INTERDECADAL VARIATIONS OF SURFACE WIND DIRECTION IN LUND, SOUTHERN SWEDEN, 1741-1990

By uni- and bimodal mean vector analysis it is concluded that the decadal pattern of surface-wind-direction frequencies in Lund, southern Sweden, has changed substantially between 1741 and 1990. Trend analysis shows that statistically significant decreasing trends for north and north-east winds are present during all seasons, whereas a decline in easterly wind is most prominent in July-September These trends are paralleled by increases of south-east (January-May and August-November) and south-west winds (April-September and November-January). These trends promote milder autumns, winters, and springs and a somewhat cooler summer. The investigation period is divided into three phases on the basis of similar flow patterns, which in general terms agree with Scandinavian temperature records: (i) 1741-1840-a continental low-zonality period featuring extreme bimodal flow of wind with relatively high frequencies of east winds, which indicate a continental climate. Warm summers and cold winters are produced by this flow pattern. The severity of winters was enhanced by a high frequency of north and north-east winds. (ii) 1841-1910-a transition period with decreased continentality and low yearly temperatures. This circulation type caused a temperature drop except during winter. (iii) 1911-1990-a maritime high-zonality period featuring further strengthening of the westerly flow. A warm maritime phase with least expressed warming in summer. Severe winters are further counteracted by low frequencies of north and north-east winds.