Multi-Instrument Observations of MSTIDs and Source Determination

Abstract

A multi-day (6–8 May 2013), apparently medium-scale traveling ionospheric disturbance (MSTID) event with an ∼1 hour period was recorded using both the vertical-looking and steerable Millstone Hill incoherent scatter radar (ISR) systems during quiet geomagnetic activity. The dense network of Global Positioning System (GPS) total electron content (TEC) receivers has allowed the horizontal imaging of this event across a far larger scale than is possible with the ISR(s) alone. This MSTID event was identified in the GPS-TEC dataset on the mesoscale centered at Haystack. However, GPS-TEC imaging also revealed that this event was coherent across the United States. The GPS-TEC imaging also revealed that similar events occurred globally. We conclude that this MSTID event was actually a coherent ionospheric pulsing structure (CIPS) that, when viewed locally, masqueraded as an MSTID event. The GPS-TEC images reveal that, on a global scale, the CIPS were stationary in longitude, but moved southward in the Northern Hemisphere—imaging of the southern hemisphere was not possible. The CIPS originated in high latitudes and at one instance were coherent across 23,000 km. The large-scale coherence, ubiquity, and source location of the CIPS points to an unidentified auroral zone source with sufficient energy to continually force the observed MSTID-like structures.