-- Sample SAR Arc Images
-- 75 SAR Arc Case Studies
-- New England Sites Map
-- Millstone Hill Wx/Activity Logs
| The New
England region is an ideal location for studies of coupling between the
auroral and mid-latitude ionosphere. The offset of the geomagnetic
pole from the geographic pole results in relatively high magnetic latitudes
for geographic sites near 70° W longitude. For example, at the
Millstone Hill Observatory location at 42.6° N, the corresponding geomagnetic
latitude is ~53° with L @ 3 (meaning that
its magnetic field line reaches out to ~3 Earth radii in the magnetosphere).
The incoherent scatter radar (ISR), Fabry-Perot Interferometer (FPI) and LIDAR at Millstone Hill constitute a "clustered diagnostics" upper atmospheric facitlity (UAF) operated by MIT under a cooperative agreeement with the National Science Foundation. The NSF's CEDAR Program (Coupling, Energetics and Dynamics of Atmospheric Regions) created a series of additional "class-1 facilities" to operate independently or in cooperation with UAF sites. Boston University's COTIF program (CEDAR Optical Tomographic Imaging Facility) is an example of the latter. The COTIF observing sites consist of all-sky imaging spectrographs at Farmington and Cornish (Maine) and Block Island (Rhode Island), and an all-sky camera system at Millstone Hill.
Prior to 1995, BU's CEDAR imager recorded a rich dataset of optical structure associated with sub-auroral disturbances. Table A provides references. Central to these studies was the investigation of so-called Stable Auroral Red (SAR) arcs. SAR arcs are a sub-visual form of aurora that occurs at 6300 Å, an emission line of atomic oxygen. The excitation mechanism is primarily from heat conduction from the ring current region of the inner magnetosphere. SAR arcs occur during major geomagnetic storms at locations near the plasmapause. The BU imager at Millstone Hill uncovered a class of low brightness SAR arcs that are not adequately modeled by the classic thermal excitation mechanism. The resolution of this discrepency is the major research topic being studied by the new COTIF capability.
Groundbased Atmospheric Emissions Tomography (GAET) is a new capability for aeronomy. The column integrated brightnesses from many intersecting raypaths can be deconvolved into volume emission rate profiles versus altitude and latitude. The excitation physics is strongly altitude-latitude dependent, and thus COTIF permits study of SAR arc sources in the parameter space required to understand the enigma of faint events.