Response of the polar magnetic field intensity to the exceptionally high solar wind streams in 2003



[1] The exceptionally high solar wind stream activity in 2003 caused a record intensity in the auroral electrojet currents, leading to a major reduction of the horizontal field at auroral latitudes and to a notable strengthening of the vertical geomagnetic field in the polar cap. This strengthening is clearly visible in the observatory annual values as a significant deflection in the corresponding secular variation. A similar but weaker deflection also occurs during the strongest high speed stream years of the earlier solar cycles, e.g., in 1983 and 1994. We also found that, in addition to the disturbed times, the westward electrojet was often enhanced even during the most quiet times of the strongest high speed stream years. The quiet time level was more disturbed in 2003 than in other high speed stream years, when an exceptionally clear signal was seen in the polar cap Z intensity even in the annual mean curve in this year. We exclude other current systems like the ring current or the DPY current as possible explanations.