Abstract
Abstract. Measurements of reflection heights of low-frequency (LF) radio waves at oblique incidence and estimates of mesosphere/lower thermosphere (MLT) region horizontal winds applying the D1 spaced receiver method on LF field strength registrations are analyzed with respect to possible long-term trends and interdecadal variability in the time interval from ~1980 to date. While no clear signal of mesospheric height trend is registered during the last two decades, significant trends of MLT horizontal winds are found. These trends are non-linear, in particular a change of trends around 1990 is found, which is probably connected with changes in tropospheric and stratospheric conditions at that time.
Highlights
Anthropogenic increase of greenhouse gases like CO2 results in a decrease of the middle atmosphere temperature (Lastovicka et al, 2006) owing to infrared emission
Measurements of reflection heights of lowfrequency (LF) radio waves at oblique incidence and estimates of mesosphere/lower thermosphere (MLT) region horizontal winds applying the D1 spaced receiver method on LF field strength registrations are analyzed with respect to possible long-term trends and interdecadal variability in the time interval from ∼1980 to date
Temperature proxies measured over Collm indicate that a substantial change has occurred in the MLT around 1990
Summary
Anthropogenic increase of greenhouse gases like CO2 results in a decrease of the middle atmosphere temperature (Lastovicka et al, 2006) owing to infrared emission. Cooling of the stratosphere has been reviewed by Ramaswamy et al (2001), while Beig et al (2003) and Beig (2006) have summarized the current knowledge on mesospheric cooling. They showed that this cooling amounts to about 2 K/decade for the time interval from the 1960s to date. Recent analyses using results of long-term low-frequency (LF) radio wave reflection height measurements have shown that mesospheric cooling is not linear. Measurements of winds and reflection heights using low frequency (LF) radio waves are presented to contribute to the database available for mesospheric trend analysis
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