This ftp site provides 1Hz vector variometer measurements from Greenland stations. The file format is cdf. An example matlab routine to read cdf is provided in this directory of the ftp site. The file is called read_cdf.m The cdf file contains 2 arrays: (1) time [cdf_epoch] (2) HEZ [nT] HEZ(*,1) variation along the local magnetic north component, positive north HEZ(*,2) variations along the local magnetic east component, positive east HEZ(*,3) variations along the vertical component, positive downward (geodetic) The local magnetic coordinate system is oriented along local magnetic north and east at the time of the instrument setup. The local magnetic field varies with time (secular variation), where as our HEZ system is adjusted to this variation every few years. Log-files: Comments on data quality and time stamp accuracy are provided in yearly log-files (pdf-file in each yearly directory for each station). In some cases, but not always, the reason for missing data (flagged as NaN) is described in the log files. (E.g.: 'Gap on 05' means that there was a gap on the 5th of the respective month.) If data quality issues were encountered, but the affected data was not set to NaN, then this is mentioned in the log-files. (E.g.: Periods with 2nT noise in horizontal components on 05 to 18, not flagged (not set to NaN).) Flagging of data (setting to NaN): We retain all original data. Data with obvious problems (spikes, artificial disturbances) are flagged and will show up as NaN in the cdf-files on this ftp-site. If necessary, the missing data might be retrieved in our original files on request. Spikes, artificial disturbance, jumps: Spikes and artificial disturbances are set to NaN whenever possible. Remaining spikes or artificial disturbances are usually described in the log-files with a comment that they were not set to NaN. Jumps in the data (that would lead to a jump in the quiet level are not corrected for in the variometer data), but are described in the log-files whenever detected. Quiet levels (long-term instrument trends and secular variations) are not subtracted. Time stamp accuracy: From May 2010 timing accuracy is usually +-2 seconds. The time stamp is controlled by a ntp-server. When a station gets offline (loosing contact to the ntp-server), this usually is detected within a day. On a weekly basis, the dataloggers are remotely accessed to check the time stamp and to check if the ntp-server is updating the time. Deviations are documented, for detailed information consult the log-files. To ensure that you use the latest versions of the data and log-files, we recommend checking the time stamp of the cdf files and the date of the log-files. DTU magnetic stations website: www.space.dtu.dk/MagneticGroundStations