In the west part of the country the annual cycle is very pronunciated and it explains most of the variance but in the east difference between Winter and Summer rainfall become smaller. The first three modes of the principal component analysis of the rainfall mean annual cycle in subtropical Argentina separate regions with different rainfall regimes. The first mode has a minimum in summer, especially in January, and its maximum influence in the Northeast. The second mode, with a well-marked annual cycle and a minimum in winter, has its strongest influence in the northwest of Argentina. The third mode has a semi-annual cycle with opposite action in the south-eastern and north-eastern regions. Consequently, in the southeast the rainfall annual cycle shows two maximums in early autumn and late spring, while in the northeast the first mode contributes to the almost constant precipitation throughout the year.
The first mode is related to the convection in central Brazil in a way that tends to produce a negative correlation between precipitation in Northeast Argentina and this convection. This would indicate that in this region compensatory subsidence is a possible reason for this.
There is a clear relation between tropical convection in South America and the second mode of the rainfall annual cycle of subtropical Argentina and therefore this rainfall in the western part of Argentina is positively correlated with tropical convection. This indicates that direct advection from the north or other indirect mechanisms induced by tropical convection, like the enhancement of the easterly flow from the Atlantic Ocean, overcomes any compensatory subsidence caused by the tropical convection. The zonal and meridional pressure gradients represent the humidity advection from the north and the east and they explain a significant percentage of the annual rainfall variance.
The tropical convection not only produces statistical signals in the rainfall field of subtropical Argentina but also is highly correlated with the latitude of maximum winds at 200 hPa. This parameter is closely related to the subtropical jet, giving another indication that the circulation over the subtropical region interacts with the tropical convection