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Ann. Geophys., 24, 503-513, 2006
www.ann-geophys.net/24/503/2006/
© European Geosciences Union 2006
Comparative investigations of equatorial electrodynamics and low-to-mid latitude coupling of the thermosphere-ionosphere system
M. J. Colerico1, M. Mendillo2, C. G. Fesen3, and J. Meriwether4
1MIT Haystack Observatory, Westford, Massachusetts, USA
2Center for Space Physics, Boston University, Boston, Massachusetts, USA
3Department of Physics and Astronomy, Dartmouth College, Hanover, New Hampshire, USA
4Department of Physics and Astronomy, Clemson University, Clemson, South Carolina, USA
Abstract. The thermospheric midnight temperature maximum (MTM) is a highly variable,
but persistent, large scale neutral temperature enhancement which occurs at
low latitudes. Its occurrence can impact many fundamental upper atmospheric
parameters such as pressure, density, neutral winds, neutral density, and
F-region plasma. Although the MTM has been the focus of several
investigations employing various instrumentation including photometers,
satellites, and Fabry-Perot interferometers, limited knowledge exists
regarding the latitude extent of its influence on the upper atmosphere. This
is largely due to observational limitations which confined the collective
geographic range to latitudes within ±23°. This paper investigates
the MTM's latitudinal extent through all-sky imaging observations of its
6300Å airglow signature referred to by Colerico et al. (1996) as the
midnight brightness wave (MBW). The combined field of view of three
Southern Hemisphere imaging systems located at Arequipa, Peru, and Tucuman and El
Leoncito, Argentina, for the first time extends the contiguous latitudinal
range of imager observations to 8° S-39° S in the American sector.
Our results highlight the propagation of MBW events through the combined
fields of view past 39° S latitude, providing the first evidence that the
MTM's effect on the upper atmosphere extends into mid-latitudes. The
observations presented here are compared with modeled 6300Å emissions
calculated using the NCAR thermosphere-ionosphere-electrodynamic general
circulation model (TIEGCM) in conjunction with an airglow code. We report
that at this time TIEGCM is unable to simulate an MBW event due to the
model's inability to reproduce an MTM of the same magnitude and occurrence
time as those observed via FPI measurements made from Arequipa. This work
also investigates the origins of an additional low latitude airglow feature
referred to by Colerico et al. (1996) as the pre-midnight brightness wave
(PMBW) and described as an enhancement in 6300Å emission which occurs
typically between 20:00-22:00 LT and exhibits equatorward propagation. We present
the first successful simulation of a PMBW event using the TIEGCM and the
airglow code. We find that the PMBW's origin is electro-dynamical in nature,
resulting from the expected evening decay of the inter-tropical arcs.
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