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Turbulent transport in fields of warm cumulus clouds
Author(s) -
Pasquier Jacques R. M.,
Jonas Peter R.
Publication year - 1998
Publication title -
quarterly journal of the royal meteorological society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.744
H-Index - 143
eISSN - 1477-870X
pISSN - 0035-9009
DOI - 10.1002/qj.49712454602
Subject(s) - liquid water content , turbulence kinetic energy , turbulence , cloud base , atmospheric sciences , environmental science , cloud top , buoyancy , kinetic energy , meteorology , energy budget , mechanics , cloud computing , physics , thermodynamics , classical mechanics , computer science , operating system
Simulations of fields of warm (ice‐free) cumulus clouds are made using a large‐eddy model based on observational soundings. Comparisons between numerical and experimental results show good agreement. The cumulus clouds produced by the model are similar to those observed, with cloud base, cloud top and cloud scales all in good agreement. At cloud top, vertical velocities are found to be 5 m s −1 and liquid‐water mixing ratios have a maximum of 1.6 g kg −1 , which is consistent with the observations. By considering fractional cloud cover and averaging over time, the profiles of the turbulent kinetic energy and fluxes averaged over the horizontal level and in‐cloud are derived. Much of the turbulent energy and transport in the boundary layer is found to be produced in cloud. The dominant regions of turbulent kinetic energy result from the strong surface heating and the two in‐cloud buoyancy sources of latent heating through condensation at cloud base and evaporative cooling following entrainment at cloud top. This is supported by the upward transport of energy at mid‐cloud levels and downward at cloud‐top. The terms in the turbulent kinetic‐energy budget are derived, and once again buoyant production is found to be dominant in both the cloud and the horizontal averages. The vertical turbulent fluxes of heat, moisture and liquid are analysed and found to vary in accordance with the turbulent processes driving the boundary layer. The penetration of the clouds above the main inversion shows that the clouds were effective in coupling the surface to the base of the free troposphere by transporting the heat and moisture upwards. Overall, the kinetic‐energy profiles and turbulent fluxes in the cumulus case‐study, both averaged over the layer and the clouds, show good agreement with the observations. This demonstrates the validity of the large‐eddy simulation model as a tool for studying cumulus clouds at greater vertical resolution than is possible by current observations, and provides a basis for deriving more accurate parametrization schemes of convective cloud‐capped boundary layers.