Cheltenham Magnetic Observatory April to June, 1937

(Latitude 38° 44′.0 N., longitude 76° 50′.5 or 5h 07m.4 W. of Gr.)April 24–28—A magnetic storm of great severity was in progress from noon of April 24 to midnight of April 28. The storm was not continuously severe during the full period but had the appearance of four storms with lulls between them. The range of declination for the whole storm was 72′; of vertical intensity 866 gammas; and the estimated range of horizontal intensity was 735 gammas. The storm began with moderate activity but at 19h GMT, April 24, it increased in violence and was very active until 02h, April 25, when it moderated. This period of the storm was characterized by a very high value of vertical intensity at 23h 45m when it reached a value about 425 gammas above normal. The ranges for the period were: D, 36′; H, 223 gammas; and Z, 485 gammas. After a time of comparative quiet the storm was again active from 15h 48m, April 25, to 7h, April 26. Between 19h and 23h, April 25, all three elements were very active with short‐period perturbations of moderate ranges in D and Z but large range in H. This part of the storm was characterized by high values and great range in H. The H‐trace went completely off the magnetogram, indicating a range of more than 400 gammas. The ranges in D and Z during this time were 36′ and 106 gammas respectively. The elements were again fairly quiet until 17h 40m, April 26, when the storm once more became violent for a period of 11 hours. This period was notable for the high values in both H and Z; the H‐trace again left the magnetogram. The ranges were: D, 48′; H, more than 400 gammas; and Z, 382 gammas. Another period of quiet occurred until 18h 40m, April 27. Then the storm again became violent and was characterized by low values of H and Z and a large range in D. The ranges were: D, 72′; H, 455 gammas; and Z, 523 gammas. The storm ended at midnight, April 28.