Annual Change in the Declination (‘Variation’) in Western Scandinavia and the North Sea

Abstract

THE annual change (secular variation) for about 10 years (1941–52) in the declination was remarkably constant, namely + 8′ (E.), for Norway, Denmark, Sweden and also for the North Sea (Lerwick, Shetland). However, starting in 1952, there has been a gradual decrease in the annual change, and for the period 1952–60 it was about + 5′ (dropping from 8′ to 4′). Fig. 1 gives the secular change for three magnetic observatories, Lerwick (Shetland), Rude Skov (Denmark) and Tromsø (Norway). For Rude Skov it may be seen that there is a gradual decrease, disregarding scatter, from 11′ to 4′ during the period 1927–60, apart from the temporary stagnation mentioned here. The same tendency may be shown for other north European observatories. The rough sketch in Fig. 2 shows the secular variation in declination for 1957/58 for eight north European observatories. Comparing Fig. 2 with Fig. 3, which gives the isopors (lines of equal annual secular variation) for epoke 1942.5¹, it can be seen that the pattern of isopors is still moving westward.