Global Patterns of Extreme
Convection
R. A. Houze
International Workshop on Severe Weather, Beijing, 5 July 2011
R. A. Houze
Lecture, Summer School on Severe and Convective Weather, Nanjing, 15 July 2011
Convective Clouds
Lecture Sequence
1.
2.
3.
4.
5.
6.
7.
Basic convective cloud types
Severe convection & mesoscale systems
Tropical cloud population
Convective feedbacks to large-scales
Extreme convection
Diurnal variability
Clouds in tropical cyclones
Questions
1. What are the most extreme forms of
convective storms?
2. Where do they occur around the world?
f
Example:
Mesoscale Convective System (MCS)
Three MCSs
Radar echoes showing
the precipitation
in the 3 MCSs
Stratiform
Precipitation
Convective
Precipitation
1458GMT 13 May 2004
Idealized structure of a mesoscale
convective system
Precipitation radar echo Stratiform Convective
Houze et al. 1989
Stratiform
TRMM
•Precipitation radar in space
•Has made global mapping of
convection possible
TRMM Satellite Instrumentation
 = 2 cm
Important! PR
measures 3D
structure of radar
echoes
>
Kummerow et al, 1998
Global Pattern of Deep Convection seen by
TRMM
Maximum height of TRMM radar echoes
Zipser et al. 2006
Further analysis of TRMM data
shows
Use TRMM algorithm for separating
convective and stratiform echo
STRATIFORM identified by 2 criteria:
Existence of bright band
Lack of intense echo cores
Houze et al. 2007
Use TRMM algorithm for separating
convective and stratiform echo
If not stratiform, echo is classified:
CONVECTIVE
or
“OTHER”
From the 3D gridded TRMM PR
data
1.Identify contiguous 3D “echo
objects”
2.Determine “echo object”
properties to identify extreme
forms of convection
Identify each contiguous 3D echo object
seen by TRMM PR
Convective component
Stratiform component
Extreme characteristic
Extreme characteristic
Contiguous 3D volume of
convective echo > 40 dBZ
Contiguous stratiform echo
with horizontal area > 50 000 km2
“Broad stratiform region”
Top height > 10 km
“Deep convective core”
Horizontal area > 1 000 km2
“Wide convective core”
Climatology
of extreme
convective
Deep
features in
Convective
South Asia
Cores
and South
America
Wide
Convective
Cores
First look at
these
Broad
Stratiform
Regions
JJAS
DJF
Extreme convective cores in
South Asia
Previous studies over Asia and
North America have shown…
Topography is important for
• Capping
• Triggering
Carlson et al. 1983
Mexican
Plateau
Texas
Gulf of
Mexico
Something similar happens to extreme
convective cores in the western region
of South Asia
Sawyer 1947
A more recent example observed by
TRMM
Backward trajectories (HYSPLIT/NCEP)
2.5 km
1.0 km
Consistent with
ConsistentSawyer
with 1947with
Consistent
Sawyer 1947
Sawyer 1947
Medina et al. 2010
Observations
Pakistan
India
Infrared satellite temperature (shaded, K)
and low-resolution terrain
(black contours, km)
WRF-simulation
Pakistan
India
Cloud top temperature (shaded, K)
and terrain (black contours, m)
Medina et al. 2010
TRMM PR Observations
WRF Simulation
Medina et al. 2010
WRF Simulation
Mixing ratio
CAPE
Surface wind
Medina et al. 2010
WRF Simulation
Isochrones of
integrated
hydrometeor
content
Hydrometeor
mixing ratio
just after
convection
formed
Medina et al. 2010
Extreme Convective Cores in
South America
Some similarities to U. S. and
South Asia
The geography
Average airflow
conditions for
storms with
wide convective
cores
Vertical air motions
up down
Low-level winds
moist
unstable
Rasmussen and Houze 2011
Example of
triggering over
the Sierra
Cordóba range
Rasmussen and Houze 2011
What the storm
looked like on
the TRMM
radar
Rasmussen and Houze 2011
Subdivision of precipitation of MCS
into convective and stratiform components
Old
convection
Vigorous
convection
100 km
Houze 1997
“Convective” is young & vigorous
Max w > (VT)snow
Height
Big particles fall
out near updraft
Get vertical cores
of max reflectivity
Distance
Houze 1997
“Stratiform” is old convection
Heigh
t
(VT)snow~1-2 m/s
Ice particles drift
downward
Melting produces
“bright band”
Distance
Houze 1997
JJAS
Deep
Convective
Cores
Climatology
of extreme
convective
Wide
features in Convective
Cores
South Asia
and South
America
Now look
at these
Broad
Stratiform
Regions
DJF
Examples of Bay of Bengal depressions
with large MCSs with broad stratiform
regions
SUMMER MONEX
6 July 1979
850 mb wind
Houze and Churchill 1987
Bay of Bengal depression, 3 Sep 2003
WRF simulation
White--850 mb height
Yellow--500 mb vertical velocity
Medina et al. 2010
Bay of Bengal depression, 3 Sep 2003
TRMM PR
WRF
11 August 2002
Medina et al. 2010
2010 Flood
of Indus
River in
Pakistan
was due to
MCS with
broad
stratiform
region
Broad stratiform precipitation occurred
over the mountains of Pakistan  Floods!
Broad stratiform!
Regions of extreme convection
Rockies
Andes
Himalayas
?
Conclusions
• Orographic capping and triggering lead to deep
and wide convective cores near major
mountain ranges and warm moisture sources
• MCSs with broad stratiform regions constitute
a dangerous form of extreme convection when
enhanced by terrain
• Satellite climatology of extreme convective
events over China needs to be developed
Convective Clouds
Lecture Sequence
1.
2.
3.
4.
5.
6.
7.
Basic convective cloud types
Severe convection & mesoscale systems
Tropical cloud population
Convective feedbacks to large-scales
Extreme convection
Next
Diurnal variability
Clouds in tropical cyclones
End
This research was supported by
NASA grants NNX07AD59G, NNX10AH70G
NSF grants, ATM-0820586,
Extra slides
700 mb wind (~3 km)
H
L
Water vapor anomaly
500 mb wind
Rain
L
L
L
4 August 2010
5 August 2010
500 mb
500 mb
850 mb
850 mb
University of Washington Processing:
Re-map and interpolate the PR reflectivity field
Satellite
Interpolate
Geolocate
This processing facilitates 3D visualization and
“echo object” analysis
Leh, India, August 2010
300 casualties due to flood in
a high altitude valley of the
Indus River
1200
0200
1200
0200
1200
0200
We do not have TRMM
radar data for this time
but we expect that the
flood was a
combination of
extreme convective
and stratiform rain
WRF model
simulation
of Leh
flood case
(Courtesy Anil Kumar)