Airborne observations of thermal mesoscale circulations in the coastal marine boundary layer

Detailed observations obtained from airborne meteorological measurements in an area along the Baltic coast in the southeast of Sweden are presented. The measurements were taken during late spring/early summer when the water in the Baltic is generally cool compared to typical daytime land surface temperatures which generated significant surface temperature contrasts between land and water. The measurements show the coastal marine boundary layer to be very far from the homogeneity often assumed in numerical models. The cases presented focus mainly on mesoscale circulations driven or modified by this temperature contrast and related turbulence structure such as thermal jets and sea breeze circulations and show a high degree of temporal as well as small‐scale spatial variability. Even though the synoptic scale wind direction in this area is highly variable, due to traveling mid‐latitude cyclones, the surface temperature patterns show great consistency from day to day, with the coldest water always being along the coast with a pronounced minimum localized at the southeastern part of the coastline. It is not clear to what extent the sea surface temperature inhomogeneities are responsible for some of the observed small‐scale variability, nor is it clear if they are results of ocean processes alone or are interacting in any significant way with the marine boundary layer close to the coast.