Post on 22-Dec-2015
Diurnal Variability of Deep Tropical Convection
R. A. HouzeLecture, Summer School on Severe and Convective Weather, Nanjing, 11-15 July 2011
Convective Clouds
Lecture SequenceLecture Sequence1.1. Basic convective cloud typesBasic convective cloud types
2.2. Severe convection & mesoscale systemsSevere convection & mesoscale systems
3.3. Tropical cloud populationTropical cloud population
4.4. Convective feedbacks to large-scales Convective feedbacks to large-scales
5.5. Extreme convectionExtreme convection
6.6. Diurnal variabilityDiurnal variability
7.7. Clouds in tropical cyclonesClouds in tropical cyclones
Diurnal cycle of tropical convection depends on: Diurnal cycle of tropical convection depends on:
• the the scalescale of the convective phenomenon—time scale of the convective phenomenon—time scale of large systems not separable from diurnal time of large systems not separable from diurnal time scalescale
• The The locationlocation of the convection—open ocean, near of the convection—open ocean, near coastline, over mountainscoastline, over mountains
This talk will illustrate that…
Convective systems over the West Pacific
1 <80 km2 80-170 km3 170-300 km4 >300 km
Cloud shield <208 K
Chen & Houze 1997
Convective systems over the West Pacific
Chen & Houze 1997
Time needed for large systems to reach maximum size
Convective systems over the West
Pacific
Convective systems over the West Pacific
Chen & Houze 1997
Cloud systems tracked in time in IR satellite data
Small (<80 km) Large (80-170 km)
Convective systems over the West Pacific
Chen & Houze 1997
Relationship to surface air temperature
Cooler than Day 1
Diurnal cycles of different types of
extreme convective systems in
mountainous regions
Romatschkeet al. 2010
Romatschkeet al. 2010
Wide convective core occurrenceby time of day
during monsoon season
This illustrates the effect of nocturnal downslope flow on the diurnal cycle of wide convective core occurrence
Example from pre-monsoon season in South Asia
Romatschke et al. 2010
Mountains can lead to small and medium sized systems having different diurnal cycles—mesoscale lifecycle effect
Δ Small 600-8,500 km2
Medium 8,500-35,000 km2
IEC
JASMINE 1999, Ship Track & Satellite DataJASMINE 1999, Ship Track & Satellite Data
85-90 E85-90 E
ShipTrack
Webster et al. 2002
Propagational diurnal cycle occurs over Bay Propagational diurnal cycle occurs over Bay of Bengalof Bengal
2345 LST 22 May 99 0215 LST 23 May 99 0615 LST 23 May 99
JASMINE 1999JASMINE 1999
Ship Radar DataShip Radar Data
Doppler Radial Velocity
Reflectivity
Reflectivity
JASMINE 1999JASMINE 1999
Ship Radar DataShip Radar Data
22 May 19992300 LST
Houze et al. 1981
Radar Obs. of WINTER MONEX Borneo cloud systemRadar Obs. of WINTER MONEX Borneo cloud system
Stratiform Precipitation
BORNEOS. CHINA SEA
Bintulu
Mapes et al. 2003
Pacific
Pacific
South America
South America
Andes
Andes
Diurnal gravity wave generation of mesoscale convection over coastal South America
Summary
• Over open tropical oceans: – Small systems max in late afternoon– Large MCSs max around dawn– 2-day cycle at a given location (“diurnal dancing”)
• In mountainous regions: – Isolated deep convective elements max in late afternoon– Nocturnal downslope generates early morning max MCSs– Max of small rain systems precedes max of medium systems
• Downstream of mountains and/or coastlines: – Large MCSs generated apparently as response to afternoon heating
over high terrain propagate away from the mountainous region or coastline
• Over open tropical oceans: – Small systems max in late afternoon– Large MCSs max around dawn– 2-day cycle at a given location (“diurnal dancing”)
• In mountainous regions: – Isolated deep convective elements max in late afternoon– Nocturnal downslope generates early morning max MCSs– Max of small rain systems precedes max of medium systems
• Downstream of mountains and/or coastlines: – Large MCSs generated apparently as response to afternoon heating
over high terrain propagate away from the mountainous region or coastline
Convective Clouds
Lecture SequenceLecture Sequence1.1. Basic convective cloud typesBasic convective cloud types
2.2. Severe convection & mesoscale systemsSevere convection & mesoscale systems
3.3. Tropical cloud populationTropical cloud population
4.4. Convective feedbacks to large-scales Convective feedbacks to large-scales
5.5. Extreme convectionExtreme convection
6.6. Diurnal variabilityDiurnal variability
7.7. Clouds in tropical cyclonesClouds in tropical cyclones Next
This research was supported by NASA grants NNX07AD59G, NNX07AQ89G, NNX09AM73G, NNX10AH70G, NNX10AM28G,
NSF grants, ATM-0743180, ATM-0820586, DOE grant DE-SC0001164 / ER-6
300 mb wind & sfc pressure850 mb wind
Percent High Cloudiness in the Summer MonsoonPercent High Cloudiness in the Summer Monsoon
May-September 19991999
< 235 K < 210 K
Zuidema 2002
Zuidema 2002
r < 85 km
r = 140-210 km
r = 85-140 km
r > 210 km
Location of cloud systems by horizontal dimension May-September 1999
CloudTop
< 210 K
Zuidema 2002
JASMINE Mesoscale Convective SystemsJASMINE Mesoscale Convective SystemsDefined & tracked by 218 K infrared thresholdDefined & tracked by 218 K infrared threshold
WINTER MONEXWINTER MONEXDiurnal variation of high cloudiness near BorneoDiurnal variation of high cloudiness near Borneo
08 LST08 LST 20 LST20 LST
14 LST14 LST 02 LST02 LST
S. CHINA SEA
December1978
Mean fractional
area covered
high clouds in IR images
Bintulu
BORNEO
Houze et al. 1981
Houze et al. 1981
WINTER MONEXWINTER MONEXDiurnal variation of precipitation near BorneoDiurnal variation of precipitation near Borneo
December1978
Mean fractional
area covered by radar echo
BORNEO
Bintulu
.1.5
23 May 1999 0650 LST
TRMM PR shows extensive stratiform structureTRMM PR shows extensive stratiform structure
~270 km