D. M. Kabanov

Spatial Inhomogeneities and the Spectral Behavior of Atmospheric Aerosol Optical Depth over the Atlantic Ocean

Abstract In this paper the results of investigations into atmospheric aerosol optical depth (AOD) over the Atlantic Ocean are discussed. The data were collected during five shipboard expeditions that took place between 1989 and 1996. Measurements were taken by a 0.37–4-μm multiwavelength sun photometer, specially designed for working conditions on board a ship. The analysis focuses on the spatial variability of atmospheric transparency and the spectral behavior of AOD in different oceanic areas. The genetic zoning of aerosol turbidity takes into account the influence of two factors: the type of continental aerosol and the character of airmass transport that dominates in a given latitudinal zone. The area selection by the genetic zoning method is further confirmed by the results of the “sign” classification based on the spatial distributions of AOD and the Angstrom parameter. Statistical characteristics for different areas of the Atlantic are given. The mean values of AOD (0.55 μm) range from 0.08 to 0.38 ...

Sun photometers for measuring spectral air transparency in stationary and mobile conditions

SP-9 and SPM multiwavelength sun photometers are described and briefly characterized. The SP-9 sun photometer is designed for year-round monitoring of the spectral air transparency in the 0.3–2.2 μm wavelength range in the regional network. To implement the automated measurement mode (unattended by operators), the instrument includes a solar sensor, an automatic sun pointing/tracking system, a built-in GPS detector, a flash drive, and sensors for meteorological parameters. The SPM portable photometer is a simplified version of SP-9 and is designed for the air transparency measurements in mobile conditions.

Characteristics of the annual behavior of the spectral aerosol optical depth of the atmosphere under conditions of Siberia

Based on multiyear observations in Tomsk (since 1995, in the wavelength range 0.37–4 μm) and other regions of the Asian part of Russia (2003–2008), we determined the specific features of the annual behavior of the characteristics of the spectral aerosol optical depth (AOD) of the atmosphere. It is shown that AOD peaks are observed in April (0.19 in the region of 0.5 μm) and July, a local minimum in June (less than 0.16), and minimum values in the fall (0.12). The seasonal variations of the Angström selectivity exponent are characterized by elevated values in the warm period (maximum in July) and low values in winter. The closeness of the seasonal variations of aerosol turbidity in three Siberian regions is noted, and the Siberia mean annual behavior of atmospheric AOD characteristics is suggested. The average values of the aerosol optical and microphysical characteristics of the atmospheric depth for characteristic periods of intraannual AOD variations are presented.

Simulation of aerosol direct radiative forcing under typical summer conditions of Siberia. Part 1. Method of calculation and choice of input parameters

We present a method for calculating the broadband solar radiation fluxes under clear sky conditions based on the combination of a statistic simulation algorithm and a version of the k-distribution method. An approach to the choice of the input parameters needed for calculating the fluxes and the direct component of the radiative aerosol forcing at the top and the bottom of the atmosphere is described. The approach is based on the combination of the results of multiyear sun photometer measurements of the aerosol optical thickness on the range from 0.37 to 4.0 μm and the atmospheric moisture content in the region of Tomsk with the available models of aerosols, gas components of the atmosphere, and underlying surfaces for determining the deficient parameters, such as the single scattering albedo, the scattering indicatrix of aerosol particles, and the surface albedo.

Results of spectral measurements of atmospheric aerosol optical depth with sun photometers in the 58th Russian Antarctic Expedition

We discuss the specific features of the spatiotemporal variations in the atmospheric aerosol optical depth (AOD) measured during the 58th Russian Antarctic Expedition on board RVs “Akademik Fedorov” and “Akademik Tryoshnikov” and at the Mirny station. It is shown that the main feature of the spatiotemporal AOD distribution over ocean in the Southern Hemisphere is the linear latitudinal decrease of AOD from 0.15 at the equator to 0.025 near Antarctica. We indicate that the low AOD level in Antarctica (0.022 ± 0.005) has persisted for the last 17 years.

On results of studies of atmospheric aerosol optical depth in arctic regions

We discuss the characteristics of the spectral aerosol optical depth (AOD) of the atmosphere measured using sun photometers in high-latitude regions (Spitsbergen, Tiksi, Yakutsk). The seasonal variations are characterized by a decrease in AOD from spring to fall by approximately a factor of 2 in Yakutia and by a factor of 1.5 in the region of Spitsbergen. It is shown that the high selectivity of the spectral AOD dependence in warm period (with Angström parameters varying from 1.3 to 1.8) was caused by low content of coarsely dispersed aerosol. Multiyear data of MODIS satellite observations are used to estimate the spatial distribution of turbidity; it is shown that satellite observations systematically overestimate AOD over Arctic seas.

Fine and coarse components of atmospheric aerosol optical depth in maritime and polar regions

We discuss the results of comparative analysis of the fine and coarse components of atmospheric aerosol optical depth (AOD), obtained from data of SP sun photometer measurements in 14 regions of the Atlantic, Southern, and Arctic Oceans, and Far East seas. Average (over regions) values of the coarse AOD component vary from 0.007 to 0.24, and average values of the fine AOD component vary from 0.015 to 0.25. Despite the fact that the two AOD components are independent in their origin and occur in a variety of combinations, the distributions of their average values exhibit joint growth from lowermost values in the Southern Ocean to maximal values in the zone of severe continental outflows (the Sea of Darkness and the Japan Sea). Taking into account the natural specific features, we grouped the data with respect to a few types of maritime regions; and for each, we determined the most probable values of the coarsely dispersed component and two parameters (analogous to Ångström parameters), which characterize the finely dispersed AOD component.

The influence of synoptic factors on variations of atmospheric aerosol optical depth under Siberian conditions

Based on multiyear measurements of the atmospheric aerosol optical depth (AOD) in a typical region of Siberia (Tomsk), we analyzed the relationship between the AOD and different synoptic factors. The averaged spectral AOD dependencies for two air mass types (continental polar and Arctic air) and different pressure systems are compared. The effect of cloud cover and precipitation on the AOD is estimated. We discuss the results of wavelet analysis of the time series of the AOD and columnar water vapor for a number of observation sites (AERONET stations in Tomsk, Yekaterinburg, Irkutsk, Yakutsk, and Ussuriisk). The specific features of synoptic-scale quasi-periodic variations at different measurement sites are identified and compared.

Variations in aerosol optical and microphysical characteristics along the route of Russian Antarctic Expeditions in the East Atlantic

The 12-year aerosol studies along the route of the Russian Antarctic Expeditions in the East Atlantic and the Southern Ocean are summarized. We analyzed the spatial distribution (with 5° step in latitude), seasonal (November/April) variations, and interrelations of aerosol optical and microphysical characteristics. It is shown that the latitudinally average variations in aerosol parameters in the East Atlantic exceed one order of magnitude. The lowest (maximal) values are observed near Antarctica (in tropical zone): aerosol optical depth (0.5 μm) varies from 0.02 to 0.5, number concentrations of small particles (d = 0.4–1 μm) vary in the range 0.8–19 cm–3, concentrations of large (d > 1 μm) particles vary in the range 0.04–2.2 cm–3, and aerosol and black carbon mass concentrations vary in ranges 0.5–14 μg/m3 and 0.026–0.7 μg/m3.

On daytime variations of atmospheric aerosol optical depth and aerosol radiative forcing

Based on the results of multiyear measurements of spectral atmospheric transparency in the wavelength range of 0.37–4 μm, we discuss the regularities of daytime variations of the characteristics of aerosol optical depth (AOD) and atmospheric moisture content in a typical Siberian region (Tomsk). For different atmospheric conditions (seasons, air masses), quantitative characteristics of the average daytime behavior of the spectral AOD and Angstrom parameters are presented. We suggest an empirical model for the daytime behavior of atmospheric AOD in the wavelength region of 0.37–4 μm, which is based on the use of the daily average values of the Angstrom parameters. We discuss the effect of the daytime AOD variations on the instantaneous and daily average values of the aerosol radiative forcing at the underlying surface level and at the top of the atmosphere. The aerosol radiative effects are analyzed taking into account both the average daytime variations of the AOD as well as relatively large AOD variations during the day characteristic of a concrete situation.