scholarly journals Trend analysis of the Aerosol Optical Thickness and Ångström Exponent derived from the global AERONET spectral observations

2011 ◽  
Vol 4 (4) ◽  
pp. 5325-5388 ◽  
Author(s):  
J. Yoon ◽  
W. von Hoyningen-Huene ◽  
A. A. Kokhanovsky ◽  
M. Vountas ◽  
J. P. Burrows
Keyword(s):  
Trend Analysis ◽  
Optical Thickness ◽  
Weighted Least Squares ◽  
Temporal Trends ◽  
Aerosol Optical Thickness ◽  
Anthropogenic Aerosols ◽  
Angstrom Exponent ◽  
Ångström Exponent ◽  
Ångstrom Exponent

Abstract. Regular aerosol observations based on well-calibrated instruments have led to a better understanding of the aerosol radiative budget on Earth. In recent years, these instruments have played an important role in the determination of the increase of anthropogenic aerosols by means of long-term studies. Only few investigations regarding long-term trends of aerosol optical characteristics (e.g. Aerosol Optical Thickness (AOT) and Ångström Exponent (ÅE)) have been derived from ground-based observations. This paper aims to derive and discuss linear trends of AOT (440, 675, 870, and 1020 nm) and ÅE (440–870 nm) using AErosol RObotic NETwork (AERONET) spectral observations. Additionally, temporal trends of Coarse- and Fine-mode dominant AOTs (CAOT and FAOT) have been estimated by applying an aerosol classification based on accurate ÅE and Ångström Exponent Difference (ÅED). In order to take into account the fact that cloud disturbance is having a significant influence on the trend analysis of aerosols, we introduce a weighted least squares regression depending on two weights: (1) monthly standard deviation and (2) Number of Observations (NO) per month. Temporal increase of FAOTs prevails over regions dominated by emerging economy or slash-burn agriculture in East Asia and South Africa. On the other hand, insignificant or negative trends for FAOTs are detected over Western Europe and North America. Over desert regions, both increase and decrease of CAOTs are observed depending on meteorological conditions.

scholarly journals Trend analysis of aerosol optical thickness and Ångström exponent derived from the global AERONET spectral observations

2012 ◽  
Vol 5 (6) ◽  
pp. 1271-1299 ◽  
Author(s):  
J. Yoon ◽  
W. von Hoyningen-Huene ◽  
A. A. Kokhanovsky ◽  
M. Vountas ◽  
J. P. Burrows
Keyword(s):  
Trend Analysis ◽  
Optical Thickness ◽  
Weighted Least Squares ◽  
Temporal Trends ◽  
Aerosol Optical Thickness ◽  
Anthropogenic Aerosols ◽  
Angstrom Exponent ◽  
Ångström Exponent ◽  
Ångstrom Exponent

Abstract. Regular aerosol observations based on well-calibrated instruments have led to a better understanding of the aerosol radiative budget on Earth. In recent years, these instruments have played an important role in the determination of the increase of anthropogenic aerosols by means of long-term studies. Only few investigations regarding long-term trends of aerosol optical characteristics (e.g. aerosol optical thickness (AOT) and Ångström exponent (ÅE)) have been derived from ground-based observations. This paper aims to derive and discuss linear trends of AOT (440, 675, 870, and 1020 nm) and ÅE (440–870 nm) using AErosol RObotic NETwork (AERONET) level 2.0 spectral observations. Additionally, temporal trends of coarse- and fine-mode dominant AOTs (CdAOT and FdAOT) have been estimated by applying an aerosol classification based on accurate ÅE and Ångström exponent difference (ÅED). In order to take into account the fact that cloud disturbance is having a significant influence on the trend analysis of aerosols, we introduce a weighted least squares regression depending on two weights: (1) monthly standard deviation (σt) and (2) number of observations per month (nt). Temporal increase of FdAOTs (440 nm) prevails over newly industrializing countries in East Asia (weighted trends; +6.23% yr−1 at Beijing) and active agricultural burning regions in South Africa (+1.89% yr−1 at Mongu). On the other hand, insignificant or negative trends for FdAOTs are detected over Western Europe (+0.25% yr−1 at Avignon and −2.29% yr−1 at Ispra) and North America (−0.52% yr−1 for GSFC and −0.01% yr−1 at MD_Science_Center). Over desert regions, both increase and decrease of CdAOTs (+3.37% yr−1 at Solar_Village and −1.18% yr−1 at Ouagadougou) are observed depending on meteorological conditions.

scholarly journals Some considerations about Ångström exponent distributions

2007 ◽  
Vol 7 (4) ◽  
pp. 12781-12805 ◽  
Author(s):  
F. Wagner ◽  
A. M. Silva
Keyword(s):  
Relative Error ◽  
Simulation Study ◽  
Optical Thickness ◽  
Error Distribution ◽  
Aerosol Optical Thickness ◽  
Frequency Of Occurrence ◽  
Angstrom Exponent ◽  
Ångström Exponent ◽  
Ångstrom Exponent

Abstract. A simulation study has been performed in order to show the influence of the aerosol optical thickness (AOT) distribution together with the corresponding error distribution on the resulting Ångström exponent (AE) distribution. It will be shown that the Ångström exponent frequency of occurrence distribution is only normal distributed when the relative error at the two wavelengths used for estimation of the Ångström exponent is the same. In all other cases a shift of the maximum of the AE-distribution will occur. It will be demonstrated that the Ångström exponent (or the maximum of an AE distribution) will be systematically over- or underestimated depending on whether the relative error of the shorter wavelength is larger or smaller compared with the relative error of the longer wavelength. In such cases the AE distribution are also skewed.

scholarly journals From a polar to a marine environment: has the changing Arctic led to a shift in aerosol light scattering properties?

2020 ◽  
Author(s):  
Dominic Heslin-Rees ◽  
Maria Burgos ◽  
Hans-Christen Hansson ◽  
Radovan Krejci ◽  
Johan Ström ◽  
...  
Keyword(s):  
Optical Properties ◽  
Light Scattering ◽  
Sea Ice ◽  
Trend Analysis ◽  
The Arctic ◽  
Aerosol Optical Properties ◽  
Angstrom Exponent ◽  
Ångström Exponent ◽  
Ångstrom Exponent

Abstract. The study of long-term trends in aerosol optical properties is an important task to understand the underlying aerosol processes influencing the change of climate. The Arctic, as the place where climate change manifests most, is an especially sensitive region of the world. Within this work, we use a unique long-term data record of key aerosol optical properties from Zeppelin observatory, Svalbard, to ask the question of whether the environmental changes of the last two decades in the Arctic are reflected in the observations. We perform a trend analysis of the measured particle light scattering and backscattering coefficients and the derived scattering Ångström exponent and hemispheric backscattering fraction. In contrast to previous studies, the effect of in-cloud scavenging and potential sampling losses at the site is taken explicitly into account in the trend analysis. The analysis is combined with a back trajectory analysis and satellite-derived sea ice data, to support the interpretation of the observed trends. We find that the optical properties of aerosol particles have undergone clear and significant changes in the past two decades. The scattering Angström exponent and the particle light scattering coefficient exhibit statistically significant decreasing of between −4.9 and −6.3 % per year (using wavelengths of λ = 450 and 550 nm) and increasing trends of between 2.3 and 2.9 % per year (at a wavelength of λ = 550 nm), respectively. The magnitudes of the trends vary depending on the season. These trends indicate a shift to an aerosol dominated more by coarse-mode particles, most likely the result of increases in the relative amount of sea spray aerosol. We show that changes in air mass circulation patterns, specifically an increase in air masses from the south-west, are responsible for the shift in aerosol optical properties, while the decrease of Arctic sea ice in the last two decades had only a marginal influence on the observed trends.

scholarly journals Cloud processing, cloud evaporation and Angström exponent

2009 ◽  
Vol 9 (1) ◽  
pp. 71-80 ◽  
Author(s):  
G.-J. Roelofs ◽  
V. Kamphuis
Keyword(s):  
Relative Humidity ◽  
Optical Thickness ◽  
Aerosol Optical Thickness ◽  
Relative Dispersion ◽  
Cloud Processing ◽  
Angstrom Exponent ◽  
Ambient Relative Humidity ◽  
Coarse Mode ◽  
Ångström Exponent ◽  
Ångstrom Exponent

Abstract. With a cloud parcel model we investigate how cloud processing and cloud evaporation modify the size distribution and the Angström exponent of an aerosol population. Our study provides a new explanation for the observed variability of the aerosol optical thickness and Angström exponent in the vicinity of clouds. Cloud processing causes a decrease of aerosol particle concentrations, relatively most efficiently in the coarse mode, and reduces the relative dispersion of the aerosol distribution. As a result the Angström exponent of the aerosol increases. The Angström exponent is very sensitive for changes in relative humidity during cloud evaporation, especially between 90% and 100%. In addition, kinetic limitations delay evaporation of relatively large cloud drops, especially in clean and mildly polluted environments where the coarse mode fraction is relatively large. This hampers a direct relation between the aerosol optical thickness, the Angström exponent and the ambient relative humidity, which may severely complicate interpretation of these parameters in terms of aerosol properties, such as the fine mode fraction.

scholarly journals From a polar to a marine environment: has the changing Arctic led to a shift in aerosol light scattering properties?

2020 ◽  
Vol 20 (21) ◽  
pp. 13671-13686
Author(s):  
Dominic Heslin-Rees ◽  
Maria Burgos ◽  
Hans-Christen Hansson ◽  
Radovan Krejci ◽  
Johan Ström ◽  
...  
Keyword(s):  
Optical Properties ◽  
Light Scattering ◽  
Sea Ice ◽  
Trend Analysis ◽  
The Arctic ◽  
Aerosol Optical Properties ◽  
Angstrom Exponent ◽  
Ångström Exponent ◽  
Ångstrom Exponent

Abstract. The study of long-term trends in aerosol optical properties is an important task to understand the underlying aerosol processes influencing the change of climate. The Arctic, as the place where climate change manifests most, is an especially sensitive region of the world. Within this work, we use a unique long-term data record of key aerosol optical properties from the Zeppelin Observatory, Svalbard, to ask the question of whether the environmental changes of the last 2 decades in the Arctic are reflected in the observations. We perform a trend analysis of the measured particle light scattering and backscattering coefficients and the derived scattering Ångström exponent and hemispheric backscattering fraction. In contrast to previous studies, the effect of in-cloud scavenging and of potential sampling losses at the site are taken explicitly into account in the trend analysis. The analysis is combined with a back trajectory analysis and satellite-derived sea ice data to support the interpretation of the observed trends. We find that the optical properties of aerosol particles have undergone clear and significant changes in the past 2 decades. The scattering Ångström exponent exhibits statistically significant decreasing of between −4.9 % yr−1 and −6.5 % yr−1 (using wavelengths of λ=450 and 550 nm), while the particle light scattering coefficient exhibits statistically significant increasing trends of between 2.6 % yr−1 and 2.9 % yr−1 (at a wavelength of λ=550 nm). The magnitudes of the trends vary depending on the season. These trends indicate a shift to an aerosol dominated more by coarse-mode particles, most likely the result of increases in the relative amount of sea spray aerosol. We show that changes in air mass circulation patterns, specifically an increase in air masses from the south-west, are responsible for the shift in aerosol optical properties, while the decrease of Arctic sea ice in the last 2 decades only had a marginal influence on the observed trends.

scholarly journals Climatology of aerosol optical properties in Northern Norway and Svalbard

2012 ◽  
Vol 5 (5) ◽  
pp. 7619-7640 ◽  
Author(s):  
Y.-C. Chen ◽  
B. Hamre ◽  
Ø Frette ◽  
J. J. Stamnes
Keyword(s):  
Optical Thickness ◽  
Mean Value ◽  
Aerosol Optical Thickness ◽  
Aerosol Size Distribution ◽  
Mean Values ◽  
Northern Norway ◽  
Angstrom Exponent ◽  
Ångström Exponent ◽  
Arctic Area ◽  
Ångstrom Exponent

Abstract. We present comparisons between estimates of the aerosol optical thickness and the Ångström exponent in Northern Norway and Svalbard based on data from AERONET stations at Andenes (69° N, 16° E, 379 m altitude) and Hornsund (77° N, 15° E, 10 m altitude) for the period 2008–2010. The three-year annual mean values for the aerosol optical thickness at 500 nm τ(500) at Andenes and Hornsund were 0.11 and 0.10, respectively. At Hornsund, there was less variation of the monthly mean value of τ(500) than at Andenes. The annual mean values of the Ångström exponent α at Andenes and Hornsund were 1.18 and 1.37, respectively. At Andenes and Hornsund α was found to be larger than 1.0 in 68% and 93% of the observations, respectively, indicating that fine-mode particles were dominating at both sites. Both sites had a similar seasonal variation of the aerosol size distribution although one site is in an Arctic area while the other site is in a sub-arctic area.

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