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Regional_ Seasonal_ and Diurnal

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Regional_ Seasonal_ and Diurnal Powered By Docstoc
					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
  Sponsored in part by:
NSF Award# ATM-0505739
NSF Award# ATM-0820586
NASA Award# NNX07AD59G
                 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
                      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
   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
              Distribution of radar echo structures



  Deep                              Wide
convective                        convective
  cores                             cores




                                    Precip.
   Broad
                                  climatology
 stratiform
  regions
            Regions of interest




Foothills
 North




            Foothills   La Plata
             South       Basin
Synoptic forcing
            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)
                           Foothills North
            Composites, wide convective cores, Foothills North
500 mb geopotential height anomaly      Surface pressure anomaly




                                                                   [mb]




                                        Surface winds (02 LT)
Diurnal and Topographic
         forcing
Foothills South, La Plata Basin
           Deep convective cores




           Wide convective cores




                      Broad
                    stratiform
                     regions
Foothills North
             Wide
           convective
             cores




              Broad
            stratiform
             regions
         Deep Convective cores



06 UTC             12 UTC
~02 LT             ~08 LT




18 UTC             00 UTC
~14 LT             ~20 LT
         Wide convective cores



06 UTC             12 UTC
~02 LT             ~08 LT




18 UTC             00 UTC
~14 LT             ~20 LT
         Broad stratiform regions



06 UTC               12 UTC
~02 LT               ~08 LT




18 UTC               00 UTC
~14 LT               ~20 LT
Foothills South, La Plata Basin
Composite winds and divergence, wide convective cores, La Plata Basin




                                                                           Divergence




                06 UTC                                            12 UTC
                ~02 LT                                            ~08 LT




                18 UTC                                            00 UTC
                ~14 LT                                            ~20 LT   10 m s-1
          Foothills North
Composite winds and divergence, wide convective cores




                                                                 Divergence




         06 UTC                                         12 UTC
         ~02 LT                                         ~08 LT




         18 UTC                                         00 UTC
         ~14 LT                                         ~20 LT   10 m s-1
                      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.