Short- and long-term variability of spectral solar UV irradiance at Thessaloniki, Greece: effects of changes in aerosols, total ozone and clouds
In this study, we discuss the short- and the long-term variability of spectral UV irradiance at Thessaloniki, Greece, using a long, quality-controlled data set from two Brewer spectrophotometers. Long-term changes in spectral UV irradiance at 307.5, 324 and 350 nm for the period 1994–2014 are pr...
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doaj-09c42808c42d4157a7f2ab03832c69ed2020-11-24T22:34:41ZengCopernicus PublicationsAtmospheric Chemistry and Physics1680-73161680-73242016-03-01162493250510.5194/acp-16-2493-2016Short- and long-term variability of spectral solar UV irradiance at Thessaloniki, Greece: effects of changes in aerosols, total ozone and cloudsI. Fountoulakis0A. F. Bais1K. Fragkos2C. Meleti3K. Tourpali4M. M. Zempila5M. M. Zempila6Aristotle University of Thessaloniki, Laboratory of Atmospheric Physics, Thessaloniki, GreeceAristotle University of Thessaloniki, Laboratory of Atmospheric Physics, Thessaloniki, GreeceAristotle University of Thessaloniki, Laboratory of Atmospheric Physics, Thessaloniki, GreeceAristotle University of Thessaloniki, Laboratory of Atmospheric Physics, Thessaloniki, GreeceAristotle University of Thessaloniki, Laboratory of Atmospheric Physics, Thessaloniki, GreeceAristotle University of Thessaloniki, Laboratory of Atmospheric Physics, Thessaloniki, Greecenow at: Natural Resource Ecology Laboratory, Colorado State University, Fort Collins, USAIn this study, we discuss the short- and the long-term variability of spectral UV irradiance at Thessaloniki, Greece, using a long, quality-controlled data set from two Brewer spectrophotometers. Long-term changes in spectral UV irradiance at 307.5, 324 and 350 nm for the period 1994–2014 are presented for different solar zenith angles and discussed in association with changes in total ozone column (TOC), aerosol optical depth (AOD) and cloudiness observed in the same period. Positive changes in annual mean anomalies of UV irradiance, ranging from 2 to 6 % per decade, have been detected both for clear- and all-sky conditions. The changes are generally greater for larger solar zenith angles and for shorter wavelengths. For clear-skies, these changes are, in most cases, statistically significant at the 95 % confidence limit. Decreases in the aerosol load and weakening of the attenuation by clouds lead to increases in UV irradiance in the summer, of 7–9 % per decade for 64° solar zenith angle. The increasing TOC in winter counteracts the effect of decreasing AOD for this particular season, leading to small, statistically insignificant, negative long-term changes in irradiance at 307.5 nm. Annual mean UV irradiance levels are increasing from 1994 to 2006 and remain relatively stable thereafter, possibly due to the combined changes in the amount and optical properties of aerosols. However, no statistically significant corresponding turning point has been detected in the long-term changes of AOD. The absence of signatures of changes in AOD in the short-term variability of irradiance in the UV-A may have been caused by changes in the single scattering albedo of aerosols, which may counteract the effects of changes in AOD on irradiance. The anti-correlation between the year-to-year variability of the irradiance at 307.5 nm and TOC is clear and becomes clearer as the AOD decreases.https://www.atmos-chem-phys.net/16/2493/2016/acp-16-2493-2016.pdf |
collection |
DOAJ |
language |
English |
format |
Article |
sources |
DOAJ |
author |
I. Fountoulakis A. F. Bais K. Fragkos C. Meleti K. Tourpali M. M. Zempila M. M. Zempila |
spellingShingle |
I. Fountoulakis A. F. Bais K. Fragkos C. Meleti K. Tourpali M. M. Zempila M. M. Zempila Short- and long-term variability of spectral solar UV irradiance at Thessaloniki, Greece: effects of changes in aerosols, total ozone and clouds Atmospheric Chemistry and Physics |
author_facet |
I. Fountoulakis A. F. Bais K. Fragkos C. Meleti K. Tourpali M. M. Zempila M. M. Zempila |
author_sort |
I. Fountoulakis |
title |
Short- and long-term variability of spectral solar UV irradiance at Thessaloniki, Greece: effects of changes in aerosols, total ozone and clouds |
title_short |
Short- and long-term variability of spectral solar UV irradiance at Thessaloniki, Greece: effects of changes in aerosols, total ozone and clouds |
title_full |
Short- and long-term variability of spectral solar UV irradiance at Thessaloniki, Greece: effects of changes in aerosols, total ozone and clouds |
title_fullStr |
Short- and long-term variability of spectral solar UV irradiance at Thessaloniki, Greece: effects of changes in aerosols, total ozone and clouds |
title_full_unstemmed |
Short- and long-term variability of spectral solar UV irradiance at Thessaloniki, Greece: effects of changes in aerosols, total ozone and clouds |
title_sort |
short- and long-term variability of spectral solar uv irradiance at thessaloniki, greece: effects of changes in aerosols, total ozone and clouds |
publisher |
Copernicus Publications |
series |
Atmospheric Chemistry and Physics |
issn |
1680-7316 1680-7324 |
publishDate |
2016-03-01 |
description |
In this study, we discuss the short- and the long-term variability of
spectral UV irradiance at Thessaloniki, Greece, using a long,
quality-controlled data set from two Brewer spectrophotometers. Long-term
changes in spectral UV irradiance at 307.5, 324 and 350 nm for the period
1994–2014 are presented for different solar zenith angles and discussed in
association with changes in total ozone column (TOC), aerosol optical depth
(AOD) and cloudiness observed in the same period. Positive changes in annual
mean anomalies of UV irradiance, ranging from 2 to 6 % per decade, have
been detected both for clear- and all-sky conditions. The changes are
generally greater for larger solar zenith angles and for shorter wavelengths.
For clear-skies, these changes are, in most cases, statistically significant
at the 95 % confidence limit. Decreases in the aerosol load and weakening
of the attenuation by clouds lead to increases in UV irradiance in the
summer, of 7–9 % per decade for 64° solar zenith angle. The
increasing TOC in winter counteracts the effect of decreasing AOD for this
particular season, leading to small, statistically insignificant, negative
long-term changes in irradiance at 307.5 nm. Annual mean UV irradiance
levels are increasing from 1994 to 2006 and remain relatively stable
thereafter, possibly due to the combined changes in the amount and optical
properties of aerosols. However, no statistically significant corresponding
turning point has been detected in the long-term changes of AOD. The absence
of signatures of changes in AOD in the short-term variability of irradiance
in the UV-A may have been caused by changes in the single scattering albedo
of aerosols, which may counteract the effects of changes in AOD on
irradiance. The anti-correlation between the year-to-year variability of the
irradiance at 307.5 nm and TOC is clear and becomes clearer as the AOD
decreases. |
url |
https://www.atmos-chem-phys.net/16/2493/2016/acp-16-2493-2016.pdf |
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