rain-producing systems for the sams and their moisture sources
DESCRIPTION
Rain-Producing Systems for the SAMS and their Moisture Sources. Ed Zipser University of Utah and Paola Salio and Matilde Nicolini University of Buenos Aires. OUTLINE Precipitation Systems over South America • contrasting properties north and south of ~20°S - PowerPoint PPT PresentationTRANSCRIPT
Rain-Producing Systems for the SAMS
and their Moisture Sources
Ed Zipser
University of Utahand
Paola Salio and Matilde Nicolini
University of Buenos Aires
OUTLINE
Precipitation Systems over South America• contrasting properties north and south of ~20°S• comparison with systems over global tropics
MCSs during SALLJEX using 30-minute IR data• relationship with LLJ• diurnal cycle• example of 19 Dec 02
Moisture Source • moisture source vs. theta-e (CAPE) source • shortcomings of NCEP and ERA40 reanal.
Definition of PF (Precipitation Feature)and MCS (Mesoscale Convective System)
PF is any contiguous precipitation area with 2A25 near-surface rain (can be any size, and most are small, weak, and shallow)
Original PF with MCS definition (Nesbitt et al., 2000); A PF with 2A25 Near Surface Rain area > 2000km2
and Area of 85 GHz Tb below 250K > 2000km2
and at least one pixel with 85GHz Tb < 225K
During 5 years (1/1998-11/2000 & 12/2001-12/2003),
Total number of PFs: 17,253,615 Total number of PFs with MCS: 113,246 (0.66%)Total number of PFs with ice: 1,289,366 (7.47%) (i.e, Min 85 GHz pct <250K):
TRMM Radar Algorithm Annual Rain in mm/month
Fractional rain (%) contributed by large MPFs vs. small PFsVery large
Small
Fractional rain (%) contributed by PFs with specified properties
Fractional rain (%) contributed by MPFs with 40 dBZ height </> 6 km
Fractional rain (%) contributed by MPFs with convective fraction </> 50%
Conclusions from TRMM Statistics
• SESA (south of ~23°S) dominated by MCSs
… and…(Amazonia and SACZ are not)
• Rainfall comes mostly from large systems in SESA
• More of the rainfall is from small systems north of SESA
• Systems with intense convection contribute highest % of rainfall in SESA….and…(less in Amazonia and SACZ)
• Fraction of convective rain highest on Andes slopes of Argentina
• Fraction of stratiform rain highest in western Amazonia
SALLJEX
Days
Number of MCS
Number of MCS south
of 23S
Days with
convection not meeting the MCS
criteria
Days with no
convection south of
20S
CJE 45 61 22 15 3
NCJE 16 31 8 2 2
LLJ-ARG
14 18 2 12 2
NO-LLJ
17 29 2 4 9
Number and Location of MCSs in relation to SALLJ Events
Chaco Jets (LLJs extending south of 25°S) favor MCSs south of 23°S
From Salio and Nicolini
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-25
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NCJE
LLJ-ARG
NO-LLJ
CJE
Fill symbols represent nocturnal MCS (0-12]
open symbols represent diurnal MCS (12-00]
MCSs Centroids during SALLEX MCSs Centroids during SALLEX (Nov 15, 2002 – Feb 15, 2003) (Nov 15, 2002 – Feb 15, 2003)
Initiation
UTC Time
Subtropical MCSs between 23S-40S – 65W-52WSubtropical MCSs between 23S-40S – 65W-52W
Decay
UTC Time
Relationship between SALLJ and MCSs
• When SALLJ extends south of 25°S (definition of the Chaco Jet, CJE), MCSs are favored in SESA
• Large MCSs reach peak extent during the night (but initiate in late afternoon-evening)
• SALLJ wind speed peaks during the night
Issue to be resolved: Are the diurnal cycles of MCSs and LLJs closely linked?
• MCSs are favored by high CAPE and low-level shear• MCSs reach peak extent at night wherever they occur• Is the main role of the LLJ to provide the high-CAPE
environment, or is it also necessary that a strong LLJ be present at the same time/location?
19Dec 2002 MCS near B.A. used by C. Saulo in modeling study
(Passive microwave- ice scattering) (Passive microwave- ice scattering)(IR cold cloud tops massiveand colder than -80°C)
Radar structure is that of a classicleading line-trailing stratiform Sq. line
(ignore- artifacts)
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Notice d/dt (theta-e) from tropical Atlantic to ArgentinaMCS Case Study
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Notice d/dt (theta-e) from tropical Atlantic to ArgentinaDec-Jan-Feb MEAN conditions
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x
MCS Case Study (SALLJEX 22 Jan 03) Notice d/dt (theta-e) from tropical Atlantic to Argentina
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NCEP: Wind 330° 6 m/s Theta-e: 348°KP-3: Wind 360° 10 m/s Theta-e: 358°K
Reanalysis will benefit from high resolution data assimilation including aircraft data!
Summary
• There are major, systematic, regional differences in the structure, intensity, and diurnal cycle of rainfall systems
• The LPB has a particularly extreme domination by large and intense MCSs
• Satellite databases can provide important statistical constraints on convective intensity as well as rainfall
• Modelers should accept this reality as a challenge• The role of the SALLJ in MCSs is important-- is it mostly
as a provider of high-CAPE air, or also direct mass flux?• Reanalyses should assimilate high-resolution databases
and also pay close attention to thermodynamic variables
January 19, 2005 Department of Meteorology Seminar Series, University of Utah
Thank you!Thank you!
January 26, 2005 Department of Meteorology seminar series, University of Utah
-75 -70 -65 -60 -55 -50 -45
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Initiation Maximum extent Decay
MCSs Centroids trajectoriesMCSs Centroids trajectories
Night Day00 12 black03 15 red06 18 blue09 21 green
SALLJEX wind data during CJE events
Diurnal cycle
Maximum extent
UTC Time
Hours
Lifetime
Maximum extent size
*103 km2