An alternative method for aerosol optical thickness retrieval in the UV range

Atmospheric aerosol particle size distribution data derived from almucantar scans performed by the CIMEL sunphotometer at Belsk, Poland, in 2005 are used for the estimation of aerosol optical thickness (AOT) in the UV range by applying the Mie theory. The results obtained are compared with the direct Sun measurement data from the CIMEL sunphotometer and collocated Brewer spectrophotometer No. 064, as well as with AOT obtained by Angström extrapolation from the direct Sun measurements performed by the CIMEL sunphotometer in the visible range of wavelengths. Mean differences between calculated and measured values of AOT are up to about 8% in the UV-B range, which is close to the measurement uncertainty of the Brewer spectrophotometer and much less than that obtained by means of Angstrom extrapolation (over 24% in the UV-B range).     

Variability of aerosol properties during the 2007–2010 spring seasons over central Europe

Aerosol optical properties have been studied for spring seasons when increased values of PM10 are registered. Measurements of aerosol optical properties were taken by collocated lidar and sun-photometers at Belsk, Poland, and Minsk, Belarus. A significant increase of registered aerosol optical thickness (AOT) was found during episodes with elevated PM10 concentrations. An increase of AOT at 1020 nm amounted to 50% in the case of Minsk and 18% in the case of Belsk, while an increase of AOT at 400 nm was 66% and 33%, respectively. We noted an increase of Ångström exponent by 6% at both stations and no significant increase of single scattering albedo. The LIDAR measurements together with NAAPS model results and backtrajectory analysis suggest that both the biomass burning products and the Saharan dust are responsible for increased PM10 concentrations and large AOT values during spring time. The smoke aerosol is transported over Central Europe mainly in the boundary layer, increasing both PM10 concentration and AOT. The dust aerosol transported in the free troposphere slightly affects the AOT values only. Statistically significant correlation between PM10 concentration and AOT was found during reporting period.     

A multiyear analysis of aerosol optical thickness over Europe and Central Poland using NAAPS model simulation

This study contains a comparative analysis of aerosol optical thickness (AOT) between numerical calculations obtained from the Navy Aerosol Analysis and Prediction System (NAAPS) model and direct observations from the AERONET robotic network and the Saharan Aerosol over WArsaw (SAWA) field campaign. AOT was calculated for 500 nm wavelength. The comparison shows underestimation of the total aerosol optical thickness simulated by NAAPS. The correlation coefficients between model and observation oscillates between 0.57 and 0.72. Results of seven-year (1998–2004) NAAPS simulation of aerosol components (sea salt, mineral dust, sulphate, and smoke) show large temporal and spatial variability of the aerosol optical thickness over Europe. The least polluted region is the Iberian Peninsula, while the highest aerosol burdens occurred in Central Europe, mostly due to anthropogenic sulphate particles. Finally, the analysis of mineral dust transport shows frequent episodes of Saharan dust inflow over Central Europe. There are about 20 days a year (4 days in May) when instantaneous AOT associated with mineral dust aerosol increases over 0.1.     

Erythemal UV observations at Belsk,Poland, in the period 1976–2008: Data homogenization,climatology, and trends

Measurements of erythemal irradiance have been carried out continuously at Belsk since May 1975. We present a homogenization procedure of the UV time series for the period of 1976–2008. Long-term oscillations discovered in the homogenized data set agree with those extracted from the reconstructed UV data for all-sky and clear-sky conditions. The UV climatology was established and the UV variability was determined. Positive UV trends were found for the period of 1976-2008 in the annual mean (5.6±0.9% per decade), in the seasonal mean for the warm subperiod of the year (April–October, 5.5±1.0% per decade), and in monthly means (∼2–9% per decade). A satisfactory agreement between the trend extracted from the homogenized ground-based data and that found in satellite UV data for Belsk (1979–2008) supports the reliability of satellite trend analyses over wider areas during snowless periods.     

The lidar ratio derived from sun-photometer measurements at Belsk Geophysical Observatory

The lidar ratios at 500 and 1020 nm were derived from POM 01L sun-sky scanning photometer measurements taken at Belsk Geophysical Observatory (long. 20°47′, lat. 51°50′) in the period from 2002 to 2006. The most frequently occurring lidar ratio values for the study period are 50 sr and 30 sr at 500 nm and 1020 nm, respectively. Calculations of lidar ratios for summer and winter seasons have been made as well. Back trajectory analysis was also performed to final aerosol source of origin.     

Study of vertical structure of aerosol optical properties with sun photometers and ceilometer during the MACRON campaign in 2007

This paper presents the measurements of a vertical structure of aerosol optical properties performed during the MACRON (Maritime Aerosol, Clouds and Radiation Observation in Norway) campaign, which took place in July and August 2007 at ALOMAR observatory on Andøya island (69.279°N, 16.009°E, elevation 380 m a.s.l.). The mean value of the aerosol optical thickness (AOT) at 500 nm during campaign was 0.12. Significant increase of the AOT above longtime mean value was observed on 7 and 8 August 2007 when the AOT exceeded 0.4 at 500 nm. Analyses of back trajectories show the aerosol transported from over Africa and Central Europe. The aerosol extinction coefficient obtained from the synergy of ceilometer and sun photometer observations reached 0.05–0.08 km^?1 (at 1064 nm) in the dust layer. The single scattering albedo at the ALOMAR observatory decreased during the dust episode to 0.93–0.94, which indicates some absorptive aerosols in the lower PBL.     

Seasonal variability of aerosol optical properties in Darwin,Australia

This paper investigates the annual cycle in aerosol optical thickness (AOT) and Angstrom exponent in Darwin, Australia, a coastal site in the Tropical Warm Pool where the major aerosol sources are biomass burning and sea salt. We have used radiometer measurements from the Tropical Western Pacific Atmospheric Radiation Measurement facility for the period March 2002–June 2003. Strong seasonal cycles in AOT and Angstrom exponent were observed, peaking during the burning season (May–November). Investigation of the spectral dependence of optical thickness showed that the Angstrom formula can be satisfactorily fitted to the AOT data during the burning season but not on summer and autumn afternoons due to the presence of sea salt aerosols.     

Long-term changes (1980–2003) in total ozone time series over Northern Hemisphere midlatitudes

Long-term changes in total ozone time series for Arosa, Belsk, Boulder and Sapporo stations are examined. For each station we analyze time series of the following statistical characteristics of the distribution of daily ozone data: seasonal mean, standard deviation, maximum and minimum of total daily ozone values for all seasons. The iterative statistical model is proposed to estimate trends and long-term changes in the statistical distribution of the daily total ozone data. The trends are calculated for the period 1980–2003. We observe lessening of negative trends in the seasonal means as compared to those calculated by WMO for 1980–2000. We discuss a possibility of a change of the distribution shape of ozone daily data using the Kolmogorov-Smirnov test and comparing trend values in the seasonal mean, standard deviation, maximum and minimum time series for the selected stations and seasons. The distribution shift toward lower values without a change in the distribution shape is suggested with the following exceptions: the spreading of the distribution toward lower values for Belsk during winter and no decisive result for Sapporo and Boulder in summer.     

Effects of thunderstorm activity in power spectra of the electric field in the near-surface atmosphere at Kamchatka

We have performed a spectral analysis of variations in the E _z component of a quasistatic electric field in the atmospheric surface layer in a wide band of internal gravity waves (from 5 min to 3 h) for quiet and seismically active conditions as well as high thunderstorm activity. Observational data of the field for September, 1999 and August–September, 2002, were used. It has been shown that, if there are no thunderstorms or earthquakes, the background spectrum includes oscillations with maxima at periods of T ∼ 1.8 and 1 h, 40, 30, 15, and 10–13 min. Their intensity in the range of periods of 0.5–3.0 h is two or more orders of magnitude higher than the intensity of maxima in the range of 5–30 min. Before earthquakes, with anomalies in diurnal variations of field intensity, there is a tendency of increased background spectrum at maxima noted there. In both ranges of oscillation periods, the spectral intensity increases by one to one and a half orders of magnitude. Under high thunderstorm activity, the variability is higher as compared to the spectra of earthquake precursors by both locations of maxima and their intensity. The intensity of maxima exceeds the maxima on the eve of earthquakes one to one and a half orders of magnitude in the range of periods 0.5–3.0 h and two and more orders of magnitude in the range of periods 5–30 min.     

Spectral Aerosol Transmittance in the Ultraviolet and Visible Spectra in Athens,Greece

This work investigates the spectral atmospheric transmittance due to aerosols in the urban environment of Athens during a period of one year. The spectral transmittance due to aerosols is derived using measurements of spectral direct-beam solar irradiance in the 310–575 nm spectral band. This derivation is accomplished by using a radiative transfer model for estimating the partial spectral atmospheric transmittance functions due to Rayleigh scattering, and absorption by ozone, nitrogen dioxide and water vapor. The seasonal and diurnal variation of the aerosol transmittance is investigated and the results are discussed with a view to air pollution sources, meteorological factors and topographic characteristics of the Athens basin.     

Aerosol properties over an urban site in central East China derived from ground sun-photometer measurements

Sun-photometer measurements at Hefei, an urban site located in central East China, were examined to investigate the variations of aerosol loading and optical properties. It is found that aerosol optical thickness (AOT) keeps higher in winter/spring and gets relatively lower in summer/autumn. The large AOT in winter is caused by anthropogenic sulfate/nitrate aerosols, while in spring dust particles elevate the background aerosol loading and the excessive fine-mode particles eventually lead to severe pollution. There is a dramatic decline of AOT during summer, with monthly averaged AOT reaching the maximum in June and soon the minimum in August. Meanwhile, aerosol size decreases consistently and single scattering albedo (SSA) reaches its minimum in July. During summertime large-sized particles play a key role to change the air from clean to mild-pollution situation, while the presence of massive small-sized particles makes the air being even more polluted. These complicated summer patterns are possibly related to the three key processes that are active in the high temperature/humidity environment concentrating on sulfate/nitrate aerosols, i.e., gas-to-particle transformation, hygroscopic growth, and wet scavenging. Regardless of season, the increase of SSA with increasing AOT occurs across the visible and near-infrared bands, suggesting the dominant negative/cooling effect with the elevated aerosol loading. The SSA spectra under varying AOT monotonically decrease with wavelength. The relatively large slope arises in summer, reinforcing the dominance of sulfate/nitrate aerosols that induce severe pollution in summer season around this city.     

Relation between the structure of particles of the dispersion layer and its spectral optical thickness in an optically thin environment

Summary The paper focuses on the applicability of simple optimizing methods to determining the aerosol structure based on the measured values of the spectral optical thickness of aerosol δ(λ). The necessary conditions leading to a stable solution are assessed. By applying the particle distribution function in the form of summations of modified gamma functions we obtain the simple form of δ(λ). It is not suitable for proving Gaussian functions. The application of approximate methods to determine the aerosol structure from spectral optical thickness of atmospheric aerosol is based on measurements of the direct spectral solar radiation flux density which formed a part of the radiation experiment conducted in Zingst (Germany) on the coast of the Baltic Sea in 1987. on leave from the Astronomical Institute, Slovak Academy of Sciences     

A comparison study of summer-time synoptic-scale waves in South China and the Yangtze River basin using the TRMM Multi-Satellite Precipitation Analysis daily product

Summer-time synoptic-scale waves in South China and the Yangtze River basin are quantified and compared by means of analyzing the 6-year (1998―2004) TRMM Multi-Satellite Precipitation Analysis (TMPA) daily product. An innovative 3-dimensional spectrum analysis method is applied. The results indicate that synoptic-scale waves appearing in South China prominently propagate westward within a zonal wavenumber range of 9―21 and a frequency range of-0.12―-0.22 cycles day-1, while those in the Yangtze River basin primarily move eastward with the same characteristic wavenumbers of 9―21, but within a frequency range of 0.2―0.29 cycles day?1. Zonal and meridional distributions, and seasonal variations of these waves are further explored and compared. It shows that summer-time synoptic-scale waves in the South China result from the northward migration and oscillation of the Intertropical Convergence Zone (ITCZ) in the western Pacific, whereas the ones in the Yangtze River basin are generally related to the synoptic troughs within the westerly flow, originating from the Qinghai-Tibet Plateau.     

Solar irradiance and total ozone over El Arenosillo (Spain) during the solar eclipse of 3 October 2005

The ground track of the annular eclipse of 3 October 2005 crossed the Iberian Peninsula. The main objective of this work was to analyze the variability of the solar irradiance and the total ozone column during the course of this event at El Arenosillo (Southwestern Spain). For achieving this goal, two Kipp & Zonen broadband radiometers (one for measuring total solar irradiance and other for measuring ultraviolet erythemal solar irradiance), one NILU-UV multi-band instrument and one Brewer spectroradiometer were used in this work. Total irradiance (310–2800 nm), and ultraviolet erythemal radiation (UVER) were recorded at a high frequency of 5 s, showing a strong reduction (higher than 80%) of the irradiance at the maximum solar obscuration which was of 79.6%. The irradiance decrease during the course of the eclipse was positively correlated with the percentage of eclipse obscuration, showing a very high agreement (R²～0.99). The irradiance recorded at selected wavelengths from the NILU-UV instrument shows a more pronounced decrease in the UV irradiance at the lower wavelengths during the solar eclipse. Finally, the evolution of the total ozone column (TOC) derived from Brewer and NILU instruments during the eclipse presented an opposite behavior: while the Brewer derived TOC values increase about 15 DU, the NILU derived TOC values decrease about 11 DU. This opposite behavior is mainly related to an artifact in the spectral irradiances recorded by the two instruments.     

Aerosol microphysics over a tropical coastal station inferred from the spectral dependence of Angstrom wavelength exponent and inversion of spectral aerosol optical depths

Six years of spectral aerosol optical depth (AOD) measurements have been analyzed from a tropical coastal site, Trivandrum (8.55°N, 76.9°E, 3 m msl) to infer on the seasonal changes in the microphysical properties of columnar aerosols, by examining the derivatives of the Angstrom wavelength exponent (α) in the wavelength domain (α′_λ) as well as in AOD domain (α′_τ) and by retrieving the columnar size distribution by numerical inversion of the AODs. The inference of the changes in the aerosol microphysics drawn from the features of the derivatives α′_λ and α′_τ is consistent with the pattern revealed by the aerosol properties obtained from the columnar size distributions retrieved from the AOD spectra as well as from the surface measurements of mass-size distributions, which are supported by the back-trajectory cluster analysis and the results of chemical species analysis.     

Dependence of the ionospheric response on the solar flare parameters based on the theoretical modeling and GPS data

The measurements of an increase in the total electron content (TEC) of the ionosphere during solar flares, obtained based on the GPS data, indicated that up to 30% of TEC increments corresponded to the ionospheric regions above 300 km altitude in some cases, and TEC increased mainly below altitudes of 300 km in other cases. The theoretical model of the ionosphere and plasmasphere was used to study the obtained effects. The altitude-time variations in the charged particle density in the ionospheric region from 100 to 1000 km were used depending on the solar flare spectrum. An analysis of the modeling results indicated that an intensification of the flare UV emission in the 55–65 and 85–95 nm spectral ranges results in a pronounced increase in the electron density in the topside ionosphere (above 300 km). The experimental dependences of the ionospheric TEC response amplitude on the localization and peak power of flares on the Sun in the X-ray range, obtained based on the GPS data, are also presented in the work.