Intraseasonal Modulation of South American Summer Precipitation

Abstract Intraseasonal variation of convection over South America is examined using singular spectrum analysis (SSA). The dipole convection pattern with centers of action over the SACZ and the subtropical plains is modulated by modes of different timescales. Both oscillatory modes with periods of 36–40 days (mode 40) and 22–28 days (mode 22) influence convection over the SACZ with the faster mode (mode 22) leading the variability over the subtropical plains. Mode 40 is related to the Madden–Julian oscillation. Outgoing longwave radiation anomalies (OLRA) propagate eastward from the western Pacific to the central Pacific with a period of 40–48 days. The 200-hPa streamfunction composites show a wavenumber 1 structure in the Tropics and a wave train propagating downstream from the convective area in the tropical Pacific. The development of the dipole pattern is also contributed by mode 22, which features the meridional propagation of OLRA over South America from midlatitudes to the Tropics. The streamfunctio...

[1]  M. DeMaria,et al.  Large-Scale Response of the Tropical Atmosphere to Transient Convection , 1983 .

[2]  A. W. Gandu,et al.  A Primitive Equations Model Study of the Effect of Topography on the Summer Circulation over Tropical South America , 1991 .

[3]  R. Vautard,et al.  Singular spectrum analysis in nonlinear dynamics, with applications to paleoclimatic time series , 1989 .

[4]  Richard Kleeman,et al.  A Modeling Study of the Effect of the Andes on the Summertime Circulation of Tropical South America , 1989 .

[5]  Kingtse C. Mo.  Alternating Wet and Dry Episodes over California and Intraseasonal Oscillations , 1999 .

[6]  Athanasios Papoulis,et al.  Minimum-bias windows for high-resolution spectral estimates , 1973, IEEE Trans. Inf. Theory.

[7]  R. Vautard,et al.  Singular-spectrum analysis: a toolkit for short, noisy chaotic signals , 1992 .

[8]  K. Mo,et al.  Alternating Wet and Dry Conditions over South America during Summer , 1997 .

[9]  R. Reynolds,et al.  The NCEP/NCAR 40-Year Reanalysis Project , 1996, Renewable Energy.

[10]  B. Liebmann,et al.  Description of a complete (interpolated) outgoing longwave radiation dataset , 1996 .

[11]  J. Horel,et al.  Wavelike Southern Hemisphere Extratropical Teleconnections , 1992 .

[12]  Klaus M. Weickmann,et al.  Circulation anomalies associated with tropical convection during northern winter , 1992 .

[13]  P. Dias,et al.  Analysis of Tropical–Extratropical Interactions with Influence Functions of a Barotropic Model , 1995 .

[14]  George N. Kiladis,et al.  Submonthly Convective Variability over South America and the South Atlantic Convergence Zone , 1999 .

[15]  P. Dias,et al.  Simulations of the Summer Circulation over the South American Region with an Eta Coordinate Model , 1995 .

[16]  B. Hoskins,et al.  Three Dimensional Propagation of Planetary-Waves , 1982 .