, Volume 23, Issue 3, pp 283-306

Models and observations of the growth of the atmospheric boundary layer

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Abstract

The evolution of the mixed layer during a clear day can be described with a slab model. The model equations have to be closed by a parameterization of the turbulent kinetic energy budget. Several possibilities for this parameterization have been proposed. In order to assess the practical applicability of these models for the atmosphere, field experiments were carried out on ten clear days in 1977 and 1978. Within the accuracy of the measurements the mixed-layer height in fully convective conditions (at noon on clear days) is well predicted taking a constant heat flux ratio % MathType!MTEF!2!1!+-% feaafeart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaeyOeI0Yaa0% aaaeaacqaH4oqCcaWG3bWaaSbaaSqaaiaadIgaaeqaaaaakiabg2da% 9iaaicdacaGGUaGaaGOmamaanaaabaGaeqiUdeNaam4DamaaBaaale% aacaWGZbaabeaaaaaaaa!41D4!\[ - \overline {\theta w_h } = 0.2\overline {\theta w_s } \]. In the early morning hours mechanical entrainment is also important. Good overall results are obtained with the entrainment formulation % MathType!MTEF!2!1!+-% feaafeart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaeyOeI0Yaa0% aaaeaacqaH4oqCcaWG3bWaaSbaaSqaaiaadIgaaeqaaaaakiabg2da% 9iaaicdacaGGUaGaaGOmamaanaaabaGaeqiUdeNaam4DamaaBaaale% aacaWGZbaabeaaaaGccqGHRaWkcaaI1aGaamyDamaaDaaaleaacqGH% xiIkaeaacaaIZaaaaOGaamivaiaac+cacaWGNbGaamiAaaaa!49C1!\[ - \overline {\theta w_h } = 0.2\overline {\theta w_s } + 5u_ * ^3 T/gh\].

Only large differences in the entrainment coefficients lead to significantly different results. Making the entrainment model more complex does not lead to substantial improvement.

The mean potential temperature in the mixed layer is reproduced within 0.5 °C. This temperature is insensitive to the choice of a particular entrainment formulation and depends more on the surface heat input and the temperature gradient in the stable air aloft.