The seasonal-mean profiles of ozone content and temperature in the stratosphere and lower layers of the mesosphere above Moscow for autumn, winter, and spring seasons of the decades of 1996–2006 and 2007–2017 were calculated and analyzed, as well as their standard deviations (variations) and seasonal-mean correlations and covariance coefficients. The main inter-decadal changes in the statistical parameters were found in the winter season, where in the decade of 2007–2017, there was a significant decrease in ozone variations and (above 33 km) temperature, which correlates to the strong decrease in solar activity in this decade. In this season, the greatest positive and negative values of the ozone-temperature correlation and covariance were observed. In the decade of 2007 to 2017 there was a noticeable increase in their extremes, and a shift in the height of the transition from the positive to negative region, from 33 km to 37 km.

Results of the statistical analysis of the altitude profiles of the volume ozone mixing ratio retrieved from data of 1996-2017 ground-based radiometer measurements at frequency of 142.2 GHz are presented. From comparison of the data for the 1996-2006 and 2007-2017 decades, statistically significant trends have been revealed in monthly mean ozone profiles and their variations – as well as in corresponding inter-altitude and time covariance and correlation functions. Possible explanations of the revealed trends are given.

Trends in the ozone layer remain among the major problems of the atmosphere physics; thus, results of measurements of the ozone altitude distribution (profile), carried out in the same place and via the same method, are very important. This paper presents the results of the statistical analysis of ensembles of ozone profiles obtained from ground-based microwave radiometry data acquired at the P.N. Lebedev Physical Institute over a period of two decades (1996–2017). The data collected show the significant difference between monthly mean statistical parameters of ozone profiles of the decades 1996–2006 and 2007–2017. The main and unexpected result is the drastic decrease in monthly root-mean-square (rms) variances of ozone profiles over Moscow above 30 km in cold months of the decade 2007–2017 (if compared to the variances in the decade 1996–2006) with the maximum fall by 46% at 39 km in February monthly mean variances. The decade change of variances obtained by averaging over all nine months in the analysis (from September to May) has the same decrease with maximum fall by 25% at 38 km. Additionally, significant decade changes were revealed in other monthly mean statistical parameters: probability density of ozone profile variances, inter-altitude covariance and correlation functions, and time covariance and correlation—as well as their frequency spectra. The decade change of the ozone profile obtained by averaging over the nine months appeared much less significant: the decrease by 5.7% at the altitude of 19 km (with 1.5% sampling error), minor decrease by 2.6% (with sampling error 1.5%) in the profile maximum at 37 km, and increases of 1.7% at 28 km and 2.5% at 47 km (with sampling errors 1.7%)—lower and higher of this maximum. In addition to that, the corresponding averaged mean total column (integral) ozone content above 20 km remained practically unchanged: 4.61 g/m2 for decade 1996–2006 as compared to 4.58 g/m2 for 2007–2017. Possible explanations of revealed offsets are proposed and discussed.

Data of night-time ground-based measurements of the atmospheric ozone spectral line 142.175 GHz over Moscow were used for detection of variations in the ozone mixing ratio (OMR) at altitudes of the secondary (near 90 km) and tertiary (near 65 km) night maxima in the OMR profile. The ozone spectra were recorded by low-noise microwave spectrometer MOS-4 with frequency resolution of 0.1 MHz and time resolution of 110 or 90 s, not quite evenly spaced in time. The spectra were averaged over groups of 6 ... 60 ones. The OMR values at altitudes of 90 and 65 km were determined by the improved least-squares method applied to differences of brightness temperatures within +/- 0.5 MHz frequency offsets from the ozone line centre. Then special algorithm based on the Lomb periodograms with sliding data window was used to determine spectral power and frequencies of the ozone variations. Estimates of the OMR errors depending on the instrumental noise and number of averaged spectra were obtained by computer simulations and used to calculate detection thresholds of the Lomb algorithm. Wave-type variations in the OMR values with periods of 3 ... 5 h were detected with probability of 85-90% at altitude of 90 km and 95-97% at 65 km. Spans of the variations were up to 9 ppm at 90 km and up to 2 ppm at 65 km. The paper presents descriptions of the instrumentation, observation procedure, data processing methods, and some results of the data analysis.

Description and performance of transportable microwave spectrometer MOS-4 for ground-based measurements of the atmospheric ozone at frequency of 142.2 GHz are given and improvements of the instrument are considered. Examples of the stratospheric and mesospheric ozone measurements with MOS-4 in Moscow are presented as well.

The results of ground-based microwave measurements of the stratospheric ozone profiles over Moscow during the cold half-years of 2014–2015 and 2015–2016 are presented. The causes of the observed changes in the ozone in the upper stratosphere are considered. Increased planetary wave activity, strong temperature decreases in the beginning of winter, and decreased temperatures from January to March were detected during the winter of 2014–2015. The polar vortex was long-lived but not deep; the cold air of the vortex was over Moscow in February–March. This led to a strong negative correlation of the measured ozone content with the temperature. The highest ozone content at the 2-mb level was observed in mid-March. Conversely, an intense polar vortex formed in November–December 2015 under lower planetary wave activity; it was completely destroyed by the major final warming in the beginning of March 2016. The ozone variations in the upper stratosphere over Moscow in December 2015 and January 2016 were related to the alternation of air masses of the vortex and regions outside the vortex. Higher temperatures (as compared to those in the beginning of 2015) led to a decreased ozone content in the beginning of 2016. The interannual difference in the ozone content in the first half of March exceeded 40% of the monthly mean value.

A brief description of microwave spectrometers MOS-3 and MOS-4 used at LPI for ground-based ozone measurements at 142.2 GHz is given together with the results of their intercomparison. Altitude-temporal distribution of stratospheric ozone over Moscow for winter 2016-17 is presented and discussed. Fast variations of microwave emission of night-time mesospheric ozone with periods starting from 3 min. were discovered in the winter.

New data on variations in vertical distribution of stratospheric ozone overMoscow in the cold half-year of 2015–2016 are presented. This period differed significantly from previous winters in a number of stratospheric parameters. The features of these ozone variations are considered and their relation to the stratospheric dynamics is studied. The most significant decrease in the ozone concentration in comparison with average values was observed at the beginning of March, 2016. The development of further significant ozone layer depletion similar to that occurred in spring 2011 was prevented by major sudden stratospheric warming in March 2016.

We consider the instrumentation and methods for the nighttime ground-based measurements of the atmospheric-ozone emission line at a frequency of 142.175 GHz. The ozone-radiation spectra were measured in Moscow in the 2014–2016 cold months with a time resolution of about 2 min. We performed a frequency-time analysis of variations in the differences of the brightness temperatures of the ozone-emission line for the frequency offsets 0–50, 50–150, and 150–250 kHz from the line center. Variations with periods from 6 min to 3 h, which can be related to the wave propagation in the mesosphere and the lower thermosphere, were revealed using the data windows with halfwidths of 10–60 min.

This paper reports the study data on variations in the ozone content in the middle stratosphere over Moscow based on millimeter wavelength observations during a range of midwinter sudden stratospheric warmings that occurred in the past two decades. The relation of ozone with planetary waves and the intensity of the polar stratospheric vortex has been established. The ozone vertical distribution has been monitored with a highly sensitive spectrometer with a two-millimeter wave band. The discovered phenomena of a relatively long-term lower ozone content in December in the considered cold half-year periods are related to the higher amplitude of the planetary wave with n = 1. Such phenomena preceded the development of strong midwinter stratospheric warmings, which, in turn, were accompanied by a significant increase in the ozone content in January. This ozone enrichment was related to the lower amplitude of the wave with n = 1 and higher amplitude of the wave with n = 2 and was accompanied by geopotential H c.v. growth in the polar vortex center. Specific features of variations in the ozone content under the influence of the major atmospheric processes are observed not only in certain cold half-year periods but are also well seen in the general averaged pattern for winters with strong stratospheric warmings.

The features of interannual variations of ozone in the middle stratosphere over Moscow in cold half-years since 1995 to 2015 are considered. These features are most pronounced in two separated groups of winters (six winters in each group) in December–January. It appeared that the seasonal variation of ozone averaged within each group is characterized by a higher ozone concentration \({C_{{O_3}}}\) in group I (in comparison with group II) in December and lower values in January. The differences in the seasonal variation of ozone between these groups at the level of 10 mbar in December and January exceed 2 ppm. A feature of the stratosphere circulation for half-year group I is the existence of a stable polar vortex and the absence of strong midwinter perturbations and sudden stratospheric warmings. On the contrary, for cold half-years of group II, the appearance of strong stratospheric warmings in January–February is in common. The results presented provide a quantitative estimate of the effect of these stratospheric warmings on ozone of the middle stratosphere overMoscow.

A technique of time-frequency analysis of unevenly sampled data sets is developed to study variations in the night mesospheric ozone emission spectra obtained from ground-based millimeter-wave observations. Basic computational formulas as well as results of numerical simulations with monochromatic and noise signals are presented. The results of the simulation are in good agreement with theoretical estimates.

An algorithm for time–frequency analysis of irregular time data series is developed and tested to study variations of night mesospheric ozone radiation, observed at millimeter waves from the Earth’s surface. Some results of numerical and field experiments are presented.

Results of monitoring of vertical ozone distribution at millimeter waves over Moscow during a number of mid-winter sudden stratospheric warmings that occurred over last two decades are presented. Ozone concentration in middle stratosphere over Moscow in winter months may be considered as a predictor of approaching mid-winter major stratospheric warmings.

The new results of remote sensing of atmospheric ozone over the Moscow region in the cold half-year of 2012–2013, including the period of major sudden stratospheric warming are presented. Methods for analyzing the results of observation of the vertical ozone distribution, obtained using spectral equipment operating at the frequencies of the ozone rotational line with a center at 142.175 GHz, are described. The features of the time series of the vertical stratospheric ozone distribution before, during, and after a strong disturbance of the stratospheric dynamics in January 2013 are considered. The data are compared with ozone observations during the period of previous major stratospheric warming in 2009–2010. The considered year to year differences and the diversity of the features of the dynamic processes affecting the vertical ozone distribution point to the importance of further monitoring of atmospheric ozone, which is necessary to develop numerical climate models and to predict the ozonosphere and climate evolution.

Ozone is one of the most important minor gas constituents of the atmosphere. Global depletion of the protective ozone layer in the last decades accompanied with such anomalous events as ozone holes in Antarctic and Arctic [1, 2] requires reliable long-term monitoring of ozone and ozone-related minor atmospheric gases from both satellites and ground level. Ground-based millimeter-wave (MMW) monitoring of atmospheric ozone is low-dependent on weather conditions, covers broad altitude region from the lower stratosphere to mesosphere, and is possible in day and night time [3, 4]. These features of MMW measurements provide their advantages over traditional optical methods (UV spectrometers and lidars) and ozone sondes.

Radio physical methods of remote sensing of the Earth's atmosphere based on spectral measurements of millimeter-wave (MMW) thermal emission of atmospheric gases opened new possibilities for studying changes of the atmosphere and its ozone layer. Ozone plays the key part in protection the Earth's biosphere against the UV-B solar radiation. Also ozone participates in photochemistry, dynamics, emission and thermal balance of the atmosphere, and the ozone changes are connected with all the processes. So monitoring of the vertical ozone distribution (VOD) is very important. Radio physical methods provide continuous and long-term series of observations and give the most complete picture of altitude-temporal ozone distribution and its variations including both short- and long-term ones.

We describe a low-noise superheterodyne receiver with a Schottky-diode for a new mobile microwave ozonometer operated at a frequency of 142.2 GHz, which is designed to measure the vertical profile of ozone distribution in the stratosphere and mesosphere. Calculated and experimental characteristics of the input quasioptical units of the receiver at the Gaussian beams and the measurement results for the directional pattern of the receiver antenna and the noise temperature of the receiver are presented.