Resolution experiments with the Regional Eta Model for a frost event in South America

.The purpose of this work is to evaluate the importance of the increase of resolution for forecasts of meteorological variables that are associated with events of frosts over Southern part of Brazil. This study performs numerical experiments using the regional Eta model set up with different resolutions. The model uses the horizontal Arakawa E grid and h vertical coordinate. The control run was configured with 40 km in horizontal and 38 layers in the vertical. The initial and lateral boundary conditions are obtained by the NCEP analyses. The lateral boundaries are updated every 6 hours.The results consist of experiments based on: increasing the horizontal resolution maintaining the vertical (20 km and 38 layers), maintaining the horizontal resolution and increasing the vertical (40 km and 50 layers), and finally, increasing both the horizontal and the vertical (20 km and 50 layers) resolutions. Objective evaluation of these experiments applies the statistical scores, root mean square error and bias of mean see level pressure, 500-mb geopotential height, and 850-mb temperature over model domain. Hourly observation of surface pressure, shelter temperature and humidity and 10-m wind for 3 specific sites will be compared with model simulations. The increase of the horizontal and vertical resolution improves the topography representation and adds structure to the flow, consequently phenomena of smaller scales can be better represented