Dual-frequency GNSS data processing is currently one of the most useful techniques for\nsounding the ionosphere. Hence, this work was aimed at the evaluation of ground-based GNSS data\nfor the continuous monitoring of polar patches in both hemispheres. In this contribution, we proposed\nto use epoch-wise relative STEC values in order to detect these structures. The applied indicator is\ndefined as a difference between an undifferenced geometry-free linear combination of GNSS signals\nand the background ionospheric variations, which were assessed with an iterative algorithm of\nfour-degree polynomial fitting. The occurrence of patches during the St. Patrick geomagnetic storm\nwas performed for validation purposes. The first part of the work confirmed the applicability of the\nrelative STEC values for such investigations. On the other hand, it also revealed the limitations related\nto the inhomogeneous distribution of stations, which may affect the results in both hemispheres. This\nwas confirmed with a preliminary cross-evaluation of GNSS and in situ SWARM datasets. Apart from\nthe periods with a well-established coincidence, the opposite situation, when both methods indicated\ndifferent parts of the polar ionosphere, was also observed. The second part of this contribution\ndepicted the feasibility of continuous patch detection for both regions, and thus the interhemispheric\ncomparison of the analyzed structures. It has demonstrated the strong disproportion between patches\nin the northern and southern hemispheres. This discrepancy seems to be related to the different\namount of plasma propagating from the dusk sector, which is justified by the values of relative\nSTEC at mid-latitudes. The observed structures are also strongly dependent on the orientation of the\ninterplanetary magnetic field.
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