Abstract:
In this paper is analyzed the reaction of the ionosphere over Bulgaria during the G3 (Strong) geomagnetic storm on 3-4 November 2021 on the basis of data from constantly acting monitoring of the state of the ionosphere at the National Institute of Geophysics, Geodesy and Geography – Bulgarian Academy of Sciences. The global geomagnetic indices (Kp and Dst), which characterize the time development of the storm and the data for the solar wind, are presented. The model values (MAK model, working on the NIGGG website) of the global index of geomagnetic activity, which is calculated in real time from solar wind data show good agreement with definitive values of this index from global data centers. The values of Total Electron Content (TEC) and the forecast values of the critical frequencies of the ionosphere (foF2 and MUF3000) for Bulgaria during the storm are presented. Due to the lack of data from the ionospheric station Sofia, the values foF2 and MUF3000 are calculated on the basis of TEC and are used to prepare daily forecasts for the propagation of radio waves on the territory of our country. A very good coincidence between the model values and the measured ones was reported. As a result, the reaction of the ionosphere was monitored, which in the considered interval 3-5 November and in the conditions of a geomagnetic storm is positive. An explanation of the observed behaviour of the critical frequencies of the ionosphere is also purposed. All parameters discussed in this work are subject to monitoring activities under the Project “National Geoinformation Center” (NGIC) financed by the National Roadmap for Scientific Infrastructure 2017-2023.