Low-level jet development and the interaction of different scale physical processes

Abstract

Two cases of low-level jet events and the interaction of the involved physical processes are investigated. The vertical distribution of the dominant atmospheric motions is studied, using data from a SODAR-RASS system and in situ instrumentation, at a coastal region of the Eastern Mediterranean (Messogia Plain in Attica—Greece). The first low-level jet (LLJ) case was observed during the cold period, after the passage of a cold front and could be characterized as purely synoptic. Coherent inertial motions were found to follow the frontal surface at both the wind components, with larger amplitudes at the alongfront wind component, a fact consistent with the deformation theory. The contribution of the diurnal cycle was found weak in both the components, due to the cloudiness and the small diurnal temperature range, while the synoptic scale dominated the northerly wind component. The second LLJ case represents two successive summertime large-scale jets. The absence of cloudiness and the increased solar radiation provided a favorable environment for the development of local flows which interacted with the synoptic wind field. This interaction led to a LLJ with an oscillating core and a variable depth. The diurnal cycle had a strong imprint on the wind component along the sea breeze direction (easterly), while the synoptic variations dominated the northerly wind component. Strong amplitudes of a coherent quasi 2-day variation were also found in both the cases.