Ground-based retrieval of very low to high columnar integrated water vapor using combined millimeter-wave and microwave observations

Abstract

Precipitable water vapor (PWV) and liquid water path (LWP) retrievals using zenith view passive microwave observations near the 22.235 GHz water vapor line are known to be of high accuracy for most mid-latitude profiles. However in very dry atmospheres (PWV<10 mm), such as those experienced in the Arctic winter, the percentage accuracy of these retrievals becomes poor due to the weakness of the 22 GHz feature. The authors describe an adaptable physical retrieval algorithm which uses any number of channels in the range 10-300 GHz to retrieve PWV and LWP. Using a database of model high latitude profiles, the authors investigate the performance of various channel combinations in the range 23 to 183 GHz for retrieving PWV and LWP. The authors demonstrate that the best retrieval performance over the expected range of PWV and LWP in high-latitude climates is made with combinations that include channels near the 22 GHz absorption line and the much stronger 183.31 GHz line. This analysis is applicable to optimizing the measurement strategy for studying the influence of water vapor on the Earth's radiation budget in Arctic areas.