A climatology of the easterly waves disturbances (DOLs) over Alcântara - MA was investigated using a method that compute the signal of the observational meridional wind (rawinsoundings from 1988 up to 1997). This technique has been applied to three different layers (850-700, 700-500 and 850-500 hPa) in order to identify the best layer to indicate the DOLs occurrence. The DOLs events have been confirmed by independent data-sets available: cloud cover (ISPCC data set), infra-red satellite images (from GOES-E) and power spectrum of the meridional component (ECMWF re-analysis). The method detected the presence of the DOLs during the whole year with time-scale of 3-6 days. During the wet period (jan-jun) all three layers identified these atmospheric systems. For the dry season (jul-dec), only the deeper layers (layers between 700 - 500 hPa and/or 850-500 hPa) were able to identify the events.
rawinsoundings; meridional wind; easterly waves
