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Tropical Transition in the Eastern North Pacific:
Sensitivity to Microphysics
Alicia M. BentleyATM 562
17 May 2012
Invest 91C
1 November 2006
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:
Brazil
Italy
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
Italy
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
Italy
Invest 91CUnnamed 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 2006 1200 UTC − 1 November 2006
NWS/NCEP Pacific Surface Analysis
Black contours: 850 hPa relative vorticity Shaded: on Dynamic TropopauseWhite Barbs: Winds on the DT (m s-1)
Image courtesy of Nick Metz
Invest 91CUnnamed 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 2006 2030 UTC − 1 November 2006
MODIS (VISIBLE)
Black contours: 850 hPa relative vorticity Shaded: on Dynamic TropopauseWhite Barbs: Winds on the DT (m s-1)
Image courtesy of Nick Metz
Invest 91CUnnamed 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°W 150°W 140°W 130°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 2006End time: 1200 UTC 1 November 2006
Overview
Outer = 30 kmInner = 10 km
Model Configuration
WRF Physics Package
CumulusParameterization
(Kain-Fritsch)
Land Surface(Noah)
PBL(Mellor-Yamada-
Janjic TKE)
Microphysics
WSM6 WSM3 Kessler
Run #1 Run #2 Run #3 “Warm rain” “3-class” “6-class”
Results
WSM6 WSM3
1200 UTC − 1 November 2006
Infrared (°C)
ObservationKessler
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 WSM3
1200 UTC − 1 November 2006
Kessler
Max. Reflectivityand 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 WSM3
1200 UTC − 1 November 2006
Infrared (°C)
ObservationKessler
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 (2°C @ 700 hPa)
• WSM3: sharpest temperature gradient & strongest winds
Results
WSM6 WSM3
1200 UTC − 1 November 2006
Infrared (°C)
ObservationKessler 10 m s-1
10 m s-1 10 m s-1
850 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 cyclones2) Identify asymmetry in convection3) 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. BentleyE-mail: [email protected]
Special Thanks to: Kevin Tyle, Derek Mallia, Nick Metz,
& Kristen Corbosiero
Thank you!
Any Questions?