Prof. Patrick Irwin

Abstract:

Measurements of the Venus mesosphere made in 1978/79 by the Pioneer Venus Orbiter Infrared Radiometer (OIR) have been reanalysed. An optimal estimation retrieval technique has been applied to data from individual orbits. These retrievals reveal the structure of transient features such as the polar dipole and polar collar and short term variations in water vapour abundance and cloud top height. High abundances of water vapour are observed at equatorial latitudes in the early afternoon with a spatial structure which appears consistent with the ultraviolet 'Y' shaped structure. Additionally a two to four day period is observed in both water vapour abundance and cloud top height which is the characteristic period of this ultraviolet feature. © 1997 COSPAR. Published by Elsevier Science Ltd.

Abstract:

Scientific results from NIMS observations of Venus have been extensively reported in the literature, while those of Jupiter have, at the time of writing, just barely commenced. The planning and interpretation of studies of these planets, with their massive atmospheres and exotic compositions (by terrestrial standards), requires a comprehensive treatment of radiative transfer in both. This paper describes work done at Oxford to develop the underlying theory and practical radiative transfer schemes, with particular reference to the NIMS wavelength range, spectral resolution, and scientific objectives for Jupiter. Equivalent work for Venus has already been reported in the literature (e.g. Kamp and Taylor, 1990) and will not be covered in detail here. (C) 1997 COSPAR. Published by Elsevier Science Ltd.

Abstract:

The spectrum of Saturn from 43 to 197 μm was measured with the ISO Long Wavelength Spectrometer (LWS) during the performance verification phase of the mission. The measurements were made using the LWS in grating mode, with spectral resolutions of 0.29 μm from 43 to 90 μm and 0.6 μm from 90 to 197 μm. The spectrum was compared with an atmospheric radiative-transfer model and four results were obtained: first, the slope of the measured continuum within each detector passband is in good agreement with the model; second, absorption features due to ammonia and phosphine were unambiguously detected, and all detected features were attributed to these two molecules; third, the ammonia absorption features agree reasonably well with the nominal model (based on Voyager IRIS measurements); and fourth, the phosphine absorption features disagree with the nominal model. Superior agreement with the measured spectrum was obtained with a modified PH3 profile in which the tropospheric mixing ratio was increased to 7 × 10-6 and the cutoff due to photodissociation was lowered to 300 mbar. These results are based on trial observations during performance verification of the LWS, and provide an indication of the results we expect to obtain when the spectrum of Saturn is measured comprehensively later in the mission.

Abstract:

A concept has been developed for a remote sensing experiment to investigate the physics of the Martian atmosphere from a spin-stabilized orbiter, like that planned for the InterMarsNet mission. Using coincident infrared and microwave channels and limb-to-limb scanning, it can map the planet much more extensively than previously in temperature atmospheric dust loading, and humidity. When combined with one or more surface stations measuring the same variables, the sounder experiment can contribute to major progress in understanding the general circulation and dust and water cycles of the atmosphere of Mars, and the characterization of medium-scale meteorological systems. Copyright (C) 1996 Elsevier Science Ltd