In this work the daily surface wind cycle is investigated focusing on the seasonal variation and the local circulations. The data collected by the automatic station located 25-30 km far from Petrolina and by the conventional station located in the city are used. The results show that the hourly mean wind speeds increase (decrease) during April-May-June (October-November-December) due to the intensification (weakening) of the South Atlantic subtropical high. During the three-month period July-August-September the hourly wind speeds are very close and have their highest intensities, with wind direction in the interval 120-130 degrees. In general, the daily cycle gives evidence of a maximum at 8-9 LT (local time) and two minima, one at 5-6 LT and another at 17-18 LT, in every month. The hodographs of the local wind at both stations show weak local circulations from January to May, a characteristic that may be related to a higher soil moisture content and, as a consequence, to lower values of the sensible heat flux gradient. During the remaining of the year, the dry period, the local circulations are comparatively stronger. The hodographs are irregularly drawn suggesting one local wind regime, in the southeast-northwest direction. The local circulations are stronger at 9 and 18 LT, the times of maximum and minimum wind speeds during the daily cycle, respectively.
daily wind cycle; local circulation; trade winds; seasonality; Northeast Brazil
