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Rain-Producing Systems for the SAMS and their Moisture Sources

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

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Rain-Producing Systems for the SAMS and their Moisture Sources

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  1. 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

  2. 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.

  3. 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):

  4. TRMM Radar Algorithm Annual Rain in mm/month

  5. Fractional rain (%) contributed by large MPFs vs. small PFs Very large Small

  6. Fractional rain (%) contributed by PFs with specified properties

  7. Fractional rain (%) contributed by MPFs with 40 dBZ height </> 6 km

  8. Fractional rain (%) contributed by MPFs with convective fraction </> 50%

  9. 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

  10. 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

  11. MCSs Centroids during SALLEX (Nov 15, 2002 – Feb 15, 2003) CJE NCJE LLJ-ARG NO-LLJ Fill symbols represent nocturnal MCS (0-12] open symbols represent diurnal MCS (12-00]

  12. Subtropical MCSs between 23S-40S – 65W-52W Initiation UTC Time

  13. Decay UTC Time

  14. 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?

  15. 19Dec 2002 MCS near B.A. used by C. Saulo in modeling study (IR cold cloud tops massive and colder than -80°C) (Passive microwave- ice scattering) (Passive microwave- ice scattering) Radar structure is that of a classic leading line-trailing stratiform Sq. line (ignore- artifacts)

  16. x x x x Notice d/dt (theta-e) from tropical Atlantic to Argentina MCS Case Study

  17. x x x x Dec-Jan-Feb MEAN conditions Notice d/dt (theta-e) from tropical Atlantic to Argentina

  18. x x x x MCS Case Study (SALLJEX 22 Jan 03) Notice d/dt (theta-e) from tropical Atlantic to Argentina

  19. x x NCEP: Wind 330° 6 m/s Theta-e: 348°K P-3: Wind 360° 10 m/s Theta-e: 358°K Reanalysis will benefit from high resolution data assimilation including aircraft data!

  20. 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

  21. MCSs Centroids trajectories Initiation Maximum extent Decay

  22. SALLJEX wind data during CJE events Day Night Diurnal cycle 00 12 black 03 15 red 06 18 blue 09 21 green

  23. Maximum extent UTC Time

  24. Lifetime Hours

  25. Maximum extent size *103 km2

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