mesoscale convective systems: recent observational and diagnostic studies robert houze
DESCRIPTION
Mesoscale Convective Systems: Recent Observational and Diagnostic Studies Robert Houze Department of Atmospheric Sciences University of Washington. 10 th Conf. on Mesoscale Meteorology, Portland, OR, June 23-27 2003. DEFINITION Mesoscale Convective System (MCS) - PowerPoint PPT PresentationTRANSCRIPT
Mesoscale Convective Systems: Recent Observational and Diagnostic Studies
Robert Houze
Department of Atmospheric SciencesUniversity of Washington
10th Conf. on Mesoscale Meteorology, Portland, OR, June 23-27 2003
DEFINITION
Mesoscale Convective System (MCS)
A cumulonimbus cloud system that produces a contiguous precipitation area ~100 km or more in at least one direction
Questions
Why do tropical and midlatitude MCSs look different?
Does layer lifting occur in a mature MCS?
Is rear inflow really from the rear?
What controls the size of MCSs?
What controls the movement of MCSs?
Houze et al. 1989, 1990
Tropical & midlatitudes“Symmetric”
Midlatitudes(later stages)“Asymmetric”
Radarreflectivity
Conv.
Strat.
Skamarock et al. 1994
Symmetric(Tropics & midlatitudes)
No Coriolis Coriolis
Asymmetric(Midlatitudes)
Questions
Why do tropical and midlatitude MCSs look different?
Does layer lifting occur in a mature MCS?
Is rear inflow really from the rear?
What controls the size of MCSs?
What controls the movement of MCSs?
Parcel viewpointZipser 1977
CrossoverZone
Layer viewpoint: Bryan and Fritsch 2000
“Slab” or Layer Overturning
MAUL
TOGA COARE Airborne Doppler Observations of MCSs
Convective region flights
0.5-4.5 km
Note!
Layer viewpoint: Kingsmill & Houze 1999
0ze
1000 km
1000
km
Moncrieff & Klinker 1997
plan view
cross section
A B
A B
TOGA COARE convection in
a GCMwith ~80 kmresolution
Mean heatingin convective
line
Horizontalwind
Pandya & Durran 1996
gravity wave response to heating
Questions
Why do tropical and midlatitude MCSs look different?
Does layer lifting occur in a mature MCS?
Is rear inflow really from the rear?
What controls the size of MCSs?
What controls the movement of MCSs?
Diversity of stratiform structure: Parker & Johnson 2000PATTERNS OFEVOLUTION OF STRATIFORM PRECIPITATION IN MIDLATITUDESQUALL LINES
Kingsmill & Houze 1999 Documented airflow
shown by airborne Doppler inTOGA COARE MCSs
Stratiform region flights
0°C
0 192Horizontal Distance (km)
11
0
Hei
ght (
km)
192
11
0
Hei
ght (
km)
0
90 km
Horizontal Distance (km) 100 km
Refl.
Radial Velocity3.5 km level
JASMINE: Ship radar, Bay of Bengal, 22 May 1999
RadialVelocity
Reflectivity1.5 km level
0 192Horizontal Distance (km)
12
0
Hei
ght (
km)
192Horizontal Distance (km)
12
0
Hei
ght (
km)
0Horizontal Distance (km) 100 km
Radial Velocity3.5 km level
JASMINE: Ship radar, Bay of Bengal, 22 May 1999
Reflectivity1.5 km level
Horizontal Distance (km) 100 km
Refl.
Radial Velocity3.5 km level
JASMINE: Ship radar, Bay of Bengal, 22 May 1999
RadialVelocity
Reflectivity1.5 km level
90 km
Questions
Why do tropical and midlatitude MCSs look different?
Does layer lifting occur in a mature MCS?
Is rear inflow really from the rear?
What controls the size of MCSs?
What controls the movement of MCSs?
Chen et al. 1996
Sizes of MCSs observed in TOGA COARE
“Super Convective Systems”(SCS)
Yuter & Houze 1998Percent of 24 km square grid covered by A/C radar echo in all the MCS
All TOGA COARE satellite/radar comparisons
Precipitation Convective Stratiform
% % %
Yuter & Houze 1998Percent of 240 km square covered by A/C radar echo in all the MCS
All TOGA COARE satellite/radar comparisons
Hypothesis:
The size of the MCS is determined by the environment’s
ability to sustain an ensemble of convection over time.
Question:
What factors control and limit sustainability?
Kingsmill & Houze 1999: TOGA COARE a/c soundings
Hei
ght (
m)
Schumacher & Houze 2003
TRMM Precipitation radar:% of 2.5 deg grid covered by stratiform radar echo
Annual Average
Inference: Sustainability promoted by moist boundary layer that is
not interrupted by the diurnal cycle
Stratiform Rain Fraction
Questions
Why do tropical and midlatitude MCSs look different?
Does layer lifting occur in a mature MCS?
Is rear inflow really from the rear?
What controls the size of MCSs?
What controls the movement of MCSs?
Traditional view:
Cold pool dynamics
Recent studies:
Waves in environment
Chen, Houze,& Mapes 1996
AnalyzedIR data
3°N-10°S208°K threshold
IN TOGA COARE
MCSs moved individually
with wave much of the
time 12
13
15
14
Longitude
Tim
e (d
ay)
A/Cflights
on 12-14Dec
equator
40NJASMINE: May 1999
60E 100E
NOAA Ship R.H. Brown
Webster et al. 2002 IR over Bay of Bengal during JASMINE
Ship track
5 10 25 302015May 1999
Mapes et al. (2002)
West Coast of
South Am.
GravityWave
hypothesis
JASMINEMCS
JASMINEMCS
ConclusionsCoriolis effect explains why midlatitude MCSs exhibit late-stage asymmetry not observed in the tropics.Layer lifting occurs in mature MCSs, possibly as a gravity wave response to the net heating in the convective region.Midlevel inflow enters stratiform regions from various directions—controlled by environment wind.Max size of MCSs related to sustainability of low-level moist inflow—get biggest systems over oceans and with LLJsMovement of an individual MCS may be in part determined by waves propagating through the environment—gravity waves, inertio-gravity waves,…
Layer viewpoint: Mechem, Houze, & Chen 2002
TOGA COARE23 Dec 92
200X (km)
150 250200150 250X (km)
Z (k
m)
Y (k
m)
0
2
4
6
8
10
12
14
50
100
150
Yuter & Houze 1998CS map Convective echo
Stratiform echo Satellite IR
% o
f grid
% o
f grid
Mea
n IR
tem
p (K
)
x (km)
y(km)
Nakazawa 1988
INTRASEASONALENSEMBLE VARIATION
SUB-ENSEMBLE
MESOSCALE CONVECTIVE SYSTEM
JASMINE IR sequence
(courtesy P. Zuidema)
Serra & Houze 2002
TEPPS—East Pacific ITCZ
Ship radardata
Easterly wave and cold pool propagation hard to distinguish
Carbone et al. 2002
WSR88-Dradar dataover U.S.in time/
longitudeformat
Examplesof TOGACOAREMCSs
Satellite IR overlaid with A/C
radar
240 km