# On the Feasibility of Interhemispheric Patch Detection Using Ground-Based GNSS Measurements
## 5 Conclusions  
This contribution evaluated the applicability of ground-based GNSS measurements for the continuous detection of polar patches. In contrast to earlier analyses performed with regional TEC mapping, this study takes advantage of epoch-wise relative STEC values. The adopted indicator represents the point information on STEC enhancement and allows the efficient monitoring of structures in the polar area. Furthermore, its definition enables the common processing of data from a network of GNSS stations and provides maps of ionospheric irregularity occurrence.  
The analysis of current spatial distribution of GNSS data in the polar regions indicates the feasibility of patch monitoring with the proposed technique. As it was shown, the signatures of structures with STEC enhancement at the level of a few TECu can be easily detected. Nevertheless, the efficiency of the proposed methodology is restricted by the distribution of permanent stations and the land mass configuration. Thus, most of the samples cover one sector of the polar ionosphere, and, according to the given comparison with SWARM in situ data, may not provide the full view of ionospheric conditions. On the other hand, if both techniques sounded the same part of the ionosphere, their results were consistent. The undoubted advantage of ground-based GNSS data is better spatial coverage, which allows the tracking of patch propagation.  
The results also depict the applicability of the GNSS technique for the continuous interhemispheric comparison of analyzed structures. In the case of the St. Patrick's Day storm and its recovery phase, the patches were observed simultaneously in both hemispheres. However, they were characterized by a strong disproportion of plasma enhancement. According to the presented investigations involving mid-latitudes as well, the reason for discrepancy is the denser tongue of ionization in the southern hemisphere. In the analyzed period, the more intense structure was observed for southwardly oriented IMF Bz, which confirms the previous conclusions. For the opposite case, the structures were significantly weaker.  
Finally, it is believed that epoch-wise ionospheric information from ground-based GNSS receivers represent an interesting alternative for the other methods of patch monitoring. Our preliminary comparison with SWARM data indicated that the integration of different data sets should enable more comprehensive studies.  
Conceptualization of the manuscript idea, R.S.; Methodology and Software, R.S.; Investigations, R.S. and J.P.; Writing-Original Draft Preparation, R.S; Writing-Review & Editing, J.P.; Supervision and Funding Acquisition, J.P.  
This research was funded by the National Science Centre, Poland, grant number 2016/23/D/ST10/01546. The APC was funded by University of Warmia and Mazury in Olsztyn.  
The authors are grateful for GNSS data and products provided by IGS/EPN, ESOC and UNAVCO. We acknowledge use of NASA/GSFC's Space Physics Data Facility's OMNIWeb service and OMNI data. We also acknowledge use of Polar Cap Project data founded by ESA and realized by Department of Physics, University of Oslo.  
The authors declare no conflict of interest