2021 EGU (Session AS1.5 -Tropical meteorology and Tropical ...
Transcript of 2021 EGU (Session AS1.5 -Tropical meteorology and Tropical ...
The Synoptically-Influenced Extreme Precipitation Systems
over Asian-Australian Monsoon Regionobserved by TRMM Precipitation Radar
Wei-Ting ChenDepartment of Atmospheric Sciences,
National Taiwan University, Taipei, Taiwan
Collaborators: Hong-Wen Jian, Peng-Jen Chen, Chien-Ming Wu (NTU) & Kristen Rasmussen (CSU, USA)
2021 EGU (Session AS1.5 - Tropical meteorology and Tropical Cyclones)
Jian, H.-W., W.-T. Chen*, C.-M. Wu, and K. L. Rasmussen (2021), The synoptically-influenced extreme precipitation systems over Asian-Australian monsoon region from TRMM PR Measurements, J. Meteo. Soc. Japan, 99 (2), 269-285, doi:10.2151/jmsj.2021-013
Extreme Rainfall in the Asian-Australian Monsoon Region
• Extreme rainfall events have caused severe loss of life and properties over the Asian-Australian Monsoon (AAM) region
• Previous satellite (TRMM) studies have provided statistics of the spatial-temporal distribution, size, intensity, and internal structures of extreme systems [e.g., Hamada et al., 2014; 2015; Rasmussen et al., 2015]• Coastal areas are hotspots of extensive type extreme systems• Occurrence is strongly tied to the seasonal monsoon circulation
• Understanding of the various “ingredients” producing the extreme systems still requires further research, especially over the lower latitudes• Mid-latitude – dominant synoptic control of extreme case [e.g., Yokoyama et
al., 2020, JMSJ]• Tropics -- synoptic condition, topographical effects, coastal land-sea breeze
circulation, meso-scale organization processes…
“Ingredients” for Extreme System can be Multi-scale -- Example 1: W Coast Philippines with remote vortex (boreal summer)
• Synoptic: Onshore westerly enhanced by remote TY
• Topography and probably land-sea breeze effects
• High CWV, strong low-level shear à favors convection organization
• Extreme rain rate occurs in the boundary of convective and stratiform rainfall
[Jian et al., 2021, JMSJ]
Goal: Identify the different synoptic states
associated with extreme rainfall systems over the AAM region,
then examine the linkage between extreme and environment
Convection: System-based approach +
Synoptic: Minimalist approach (get the most distinct feature first)
Step 1: Rainy Systems from TRMM PR
Rainy system database over the TRMM PR area (37.5N-37.5S) during 1998-2014
Step 2: Define Tropical Extreme Systems that are both Large and Intense
• Rank the maximum rainfall within system and the horizontal size of all systems
• Top 0.1 % intense (>60.7 mm/hr) and top 0.1 % extensive (>271 km)
à N=3457 extreme systems (0.015% of all systems) during 1998-2014
à 27.8% (N=916) of these extreme systems are over the AAM region (black box; 90-160E, 12S-27N)
[Jian et al., 2021, JMSJ]
Step 3: Classify into Four Major Types of Synoptic Flow Patterns
Vortex type:Convection system embedded in TY/TD
• Subjectively classify the 916 extreme systems into four synoptic types, based on 850 hPa circulation patterns, rainfall distribution, and distance to coastlines < 2.5o
Coastal type:System close to coastlines with monsoonal background wind
Remote VortexCoastal:System close to coastlines with remote vortex enhancing onshore wind
(vortex=closed cyclonic circulation of TY, TD, monsoon lows, tropical waves…)
Percentage of Synoptic Types of Extreme Systems
N= 402 268 66 153(total N =916)Lightning probability 41% 54% 56% 35%
Intensity, Size, and Lightning of Extreme Types
• Similar median values of max rain rate among four types
• Vortex type has highest variability
• Similar horizontal scales for V, VC and C types (median ~ 300 km)
• N type has larger size
Seasonal distribution: Boreal Winter (blue) vs. Summer (red)
Vortex type (44%)
Vortex-impacted Coastal type (7%)
Costal type (29%)
None of the above type (20%)
[Jian et al., 2021, JMSJ]• Vortex type: mainly over the off-equatorial areas in boreal summer. • C and VC types: significant seasonal variations in occurrence locations
• Similar internal structure across all four types:• Broad stratiform and wide convective core. • Max. rainfall locates mostly in convective area, near convective-stratiform boundary in
the system
Internal Structures and Environment
• Environment for C and VC types : high CWV and existence of low-level shear
[Jian et al., 2021, JMSJ]
Conclusion
• AAM contains 28% of the extremely large and intense systems (>271.2 km & >60.7 mm/hr) over the Tropics• Four types of the synoptic patterns associated with
extreme systems in AAM: V (44%), C (29%), VC (7%), N (20%)• V type can be the most intense; N type can be the largest;
C and VC more frequently accompanied by lightning flash, with seasonally distinct locations; • Similar internal structure: either WCC or B; max. rainfall
near the convective-stratiform boundary
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