A.N. Lukin

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.

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).

Two-dimensional self-similar plasma equilibria

Force-free plasma equilibria are expected to form in the solar corona, while in-situ spacecraft observations have shown that force-free equilibria are formed in the planetary magnetotails. In this paper, we develop fluid models of two-dimensional axially symmetric force-free equilibria and discuss similar slab equilibria. The group theory approach is used to find the symmetry groups and reduce the Grad-Shafranov equation with exponential and power law nonlinearities to ordinary differential equations for the self-similar (automodel) solutions that we analyze analytically and numerically. Force-free equilibria of the developed class have a magnetotail-type configuration with magnetic field lines stretched in the radial direction and represent nonlinear force-free equilibria, because rot B=α(r) B with α(r)≠const. Making use of the same symmetry groups, we generalize the developed force-free equilibria by including a finite plasma pressure gradient and compare different equilibria of the developed class. The...

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.

Ground-based millimeter-wave ozone monitoring in Moscow during sudden stratospheric warmings

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.

Millimeter-wave remote sensing of ozone vertical distribution over Moscow in periods of considerable changes in the ozone layer in 2010–2012

Radio physical methods of remote sensing of the Earths 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 Earths 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.