[A-CG31] 北極域の科学

[ACG31-P08] Upper atmosphere cooling over the past 33 years

*小川 泰信¹、元場 哲郎²、Stephan Buchert³、Ingemar Haggstrom⁴、野澤 悟徳² (1.国立極地研究所、2.名古屋大学太陽地球環境研究所、3.Swedish Institute of Space Physics、4.EISCAT Scientific Association)

Theoretical models and observations have suggested that the increasing greenhouse gas concentration in the troposphere causes the upper atmosphere to cool and contract. However, our understanding of the long-term trends in the upper atmosphere is still quite incomplete, due to a limited amount of available and well-calibrated data. The European Incoherent Scatter (EISCAT) radar has gathered data in the polar ionosphere above Tromso for over 33 years. Using this long-term data set, we have estimated the ?rst significant trends of ion temperature at altitudes between 200 and 450 km. The estimated trends indicate a cooling of 10-15 K/decade near the F region peak (220-380 km altitude), whereas above 400 km the trend is nearly zero or even warming. The height profiles of the observed trends are close to those predicted by recent atmospheric general circulation models. Our results are the ?rst quantitative confirmation of the simulations and of the qualitative expectations.