Earth Observation Data Group

Abstract:

Aerosol data obtained by the advanced very high resolution radiometer on NOAA 11, the improved stratospheric and mesospheric sounder on the upper atmospheric research satellite, one airborne lidar system, and several ground-based lidar systems up to 2-1/2 years after the eruption of Mount Pinatubo are used to study stratospheric dynamics. In particular, this study focuses on the tropical stratospheric reservoir and transport from it to northern midlatitudes following the eruption of Mount Pinatubo. This includes: The build-up and removal rates for sulfate aerosol, the position and motion of the center of the reservoir, and the position and width of its boundaries at altitudes of the volcanic aerosols. Ozone data from the total ozone mapping spectrometer were also used to study the position and width of the reservoir boundaries. In addition, ground-based lidar stratospheric aerosol data are used to study aerosol transport from the reservoir to the northern hemisphere as it relates to winds in the tropical stratosphere. Finally, historical in situ and satellite data were used to examine how the time and location of volcanic injections into the stratosphere affect the aerosol decay rates and seasonal variations of aerosol optical depth in the midlatitude stratosphere. Copyright 1996 by the American Geophysical Union.

Abstract:

Atmospheric temperature measurements from the improved stratospheric and mesospheric sounder (ISAMS) are evaluated. Flown on the Upper Atmosphere Research Satellite (UARS), ISAMS obtained 180 days of science data between September 26, 1991 and July 29, 1992. Typically, over 2600 temperature profiles/day were retrieved, spaced every 200 km along the limb-viewing track and nominally extending from 100 to 0.01 mbar (15-80 km). The latitude coverage ranged from 80°S to 80°N, depending on the particular ISAMS/UARS viewing geometry on any day. UARS is in a near-Sun-synchronous orbit, so that while the 15 orbits/d are spaced approximately every 24° longitude around the equator, the sampled local solar time actually changes by 20 min/d. The ISAMS temperature retrieval process is outlined and the various products are described. A detailed error budget for the retrieval is presented and comparisons are made with temperature measurements from other sources. Finally, a table is provided summarizing the best estimates of ISAMS temperature bias and precision. The results suggest a general cold bias of around 1 K in the stratospheric temperatures, with a superimposed 2-3 K warm bias associated with the densest part of the Pinatubo aerosol cloud. The precision of individual profiles is ±2 K throughout the stratosphere but falls off in the mesosphere to about ±10 K at 80 km. The error bars produced by the retrieval appear to be reasonable (although slightly pessimistic) estimates of the precision. Copyright 1996 by the American Geophysical Union.

Abstract:

A technique is presented for estimating the effective radius, surface area density, and volume density of stratospheric aerosols from infrared emission measurements. These parameters are required to assess the perturbation of the climate and chemical balance of the stratosphere following the largest volcanic eruption so far this century: that of Mount Pinatubo in the Philippines, The method uses a relationship between the surface area density and the volume density derived from balloon-borne measurements of the Mount Pinatubo aerosol cloud made at Laramie, Wyoming. It is shown that the aerosol emission value is well approximated by a linear function of effective radius and aerosol volume density. The technique relies on knowing the refractive index of the aerosol cloud, which is assumed to be composed of liquid spheres of sulphuric acid and water. It is shown that the uncertainties in the current knowledge of the refractive index of sulphuric acid solutions limit the accuracy of the inversion technique. As a case study, the aerosol effective radius, surface area density, and volume density are determined from emission measurements at 12.1 mu m of the Mount Pinatubo aerosol cloud made by the improved stratospheric and mesospheric sounder (ISAMS) carried on the Upper Atmospheric Research Satellite (UARS). From these measurements it is shown that five months after the eruption the core of the Mount Pinatubo cloud had a size distribution with an effective radius of 0.5 mu m, a surface area density of 35 mu m(2) cm(-3), and a volume density of 6 mu m(3) cm(-3).