This file is comprised of absolute mean hourly values of the geomagnetic components D, H and Z or X, Y and Z. These values, on magnetic tape, are available from approximately 220 of the 400 worldwide observatories which have ever operated. Most of the values were hand-scaled from the analog recordings (magnetograms) and were added to the file via punched cards. From some observations, for more recent years, there are means of values recorded directly on magnetic tape from digital magnetometers at various sample rates, for example, each minute. The accuracy of these data varies but is generally good, particularly for the more recent years. Approximately 60 observation-years of these data are added to the files each year.

Geomagnetic 10 second data provides high temporal resolution of geomagnetic variations

The Geomagnetic Indices Bulletin is a one page sheet containing the magnetic indices Kp, Ap, Cp, An, As, Am and the provisional aa indices. The bulletin is published monthly.

The NOAA National Centers for Environmental Information (formerly National Geophysical Data Center) receives the K indices on a current basis from approximately 85 observatories. The K index is a quasi-logarithmic local index of the 3-hourly range in magnetic activity relative to an assumed quiet-day curve for the recording site. First introduced by J. Bartels in 1938, it consists of a single digit 0 through 9 for each 3-hourly interval. The K indices are received on a monthly basis from the various observatories and are available from 1938 to present. The NOAA National Centers for Environmental Information (formerly National Geophysical Data Center) also receives KP indices from the Institute for Geophysik in Gottingen, Germany on a monthly basis. The KP index is a planetary index based on the K index from 12 or 13 selected stations and has been derived routinely from 1932.

The geomagnetic aa index provides a long climatology of global geomagnetic activity using 2 antipodal observatories at Greenwich and Melbourne- IAGA Bulletin 37, 1975 p. 128

Report on the status of world wide geomagnetic observatories

1 minute and hourly values reported as definitive from Intermagnet observatories.

This data file is comprised of instantaneous values of the geomagnetic components D, H, and Z or X, Y, and Z at 2.5-minute intervals. These values were derived from analog recordings (magnetograms) with the aid of semi-automatic digitizing equipment from a worldwide network of about 75 observatories.

The abbreviations used for observatory names are as follows: GEOMAGNETIC OBSERVATORIES Code Station Geomagnetic Latitude ABG Alibag AMS Martin de Vivie. These data present the principal magnetic storms for the month as reported by several observatories through cooperation with the International Association of Geomagnetism and Aeronomy (IAGA). These are the data formerly published in the Journal of Geophysical Research. They are now, however, grouped by the storm rather than by station. The geomagnetic latitude of the station is indicated. The beginning time is given to the hour and minute in UT. The tupe of sudden commencement, if any, together with its magnitude in each element D, H or Z is next in the format: sc = sudden commencement; sc* = small initial impulse followed by main impulse (in this case the amplitude is that of the main pulse only, neglecting the initial brief pulse); dots in these columns represent a stomr with gradual commencement; blanks indicate no data entries. Signs of amplitudes of D and Z are taken albegraically; D reckoned positive if toward the east and Z reckoned positive if vertically downward. In the next columns the day and the three-hour periods on that day when the K index reached its maximum are given followed by the K index value. In the next three columns the maximum ranges in D, H and Z during the storm are given. The ending time is given only to the nearest hour. This is the time of cessation of reasonably marked disturbance movements in the trace. More specifically, it is the time when the K index measure has diminished to 2 or less for a reasonable period. For each date the data are listed in north-to-south geomagnetic latitude order.

Storm Sudden Commencements (ssc) 1868 to present: STORM1 and STORM2 Lists: (Some text here is taken from the International Association of Geomagnetism and Aeronomy (IAGA) Bulletin 39) 1868-1967 data (STORM1.SSC) are from IAGA Bulletin 33. These data are based on 3 observatories. Only one of them was at low latitude; the other two, with an invariant magnetic latitude of 50 degrees, were strongly sensitive to the auroral effect. 1968-1975 data (STORM2.SSC) are from IAGA Bulletin 39. These data are much more reliable. The monthly reports from all observatories guarantee that very few events are omitted. With the examination of five low-latitude records, the changes of rhythm could be evaluated much better, and events were kept of rejected on a more rational basis. However, it is probable that, for statistical use, both lists will be relatively homogeneous. Indeed, Alibag was the low-latitude observatory of the 100-year list and belongs, in the 1968-1975 list, to the group form which the amplitudes are close to the average of five observatories. 1976-1982 data are from IAGA Bulletin 32 series. These data are reduced in the same manner as the 1968-1975 data. 1983-present data are from the monthly ISGI Bulletins (DeBilt, Netherlands - 1983-1987 data; Institut de Physique du Globe, Paris, France - 1988-present data.