The Post-Fuego Stratospheric Aerosol: Lidar Measurements, with Radiative and Thermal Implications

Sulfate aerosol concentrations in the stratosphere have been measured for 11 years (1971–1981) using portions of filters collected by the Department of Energy's High Altitude Sampling Program. Data collected seasonally at altitudes between 13 km and 20 km spanning latitudes from 75°N to 51°S are reported. These data are compared with the reported altitudes of volcanic eruption plumes during the same decade. From this comparison it is concluded that (1) several unreported volcanic eruptions or eruptions to altitudes higher than reported did occur during the decade, (2) the e‐fold removal time for sulfate aerosol from the stratosphere following the eruption of Volcan Fuego in 1974 was 11.2±1.2 months, (3) the volcanic contribution to the average stratospheric sulfate concentration over the decade was greater than 50%, and (4) there may be evidence for an anthropogenic contribution to stratospheric sulfate that increases at the rate of 6 to 8% per year.

supporting

confidence: 89%

A decade of stratospheric sulfate measurements compared with observations of volcanic eruptions

Sedlacek¹,

Mroz²,

Lazrus³

et al. 1983

“…Similar differences between the estimated decay times have been observed earlier, both after the Fuego eruption as well as in the case of El Chichon eruption. In the case of Fuego, the 1/e-folding times for the vertically integrated backscattering coefficient (IBC) and the peak scattering ratio have been 8 and 11 months, respectively [Russell and Hake, 1977]. In the case of El Chichon, the 1/e-folding time for IBC is reported as 11.5 months [Jiiger and Carnuth, 1987].…”

Section: Resultsmentioning

confidence: 99%

Pinatubo volcanic aerosol layer decay observed at Ahmedabad (23°N), India, using neodymium:yttrium/aluminium/garnet backscatter lidar

Jayaraman¹,

Ramachandran²,

Acharya³

et al. 1995

Pinatubo volcanic aerosol layer is studied with a neodymium:yttrium/aluminium/garnet (Nd:YAG) (532 nm) backscatter lidar system at the Physical Research Laboratory, Ahmedabad (23°N, 72.5°E), India, from April 1992 to May 1994. The results obtained on the integrated mass densities and aerosol backscatter from 17 to 30 km show a 1/e‐folding time of 9 months, for the Pinatubo aerosol layer to decay. Calculations show that if the layer decays at the same rate, then it may take about 4.5 years for the stratosphere to attain its background aerosol level over the tropics. However, the peak scattering ratio value shows a longer decay time of 12.5 months as has been reported earlier in the case of Fuego and El Chichon eruptions which could be due to faster removal of particles below the peak altitude. The aerosol size distribution has not undergone any considerable change throughout the decay phase of the layer from 1 year to 3 years after the eruption. Also, about 2 years after the eruption the estimated layer mass and the integrated backscattering coefficient are found similar to the values reported in the case of El Chichon eruption. The results obtained on the aerosol extinction coefficients are found to compare well with Stratospheric Aerosol and Gas Experiment (SAGE) II results.

“…Lidars provide remote, vertically resolved measurements of atmospheric backscatter from both molecules and aerosols at one or more wavelengths. To obtain aerosol backscatter profiles from a lidar requires accounting for three factors which affect the backscattered light received by the lidar telescope: (1) two way light extinction, (2) molecular backscatter, and (3) instrument normalization [e.g., Russell and Hake , 1977]. Molecular backscatter and extinction is typically calculated from pressure/temperature profiles provided by a nearby radiosonde station.…”

Section: Instrumentsmentioning

confidence: 99%

Trends in the nonvolcanic component of stratospheric aerosol over the period 1971–2004

Deshler¹,

Anderson-Sprecher²,

Jäger³

et al. 2006

[1] The six longest records of stratospheric aerosol (in situ measurements at Laramie, Wyoming, lidar records at: Garmisch-Partenkirchen, Germany; Hampton, Virginia; Mauna Loa, Hawaii; São José dos Campos, Brazil, and SAGE II measurements) were investigated for trend by (1) comparing measurements in the 3 volcanically quiescent periods since 1970 using standard analysis of variance techniques, and (2) analyzing residuals from a time/volcano dependent empirical model applied to entire data sets. A standard squared-error residual minimization technique was used to estimate optimum parameters for each measurement set, allowing for first order autocorrelation, which increases standard errors of trends but does not change magnitude. Analysis of variance over the 3 volcanically quiescent periods is controlled by the end points (pre-El Chichón and post-Pinatubo), and indicates either no change (Garmisch, Hampton, São José dos Campos, Laramie-0.15 mm) or a slight, statistically insignificant, decrease (Mauna Loa, Laramie-0.25 mm), À1 ± 0.5% yr À1 . The empirical model was applied to the same records plus 1020 nm SAGE II data separated into 33 latitude/altitude bins. No trend in stratospheric aerosol was apparent for 31 of 33 SAGE II data sets, 3 of 4 lidar records, and in situ measurements at 0.15 mm. For Hampton and Laramie-0.25 mm, the results suggest a weak negative trend, À2 ± 0.5% yr À1, while 2 SAGE II data sets (30-35 km, 30°and 40°N) suggest a positive trend of similar magnitude. Overall we conclude that no long-term change in background stratospheric aerosol has occurred over the period 1970-2004.