Influences on atmospheric blocking regimes on Southern Brazil in scenarios of future climate change

Throughout the year, a wide range of transient weather systems act on South America. Among them we can mention the atmospheric blocking phenomena occurring especially in middle latitudes with duration ranging from a few days, staying active for weeks. During the occurrence of an atmospheric blocking, there is a persistent high pressure anomaly, located south of the belt of semi permanent subtropical highs. This situation prevents the systems from moving in a normal course, featuring a c1assic situation of blocking. To detect these events we used the index proposed by Pelly and Hoskins (2003 - PH03). This index detected the reversal of the meridional gradient of potential temperature on the dynamic tropopause (high levels) caused by persistent anomalous circulation. The situation must remain active for more than three consecutive days and be present in an area greater than 10 o longitude. The events will be evaluated on HadGEM2-ES data which is part of the CMIP5, within the c1imate change scenario RCP4.5. To verify the functionality of the index PH03, an atmospheric blocking event which occurred in the Pacific southeast was selected. This region of the globe concentrates most of the activities that remotely influence the temperature and precipitation regimes in South America. Besides this, there are two other preferential regions of occurrence in HS, concentrating near southwestem Australia and in the southwestem portion of the Atlantic, van Loon (1956). In the context of this work, the remo te effects of blocking will be analyzed later, however, at this stage the concem focuses in verifying the functionality of the index PH03. Thus, the index is calculated for the 1986 winter period; moreover, we will analyze the meteorological fields that characterize its synoptic conditions. The blocking remained active in the region for several days between the end of July and the first half of August. The preliminary results were satisfactory; in such a way that the analysis of meteorological fields showed the establishment of the blocking condition. The analysis of other cases can be done to confirm the functionality of the PH03 index in hístorical database to prepare a blocking climatology ,update and evaluate the remote influences in a future c1imate scenario