robert a. houze, jr., darren c. wilton, and bradley f. smull university of washington robert a....

Robert A. Houze, Jr., Darren C. Wilton, and Bradley F. SmullRobert A. Houze, Jr., Darren C. Wilton, and Bradley F. SmullUniversity of WashingtonUniversity of Washington


Monsoon Convection in the Himalayan RegionMonsoon Convection in the Himalayan Regionas seen by the TRMM Precipitation Radaras seen by the TRMM Precipitation Radar


Thompson Lecture, NCAR, Boulder, 31 October 2006

Precipitation





Thompson Lecture, NCAR, Boulder, 31 October 2006

GoalGoalGoalGoal

To gain insight into the physical mechanisms by which heavy monsoon precipitation is producedTo gain insight into the physical mechanisms by which heavy monsoon precipitation is produced

ApproachApproachApproachApproach

•Use data from the Precipitation Radar (PR) on the Tropical Rainfall Measuring Mission (TRMM) satellite.

•Examine the three-dimensional structure of the storms producing intense monsoon precipitation.

•Determine how the 3D echo structure varies in relation to details of the Himalayan topography and proximity to surrounding oceans.

•Use data from the Precipitation Radar (PR) on the Tropical Rainfall Measuring Mission (TRMM) satellite.

•Examine the three-dimensional structure of the storms producing intense monsoon precipitation.

•Determine how the 3D echo structure varies in relation to details of the Himalayan topography and proximity to surrounding oceans.

TRMM Precipitation Radar Data Set Used in TRMM Precipitation Radar Data Set Used in This StudyThis Study

TRMM Precipitation Radar Data Set Used in TRMM Precipitation Radar Data Set Used in This StudyThis Study

• June-September 2002, 2003June-September 2002, 2003

• 1648 Overpasses over Himalayan region1648 Overpasses over Himalayan region

• Data specially processed at UW to optimize vertical structure analysisData specially processed at UW to optimize vertical structure analysis

Analysis SubregionsAnalysis SubregionsAnalysis SubregionsAnalysis Subregions

WesternWesternSubregionSubregion

Central Central SubregionSubregion Eastern Eastern

SubregionSubregion

Mountain

Mountain

Lowland

Lowland

Foothills

Foothills

Arabian Arabian SeaSea

Bay of Bay of BengalBengal

°N

°E

INDIAINDIA

TRMM Satellite InstrumentationTRMM Satellite InstrumentationTRMM Satellite InstrumentationTRMM Satellite Instrumentation

Kummerow et al, 1998

= 2 cmImportant! PR measures 3D structure of radar echoes

Analysis of three-dimensional echo regionsAnalysis of three-dimensional echo regionsAnalysis of three-dimensional echo regionsAnalysis of three-dimensional echo regions

Used TRMM algorithm for separating echoes into stratiform & convective regions

STRATIFORMSTRATIFORM identified by 2 criteria:

Non-stratiform is either CONVECTIVECONVECTIVE or “OTHER”“OTHER”

Existence of bright band Lack of intense echo cores

Used TRMM algorithm for separating echoes into stratiform & convective regions

STRATIFORMSTRATIFORM identified by 2 criteria:

Non-stratiform is either CONVECTIVECONVECTIVE or “OTHER”“OTHER”

Analysis of Convective Echo CoresAnalysis of Convective Echo CoresAnalysis of Convective Echo CoresAnalysis of Convective Echo Cores

To study the vertical structure of convective To study the vertical structure of convective regions we first define 3D echo “regions we first define 3D echo “corescores””

To study the vertical structure of convective To study the vertical structure of convective regions we first define 3D echo “regions we first define 3D echo “corescores””

• The TRMM Precipitation Radar data are provided in “bins” ~5 km in the horizontal and ~0.25 km in the vertical

• Echo corecoress are formed by contiguous bins (in 3D3D space) of reflectivity values which exceed the threshold of 40 dBZ40 dBZ.

3D radar echo bounded by 40 dBZ contour

landland

echoechocorecore

Deep Intense Cores Deep Intense Cores 40 dBZ echo 40 dBZ echo > 10 km in height> 10 km in height

Deep Intense Cores Deep Intense Cores 40 dBZ echo 40 dBZ echo > 10 km in height> 10 km in height

WesternWesternCentralCentral

EasternEastern

Wide Intense CoresWide Intense Cores 40 dBZ echo 40 dBZ echo > 1000 km> 1000 km22 area area

Wide Intense CoresWide Intense Cores 40 dBZ echo 40 dBZ echo > 1000 km> 1000 km22 area area

Broad Stratiform EchoBroad Stratiform Echo stratiform echo stratiform echo > 50,000 km> 50,000 km22

Broad Stratiform EchoBroad Stratiform Echo stratiform echo stratiform echo > 50,000 km> 50,000 km22

Lightning frequency based on TRMM satellite Lightning frequency based on TRMM satellite observationsobservations

Lightning frequency based on TRMM satellite Lightning frequency based on TRMM satellite observationsobservations

Carlson et al. 1983Carlson et al. 1983Carlson et al. 1983Carlson et al. 1983

moist

dry,hot

Sawyer 1947Sawyer 1947Sawyer 1947Sawyer 1947

A case of deep isolated 40 dBZ coreA case of deep isolated 40 dBZ core14 June 200214 June 2002


10 meter level10 meter level 200 mb level200 mb level



0900 UTC 0930 UTC



0900 UTC

Deep cores over the Tibetan PlateauDeep cores over the Tibetan Plateau14 July 200214 July 2002

Deep cores over the Tibetan PlateauDeep cores over the Tibetan Plateau14 July 200214 July 2002

1227 UTC

In western region--In western region--graupel particles graupel particles

lofted to great lofted to great heights by strong heights by strong

updraftsupdrafts

Height of 40 dBZ cores by regionHeight of 40 dBZ cores by regionHeight of 40 dBZ cores by regionHeight of 40 dBZ cores by region


A case of wide 40 dBZ echo coreA case of wide 40 dBZ echo core22 July 200222 July 2002




1300 UTC 1400 UTC



1300 UTC

A typical case of wide 40 dBZ echo core with line A typical case of wide 40 dBZ echo core with line organizationorganization

A typical case of wide 40 dBZ echo core with line A typical case of wide 40 dBZ echo core with line organizationorganization

3 Sep 20033 Sep 20033 Sep 20033 Sep 2003

2208 UTC

A wide 40 dBZ echo core with squall-line A wide 40 dBZ echo core with squall-line organization—rare! organization—rare!

A wide 40 dBZ echo core with squall-line A wide 40 dBZ echo core with squall-line organization—rare! organization—rare!

5 June 20035 June 20035 June 20035 June 2003

2017 UTC


A of wide 40 dBZ echo core with squall-line A of wide 40 dBZ echo core with squall-line organization—rare! organization—rare!

A of wide 40 dBZ echo core with squall-line A of wide 40 dBZ echo core with squall-line organization—rare! organization—rare!

5 June 20035 June 20035 June 20035 June 2003

500 mb jet over 500 mb jet over and parallel to and parallel to the Himalayasthe Himalayas

Horizontal area of 40 dBZ cores by regionHorizontal area of 40 dBZ cores by regionHorizontal area of 40 dBZ cores by regionHorizontal area of 40 dBZ cores by region

In western regionIn western region—wide convective —wide convective

areas more areas more frequentfrequent

Area (km2)

Cum

ulat

ive

Fre

quen

cy

Analysis of Stratiform EchoesAnalysis of Stratiform EchoesAnalysis of Stratiform EchoesAnalysis of Stratiform Echoes

Intraseasonal Variation of the MonsoonIntraseasonal Variation of the MonsoonIntraseasonal Variation of the MonsoonIntraseasonal Variation of the MonsoonWebster & Tomas 1997

39 events1985-95

Day 0:8 mm/d5N-5S80-90E

“Break”

“Active”


Broad stratiform caseBroad stratiform case11 Aug 200211 Aug 2002




0252 UTC

0455 UTC

Broad stratiform caseBroad stratiform caseUpstream of mountainsUpstream of mountains

Broad stratiform caseBroad stratiform caseUpstream of mountainsUpstream of mountains

Size of stratiform precipitation area by Size of stratiform precipitation area by geographical regiongeographical region

Size of stratiform precipitation area by Size of stratiform precipitation area by geographical regiongeographical region

Analysis of All the Reflectivity DataAnalysis of All the Reflectivity DataAnalysis of All the Reflectivity DataAnalysis of All the Reflectivity Data

Reflectivity data for 2 monsoon seasonsReflectivity data for 2 monsoon seasonsReflectivity data for 2 monsoon seasonsReflectivity data for 2 monsoon seasons

Relative frequency of occurrence


Convection is Convection is stronger & stronger & deeper in westdeeper in west

Stratiform more Stratiform more pronounced in pronounced in easteast


Convection is Convection is slightly deeper & slightly deeper & stronger over the stronger over the

lowlands than lowlands than the foothillsthe foothills

SummarySummarySummarySummary• West:West: “Deep” & “wide” “Deep” & “wide”

cores prone to occur just cores prone to occur just upstream & over the upstream & over the foothills, esp. in the west, foothills, esp. in the west, near confluence of dry near confluence of dry downslope & maritime downslope & maritime flows. flows.

• West:West: “Deep” & “wide” “Deep” & “wide” cores prone to occur just cores prone to occur just upstream & over the upstream & over the foothills, esp. in the west, foothills, esp. in the west, near confluence of dry near confluence of dry downslope & maritime downslope & maritime flows. flows.

• Strongest over lowlandsStrongest over lowlands

• Vertical cellsVertical cells

• Wide cores—amorphous Wide cores—amorphous or parallel to mt. rangeor parallel to mt. range

• Lots of lightning Lots of lightning

• No squall lines No squall lines

• Strongest over lowlandsStrongest over lowlands

• Vertical cellsVertical cells

• Wide cores—amorphous Wide cores—amorphous or parallel to mt. rangeor parallel to mt. range

• Lots of lightning Lots of lightning

• No squall lines No squall lines

• Central:Central: Get both deep Get both deep and wide cores, as in and wide cores, as in west, but not as frequent.west, but not as frequent.

• Central:Central: Get both deep Get both deep and wide cores, as in and wide cores, as in west, but not as frequent.west, but not as frequent.

• Squall lines when jet Squall lines when jet parallel to Himalayasparallel to Himalayas

• Isolated cells over Isolated cells over plateauplateau

• Squall lines when jet Squall lines when jet parallel to Himalayasparallel to Himalayas

• Isolated cells over Isolated cells over plateauplateau

• East:East: Get mesoscale, Get mesoscale, partially stratiform cloud partially stratiform cloud systems associated with systems associated with depressions over the Bay depressions over the Bay of Bengalof Bengal

• East:East: Get mesoscale, Get mesoscale, partially stratiform cloud partially stratiform cloud systems associated with systems associated with depressions over the Bay depressions over the Bay of Bengalof Bengal

• Mesoscale systems like Mesoscale systems like oceanic convection with oceanic convection with large stratiform regionslarge stratiform regions

• Get broad stratiform Get broad stratiform regions associated with regions associated with depressions propagating depressions propagating from equatorial regionfrom equatorial region

• Mesoscale systems like Mesoscale systems like oceanic convection with oceanic convection with large stratiform regionslarge stratiform regions

• Get broad stratiform Get broad stratiform regions associated with regions associated with depressions propagating depressions propagating from equatorial regionfrom equatorial region

EpilogueEpilogueEpilogueEpilogue

• What has this study accomplished?

1) Particular structure and organization of summer monsoon convection over the subcontinent of South Asia

2) Behavior of highly convective clouds in a moist flow impinging on a mountain barrier

• What questions remain?

1) Why does the intense convection trigger just upstream of the barrier?

2) In depressions, what are the relative roles of orography and synoptic dynamics?

3) Can high-resolution models predict the observed structures?

• What has this study accomplished?

1) Particular structure and organization of summer monsoon convection over the subcontinent of South Asia

2) Behavior of highly convective clouds in a moist flow impinging on a mountain barrier

• What questions remain?

1) Why does the intense convection trigger just upstream of the barrier?

2) In depressions, what are the relative roles of orography and synoptic dynamics?

3) Can high-resolution models predict the observed structures?

ThanksThanks

robert a. houze, jr., darren c. wilton, and bradley f. smull university of washington robert a....

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