A description of the main characteristics of the Bolivian High and what is now called the South American Monsoon System (SAMS) is presented. The water origin for the Altiplano can be inferred from both descriptions, being this supply mostly from the Amazon basin. From this premise, an analysis of ground weather station data and radiometers data from Chajnantor was performed.
During a summer event of high PWV, an anomalous increase of easterly winds is observed, confirming the previous "Amazon origin" assumption.
A summer climatology for Chajnantor is obtained and a daily index of U wind and PWV is defined. Both indexes present a high negative correlation during summer when U wind is negative. An event of high PWV during summer is also defined and a very significant contrast with a no event day is found. A composite analysis (averages) is done presenting the behaviour of PWV, winds, and temperature before, during, and after an event and a no event day.
These results produce a significant progress in the characterization of summer events of high PWV, its origin, and the planning for the implementation of future local weather forecasts.
View a pdf version of ALMA Memo 379.
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