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Mesoscale Convective Systems: Recent Observational and Diagnostic Studies Robert Houze Department of Atmospheric Sciences University of Washington. DEFINITION Mesoscale Convective System (MCS)

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Mesoscale Convective Systems: Recent Observational and Diagnostic Studies

Robert Houze

Department of Atmospheric Sciences

University of Washington


DEFINITION

Mesoscale Convective System (MCS)

A cumulonimbus cloud system that produces a contiguousprecipitationarea ~100 km or more in at least one direction


  • Questions

  • Why do tropical and midlatitude MCSs look different?

  • Does layer lifting occur in a mature MCS?

  • Is rear inflow really from the rear?

  • What controls the size of MCSs?

  • What controls the movement of MCSs?



Radarreflectivity

Strat.

Conv.

Houze et al. 1989, 1990

Tropical & midlatitudes

“Symmetric”

Midlatitudes(later stages)

“Asymmetric”


MCV

Skamarock et al. 94

No Coriolis

Coriolis

Symmetric

Asymmetric

(Tropics & midlatitudes)

(Midlatitudes)



CrossoverZone

Parcel viewpointZipser 1977


MAUL

Layer viewpoint: Bryan and Fritsch 2000

“Slab” or Layer Overturning


Note!

0.5-4.5 km

Layer viewpoint: Kingsmill & Houze 1999

TOGA COARE

Airborne Doppler Observations of MCSs

Convective region flights


Layer viewpoint: Mechem, Houze, & Chen 2002

14

TOGA COARE

23 Dec 92

12

10

150

8

Z (km)

6

100

Y (km)

4

50

2

0

150

200

250

150

200

250

X (km)

X (km)


A

A

B

B

Moncrieff & Klinker 1997

plan view

1000 km

1000 km

cross section



Diversity of stratiform structure: Parker & Johnson 2000

PATTERNS OFEVOLUTION OF STRATIFORM PRECIPITATION IN MIDLATITUDESQUALL LINES


Kingsmill & Houze 1999Documented airflow

shown by airborne Doppler inTOGA COARE MCSs

Stratiform region flights

0°C


JASMINE: Ship radar, Bay of Bengal, 22 May 1999

Refl.

Reflectivity1.5 km level

100 km

Horizontal Distance (km)

RadialVelocity

Radial Velocity3.5 km level

11

Height (km)

0

0

192

11

Height (km)

0

0

192

Horizontal Distance (km)

90 km


JASMINE: Ship radar, Bay of Bengal, 22 May 1999

Refl.

Reflectivity1.5 km level

100 km

Horizontal Distance (km)

RadialVelocity

Radial Velocity3.5 km level

JASMINE: Ship radar, Bay of Bengal, 22 May 1999

12

Height (km)

Reflectivity1.5 km level

0

0

192

100 km

Horizontal Distance (km)

Horizontal Distance (km)

12

Height (km)

Radial Velocity3.5 km level

0

0

192

Horizontal Distance (km)

90 km


Factors determining the size of MCS

ICAPE, sustainability, diurnal cycle


“Super Convective Systems”(SCS)

Sizes of MCSs observed in TOGA COARE

Chen et al. 1996



Examplesof TOGACOAREMCSs

Satellite IR overlaid with A/C radar

100 km


Yuter & Houze 1998

CS map

Convective echo

% of grid

Stratiform echo

Satellite IR

y

(km)

% of grid

Mean IR temp (K)

x (km)


Statistics for all TOGA COARE satellite/radar comparisons

Yuter & Houze 1998

Percent of 24 km square grid covered by A/C radar echo in all the MCS


Statistics for all TOGA COARE satellite/radar comparisons

Yuter & Houze 1998

Portion of 240 km scale grid covered by convective radar echo


Schumacher & Houze 2003

TRMM Precipitation radar:% of 2.5 deg grid covered by stratiform radar echo

Annual Average


Factors determining the movement of MCS:

Waves in the environment, cold pool dynamics


Nakazawa 1988

INTRASEASONALENSEMBLE VARIATION

SUB-ENSEMBLE

MESOSCALE CONVECTIVE SYSTEM


12

13

14

15

IN TOGA COAREMCSs moved individually with wave much of the time

Chen, Houze,& Mapes 1996AnalyzedIR data3°N-10°S208°K threshold

A/Cflightson 12-14Dec

Time (day)

Longitude


Serra & Houze 2002TEPPS—East Pacific ITCZ

Ship radardata

Easterly wave and cold pool propagation hard to distinguish


NOAA Ship R.H. Brown

JASMINE: May 1999

40N

equator

60E

100E


JASMINE IR sequence

(courtesy P. Zuidema)


Ship track

5

10

15

20

25

30

May 1999

Webster et al. 2002

IR over Bay of Bengal during JASMINE


Mapes et al. (2002)

West Coast of South Am.

Gravity

Wave hypothesis




Carbone et al. 2002

WSR88-Dradar dataover U.S.in time/longitudeformat


  • Conclusions

  • Coriolis effect explains why midlatitude MCSs exhibit asymmetry and develop MCVs as they evolve—and why tropical MCSs don’t have asymmetry

  • Parcel lifting gives way to layer lifting in mature MCSs when potentially unstable inflow air becomes moistened—circulations become mesoscale!

  • Midlevel inflow enters stratiform regions from various directions—controlled by environment shear

  • Max size of MCSs related to sustainability of low-level moist inflow—get biggest systems over oceans and with LLJs

  • MCSs motion may be determined by waves propagating through the environment—gravity waves, inertio-gravity waves,…


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