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 Deep convective cores Deep convective cores Broad stratiform regions Broad stratiform regions Wide convective cores Wide convective cores Precip. climatology Precip. climatology

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

8. Synoptic forcing

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

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

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 06 UTC ~02 LT 00 UTC ~20 LT 00 UTC ~20 LT 18 UTC ~14 LT 18 UTC ~14 LT 12 UTC ~08 LT 12 UTC ~08 LT

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

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

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

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

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.