Earth Observation Data Group

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.

Abstract:

[1] The six longest records of stratospheric aerosol ( in situ measurements at Laramie, Wyoming, lidar records at: Garmisch-Partenkirchen, Germany; Hampton, Virginia; Mauna Loa, Hawaii; Sao Jose dos Campos, Brazil, and SAGE II measurements) were investigated for trend by ( 1) comparing measurements in the 3 volcanically quiescent periods since 1970 using standard analysis of variance techniques, and ( 2) analyzing residuals from a time/volcano dependent empirical model applied to entire data sets. A standard squared-error residual minimization technique was used to estimate optimum parameters for each measurement set, allowing for first order autocorrelation, which increases standard errors of trends but does not change magnitude. Analysis of variance over the 3 volcanically quiescent periods is controlled by the end points (pre-El Chichon and post-Pinatubo), and indicates either no change (Garmisch, Hampton, Sao Jose dos Campos, Laramie-0.15 mu m) or a slight, statistically insignificant, decrease ( Mauna Loa, Laramie-0.25 mu m), - 1 +/- 0.5% yr(-1). The empirical model was applied to the same records plus 1020 nm SAGE II data separated into 33 latitude/altitude bins. No trend in stratospheric aerosol was apparent for 31 of 33 SAGE II data sets, 3 of 4 lidar records, and in situ measurements at 0.15 mu m. For Hampton and Laramie-0.25 mu m, the results suggest a weak negative trend, - 2 +/- 0.5% yr(-1), while 2 SAGE II data sets ( 30 - 35 km, 30 degrees and 40 degrees N) suggest a positive trend of similar magnitude. Overall we conclude that no long-term change in background stratospheric aerosol has occurred over the period 1970 - 2004.

Abstract:

The Michelson Interferometer for Passive Atmospheric Sounding is a polar orbiting high resolution mid-infrared emission limb sounder with a nominal vertical resolution of 3 km. Work to extend the list of routinely retrieved species led to the examination of ammonia, NH3. In this paper, we explore the feasibility of upper tropospheric retrievals around 6-km altitude, discussing appropriate methods. We demonstrate a weak north to south gradient outside the error bars, using co-addition to improve signal-to-noise and compare these first results with a model. (c) 2006 Published by Elsevier Ltd on behalf of COSPAR.

Abstract:

Information on cloud properties from ATSR-2 radiances originates from the interaction of solar and terrestrial radiation with the cloud. Due to the spectral dependence of cloud optical properties, observations in different channels of ATSR-2 can be combined to provide information on a cloud phase, top height, effective radius cloud fraction and optical depth. These parameters are retrieved using an optimal estimation approach which enables us to extract information from all channels simultaneously. The method allows us to characterize the error on each parameter assuming the observed cloud is consistent with the modelled cloud (i.e. reasonably plane-parallel in nature). It is also possible to identify when model assumptions are inappropriate by examining the fit between simulated and observed radiances. This technique has been used in the NERC GRAPE (Global Retrieval of Clouds and Evaluation) project. In this paper the optimal estimation algorithm will be outlined and products and validation from the 5 year data set will be presented.