Downslope Windstorms of San Diego County. Part I: A Case Study

AbstractThe “Santa Ana” wind is an offshore flow that affects Southern California periodically during the winter half of the year, typically between September and May. The winds can be locally gusty, particularly in the complex terrain of San Diego County, where the winds have characteristics of downslope windstorms. These winds can cause and/or rapidly spread wildfires, the threat of which is particularly acute during the autumn season before the onset of winter rains. San Diego’s largest fires, including the Cedar fire of 2003 and Witch Creek fire of 2007, occurred during Santa Ana wind events.A case study of downslope flow during a moderately intense Santa Ana event during mid-February 2013 is presented. Motivated by the need to forecast winds impinging on electrical lines, the authors make use of an exceptionally dense network of near-surface observations in San Diego County to calibrate and verify simulations made utilizing the Advanced Research version of the Weather Research and Forecasting (WRF) M...

[1]  J. Wieringa,et al.  An objective exposure correction method for average wind speeds measured at a sheltered location , 1976 .

[2]  G. Ellis,et al.  The Santa Ana Winds of Southern California , 1962 .

[3]  Yuh-Lang Lin,et al.  Synoptic-Scale and Mesoscale Environments Conducive to Forest Fires during the October 2003 Extreme Fire Event in Southern California , 2007 .

[4]  Z. Janjic.  The Step-Mountain Eta Coordinate Model: Further Developments of the Convection, Viscous Sublayer, and Turbulence Closure Schemes , 1994 .

[5]  Climate in a small area: An introduction to local meteorology: M. M. Yoshino. University of Tokyo Press, Tokyo, 1975, 549 pp., £16.00. , 1976 .

[6]  Dale R. Durran,et al.  NOWCAST: THE MAP ROOM: Recent Developments in the Theory of Atmospheric Rotors , 2004 .

[7]  J. W. Verkaik.  Evaluation of Two Gustiness Models for Exposure Correction Calculations , 2000 .

[8]  Kenneth J. Westrick,et al.  Does Increasing Horizontal Resolution Produce More Skillful Forecasts , 2002 .

[9]  Climate in a small area : an introduction to local meteorology , 1975 .

[10]  J. Oliver,et al.  Climate in a Small Area: An Introduction to Local Meterology , 1976 .

[11]  J. Pleim.  A Combined Local and Nonlocal Closure Model for the Atmospheric Boundary Layer. Part I: Model Description and Testing , 2007 .

[12]  Thorsten Mauritsen,et al.  Performance of an Eddy Diffusivity-Mass Flux Scheme for Shallow Cumulus Boundary Layers , 2010 .

[13]  G. Mayr,et al.  Dynamically-Driven Winds , 2013 .

[14]  W. Sommers.  LFM Forecast Variables Related to Santa Ana Wind Occurrences , 1978 .

[15]  J. Pleim.  A Combined Local and Nonlocal Closure Model for the Atmospheric Boundary Layer. Part II: Application and Evaluation in a Mesoscale Meteorological Model , 2007 .

[16]  D. Durran,et al.  Another Look at Downslope Winds. Part II: Nonlinear Amplification beneath Wave-Overturning Layers , 1987 .

[17]  Dale R. Durran,et al.  Another Look at Downslope Windstorms. Part I: The Development of Analogs to Supercritical Flow in an Infinitely Deep, Continuously Stratified Fluid. , 1986 .

[18]  D. Durran,et al.  Initial-Condition Sensitivities and the Predictability of Downslope Winds , 2009 .

[19]  J. Dudhia,et al.  Coupling an Advanced Land Surface–Hydrology Model with the Penn State–NCAR MM5 Modeling System. Part I: Model Implementation and Sensitivity , 2001 .

[20]  D. Stensrud.  Parameterization Schemes: Keys to Understanding Numerical Weather Prediction Models , 2007 .

[21]  Interacting Mountain Waves and Boundary Layers , 2007 .

[22]  J. Klemp,et al.  The Dynamics of Wave-Induced Downslope Winds , 1975 .

[23]  J. D. Tarpley,et al.  Implementation of Noah land surface model advances in the National Centers for Environmental Prediction operational mesoscale Eta model , 2003 .

[24]  Günther Zängl,et al.  The impact of the PBL scheme and the vertical distribution of model layers on simulations of Alpine foehn , 2008 .

[25]  Jimy Dudhia,et al.  Impacts of the Lowest Model Level Height on the Performance of Planetary Boundary Layer Parameterizations , 2012 .

[26]  Marilyn N. Raphael,et al.  The Santa Ana Winds of California , 2003 .

[27]  J. Dudhia,et al.  A New Vertical Diffusion Package with an Explicit Treatment of Entrainment Processes , 2006 .

[28]  Simon Vosper,et al.  Inversion effects on mountain lee waves , 2004 .

[29]  W. Collins,et al.  Radiative forcing by long‐lived greenhouse gases: Calculations with the AER radiative transfer models , 2008 .

[30]  C. Jones,et al.  Forecast Skill of Synoptic Conditions Associated with Santa Ana Winds in Southern California , 2010 .

[31]  Ronald B. Smith,et al.  Alpine gravity waves: Lessons from MAP regarding mountain wave generation and breaking , 2007 .

[32]  A. Aiyyer,et al.  An Examination of Wind Decay, Sustained Wind Speed Forecasts, and Gust Factors for Recent Tropical Cyclones in the Mid-Atlantic Region of the United States , 2015 .

[33]  Aijun Xiu,et al.  Development and Testing of a Surface Flux and Planetary Boundary Layer Model for Application in Mesoscale Models , 1995 .

[34]  Semion Sukoriansky,et al.  A quasi-normal scale elimination model of turbulence and its application to stably stratified flows , 2006 .

[35]  Dale R. Durran,et al.  Mountain Waves and Downslope Winds , 1990 .

[36]  W. Brinkmann.  Strong Downslope Winds at Boulder, Colorado , 1974 .

[37]  Yang Cao.  The Santa AnaWinds of Southern California in the context of Fire Weather , 2015 .

[38]  W. Gallus,et al.  Sensitivity of simulated regional surface thermal fluxes during warm advection snowmelt to selection of the lowest model level height , 2001 .

[39]  P. F. Sheridan,et al.  A flow regime diagram for forecasting lee waves, rotors and downslope winds , 2006 .

[40]  Hubert Chanson,et al.  Current knowledge in hydraulic jumps and related phenomena: A survey of experimental results , 2009 .

[41]  G. Powers,et al.  A Description of the Advanced Research WRF Version 3 , 2008 .

[42]  J. Monteith,et al.  Boundary Layer Climates. , 1979 .

[43]  Jonathan E. Pleim,et al.  Development of a Land Surface Model. Part I: Application in a Mesoscale Meteorological Model , 2001 .

[44]  Terry L. Clark,et al.  The Evolution and Stability of Finite-Amplitude Mountain Waves. Part II: Surface Wave Drag and Severe Downslope Windstorms , 1979 .

[45]  Alex Hall,et al.  Local and synoptic mechanisms causing Southern California’s Santa Ana winds , 2010 .

[46]  D. Durran,et al.  The Overamplification of Gravity Waves in Numerical Solutions to Flow over Topography , 2009 .

[47]  J. Dudhia,et al.  Coupling an Advanced Land Surface–Hydrology Model with the Penn State–NCAR MM5 Modeling System. Part II: Preliminary Model Validation , 2001 .

[48]  Kevin W. Manning,et al.  The community Noah land surface model with multiparameterization options (Noah-MP): 1. Model description and evaluation with local-scale measurements , 2011 .

[49]  Frederic Paik Schoenberg,et al.  Testing separability in marked multidimensional point processes with covariates , 2011 .

[50]  Timothy J. Brown,et al.  Climate, Santa Ana Winds and Autumn Wildfires in Southern California , 2004 .