Vol 32, No 1 (2019)

Experimental data on lidar signal amplification in a turbulent atmosphere and its dependence on the structure parameter of the turbulent fluctuations of the refractive index of air are presented. It is ascertained that the amplification coefficient first increases up to its maximum with the structure parameter of the refractive index and then decreases under the conditions of strong optical turbulence along a sounding path. The maximum of the amplification coefficient attainable at a certain distance depends on the turbulence strength during measurements. The time variations in the backscatter amplification coefficient are in a good agreement with the time variations in the structure parameter of the refractive index determined from independent measurements.

The coherence length and the degree of broadening of a laser beam under the turbulence effect are estimated from the results of remote acoustic sounding of the atmospheric boundary layer with a Volna-4M sodar. The daily average profile of the coherence length in different seasons is considered. Corrections to the effective radius of a laser beam due to turbulence and the monthly average values of these corrections are calculated. A noticeable excess of the possible broadening of the laser beam in winter above that in summer was found.

We discuss the results of comparison of the average physicochemical aerosol characteristics in neighboring regions: in the Arctic settlement Barentsburg (Spitsbergen Archipelago) and over the Barents Sea. A small (less than 0.02) excess of the atmospheric aerosol optical depth in the island area over the maritime region is noted. The aerosol microphysical characteristics in the near-ground layer differ strongly: the black carbon concentrations are (a factor of 4) larger in Barentsburg, and particle concentrations are (a factor of 2.4) larger over the sea. The absolute concentrations of ions in the atmosphere of Barentsburg are several-fold smaller than over the sea. However, with respect to the relative content, Na⁺, Cl⁻ and \({\text{NH}}_{4}^{ + }\), \({\text{SO}}_{4}^{{2 - }}\) ions predominate in both regions, indicating equivalent contributions of continental and maritime sources.

We present the results of two-wavelength lidar sensing of the middle atmosphere in the altitude range from 30 to 60 km over Obninsk (55.1° N, 36.6° E) in 2012–2017. Monthly average values of the ratio of aerosol and Rayleigh backscattering coefficients (RARC) at a wavelength of 532 nm, averaged over the layers of 40–50 km and 50–60 km, vary from 0 to 0.02, while the average peak RARC levels in these layers vary from 0.1 to 0.2. Short-term (shorter than 1 month) and long-term (half-year and longer) variations in backscattering are observed. Short-term variations are time concurrent with the occurrence of meteor showers. Long-term enhancements of backscattering in the layer of 50–60 km were observed in 2013 after the Chelyabinsk meteorite fall, as well as in the first half of 2016. In 2014–2015, the monthly average RARC was zero within measurement errors at altitudes from 40 to 60 km. We analyzed the possibility for meteoric aerosol to manifest in backscattering, taking into account the fluxes of meteoric material, gravitational sedimentation of aerosol, and the effect of vertical wind. The flux of visible meteors with masses larger than 10⁻⁶ kg and bolides is shown to be insufficient for a long-term enhancement of backscattering in the layer of 50–60 km. It is hypothesized that the enhancement in backscattering is most likely to be due to the occurrence of an enlarged fraction of meteoric smoke particles, formed by ablation of radio meteors and penetrating into the upper stratosphere in the region of the stratospheric polar vortex. In early 2016, this was favored by the formation of an extremely strong stratospheric polar vortex and its shift toward Eurasia.

The optimal control problem for deliberate intervention in the Earth’s climate system with the aim of stabilizing the global surface temperature is considered. The deliberate action on the climate system is implemented via the controlled radiative disturbance created by artificial aerosols injected into the stratosphere. The controlled object is described by a two-component energy-balance model subject to radiative action caused by an increase in the concentration of greenhouse gases in the atmosphere. The human impact on the climate system is specified in accordance with Representative Concentration Pathway (RCP) scenarios, as well as with the scenario corresponding to a 1% increase in atmospheric carbon dioxide per year. The albedo of the artificial aerosol global layer represents the control variable. The optimal control and the corresponding phase trajectory of the climate system are obtained analytically using Pontryagin’s maximum principle. The approach discussed in this paper can be considered as a basis for developing scenarios for deliberate intervention in the climate system using various geoengineering methods.

The upward and downward fluxes of solar and thermal radiation are simulated for the meteorological conditions typical for midlatitude summer. The atmospheric radiation balance due to cirrus clouds of different depth is estimated. The sensitivity of the radiative forcing to different models of the water vapor continuum absorption is estimated.

It is shown that the daily variation in the radiation extinction coefficient due to midges (RECM) has a statistically significant morning maximum at 09:00. This maximum is not connected with extremes of the air temperature or relative humidity. RECM maxima are observed at air temperatures of 12–17°C and relative air humidity of 60–80%. Correlations between RECM, air temperature, and relative humidity are statistically significant. The slope coefficient of the straight line in dependences of the midges-caused radiation extinction on the air temperature and relative humidity are –0.04 km^–1/5°C and +0.04 km^–1/20%, respectively. It is revealed that the RECM maxima are observed at winds of 2–4 m/s, directed from boggy forest areas, and minima, at winds of 1–4 m/s, directed from Ob River and dry, mixed, and boreal coniferous forests.

Measurements (2012–2014) of black carbon (BC) concentration in the surface air in the region of Tiksi International Hydrometeorological Observatory, located near the delta of the Lena River, are analyzed. Variations in the BC concentration with different magnitudes and durations are revealed. Anomalous (larger than 1000 ng/m³) peaks of BC concentration are shown to be rarely encountered, predominately in the warm season of the year (May–September), for no longer than two days. The longest episodes of high BC concentration are associated with long-range atmospheric transport of wildfire products. During such episodes, the air temperature and radiation budget significantly change in the surface atmosphere. The increases in the surface air temperature on days when smoke aerosol comes from nearby fires in July may reach 10°C (at the climatic norm 10–11°C).

Results of laboratory experiments on studying the influence of scattering and absorbing media on the quality of object imaging with active pulsed television optoelectronic systems (OESs) are discussed. It is shown that the quality of object images in active pulsed vision systems or their frequency-contrast characteristics can be studied both by direct measurements or indirectly using Fourier transforms of test object images or derivatives of functions determined in experiments. A previously formulated theoretical statement that the image quality for objects screened by turbid media when using active pulsed OESs with backscattered noise signal selection can be higher almost by an order of magnitude than when using an OES operating with laser side illumination and constantly opened receiver has been confirmed experimentally.