Dayside magnetic ULF power at high latitudes: A possible long-term proxy for the solar wind velocity?

• Main Author: Vennerstrøm, Susanne
• Format: Article in Journal/Newspaper
• Language: English
• Published: 1999
• Subjects: Greenland
• Online Access: https://orbit.dtu.dk/en/publications/6a9b2c47-68b8-47ba-b6e4-0aa385079fa7

We examine the occurrence of dayside high-latitude magnetic variations with periods between 2 and 10 min statistically using data from around 20 magnetic stations in Greenland, Scandinavia, and Canada, many of which have been in operation for a full solar cycle. We derive time series of the power spectral density (psd) in two different frequency bands: 2-4 min period and 5-10 min period. The average psd in these bands maximizes in the early morning sector between auroral and cusp latitudes. The solar cycle variation of the average psd in the two bands during the morning hours is markedly different from the solar cycle variation of regular geomagnetic activity, measured by indices such as aa and Dst. The spectral band power is generally at minimum just prior to solar maximum and has a strong maximum in the late declining phase associated with high-speed streams from coronal holes. We have compared the spectral band power with satellite observations of the solar wind velocity and find a high log-linear correlation in the range 0.7-0.8. The highest correlation is found in the 2-4 min band. Contrary to this, the correlation with Bs and upsilon Bs is very weak (similar to 0.0-0.2), except in the 5-10 min band for the auroral stations. We find the results encouraging for the use of dayside spectral band power at high-latitude stations as a tool for investigating past solar wind variations.