TABLE 94. AVERAGE AMPLITUDES OF THE TIDE (IN METERS) AT SOLOMBALA 

 ON THE SEVERNAYA DVINA FOR 1917 TO 1929 



Winter 



Siunmer 



Nov. 

 0/53 



Dec. 



0.51 



Jan. 



0.45 



Feb. 

 0.37 



Mar. 

 0.42 



Apr. 

 0.37 



May 

 0.31 



June 

 0.56 



July 

 0.70 



Aug. 

 0.68 



Sept. 

 0.72 



Oct. 

 0.64 



Table 94 shows the monthly average amplitudes of the tide on the Severnaya Dvina, accord- 

 ing to observations made from 1917 to 1929. From the table it may be seen that in the summer 

 the amplitudes of the tide is almost twice as large as in the winter. 



As a supplement, to the above table, the following should be noted: 



In 1942 on the Severnaya Dvina at Solombala the normal tide continued until 10 May along 

 with the maniKha* typical of this river. By that time the irregularity had already begun result- 

 ing in the level at Solombala reaching 200 cm (reckoning from the zero of 1881). 



The amplitude of tide was at winter level, and varied from 25 to 45 cm. On 11 May the 

 anomaly reached its peak (326 cm) and the river opened up at Archangel. On 14 May the level fell 

 to 200 cm and the regular tide occurred again, once more with the characteristic manikha. On 16 

 May the Severnaya Dvina was finally cleared of ice but the amplitude continued to remain at its 

 winter level. Such a situation continues, as a rule, right up to the complete clearing of ice from 

 the neck of the White Sea. Actually, the tides on the Severnaya Dvina are only the result of the 

 tidal wave passing through the neck of the White Sea from the Barents Sea. It follows that as long 

 this wave is weakened by the ice in the neck of the sea the tide amplitude in the whole of the White 

 Sea will remain small. This explains the comparatively small average amplitude of tide in May 

 when the basin and Dvinski Bay are often completely free of ice while the neck of the White Sea is 

 still not yet clear. 



It is clear that the less ice present, the less noticeable are these phenomena. A part of the 

 tidal energy is expended on moving and bending the ice and thus the tidal amplitude is correspond- 

 ingly decreased. It is obvious also that sparse brash ice, which very strongly extinguishes the 

 energy of wind waves, cannot have much effect on the energy of the very long tidal wave. 



In addition to decreasing tidal amplitude and speed of tidal currents, the ice cover also has 

 an effect on other elements of the tide. For example, according to the observations of Lyakhnit- 

 ski, in the mouth of the Severnaya Dvina in 1915 and 1916 the difference in time of the tide 

 between Solombala and Lapominskaya Gavan, which is equal to 1.5 hours in summer, increases 

 to 3.5 hours in winter. It is calculated that the times of high and low tide in the period with com- 

 plete ice coverage are approximately one hour later than the times of high and low tide in the 

 summer season. 



Table 95 shows the phase angles (according to Maksimov) of the main semidiurnal waves for 

 certain points of the Soviet Arctic. From the table it is evident that with the presence of ice, the 

 phases of the tidal waves are later in comparison with phases of the same waves in absence of ice . 



*The phenomenon of manikha consists of the following: in the course of a rising tide the 

 level stops rising or even declines for a certain time and then the increase in level continues 

 again until fall tide . 



329 



