Tropical Transition in the Eastern North Pacific: Sensitivity to Microphysics Alicia M. Bentley ATM 562 17 May 2012.

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?