WIND DIRECTION IN SOUTHERN SWEDEN 1740-1992 - VARIATION AND CORRELATION WITH TEMPERATURE AND ZONALITY

Wind direction variation in Lund, s. Sweden is investigated for the period 1740-1992. Around 1860 the initial bidirectional (W-E) continental flow pattern changed to a combined uni- (W) and bi-directional pattern, which has increased the maritimity; in recent decades, an exceptionally high W'ly influence is present. The process toward a higher degree of maritimity has not been a strictly linear one; the 1820's-1830's and the 1940's-1960's are exceptions from this generalization. Trends of declining N'ly and NE'ly winds are accompanied by increased frequencies of SE'ly and SW'ly winds. From the wind direction data, using multiple regression analysis, hindcasting models for temperature and zonality (zonality index P-45 degrees N-P-65 degrees N in the sector 5 degrees E-40 degrees E) are established for the time when such meteorological observations are unavailable (i.e. before 1860; temperature and before 1899; zonality). The accuracy of monthly zonality index estimations varies between R = 0.76-0.93; temperature R = 0.35-0.80. Models for January temperature and zonality are the most reliable ones. Presence of a very low zonal index in January characterised the mid 18th century (average 4 hPa compared to the current value 10 hPa) which resulted in colder winters, according to the January estimate, 1.5 degrees C colder than present.