Atmospheric boundary layer evening transitions over West Texas

Date

2008-12

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Publisher

Texas Tech University

Abstract

In the circadian Atmospheric Boundary Layer (ABL) cycle over land, transitions occur between two fundamental modes through near-neutral conditions. Such diurnal cycles show two major stages: first, the unstable mode and its mixed layer take place after sunrise and persist until the late afternoon or the evening when a transition happens. Second, the stable mode and its stable layer form after sunset and begin to dissipate the following morning giving room to a transition after which the mixed layer will occur again. The transition periods are not fully understood, but surely important. In particular, the features of the evening transition (ET) period may influence the inception and strength of the nocturnal low level jet (LLJ) and the whole structure of the nocturnal atmospheric boundary layer (NABL). If moisture sources are available, they also might determine whether the nocturnal surface is going to be characterized by condensation (weak LLJ and shallow NABL) or by continued evaporation (windy deep NABL). In this dissertation, three data subsets (radiation, meteorology, scintillometry) proved very useful in the characterization of the ET; within each of these subsets, particular selected quantities allowed the precise determination of ET timelines. Numerical modeling also played an important role in understanding and characterizing the ET.

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