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Abraham Arnold

Abstract

Using moisture as a source identifier and as a tracer, a pair of lapse rates were constructed which give the temperatures associated with rising and with descending air. This lapse rate depiction is discussed both in terms of what it exhibits and in what it describes of the clear-air convective process. The data for this depiction were taken by an aircraft in a field of convective cells.

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Ivo G. S. van Hooijdonk
,
Herman J. H. Clercx
,
Carsten Abraham
,
Amber M. Holdsworth
,
Adam H. Monahan
,
Etienne Vignon
,
Arnold F. Moene
,
Peter Baas
, and
Bas J. H. van de Wiel

Abstract

This study aims to find the typical growth rate of the temperature inversion during the onset of the stable boundary layer around sunset. The sunset transition is a very challenging period for numerical weather prediction, since neither accepted theories for the convective boundary layer nor those for the stable boundary layer appear to be applicable. To gain more insight in this period, a systematic investigation of the temperature inversion growth rate is conducted. A statistical procedure is used to analyze almost 16 years of observations from the Cabauw observational tower, supported by observations from two additional sites (Dome C and Karlsruhe). The results show that, on average, the growth rate of the temperature inversion (normalized by the maximum inversion during the night) weakly declines with increasing wind speed. The observed growth rate is quantitatively consistent among the sites, and it appears insensitive to various other parameters. The results were also insensitive to the afternoon decay rate of the net radiation except when this decay rate was very weak. These observations are compared to numerical solutions of three models with increasing complexity: a bulk model, an idealized single-column model (SCM), and an operational-level SCM. It appears only the latter could reproduce qualitative features of the observations using a first-order closure. Moreover, replacing this closure with a prognostic TKE scheme substantially improved the quantitative performance. This suggests that idealized models assuming instantaneous equilibrium flux-profile relations may not aid in understanding this period, since history effects may qualitatively affect the dynamics.

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