Estimating the probability of convection events from statistical analysis of temperature and humidity vertical profiles, shear and helicity

ARANEO D.; SIMONELLI S.; NORTE F.; SANTOS R.; BUSTOS C.

Helsinki

Conferencia; 7th European Conference on Severe Storms; 2013

European Severe Storms Laboratory

The objective of this work is to determine the vertical profile patterns of temperature (T) and dew point (Td) for the Northern of Mendoza Province and to obtain a statistical forecast model of convection using these profiles as predictors. Rawinsondes at 12 UTC from Mendoza-Aero weather station (National Weather Service) were used in order to obtain the profiles and to adjust the forecast model. Several 1987-2005 October-March periods were used for the analysis and the 2006-2010 November-March periods were used to validate the predictions. We defined a Convection Occurrence Index (C) according to the reported observations during 24 hours, starting at 9 UTC before the rawinsonde observation. The Principal Component Analysis (PCA) was applied in order to determine the vertical profiles patterns of T and Td. In order to build the forecast model, the resulting component loadings were used as predictors in a logistic multiple-regression fit with the C index as response variable. The helicity and 850-400 hPa shear were also incorporated as predictors in the logistic multiple-regression fit. The PCA resulted useful to obtain the vertical profile patterns of T and Td. The resulting patterns in direct and reverse modes represent real cases. The analysis of T and Td sheds 6 significant components explaining 92% of the system variability. In the studied cases, over than 70% of the forecast model effectiveness is obtained using only the T and Td profiles (similar to that found in other studies by traditional indices). The effectiveness could be improved by changing the definition of C and the incorporation of shear and helicity as predictors. Profile patterns of T and Td reveals that the probability of convection increases (decreases) with strong (weak) T lapse-rate between low and middle levels of the troposphere and high (low) moisture content in the lower layers.