Abstract
Abstract. Monitoring of water vapour in the Arctic on long timescales is essential for predicting Arctic weather and understanding climate trends, as well as addressing its influence on the positive feedback loop contributing to Arctic amplification. However, this is challenged by the sparseness of in situ measurements and the problems that standard remote sensing retrieval methods for water vapour have in Arctic conditions. Here, we present advances in a retrieval algorithm for vertically integrated water vapour (total water vapour, TWV) in polar regions from data of satellite-based microwave humidity sounders: (1) in addition to AMSU-B (Advanced Microwave Sounding Unit-B), we can now also use data from the successor instrument MHS (Microwave Humidity Sounder), and (2) artefacts caused by high cloud ice content in convective clouds are filtered out. Comparison to in situ measurements using GPS and radiosondes during 2008 and 2009, as well as to radiosondes during the N-ICE2015 campaign and to ERA5 reanalysis, show the overall good performance of the updated algorithm.
Highlights
Water vapour is a key element of the hydrological cycle (Chahine, 1992; Serreze et al, 2006; Jones et al, 2007; Hanesiak et al, 2010), with shifts in it affecting atmospheric transport processes, creating and intensifying droughts and flooding (Trenberth et al, 2013)
The bias and root-mean-square differences (RMSDs) are small for all four surface types but slightly higher in two cases with ice surfaces, which agrees with the higher error of our method for higher water vapour values
We provide an updated version of the TWV retrieval algorithm that originally uses as input microwave humidity sounder data from Advanced Microwave Sounding Unit-B (AMSU-B)
Summary
Water vapour is a key element of the hydrological cycle (Chahine, 1992; Serreze et al, 2006; Jones et al, 2007; Hanesiak et al, 2010), with shifts in it affecting atmospheric transport processes, creating and intensifying droughts and flooding (Trenberth et al, 2013). The key concept of this method is the use of several microwave channels with similar surface emissivity but different water vapour absorption These are the three channels near the 183.31 GHz water absorption line (183.31 ± 1, ±3 and ±7 GHz), which, together with the channel at the 150 GHz window frequency, allow retrieval of TWV values up to about 7 kg m−2. In other words, when the TWV reaches a certain threshold, the brightness temperature at these Advanced Microwave Sounding Unit-B (AMSU-B) channels does not change with increasing TWV (Miao, 1998; Melsheimer and Heygster, 2008) This limited range is enough for Antarctica and suffices for the Arctic in winter conditions (in the polar winter atmosphere, the water vapour column is typically around 3 kg m−2, according to Serreze et al, 1995), as well as for the central Arctic (above 70◦ N) most of the year.
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