Long‐term trends and solar cycle variations of mesospheric temperature and dynamics

Abstract

[1] Mesospheric and stratospheric temperatures and winds from several stations in Germany are analyzed for long-term trends in 1988-2008. Emphasis is on upper mesosphere (87 km) hydroxyl (OH) temperatures at Wuppertal (51°N, 7°E) that agree favorably with satellite-borne observations from Sounding of the Atmosphere Using Broadband Emission Radiometry and a twin OH instrument at Hohenpeißenberg (48°N, 11°E) that is operational since 2003. The two twin stations yield a combined data set with 80% time coverage suitable for high time resolution analyses. Annual mean temperatures at Wuppertal show a long-term trend of −0.23 K/yr and a solar flux sensitivity of 0.035 K/solar flux unit. Trend analysis of monthly mean temperatures yields substantial variations from one month to another, between 0 and −0.6 K/yr, hence questioning the value of seasonal mean trends. The OH temperatures have a well-known characteristic form of seasonal variation. This form changes during the 21 years of observation. The changes are compared to modifications of the summer length in the stratosphere and are interpreted as dynamics/circulation changes extending to the uppermost parts of the middle atmosphere.

Change in turbopause altitude at 52 and 70° N

“…Again the simple idea of superimposing a gradual temperature change (the same for all heights) on the temperature model used for the turbulence determination thus fails to alter the change in turbopause height significantly, for the approximate decade of observations. Although direct temperature measurements are not available for the 52 • N site, Offermann et al (2010) …”

Long-term dynamics of OH * temperatures over central Europe: trends and solar correlations

“…Thus, a continuous data series throughout the year is obtained with data gaps caused by cloudy conditions only. This results in approximately 220 nights of measurements per year (Oberheide et al, 2006;Offermann et al, 2010). The relative intensities of the three lines are used to derive rotational temperatures in the region of the OH * emission layer (see Bittner et al, 2000, and references therein).…”

“…Bittner et al, 2000;Offermann et al, 2009;Perminov et al, 2014) and on the timescale of several minutes in the case of gravity waves (e.g. Offermann et al, 2011;Perminov et al, 2014). Beside these rather short-term fluctuations the temperature in the mesopause region also exhibits long-term variations on a timescale of several years.…”

“…In the mesopause region of the Northern Hemisphere such trends range from about zero up to a cooling of 3 K decade −1 (for a review of mesopause temperature trends see Beig, 2011b). Trend breaks also seem to be possible where the linear trend switches its sign (positive or negative trend) or the magnitude of the trend significantly changes (for an example of the latter case see Offermann et al, 2010). In cases of such changes in trend (e.g.…”

Neutral atmosphere temperature trends and variability at 90 km, 70 °N, 19 °E, 2003–2014

“…Hall et al (2012) report a negative trend of −4 K ± 2 K decade −1 for temperatures derived from the meteor radar over Longyearbyen,Svalbard (78 • N,16 • E) at 90 km height over the time period 2001 to 2011, while Holmen et al (2014) find a near-zero trend for OH * airglow temperatures at ∼ 87 km height over Longyearbyen over the longer time period 1983 to 2013. Offermann et al (2010) report a trend of −2.3 K ± 0.6 K decade −1 for ∼ 87 km height using OH * airglow measurements from Wuppertal (51 • N, 7 • E). It must be noted that the peak altitude of the OH * airglow layer can vary and thus affect the comparability of OH * airglow temperature trends and meteor radar temperature trends.…”