Thessaloniki '91 field measurement campaign—I. Wind field and atmospheric boundary layer structure over greater Thessaloniki area, under light background flow

In this study, the major characteristics of the sea and land breeze circulation cells over the Greater Thessaloniki Area (GTA) are presented. During the Thessaloniki '91 Field Measurement Campaign (15 September–13 October) the local flows were examined under different conditions of background wind using a network of ten surface measuring stations, two tethered balloons and a high-resolution monostatic Sodar. The measurements showed that the sea breeze developing over the area maintained two circulation cells. The first was generated over the Thessaloniki Bay during the morning hours and caused sea breeze spreading with the wind direction perpendicular to the long convoluted shoreline at moderate wind speed. The second circulation cell was established over the entire Thermaikos Gulf at noon and was maintained with a southerly wind direction. During the night, a land breeze developed and the wind pattern was influenced by various drainage flows resulting from the surrounding complex topography. The measurements also confirmed the influence of the heat island effect and the creation of a shallow convection layer, during the night which gave rise to layering aloft. Finally, tethersonde ascents revealed the depth of the sea breeze, which was found to range from 300 m to more than 500 m, depending on the prevailing synoptic flow.