Chris Birchfield Atmospheric Sciences, Spanish minor

 Center of low pressure  Warm Core  No fronts attached

 Warm tropical oceans between 8° and 20° latitude  Typically 80°F<  Tropical disturbance  Convection - Thunderstorms form  Rotation due to Coriolis Force  Depression  Tropical Storm  Hurricane

 Inner-core observations of hurricanes limited to dropsondes or buoys  Modelers forced to use high-sensitivity PBL parameterizations  Importance of surface fluxes & vertical mixing  Equivalent potential temperature (Θ e )

 Burk-Thompson PBL scheme  Bulk-Aerodynamic PBL scheme  Blackadar PBL scheme  MRF PBL scheme  BL/BT  BL/BU1  BL/BU2  BU/BT  MRF/BT

 Domain A – 36-km grid  Domain B – 12-km grid  C1 & C2 – moving 4-km grids

 Used to conduct 72-hr simulations  Uses course grid of 193 X 163 grid points  Uses x,y spacing of 36 km (fig.1)  Grid centered at 33°N, 84°W  Conditions were obtained from ECMWF  9 high-resolution simulations

 Shows max winds in excess of 50 m/s E  Shaded region = winds of 35< m/s

 BT yields winds of 55< m/s  BA has wavenumber 2 pattern. 100 km area of 35 m/s winds  BL and MRF display weaker winds

 Indicates partial eyewall  Radius of ~25km  Northern convective bands showed high reflectivities

 Each case shows defined eyewall  Precipitation less defined – more scattered

 BT  BA  BL  MRF Vertical Velocity Tangential Velocity

 BT  BA  BL  MRF Radial Velocity Equivalent Potential Energy (Θ e )

 BT  BA  BL  MRF Avg. Tangential Velocity Temp. Tendency

 BT  BA  BL  MRF Water Vapor Tendencies Eddy Diffusivity Coefficient

 q v = Vapor mixing ratio  K = Eddy diffusivity  L v = Latent heat of vaporization  ρ = Density of air  Δz 1 = Vertical grid increment of lowest layer

 E s & C q = Moisture  H s & C 0 = Heat  τ s & C D = Momentum  C k = Enthalpy

 Blackadar agrees with Hawkins and Imbembo up to 45 m/s  BT values parallel, but lower due to weaker dependence of z o.  BA is uniform due to lack of wind speed dependence z o

 Original Blackadar produces weakest storm (C k /C D ) is smallest  BL/BU1 neglecting z o produces the strongest storm  BL/BU2 including z o does not produce strongest

 The MM5 model simulated Hurricane Bob in high resolution  Results exhibited high sensitivity to PBL processes.  Min SLP and max winds varied by 16mb and 15 m/s  BT & BA produced the strongest storms  Vertical structures similar in BT, BL and BA  Each PBL scheme differed in vertical mixing

 Intensity increases as C k /C D increases  Surface fluxes & vertical mixing differ  difficult to ascertain individual roles.  Simulated intensity varies depending on wind speed dependence of the surface roughness parameter z 0  Precipitation forecasts very sensitive  Obtaining measurements for heat, moisture, momentum essential.  Dropsondes & Doppler Radar play significant role in observing the depth.

 More measurements  Dissipative heating  Sea spray  Ocean-atmosphere coupling