Measurements of atmospheric temperatures show a variety of long-term oscillations. These can be simulated by computer models and exhibit multi-annual, decadal, and even centennial periods. They extend from the ground up to the lower thermosphere. Recent analyses have shown that they exist in the models even if the model boundaries are kept constant with respect to influences of the sun, ocean, and greenhouse gases. Therefore, these parameters appear not to be responsible for the excitation of these oscillations, i.e. the oscillations might be rather self-excited. However, influences of land surface and vegetation changes had not been entirely excluded. This is studied in the present analysis. It turns out that such influences might be active in the lowermost atmospheric levels.Long-term trends of atmospheric parameters such as the temperature are important for the understanding of the ongoing climate change. Their study is mostly based on data sets that are 1 to a few decades long. The trend values are generally small and so are the amplitudes of the long-period oscillations. It can therefore be difficult to disentangle these structures, especially if the interval of trend analysis is comparable to the period of the oscillations. If the oscillations are self-excited, there may be a non-anthropogenic contribution to the climate change which is difficult to determine. Long-term changes of the cold-point tropopause are analysed here as an example.

Multi-annual oscillations have been observed in measured atmospheric data. These oscillations are also present in general circulation models. This is the case even if the model boundary conditions with respect to solar cycle, sea surface temperature, and trace gas variability are kept constant. The present analysis contains temperature oscillations with periods from below 5 up to more than 200 years in an altitude range from the Earth's surface to the lower thermosphere (110 km). The periods are quite robust as they are found to be the same in different model calculations and in atmospheric measurements. The oscillations show vertical profiles with special structures of amplitudes and phases. They form layers of high or low amplitudes that are a few dozen kilometres wide. Within the layers the data are correlated. Adjacent layers are anticorrelated. A vertical displacement mechanism is indicated with displacement heights of a few 100 m. Vertical profiles of amplitudes and phases of the various oscillation periods as well as their displacement heights are surprisingly similar. The oscillations are related to the thermal and dynamical structure of the middle atmosphere. These results are from latitudes and longitudes in central Europe.

Abstract. Self-generated (self-sustained) oscillations have been observed in measured atmospheric data at multi-annual periods. These oscillations are also present in General Circulation Models even if their boundary conditions with respect to solar cycle, sea surface temperature, and trace gas variability are kept constant. The present analysis contains temperature oscillations with periods from below 5 yr up to 341 yr in an altitude range from the Earth’s surface to the lower thermosphere (110 km). The periods are quite robust as they are found to be the same in different model calculations and in atmospheric measurements. The oscillations show vertical profiles with special structures of amplitudes and phases. They form layers of high/low amplitudes that are a few dozen km wide. Within the layers the data are correlated. Adjacent layers are anticorrelated. A vertical displacement mechanism is indicated with displacement heights of a few 100 metres. Vertical profiles of amplitudes and phases of the various oscillation periods as well as their displacement heights are surprisingly similar. The oscillations are related to the thermal and dynamical structure of the middle atmosphere. These results are from latitudes/longitudes in Central Europe.

Nitrogen dioxide and trioxide have been observed from balloons, plane and from the ground during MAP/GLOBUS 1983. Comparison between NO2 mixing ratios measured from balloons shows some agreement between remote sensing techniques on the one hand and in situ methods on the other. The two sets of data which agree in the lower stratosphere at 20 km diverge at higher altitudes by a factor of 2 around 27 km and 4 around 33 km. The NO2 column densities observed at sunset from the ground are in agreement with plane and balloon determinations, provided that the average mixing ratio below 16 km was indeed lower than 1.5 × 10−10. The diurnal variation of the NO2 column as determined from ground observations during the second half of September differs from the one seen in the stratosphere. A first comparison between NO3 night-time remote measurement and preliminary in situ results show a disagreement by a factor of 2.

We present the analysis of annual average OH* temperatures in the mesopause region derived from measurements of the Ground-based Infrared P-branch Spectrometer (GRIPS) at Wuppertal (51° N, 7° E) in the time interval 1988 to 2015. The new study uses a temperature time series which is 7 years longer than that used for the latest analysis regarding the long-term dynamics. This additional observation time leads to a change in characterisation of the observed long-term dynamics. We perform a multiple linear regression using the solar radio flux F10.7 cm (11-year cycle of solar activity) and time to describe the temperature evolution. The analysis leads to a linear trend of (−0.089 ± 0.055) K year−1 and a sensitivity to the solar activity of (4.2 ± 0.9) K (100 SFU)−1 (r2 of fit 0.6). However, one linear trend in combination with the 11-year solar cycle is not sufficient to explain all observed long-term dynamics. In fact, we find a clear trend break in the temperature time series in the middle of 2008. Before this break point there is an explicit negative linear trend of (−0.24 ± 0.07) K year−1, and after 2008 the linear trend turns positive with a value of (0.64 ± 0.33) K year−1. This apparent trend break can also be described using a long periodic oscillation. One possibility is to use the 22-year solar cycle that describes the reversal of the solar magnetic field (Hale cycle). A multiple linear regression using the solar radio flux and the solar polar magnetic field as parameters leads to the regression coefficients Csolar = (5.0 ± 0.7) K (100 SFU)−1 and Chale = (1.8 ± 0.5) K (100 µT)−1 (r2 = 0.71). The second way of describing the OH* temperature time series is to use the solar radio flux and an oscillation. A least-square fit leads to a sensitivity to the solar activity of (4.1 ± 0.8) K (100 SFU)−1, a period P = (24.8 ± 3.3) years, and an amplitude Csin = (1.95 ± 0.44) K of the oscillation (r2 = 0.78). The most important finding here is that using this description an additional linear trend is no longer needed. Moreover, with the knowledge of this 25-year oscillation the linear trends derived in this and in a former study of the Wuppertal data series can be reproduced by just fitting a line to the corresponding part (time interval) of the oscillation. This actually means that, depending on the analysed time interval, completely different linear trends with respect to magnitude and sign can be observed. This fact is of essential importance for any comparison between different observations and model simulations.

The paper seeks to explore an alternative explanation for the change in slope of the OH temperature time series previously reported in earlier publications using a shorter time series. While the results are promising, I believe there is an overall shortcoming in the analysis technique. While this may not substantially change the overall results, it does put into question their statistical significance. When fitting data using an orthogonal basis set, one can fit the functions simultaneously or sequentially, where the first function is subtracted from the data and the next fit to the residuals. However, in this paper there is a combination orthogonal functions (sinusoids in the case of the periodogram) and non-orthogonal functions (solar cycles and trends) fitted to the data sequentially. For example in Section 4.1, the solar 10.7 cm flux and a trend first are correctly fitted simultaneously as they are non-orthogonal. However, on page 7, lines 1-13, a periodogram, which fits a set of orthogonal sinu-C1

SABER temperature measurements from 2002 to 2012 are analyzed from 18 to 110 km altitude in Middle Europe. Data are complemented by radiosonde measurements in the altitude range from 0 to 30 km. Low frequency oscillations with periods of about 2.4-2.2 yr, 3.4 yr, and 5.5 yr are seen in either data set. Surprising vertical structures in amplitudes and phases are observed with alternating minima and maxima of amplitudes, steep phase changes (1800) at the altitudes of the minima, and constant phase values in between. HAMMONIA CCM simulations driven by boundary conditions for the years 1996-2006 are analyzed for corresponding features, and very similar structures are found. Data from another CCM, the CESM-WACCM model, are also analyzed and show comparable results.Similar oscillation periods have been reported in the literature for the ocean. A possible forcing of the atmospheric oscillations from below was therefore tested with a special HAMMONIA run. Here, climatological boundary conditions were used, i.e. the boundaries in all eleven years were the same. Surprisingly also in this data set the same atmospheric oscillations are obtained. We therefore conclude that the oscillations are intrinsically forced, self-sustained in the atmosphere. The oscillations turned out to be quite robust as they are still found in a HAMMONIA run with strongly reduced vertical resolution. Here only the form of the vertical amplitude and phase profile of the 2.2 yr feature is lost but the oscillation itself is still there, and the two other oscillations are essentially unchanged.Similar oscillations are seen in the earth surface temperatures. Global Land Ocean Temperature Index data (GLOTI) reaching back to 1880 show such oscillations during all that time. The oscillations are also seen in parameters other than atmospheric temperature. They are found in surface data such as the North Atlantic Oscillation Index (NAO) and in zonal winds in the troposphere and lower stratosphere. The oscillations found are tentatively discussed in terms (of synchronization) of self-sustained non-linear oscillators, as many of their properties resemble such oscillators described in the literature. (C) 2015 Elsevier Ltd. All rights reserved.

Measured data of wind and temperature changes (waves) in the middle atmosphere are obtained from several ground stations in Middle Europe (wind radar, OH temperature, intensity) and from the CRISTA, SABER, and MLS satellite instruments. Emphasis of the data interpretation is on the dynamics of the mesosphere with long-term changes and solar cycle influences. A comparative analysis of global wave activity shows that gravity waves play a leading role in most part of the year, at latitudes 20°N–70°N and altitudes 70–100 km. Traveling planetary waves are in second place. Very short period oscillations are studied down to 3 min period, i.e. to well below the Brunt-Väisälä period (5 min). They are interpreted in terms of gravity wave activity and dissipation. This applies as well to pronounced seasonal variations (with maxima near equinox) as to long-term trends. Similar seasonal variations are also found in turbulent eddy coefficients K zz of a General Circulation Model (WACCM 3.5) and in the turbopause altitude. Short period gravity wave activity/dissipation is compared to changes of the zonal wind speed. A long-term increase of the wind (0.5 m/s/year) and of gravity wave intensity (1.5 %/year in 16 years at 87 km altitude) is found. This is related to an increase of the summer duration that is observed since 1988 at a rate of 1.2 days/year at 87 km. Corresponding changes are found in the middle stratosphere. A long-term change is also seen in very short period planetary waves, i.e. the Quasi-Two Day Waves. These waves have been analyzed since 1988 (at 87 km altitude) and exhibit threefold maxima in summer. They show a considerable long-term change of the stability structure of the mesosphere. These different dynamical results suggest an important long-term change in the general circulation.

The long-term development of short-period gravity waves is investigated using the analysis of temperature fluctuations in the mesosphere. The temperature fluctuations are quantified by their standard deviations sigma based on data from OH measurements at Wuppertal (51 degrees N, 7 degrees E) and Hohenpeissenberg (48 degrees N, 11 degrees E) obtained from 1994 to 2009 at 87 km altitude. The temperatures are Fourier analyzed in the spectral regime of periods between 3 and 10 min. The resulting oscillation amplitudes correlate very well with the standard deviations. Shortest periods are taken as "ripples" that are indicative of atmospheric instabilities/breaking gravity waves. In consequence the standard deviations are used as proxies for gravity wave activity and dissipation. This data set is analyzed for seasonal, intradecadal, and interdecadal (trend) variations. Seasonal changes show a double peak structure with maxima occurring slightly before circulation turnaround in spring and autumn. This is found to be in close agreement with seasonal variations of turbulent eddy coefficients obtained from WACCM 3.5. The intradecadal variations show close correlations with the zonal wind and the annual amplitude of the mesopause temperature. The long-term trend (16 years) indicates an increase of gravity wave activity of 1.5% per year. Correspondences with dynamical parameters such as zonal wind speed and summer length are discussed.

Upper mesosphere OH temperature measurements are compared at the stations of Wuppertal (51 degrees N, 7 degrees E) and Hohenpeissenberg (48 degrees N, 11 degrees E) for 2004-2009 in order to form a combined data set which considerably improves the measurement statistics. This allows time analyses near the Nyquist frequency (2 days) which is used for a study of the quasi 2 day wave (QTDW) in summer. The well-known maximum near solstice is observed. In addition, there are two unexpected side maxima about 45-60 days before and after the center peak. A similar triplet is seen in the QTDW analysis of Microwave Limb Sounder temperature data. The triple structure is also found in a very similar form 15 years earlier in the interval 1988-1993 in early Wuppertal data. In these 15 years the time distance between the first and last triple peak has increased by about 22 days. Amplitudes of the QTDW correspond to the meridional gradient of the quasi-geostrophic potential vorticity (from MLS data) and baroclinic instabilities (bc) from radar winds (at Juliusruh, 55 degrees N, 13 degrees E). Parameter bc also shows a triple structure, when mean values 2003-2008 are calculated. The QTDW triplet results from the combination of atmospheric (in) stability and critical wind speed. The widening of the QTDW triple structure suggests a long-term change of mesospheric stability and wind structure. This is found, indeed, in the bc and zonal wind data. The changes likely reflect a long-term circulation change in the middle atmosphere extending up to the mesopause.

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 degrees N, 7 degrees 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 degrees N, 11 degrees 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.

(1) German Aerospace Center (DLR), German Remote Sensing Data Center (DFD), Wessling, Germany (kathrin.hoeppner@dlr.de), (2) Institute of Cosmophysical Research and Aeronomy, Yakutsk, Russia, (3) Australian Antarctic Division, Tasmania, Australia, (4) University of Wuppertal, Wuppertal, Germany, (5) Instituto de Astrofísica de Andalucía (CSIC), Granada, Spain, (6) Instituto de Astronomia y Fisica del Espacio (IAFE), Buenos Aires, Argentina, (7) Institute of Atmospheric Physics, Moscow, Russia, (8) German Meteorological Service, Hohenpeissenberg, Germany

Climatologies of gravity waves, quasi‐stationary planetary waves, and tides are compared in the upper stratosphere, mesosphere, and lower thermosphere. Temperature standard deviations from zonal means are used as proxies for wave activity. The sum of the waves is compared to directly measured total temperature fluctuations. The resulting difference is used as a proxy for traveling planetary waves. A preliminary climatology for these waves is proposed. A ranking of the four wave types in terms of their impact on the total wave state of the atmosphere is achieved, which is dependent on altitude and latitude. At extratropical latitudes, gravity waves mostly play a major role. Traveling planetary waves are found to play a secondary role. Quasi‐stationary planetary waves and tides yield a lesser contribution there. Vertical profiles of total temperature fluctuations show a sharp vertical gradient change (“kink” or “bend”) in the mesosphere. This is interpreted in terms of a change of wave damping, and the concept of a “wave turbopause” is suggested. The altitude of this wave turbopause is found to be mostly determined by the relative intensities of gravity waves and planetary waves. The turbopause is further analyzed, including earlier mass spectrometer data. It is found that the wave turbopause and the mass spectrometer turbopause occur rather close together. The turbopause forms a layer about 8 km thick, and the data suggest an additional 3 km mixing layer on top.