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Directions of the Straight Currents in the Central Part of the Polar Cap [ I ]
An attempt is made to examine the directions of straight currents at Thule in the central part of the polar cap using the hourly values of 5 disturbed days and 20 geomagnetic storms which occurred during IGY. The important results obtained in the present analysis are summarized as follows:
(1) The current was directed mainly towards 7h-12h meridians in local geomagnetic time but sometimes towards night time meridians.
(2) During IGY the mean direction was 9.1h meridian.
(3) The seasonal shift of the directions of straight currents showed the direction of 11h in summer solstice and that of 7h in winter solstice. The shift correlated negatively with the seasonal change of the intensity of horizontal vectors at Thule.
(4) The daily variation of the directions of straight currents had an amplitude of about 土lh, showing the earliest at midnight and the latest at noon.
(5) There are two typical pattern in relation with developing and recovering stage of Dst.One is the counterclockwise rotation of the direction from morning meridian towards afternoon meridian，and the other is the clockwise rotation from forenoon towards midnight.
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