The local orographic influence and precipitation events on the coast of Santa Catarina

Abstract

The objective of the study is to analyze the main synoptic features associated with the occurrence of extreme precipitation on the coast of Santa Catarina (SC), for events with influence of orography. To the precipitation data of 5 consecutive days (01/01/1969 to 31/12/2009), region of Florianópolis (INMet station), located in the central portion of the Santa Catarina coast, it was considered as extreme value the quantile 99.5%. Amounts accumulated extremes were found in all seasons, and most of the summer, especially in February. Synoptic fields at low and high levels were analyzed in the period 1979-2009, through the ERA lnterim reanalysis (ECMWF). As the pressure fields at sea level and 10 m wind, the events were divided into 3 groups. Group 1: east wind more intense and persistent than the other cases, at least 5 days in the coastal area, and accumulated precipitation occurs far distributed around 3 days. Group 2: east wind is observed after the cold front, for 1 or 2 days, same period of occurrence of the accumulated extreme precipitation. ln both groups, the flow east is from the high pressure in the Atlantic, and it find a mountain barrier formed by the presence of the Serra do Mar. Group 3: flow east was not observed, verifying wind northeast or cold front during the occurrence of rain. ln this work, it analyzed the atmospheric fields of Group 1. At middle levels, there is trough in SC, sometimes with closed vortices, for an period of about 3 days. The slow movement of surface systems and higher levels, suggests a possible atmospheric blocking that needs to be investigated. ln most of the study period, the precipitation concentrated along the coast of SC, not reaching the interior of the state. On 700hPa and 850 hPa, the flow is between the east andonortheast in the coast of SC. Tt is observed in the interior an area of moisture convergence at 850 hPa. It is observed in the coast an area of moisture divergence at 850 hPa and -moisture convergence at 700hPa, indicating the importance of mesoscale analysis. For the days when high values of CAPE were found, is also observed significant amount of mass divergence at 250hPa. On most days before the rain, however, there is neither significant amounts of CAPE nor mass divergence, suggesting stratiform precipitation.