HR: 16:15h
AN: SA24A-02    [Abstracts]
TI: Long-term Temperature Trends in the Thermosphere Based on Incoherent Scatter Radar Data
AU: * Holt, J M
EM: jmh@haystack.mit.edu
AF: MIT Haystack Observatory, Off Route 40, Westford, MA 01886, United States
AU: Zhang, S
EM: shunrong@haystack.mit.edu
AF: MIT Haystack Observatory, Off Route 40, Westford, MA 01886, United States
AU: Kurdzo, J M
EM: jmkurdzo@marauder.millersville.edu
AF: Millersville University, PO Box 1002 1 South George St, Millersville, PA 17551, United States
AB: We have developed a series of empirical models of Earth's ionosphere and thermosphere based on data from most of the world's incoherent scatter radars (ISRs). These models depend on solar and geomagnetic activity, but until recently have not included any long-term trend independent of those due to differences in geophysical indices from solar cycle to solar cycle. Greenhouse gases such as CO2 and CH4 are well known to be increasing in the lower atmosphere. The effect of this on the upper atmosphere, in particular, the ionosphere, has become an active topic of research since the publication of a theoretical modeling study by Roble and Dickinson suggesting a major greenhouse cooling in the thermosphere in response to increases in CO2 and CH4 concentration at 60 km. This cooling effect leads to a global reduction in neutral densities including O, N2 and total neutral mass density as the neutral temperature Tn decreases. We have addressed this using almost three solar cycles of Millstone Hill measurements of the ion temperature Ti, which is closely coupled to Tn. There is a statistically highly-significant long-term Ti trend ranging from -4 K/year to -8 K/year depending on time-of-day and altitude. Using the ion energy equation we find a similar trend for Tn.
DE: 2443 Midlatitude ionosphere
DE: 3305 Climate change and variability (1616, 1635, 3309, 4215, 4513)
SC: SPA-Aeronomy [SA]
MN: 2007 Fall Meeting