Life Cycle of Numerically Simulated Shallow Cumulus Clouds. Part I: Transport

This paper is the first in a two-part series in which the life cycles of numerically simulated shallow cumulus clouds are systematically examined. The life cycle data for six clouds with a range of cloud-top heights are isolated from an equilibrium trade cumulus field generated by a large-eddy simulation (LES) with a uniform resolution of 25 m. A passive subcloud tracer is used to partition the cloud life cycle transport into saturated and unsaturated components; the tracer shows that on average cumulus convection occurs in a region with time-integrated volume roughly 2 to 3 times that of the liquid-water-containing volume. All six clouds exhibit qualitatively similar vertical mass flux profiles with net downward mass transport at upper levels and net upward mass flux at lower levels. This downward mass flux comes primarily from the unsaturated cloud-mixed convective region during the dissipation stage and is evaporatively driven. Unsaturated negatively buoyant cloud mixtures dominate the buoyancy and mass fluxes in the upper portion of all clouds while saturated positively buoyant cloud mixtures dominate the fluxes at lower levels. Small and large clouds have distinct vertical profiles of heating/cooling and drying/moistening, with small clouds cooling and moistening throughout their depth, while larger clouds cool and moisten at upper levels and heat and dry at lower levels. The simulation results are compared to the predictions of conceptual models commonly used in shallow cumulus parameterizations.

[1]  S. Moorthi,et al.  Relaxed Arakawa-Schubert - A parameterization of moist convection for general circulation models , 1992 .

[2]  A. P. Siebesma,et al.  Model Impacts of Entrainment and Detrainment Rates in Shallow Cumulus Convection. , 1996 .

[3]  Kerry Emanuel,et al.  Development and Evaluation of a Convection Scheme for Use in Climate Models , 1999 .

[4]  S. Esbensen,et al.  Heat and Moisture Budget Analyses Using BOMEX Data , 1974 .

[5]  D. Randall,et al.  Cloud resolving modeling of the ARM summer 1997 IOP: Model formulation, results, uncertainties, and sensitivities , 2003 .

[6]  Christopher S. Bretherton,et al.  A New Parameterization for Shallow Cumulus Convection and Its Application to Marine Subtropical Cloud-Topped Boundary Layers. Part I: Description and 1D Results , 2004 .

[7]  K. Salzen,et al.  Parameterization of the Bulk Effects of Lateral and Cloud-Top Entrainment in Transient Shallow Cumulus Clouds , 2002 .

[8]  A. P. Siebesma,et al.  A Large Eddy Simulation Intercomparison Study of Shallow Cumulus Convection , 2003 .

[9]  Christopher S. Bretherton,et al.  Mass-Flux Budgets of Shallow Cumulus Clouds , 2001 .

[10]  Jean-Christophe Golaz,et al.  Large‐eddy simulation of the diurnal cycle of shallow cumulus convection over land , 2002 .

[11]  Jonker,et al.  Anomalous scaling of cumulus cloud boundaries , 2000, Physical review letters.

[12]  M. Lemone,et al.  The Relationship of Trade Wind Cumulus Distribution to Subcloud Layer Fluxes and Structure , 1976 .

[13]  K.,et al.  Simulations of Trade Wind Cumuli under a Strong Inversion , 2001 .

[14]  A. P. Siebesma,et al.  Evaluation of Parametric Assumptions for Shallow Cumulus Convection , 1995 .

[15]  Roland B. Stull,et al.  A Fair-Weather Cumulus Cloud Classification Scheme for Mixed-Layer Studies , 1985 .

[16]  R. Stull.  An Introduction to Boundary Layer Meteorology , 1988 .

[17]  Roel Neggers,et al.  A Multiparcel Model for Shallow Cumulus Convection , 2002 .

[18]  K. Emanuel.  A Scheme for Representing Cumulus Convection in Large-Scale Models , 1991 .

[19]  Ming Zhao.  Episodic mixing and buoyancy-sorting representations of shallow cumulus convection , 2003 .

[20]  A..  A new convective adjustment scheme. Part I: Observational and theoretical basis , 2006 .

[21]  A. Arakawa,et al.  The Macroscopic Entrainment Processes of Simulated Cumulus Ensemble. Part I: Entrainment Sources , 1997 .

[22]  Joanne Simpson,et al.  Statistical properties of a cloud ensemble - A numerical study , 1987 .

[23]  David E. Stevens,et al.  Vertical Mass Flux Calculations in Hawaiian Trade Cumulus Clouds from Dual-Doppler Radar , 1996 .

[24]  J. Kain,et al.  A One-Dimensional Entraining/Detraining Plume Model and Its Application in Convective Parameterization , 1990 .

[25]  Ming Zhao,et al.  Episodic Mixing and Buoyancy-Sorting Representations of Shallow Convection: A Diagnostic Study , 2003 .

[26]  R. Carpenter,et al.  Entrainment and Detrainment in Numerically Simulated Cumulus Congestus Clouds. , 1998 .

[27]  Ming Zhao,et al.  Life Cycle of Numerically Simulated Shallow Cumulus Clouds. Part II: Mixing Dynamics , 2005 .

[28]  A. Arakawa,et al.  Interaction of a Cumulus Cloud Ensemble with the Large-Scale Environment, Part I , 1974 .

[29]  T. Nitta.  Observational Determination of Cloud Mass Flux Distributions , 1975 .

[30]  Kelvin K. Droegemeier,et al.  Entrainment and Detrainment in Numerically Simulated Cumulus Congestus Clouds. Part I: General Results , 1998 .

[31]  Roel Neggers,et al.  Size Statistics of Cumulus Cloud Populations in Large-Eddy Simulations , 2003 .

[32]  S. Esbensen.  Bulk Thermodynamic Effects and Properties of Small Tropical Cumuli , 1978 .

[33]  A. Blyth,et al.  A Stochastic Mixing Model for Nonprecipitating Cumulus Clouds , 1986 .

[34]  Piotr K. Smolarkiewicz,et al.  Gravity Waves, Compensating Subsidence and Detrainment around Cumulus Clouds , 1989 .

[35]  L. Margolin,et al.  Large-eddy simulations of convective boundary layers using nonoscillatory differencing , 1999 .

[36]  M. Baker,et al.  Entrainment and Detrainment in Cumulus Clouds , 1991 .

[37]  T. Clark,et al.  Dynamics of the Cloud-Environment Interface and Entrainment in Small Cumuli: Two-Dimensional Simulations in the Absence of Ambient Shear , 1985 .

[38]  W. Grabowski,et al.  The multidimensional positive definite advection transport algorithm: nonoscillatory option , 1990 .

[39]  T. Clark,et al.  Cloud-Environment Interface Instability: Part II: Extension to Three Spatial Dimensions , 1993 .

[40]  J. Slingo,et al.  Tropical forecasting at ECMWF: The influence of physical parametrization on the mean structure of forecasts and analyses , 2006 .

[41]  G. Raga,et al.  Characteristics of Cumulus Band Clouds off the Coast of Hawaii. , 1990 .

[42]  H. Stommel.  ENTRAINMENT OF AIR INTO A CUMULUS CLOUD , 1947 .