trmm observations of convection over the himalayan region r. a. houze and d. c. wilton university of...
Post on 15-Jan-2016
213 Views
Preview:
TRANSCRIPT
TRMM Observations of Convection over the TRMM Observations of Convection over the Himalayan RegionHimalayan RegionR. A. Houze and D. C. WiltonR. A. Houze and D. C. Wilton
University of WashingtonUniversity of Washington
Presented 1 February 2005 at the International Brainstorming Meeting on “Modeling and Prediction over Indian Monsoon Region: Vision 2015”, National Centre for Medium Range Weather Forecasting Department of Science & Technology, Noida, UP, India
TRMM Precipitation Radar Data Set Used in TRMM Precipitation Radar Data Set Used in This StudyThis Study
• June-September 2002, 2003• 1648 Overpasses over Himalayan region
• Data specially processed at University of Washington• Cartesianized to facilitate analysis in “Mountain Zebra”
• This data set optimized to analyze vertical structure of echoes
TRMM Satellite InstrumentationTRMM Satellite Instrumentation
Kummerow et al, 1998
= 2 mmImportant! PR measures 3D structure of radar echoes
Idealized Idealized HorizontalHorizontal Pattern of the Radar Echo Pattern of the Radar Echo Pattern in a Mesoscale Convective SystemPattern in a Mesoscale Convective System
Radar reflectivity Echo type
Plan View
Houze 1997
Conceptual Model of Conceptual Model of VerticalVertical Structure Structure “Convective” Rain Elements“Convective” Rain Elements
Houze 1997
Houze 1997
Conceptual Model of Conceptual Model of VerticalVertical Structure Structure “Stratiform ” Rain Elements“Stratiform ” Rain Elements
To study the vertical structure of convective To study the vertical structure of convective regions we define 3D echo regions we define 3D echo “cores”“cores”
• 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 3D space) of reflectivity values which exceed the threshold of 40 dBZ.
3D radar echo bounded by 40 dBZ contour
land
echocore
““Deep Convection” Core: 14 June 2002, 0859 UTCDeep Convection” Core: 14 June 2002, 0859 UTC
“deep convection” cores are those for which the maximum height of the 40 dBZ core are greater than 10 km
16
8
0 55 110
Distance (km)
Hei
ght
(km
)28N
30N
4 km level
74E 76E
Analysis SubregionsAnalysis Subregions
Arabian Sea
Bay of Bengal
°N
°E
WesternWesternSubregionSubregion
Central Central SubregionSubregion Eastern Eastern
SubregionSubregion
INDIA
Normalized Frequency Distribution Normalized Frequency Distribution of of 40 dBZ40 dBZ Convective Echo Core HeightsConvective Echo Core Heights
In western region--graupel particles
lofted to great heights by strong
updrafts
Barros et al. 2004
Lightning Frequency Based on TRMM Satellite Lightning Frequency Based on TRMM Satellite ObservationsObservations
““Wide Convection” Core: 22 July 2002, 13:09 UTCWide Convection” Core: 22 July 2002, 13:09 UTC
“wide convection” cores are those for which the area of the 40 dBZ core are greater than 1,000 km2, corresponding to a dimension of approximately 30km
16
8
Distance (km)
Hei
ght
(km
)
0 120 240
30N
34N
4 km level
72E 76E
Cumulative Distribution of Convective Core BreadthCumulative Distribution of Convective Core Breadth
In western region—wide convective
areas more frequent
Analysis of stratiform echo regionsAnalysis of stratiform echo regions
Used TRMM algorithm for separating echoes into stratiform & convective regions
Two criteria:
Existence of bright band Lack of intense echo cores
22N
30N
92E 100E
4.5 km level
22N
30N
92E 100E
Echo Classified as Stratiform
“broad stratiform” cases are those for which the area classified by the TRMM algorithm as stratiform precipitation is greater than about
50,000 km2, corresponding to a dimension of approximately 225 km
““Broad Stratiform” Case: 5 June 2003, 13:47 UTCBroad Stratiform” Case: 5 June 2003, 13:47 UTC
24N
28N
94E 98E
4.5 km level
16
8
0 576 Distance (km)
Hei
ght
(km
)288
Cross Section
Cumulative Distribution FunctionCumulative Distribution Functionfor Stratiform Precipitation Areas for Stratiform Precipitation Areas
TRMM Satellite InstrumentationTRMM Satellite Instrumentation
Kummerow et al, 1998
= 2 cmImportant! PR measures 3D structure of radar echoes
Contoured Frequency by Altitude DiagramContoured Frequency by Altitude Diagram
Relative frequency of occurrence
All data1648 overpasses
Conve
cti
veStratifor
mReflectivity Statistics by Sub-Region, Rain-Type, & AltitudeReflectivity Statistics by Sub-Region, Rain-Type, & Altitude
Convection is stronger & deeper in west
Statiform more pronounced in east
Terrain Elevation CategoriesTerrain Elevation Categories
Mountain
MountainLowland
Lowland
Foothill
Foothill
°N
°E
Lowland 0-300 m, Foothills 300-3000 m, Mountain >3000 km
Reflectivity Statistics by Subtending TerrainReflectivity Statistics by Subtending TerrainL
ow
lan
dF
oo
thill
sM
ou
nta
in
Convection is slightly deeper & stronger over the
lowlands than the foothills
Intense Convective Wide Stratiform
°N
°E
Locations of Intense Convective Cases and Wide Stratiform Locations of Intense Convective Cases and Wide Stratiform CasesCases
Concavities lead to concentration
of intense convection in
NW and stratiform
systems in NE
ConclusionsConclusions
2 years of TRMM PR data have been processed for analysis of vertical structure of convection over the Himalayan region40 dBZ cores deepest & broadest over NW region40 dBZ cores in NW region can reach 17+ km—indicating graupel lofted to high levels by strong updraftsIntense convection occurs primarily over lowlands and foothillsIntense convection is concentrated in the NW concavity of the Himalayas—continental regimeStratiform areas larger & more frequent over NE, concentrated in the NE concavity—indicating a more maritime convective regime.
End
Maheshwari & Mathur 1968
Thunderstorm over IndiaThunderstorm over India
“low echo centroid”
(coalescence & riming)
Caracena et al. 1979
Colorado Rockies Big Thompson Storm 1976Colorado Rockies Big Thompson Storm 1976
“low echo centroid”
Contoured Frequency by Altitude DiagramsContoured Frequency by Altitude Diagrams
Contoured Frequency by Altitude DiagramsContoured Frequency by Altitude Diagrams
Contoured Frequency by Altitude DiagramsContoured Frequency by Altitude Diagrams
Contoured Frequency by Altitude DiagramsContoured Frequency by Altitude Diagrams
Contoured Frequency by Altitude DiagramContoured Frequency by Altitude Diagram
Relative frequency of occurrence
All data1648 overpasses
Reflectivity by Sub-RegionReflectivity by Sub-Region
Wide Area of Convection Case: 1309 UTC 22 July 2002Wide Area of Convection Case: 1309 UTC 22 July 200200 UTC Soundings00 UTC Soundings
Wide Area of Convection Case: 1309 UTC 22 July 2002Wide Area of Convection Case: 1309 UTC 22 July 200212 UTC Soundings12 UTC Soundings
Broad Stratiform Case: 13:47 UTCBroad Stratiform Case: 13:47 UTC 5 June 2003 5 June 2003 12 UTC Soundings12 UTC Soundings
Z=R^1.25
0
5
10
15
20
25
0 10 20 30 40 50
dBZ
R (
mm
/h)
Series1
Reflectivity Related to Rain RateReflectivity Related to Rain Rate
20-year Alpine Autumn Precipitation Climatology
(rain gauge analysis by Frei and Schaer 1998)
top related