Large-Scale Patterns Linked To Low-Frequency Variability Of Daily Intensity Of Extreme Rainfall Over Argentina

ROBLEDO F. PENALBA O. VERA C.

Nouméa

Conferencia; 10th International Conference on Southern Hemisphere Meteorology and Oceanography; 2012

The main goal of this work is to describe large-scale and regional features of the atmospheric circulation anomalies impacting extreme daily rainfall activity that occur in Argentina. The analysis has been made on the basis of the leading pattern of covariabilty between spring daily intensity of extreme rainfall (DIER) in Argentina and sea surface temperature (SST) for all the oceans from 17.5o N to 90o S.This analysis was performed using a Singular Values Decomposition (SVD) for spring in the period 1962 to 2005.Monthly SST fields are from the Kaplan SST V2dataset, streamfunction fields from the NCEP/NCAR reanalysis are considered, and high-quality daily rainfall observations for 35 surface stations distributed throughout Argentina are used. The two leading SVD modes of the coupled SST and DIER variations account around 62 percent for spring of the total square covariance (TSC). The first mode of spring explains 45% of TSC and its spatial pattern is associated with SST anomalies resembling those typically linked to ENSO with 4-year temporal cycles and enhanced DIER in central and eastern Argentina. The corresponding regression maps of circulation anomalies depict Rossby-like wave trains emanating from central tropical Pacific and equatorial Indian oceans, in a similar way than those previously identified by other papers as induced by ENSO. The second SVD mode explains 17% of TSC and shows a significant decadal variability. It is associated to an anomalous cooling in the tropical Atlantic Ocean surface conditions as well as in the Indonesian Sea associated with low DIER values over northeastern Argentina. The related upper-level circulation anomaly pattern exhibits an anticyclonic circulation over southeastern South America that seems to be part of a Rossby-like wave train extending from western tropical Pacific Ocean arching toward South America. Evidences of an annular circulation structure are also observed over the Polar Regions in association with this particular SVD mode.