Persistent Excitation Over Several Days of EMIC waves in Association With a High Speed Stream

Data are presented that show the persistent generation of electromagnetic ion cyclotron (EMIC) events over the course of several days. The event is associated with a Stream Interaction Region ahead of a fast stream associated with a coronal hole on 12-13 April 2010. In situ measurements from the WIND satellite showed a typical stream interface between the slow and fast winds, though with an extended period of enhanced dynamic pressure over the course of a few days. EMIC waves caused by the fast stream were detected at local magnetic noon for about five days (14-18 April 2010) by ground based induction coil magnetometers at more than 15 stations around the globe. When the spectrogram plots are aligned by local magnetic noon, the EMIC waves are clearly seen to appear at all the stations as they rotate through the noon region. The power of the waves increases and decreases in intensity over the five days, perhaps in response to pressure fluctuations in the solar wind (and, presumably, a resulting temperature anisotropy in the magnetosphere). EMIC waves shown from magnetometers around the globe aligned by local magnetic noon.