A. L. Morozova, R. Rebbaha, P. Ribeiro

Abstract
The datasets of daily variations is obtained from the geomagnetic field raw observations at the Coimbra Magnetic Observatory (COI, Portugal). The data set was obtained for the 01.01.2007-31.12.2017 time interval and covers almost the entire solar cycle 24.
The raw data were processed using two methods to extract daily variability. The first method uses the so-called “geomagnetically quiet days” to calculate S-type variations as daily means resulting in the data sub-set named “IQD Sq and SD”. The second method uses the principal component analysis (PCA) to extract main variability modes of the original data. The first three modes produced by PCA and explaining up to 98% of the variability of the raw data are in the data sub-set named “PCA modes”. Both methods allow to extract regular geomagnetic field variations related to daily variations (S-type variations) in the ionospheric dynamo region and some magnetospheric currents (e.g., field-aligned currents).
The COI location in middle latitudes near the mean latitude of the ionospheric Sq current vortex's focus allows studying its seasonal and decadal variability using the S-type regular variations of the geomagnetic field measured near the ground. The S-type variations for the X and Y components of the geomagnetic field obtained at the COI observatory can also be re-scaled and used to analyze geomagnetic field variations obtained at other European geomagnetic observatories at close latitudes. The S-type variations for the Z component of the geomagnetic field obtained at the COI observatory can be compared to similar variations observed at more continental regions to study the so-called “coastal effect” in the geomagnetic field variations.

Keywords
Geomagnetic field Coimbra Magnetic Observatory (COI) Regular geomagnetic field variations Solar quiet variation (Sq) Disturbed solar variation (SD) Principal component analysis

Data in Brief
Volume 37
2021 August

>> DOI