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Synoptic, Topographic, and Diurnal Effects on Summer Convection in South America

Investigate distribution and intensity of summer convection in South America using radar data and climatology. Study synoptic, topographic, and diurnal influences on a range of convective echo structures. Analyze forcing mechanisms and connection with precipitation patterns.

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Synoptic, Topographic, and Diurnal Effects on Summer Convection in South America

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  1. Synoptic, Topographic, and Diurnal Effects on Summer Convection in South America Ulrike Romatschke University of Washington, University of Vienna Robert A. Houze Jr., Socorro Medina, Kristen Rasmussen University of Washington ICAM, Rastatt, Germany, May 15, 2009

  2. Sponsored in part by: NSF Award# ATM-0505739 NSF Award# ATM-0820586 NASA Award# NNX07AD59G

  3. Objectives Investigate Distribution of convection Find regions of maximum convective intensity maximum precipitation Forcing of convection by Synoptic conditions Topography Diurnal heating Connection with precipitation climatology

  4. Data Tropical Rainfall Measuring Mission Precipitation Radar (TRMM PR) 3D reflectivity 10 years (December 1998 – February 2008) Summer months: December, January, February NCEP reanalysis Large-scale environment

  5. Classification of radar echo structures within convective systems Deep Convective Cores Contiguous convective echo ≥ 40 dBZ and ≥ 10 km in height Wide Convective Cores Contiguous convective echo ≥ 40 dBZ and ≥ 1000 km² in area Broad Stratiform Regions Contiguous stratiform echo ≥ 50 000 km² in area

  6. Distribution of radar echo structures Wide convective cores Deep convective cores Precip. climatology Broad stratiform regions

  7. Regions of interest Foothills North Foothills South La Plata Basin

  8. Synoptic forcing

  9. Foothills South, La Plata Basin Composites, wide convective cores, La Plata Basin 500 mb geopotential height anomaly Surface pressure anomaly [mb] Surface winds (~02 LT)

  10. Foothills North Composites, wide convective cores, Foothills North 500 mb geopotential height anomaly Surface pressure anomaly [mb] Surface winds (02 LT)

  11. Diurnal and Topographic forcing

  12. Foothills South, La Plata Basin Deep convective cores Wide convective cores Broad stratiform regions

  13. Foothills North Wide convective cores Broad stratiform regions

  14. Deep Convective cores 06 UTC ~02 LT 12 UTC ~08 LT 18 UTC ~14 LT 00 UTC ~20 LT

  15. Wide convective cores 06 UTC ~02 LT 12 UTC ~08 LT 18 UTC ~14 LT 00 UTC ~20 LT

  16. Broad stratiform regions 06 UTC ~02 LT 12 UTC ~08 LT 18 UTC ~14 LT 00 UTC ~20 LT

  17. Foothills South, La Plata Basin Composite winds and divergence, wide convective cores, La Plata Basin Divergence 06 UTC ~02 LT 12 UTC ~08 LT 00 UTC ~20 LT 18 UTC ~14 LT 10 m s-1

  18. Foothills North Composite winds and divergence, wide convective cores Divergence 06 UTC ~02 LT 12 UTC ~08 LT 00 UTC ~20 LT 18 UTC ~14 LT 10 m s-1

  19. Conclusions Synoptic low location critical Moisture transport by low-level jet from tropics to subtropics Diurnal heating Daytime deep and wide convective cores in Foothills South triggered by lifting over lower slopes Divergence at the Foothills North prevents convection Nocturnal cooling Downslope flow and convergence at the foothills leads to maxima in wide convective cores and broad stratiform regions.

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