Developing an MCS index using the climatology of South America

• Published in: Meteorological applications Vol. 25; no. 3; pp. 394 - 405
• Main Authors: Rasera, Gustavo, Anabor, Vagner, Scremin Puhales, Franciano, Dal Piva, Everson
• Format: Journal Article
• Language: English
• Published: Chichester, UK John Wiley & Sons, Ltd 01.07.2018; John Wiley & Sons, Inc
• Subjects: Advection; Climate; Climatic indexes; Climatology; Convection; Environmental conditions; forecast; instability index; MCS; Mesoscale convective systems; Precipitation; Rainfall; Severe weather; South America; Temperature; Vertical velocities; Vertical wind shear; Wind shear
• ISSN: 1350-4827; 1469-8080
• DOI: 10.1002/met.1707

ABSTRACT Even though mesoscale convective systems (MCS) are of great importance in precipitation regimes besides being related to severe weather events, they are still not easy to predict. This study builds an objective index for South American MCS based on synoptic features present before the initiation of the MCS between 2005 and 2010. The National Centers for Environmental Prediction (NCEP) Climate Forecast System Reanalysis (CFSR) product is used to access environmental conditions near the MCS‐initiation centroid and in unorganized convective environments to obtain a South American MCS index (SA‐MCS index). Upper and middle atmospheric levels presented the main patterns used to identify the MCS environments and unorganized convection, with the jet streak downstream of a short trough at medium levels frequently present in the convectively organized environment. The SA‐MCS index is shown to depend on a vertical wind shear between 0 and 6 km high, temperature advection at 775 hPa, lifted index (LI) and vertical velocity omega at 800 hPa. When compared with the MCS index developed through the United States MCS climatology, the SA‐MCS index was able to predict more than twice as many MCS at a distance of less than 1° from the point of maximum intensity of the index. This paper evaluated a new mesoscale convective system (MCS) index developed for South America (SA‐MCS index). It was used in the Climate Forecast System Reanalysis (CFSR) product for 115 MCS that occurred over six years. The SA‐MCS index predicted more than twice as many MCS at a distance of less than 1° from the point of maximum intensity of the index when compared with the existing index.