Elevated Moist Layers – Using HALO during EUREC4A to explore a blind spot in the global satellite observing system

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Data from two previous HALO campaigns (NARVAL-1 and NARVAL-2) indicate that elevated moist layers are not uncommon in the tropical lower troposphere. Perhaps the main reason why elevated moist layers have hitherto not received more attention is that they are difficult to detect in satellite humidity profile measurements. This blind spot in the global observing system is an important issue for climate research, since it would make humidity profiles on average appear more bottom-heavy than they are in reality, which would affect climate sensitivity estimates, since a large part of the variance in climate sensitivity can be explained by model diversity in the vertical mixing of moisture within the lower troposphere over oceans, for which the mean vertical moisture profile is a good diagnostic.It is not at all obvious why passive sounders like SAPHIR and IASI are so poor in detecting elevated moist layers. The project will test the hypothesis that it is related to the temperature inversions that tend to accompany moist layers. Using the EUREC4A campaign data, it will quantify and analyse the problem, and on the basis of this analysis attempt to develop a new IASI humidity profile data product that better represents the elevated moist layers. The HALO campaign data will also be used to validate the new product. Furthermore, the project will contribute improved satellite humidity profiles across the entire campaign area for use by other EUREC4A projects and the international scientific community.