Professor Roy Grainger

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).

Abstract:

Satellites are a relatively new tool for investigating atmospheric chemical processes and their products. The precision and, in particular, the space and time coverage, now being achieved is immensely useful, and often essential, where global-scale phenomena like the variability of the stratospheric ozone layer are under study. The IR remote-sensing method using pressure modulator radiometry has recently been extended to the mapping of trace species. The technique is described, and its capabilities demonstrated with some selected new results from the improved stratospheric and mesopheric sounder (ISAMS) on the upper atmosphere research satellite (UARS). ISAMS was designed to study nitrogen-catalysed ozone chemistry, plus transport and other processes involving water vapour, methane and carbon monoxide, in the middle atmosphere. Its primary products are fields of temperature and composition, including all of the important members of the active nitrogen family, water, methane, carbon monoxide, ozone, aerosols and ice clouds. In the new data, all of these show large variations with time, height and latitude. The results have not yet been fully analysed, but early indications are that they confirm some models based on theoretical predictions and earlier, more limited, data, while in other cases they show that the situation is more complex than had been assumed. Sophisticated studies of the radiative-chemical-dynamical system in the stratosphere using satellite data and computer models are now in progress. In the future, even more advanced sensors now being built will obtain improved spatial resolution in the stratosphere, and map the global budgets of tropospheric trace gases as well.