WHITE SEA SURGE LEVEL FLUCTUATIONS ACCORDING TO OBSERVATION DATA 2004-2020

Fluctuations of the residual level of the White Sea in the synoptic range of time scales, including surge fluctuations, are considered on the basis of observation data covering 2004-2020 period. Hourly data on the level at coastal points of Sosnovets, Severodvinsk, Solovki and Kandalaksha were analyzed. The surge run-ups and run-offs are studied based on the analysis of residual sea level (RSL) fluctuations, which is calculated by removing the tidal component from the observation data. The Dvina Bay RSL fluctuations are characterized by the greatest variance. The RSL fluctuations at Sosnovets and Solovki have approximately the same variance, which is significantly lower than in Dvina Bay. The lowest variance is observed in Kandalaksha. According to the data obtained at the Severodvinsk and Solovki stations, a noticeable increase in the variance of RSL fluctuations is observed over the considered period of time, which indicates an increase in their intensity. If five-year periods are compared, the average dispersion in Severodvinsk is 327,3 cm2 in 2004-2008, 341,4 cm2 in 2009-2013, and 386,8 cm2 in 2016-2020. This conclusion is confirmed by the calculations of the probability of positive RSL deviations, as well as by the fact that the number of surge run-ups with a height no less than 100 cm was only two during 12 years from 2004 to 2015, and there were already five such surges in the five-year period 2016-2020. Seven types of synoptic situations are described in which surge run-ups occurred in the White Sea, two of which were not previously considered. Western cyclones of various trajectories account for 73 (74,5%) out of 98 cases of surge run-ups considered in the paper. The largest surge run-ups in Severodvinsk during the period under review reached a height of 130 cm (August 22, 2018) and 153 cm (November 15, 2011). Significant surge run-offs are less frequent than surge run-ups, being, as a rule, lower in their absolute value. The surge run-off on January 31, 2005 was the most pronounced for the entire period 2004-2020. The RSL in Severodvinsk dropped by 123 cm below the monthly average, and by 112 cm in Solovki.