A Numerical Investigation of the Effects of Dry Air Aloft on Deep Convection

Abstract A three-dimensional cloud model was used to investigate the sensitivity of deep convective storms to dry air above the cloud base. In simulations of both quasi-linear convective systems and supercells, dry air aloft was found to reduce the intensity of the convection, as measured by updraft mass flux and total condensation and rainfall. In high-CAPE line-type simulations, the downdraft mass flux and cold pool strength were enhanced at the rear of the trailing stratiform region in a drier environment. However, the downdraft and cold pool strengths were unchanged in the convective region, and were also unchanged or reduced in simulations of supercells and of line-type systems at lower CAPE. This result contrasts with previous interpretations of the role of dry air aloft in the development of severe low-level outflow winds. The buoyancy-sorting framework is used to interpret the influence of environmental humidity on the updraft entrainment process and the observed strong dependence on the environme...

[1]  Joseph B. Klemp,et al.  The Influence of the Shear-Induced Pressure Gradient on Thunderstorm Motion , 1982 .

[2]  Joseph B. Klemp,et al.  The Dependence of Numerically Simulated Convective Storms on Vertical Wind Shear and Buoyancy , 1982 .

[3]  Joseph B. Klemp,et al.  Structure and Evolution of Numerically Simulated Squall Lines , 1988 .

[4]  Roger M. Wakimoto,et al.  Wet Microburst Activity over the Southeastern United States: Implications for Forecasting , 1991 .

[5]  Chidong Zhang,et al.  Variability of midtropospheric moisture and its effect on cloud-top height distribution during TOGA COARE , 1997 .

[6]  Ariel E. Cohen,et al.  Discrimination of Mesoscale Convective System Environments Using Sounding Observations , 2007 .

[7]  Louis J. Wicker,et al.  Time-Splitting Methods for Elastic Models Using Forward Time Schemes , 2002 .

[8]  B. Ferrier,et al.  Sensitivity of Tropical West Pacific Oceanic Squall Lines to Tropospheric Wind and Moisture Profiles , 2000 .

[9]  Scott A. Braun,et al.  Sensitivity of High-Resolution Simulations of Hurricane Bob (1991) to Planetary Boundary Layer Parameterizations , 2000 .

[10]  Robert H. Johns,et al.  Derechos: Widespread Convectively Induced Windstorms , 1987 .

[11]  F. Carr,et al.  A Composite Study of Comma Clouds and their Association with Severe Weather over the Great Plains , 1985 .

[12]  Mitchell W. Moncrieff,et al.  A Numerical Investigation of the Organization and Interaction of the Convective and Stratiform Regions of Tropical Squall Lines , 1988 .

[13]  E. McCaul,et al.  The Impact on Simulated Storm Structure and Intensity of Variations in the Mixed Layer and Moist Layer Depths , 2002 .

[14]  Evan L. Kuchera,et al.  Severe Convective Wind Environments , 2006 .

[15]  G. Thompson,et al.  Impact of Cloud Microphysics on the Development of Trailing Stratiform Precipitation in a Simulated Squall Line: Comparison of One- and Two-Moment Schemes , 2009 .

[16]  R. Johns,et al.  Severe Local Storms Forecasting , 1992 .

[17]  Edward J. Zipser,et al.  Environmental Variability during TOGA COARE , 2000 .

[18]  Charles A. Doswell,et al.  On the Environments of Tornadic and Nontornadic Mesocyclones , 1994 .

[19]  K. Browning,et al.  Airflow in convective storms , 1962 .

[20]  Thermodynamic characteristics of air flowing into and out of precipitating convection over the west Pacific warm pool , 1999 .

[21]  Brian E. Mapes,et al.  Gregarious Tropical Convection , 1993 .

[22]  Charles Cohen,et al.  A Quantitative Investigation of Entrainment and Detrainment in Numerically Simulated Cumulonimbus Clouds , 2000 .

[23]  Joseph A. Rogash,et al.  Multiscale Review of the Development and Early Evolution of the 9 April 1991 Derecho , 1992 .

[24]  M. Weisman,et al.  The Sensitivity of Simulated Supercell Structure and Intensity to Variations in the Shapes of Environmental Buoyancy and Shear Profiles , 2001 .

[25]  P. Zuidema,et al.  Radiative-Dynamical Consequences of Dry Tongues in the Tropical Troposphere , 1996 .

[26]  G. Bryan,et al.  A Multimodel Assessment of RKW Theory’s Relevance to Squall-Line Characteristics , 2006 .

[27]  A synoptic climatology of derecho producing mesoscale convective systems in the North‐Central Plains , 2000 .

[28]  D. Dawson.  Improvements in the treatment of evaporation and melting in multi-moment versus single-moment bulk microphysics: results from numerical simulations of the 3 May 1999 Oklahoma tornadic storms , 2008 .

[29]  George H. Bryan,et al.  A Benchmark Simulation for Moist Nonhydrostatic Numerical Models , 2002 .

[30]  Kevin W. Manning,et al.  Explicit Forecasts of Winter Precipitation Using an Improved Bulk Microphysics Scheme. Part I: Description and Sensitivity Analysis , 2004 .

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

[32]  Morris L. Weisman,et al.  The Use of Vertical Wind Shear versus Helicity in Interpreting Supercell Dynamics , 2000 .

[33]  R. Rotunno,et al.  The Triggering of Orographic Rainbands by Small-Scale Topography , 2007 .

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

[35]  J. Deardorff.  Stratocumulus-capped mixed layers derived from a three-dimensional model , 1980 .

[36]  David J. Stensrud,et al.  An Observational Study of Derecho-Producing Convective Systems , 2004 .

[37]  Adrian M. Tompkins,et al.  Organization of Tropical Convection in Low Vertical Wind Shears: The Role of Water Vapor , 2001 .

[38]  R. C. Miller,et al.  A Basis for Forecasting Peak Wind Gusts in Non-Frontal Thunderstorms , 1954 .

[39]  D. S. Foster.  THUNDERSTORM GUSTS COMPARED WITH COMPUTED DOWNDRAFT SPEEDS , 1958 .

[40]  Edward J. Zipser,et al.  Mesoscale and convective-scale downdrafts as distinct components of squall-line structure , 1977 .

[41]  R. Johns,et al.  Synoptic and Mesoscale Analysis of a High-Latitude Derecho Severe Thunderstorm Outbreak in Finland on 5 July 2002 , 2006 .

[42]  David B. Parsons,et al.  The evolution of the tropical western Pacific atmosphere‐ocean system following the arrival of a dry intrusion , 2000 .

[43]  Charles A. Doswell,et al.  Is buoyancy a relative quantity , 2004 .

[44]  T. Warner,et al.  A Synoptic Climatology of the Elevated Mixed-Layer Inversion over the Southern Great Plains in Spring. Part I: Structure, Dynamics, and Seasonal Evolution , 1991 .

[45]  M. Weisman.  The Role of Convectively Generated Rear-Inflow Jets in the Evolution of Long-Lived Mesoconvective Systems , 1992 .

[46]  J. Fritsch,et al.  Bow Echo Sensitivity to Ambient Moisture and Cold Pool Strength , 2006 .

[47]  P. Markowski,et al.  Observations of Vertical Wind Shear Heterogeneity in Convective Boundary Layers , 2007 .

[48]  D. Dawson.  Impact of multi-moment microphysics and model resolution on predicted cold pool and reflectivity intensity and structures in the Oklahoma tornadic supercell storms of 3 May 1999 , 2007 .

[49]  Charles A. Doswell,et al.  Examination of Derecho Environments Using Proximity Soundings , 2001 .

[50]  Mitchell W. Moncrieff,et al.  Two‐dimensional convection in non‐constant shear: A model of mid‐latitude squall lines , 1982 .

[51]  Roscoe R. Braham,et al.  THUNDERSTORM STRUCTURE AND CIRCULATION , 1948 .

[52]  Matthew S. Gilmore,et al.  The Influence of Midtropospheric Dryness on Supercell Morphology and Evolution , 1998 .

[53]  E. Kessler.  On the distribution and continuity of water substance in atmospheric circulations , 1969 .

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

[55]  D. Parsons,et al.  Structure and Evolution of the 22 February 1993 TOGA COARE Squall Line: Numerical Simulations , 1996 .

[56]  Erik N. Rasmussen,et al.  Precipitation and Evolution Sensitivity in Simulated Deep Convective Storms: Comparisons between Liquid-Only and Simple Ice and Liquid Phase Microphysics* , 2004 .