Hourly Means

The hourly mean data are from the three UK observatories Eskdalemuir, Lerwick and Hartland. Eskdalemuir data are available from 1911, Lerwick from 1926, Hartland from 1957 and all three are available up to yesterday's date. Values up to the end of 2003 have had final baseline corrections applied and are the definitive absolute hourly mean values. Data from 2004 onwards are all provisional and have not had final baseline corrections applied.

Values of declination (D), horizontal intensity (H) and vertical intensity (Z) are available. The units of declination are degrees. Declination is negative when west of true north. The units of horizontal intensity and vertical intensity are nT. Vertical intensity is positive in the downwards direction.

Note :

• Although the provisional data can sometimes be missing (denoted by *****) when they are first made available, these gaps are usually filled no later than one week after the end of the month and often earlier than this.
• The following jumps have been applied to the data to correct for site changes. All the jump values are given as new values minus old values and have the units of minutes of arc for declination and nT for horizontal and vertical intensity.
  Eskdalemuir
  1990.0 - Dec. 0; Horiz. 11; Vert. 22
  1994.0 - Dec. 0; Horiz. -8; Vert. -23
  Lerwick
  1934.0 - Dec. 0; Horiz. 0; Vert. 144
  1990.0 - Dec. 0; Horiz. 5; Vert. -8
  1996.0 - Dec. 0; Horiz. 0; Vert. 8
  Hartland
  1980.0 - Dec. 0; Horiz. 0; Vert. -6
  1990.0 - Dec. 0; Horiz. -6; Vert. 23