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Radar-observed characteristics of precipitating systems

This study analyzes the radar observations of precipitating systems and identifies their different characteristics, diurnal cycles, and rainfall patterns. The results suggest the need for new convective parameterizations to improve understanding and prediction of these systems.

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Radar-observed characteristics of precipitating systems

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  1. RADAR-OBSERVED CHARACTERISTICS OF PRECIPITATING SYSTEMS Tim Lang, Dave Ahijevych, Steve Nesbitt, Rit CarboneSteve Rutledge, Rob Cifelli CSUNCAR

  2. Reduced Dimension Analysis zone GUASAVE S-Pol CABO SAN LUCAS

  3. Gulf of California Coastal Plain SMO Foothills SMO Peaks

  4. Regime A Gulf of California Coastal Plain Regime B 31 Jul 1 Aug 2 Aug 3 Aug 4 Aug 5 Aug 6 Aug

  5. Composite Reflectivity from 00 Z 5 Aug - 00 Z 7 Aug

  6. Diurnal Cycle43 day period of record

  7. Diurnal Cycle Regime A (14) vs Other Days (29)

  8. Diurnal CycleRegime B (14) vs Other Days (29)

  9. Period of Record StatisticsIt rains more on regime days and the rain is mainly from organized convection.

  10. Diurnal StatisticsIt rains more on regime days, most of the rain is from organized convection.

  11. Diurnal StatisticsStratified by locationOpposing phases of organized convection over land and sea

  12. More Shear, Stronger SE Wind

  13. Easterly Waves and Humidity

  14. Most rainfall is triggered by the SMO heat source and sea breeze. • Intraseasonal variability appears to be systematic. • Surges were associated with a small fraction of this variability and may not be as important to the big picture as originally hypothesized. • The A, B, and AB Regimes are associated with the capacity for convection to organize, scale upwards and propagate. • Regime days have enhanced shear, enhanced CIN, and ordinary CAPE. • The organized convection produces more rainfall, and propagates with respect to the local forcings and the steering winds (~6m/s). • Propagation, combined with triggering by the elevated heat source, leads to a well defined pattern of the diurnal cycle (“globally phase locked”). • Rainfall patterns are also consistent with the GoC acting as a nocturnal heat source and the land breeze front as “triggering topography”. Preliminary Conclusions New convective parameterizations are needed to get this stuff right.

  15. These findings are part of a larger picture…

  16. RESULTS published, emerging, analysis in progress, new study Continental Warm Season Rainfall Studies Background after Laing and Fritsch 1997

  17. Original US Findings, JAS 2002 Radar <Rainrate> “EPISODES”Sequences of convective systems often result from a coherent regeneration of organized convection. “Episodes” span substantial distances over North America on a daily basis in summer.(~1000 km, 20 h)

  18. 0 0 6 6 12 12 18 18 UTC Original US Findings, JAS 2002 Diurnal Cycle July 1997 % Time Radar Precipitation Echo We refer to this pattern as “globally phase-locked” Essentially all forcing is diurnal. Effects are both local and remote. Remote effects result from coherent regeneration of convection and propagation Longitude

  19. AFRICA: NH Summer (5S – 20N) Arlene Laing 1 2 3 4 5 6 7 2 2 2 Average Elevation, 0-20N (km) Average Elevation, 0-20N (km) Average Elevation, 0-20N (km) 20W 20W 20W 0 0 0 20E 20E 20E 40 40 40 1 1 1 0 0 0 Diurnal Cycle: July 1999 1 – 7 July 1999 UTC UTC

  20. RADAR-OBSERVED CHARACTERISTICS OF PRECIPITATING SYSTEMS Tim Lang, Dave Ahijevych, Steve Nesbitt, Rit CarboneSteve Rutledge, Rob Cifelli THANKS! CSUNCAR

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