Evidence of solar cycle effect in the mesopause region: observed temperatures in 1999 and 2000 at 98.5 km over Fort Collins, Co (41°N, 105°W)

摘要

Based on 417 nights of observation of temperatures in the mesopause region over Fort Collins, CO (41°N, 105°W) from Spring of 1999 to March of 1999, climatological temperatures between 83 and 105km were recently published. In the same article, a ～ 5K cooler temperature climatology with the effect of the observed episodic warming (peaked near 1993 attributable to Mt. Pinatubo's eruption) removed was also published. It was further established that in both the cases, the maximum and minimum annual temperature variations in the mesopause region occur near 85.5 and 98.5 km, respectively, over Fort Collins, CO. With only minimal annual and semi-annual variations, the time series of temperatures at 98.5 km may serve as a qualitative proxy for the long-term temperature change in the region, relatively free from model bias. This paper reports the nightly mean temperatures at 98.5 km between April 1999 and December 2000, during which the flux of Solar Cycle 23 approached its maximum. When these temperatures are compared to the 8-yr climatology with episodic warming removed, one finds that the mean temperatures for 1999 and 2000 are higher than the climatology mean by 3.6 and 16.8K, respectively. We suggest that the observation of these higher mean temperatures as the solar max approaches is a signature of the solar cycle's effect on the temperatures in a midlatitude mesopause region.