The assimilation of AIRS radiance data at ECMWF

Abstract

SUMMARYThe development of an assimilation system for radiance data from the Atmospheric InfraRed Sounder (AIRS) is described, in particular the identification of cloud contamination, bias correction and the characterization of errors in the measured radiances and radiative-transfer model. The results of assimilation experiments are presented. These show that a conservative use of AIRS radiance data (in a system already extensively observed with other satellite data) results in a small, but consistent, improvement in the quality of analyses and forecasts. Larger impacts of AIRS are found in hypothetical experiments that test the use of radiances from only a single sounding instrument. In these, the use of AIRS is found to outperform the use of data either from a single Advanced Microwave Sounding Unit-A (AMSU-A) or from a single High-resolution InfraRed Sounder (HIRS). In this hypothetical context the relative forecast performance of each sensor is found to correlate with the size and vertical scale of increments caused by the assimilation of the radiances.

A decadal satellite record of gravity wave activity in the lower stratosphere to study polar stratospheric cloud formation

“…We considered analysis data at 00:00 and 12:00 UTC and forecast data at 03:00, 06:00, 09:00, 15:00, 18:00, and 21:00 UTC. AIRS radiance data have been used for operational forecasting since October 2003 (McNally et al, 2006;Dee et al, 2011). Observations of up to 210 channels are used in the assimilation procedure, of which 10 are also considered in our AIRS data product.…”

A weak‐constraint four‐dimensional variational analysis system in the stratosphere

“…Substantial model errors do exist, for example, in the upper stratosphere (e.g. McNally 2003), especially near the Poles during winter seasons.…”

The use of principal component analysis for the assimilation of high‐resolution infrared sounder observations for numerical weather prediction

“…AIRS radiances have been assimilated operationally at ECMWF since (McNally et al, 2006 using data supplied in near-real time by NOAA/NESDIS. Only 324 channels out of the total of 2378 AIRS channels are supplied, for communication bandwidth reasons.…”

“…This provided NWP centres with four years experience with this data type before the first data from the true operational missions arrived (e.g. Auligné et al, 2003;Collard et al, 2003;Le Marshall et al, 2006;McNally et al, 2006). AIRS measures the radiance emitted from the Earth in 2378 channels covering the spectral interval from 650 to 2665 cm −1 at a resolution of around 1 cm −1 .…”