Professor Roy Grainger

Abstract:

A simple physical model of the atmospheric effects of large explosive volcanic eruptions is developed. Using only one input parameter-the initial amount of sulphur dioxide injected into the stratosphere-the global-average stratospheric optical-depth perturbation and surface temperature response are modelled. The simplicity of this model avoids issues of incomplete data (applicable to more comprehensive models), making it a powerful and useful tool for atmospheric diagnostics of this climate forcing mechanism. It may also provide a computationally inexpensive and accurate way of introducing volcanic activity into larger climate models. The modelled surface temperature response for an initial sulphur-dioxide injection, coupled with emission-hi story statistics, is used to demonstrate that the most climatically significant volcanic eruptions are those of sufficient explosivity to just reach into the stratosphere (and achieve longevity). This study also highlights the fact that this measure of significance is highly sensitive to the representation of the climatic response and the frequency data used, and that we are far from producing a definitive history of explosive volcanism for at least the past 1000 years. Given this high degree of uncertainty, these results suggest that eruptions that release around and above 0.1 Mt SO2 into the stratosphere have the maximum climatic impact.

Abstract:

The Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) is a polar orbiting high resolution mid-infrared emission stratospheric limb sounder with a nominal vertical resolution of 3 km. Work to extend the list of interesting, routinely retrieved species led to the examination of SF6, a potent greenhouse gas and a useful tracer species. We demonstrate the feasibility of profile retrievals in the range 6-30 km based on single scans. Additionally, we investigate latitudinal variation using coaddition to improve signal-to-noise. A mean mid-latitude profile shows tropospheric (4.32 +/- 0.03 pptv, 6-12 km) and stratospheric (3.50 +/- 0.03 pptv, 21-30 km) regimes, in September 2002, similar to accepted values. The global mean contains an interhemispheric variability of the order of 0.3 pptv in the lower stratosphere, in line with age of air. Finally, the continuation of acknowledged global trends in atmospheric concentration, is estimated at +0.28 pptv yr(-1) (6.5 +/- 1.3% yr(-1)).

Abstract:

We present a new method to determine mesospheric electron densities from partially reflected medium frequency radar pulses. The technique uses an optimal estimation inverse method and retrieves both an electron density profile and a gradient electron density profile. As well as accounting for the absorption of the two magnetoionic modes formed by ionospheric birefringence of each radar pulse, the forward model of the retrieval parameterises possible Fresnel scatter of each mode by fine electronic structure, phase changes of each mode due to Faraday rotation and the dependence of the amplitudes of the backscattered modes upon pulse width. validation results indicate that known profiles can be retrieved and that chi(2) tests upon retrieval parameters satisfy validity criteria. Application to measurements shows that retrieved electron density profiles are consistent with accepted ideas about seasonal variability of electron densities and their dependence upon nitric oxide production and transport. (C) 2004 Elsevier Ltd. All rights reserved.