Mesoscale Air-Sea interaction during the EUREC4A campaign: case studies analysis

The world ocean is rich in mesoscale structures that locally affect the overlying atmosphere. The interaction of these mesoscale oceanic features with the overlying atmosphere is an interesting topic because of the ubiquity of mesoscale structures in the ocean and the lacking of a definitive representation of the interaction mechanisms. This thesis presents two case studies of air-sea interaction using data collected during the EUREC4A campaign in the tropical north-western Atlantic. The objective is to learn about mesoscale air-sea interaction by case study analysis, particularly for what concerns the effect of sea surface temperature structures. SST measurements from Merian’s thermosalinograph identify the case studies. Then, ship-borne observations from the two weather stations, wind lidar, cloud radar on the R/V Merian, characterize each case study. Radiosondes launched from the R/Vs Merian and Atalante complete the ground-based dataset. Satellite SST and cloud cover observations complement the dataset and allow for comparison. Also, wind data from the ICON-LEM model output are exploited to provide field information to the ship-based point measurements. For the first case study, no effects of the SST on the overlaying atmosphere can be detected. The absence of a detectable SST effect in the first case study is attributed to the limited temporal and spatial extent of the SST anomaly. In the second case study a connection between an SST cold front, vertical velocity, and cloud cover is found. It is proposed that the colder SST dampen the vertical motion on the overlaying atmosphere reducing cloud formation.