Extended Abstract (212K)11.10
A Model Study of Intraseasonal Oscillations over South America South America
Baode Chen, GEST, University of Maryland Baltimore County, Baltimore, MD; and W. Chao
Recent observations have revealed that there are intraseasonal oscillations (ISO) of convection over South America (SA). A reconstruction of the flow pattern in association with the SA ISO suggests that their sources could be (1) the Madden-Julian Oscillation (MJO) from the Western Pacific and (2) a local forcing mechanism (Zhou and Lau, 1999). In the present study, the physical mechanism of the SA ISO has been investigated by using the National Center for Atmospheric Research (NCAR) regional climate model (RegCM2). The National Centers for Environmental Prediction (NCEP) reanalysis was used to provide initial conditions and time-dependent or time-averaged lateral boundary conditions for the model integration. Our results indicate that the SA ISO still exists with time-averaged lateral boundary conditions, which prevent the MJO and other outside disturbances from entering the model's domain, suggesting a local forcing mechanism for the SA ISO in addition to the MJO. Further experiments show that the SA ISO still exist even with temporally constant radiative cooling rates, a result distinct from the theory proposed by Hu and Randall (1994).
Session 11, Observed Seasonal/Interannual Variability (Room 608)
Thursday, 15 January 2004, 11:00 AM-3:00 PM, Room 608
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