Secular Variation of Geomagnetic Field at Karachi Observatory

In this work, the secular variation of noon/midnight geomagnetic observed field has been investigated at Karachi observatory using the data of total geomagnetic field (I) for the period of 1983-2007. It can be predicted that the field for Karachi observatory has oscillating behavior, however the period of oscillation cannot be estimated. Moreover, the correlation of different solar parameters, i.e. solar flux f10.7cm and sunspot number (SSN) and Earth's indices have been calculated for different time periods. The solar activity and geomagnetic indices show negligible correlation which represents there is no such contribution in secular variation of total geomagnetic field observed in magnetic quite days. The comparison has made between the geomagnetic field and the International Geomagnetic Reference Field (IGRF) model, and it is found that the IGRF model underestimates both noon and midnight observed field. The 5th order polynomial has fitted over the annual mean of observed field, which is quite good fit with R-2 value of 99.60% for midnight and 99.43% for noon observed field.