BORA ON THE ADRIATIC COAST DURING ALPEX SOP ON 27 TO 30 APRIL 1982

The periodically blowing bora wind on the Yugoslav Adriatic coast at the end of the ALPEX SOP (27-30 April) was analysed. The first case on 27 April was a consequence of the frontal passage, the second one on 28 and 29 April, of the cold north outbreak and the third case on 30 April was triggered by the Genoa lee cyclogenesis. General characteristics of the surface pressure field were the relatively weak gradients which resulted in generally weak bora, while the periods of locally stronger bora were rather brief. The cold stable airmass from inland poured over the mountainous barrier in the direction of the strongest gradients causing the relative humidity and temperature decrease and local pressure increase in the lee. The most pronounced bora was close to the lowest mountain passes and where the channelling effects were the strongest. The upper level wind usually had two maxima: the main in the upper trposphere due to macroscale motions and the secondary in the lowest few kilometres due to the surface accelerating mesoscale flow, defined as the bora layer. Assuming that bora has a certain similarity with the supercritical flows described by the hydraulic theory, the parameters of the real flow and those predicted by the theory are compared. lt was concluded that a distinction should be made between the cases with the sharply defined bora layer (by strong inversion or flow reversal - like on 27 and 30 April) and continuously stratified cases (as on 28/29 April) where the upstream bora layer usually cannot be immediately determined