CANONICAL AND MODOKI ENSO AND INFLUENCES ON LA PLATA BASIN EXTREME EVENTS OF PRECIPITATION

1. CANONICAL AND MODOKI ENSO AND INFLUENCES ON LA PLATA BASIN EXTREME EVENTS OF PRECIPITATION Renata G. Tedeschi1 (rgtedeschi@gmail.com), Alice M. Grimm2 (grimm@fisica.ufpr.br), Iracema F. A. Cavalcanti1 (iracema.cavalcanti@gmail.com), 1 Instituto Nacional de Pesquisas Espaciais – INPE Centro de Previsão do Tempo e Estudos Climáticos – CPTEC Cachoeira Paulista, São Paulo – Brasil 2 Department of Physics Universidade Federal do Paraná – UFPR Curitiba – Brasil Abstract: The frequency of extreme events of precipitation is very influenced by the occurrence of ENSO episodes . However, Sea Surface Temperature (SST) anomalies in the Pacific Ocean may display different positions in different types of ENSO events. The objective of this study is to analyze how the two types of ENSO (Canonical and Modoki) influence the frequency of extreme precipitation events over La Plata Basin (LPB) during different seasons. • Data and Methods: • Data: SST -> ERSST-V3; precipitation -> raingauge dataPeriod: 1960-2008. • ENSO years • CalculateSST anomalies of four regions in each season (Fig.1); • Modoki ENSO:This method is based on Ashok et al. (2007) • Calculate EN Modoki index (EMI): EMI=[SSTA]A-0.5[SSTA]B-0.5[SSTA]c and choose the years in which EMI is greater (lesser) than 0,7σM and the anomaly in region A is greater (lesser) than 0,7σA : these are the EN (LN) Modoki years. • Canonical ENSO: • If the anomaly of the Canonical region (Fig.1) is greater (lesser) than 0,7σCan . • Extreme Events of precipitation: • Running means over three days are computed and the values attributed to the central days. Gamma distributions were fit to precipitation in each day of the year.Extreme events are those with a three-day mean percentile above 90. • The mean frequency of extreme events for each season and each month, within each category of year (ENC, LNC, ENM, LNM, ENCM, LNCM and neutral), and the difference between these mean frequencies for EN (ENC, ENM and ENCM) and normal years, and for LN (LNC, LNM and LNCM) and normal years are computed, as well as their statistical significance. Fig. 1: Equatorial Pacific regions Fig. 2: Diference of extreme events of precipitation between ENSO years [ENC (1st column), ENM (2nd), ENCM (3rd), LNC (4th), LNM (5th) and LNCM (6th)] and Neutral, in each season [SON (1st line), DJF (2nd), MAM (3rd) and JJA (4th)] • Fig. 2 (ENSO Modoki): • SON: decrease of extreme events in the north of LPB and increase in the south during ENM. During LNM there are anomalies of opposite sign to ENM in the south and in the middle of LPB, but this composite is based on only two years. • DJF:mild decrease of extreme events almost all over LPB during ENM. There was only one case of LNM, and therefore there is not a composite for this category. • MAM: weak increase of extreme events in the south and stronger in the north of LPB, with decrease in the middle of the basin during ENM; little difference for LNM. • JJA: mixed impacts, with increase of extreme events in the middle of the basin and decrease to the north and south during ENM. During LNM only parts of the region show opposite impact. • Fig. 2 (ENSO Canonical and Modoki): • SON: just one year was characterized as ENCM, and the composite was not done. In the case of LNCM there is a strong increase of extreme events in Uruguay and Paraná state. This pattern bears greater resemblance to LNC than to LNM. • DJF: the patterns resemble those of the Canonical EN and LN. • MAM: No case of ENCM. For LNCM, there is a strong decrease of the extreme events all over the Brazilian LPB, but there are only two cases in this composite. • JJA: during ENCM the pattern in the northern part of LPB resembles that of ENM, while in the southern part it resembles the ENC. There is no composite for LNCM; Table 1: Years of El Niños: Canonical (ENC), Modoki (ENM), and two types together (ENCM);, years of La Niñas: Canonical (LNC), Modoki (LNM) and two types together (LNCM). • Results: • Table 1: • Number of Canonical events is much larger than Modoki events. • Most of EN Modoki years happen after 1979. • The spring and summer seasons do not have many LN Modoki events, the joint canonical and Modoki events are more frequent. • All composites are made using the years displayed on Table 1. • Fig. 2 (Canonical ENSO): • During ENC events there is an increase on extreme events of precipitation in relation to neutral years in the LPB in all seasons. • The inversion of signal expected on LNC years does not happen in all seasons. It happens in SON in all LPB, in DJF and MAM in south of LPB and in MAM and JJA in the São Paulo state. Conclusions: In the period of study there is more canonical events than Modoki events, and in the case of LN this difference is even greater. There are some regions in LPB with opposite impacts of Canonical and Modoki events. When one episode can be classified as Canonical and Modoki at the same time, the patterns are a mixture of the two types of impact, but sometimes the canonical pattern type predominates. Acknowledgments:CNPq, CAPES, and Claris LPB for the financial support.