Nature versus Nurture in Shallow Convection

Abstract Tracers are used in a large-eddy simulation of shallow convection to show that stochastic entrainment (and not cloud-base properties) determines the fate of convecting parcels. The tracers are used to diagnose the correlations between a parcel’s state above the cloud base and both the parcel’s state at the cloud base and its entrainment history. The correlation with the cloud-base state goes to zero a few hundred meters above the cloud base. On the other hand, correlations between a parcel’s state and its net entrainment are large. Evidence is found that the entrainment events may be described as a stochastic Poisson process. A parcel model is constructed with stochastic entrainment that is able to replicate the mean and standard deviation of cloud properties. Turning off cloud-base variability has little effect on the results, which suggests that stochastic mass-flux models may be initialized with a single set of properties. The success of the stochastic parcel model suggests that it holds promi...

[1]  R. Neggers.  A Dual Mass Flux Framework for Boundary Layer Convection. Part II: Clouds , 2009 .

[2]  Z. Kuang,et al.  Do Undiluted Convective Plumes Exist in the Upper Tropical Troposphere , 2010 .

[3]  David M. Romps,et al.  The Dry-Entropy Budget of a Moist Atmosphere , 2008 .

[4]  David M. Romps,et al.  A Direct Measure of Entrainment , 2010 .

[5]  M. Tiedtke.  A Comprehensive Mass Flux Scheme for Cumulus Parameterization in Large-Scale Models , 1989 .

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

[7]  Q. Fu,et al.  Improvements of an ice-phase microphysics parameterization for use in numerical simulations of tropical convection , 1995 .

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

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

[10]  H. D. Orville,et al.  Bulk Parameterization of the Snow Field in a Cloud Model , 1983 .

[11]  Steven K. Krueger,et al.  Modeling Entrainment and Finescale Mixing in Cumulus Clouds , 1997 .

[12]  E. Rasmusson,et al.  Measurements of the Atmospheric Mass, Energy, and Momentum Budgets Over a 500-Kilometer Square of Tropical Ocean , 1973 .

[13]  J. Warner,et al.  Time Variation of Updraft and Water Content in Small Cumulus Clouds , 1977 .

[14]  Stephen J. Lord,et al.  Role of a Parameterized Ice-Phase Microphysics in an Axisymmetric, Nonhydrostatic Tropical Cyclone Model , 1984 .

[15]  P. R. Jonas,et al.  Observations of cumulus cloud entrainment , 1990 .

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

[17]  M. Köhler,et al.  A Dual Mass Flux Framework for Boundary Layer Convection. Part I: Transport , 2009 .