Solar Cycle Activity
As can be seen in the longitudinal average synoptic map of the solar magnetic flux from 1975 to May 2013 (David Hathaway) the present solar cycle 24 started late. We therefore did not expect it to be a strong cycle. However, severe solar storms (solar flares and coronal mass ejections) might still occur. Extreme solar flares occurred in 2006 near minimum and extreme solar storms occurred in May 1921 during a weak solar cycle.
Solar activity on far-side
The appearance of large active regions on the Sun’s far-side gives us a warning time of space weather effects up to seven days in advance. During the Halloween events in 2003, that kind of warnings played an important role to mitigate space weather effects on e.g. power grids.
Solar activity on behind solar eastern limb
Discovering active regions behind solar eastern limb by STEREO gives us extra days of warning time.
Solar magnetic surface activity
Measurements of the solar magnetic vector field by Solar Dynamics Observatory (SDO) makes it possible to estimate the magnetic complexity: How twisted and winded the field is. The Sun is then reducing the complexity by producing a solar storm. These measurements will further improve our warnings day to days ahead.
The electromagnetic radiation from solar flare reaches earth within 8 minutes. Energetic protons reach us within about an hour. A coronal mass ejection (CME) reaches earth within 14 hrs to days, dpending on its velocity.
The arrival time of a CME is estimated by the WSA-Enlil model. As input the MHD model uses solar surface magnetic field and coronal measurements.
Space Weather Effects during the Halloween events 2003
Solar wind/CME plasma-magnetic field measurements at L1 by ACE/NASA make 30 min ahead forecasts possible.