Abstract
Abstract. A new microwave satellite water vapour retrieval for the polar winter atmosphere is presented. The retrieval builds on the work of Miao et al. (2001) and Melsheimer and Heygster (2008), employing auxiliary information for atmospheric conditions and numerical optimization. It was tested using simulated and actual measurements from the Microwave Humidity Sounder (MHS) satellite instruments. Ground truth was provided by the G-band vapour radiometer (GVR) at Barrow, Alaska. For water vapour columns less than 6 kg m−2, comparisons between the retrieval and GVR result in a root mean square (RMS) deviation of 0.39 kg m−2 and a systematic bias of 0.08 kg m−2. These results are compared with RMS deviations and biases at Barrow for the retrieval of Melsheimer and Heygster (2008), the AIRS and MIRS satellite data products, and the ERA-Interim, NCEP, JRA-55, and ASR reanalyses. When applied to MHS measurements, the new retrieval produces a smaller RMS deviation and bias than for the earlier retrieval and satellite data products. The RMS deviations for the new retrieval were comparable to those for the ERA-Interim, JRA-55, and ASR reanalyses; however, the MHS retrievals have much finer horizontal resolution (15 km at nadir) and reveal more structure. The new retrieval can be used to obtain pan-Arctic maps of water vapour columns of unprecedented quality. It may also be applied to measurements from the Special Sensor Microwave/Temperature 2 (SSM/T2), Advanced Microwave Sounding Unit B (AMSU-B), Special Sensor Microwave Imager/Sounder (SSMIS), Advanced Technology Microwave Sounder (ATMS), and Chinese MicroWave Humidity Sounder (MWHS) instruments.
Highlights
The polar winter troposphere is very dry, with water vapour columns typically near 3 kg m−2 (Serreze et al, 1995)
The results show that when the auxiliary information is severely degraded, the PLDC16 retrieval can be expected to perform comparably to MH08 for the low and mid regimes
A new retrieval based on the microwave formulation developed by Miao et al (2001) was introduced
Summary
The polar winter troposphere is very dry, with water vapour columns typically near 3 kg m−2 (Serreze et al, 1995). Infrared and visible satellite measurements have better spatial coverage but are challenged by scattering and absorption from clouds and the lack of solar radiation during polar winter. Microwaves have a strong water vapour absorption line at 183 GHz that is useful for dry conditions, with emissions that can be observed during any part of the diurnal cycle. Microwaves are less affected by scattering and absorption from clouds, allowing for water vapour measurements in most weather conditions (Miao et al, 2001). Microwave instruments aboard a series of polar-orbiting satellites since 1991 (F11 to 19, NOAA-15 to 19, MetOP-A and B, FY3A to C, and NPP) already provide a substantial data set for water vapour studies. Planned missions include JPSS-1 and 2, MetOP-C, MetOP-SG, and DMSP-S20
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