CLARIS-LPB conclusive efforts: CMCC contribution to study temperature extremes in South America

CHERCHI A.; ZAMBONI L.; CARRIL A.F.

Otranto

Encuentro; CMCC Annual Meeting; 2012

CMCC

Heat waves over LPB are characterized on the basis of percentile thresholds and persistence criteria: they are short-lasting events whose typical duration is 2-3 days. With a threshold of 4 events per year lasting at least 2 days, about 10-20% of the years experience those kind of events and their spatial distribution is roughly homogeneous, with the Andes and the central stretch of the LPB (along 60W) having the largest occurrence. Considering 1961-2000 period, a high number of heat waves over central north LPB occur in the first part of the record. The search of years characterized by heat waves of a broad spatial extension provided very few years, insufficient to design an analysis of the relationship between HW occurrences and large-scale circulation. When the threshold for the identification of HW is reduced to 80th percentile the main characteristics of the events are unchanged (with the majority of the events lasting 2-3 days), but in this case it is possible to obtain a larger number of years and cases, at least for statistical purposes. Over South America, temperature extremes are sensitive to the phase and location of the tropical SST forcing in the Pacific sector. In some continental regions, the statistical distribution of Tmax moves towards higher temperatures when a tropical warm pool in eastern or central Pacific region is turned on. Although the opposite phase in the forcing produces roughly symmetrical patterns in the frequency of occurrence of extremes, the sensitivity is greater for positive than for negative pools. Sensitivity of extremes in TN is similar to that observed in TX, but the signal maximizes in tropical regions, while in La Plata Basin and in Patagonia the signal vanishes. Sensitivity of extremes could be partially explained trough anomalies advections (e.g., tropical-extratropical teleconnections). Decadal variations in the character of ENSO events and changes related with global warming may impact in the frequency of occurrence of extremes in the entire South America. Because of the sensitivity to evaporation-temperature feedback, mainly in the southern part of SA, it could be possible to specifically isolate the role of land-atmosphere coupling in interannual to decadal climate variability, when the system is forced by idealized SST anomalous conditions, focusing on the occurrence of extremes in those regions.