Cirrus Production by Tropical Mesoscale Convective Systems

Jasmine Cetrone and Robert Houze8 February 2008

Are Cirrus Clouds Important?

Sherwood et al. (1994)

?

With high clouds Without high clouds

Global Distribution of High Clouds

• Majority of high clouds confined to the tropics

Wylie et al. (1994)

JJA

DJF

Cirrus and Precipitation

• Precipitation intimately tied to cirrus

ISCCP High Cloud Amounts

Schumacher and Houze (2003)

MCSs as Major Contributors to Upper-level Hydrometeors

Houze (1982)

Distribution of MCS Properties

TRMM TMI 85-GHz ice scattering

TRMM-derived summer time stratiform rain fraction

Water Budget of a MCS

*

Ecd

Ccu

Csu

Esd

CT

Ac As

HEIGHT

MIXED ANVIL

Rc Rs

STRATIFORMCONV.ANVIL

Ece

ΔXA

Ese

ΔXSΔXC

(ΔZA )I

(ΔXA)M (ΔXA)I

* *

* **** *

*ICE ANVIL

(ΔZA)M

**

**

Ecd

Ccu

CsuCsu

EsdEsd

CT

Ac As

HEIGHT

MIXED ANVIL

Rc Rs

STRATIFORMCONV.ANVIL

Ece

ΔXA

Ese

ΔXSΔXC

(ΔZA )I

(ΔXA)M (ΔXA)I

* *

* **** *

*ICE ANVIL

(ΔZA)M

**

*

SW LW

LW

Adapted from Houze et al. (1980)

Goals

• Establish climatologies of precipitation and anvil regions of MCSs over regions of the tropics

• Determine relationships between the precipitation and anvil regions of MCSs

• Complete the conceptual model of cloud and precipitation structure of MCSs

Regions of Interest

Schumacher and Houze (2003)

Summer timeSF rain frac

ContinentalMonsoon

OceanicMonsoon

Maritime ContinentMonsoon

West Africa

• Influenced by African Monsoon during NH summer months (continental monsoon climate)

• Many squall-like MCSs• Summer 2006: AMMA project

– Scanning precipitation radar

– 4xdaily soundings – Vertically pointing cloud

radar

Maritime Continent

• Influenced by Australian Monsoon during SH summer months (island monsoon climate)

• Massive MCSs influenced by monsoonal flow• Long-term dataset at Darwin, Australia:

– 2 scanning precipitation radars (dual-Doppler)

– Vertically pointing cloud radar– 2xdaily soundings– Satellite coverage

Bay of Bengal

• Influenced by Asian Monsoon during NH summer months (oceanic monsoon climate)

• Southward-propagating leading-convection, trailing stratiform type MCSs

• May 1999: JASMINE project– Scanning precipitation

radar– 3-hourly soundings – Vertically pointing cloud

radar

JASMINE Ship RadarData

TRMM PrecipitationRadar Swath

23 May 1999 0650 LST

JASMINE

Bay of Bengal

India

JASMINE Ship RadarData

TRMM PrecipitationRadar Swath

23 May 1999 0650 LST

JASMINE

Bay of Bengal

India

Methodology

• TRMM PR and CloudSat reflectivity data from over three regions only from MCSs– 2006 Monsoon season in W Africa– 2006 Monsoon season in Bay of Bengal– 2006-2007 Monsoon season in Maritime

Island

– Use of hourly IR geostationary satellite data insured selection of MCS cases

TRMM PR Convective CFADs

• Convective precip in W Africa MCSs are taller and more intense

• Convective precip in Maritime and Bengal MCSs is similar, with Maritime being slightly taller

W Africa Maritime Continent Bay of Bengal

TRMM PR Stratiform CFADs

• Stratiform precip in W Africa MCSs taller and high reflectivities at high altitudes (indicating large ice aloft, consistent with Nesbitt et al 2000.)

• Stratiform precip in Maritime MCSs slightly taller and with higher reflectivities aloft than Bengal

W Africa Maritime Continent Bay of Bengal

TRMM PR Convective Rain Fraction

• Very high convective rain fractions in W Africa MCSs, indicating stratiform regions that are smaller and/or shorter in duration

• Maritime has lowest convective rain fraction, influence of monsoonal systems with large, long lasting stratiform regions

• Bengal distribution indicates moderate convective rain fraction, and narrow shows that MCSs in that region are very similar to each other

W Africa Maritime Continent Bay of Bengal

CloudSat Anvil CFADs

• W Africa anvil clouds shallower!• Maritime anvil clouds reach the highest

W Africa Maritime Continent Bay of Bengal

CloudSat Thick Anvil (>6km) CFADs

• W Africa anvils have high frequency of high reflectivity near cloud bottom(large crystals)

• Maritime and Bengal distributions similar• Evidence of aggregation below thick anvil?• High IWP for W Africa anvils compared to

Bengal/Maritime anvils

W Africa Maritime Continent Bay of Bengal

Conditional Instability

• W Africa has layer of strong instability from surface to ~600 hPa, leads to violent convective updrafts

• Maritime has layer of instability from surface to ~600 hPa, while Bengal has more shallow layer of instability

SS S

S SS

W Africa Maritime Continent Bay of Bengal

What Controls Anvil?• Bengal and Maritime MCSs show many

similarities in anvil, while W Africa MCSs have different anvil features

• W Africa MCSs have precipitation CFADs that show deeper, more intense convection

• Possibly the intensity of convection and/or fraction of convective rainfall affects the type of anvil

• Much anvil comes out of stratiform precipitation regions…so smaller stratiform precipitation areas leads to less anvil

SS S

S SS

Convection and Anvils in MCSsSS S

S SS

• When deep, intense, continental convection is present, see a “settling” of the anvil– Overshooting top– Large ice falling

Preliminary ConclusionsSS S

S SS

• W Africa MCSs―Deep, intense convection, small stratiform area―Anvils shallower, but high IWP

• Maritime MCSs―Moderate convection, large stratiform areas―Deep anvils

• Bengal MCSs―Moderate convection, moderate stratiform areas―Deep anvils

• Anvil height and density in MCSs influenced by convective intensity and amount

• Anvil longevity possibly moderated by amount of stratiform precipitation (need case studies)

Future WorkSS S

S SS

• Environmental conditions also a factor―Case studies in each region for different

environmental conditions

• Examine TRMM / CloudSat coincident cases for coherent view