Distribution of extreme events associated with deep convection.

CYNTHIA MATSUDO; PAOLA SALIO

Lanshut - Alemania

Congreso; European Conference on Severe Storm; 2009

European Severe Storm Laboratory

Infrared satellite imagery and conventional surface data are used to document the 4 occurrence and spatial distribution of severe weather phenomena associated with deep moist 5 convection over southeastern South America. 6 7 24-hour rainfall, maximum hourly gusts and present weather reports from the surface 8 station network are used over Argentina to the north of 40ºS during the period 2000-2005 and 9 hourly rainfall estimations provided by the CMORPH technique (CPC MORPHing technique, 10 Joyce, R. J., J. E. Janowiak, P. A. Arkin and P. Xie, 2004) were considered in order to 11 increase the precipitation data base density from January 2003 to December 2005. To gain 12 insight into the detection of extreme events, a 95th-percentile of the 24-hour rainfall and wind 13 analysis is performed showing that values over 30 mm and 25 m s-1 respectively are in 14 agreement to extreme values over the area of study. These results were related to the presence 15 of deep convection by considering the 235 K and 218 K cloud shield evolution evaluated by 16 the Forecasting and Tracking of Cloud Cluster technique (FORTRACC). The spatial 17 distribution of the 30 mm day-1 rainfall events and present weather events associated with the 18 presence of convection shows a marked preference over the northeastern region of the 19 country. 20 21 Finally, we analyzed the relationship between severe phenomena and the location and 22 lifecycle of Mesoscale Convective Systems (MCSs) defined by the 218 K or the 235 K levels. 23 Favorable locations of severe weather are found to be concentrated to the northeastern relative 24 to the cloud shield anvil centroid although the greatest amount of them is found to the 25 northwestern. This feature can be seen in systems with anvil areas larger than 250 000 km2 in 26 association to the predominant mid-level wind shear direction from the northwest over the 27 area. Moreover, systems with centers located north of 30ºS present a more circular shape 28 while those to the south are more elongated with a NW-SE main axis clearly related to the 29 presence and interaction with frontal zones over the area. Most of the events occur previous to 30 the moment when the systems reach their maximum extension, between two to ten hours after 31 the initiation of the system depending on the size of the MCSs.-1 respectively are in 14 agreement to extreme values over the area of study. These results were related to the presence 15 of deep convection by considering the 235 K and 218 K cloud shield evolution evaluated by 16 the Forecasting and Tracking of Cloud Cluster technique (FORTRACC). The spatial 17 distribution of the 30 mm day-1 rainfall events and present weather events associated with the 18 presence of convection shows a marked preference over the northeastern region of the 19 country. 20 21 Finally, we analyzed the relationship between severe phenomena and the location and 22 lifecycle of Mesoscale Convective Systems (MCSs) defined by the 218 K or the 235 K levels. 23 Favorable locations of severe weather are found to be concentrated to the northeastern relative 24 to the cloud shield anvil centroid although the greatest amount of them is found to the 25 northwestern. This feature can be seen in systems with anvil areas larger than 250 000 km2 in 26 association to the predominant mid-level wind shear direction from the northwest over the 27 area. Moreover, systems with centers located north of 30ºS present a more circular shape 28 while those to the south are more elongated with a NW-SE main axis clearly related to the 29 presence and interaction with frontal zones over the area. Most of the events occur previous to 30 the moment when the systems reach their maximum extension, between two to ten hours after 31 the initiation of the system depending on the size of the MCSs.2 in 26 association to the predominant mid-level wind shear direction from the northwest over the 27 area. Moreover, systems with centers located north of 30ºS present a more circular shape 28 while those to the south are more elongated with a NW-SE main axis clearly related to the 29 presence and interaction with frontal zones over the area. Most of the events occur previous to 30 the moment when the systems reach their maximum extension, between two to ten hours after 31 the initiation of the system depending on the size of the MCSs.