Interdecadal changes in the precipitation seasonal cycle over Southern South America and their relationship with surface temperature

The decadal variability in the structure of the annual precipitation cycle over Southern South America (SSA) is analysed with the purpose of investigating whether the lower frequency vari- ability laid bare by annual data is also evident in the annual precipitation structure. Climatic analy- sis shows that the annual cycle plus the semi-annual cycle dominate the annual variability of precip- itation in SSA and represent most of the physical factors responsible for the observed patterns. The percentage of variance explained by the annual cycle shows 2 local maxima, in northwestern Argentina and southern Chile, with opposite phases, summer and winter. The interdecadal analysis of the annual cycle shows 2 areas of relevant variability: one over the central east and the other over the north east. In the first area, there is a positive trend in the variance explained by the first har- monic, indicating that precipitation tends to be better represented by an annual cycle, a fact that might indicate a climatic change in so far as this variable is concerned. In view of global warming, and as a first step towards quantifying the relationship between temperature and precipitation in the region, correlation coefficients are evaluated. The correlation structure of the warmer period 1943-52 generally shows a slight correlation pattern when compared to the 2 colder periods, 1955-64 and 1966-75. In northwestern Argentina, the highest positive correlation coefficients are found at the coldest times in 1955-64, and are probably related to an increase in cloudiness. During summer months (November to February), there is an inverse relationship between precipitation and temperature over most of SSA. That is, warmer/colder summers are associated with precipitation below/above the mean. In autumn and spring months, the correlation is positive in the eastern part of Argentina and Paraguay, and represents well the mechanism of maximum precipitation in this area, which is mainly the result of cyclogenesis. Winter correlation shows a weak positive pattern over SSA and a negative correlation area to the east of the Cordillera de los Andes, which is more intense in spring.

[1]  A. Pittock.  Patterns of Climatic Variation in Argentina and Chile—II. Temperature, 1931–60 , 1980 .

[2]  S. Hameed,et al.  Harmonic analysis of the seasonal cycle in precipitation over the United States: a comparison between observations and a general circulation model , 1989 .

[3]  P. L. Finkelstein,et al.  Spatial Distribution of Precipitation Seasonality in the United States , 1991 .

[4]  Neil J. Holbrook,et al.  Decadal climate variability in Australia during the twentieth century , 1999 .

[5]  J. Wallace,et al.  The Global Distribution of the Annual and Semiannual Cycles in Precipitation , 1976 .

[6]  N. Graham,et al.  Decadal Variability of Precipitation over Western North America , 1998 .

[7]  H. Loon,et al.  Decadal Variation of the Annual Cycle in the Australian Dataset , 1993 .

[8]  M. D. Shulman,et al.  An Areal and Temporal Analysis of Precipitation in the Northeastern United States , 1979 .

[9]  C. Mechoso,et al.  A Recent Increasing Trend in the Streamflow of Rivers in Southeastern South America , 1998 .

[10]  J. Wallace,et al.  ENSO-like Interdecadal Variability: 1900–93 , 1997 .

[11]  James W. Hurrell,et al.  A modulation of the atmospheric annual cycle in the Southern Hemisphere , 1994 .

[12]  P. Aceituno,et al.  RECENT TEMPERATURE VARIATIONS IN SOUTHERN SOUTH AMERICA , 1997 .

[13]  Andrew F. Siegel,et al.  Testing for Periodicity in a Time Series , 1980 .

[14]  C. Mechoso,et al.  Relationships between Precipitation Anomalies in Uruguay and Southern Brazil and Sea Surface Temperature in the Pacific and Atlantic Oceans , 1998 .

[15]  M. Khalil,et al.  The relationship between precipitation and temperature over the contiguous United States , 1993 .

[16]  C. Ropelewski,et al.  Global and Regional Scale Precipitation Patterns Associated with the El Niño/Southern Oscillation , 1987 .

[17]  M. Yen,et al.  Interdecadal Variation of the Southern Hemisphere Circulation. , 1997 .

[18]  M. Haylock,et al.  Circulation Features Associated with the Winter Rainfall Decrease in Southwestern Australia. , 1993 .

[19]  J. Pierini,et al.  Time and Space Variability of Rainfall in Central-East Argentina , 1989 .

[20]  R. Compagnucci,et al.  Surface Pressure Patterns During The Year Over Southern South America , 1997 .

[21]  A. Pittock.  Patterns of Climatic Variation in Argentina and Chile—I Precipitation, 1931–60 , 1980 .