Transcript 080312Norfolk_ARMSciTeamV02_CetroneHouze.ppt

Cirrus Production by Tropical Mesoscale Convective Systems
Jasmine Cetrone and Robert Houze
University of Washington
ARM Science Team Meeting,
Norfolk, 12 March 2008
University of Washington
Atmospheric Sciences
Motivation
Precipitation Climatologies
• Anvil height and density in MCSs influenced by
convective intensity and amount
TRMM PR MCS Convective CFADs
16
14
Height (km)
Atmospheric heating by high clouds is important for
tropical circulation. Many of the high clouds in the
tropics are intimately tied to the mesoscale convective
systems (MCSs) producing most tropical precipitation.
Summary
West Africa
Maritime Continent
Bay of Bengal
12
• Anvil longevity possibly related to the amount of
stratiform precipitation (need case studies)
10
8
6
4
West Africa MCSs
Deep, intense convection, small stratiform area
Anvils shallower, but high IWP
Maritime Continent MCSs
Moderate convection, large stratiform areas
Deep anvils
Bay of Bengal MCSs
Moderate convection, moderate stratiform areas
Deep anvils
2
Summertime Cirrus Coverage
0
0
10
Summertime Precipitation
Schumacher and Houze (2003)
The goals of this study are to:
• Establish the characteristics of precipitation and anvil
regions of tropical MCSs
• Relate ARM site ground-based observations to
satellite observations of MCS anvils
• Expand the conceptual model of cloud and
precipitation structure of MCSs
Regions of Interest
Height (km)
16
14
0
10
20 30 40 50
Reflectivity (dBZ)
60
0
10
20 30 40 50
Reflectivity (dBZ)
60
West Africa
Maritime Continent
Bay of Bengal
12
10
8
6
4
2
0
0
10
20 30 40 50
Reflectivity (dBZ)
60
0
10
20 30 40 50
Reflectivity (dBZ)
60
0
10
20 30 40 50
Reflectivity (dBZ)
60
• Consistency of time-continuous ARM site radar data
with CloudSat implies that ARM data will provide
physical and dynamical insight into CloudSat-based
climatologies
• Stratiform precipitation in W Africa MCSs taller and
high reflectivities aloft, indicating large ice aloft
• Stratiform precipitation in Maritime MCSs slightly taller
and with higher reflectivities aloft than Bengal
TRMM PR MCS Convective Rain Fraction
Anvil Climatologies
CloudSat MCS Anvil CFADs
16
West Africa
40
Maritime Continent
Schumacher and Houze (2003)
20
West Africa: continental monsoon climate, squall-line
MCSs, site of the 2006 AMMA project (ground-based
scanning precipitation radar and ARM WACR)
Maritime Continent: island monsoon climate, massive
MCSs, long-term data set of scanning precipitation
radar and ARM MMCR at Darwin, Australia
Bay of Bengal: oceanic monsoon climate, southward
propagating MCSs, site of the 1999 JASMINE project
(ship-borne scanning precipitation radar and a
vertically pointing cloud radar)
Methodology
Create climatologies of TRMM Precipitation Radar (PR)
and CloudSat reflectivities from each of the three
regions ONLY for MCSs during the following monsoon
seasons:
•W. Africa: 2006 monsoon season
•Maritime Continent: 2006-2007 monsoon season
•Bay of Bengal: 2006 monsoon season
Hourly IR geostationary satellite data insured that the
data collected was from MCSs.
Height (km)
12
10
8
6
2
0
0
20
40
60
80 100 0
20
40
60
80 100 0
20
40
60
80 100
Convective Rain Fraction (%)
Convective Rain Fraction (%)
Convective Rain Fraction (%)
• West Africa has very high convective rain fractions in
MCSs, indicating stratiform regions that are smaller
and/or shorter in duration
• Maritime Continent has lowest convective rain fraction,
influence of monsoonal systems with large, long
lasting stratiform regions
• Bengal distribution indicates moderate convective rain
fraction, and narrow distribution shows that MCSs in
that region are very similar to each other
Niamey WACR
Darwin MMCR
West Africa
Bay of Bengal
CloudSat MCS Thick Anvil CFADs
20
18
16
14
12
10
8
6
4
2
0
West Africa
Maritime Continent
Bay of Bengal
-30 -20 -10
0
10 20 30 -30 -20 -10
0 10 20 30 -30 -20 -10
0 10 20 30
Reflectivity (dBZ)
Reflectivity (dBZ)
Reflectivity (dBZ)
• Thick anvil defined as anvil greater than 6 km thick
• Thick anvil in all regions have double minima,
indicating high frequency of high reflectivity near
cloud bottom
• Lower maximum likely due to large aggregates?
-40 -30 -20 -10 0 10 20 30 -40 -30 -20 -10 0 10 20 30
Reflectivity (dBZ)
Reflectivity (dBZ)
• Ground-based ARM WACR deployed at Niamey, Niger
in West Africa during summer of 2006
• Ground-based ARM MMCR deployed at Darwin,
Australia in the Maritime Continent (long-term dataset)
• Statistics of reflectivity CFADS for thick anvil (>6 km)
from CloudSat and ARM vertically pointing cloud
radars indicate that the ground-based instruments are
capturing similar features
• CloudSat and TRMM only provide snap-shot views of
MCSs. Ground-based instruments at Niamey and
Darwin will allow for a time-continuous view of the
precipitation and anvil systems, so it is important to
use case-studies from these regions to analyze the
evolution of the anvil production
Maritime Continent
• W Africa anvil clouds have lower tops (even though
convection is deeper!!)
• Maritime anvil clouds reach the highest
ARM Ground-based Validation
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18
16
14
12
10
8
6
4
2
0
20
18
16
14
12
10
8
6
4
2
0
-30 -20 -10
0 10 20 30 -30 -20 -10
0 10 20 30 -30 -20 -10
0 10 20 30
Reflectivity (dBZ)
Reflectivity (dBZ)
Reflectivity (dBZ)
Height (km)
60
Bay of Bengal
CloudSat MCS Thick Anvil Ice Water Path
25
Frequency (%)
Bay of Bengal
Maritime Continent
4
Height (km)
%
Frequency (%)
14
MCS characteristics vary from one tropical location to
another. We focus on three different tropical locations,
chosen because of their monsoon environments and
because of the availability of time-continuous groundor ship-based cloud radar observations.
West Africa
60
• Convective precipitation in W Africa MCSs is taller and
more intense
• Convective precipitation in Maritime and Bengal MCSs
is similar, with Maritime being slightly taller
TRMM PR MCS Stratiform CFADs
Wylie et al. (1994)
Summertime Stratiform Rain Fraction
20 30 40 50
Reflectivity (dBZ)
West Africa
Maritime Continent
Bay of Bengal
20
15
10
5
0
0
1
2
3
-2
IWP (g m )
4 0
1
2
3
-2
IWP (g m )
4 0
1
2
3
-2
IWP (g m )
4
• High IWP for W Africa thick anvils, Maritime moderate
IWP (mostly due to thicker anvil), Bengal low IWP
• Ice particles in intense W Africa convection likely
larger, so particles are heavier and fall out rapidly
producing very dense anvils (high IWP) but with lower
tops