Forecasting the solar wind high-speed-streams and the associated geomagnetic disturbances 
utilizing coronal hole observations

Bojan Vrınak
Hvar Observatory, Faculty of Geodesy, Zagreb, Croatia 
Manuela Temmer
Hvar Observatory, Faculty of Geodesy, Zagreb, Croatia 
Astrid Veronig
IGAM/Institute of Physics, University of Graz, Graz, Austria 

The relationship between the coronal hole (CH) area/position and physical characteristics 
of the associated corotating high-speed stream (HSS) in the solar wind at 1 AU is studied. 
For the analysis we utilize the data in the period

The relationship between the coronal hole (CH) area/position and physical characteristics of
 the associated corotating high-speed stream (HSS) in the solar wind at 1 AU is studied. 
For the analysis we utilize the data in the period DOY 25-125 of 2005, characterized by a 
very low coronal mass ejection (CME) activity. Distinct correlations between the daily averaged 
CH parameters and the solar wind characteristics are found, which allows us to forecast the solar 
wind velocity v, proton temperature T, proton density n, and magnetic field strength B, several 
days in advance in periods of low CME activity. The forecast is based on monitoring fractional areas 
A, covered by CHs in the meridional slices embracing the central meridian distance ranges 
[?40,?20], [?10, 10], and [20, 40] deg. On average, the peaks in the daily values
of n, B, T, and v. The most accurate prediction can be obtained for the solar wind velocity, 
for which the average relative difference between the calculated and the observed peak values 
amounts to |?| ? 10 %. The forecast reliability is somewhat lower in the case of T, B, and n (|?| ? 
20, 30, and 40%, respectively). The SpaceWeather implications are discussed, including the perspectives 
for advancing the real-time calculation of the Sun-Earth transit times of coronal mass ejections and 
interplanetary shocks, by including more realistic real-time estimates of the solar wind characteristics.
Finally, a simple method of forecasting the geomagnetic storms caused by high-speed streams in the 
solar wind is presented. It is shown that in periods of low ICME activity the amplitude of the daily 
(hourly) averaged Dst index can be forecasted with an accuracy usually better than 10~nT (20 nT), 
and is always within 30 % of the ``predicted" value. The time of the Dst minimum cannot be predicted 
to better than ?2 days.

Work supported by Air Force Office of Scientific Research, USAF