### Abstract

A tendency equation for evaporation in a growing convective boundary layer (CBL)
is derived. This derivation allows for a process-based decomposition in which each
involved land-atmosphere feedback accounts for one term in the equation. Therefore,
the influence of entrainment processes on evaporation can be quantified and separated
from other land-atmosphere feedbacks.
An expression for equilibrium evaporation is derived from the tendency equation and
it is investigated how the magnitude of the equilibrium evaporation and the involved
time scales depend on the land-atmosphere feedbacks. It is shown that entrainment
can enhance the equilibrium evaporation significantly. In addition, the relative enhancement
explains very well the characteristic Priestley-Taylor coefficient of 1.26
over well-watered surfaces. Entrainment increases the characteristic time scale of the
system if the evaporation exceed

Original language | English |
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Title of host publication | EMS Annual Meeting Abstracts, Eighth Annual Meeting of the European Meteorological Society, Amsterdam, 29 September-3 October 2008 |

Publisher | EMS |

Pages | A-00148 |

Publication status | Published - 2008 |

Event | Eighth Annual Meeting of the European Meteorological Society - Duration: 29 Sep 2008 → 3 Oct 2008 |

### Conference

Conference | Eighth Annual Meeting of the European Meteorological Society |
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Period | 29/09/08 → 3/10/08 |

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## Cite this

van Heerwaarden, C. C., & Vilà-Guerau de Arellano, J. (2008). A tendency equation for evaporation over a convective boundary layer. In

*EMS Annual Meeting Abstracts, Eighth Annual Meeting of the European Meteorological Society, Amsterdam, 29 September-3 October 2008*(pp. A-00148). EMS.