S. V. Solomonov

Low-noise cooled planar Schottky diode receivers for ground-based spectral ozone measurements at 142 GHz

Two new low-noise cooled receivers based on planar Schottky diode mixers were designed and built for the Lebedev Physics Institute (LPI) spectrometer for ground-based measurements of the atmospheric ozone spectral line of 142.175 GHz central frequency. The receivers differ in the intermediate frequency (IF) bands, of around 3.7 and 1.5 GHz. Review description of the spectrometer equipped with the 3.7–GHz IF receiver is given, and its performance is compared with other millimeter-wave ground-based ozone spectrometers. Special attention was paid to design of the input Gaussian optics and the mixers. Techniques of laboratory tests of the receivers and results of the tests through all 2–mm wavelength range are considered and discussed. SSB mixer noise temperature of 460±60 K was obtained at 151 GHz for room temperature mixer, and the value of 180±30 K was measured at 134 GHz under cooling to 85 K in liquid nitrogen cryostat. SSB mixer conversion losses were less than 5.5 dB in both the cases. SSB noise temperature of the spectrometer is less than 1500 K without cooling and less than 700 K at cryogenic operation at 142 GHz. This provides sensitivity of about 0.2 and 0.1 K for the narrowest spectral channel width of 0.1 MHz and signal integration time of 1 hour. Using the optimized spectrum analyzers delivers data on high-accuracy retrieval of the ozone vertical profile in the atmosphere at altitudes about from 15 to 75 km. Examples of the ozone observation data are given.

Some features of the vertical ozone distribution from millimeter wave measurements at Pushchino and Onsala observatories

Abstract A number of features of the stratospheric ozone distribution were revealed by joint millimeterwave observations of ozone emission lines at 142,175 and 110,836 GHz carried out during the winter periods of 1988–1989 and 1989–1990 at the Radioastronomical Observatory of the P.N. Lebedev Physical Institute of the Russian Academy of Sciences and at the Onsala Space Observatory of Chalmers University of Technology, Sweden. It is shown that vertical ozone variations observed at the two observatories were connected with large scale dynamical processes that occurred in the stratosphere. When the stratosphere was relatively undisturbed the ozone profiles obtained at both observatories were close to the ozone reference model given by Keating and Pitts. There were periods during a stratospheric warming when the ozone content measured at the two observatories in the 25–40 km altitude range was higher by a factor ~ 1.5 than the model values. Dynamical processes in the stratosphere also gave rise to rapid (4 h duration) and large deviations from the model ozone profile. An ozone layer depletion was observed in the 27–55 km altitude range. The observed ozone variations illustrate the sensitivity of the ozone distribution to stratospheric disturbances including stratospheric warmings.

Techniques of ground-based remote sensing of the ozone layer by millimeter-wave heterodyne spectroscopy

MM-wave heterodyne spectroscopy is successfully used for measuring of the atmospheric ozone at altitudes from about 15 to 80 km. Remote sensing of trace gases, including ozone at MM waves has a number of obvious advantages. The required performance of a ground-based instrument for ozone observations at wavelength of 2 mm has bene determined using results of computer simulations. Main features of the Lebedev Physics Institute heterodyne radio spectrometer for 142.2 GHz ozone spectral line measurements are described, and key parts of the spectrometer receiver, such as input optics and low- noise Schottky diode mixer, are considered in greater detail. The receiver and the mixer have been tested throughout the 22- mm band at both room and liquid nitrogen temperatures and main results of the tests are presented. Blackbody cold loads have been used in the calibration/observation procedure, with special attention paid to accurately measuring their brightness temperatures. Some results of ozone observations for various atmosphere states are presented to demonstrate possibilities of ground-based MM-wave heterodyne spectroscopy.

Spectral instrumentation for monitoring atmospheric ozone at millimeter waves

A spectroradiometer operating in the 2-mm wavelength range for monitoring the ozonosphere from the Earth’s surface is described. Unique data on the vertical ozone distribution in layers of the stratosphere and mesosphere difficultly accessed by other techniques have been obtained with this instrument. The reliability of the results of measuring the vertical ozone distribution at millimeter waves is due to the high sensitivity of the spectroradiometer, its optimized characteristics, and highly efficient data-processing techniques.

Features of the altitude-time distribution of ozone over Moscow during the strong ozone depletion in spring 2011 and during the statospheric warming in 2010 according to observations at millimeter wavelengths

The new observational data at millimeter wavelengths of the vertical distribution of stratospheric ozone over Moscow during the significant ozone depletion in the Northern Hemisphere in spring 2011 and during the circulation disturbance in the mid-winter sudden stratospheric warming in 2010 are presented. Significant interannual variations in the altitude distribution of ozone concentration are detected. The revealed significant ozone variations due to large-scale atmospheric processes show the importance of the monitoring of ozonosphere by radio physical methods for studying its evolution.

Remote sensing of the atmospheric ozone at millimeter waves

Ground-based remote sensing of atmospheric ozone at millimeter (MM) waves is necessary for continuous day-and-night monitoring of the ozone layer. A valuable feature of the method and its advantage over observations at shorter wavelengths is low dependence on weather conditions because of the small effects of aerosols and clouds on the propagation of MM waves in the atmosphere. A low-noise heterodyne MM-wave radio spectrometer was built at the P.N. Lebedev Physical Institute (LPI) for ground-based measurements of the atmospheric ozone spectral line of 142.175 GHz (central frequency). High sensitivity and frequency resolution of the spectrometer allow to get accurate pressure-broadened ozone spectra which are used for the solution the inverse problem-retrieval the vertical ozone distribution (VOD) in the atmosphere. Regular ground-based ozone measurements have been carried out at the LPI since 1987 to study various processes and changes in the Earths ozonosphere. The VOD for altitudes from about 15-20 to 75 km is retrieved from the spectra measured. The upper boundary of the altitude range is essentially higher than for balloons and ozone sondes and ground-based optical spectrometers and lidars. The LPI MM-wave spectrometer was incorporated into a ground-based network for ozone measurements during the international campaigns DYANA (1989-90), CRISTA/MAHRSI (1994), and CRISTA/MAHRSI-2 (1997).

Transportable millimeter-wave spectrometer for monitoring of the atmospheric ozone

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.

Study of ozone concentration variations in the upper stratosphere using millimeter wave spectroscopy methods

New results of the study of ozone concentration variations in the upper stratosphere over Moscow in the layer at a height of 40 km, which is most sensitive to anthropogenic impacts, are presented. Changes in the ozone concentration and its relation to other atmospheric parameters in cold periods of 2008–2009 and 2009–2010 are analyzed. It was shown that there exist regions with decreased ozone content in the polar vortex and outside of it in air with higher temperature in the upper stratosphere. These phenomena cause deformations of vertical ozone distribution profiles and an appreciable shift of the maximum of the relative content of ozone to lower stratosphere layers.

Variations in the Ozone Concentration in the Stratosphere over Moscow due to Dunamic Processes in the Cold Period of 2015–2016

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.

Influence of strong sudden stratospheric warmings on ozone in the middle stratosphere according to millimeter wave observations

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 Hc.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.