4

Correction: Lidar data from Mauna Loa, Hawaii, for July-December 1996 (Bulletin v. 22, no. 3) was incorrect by a factor of 1,000. Corrected data is presented in this issue (table 11).

Information Contacts: Horst Jager, Fraunhofer-Institut fur Atmospharische Umweltforschung, Kreuzeckbahnstrasse 19, D-8100 Garmisch-Partenkirchen, Germany.


October 1997 (BGVN 22:10) Citation IconCite this Report

Lidar data from Germany

The Pinatubo aerosol layer at Garmisch-Partenkirchen declined to a minimum in the summer of 1996 (Bulletin v. 21, no. 12, and v. 22, no. 5). Since then no further decay has been observed. The backscattering ratio during June-October 1997 was consistently in the 1.05-1.08 range (Nd-YAG) with the peak layer altitude at 16.4-19.2 km (table 12).

Table 12. Lidar data from Germany (June-October 1997) showing altitudes of aerosol layers. Backscattering ratios are for the Nd-YAG wavelength of 0.53 µm with equivalent ruby values in parentheses. The integrated value shows total backscatter, expressed in steradians-1, integrated over 300-m intervals from the tropopause to 30 km. The "ci" stands for cirrus clouds; their presence in the tropopause region usually obscures the lower boundary of the aerosol layer. Courtesy of Horst Jager.

DATE LAYER ALTITUDE (km) (peak) BACKSCATTERING RATIO BACKSCATTERING INTEGRATED
Garmisch-Partenkirchen, Germany (47.5°N, 11.0°E)
04 Jun 1997 ci-25 (19.9) 1.08 (1.16) --
29 Jun 1997 9-26 (16.8) 1.08 (1.15) --
11 Jul 1997 13-27 (17.9) 1.06 (1.12) --
15 Jul 1997 12-27 (17.7) 1.07 (1.14) --
20 Jul 1997 10-27 (18.5) 1.07 (1.14) --
30 Jul 1997 13-24 (18.2) 1.05 (1.10) --
04 Aug 1997 12-25 (18.8) 1.06 (1.12) --
18 Aug 1997 12-25 (17.7) 1.05 (1.10) --
08 Sep 1997 14-25 (18.3) 1.08 (1.15) --
26 Sep 1997 14-28 (16.5) 1.08 (1.16) --
06 Oct 1997 13-28 (16.4) 1.07 (1.14) --
17 Oct 1997 14-26 (17.7) 1.06 (1.13) --
28 Oct 1997 11-28 (19.2) 1.08 (1.16) --

Information Contacts: Horst Jager, Fraunhofer-Institut fur Atmospharische Umweltforschung, Kreuzeckbahnstrasse 19, D-8100 Garmisch-Partenkirchen, Germany.


November 1997 (BGVN 22:11) Citation IconCite this Report

Volcanic aerosol optical thicknesses since 1960

Richard A. Keen submitted the following report. About once per year, on average, the moon is eclipsed as it passes into the earth's shadow; at these times it can be used a remote sensor of the globally averaged optical depth of stratospheric aerosols of volcanic origin. Conceptually, the linkage between volcanic aerosols and lunar eclipses is as follows: 1) The moon is visible during total lunar eclipses due to sunlight refracted into the shadow (umbra) by the earth's atmosphere (primarily the stratosphere); 2) Stratospheric aerosols reduce the transmission of sunlight into the umbra; and 3) The path length of sunlight through a stratospheric aerosol layer is ~40x the vertical thickness of the layer. Therefore, the brightness of the eclipsed moon is extremely sensitive to the amount of aerosols in the stratosphere.

Methodology and data reduction. Aerosol optical thicknesses can be calculated for the date of an eclipse from the difference between the observed brightness of the eclipse and a modeled brightness computed for an aerosol-free standard atmosphere, modified by assumed distributions of ozone and cloud. A report on this technique, applied to observations during 1960 through 1982, appeared in Keen (1983); an update following the eruption of Pinatubo was reported in February 1993 (Bulletin v. 18, no. 2).

This report updates the time series from 1960 through the lunar eclipse of 16 September 1997 (figure 4), the last total lunar eclipse until January 2001. Plotted values are actual derived optical depths, modified as described below. Due to the higher concentration of Agung and El Chichón aerosols in the southern and northern hemispheres, respectively, a sampling bias due to the moon's passing though the southern or northern portion of the umbra was removed by using an empirical adjustment factor of 0.8 (thus, if the moon passed south of the earth's shadow axis during an eclipse following Agung, the derived optical thickness was multiplied by 0.8, while the derived value was divided by 0.8 if the moon passed north of the axis).

Figure with caption Figure 4. Volcanic aerosol optical thicknesses derived from 35 total or near-total lunar eclipses during 1960-97. Courtesy of Richard Keen.

No lunar eclipses occurred until 18 months after the June 1991 Pinatubo eruption, while results from Agung and El Chichón indicate that peak optical depths occurred about 9 months after those eruptions. Therefore, for plotting purposes, the time series of optical thicknesses following Pinatubo was extrapolated backwards to a date 9 months after the eruption using a composite decay curve derived from the Agung and El Chichón data. Finally, the global optical depths were set to zero on the dates of the eruptions of Agung, Fuego, and Pinatubo; observed values were near zero for eclipses close to the eruption dates of Fernandina and El Chichón.

Time series. The volcanic eruptions probably responsible for the major peaks in the time series are identified, although the correlation of Fernandina with the 1968 peak is highly uncertain. Comparative maximum global optical thicknesses are: Pinatubo (1991), 0.15; Agung (1963), 0.10; El Chichón (1982), 0.09; Fernandina (1968), 0.06; Fuego (1974), 0.04. The results indicate that the volcanic aerosol veil from Pinatubo disappeared between the eclipses of November 1993 and April 1996, with optical depth probably reaching zero sometime in 1995. A slight increase to an observed value of 0.01 for the September 1997 eclipse is close to the noise level due to the uncertainty in the brightness observations; if real, it could indicate aerosols from the eruption of Soufriere Hills. Interestingly, a similarly slight increase in optical depth in 1979 may have been due to the eruption of Soufriere of St. Vincent.

Acknowledgments. Thanks are due to the following who supplied observations of the four eclipses in 1996-97: K. Hornoch and M. Plsek (Czech Republic), G. Glitscher (Germany), K. Yoshimoto (Japan), K. Al-Tell, N. Abanda, M. Odeh, S. Abdo (Jordan), R. Bouma, G. Comello, H. Feijth, and E. van Dijk (Netherlands), B. Granslo and O. Skilbrei (Norway), C. Vitorino and A. Pereira (Portugal), P. Schlyter (Sweden), R. Pickard, A. Moss, J. Shanklin, and W. Worraker (UK), and D. Green (USA).

Reference. Keen, R., 1983, Volcanic aerosols and lunar eclipses: Science, v. 222, p. 1011- 1013.

Information Contacts: Richard A. Keen, 34296 Gap Road, Golden, CO 80403 USA.


March 1998 (BGVN 23:03) Citation IconCite this Report

Lidar data from Germany and Virginia

Table 13 lists atmospheric lidar data from Hampton, Virginia for 8 April 1997 through 26 February 1998, and from Garmisch-Partenkirchen, Germany for 3 November 1997 to 14 April 1998. The aerosol backscatter measured at Hampton on 26 February 1998 shows a typical winter increase in stratospheric aerosol compared to measurements made the previous summer. The increase from summer to winter is generally a function of the difference in tropopause height between the two seasons. In this case there is a significant decrease in integrated stratospheric aerosol compared to measurements obtained during the winter of 1997 (Bulletin v. 22, nos. 1, 3).

Table 13. Lidar data collected for Virginia (April 1997-February 1998) and Germany (November 1997-April 1998) showing altitudes of aerosol layers. Backscattering rations from Hampton are for the ruby wavelength of 0.69 µm; those from Garmisch-Partenkirchen are for the Nd-YAG wavelength of 0.53 µm, with equivalent ruby values in parentheses. The integrated value shows total backscatter, expressed in steradians-1, integrated over 300-m intervals from the tropopause to 30 km for both Virginia and Germany. Courtesy of Mary Osborne and Horst Jäger.

DATE LAYER ALTITUDE (km) (peak) BACKSCATTERING RATIO BACKSCATTERING INTEGRATED
Hampton, Virginia (37.1°N, 76.3°W)
08 Apr 1997 17-27 (20.5) 1.12 5.02 x 10-5
16 Apr 1997 17-27 (19.6) 1.17 6.90 x 10-5
07 May 1997 17-27 (20.3) 1.14 4.90 x 10-5
22 May 1997 15-28 (20.5) 1.13 4.76 x 10-5
11 Jun 1997 15-25 (20.6) 1.12 3.01 x 10-5
15 Jul 1997 15-27 (18.1) 1.14 3.73 x 10-5
01 Aug 1997 15-28 (23.6) 1.11 3.53 x 10-5
05 Sep 1997 14-30 (21.7) 1.11 4.06 x 10-5
26 Feb 1998 12-28 (16.4) 1.10 4.28 x 10-5
Garmisch-Partenkirchen, Germany (47.5°N, 11.0°E)
03 Nov 1997 13-26 (17.4) 1.07 (1.13) --
08 Nov 1997 10-26 (19.9) 1.06 (1.13) --
10 Nov 1997 9-25 (18.9) 1.08 (1.15) --
19 Nov 1997 10-24 (20.3) 1.06 (1.12) --
27 Nov 1997 10-23 (16.0) 1.07 (1.13) --
09 Jan 1998 10-26 (21.9) 1.08 (1.15) --
30 Jan 1998 11-28 (14.7) 1.07 (1.13) --
13 Feb 1998 12-30 (18.1) 1.08 (1.16) --
18 Feb 1998 12-27 (18.3) 1.09 (1.18) --
10 Mar 1998 11-33 (17.3) 1.10 (1.20) --
25 Mar 1998 10-28 (17.0) 1.05 (1.09) --
14 Apr 1998 11-32 (16.3) 1.07 (1.13) --

A graph of integral stratospheric aerosol backscatter (figure 5) shows how the stratospheric aerosol load had declined by the end of 1997 to pre-Pinatubo values. More observations are needed to decide whether a new background level has been reached or will be reached in the near future.

Figure with caption Figure 5. Graph showing the log of the lidar backscatter versus time at Garmisch-Partenkirchen, Germany for the latter two-thirds of 1991 through end-1997. The plotted data are preliminary 532 nm integral values of stratospheric aerosol backscatter (integrated from the tropopause or cirrus to the top of the aerosol layer) versus time. Labeled arrows indicate the eruptions of Pinatubo and Kliuchevskoi. Courtesy of Horst Jäger.

Information Contacts: Mary Osborn, NASA Langley Research Center (LaRC), Hampton, VA 23665 USA; Horst Jäger, Fraunhofer -- Institut für Atmosphärische Umweltforschung, Kreuzeckbahnstrasse 19, D-82467 Garmisch-Partenkirchen, Germany.


June 1998 (BGVN 23:06) Citation IconCite this Report

Lidar data from Hawaii and Germany

Table 14 lists atmospheric lidar data from Mauna Loa, Hawaii for 2 July 1997 through 21 January 1998, and from Garmisch-Partenkirchen, Germany for 20 April through 24 June 1998. Measurements indicate that the aerosol layer peak location over Hawaii was at a consistently lower elevation in the second half of 1997 (19.2-25.3 km) compared to the second half of 1996 (21.7-28.0 km) (Bulletin v. 22, no. 5). Measurements from Germany showed no significant change compared to earlier in 1998 (Bulletin v. 23, no. 3).

Table 14. Lidar data from Hawaii (July 1997-January 1998) and Germany (April-June 1998) showing altitudes of aerosol layers. Backscattering ratios from Mauna Loa are for the ruby wavelength of 694 nm; those from Garmisch-Partenkirchen are for the Nd-YAG wavelength of 532 nm, with equivalent ruby values in parentheses. Integrated values show total backscatter, expressed in steradians-1, integrated over 300-m intervals from 15.8-33 km for Hawaii, and from the tropopause to 30 km for Germany. Courtesy of John Barnes and Horst Jäger.

DATE LAYER ALTITUDE (km) (peak) BACKSCATTERING RATIO BACKSCATTERING INTEGRATED
Mauna Loa, Hawaii (19.5°N, 155.6°W)
02 Jul 1997 16-28 (23.8) 1.26 0.69 x 10-4
11 Jul 1997 17-29 (18.4) 1.50 0.72 x 10-4
16 Jul 1997 16-28 (23.2) 1.26 0.78 x 10-4
23 Jul 1997 16-29 (22.9) 1.31 0.97 x 10-4
01 Aug 1997 16-27 (19.9) 1.23 0.55 x 10-4
06 Aug 1997 16-28 (19.5) 1.37 0.98 x 10-4
14 Aug 1997 17-28 (22.3) 1.30 0.67 x 10-4
21 Aug 1997 17-30 (22.6) 1.24 0.54 x 10-4
27 Aug 1997 16-27 (21.4) 1.31 0.89 x 10-4
03 Sep 1997 16-28 (24.7) 1.24 0.62 x 10-4
10 Sep 1997 17-28 (25.3) 1.28 0.67 x 10-4
17 Sep 1997 16-27 (25.3) 1.25 0.80 x 10-4
22 Oct 1997 16-27 (23.5) 1.26 0.83 x 10-4
07 Nov 1997 16-29 (21.4) 1.20 0.68 x 10-4
12 Nov 1997 17-27 (19.9) 1.18 0.85 x 10-4
06 Dec 1997 16-28 (24.1) 1.28 1.18 x 10-4
19 Dec 1997 16-27 (19.6) 1.28 0.95 x 10-4
24 Dec 1997 16-28 (20.2) 1.27 0.99 x 10-4
07 Jan 1998 17-28 (19.2) 1.50 1.00 x 10-4
16 Jan 1998 16-29 (19.3) 1.41 1.33 x 10-4
21 Jan 1998 16-28 (20.8) 1.61 1.27 x 10-4
Garmisch-Partenkirchen, Germany (47.5°N, 11.0°E)
20 Apr 1998 11-34 (18.5) 1.06 (1.12) --
23 Apr 1998 13-30 (19.0) 1.06 (1.11) --
29 Apr 1998 11-33 (15.5) 1.06 (1.13) --
07 May 1998 14-33 (18.6) 1.05 (1.10) --
11 May 1998 13-28 (19.4) 1.05 (1.09) --
14 May 1998 12-28 (20.3) 1.05 (1.10) --
20 May 1998 12-27 (19.2) 1.05 (1.10) --
30 May 1998 11-27 (22.5) 1.04 (1.08) --
09 Jun 1998 13-29 (15.8) 1.05 (1.10) --
24 Jun 1998 13-30 (19.4) 1.04 (1.08) --

Information Contacts: John Barnes, Mauna Loa Observatory, P.O. Box 275, Hilo, HI 96720 USA; Horst Jäger, Fraunhofer -- Institut für Atmosphärische Umweltforschung, Kreuzeckbahnstrasse 19, D-82467 Garmisch-Partenkirchen, Germany.


November 1998 (BGVN 23:11) Citation IconCite this Report

Lidar data from Hampton, Virginia, USA

Table 15 lists the ground-based 48-inch lidar measurements at 0.69 µm taken with a ruby laser in Hampton, Virginia (37.1°N, 76.3°W) during 1998. The lowest levels of aerosol loading ever reported in the 24-year lidar record at Hampton were measured during the summer of 1998.

Table 15. Lidar data from Virginia, USA, for April-December 1998 showing altitudes of aerosol layers. Backscattering ratios are for the ruby wavelength of 0.69 µm. The integrated values show total backscatter, expressed in steradians-1, integrated over 300-m intervals from the tropopause to 30 km. Courtesy of Mary Osborne.

DATE LAYER ALTITUDE (km) (peak) BACKSCATTERING RATIO BACKSCATTERING INTEGRATED
Hampton, Virginia (37.1°N, 76.3°W)
03 Apr 1998 13-26 (19.6) 1.09 4.11 x 10-5
07 Apr 1998 12-27 (14.5) 1.10 5.38 x 10-5
13 Apr 1998 15-25 (21.5) 1.06 2.98 x 10-5
20 May 1998 13-28 (25.9) 1.08 3.42 x 10-5
19 Jun 1998 13-23 (20.9) 1.04 1.70 x 10-5
02 Jul 1998 14-29 (18.8) 1.06 1.17 x 10-5
14 Jul 1998 15-29 (18.5) 1.05 1.62 x 10-5
10 Sep 1998 17-30 (27.7) 1.06 0.89 x 10-5
24 Sep 1998 13-29 (16.6) 1.11 2.99 x 10-5
15 Oct 1998 13-33 (14.2) 1.11 4.81 x 10-5
24 Nov 1998 14-29 (17.9) 1.10 3.79 x 10-5
02 Dec 1998 12-27 (18.2) 1.09 3.15 x 10-5

Information Contacts: Mary Osborn, NASA Langley Research Center (LaRC), Hampton, VA 23681 USA.


December 1998 (BGVN 23:12) Citation IconCite this Report

Lidar data from Garmisch-Partenkirchen, Germany

Atmospheric lidar measurements from Germany (table 16) from July through December 1998 showed no significant change compared to levels recorded earlier in 1998 (Bulletin v. 23, no. 6). Layer altitudes were in the 12-29 km range, with peaks at 14.0-21.9 km.

Table 16. Lidar data from Germany (July-December 1998) showing altitudes of aerosol layers. Backscattering ratios are for the Nd-YAG wavelength of 532 nm, with the equivalent ruby values (690 nm) in parentheses. Courtesy of Horst Jäger.

DATE LAYER ALTITUDE (km) (peak) BACKSCATTERING RATIO BACKSCATTERING INTEGRATED
Garmisch-Partenkirchen, Germany (47.5°N, 11.0°E)
29 Jul 1998 14-29 (16.6) 1.05 (1.09) --
06 Aug 1998 12-28 (15.4) 1.06 (1.11) --
19 Aug 1998 12-30 (14.0) 1.06 (1.12) --
26 Aug 1998 12-29 (14.6) 1.07 (1.13) --
09 Sep 1998 13-27 (15.5) 1.10 (1.19) --
22 Sep 1998 15-29 (19.8) 1.04 (1.08) --
25 Sep 1998 12-30 (21.9) 1.04 (1.08) --
13 Oct 1998 11-30 (15.2) 1.06 (1.12) --
16 Oct 1998 12-24 (15.9) 1.04 (1.09) --
18 Nov 1998 11-29 (14.9) 1.06 (1.11) --
08 Dec 1998 12-27 (17.9) 1.08 (1.15) --

Information Contacts: Horst Jäger, Fraunhofer-Institut fuer Atmosphaerische, Umweltforschung, IFU, Kreuzeckbahnstr., 19 D-82467, Garmisch-Partenkirchen, Germany.


April 1999 (BGVN 24:04) Citation IconCite this Report

Tracing recent ash by satellite-borne sensors and ground-based lidar

Observers at the Alaska Volcano Observatory initially inferred that the 19 April Shishaldin plume reached ~13-14 km altitude based on what appeared to be as the most reliable pilot reports (see above and Bulletin v. 24, no. 3). Yet, one pilot reported the plume to 18.3 km altitude and satellite data suggested similar altitudes. Through at least late May, scientists continued to detect and track stratospheric aerosols. At the time of this writing we have learned of successful satellite detection by GOES 10, the Total Ozone Mapping Spectrometer (TOMS), Stratospheric Aerosol and Gas Experiment (SAGE II), and the Polar Ozone and Aerosol Measurement (POAM). Ground-based lidar also detected presumed Shishaldin aerosol layers far from the source.

GOES observations. GOES 10 data portrayed early images of the plume (figure 6). According to Dave Schneider, thermal split-window imagery showed curiously little evidence of the plume in the stratosphere. Detection conditions were non-ideal: a warmer stratospheric cloud (the plume) overlying a colder tropospheric cloud deck. He also commented on a lack of evidence for ash at lower levels and wondered what role sulfate may have played.

Figure with caption Figure 6. Detailed view of the spreading eruption cloud from Shishaldin on 19 April, taken from a series of images taken by the GOES 10 satellite (channel 1). Unimak Island is outlined. The top frame was imaged at 1200; the following frames at subsequent half-hour increments. The cloud labeled "A" was at higher altitude and moved N; cloud "B" was at lower altitude and moved S. Courtesy of NOAA/NESDIS.

TOMS observations. The TOMS instrument rides aboard NASA's Earth Probe satellite and collects information about airborne gases and particles, including ozone, SO2, and volcanic ash. TOMS passed over Shishaldin at 2142 GMT on 19 April, two hours after the eruption began as a small white plume in the GOES images. Thus, TOMS captured an early stage of the event while the eruption column was actively growing. This early post-eruption data reflected very high concentrations of SO2 and ash in a pixel over the volcano and smaller amounts in two adjacent pixels (unshaded boxes, figure 7). The TOMS images can now retrieve ash as well as SO2 concentrations; the dense 19 April plume, however, was not conducive to realistic SO2 measurement.

Figure with caption Figure 7. TOMS measurements of SO2 near Alaska on 19 April (unshaded boxes, no scale) and 20 April 1999 (shaded boxes, see scale at right) with respect to local coastal margins (lines) and Shishaldin volcano (triangle). For 20 April, shaded boxes (pixels) indicate SO2 gas concentrations of up to 40 milliAtm · cm. Each pixel represents a footprint of TOMS (about 40 x 40 km) containing SO2. The total SO2 depicted in the 20 April image, obtained by summing the pixels, was 20 ktons. (TOMS Orbits 15142 and 15168.) Courtesy of Arlin Krueger and Steve Schaefer, NASA/GSFC.

On 20 April the Shishaldin cloud was still found close to the volcano as an arc-shaped plume of SO2 (figure 7) to the N of and disconnected from the volcano. However, no detectable ash remained in the plume. This dispersed cloud was used to determine that the mass of SO2 in the eruption was 20 ktons. Traces of this SO2 cloud still remained on 21 April after drifting slightly to the N, but were gone on 22 April.

POAM III and SAGE II satellite observations. As discussed on their web site (NRL, 1999) the POAM instrument was developed by the U.S. Naval Research Laboratory (NRL) to measure the vertical distribution of atmospheric ozone, water vapor, nitrogen dioxide, aerosol extinction, and temperature. Solar extinction by the atmosphere is measured using the solar occultation technique; the sun is observed through the Earth's atmosphere as it rises and sets as viewed from the satellite. POAM data on stratospheric aerosols provide information on how the aerosol burden varied with altitude, latitude, season, and annually in a record going back over 3 years. The data have good vertical resolution (1 km), wide geographic coverage, and dense sampling in the polar regions over the latitude range 55°N-71°N. The following discusses data collected by the instrument's latest version (POAM III). SAGE II, another very similar satellite-based, limb-profiling technique has also contributed data.

As shown on figures 8 and 9, trajectory modeling and observational data from POAM III and SAGE II indicated that air parcels moving away from the eruption column at different altitudes took very different paths during the days following the eruption. The forward trajectory model (figure 8) shows strong correspondance with those run independantly by Barbara Stunder at the same altitudes. The modeling indicated that the part of the plume at ~12 km altitude first moved slightly SW, then E, then NE, and finally ESE. Modeling also indicated that the part of the plume at ~18-19 km altitude moved N and varying amounts to the E. In accord with this, high altitude volcanic aerosol material was detected N of 70°N latitude on 23 April by SAGE II. Finally, the modeling indicated that the part of the plume at ~14-16 km altitude branched away from the higher altitude material and began heading E. On 23 April the plume was observed on a POAM III profile (figures 8 and 9).

Figure with caption Figure 8. Simulated air parcel trajectories that originated at Shishaldin on 19 April (squares), and profiles actually observed by POAM III (open circles). The figure illustrates stratospheric circulation and observations during 9 days beginning at 2000 GMT on 19 April and ending at 2000 GMT on 28 April. The trajectory paths were estimated from the motion of their respective associated air parcels at the indicated altitudes; each successive square indicates the results of 24 hours movement. The three aerosol layers sensed by POAM III limb profiling are depicted as circles that have these dates, center coordinates, and altitudes: 23 April at 62.7°N, 197.1°W, 15 km altitude; 25 April at 62.4°N, 207.9°W, 14 km altitude; and 27 April at 62.0°N, 218.7°W, 13 km altitude. Courtesy of Mike Fromm, NRL.
Figure with caption Figure 9. POAM III aerosol extinction ratios on 23, 25, and 27 April. The peaks are due to volcanic aerosols from Shishaldin. The measurement locations are given in the caption for figure 12. Normal background ratios are 1-2. Courtesy of Mike Fromm, NRL.

Figure 9 illustrates aerosol extinction ratios for the aerosol layers seen on 23, 25, and 27 April (circles, figure 8). The peak values shown in figure 9 lie 3-4 standard deviations above the normal background. Anomalously high extinction ratios in the lower stratosphere such as these continued well into May. The plot indicates the plume's height progressively decreased during the course of the three observations, descending from altitudes of ~15 to ~13 km, implying that the volcanic particulate settled out at roughly 0.5 km per day.

Figure 10 illustrates the POAM III results for several weeks following the 19 May Shishaldin eruption. It maps the location of all available POAM profiles (+ symbols) and 14 profiles with varying loads of enhanced stratospheric aerosols (circles). Larger circles indicate larger aerosol loads; more specifically, the circle sizes vary in proportion to the peak aerosol enhancement, determined in relation to the standard deviation of the aerosol extinction ratio in relevant background conditions. The altitudes of peak extinctions varied from 12-15 km.

Figure with caption Figure 10. A polar orthographic projection showing POAM III profiles taken 23 April-11 May 1999. The locations of all possible profiles during the period appear as crosses. The locations of 14 profiles with enhanced stratospheric extinction appear as open circles (labeled with their observation dates). Circle sizes vary in proportion to the peak aerosol enhancement (see text). In back-trajectory models, the profiles with starred dates can be traced back to Shishaldin on 19 April (see text). The map's line-spacings are as follows: latitude, 10°; longitude, 30°. Courtesy of Mike Fromm, NRL.

Looked at on the scale of weeks after the eruption, the atmospheric circulation carried 19 April eruptive products towards the W. For the starred profiles on figure 10, isentropic (constant entropy, which assumes conservation of potential temperature) modeling of back trajectories strongly suggested Shishaldin as the source. POAM III continued to detect enhancements of aerosols in the lowest stratosphere at least until 23 May. The latitudes of the profile's center points moved gradually from about 62°N in late April to 57°N in late May.

Attempts to link additional POAM III observations (those that lack stars) with Shishaldin through isentropic trajectory analysis is in progress, but thus far some of them have failed to lead either back to Shishaldin or to another clear source. Around 5-6 May, for example, two stratospheric aerosol layers resided over or near Hudson Bay, Canada and were also not traceable to Shishaldin in trajectory models. As for another layer at that time, S of Iceland, the models indicate a likely source at the eruption.

Ground-based lidar observations. Lidars (light radars), which measure the amount of backscattered laser energy due to plume and atmospheric conditions (Jørgensen and others, 1997), detected aerosol layers over Germany, Virginia, and Greece. Beginning on the evening of 6 May, Horst Jäger detected a stratospheric layer while profiling with a 532-nm wavelength lidar operated in Garmisch-Partenkirchen, Germany (47.5°N, 11.0°E). His 6 May data showed a small but pronounced peak in the scattering ratio (figure 11). The source of the anomaly was between 15.1 and 15.4 km altitude, well above the estimated maximum altitude of the local troposphere (11.4 km, as determined by a midnight radiosonde from Munich). A maximum scatter ratio of 1.35 occurred at 15.2 km.

Figure with caption Figure 11. Lidar backscatter ratios as a function of height as measured from the 532-nm lidar at Garmisch-Partenkirchen, Germany on 16 May 1999. Courtesy of Horst Jäger.

On 9 May the atmosphere lacked detectible layers in the expected altitude region. On 16 May the lidar achieved maximum scatter ratios of 1.1-1.2 at 14.3, 15.6, 16.3, and 17.3 km. Thus, over Germany, the layers did not form a major perturbation to the stratosphere; these faint backscatters became prominent only because of the low aerosol background during the times of measurement.

The altitude and timing of the peak in German lidar suggested a link to the 19 April Shishaldin eruption plume. The last eruption to produce similar results at the Garmisch-Partenkirchen site was the October 1994 eruption of Kliuchevskoi (Bulletin v. 19, no. 10). That plume reached heights of 25 km.

At Hampton, Virginia, ground-based 694-nm lidar also showed high-altitude peaks (table 17). Measurements there on 11 May detected a diffuse layer (with a peak ratio of 1.17) that was narrow (~1 km thick) and located at 16.9 km altitude, well above the tropopause height. Measurements on 21 May also disclosed two narrow layers. One had a peak ratio of 1.10 at 17.5 km; the other, a peak ratio of 1.19 at 14.5 km. The presence of particles at this height are generally considered to be associated with an eruption; the timing of these observations suggested the layers were due to the 19 April Shishaldin eruption. This may imply that the erupted aerosols had reached mid-latitudes during the month following the eruption.

Table 17. Lidar data from Virginia, USA, for February-May 1999 showing altitudes of aerosol layers. Backscattering ratios are for the ruby wavelength of 0.69 µm. The integrated values show total backscatter, expressed in steradians-1, integrated over 300-m intervals from the tropopause to 30 km. Courtesy of Mary Osborne.

DATE LAYER ALTITUDE (km) (peak) BACKSCATTERING RATIO BACKSCATTERING INTEGRATED
Hampton, Virginia (37.1°N, 76.3°W)
11 Feb 1999 11-27 (23.5) 1.10 5.03 x 10-5
23 Feb 1999 10-27 (24.1) 1.09 5.93 x 10-5
05 Mar 1999 09-25 (10.7) 1.11 6.61 x 10-5
14 Apr 1999 15-27 (22.1) 1.09 2.49 x 10-5
11 May 1999 12-26 (16.9) 1.17 4.72 x 10-5
21 May 1999 13-27 (14.5) 1.19 4.48 x 10-5

Commenting on research conducted on the Mediterranean island of Crete (35°30'N, 23°43'E), Christos S. Zerefos reported that the portable VELIS lidar instrument of Gian P. Gobbi also detected an aerosol layer during 10-13 May. Profiles disclosed increased aerosols at 15-16 km altitudes. Aerosols were seen again on 14 May, but they were not detected on 15 May. The optical depth at 532 nm was at most 0.02.

Conclusions. The 19 April Shishaldin eruption provided a modest injection to ~17-19 km altitude and a TOMS estimate the next day found ~20 kt of SO2 . In trajectory models, components of the plume at various altitudes moved away from the source in 3 branches; POAM III profiles on the ENE-directed path showed the plumes there decreased in altitude with time. Trajectory models have yet to confirm that several POAM III profiles came from the Shishaldin eruption and at this point their source remains ambiguous. The exact trajectories that presumably carried the Shishaldin aerosols over the German, Crete, and Virginia lidar systems have yet to be either consistently traced or modeled.

References. Hans, E., Jørgensen, H.E., Mikkelsen, T., Streicher, J., Herrmann, H., Werner, C., and Lyck, E., 1997, Lidar calibration experiments, Applied Physics B, Lasers and optics, v. 64, no. 3, Springer-Verlag, p. 355-61.

F. Congeduti, F. Marenco, E. Vincenti, P. Baldetti, and G.P. Gobbi, 1998, The new transportable lidar facilities at IFA: 9-eyes and VELIS, in Proceedings of the Workshop onSynergy of Active Instruments in the Earth Radiation Mission,M. Quante and others (eds.), http://aragorn.gkss. de/deutsch/Radar/workshop_papers.html

Naval Research Lab, 1999, Remote Sensing Division, Remote Sensing Physics Branch, Middle Atmospheric Physics Section, POAM Home page, http://wvms.nrl. navy.mil/POAM/poam.html.

Lidar Researchers Directory (including a bibliography produced by NASA) URL: http://arbs8.larc.nasa.gov/lidar/directory.html.

Sparks, R.S.J., Bursik, M.I., Carey, S.N., Gilbert, J.S., Glaze, L.S., Sigurdsson, H., and Woods, A.W., 1997, Volcanic plumes: John Wiley and Sons, Ltd., ISBN-0-471-93901-3, 574 p.

Information Contacts: Horst Jäger, Fraunhofer - Institut für Atmosphärische Umweltforshung (IFU), Kreuzeckbahnstrasse 19, D-82467 Garmisch-Partenkirchen, Germany; Mike Fromm, Computational Physics, Inc., 2750 Prosperity Avenue, Fairfax, Virginia, 22031 USA; Naval Research Laboratory, 4555 Overlook Ave. SW, Washington, DC 20375 (URL: http://www.nrl. navy.mil); Barbara Stunder, U.S. National Oceanic and Atmospheric Administration (NOAA), Air Resources Laboratory, SSMC3, Rm. 3151 (R/E/AR), 1315 East-West Highway, Silver Spring, MD 20910, USA; Mary Osborn, NASA Langley Research Center (LaRC), Hampton, VA 23681 USA; Christos S. Zerefos, Aristotle University of Thessaloniki, Physics Department, Laboratory of Atmospheric Physics, Campus Box 149, 540 06 Thessaloniki, Greece; Arlin J. Krueger and Steve Schaefer; TOMS Instrument Scientists, Code 916, Building 33, Room E413, Goddard Space Flight Center, Greenbelt, MD 20771, USA, Dave Schneider, Alaska Volcano Observatory (see Shishaldin).


May 2001 (BGVN 26:05) Citation IconCite this Report

Volcanic aerosol optical thicknesses derived from lunar eclipse observations

The following report, discussing volcanic aerosol optical thicknesses since 1960 as derived from lunar eclipse observations, was provided by Richard Keen. About once per year, on average, the moon is eclipsed as it passes into the Earth's shadow; at these times the moon can be used as a remote sensor of the global average optical depth of stratospheric aerosols of volcanic origin. Volcanic aerosols and lunar eclipses can be linked because the moon is visible during total lunar eclipses due to sunlight refracted into the shadow (umbra) by the Earth's atmosphere (primarily by the stratosphere), stratospheric aerosols reduce the transmission of sunlight into the umbra, and the path length of sunlight through a stratospheric aerosol layer is about 40 times the vertical thickness of the layer. Therefore, the brightness of the eclipsed moon is extremely sensitive to the amount of aerosols in the stratosphere.

Methodology and data reduction. Aerosol optical thicknesses can be calculated for the date of an eclipse from the difference between the observed brightness of the eclipse and a modeled brightness computed for an aerosol-free standard atmosphere, modified by assumed distributions of ozone and cloud. Details of this technique, applied to observations during 1960 through 1982, appear in Keen (1983); updates following the eruption of Pinatubo appeared in February 1993 (Bulletin v. 18, no. 2) and November 1997 (Bulletin v. 22, no. 11). This report updates the time series through the lunar eclipse of 9 January 2001, the last total lunar eclipse until May 2003.

Figure 12 plots the global optical thicknesses derived from 38 total or near-total lunar eclipses during 1960-2001. Results from eight eclipses during 1880-1888 have been added to figure 12 to allow comparison with the effects of Krakatau in 1883. The plotted values are actual derived optical depths, modified as follows: Due to the higher concentration of aerosols from Agung and El Chichón in the Southern and Northern Hemispheres, respectively, a sampling bias due to the moon's passing though the southern or northern portion of the umbra was removed by using an empirical adjustment factor of 0.8 (thus, if the moon passed S of the Earth's shadow axis during an eclipse following an Agung eruption, the derived optical thickness was multiplied by 0.8, while the derived value was divided by 0.8 if the moon passed N of the axis). Furthermore, no lunar eclipses occurred until 18 months following the Pinatubo eruption in June 1991, while results from Agung and El Chichón indicate that peak optical depths occurred about 9 months after those eruptions. Therefore, for plotting purposes on figure 12, the time series of optical thicknesses following Pinatubo was extrapolated backwards to a date 9 months after the eruption using a composite decay curve (with a time constant of 1.92 years) derived from the Agung and El Chichón eclipse data. Finally, the global optical depths were set to zero on the dates of the eruptions of Krakatau, Agung, Fuego, and Pinatubo; observed values were near zero for eclipses close to the dates of the eruptions of Fernandina and El Chichón.

Figure with caption Figure 12. Global optical thicknesses derived from 38 total or near-total lunar eclipses during 1880-1888 and 1960-2001. Details about the methodology and data reduction used to construct this figure are in the report text. Courtesy of Richard Keen.

The time series. The volcanic eruptions probably responsible for the major peaks in the times series are identified, although the identification of Fernandina with the 1968 peak is highly uncertain. Comparative maximum global optical thicknesses are: Pinatubo (1991), 0.15; Krakatau (1883), 0.13; Agung (1963), 0.10; El Chichón (1982), 0.09; Fernandina (1968), 0.06; Fuego (1974), 0.04.

The results indicate that the volcanic aerosol veil from Pinatubo disappeared between the eclipses of November 1993, and April 1996, with optical depth probably reaching zero sometime in 1995. Since 1995, optical depths have stayed near zero ( ± 0.01), indicating no further major injections of volcanic aerosols into the stratosphere. However, slight increases to observed values slightly above 0.01 in 1979 and in late 1997 are close to the noise level due to the uncertainty in the brightness observations; if real, they could indicate aerosols from the eruptions of Soufriere St. Vincent (1979) and Soufriere Hills on Montserrat (1997).

Acknowledgments. Thanks are due to the following observers who supplied observations of the three eclipses in the 2000-2001 series: C. Drescher, F. Farrell, M. Matiazzo, A. Pearce, and D. Seargent (Australia), W. de Souza and J. Aguiar (Brazil), J. Finn (Canada), K. Hornoch (Czech Republic), A. Shahin (Dubai, United Arab Emirates), G. Glitscher (Germany), N. Abanda, S. Abdo, W. Abu Alia, E. Al-Ashi, H. Al-Dalee', A. Al-Niamat,K. Al-Tell, and M. Odeh (Jordan), R. Bouma (Netherlands), B. Granslo and O. Skilbrei (Norway), A. Pereira and C. Vitorino (Portugal), J. Atanackov and J. Kac (Slovenia), T. Cooper (South Africa), T. Karhula and P. Schlyter (Sweden), R. Eberst and A. Pickup (UK), R. Keen, T. Mallama, and J. Marcus (USA).

References. Keen, R., 1983, Volcanic aerosols and lunar eclipses: Science, v. 222, p. 1011-1013.

Information Contacts: Richard A. Keen, Program for Atmospheric and Oceanic Sciences (PAOS) , 311 UCB, University of Colorado, Boulder, CO 80309 USA.


December 2001 (BGVN 26:12) Citation IconCite this Report

Multi-year lidar from Hampton, VA, USA shows peaks and current low

Despite their infrequent recent reporting in the Bulletin, lidar measurements remain relevant when discussing the atmospheric impact of volcanic eruptions. As discussed below, following the large-scale atmospheric perturbation caused by Pinatubo, smaller atmospheric perturbations have been infrequent, but the eruption of Shishaldin in April 1999 produced aerosol layers that were detected in North America and Europe (Bulletin v. 24, no. 4).

Reports about atmospheric effects of volcanic activity were last provided as follows: Bulletin v. 26, no. 5, "Volcanic aerosol optical thicknesses derived from lunar eclipse observations;" Bulletin v. 24, no. 4, "Tracing recent ash by satellite-borne sensors and ground-based lidar;" Bulletin v. 23, no. 12, "Lidar data from Garmisch-Partenkirchen, Germany;" and Bulletin v. 23, no. 11, "Lidar data from Hampton, Virginia, USA."

NASA lidar measurements at Virginia, USA. Mary Osborn provided measurements from the 48-inch ground-based lidar system at NASA Langley Research Center (table 18) since May 1999. All measurements were taken at a wavelength of 694 nm. Their 48-inch lidar system was out of commission for ~8 months in late 1999 and early 2000, as they used some of its components to conduct the SAGE III Ozone Loss Validation Experiment (SOLVE). That campaign took place during November 1999-March 2000 based out of Kiruna, Sweden.

Table 18. Lidar data from Virginia, USA, for May 1999-December 2001 showing altitudes of aerosol layers. Backscattering ratios are for the ruby wavelength of 0.69 µm. The integrated values show total backscatter, expressed in steradians-1, integrated over 300-m intervals from the tropopause to 30 km. Courtesy of Mary Osborn.

DATE LAYER ALTITUDE (km) (peak) BACKSCATTERING RATIO BACKSCATTERING INTEGRATED
Hampton, Virginia (37.1°N, 76.3°W)
28 May 1999 15-26 (11.0) 1.14 5.28 x 10-5
24 Sep 1999 12-28 (20.3) 1.09 2.93 x 10-5
09 May 2000 16-27 (20.5) 1.08 2.65 x 10-5
08 Sep 2000 14-30 (20.5) 1.08 2.06 x 10-5
12 Oct 2000 15-28 (17.5) 1.08 2.72 x 10-5
20 Oct 2000 14-30 (17.5) 1.12 5.65 x 10-5
30 Oct 2000 12-30 (28.6) 1.12 6.31 x 10-5
27 Feb 2001 12-28 (22.1) 1.12 4.97 x 10-5
01 May 2001 15-27 (19.4) 1.09 2.26 x 10-5
24 May 2001 17-28 (21.8) 1.09 3.28 x 10-5
07 Sep 2001 15-28 (17.0) 1.11 2.88 x 10-5
04 Oct 2001 15-30 (16.9) 1.08 2.38 x 10-5
16 Oct 2001 15-30 (17.5) 1.08 2.36 x 10-5
07 Nov 2001 12-29 (18.5) 1.08 3.56 x 10-5
22 Nov 2001 13-30 (18.8) 1.10 5.01 x 10-5
04 Dec 2001 12-28 (24.8) 1.12 4.85 x 10-5

Figure 13 presents an overview of stratospheric integrated aerosol backscatter since 1974. A slight increase in stratospheric integrated backscatter occurred during late 1998-99, at least partly attributed to the Shishaldin event and several smaller eruptions. After that, the stratospheric integrated backscatter returned to the "background" aerosol loading measured in 1978-1979. Although the current level of stratospheric aerosol loading remains low, another major volcanic eruption could change the situation quite suddenly.

Figure with caption Figure 13. A plot of the 48-inch lidar data versus time showing the stratospheric integrated aerosol backscatter measured since 1974. Important volcanic eruptions that may have led to increased northern mid-latitude aerosol loading are noted on the time axis. Courtesy of Mary Osborn.

Information Contacts: Mary Osborn, NASA Langley Research Center (LaRC), MS 475, Hampton, VA 23681, USA.