Naslov
Coronal holes and solar wind high-speed streams: II. Forecasting the geomagnetic effects

Autori
Vršnak, Bojan ; Temmer, Manuela ; Veronig, Astrid

Izvornik
Solar Physics (0038-0938) 240 (2007), 2; 331-346

Vrsta, podvrsta i kategorija rada
Radovi u časopisima, članak, znanstveni

Ključne riječi
solar wind; coronal holes; space weather; geomagnetic storms

Sažetak
We present a simple method of forecasting the geomagnetic storms caused by high-speed streams (HSSs) in the solar wind. The method is based on the empirical correlation between the coronal hole area/position and the value of the Dst index, which is established in a period of low interplanetary coronal mass ejection (ICME) activity. On average, the highest geomagnetic activity, i.e., the minimum in Dst occurs four days after a low-latitude coronal hole (CH) crosses the central meridian. The amplitude of the Dst dip is correlated with the CH area, and depends on the magnetic polarity of the CH due to the Russell-McPherron effect. The Dst variation may be predicted employing the expression Dst(t) = (− 65 &plusmn ; ; ; 25 × cos )[A(t∗ )]0.5, where A(t∗ ) is the fractional CH area measured in the central meridian slice [− 10◦ , 10◦ ] of the solar disc,  is the ecliptic longitude of the Earth, &plusmn ; ; ; stands for positive/negative CH polarity, and t − t∗ = 4 days. In periods of low ICME activity, the proposed expression provides fore- casting of the amplitude of the HSS-ssociated Dst dip to an accuracy of ≈ 30%. However, the time of occurrence of the Dst minimum cannot be predicted to better than &plusmn ; ; ; 2 days, and consequently, the overall mean relative-difference between the observed and calculated daily values of Dst ranges around 50%.

Izvorni jezik
Engleski

Znanstvena područja
Fizika

POVEZANOST RADA