Dr Scott Osprey FRMetS

Abstract:

Significant differences in heating rates are found when two solar irradiance spectra are used in a line-by-line radiative transfer code. Compared with a spectrum of recent satellite data an older theoretical spectrum gives 20-40% more heating in the ozone Hartley band, important in the upper stratosphere. The spectra are implemented in a broadband radiation code to which some improvements are also made to the ozone absorption parameterization. A widely-used spectrum of ground-based data from 1960s gives somewhat lower heating rates. The effects of the changes in the spectrum, and the broad-band scheme, on the temperatures simulated by a middle atmosphere GCM are investigated. The model has previously shown a warm bias, compared with climatology, around the stratopause but this is significantly reduced when the former spectrum is substituted for the latter, and the new ozone parameterization incorporated. The change in spectrum accounts for two-thirds of the improvement. Copyright 2008 by the American Geophysical Union.

Abstract:

The High Resolution Dynamics Limb Sounder (HIRDLS) instrument was launched oil the NASA Aura satellite in July 2004. HIRDLS is a joint project between the UK and USA, and is a mid-infrared limb emission sounder designed to measure the concentrations of trace species, Cloud and aerosol, and temperature and pressure variations in the Earth’s atmosphere front the upper troposphere to the mesophere. The instrument is intended to make measurements at both high vertical and horizontal spatial resolutions, but validating those measurements is difficult because few other measurements provide that vertical resolution sufficiently closely in time. However, the FOPMOSAT-3/COSMIC suite of radio occultation satellites that exploit the U.S. GPS transmitters to obtain high resolution (similar to 1 km) temperature profiles in the stratosphere does provide sufficient profiles nearly coincident with those from HIRDLS. Comparisons show a good degree intercorrelation between COSMIC and HIRDLS down to about 2 km resolution, with similar amplitudes for each, implying that HIRDLS and COSMIC are able to measure the same small scale features. The optical blockage that occurred within HIRDLS during launch does not seem to have affected this capability.

Abstract:

An examination of zonal asymmetries in meridional momentum flux reaching the mesosphere is made using the Hines Doppler spread parameterization of gravity waves. As expected a general correspondence is seen between wave one wind in the stratosphere and wave one signals in gravity wave momentum flux leaving the stratosphere. However, a significant difference is the presence of wave one features in the gravity-wave momentum flux at 56 km and ∼70°N during mid-summer which contrast with minimal signals in stratospheric wave one wind. The prominence of this feature is accounted for by a significant wave one Brunt-Väisälä feature at the tropopause amplifying a wave one signal in momentum flux which can then propagate to great heights. Such a feature could result in mesospheric planetary waves which are coupled to the tropopause forcing without intervening planetary wave signals in the stratosphere.