Night-time Geomagnetic Field Observations on the POKUpsko Repeat Station

The analysis of the night-time magnetic declination D and magnetic total intensity F observations at the POKUpsko (POKU) repeat station as well as the comparison with simultaneous Tihany (THY) observatory (Hungary) data have been presented. Generally, the geomagnetic field is less disturbed during the night-time when smaller ranges and scatters are achieved leading to a more reliable determination of the geomagnetic element values. The cross-correlation analysis of the simultaneous observations has confirmed the similarity of the geomagnetic field variation between the THY observatory and POKU repeat station. Compared to day-time surveys, the observations during the night are more demanding and special equipment and organization are needed as well. The analysis of all repeat station surveys in the period 2004-2012 on the POKU repeat station has been given and was shown that the most reliable geomagnetic element values were determined from night-time observations. Performing the first night-time geomagnetic field surveys in the Republic of Croatia, the valuable experience has been achieved and measuring instruments and equipment have been tested.