Increasing Power of Central Coronal Hole as a Precursor of Geo-Storm

Abstract:

The coronal holes (CH) are observed in the EUV and soft X-ray wavelengths on the solar disc as the more cold and less bright regions as compared to the background brightness. The magnetic field lines of CH stay open and generate high speed solar wind (HSS). When a coronal hole is positioned near the center of the Earth-facing solar disk, the plasma flows towards Earth at a higher speed than the regular solar wind and cause geomagnetic and ionospheric disturbances on Earth with enhanced auroral activity. We present here the results of analysis of the CH Power index, Pch, for a period from 2011 to 2018, built up with SOHO EIT 284 Å observations by Luo B. et al. [1]. The Pch index is daily evaluated from the SDO/AIA images (Fe XII 193Å) by the Space Environment Prediction Centre, Beijing, China, for forecasting the solar wind velocity three days in advance (Vsw) from the intensity of brightness of the CH near the center of solar disc at [10°E,10°W], [30°N, 30°S]. It is found that the long-term variation of the Pch index shows a trend of growing Pch towards the minimum of solar cycle while most of other identities of solar activity tend to diminish [2]. In a short-term scale, an instant increase of Pch index is suggested to serve as a precursor of geo-storm which is testified by delayed response of the solar wind, interplanetary magnetic field, magnetosphere and ionosphere storm events for the 24^th solar cycle.

References.

[1] Luo B., Zhong Q., Liu S., Gong J. (2008) A new forecasting index for solar wind velocity based on EIT 284 Å observations. Solar Phys., 250, 159-170, https://doi.org/10.1007/s11207-008-9198-4.

[2] Gulyaeva, T.L., Gulyaev, R.A. (2018) Coherent changes of solar and ionospheric activity during long-lived coronal mega-hole from Carrington rotation CR2165 to CR2188. J. Atmos. Solar-Terr. Phys., 179, 165-173, https://doi.org/10.1016/j.jastp.2018.07.007.