Entrainment and Detrainment Rates in Shallow Cumulus Clouds Diagnosed from LES under Various Modeling Assumptions
Abstract
Data from large eddy simulations allow empirical evaluation of parameters appearing in cloud and boundary layer closures that are otherwise often poorly constrained by theoretical considerations. In particular, entrainment and detrainment rates used in mass-flux closures are often determined from LES data. Most commonly, this analysis is based on a steady-state, bulk plume equation set. Thus, the entrainment and detrainment rates so determined implicitly account for the approximations made in the underlying equation set, as manifested in the particular case under consideration. Hence they may lack generalizability to other physical scenarios, such as conditions under climate change. They may also prove unsatisfactory when combined with the kind of modified mass flux closures proposed in response to increasing spatial and temporal resolution of models. Here we evaluate entrainment and detrainment rates from LES of shallow cumulus clouds under various modeling assumptions. In particular, we identify coherent updrafts from LES data, allowing us to consider the behavior of sub-ensembles of updrafts as well as individual updrafts. The importance of non-steady state behavior is also considered under various levels of updraft aggregation. Thus, going beyond a simple diagnosis of parameter values, this detailed evaluation of entrainment and detrainment rates allows greater understanding of mixing processes between clouds and their environment.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2016
- Bibcode:
- 2016AGUFM.A33I0384K
- Keywords:
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- 3307 Boundary layer processes;
- ATMOSPHERIC PROCESSESDE: 3311 Clouds and aerosols;
- ATMOSPHERIC PROCESSESDE: 3354 Precipitation;
- ATMOSPHERIC PROCESSESDE: 3359 Radiative processes;
- ATMOSPHERIC PROCESSES