How shallow circulations couple to moisture in the trades - A perspective from satellites

Measurements over the north-Atlantic trade wind regions from the recent EUREC⁴A field campaign (ElUcidating the RolE of Cloud–Circulation Coupling in ClimAte) have revealed a large variability in mesoscale (ca. 200 km) vertical velocity. This variability is primarily attributable to shallow mesoscale overturning circulations (SMOCs) , which have also been shown to influence mesoscale moisture variability. From EUREC⁴A observations, it is found that the mesoscale horizontal divergence (D) averaged over the mixed layer covaries strongly with surface D. We exploit this finding by using satellite observations of surface divergence to understand SMOCs further. We mainly use WindSAT measurements for surface divergence due to its larger swath compared to scatterometers and its superior performance under precipitating conditions. In WindSAT observations, surface divergence shows a negative correlation with integrated water vapour (IWV), but also shows the large variance when IWV is large, indicating that there might be two regimes in the divergence-moisture relationship. To further investigate the divergence-moisture relationship, we perform object-identification in the IWV field and characterize surface divergence therein. A synergy with geostationary cloudiness fields from GOES-16 helps us further interpret these characteristics in the context of the spatial organization of clouds. As satellite observations go beyond the space-time coverage of field campaigns, we are able to document (a) statistics of the spatial scales of SMOCs as well as (b) some consistent relationships between SMOCs and atmospheric moisture.