Home – Home – Jornals – Atmospheric and Oceanic Optics 2022 number 11

The calculated line intensities of the 1-0, 2-0 and 3-0 absorption bands of the radioactive hydrogen chloride isotopologue H³⁶Cl are presented. The line positions were calculated using the Dunham coefficients obtained with the help of the isotopic independent spectroscopic constants. The line intensities of these bands were calculated using the effective dipole moment parameters obtained with the help of the isotopic substitution equations based on the effective dipole moment parameters of the H³⁵Cl isotopologue. The latter were fitted to the line intensities presented in the HITRAN2020 database.

The methane spectrum is studied near R (3) and R (4) multiplets of the first vibrational overtone in the 298-720 K temperature range with a tuning diode laser. We have developed the technique for laser radiation measurement and frequency calibration with the use of a high-stability plain-mirror interferometer. The coefficients of collisional broadening by nitrogen are calculated at different temperatures.

The results of experimental studies of absorption spectra of pure NH₃ at room temperature in the ranges 6604.3-6606.3 and 6611.6-6613.5 cm^-1 and pressure of up to 0.04 atm are presented. The measurements were carried out at the Department of Diode Laser Spectroscopy of the Institute of General Physics at a high-sensitivity high-resolution diode laser spectrometer with a signal-to-noise ratio of ~ 1400. The spectra were analyzed using a Voigt contour. The results of retrieving the parameters of spectral absorption lines are presented: the positions of centers, intensities, and coefficients of collisional self-broadening and shifts. A comparison was made with the parameters from HITRAN database. A two-fold difference between the measured intensities of a number of lines and the HITRAN values was found.

The absorption spectrum of stable dimers in the long-wave wing of the rotation H₂O band is estimated proceeding from available experimental data on the H₂O continuum absorption in this region and calculations on the basis of the asymptotic line wing theory. The spectral line contour of the rotational band describing the spectral and temperature behavior of the H₂O continuum absorption in the 8-12 mm range was used in the calculations. The spectrum derived does not conflict with computations with the dimer model of the continuum absorption.

Nitric acid plays an important role in atmospheric chemistry; therefore, it is currently monitored by various methods and instruments. Ground-based FTIR method based on spectral measurements of solar radiation by Bruker Optics IFS 125HR spectrometers allows to retrieve not only the total column HNO₃, but also its content in several atmospheric layers. We analyze time series of HNO₃ measurements at St. Petersburg NDACC site between 2009 and 2021. We demonstrate that FTIR measurements can provide information on HNO₃ content in at least two atmospheric layers; the degrees of freedom for signal in average totals 3.1. The mean random error of HNO₃ measurements amount to 3.9, 14 and 1.6% for total atmospheric, tropospheric (up to 15 km), and stratospheric (above 15 km) content, respectively. Thus, the FTIR-method considered is more sensitive to changes in the stratospheric HNO₃ content. The absorption of solar radiation by nitric acid in the measured spectra overlaps with the absorption by water vapor; therefore, the information content and accuracy of HNO₃ measurements are maximal in winter and minimal in summer: in winter, measurements are carried out mainly at low sun and low humidity, and in summer, vice versa.

The results of a comparison of the time series of the turbulent mixing layer height, which is determined from the height-time distributions of the kinetic energy dissipation rate of turbulence and from the height-time distributions of the gradient Richardson number are presented. It is found that only under conditions of atmospheric boundary layer instability due to convection, estimation of the height of the turbulent mixing layer from the height-time distributions of the Richardson number gives results close to those obtained from the distributions of the kinetic energy dissipation rate of turbulence. In other cases, the height of the mixing layer found from the Richardson number can be significantly underestimated.

The phenomenon of reflection of light radiation from crystalline particles oriented in the atmosphere, as well as the physical laws and possible conditions contributing to its occurrence, are considered. A variant of registration of mirror layers using a panoramic optical station (AllSky system) is described.

The time and space derivatives of the air temperature and its products with the wind vector components are analyzed for the cases where the temperature and wind fields are resolved into the deterministic, meso-gamma scale, and turbulent parts. Ultrasonic thermoanemometer measurements in the surface air layer are used for the analysis. The variability ranges of the derivatives are estimated including meso-gamma scale variations in the temperature and wind fields. The variability ranges of these derivatives are compared with those of the “classical” derivatives (when only deterministic and turbulent parts are considered). The derivatives of the components which contain meso-gamma scales are shown to be comparable with the components which include only turbulent parts.

The influence of physical parameters, which describe the St. Petersburg surface properties in the WRF-ARW model, on the forecast of surface meteorological elements is studied. The results are estimated for the cases June 14-22, 2015, when intense positive temperature anomaly occurred in St. Petersburg in comparison with the surroundings. The parameters were chosen from the analysis of similar studies for several cities of the world. Experiments with serial variations in the parameters selected showed that decrease in the surface albedo, soil moisture content, and surface emissivity and an increase in the roughness length improved the forecast quality for the city in comparison with a control experiment. In final experiment, the concurrent variations in the urban surface physical parameters, in accordance with the results of serial experiments, significantly improved the simulation of the city’s thermal anomaly in the model. In the time periods corresponding to the intense urban heat island occurrence, the difference in the surface temperatures between the control and final forecasts could attain 2 °C for the St. Petersburg model area. Under certain synoptic conditions, the variations in the urban surface parameters in the model affect the forecast of meteorological fields within a radius of 150 km from the center of the metropolis.

The conditions for applicability of the Bouguer-Lambert-Beer law for aerosol clouds with particles much larger than the photon wavelength are derived in the form of an analytical formula. The corrections to this law due to diffraction scattering and the geometry of a measuring device are estimated. The resulting formula is useful for processing single experiments that cannot be repeated for some reason.

The limiting sensitivity of a method for detecting vapors of nitrocompounds in the atmosphere based on laser fragmentation/laser-induced fluorescence is estimated in calculations with the developed kinetic model of the LF/LIF process. The calculations take into account the influence of atmospheric nitrogen dioxide as a limiter of the sensitivity of the method when operating in a real atmosphere. It is shown that if the concentration of nitrogen dioxide in the atmosphere does not exceed 10 ppb, the maximum detectable concentrations of nitrobenzene and o -nitrotoluene vapors are ppb-level. It was also shown that the one-color excitation method usually used for the detection of nitrocompounds does not allow attaining the maximum efficiency of the LF/LIF process.

The paper describes the results related to variations in precipitable water vapor at the peak Terskol site. Applying MPM Liebe model and MOLIERE model and using JPL and HITRAN configurations, we estimated optical thickness of the atmospheric column above peak Terskol for 100, 150 and 225 GHz.

The electro-physical process in the discharge circuit of a copper vapor laser (CVL) with an LT-10Cu industrial gas-discharge tube has been studied. It is shown that the pumping of the active medium of the CVL is carried out in two stages. During the first (preparatory) stage, the capacitive components of the laser discharge circuit are charged from the storage capacitor, and during the second stage, the active medium is directly pumped. The transition from the preparatory stage to the pumping stage is carried out as a result of “breakdown”. It is shown that under these conditions it is possible to achieve a practical CVL efficiency of ~ 1% in pump circuits with magnetic compression units and ~ 2.5-3% when the energy input is cut off after the generation pulse. The conditions for implementing the mode of cutting off the energy input after the generation pulse are considered.