Professor Roy Grainger

Abstract:

The differing path lengths of the forward and nadir views of the Advanced Along-Track Scanning Radiometer (AATSR) are used to separate the contributions from aerosol scattering and surface reflectance in the observed top-of-atmosphere (TOA) radiance. This poster presents an effort to extend the Oxford-RAL retrieval of Aerosols and Clouds (ORAC) scheme used by the GRAPE and GlobAEROSOL projects [1], which currently uses data from the nadir viewing geometry only, to take advantage of the dual-view capabilities AATSR offers. The new algorithm uses optimal estimation to retrieve aerosol optical depth at 550 nm, effective radius and surface albedo at 550 nm for both forward and nadir viewing geometries (with the spectral shape of the surface constrained by a model based on Cox and Munk statistics [2,3] for the sea, and MODIS data [4] for the land).

Abstract:

A case-study is presented comparing the Oxford-RAL retrieval of Aerosol and Cloud (ORAC) algorithm, applied to AATSR and Meteosat-8 SEVIRI data, and the dual-view AATSR aerosol retrieval developed at TNO. The study compares data from an AATSR overpass of the Northern Adriatic and Po Valley region on 4 September 2004, during which time there were two AERONET sunphotometer stations operating in the Venice region as part of the ADRIEX campaign.We present the results of a comparison of the optical depth determined from the two AATSR retrievals and the SEVIRI retrieval at the time of the AATSR overpass. The comparison shows that the satellite retrievals consistently overestimate the aerosol optical depth compared to the AERONET site. A possible reason for this over sea is an inability of the algorithms at present to take into account the ocean colour of coastal waters. Future improvements to the algorithms are suggested. Copyright (C) 2007 Royal Meteorological Society.

Abstract:

The deuterium content of water vapour in a given air mass is sensitive to its temperature and condensation history. Isotopic measurements therefore have the potential to shed light on the transport of air and water vapour into the stratosphere. Previous measurements of the isotopic composition in the upper troposphere and stratosphere have been sparse in terms of both spatial and temporal coverage. Presented here are retrievals of the deuterium content of water vapour (HDO or delta D) from the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) satellite instrument. These retrievals offer the first global scale coverage of the isotopic composition of water vapour in this altitude region and span a time period of almost two years. The spatial coverage and the time span of the dataset offer previously unattainable insight into the mean seasonal and spatial distributions of the isotopic composition of water vapour in the upper troposphere and stratosphere. Measurements of HDO are extremely challenging due to low sensitivity in the spectra at low temperatures and water vapour amounts. Nonetheless, the data show a number of interesting results. Zonal mean profiles show the greatest depletion in delta D in the tropical upper troposphere, with decreasing depletion with altitude in the stratosphere due to the influence of methane oxidation. Seasonal zonal means also show a strong depletion in the southern polar spring at around 300 mbar, which is thought to be related to the occurrence of polar stratospheric clouds and dehydration events in the polar vortex. Geographically, the regions and time periods where the greatest depletions are observed in the tropical upper troposphere are those associated with strong convective activity. Results confirm that temporal variability is central to the transport of water vapour into the tropical tropopause layer (TTL) and stratosphere. The data presented here show an annual cycle in delta D in the TTL which is tied to temperature and suggests that this signature propagates upwards into the stratosphere. The data also show a number of points where extremely dry air is associated with relatively enriched delta D values. We postulate that these points are evidence of ice lofting. Copyright (C) 2007 Royal Meteorological Society.

Abstract:

The Aerosol Direct Radiative Experiment (ADRIEX) took place over the Adriatic and Black Seas during August and September 2004 with the aim of characterizing anthropogenic aerosol in these regions in terms of its physical and optical properties and establishing its impact on radiative balance. Eight successful flights of the UK BAE-146 Facility for Atmospheric Airborne Measurements were completed together with surface-based lidar and AERONET measurements, in conjunction with satellite overpasses. This paper outlines the motivation for the campaign, the methodology and instruments used, describes the synoptic situation and provides an overview of the key results. ADRIEX successfully measured a range of aerosol conditions across the northern Adriatic, Po Valley and Black Sea. Generally two layers of aerosol were found in the vertical: in the flights over the Black Sea and the Po Valley these showed differences in chemical and microphysical properties, whilst over the Adriatic the layers were often more similar. Nitrate aerosol was found to be important in the Po Valley region. The use of new instruments to measure the aerosol chemistry and mixing state and to use this information in determining optical properties is demonstrated. These results are described in much more detail in the subsequent papers of this special issue. Copyright © 2007 Royal Meteorological Society.

Abstract:

MIPAS is a Fourier transform interferometer on Envisat, observing the infra-red thermal self emission of the atmosphere. We investigate the trend in the observed concentrations of CFC-11 (CCl3F) and CFC-12 (CCl 2F2) throughout the life of the instrument. From September 2002 to March 2004, the nominal 'high resolution' (0.025 cm -1) reprocessed L1B data is used. New work was performed to enable the use of the 'reduced resolution' (0.0625cm-1) data now being taken so the trend calculation could be extended to early 2006. CFCs are implicated in the catalytic destruction of ozone and the polar 'ozone holes'. They are controlled by the Montreal protocol, and this work provides some means of quantifying its effect. The long time series from a single satellite instrument is useful for tracking the evolution of the CFC stratospheric loading, and checking the accuracy of simulations. The profiles of these species were determined using 'MORSE', developed at Oxford. It uses optimal estimation. Resulting profiles were combined a posteriori and three-day means calculated on a monthly basis. These means were used to determine the trends in various zonal latitude bands and globally.