Robert A. Houze, Jr., Darren C. Wilton, and Bradley F. Smull University of Washington Robert A. Houze, Jr., Darren C. Wilton, and Bradley F. Smull University of Washington Monsoon Convection in the Himalayan Region as seen by the TRMM Precipitation Radar Thompson Lecture, NCAR, Boulder, 31 October 2006

Precipitation Robert A. Houze, Jr., Darren C. Wilton, and Bradley F. Smull University of Washington Robert A. Houze, Jr., Darren C. Wilton, and Bradley F. Smull University of Washington Monsoon Convection in the Himalayan Region as seen by the TRMM Precipitation Radar Thompson Lecture, NCAR, Boulder, 31 October 2006

GoalGoal To gain insight into the physical mechanisms by which heavy monsoon precipitation is produced ApproachApproach 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 This Study June-September 2002, 2003June-September 2002, 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 Subregions Western Subregion Central Subregion Eastern Subregion Mountain Lowland Foothills Arabian Sea Bay of Bengal °N °E INDIA

TRMM Satellite Instrumentation Kummerow et al, 1998  = 2 cm Important! PR measures 3D structure of radar echoes

Analysis of three-dimensional echo regions Used TRMM algorithm for separating echoes into stratiform & convective regions  STRATIFORM  STRATIFORM identified by 2 criteria: CONVECTIVE“OTHER”  Non-stratiform is either CONVECTIVE or “OTHER” Existence of bright bandLack of intense echo cores Used TRMM algorithm for separating echoes into stratiform & convective regions  STRATIFORM  STRATIFORM identified by 2 criteria: CONVECTIVE“OTHER”  Non-stratiform is either CONVECTIVE or “OTHER”

Analysis of Convective Echo Cores

To study the vertical structure of convective regions we first define 3D echo “cores” The TRMM Precipitation Radar data are provided in “bins” ~5 km in the horizontal and ~0.25 km in the vertical cores3D 40 dBZEcho cores are formed by contiguous bins (in 3D space) of reflectivity values which exceed the threshold of 40 dBZ. 3D radar echo bounded by 40 dBZ contour land echo core

Deep Intense Cores 40 dBZ echo 40 dBZ echo > 10 km in height > 10 km in height Deep Intense Cores 40 dBZ echo 40 dBZ echo > 10 km in height > 10 km in height Western Central Eastern Wide Intense Cores 40 dBZ echo 40 dBZ echo > 1000 km 2 area > 1000 km 2 area Wide Intense Cores 40 dBZ echo 40 dBZ echo > 1000 km 2 area > 1000 km 2 area Broad Stratiform Echo stratiform echo stratiform echo > 50,000 km 2 > 50,000 km 2 Broad Stratiform Echo stratiform echo stratiform echo > 50,000 km 2 > 50,000 km 2

Lightning frequency based on TRMM satellite observations

Carlson et al moist dry,hot

Sawyer 1947

A case of deep isolated 40 dBZ core 14 June meter level 200 mb level

A case of deep isolated 40 dBZ core 14 June UTC0930 UTC

A case of deep isolated 40 dBZ core 14 June UTC

Deep cores over the Tibetan Plateau 14 July UTC

In western region-- graupel particles lofted to great heights by strong updrafts Height of 40 dBZ cores by region

10 meter level 200 mb level A case of wide 40 dBZ echo core 22 July 2002

1300 UTC1400 UTC

A case of wide 40 dBZ echo core 22 July UTC

A typical case of wide 40 dBZ echo core with line organization 3 Sep UTC

A wide 40 dBZ echo core with squall-line organization—rare! 5 June UTC

10 meter level 500 mb level A of wide 40 dBZ echo core with squall-line organization—rare! 5 June mb jet over and parallel to the Himalayas

Horizontal area of 40 dBZ cores by region In western region—wide convective areas more frequent Area (km 2 ) Cumulative Frequency

Analysis of Stratiform Echoes

Intraseasonal Variation of the Monsoon Webster & Tomas events Day 0: 8 mm/d 5N-5S 80-90E “Break” “Active”

10 meter level 200 mb level Broad stratiform case 11 Aug 2002

0252 UTC

0455 UTC Broad stratiform case Upstream of mountains

Size of stratiform precipitation area by geographical region

Analysis of All the Reflectivity Data

Reflectivity data for 2 monsoon seasons Relative frequency of occurrence

Reflectivity data for 2 monsoon seasons  Convection is stronger & deeper in west  Stratiform more pronounced in east

Reflectivity data for 2 monsoon seasons Convection is slightly deeper & stronger over the lowlands than the foothills

SummarySummary West: “Deep” & “wide” cores prone to occur just upstream & over the foothills, esp. in the west, near confluence of dry downslope & maritime flows.West: “Deep” & “wide” cores prone to occur just upstream & over the foothills, esp. in the west, near confluence of dry downslope & maritime flows. Strongest over lowlandsStrongest over lowlands Vertical cellsVertical cells Wide cores—amorphous or parallel to mt. range Wide cores—amorphous or parallel to mt. range Lots of lightningLots of lightning No squall linesNo squall lines Strongest over lowlandsStrongest over lowlands Vertical cellsVertical cells Wide cores—amorphous or parallel to mt. range Wide cores—amorphous or parallel to mt. range Lots of lightningLots of lightning No squall linesNo squall lines Central: Get both deep and wide cores, as in west, but not as frequent.Central: Get both deep and wide cores, as in west, but not as frequent. Squall lines when jet parallel to HimalayasSquall lines when jet parallel to Himalayas Isolated cells over plateauIsolated cells over plateau Squall lines when jet parallel to HimalayasSquall lines when jet parallel to Himalayas Isolated cells over plateauIsolated cells over plateau East: Get mesoscale, partially stratiform cloud systems associated with depressions over the Bay of BengalEast: Get mesoscale, partially stratiform cloud systems associated with depressions over the Bay of Bengal Mesoscale systems like oceanic convection with large stratiform regionsMesoscale systems like oceanic convection with large stratiform regions Get broad stratiform regions associated with depressions propagating from equatorial regionGet broad stratiform regions associated with depressions propagating from equatorial region Mesoscale systems like oceanic convection with large stratiform regionsMesoscale systems like oceanic convection with large stratiform regions Get broad stratiform regions associated with depressions propagating from equatorial regionGet broad stratiform regions associated with depressions propagating from equatorial region

EpilogueEpilogue 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?

Thanks