Professor Roy Grainger

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.

Abstract:

Observations of polar stratospheric clouds by the Improved Stratospheric and Mesospheric Sounder (ISAMS) experiment on the Upper Atmospheric Research Satellite (UARS) have revealed new details of their global properties and behavior. These include the vertical and horizontal spatial distributions of Arctic and Antarctic polar stratospheric clouds (PSCs) as a function of time and air temperature, their optical thicknesses and estimated densities, their spectral properties, and their inferred composition. In particular, ISAMS spectral data allows different PSC types to be distinguished from each other and from volcanic aerosol by their compositional differences. Northern PSCs during the 1991/92 season are found to be more ephemeral and more compact than reported in previous years and to differ markedly in scale from those in Southern Hemisphere, which cause the Antarctic ozone hole by activating stratospheric chlorine chemistry. There were only two episodes of dense PSC formation in the 1991/92 northern winter, one of which took place in sunlight. The latter correlates well with UARS/Microwave Limb Sounder observations of enhanced chlorine monoxide, but substantial amounts of chlorine monoxide were also reported at times and places with at most very minor PSC activity.

Abstract:

The Improved Stratospheric and Mesospheric Sounder (ISAMS) aboard the Upper Atmosphere Research Satellite (UARS) senses in 14 wideband channels in the infrared. The absorption by the Mt. Pinatubo aerosol cloud for nine of the channels was averaged over heights from 20 km to 30 km for a 60-degrees latitude band centred on the Equator. The absorption spectrum for sulphuric acid-water aerosols was calculated for wavelengths from 4 mum to 17 mum and investigated as a function of the particle size distribution and the particle composition. The infrared spectrum is shown to be more sensitive to changes in particle composition than to drop size; the ISAMS results are consistent with drops composed of a 59% to 77% solution of sulphuric acid in water.