Long-term trends and solar response of the mesopause temperatures observed by TIMED/SABER during the 2002-2019 period

The global distribution and variations of the monthly mesopause temperature are presented during 2002-2019 covering the latitudes of 83°S-83°N based on Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) observations. To investigate the long-term trend and solar response of the mesopause temperature, a three-component harmonic fit is first applied to remove the seasonal variation from the monthly temperature data series. Then a multiple linear regression model is performed to residual temperatures versus constant, time series, solar activity, and geomagnetic activity terms. In this study, the mesopause temperature shows a cooling trend through all latitudes ranging from -0.002 to -0.113 K/year with a mean of -0.069 ± 0.036 K/year. The cooling trends in the southern hemisphere are observed to be relatively stronger than those in the northern hemisphere. For high latitudes (60°– 80°), significant negative trends can be detected during the non-summer time, while no significant trends are found for summertime. The mesopause temperature shows apparent positive responses to solar activity through all latitudes ranging from 2.74 to 4.76 K/100sfu with a mean of 3.94 ± 0.59 K/100sfu, which are more significant and stable in the northern hemisphere. There is a pronounced drop in solar response near the equator, which could be caused by tidal forcing at low latitudes. It is noteworthy that the length of the time interval for analysis is the main factor influencing the quality of the results. Our results, using an eighteen years interval, are expected to be a robust reference for the mesopause temperature variations.