Synoptic, Topographic, and Diurnal Effects on Summer Convection in South America - PowerPoint PPT Presentation

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

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Title: Regional, Seasonal, and Diurnal Variations of Convection in the Himalayan Region Author: ulli Last modified by: Robert Houze Created Date – PowerPoint PPT presentation

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


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
La Plata Basin
Foothills South
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
00 UTC 20 LT
18 UTC 14 LT
15
Wide convective cores
06 UTC 02 LT
12 UTC 08 LT
00 UTC 20 LT
18 UTC 14 LT
16
Broad stratiform regions
06 UTC 02 LT
12 UTC 08 LT
00 UTC 20 LT
18 UTC 14 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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