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

Abstract

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.

Comparison of aerosol extinction between lidar and SAGE II over Gadanki, a tropical station in India

“…Parameswaran et al (1991) reported an agreement that was satisfactory between lidar and SAGE II with large variability in tropospheric extinction. Aerosol extinctions between lidar and SAGE II compared well in the 17-30 km altitude region after the Mt Pinatubo eruption (Jayaraman et al, 1995). The lidar profiles were found to match fairly well with the SAGE II profiles (version 6.20) when the spatial separation between the instruments was in the order of a few hundreds of kilometres .…”

“…(1) at Trivandrum (Parameswaran et al, 1991) during volcanically quiescent conditions, (2) at Ahmedabad after the Mt Pinatubo volcanic eruption (Jayaraman et al, 1995) and (3) at Gadanki . It is to be noted that, in general, the comparisons between lidar and SAGE II focussed on instrument capabilities and were restricted to a limited number of days in the case of (1) and (2).…”

Spatial and temporal variability of the stratospheric aerosol cloud produced by the 1991 Mount Pinatubo eruption

“…One of them was done under stratospheric aerosol background conditions using data from Trivandrum, India (8.6°N, 77°E) for the first months of 1987 [ Parameswaran et al , 1991]. The other comparison was conducted right after the Mount Pinatubo eruption at Ahmedabad (23°N, 72.5°E) in April 1992 [ Jayaraman et al , 1995].…”

Latitudinal dependence of the seasonal variation of particulate extinction in the UTLS over the Indian longitude sector during volcanically quiescent period based on lidar and SAGE-II observations

“…Pinatubo whenever SAGE II had an occultation pass around the respective lidar location. Most of the earlier inter-comparisons between the aerosol extinction profiles obtained from SAGE-II and lidar (Lu et al, 1997;Russell and McCormick, 1989;Rizi et al, 2000;Yue et al, 1995;Jayaraman et al, 1995) were carried out over the mid and high latitudes when the lower stratosphere was volcanically disturbed. Only very few such comparisons exist over the tropics under volcanically quiescent conditions.…”