On the validation of K index values at Italian geomagnetic observatories

Abstract. Local K index and the consequent global Kp index are well established three-hour range indices used to characterize the geomagnetic activity. K index is one of the parameters which INTERMAGNET observatories can provide and it’s widely used since several decades, although many other activity indices have been proposed in the meanwhile. The method for determining the K values should be the same for all observatories; so INTERMAGNET consortium recommends a software code, KASM designed for an automatic calculation of K index according to the Adaptive Smoothed method. K values should be independent on the local dynamic response, therefore for their determination each observatory has its own specific scale regulated by the K9 lower limit, which represents the main input parameter for KASM. The determination of an appropriate K9 value for any geomagnetic observatory is then fundamental. In this work we statistically analyze the K values estimated by means of KASM code for the Italian geomagnetic observatories of Duronia (corrected geomagnetic latitude λ ~ 36° N) and Lampedusa (λ ~ 28° N) comparing them with the German observatories of Wingst and Niemegk. Our comparative analysis is finalized to establish the best estimation of the K9 lower limit for these two stations. A comparison of K9 lower limits found for the Italian observatories with results from a previous empirical method was also applied and used to verify the consistency and reliability of our outcomes.