Tropical Transition in the Eastern North Pacific: Sensitivity to Microphysics Alicia M. Bentley ATM May 2012

Tropical Transition Image: MODIS (VISIBLE) Hurricane Catarina (March 2004) Image: EUMETSAT (VISIBLE) Mediterranean Cyclone (October 1996) Tropical cyclones (TCs) are not exclusive to the tropics Warm core cyclones observed in atypical basins:

Tropical Transition Image: EUMETSAT (VISIBLE) Mediterranean Cyclone (October 1996) Effect of upshear convection Fig. 3b from Davis and Bosart (2004) Upper-level trough forcing and convectively driven diabatic potential vorticity (PV): 1) Enhance mesoscale convective vortex 2) Reduce shear over cyclone

Tropical Transition Effect of upshear convection Fig. 3b from Davis and Bosart (2004) Upper-level trough forcing and convectively driven diabatic potential vorticity (PV): 1) Enhance mesoscale convective vortex 2) Reduce shear over cyclone Image: NOAA (VISIBLE) Mediterranean Cyclone (October 1996) Pre-Tropical Transition L

Invest 91C Unnamed TC in Eastern North Pacific (Invest 91C) –Baroclinic cyclone (28 October 2006) –Convection associated with bent-back frontal structure reduces vertical wind shear (29 October 2006) –Occludes and becomes warm core (1 November 2006) 1200 UTC − 29 October UTC − 1 November 2006 NWS/NCEP Pacific Surface Analysis Black contours: 850 hPa relative vorticity Shaded:  on Dynamic Tropopause White Barbs: Winds on the DT (m s -1 ) Image courtesy of Nick Metz 0000 UTC − 2 November 2006 Fig. 18b from Hulme and Martin (2009) Thin black contours:  e (K) Shaded: Tropospheric PV (PVU)

Invest 91C Unnamed TC in Eastern North Pacific (Invest 91C) –Warming in TC core due to the combination of diabatic heating in the eyewall and dry adiabatic descent within the eye –Structure of a TC is sensitive to the microphysical parameterization (MP) scheme used (Stern and Nolan 2012) 1200 UTC − 29 October UTC − 1 November 2006 MODIS (VISIBLE) Black contours: 850 hPa relative vorticity Shaded:  on Dynamic Tropopause White Barbs: Winds on the DT (m s -1 ) Image courtesy of Nick Metz

Invest 91C Unnamed TC in Eastern North Pacific (Invest 91C) –Warming in TC core due to the combination of diabatic heating in the eyewall and dry adiabatic descent within the eye –Structure of a TC is sensitive to the microphysical parameterization (MP) scheme used (Stern and Nolan 2012) OBJECTIVE: Identify the structural differences in Invest 91C that result from changing the complexity of the MP scheme 2030 UTC − 1 November 2006 MODIS (VISIBLE)

Model Configuration 160°W150°W140°W130°W 30°N 40°N 50°N Domain British Columbia Weather Research and Forecasting (WRF) V3.4 1° Global Forecast System (GFS) analysis data Two-way nested grid Resolution 35 vertical levels Start time: 1200 UTC 29 October 2006 End time: 1200 UTC 1 November 2006 Overview Outer = 30 km Inner = 10 km

Model Configuration WRF Physics Package Cumulus Parameterization (Kain-Fritsch) Land Surface (Noah) PBL (Mellor-Yamada- Janjic TKE) Microphysics WSM6WSM3Kessler Run #1Run #2Run #3 “Warm rain” “3-class” “6-class”

Results WSM6 WSM UTC − 1 November 2006 Infrared (°C) Observation Kessler Max. Reflectivity and MSLP Red contours: MSLP (hPa) All MP schemes: - correctly identify asymmetry - highlight remains of occluded front to the northeast Same location in all simulations Kessler: lowest MSLP (< 984 hPa) WSM6 & WSM3: MSLP < 988 hPa

Results WSM6 WSM UTC − 1 November 2006 Kessler Max. Reflectivity and MSLP Red contours: MSLP (hPa) All MP schemes: - correctly identify asymmetry - highlight remains of occluded front to the northeast Same location in all simulations Kessler: lowest MSLP (< 984 hPa) WSM6 & WSM3: MSLP < 988 hPa NWS/NCEP Pacific Surface Analysis Yellow contours: MSLP (hPa) 140°W150°W 40°N

Results Red contours: 700 hPa temperature (°C) Blue contours: 700 hPa heights (m) Barbs: 700 hPa winds (m s -1 ) WSM6 WSM UTC − 1 November 2006 Infrared (°C) Observation Kessler 700 hPa Height, Temperature, and Winds All MP schemes: - indicate a warm core - asymmetry in wind field matches convection Kessler: deepest cyclone with the warmest core 700 hPa) WSM3: sharpest temperature gradient & strongest winds

Results WSM6 WSM UTC − 1 November 2006 Infrared (°C) Observation Kessler 10 m s hPa Absolute Vorticity and Wind All MP schemes: - persistent asymmetry in the wind field - consistently place center at ~41.5°N,146°W WSM3 and Kessler: absolutely vorticity maximum removed from the center of circulation

Results WSM6 WSM3 Kessler Infrared (°C) Observation 1200 UTC − 1 November 2006 Outgoing Longwave Radiation WSM6 & WSM3: - correctly identify asymmetry - different because of binning hydrometers (mixed-phase) Kessler: - lofting condensate into the atmosphere - GIANT anvil

Results Kessler 1200 UTC − 1 November 2006 Vertical cross sections of condensate (g kg -1 ; shaded) and virtual temperature perturbations from the initial state (K; contoured) [Fig. 7 from Fovell et al. 2009] WSM3 Kessler WSM3

Conclusions Invest 91C: TT in Eastern North Pacific (October 2006) –Occludes and becomes warm core by 1200 UTC 1 November Structure of TC sensitive to MP scheme –WRF V3.4 – MP schemes: WSM6; WSM3; Kessler All MP schemes: 1) Produce warm core cyclones 2) Identify asymmetry in convection 3) Indicate stronger winds to the north of TC center WSM6: solution consistently closer to reality WSM3: strongest winds and largest vorticity values Kessler: warmest core, deepest cyclone, horrible OLR field –Lofting too much condensate into the atmosphere, spurious results

Alicia M. Bentley Special Thanks to: Kevin Tyle, Derek Mallia, Nick Metz, & Kristen Corbosiero Thank you! Any Questions?