Relationship between the occurrence of South American Low Level Jet and daily precipitation and temperature extreme events.

PENALBA OC., RUSTICUCCI M.M., BENEDICTIS L.

Hangzhou

Workshop; 3rd International Workshop on Monsoons (IWM-III); 2004

Summer precipitation over northeastern Argentina is influenced, among other features, by the moisture transport. This could be from the tropical North Atlantic into the Amazon Basin and then towards the southern Brazil-Northern Argentina region or from the tropical South Atlantic both converging into the South American Low Level Jet (SALLJ). This circulation could also influence Maximum (MaxT) and Minimum (MinT) Temperatures in the affected region.This study introduces climatology of daily precipitation and daily MaxT and MinT associated with SALLJ episodes, classified in ChacoLLJ, no Chaco LLJ and no LLJ, during the warm semester (September to February) in Argentina (northern of 40°S).The daily quintiles of MaxT, MinT and rainfall for each month in a climatological period (1959-1998) was calculated. The daily quintiles of rainfall were calculated without considering the zero rainfall. In general there are little intraseasonal differences, considering the temperatures probability patterns. During Chaco LLJ days, there is very low probability of having a cold extreme temperature over the North, and a high probability of having a cold extreme MaxT or MinT (1st quintile) over the central region. The opposite pattern occurs for high Temperatures (5th Quintile). The cases of NO LLJ are opposite to the Chaco LLJ and the cases of no Chaco LLJ are intermediate. MinT is stronger related to the occurrence of Chaco LLJ than MaxT, with probabilities less than 5% of having extremely cold temperatures and higher than 50% of having extremely warm temperatures if it is a Chaco LLJ day.During the No Chaco LLJ, the monthly pattern of the conditional probabilities, taking into account only the rainy days, presents more intraseasonal variability than the temperatures. If there is a Chaco LLJ day, the probability patterns show a N-S or NW-SE gradient. In the northeastern region, low probability of having low rainfall amount or high probability of having high rainfall amount is associated. The opposite pattern occurs during the cases of No Chaco LLJ. Taking into account every day of the months, including the zeros, the probability of having No Rain is higher (greater than 80%) during No LLJ than during Chaco LLJ (lower than 50%).