Interannual variability of the storm track over the
        South America-Southwest Atlantic sector 


PI: Isidoro Orlanski   io@gfdl.gov               
Geophysical Fluid Dynamics Laboratory/NOAA
Princeton University, Princeton NJ. 08540
CO-PI's:Drs. Mario Nunez, Claudio Menendez and Silvina Solman
'solman'@at1.fcen.uba.ar
Centro de Investigacion para el Mar y la Atmosfera
CONICET-UBA
Pabellon 2-Piso 2
Ciudad Universitaria (1428)
(1402) Buenos Aires, Argentina 
          








2. Summary of Proposed Project.

 The objective of the proposed research will be to characterize 
the interannual variability of the storm track over the South 
America-Southwest Atlantic sector (SA-SWA), particularly with 
respect to variations in cyclone development over SA-SWA during 
the warm and cold phases of the ENSO cycle. Of related interest 
is the role of the quasi-stationary circulation of the ENSO cycle 
in inducing topographic or dynamic upstream blocking and the 
effect of this blocking on downstream cyclonic development over 
SA-SWA. This research represents one of the first attempts at 
integrating high frequency statistical analysis with numerical 
simulation of actual cases in a storm track environment. It is 
believed that this combination of methodologies will provide a 
more complete picture of the interannual variability of high 
frequency disturbances in the SA-SWA region.
 
 The proposed study will proceed in two phases. The first phase 
will have two components, to be carried out simultaneously at 
GFDL and CIMA. GFDL will determine the mean circulation over the 
SA-SWA region, for mean winter time conditions, as well as for 
conditions corresponding to warm and cold ENSO events. Regression 
analysis will be used to characterize the predominant wave 
structures. This regression technique (Chang, 1993)will provide 
an estimate of the change in vertical structure for positions 
downstream of the South America continent, as well as information 
about the sources of heat and moisture fluxes that contribute to 
cyclone development. 
At the same time, CIMA will select several winter storms for each 
of the warm and cold events, following an approach similar to 
that used in case studies discussed in Orlanski et al (1989, 
1991), and Menedez (1994). Control simulations of each will be 
carried out using the LAHM-GFDL limited area model (Orlanski and 
Katzfey 1987)). A "composite" analysis of energetics (Orlanski 
and Katzfey, 1991, Orlanski and Sheldon, 1993, 1995: Chang, 1993) 
will be compared with the energetics obtained by regression 
techniques (Chang, 1993).

 The second phase of the study will complement the results of 
the first phase. For the limited area simulations, the sensitivity 
of particular cases to surface fluxes will be analyzed (Orlanski 
et al, 1991)with the goal of determining what part the 
environment, dynamics, and surface fluxes play in producing the 
observed interannual variability. For the quasi-stationary scale, 
the role of the synoptic-scale feedback into the larger scale 
circulation will be determine (Orlanski, 1996). Given the 
differences in the shape of the storm track over the Atlantic 
Ocean between the warm and cold ENSO phases (Fig 2.), it is 
expected that marked differences in the feedback from cyclone 
scale eddies will be found.