Observations of midlatitude ionospheric instabilities generating meter-scale waves at the magnetic equator

Abstract

We present data from a spectacular low-latitude ionospheric event obtained using two ionospheric imaging systems located on the Haleakala Volcano on Maui, Hawaii (geographic: 20.7°N, 203.8°E; geomagnetic: 21.0°N, 271.9°E), and a 50-MHz coherent scatter radar located on Christmas Island (geographic: 2.0°N, 202.6°E; geomagnetic: 3.1°N, 273.6°E). During the event, structure is seen to develop in the imaging data, extending out of the northern edge of the imaging systems' fields of view. Using data from dual-frequency Global Positioning System receivers located throughout Hawaii, the structures are seen to evolve against an enhanced background of total electron content caused by an ongoing geomagnetic storm suggesting that the pertinent features in the event are electron density enhancements, rather than depletions that typify structure in the postsunset data from these instruments. Early in the evening, 3-m backscatter, as measured by the radar on Christmas Island, occurs at the magnetic equator on magnetic field lines that are connected to the edges on both sides of this enhanced structure seen in the images. We discuss how multiple irregularity processes must be responsible for this unusual facet of the radar data, as individual processes can only explain the development of irregularities on electron density gradients in one direction. We conclude that one of the processes responsible for the irregularities must occur in the local, off-equator ionosphere. The larger-scale electric fields associated with these irregularities map to the magnetic equator where they generate the instabilities observed by the radar. Copyright 2009 by the American Geophysical Union.