scholarly journals Variability and trends of the surface solar spectral ultraviolet irradiance in Italy: a possible influence of lower and upper stratospheric ozone trends

2021 ◽  
Author(s):  
Ilias Fountoulakis ◽  
Henri Diémoz ◽  
Anna Maria Siani ◽  
Alcide di Sarra ◽  
Daniela Meloni ◽  
...  
Keyword(s):  
Total Ozone ◽  
Stratospheric Ozone ◽  
Additional Indication ◽  
Uv Irradiance ◽  
Long Term Changes ◽  
Ozone Trends ◽  
Ultraviolet Irradiance ◽  
Solar Uv Irradiance ◽  
Increasing Trends

Abstract. In this study the short- and long-term variability of the surface spectral solar ultraviolet (UV) irradiance are investigated over Italy using high quality ground based measurements from three sites located at quite different environmental conditions, and covering the full latitudinal extent of the Italian territory: Aosta (45.7° N, 7.4°  E, 570 m a.s.l.), Rome (41.9° N, 12.5° E, 75 m a.s.l.), and Lampedusa (35.5° N, 12.6° E, 50 m a.s.l.). The variability of the irradiances at 307.5 nm, 324 nm, and of the ratio between the 307.5 nm and the 324 nm irradiances were investigated with respect to the corresponding variability in total ozone and the geopotential height at 250 hPa (GPH). The study was performed for two periods: 2006–2020 for all stations, and 1996–2020 only for Rome. A statistically significant correlation between the GPH and total ozone monthly anomalies was found for all stations and all seasons of the year. A corresponding statistically significant correlation was also found in most cases between the GPH and the 307.5 nm irradiance monthly anomalies. The correlation between GPH anomalies at different sites was statistically significant, possibly explaining the strong and significant correlation between the total ozone monthly anomalies at the three sites. A statistically significant decrease of total ozone, of ~0.1 %/year was found for Rome for the period 1996–2020, which however did not induce increasing trends in irradiance at 307.5 nm (neither increasing trends in the ratio between the 307.5 nm and the 324 nm irradiances) at SZA = 67°. Further analyses revealed positive trends in the ratio and the 307.5 nm irradiance at smaller solar zenith angles (SZA), which can be attributed to the fact that total ozone decrease is driven by a decrease in the lower stratosphere while upper stratospheric ozone increases, and the effect of changes of upper stratospheric ozone becoming disproportionately larger for increasing SZA. It was also showed that long-term changes in total ozone follow changes in GPH, which is an additional indication that negative trends in total ozone are mainly driven by changes in lower stratospheric ozone. An anti-correlation between the GPH long-term changes and total ozone was also evident for all stations in 2006–2020. Positive trends in UV irradiance for this latter period which were possibly driven by changes in clouds and/or aerosols were found for Rome and Aosta. This study clearly points out the significance of dynamical processes which take place in the troposphere for the variability of total ozone and surface solar UV irradiance.

scholarly journals Variability and trends in surface solar spectral ultraviolet irradiance in Italy: on the influence of geopotential height and lower-stratospheric ozone

2021 ◽  
Vol 21 (24) ◽  
pp. 18689-18705
Author(s):  
Ilias Fountoulakis ◽  
Henri Diémoz ◽  
Anna Maria Siani ◽  
Alcide di Sarra ◽  
Daniela Meloni ◽  
...  
Keyword(s):  
Geopotential Height ◽  
Total Ozone ◽  
Stratospheric Ozone ◽  
Extended Period ◽  
Spectral Irradiance ◽  
Positive Trend ◽  
Uv Irradiance ◽  
Ultraviolet Irradiance ◽  
Solar Uv Irradiance

Abstract. The short- and long-term variability of the surface spectral solar ultraviolet (UV) irradiance is investigated across Italy using high-quality ground-based measurements from three locations: Aosta (45.7∘ N, 7.4∘ E, 570 m a.s.l.), Rome (41.9∘ N, 12.5∘ E, 15 75 m a.s.l.), and Lampedusa (35.5∘ N, 12.6∘ E, 50 m a.s.l.). The three sites are characterized by different environmental conditions and represent almost the full latitudinal extent of the Italian territory. Data of two periods were analysed: 2006–2020 (all sites) and 1996–2020 (Rome only). The main objective of this study is to quantify the effect of the geopotential height (GPH) at 250 hPa on total ozone, and spectral irradiance at 307.5 and 324 nm. We first show that monthly anomalies in GPH, total ozone, and spectral irradiances are correlated amongst the three sites, suggesting that Italy is often affected by the same synoptical weather systems. We further find statistically significant anticorrelations between GPH and monthly anomalies in total ozone for all stations and months. Conversely, we identify positive correlations between GPH and monthly anomalies in spectral irradiance at 307.5 nm for most months. The influence of GPH on short-term variability also hold for long-term trends. For example, long-term changes in total ozone over the period 2006–2020 were associated with changes in GPH for all stations. This suggests that observed negative trends in total ozone were mainly driven by changes in lower-stratospheric ozone as upper-stratospheric ozone was increasing over this period. For several months of the year, positive trends in UV irradiance were observed, and we found that these trends were predominantly caused by changes in clouds and/or aerosols instead of total ozone. For the longer period of 1996–2020, a statistically significant annualized decrease in total ozone of ∼ 0.1 % per year was identified for Rome and could subsequently be attributed to decreasing lower-stratospheric ozone. While positive trends in spectral irradiance at 307.5 nm were observed for several months of this extended period, the negative trend in total ozone did not lead to a positive trend in the spectral irradiance at 307.5 nm in the deseasonalized data. Our study provides evidence that dynamical processes taking place in the troposphere lead to significant variability in total ozone and surface solar UV irradiance.

scholarly journals Short- and long-term variability of spectral solar UV irradiance at Thessaloniki, Greece: effects of changes in aerosols, total ozone and clouds

2016 ◽  
Vol 16 (4) ◽  
pp. 2493-2505 ◽  
Author(s):  
Ilias Fountoulakis ◽  
Alkiviadis F. Bais ◽  
Konstantinos Fragkos ◽  
Charickleia Meleti ◽  
Kleareti Tourpali ◽  
...  
Keyword(s):  
Total Ozone ◽  
Single Scattering ◽  
Data Set ◽  
Uv Irradiance ◽  
Long Term Changes ◽  
Solar Uv ◽  
Short And Long Term ◽  
Solar Uv Irradiance ◽  
Sky Conditions

Abstract. 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.

scholarly journals Short- and long-term variability of spectral solar UV irradiance at Thessaloniki, Greece: effects of changes in aerosols, total ozone and clouds

2015 ◽  
Vol 15 (24) ◽  
pp. 35753-35785
Author(s):  
I. Fountoulakis ◽  
A. F. Bais ◽  
K. Fragkos ◽  
C. Meleti ◽  
K. Tourpali ◽  
...  
Keyword(s):  
Total Ozone ◽  
Single Scattering ◽  
Data Set ◽  
Uv Irradiance ◽  
Long Term Changes ◽  
Solar Uv ◽  
Short And Long Term ◽  
Solar Uv Irradiance ◽  
Sky Conditions

Abstract. 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 to 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. Trends in irradiance during the two sub-periods are not discussed, because the length of the two datasets is too short for deriving statistically significant estimates. 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.

scholarly journals Spectral UV measurements in Austria from 1994 to 2006: investigations of short- and long-term changes

2008 ◽  
Vol 8 (23) ◽  
pp. 7033-7043 ◽  
Author(s):  
S. Simic ◽  
P. Weihs ◽  
A. Vacek ◽  
H. Kromp-Kolb ◽  
M. Fitzka
Keyword(s):  
Confidence Level ◽  
Total Ozone ◽  
Sunshine Duration ◽  
Trend Test ◽  
Total Column Ozone ◽  
Clear Sky ◽  
Uv Irradiance ◽  
Long Term Changes ◽  
Short And Long Term

Abstract. The influence of variability of atmospheric parameters on short- and long-term changes of spectral UV irradiance measured at the Sonnblick observatory (47.03° N, 12.57° E, 3106 m) during the period from 1994 to 2006 is studied. Measurements were performed with the Brewer #093 single-monochromator spectrophotometer and with a Bentham DM 150 spectroradiometer (double-monochromator). The influence of ozone, albedo, snowline and clouds on UV variability is evaluated for each parameter separately using 10-year climatology. It is found that the effect of total ozone on short-term variability of UV irradiance at 305 nm can be more than 200% and on average more than 50%. Clouds can cause variability of 150% or more and on average 35%. Variability caused by albedo reaches a maximum of 32% in April (6% on average). In summer and autumn, total ozone and clouds strongly influence the variability of UV radiation, whereas in winter and spring ozone has the more pronounced effect. A decrease in snowline height from 3000 m to 800 m a.s.l. enhances the UV irradiance by a factor of 1.24 for clear sky conditions and by a factor of 1.7 for 8/8 cloud cover. Long-term trends are investigated for the time period from 1994 to 2006 based on clear-sky measurements, using the non-parametric Mann-Kendall trend test. Significant downward trends (99% confidence level) are found for solar zenith angle 55° at wavelengths from 305 nm to 324 nm and erythemally weighted irradiance according to CIE, which are caused by an increase in sunshine duration during periods of high total column ozone. Significant trends (90% confidence level) were also found for other combinations of wavelength and SZA.

scholarly journals Solar UV Irradiance in a Changing Climate: Trends in Europe and the Significance of Spectral Monitoring in Italy

Environments ◽  
2019 ◽  
Vol 7 (1) ◽  
pp. 1 ◽  
Author(s):  
Ilias Fountoulakis ◽  
Henri Diémoz ◽  
Anna-Maria Siani ◽  
Gudrun Laschewski ◽  
Gianluca Filippa ◽  
...  
Keyword(s):  
Total Ozone ◽  
Surface Albedo ◽  
Forecast Model ◽  
Urban Site ◽  
Climate Trends ◽  
Ozone Monitoring Instrument ◽  
Uv Index ◽  
Uv Irradiance ◽  
Solar Uv Irradiance

Review of the existing bibliography shows that the direction and magnitude of the long-term trends of UV irradiance, and their main drivers, vary significantly throughout Europe. Analysis of total ozone and spectral UV data recorded at four European stations during 1996–2017 reveals that long-term changes in UV are mainly driven by changes in aerosols, cloudiness, and surface albedo, while changes in total ozone play a less significant role. The variability of UV irradiance is large throughout Italy due to the complex topography and large latitudinal extension of the country. Analysis of the spectral UV records of the urban site of Rome, and the alpine site of Aosta reveals that differences between the two sites follow the annual cycle of the differences in cloudiness and surface albedo. Comparisons between the noon UV index measured at the ground at the same stations and the corresponding estimates from the Deutscher Wetterdienst (DWD) forecast model and the ozone monitoring instrument (OMI)/Aura observations reveal differences of up to 6 units between individual measurements, which are likely due to the different spatial resolution of the different datasets, and average differences of 0.5–1 unit, possibly related to the use of climatological surface albedo and aerosol optical properties in the retrieval algorithms.

scholarly journals Solar UV Irradiance in a Changing Climate: Trends in Europe and the Significance of Spectral Monitoring in Italy

2019 ◽  
Author(s):  
Ilias Fountoulakis ◽  
Henri Diémoz ◽  
Annamaria Siani ◽  
Gudrun Laschewski ◽  
Gianluca Filippa ◽  
...  
Keyword(s):  
Total Ozone ◽  
Surface Albedo ◽  
Forecast Model ◽  
Urban Site ◽  
Climate Trends ◽  
Uv Index ◽  
Uv Irradiance ◽  
Country Analysis ◽  
Solar Uv Irradiance

Review of the existing bibliography shows that the direction and magnitude of the long-term trends of UV irradiance, and their main drivers, vary significantly throughout Europe. Analysis of total ozone and spectral UV data recorded at four European stations during 1996 – 2017 reveals that long-term changes in UV are mainly driven by changes in aerosols, cloudiness, and surface albedo, while changes in total ozone play a less significant role. The variability of UV irradiance is large throughout Italy due to the complex topography and large latitudinal extension of the country. Analysis of the spectral UV records of the urban site of Rome, and the alpine site of Aosta reveals that differences between the two sites follow the annual cycle of the differences in cloudiness and surface albedo. Comparisons between the noon UV index measured at the ground at the same stations and the corresponding estimates from the DWD forecast model and OMI/Aura observations reveal differences of up to 6 units between individual measurements, which are likely due to the different spatial resolution of the different datasets, and average differences of 0.5 – 1 unit, possibly related to the use of climatological surface albedo and aerosol optical properties in the retrieval algorithms.

scholarly journals Variability of the total ozone trend over Europe for the period 1950–2004 derived from reconstructed data

2008 ◽  
Vol 8 (11) ◽  
pp. 2847-2857 ◽  
Author(s):  
J. W. Krzyścin ◽  
J. L. Borkowski
Keyword(s):  
Total Ozone ◽  
A Priori ◽  
Smooth Curve ◽  
Ozone Level ◽  
Svalbard Archipelago ◽  
Small Areas ◽  
Ozone Data ◽  
Curve Fit ◽  
Long Term Changes

Abstract. The total ozone data over Europe are available for only few ground-based stations in the pre-satellite era disallowing examination of the spatial trend variability over the whole continent. A need of having gridded ozone data for a trend analysis and input to radiative transfer models stimulated a reconstruction of the daily ozone values since January 1950. Description of the reconstruction model and its validation were a subject of our previous paper. The data base used was built within the objectives of the COST action 726 "Long-term changes and climatology of UV radiation over Europe". Here we focus on trend analyses. The long-term variability of total ozone is discussed using results of a flexible trend model applied to the reconstructed total ozone data for the period 1950–2004. The trend pattern, which comprises both anthropogenic and "natural" component, is not a priori assumed but it comes from a smooth curve fit to the zonal monthly means and monthly grid values. The ozone long-term changes are calculated separately for cold (October–next year April) and warm (May–September) seasons. The confidence intervals for the estimated ozone changes are derived by the block bootstrapping. The statistically significant negative trends are found almost over the whole Europe only in the period 1985–1994. Negative trends up to −3% per decade appeared over small areas in earlier periods when the anthropogenic forcing on the ozone layer was weak . The statistically positive trends are found only during warm seasons 1995–2004 over Svalbard archipelago. The reduction of ozone level in 2004 relative to that before the satellite era is not dramatic, i.e., up to ~−5% and ~−3.5% in the cold and warm subperiod, respectively. Present ozone level is still depleted over many popular resorts in southern Europe and northern Africa. For high latitude regions the trend overturning could be inferred in last decade (1995–2004) as the ozone depleted areas are not found there in 2004 in spite of substantial ozone depletion in the period 1985–1994.

scholarly journals Reconciling differences in stratospheric ozone composites

2017 ◽  
Vol 17 (20) ◽  
pp. 12269-12302 ◽  
Author(s):  
William T. Ball ◽  
Justin Alsing ◽  
Daniel J. Mortlock ◽  
Eugene V. Rozanov ◽  
Fiona Tummon ◽  
...  
Keyword(s):  
Time Series ◽  
Likelihood Function ◽  
Stratospheric Ozone ◽  
Gaussian Mixture ◽  
Robust Estimate ◽  
Mixture Density ◽  
Source Data ◽  
Ozone Trends ◽  
Decadal Trend

Abstract. Observations of stratospheric ozone from multiple instruments now span three decades; combining these into composite datasets allows long-term ozone trends to be estimated. Recently, several ozone composites have been published, but trends disagree by latitude and altitude, even between composites built upon the same instrument data. We confirm that the main causes of differences in decadal trend estimates lie in (i) steps in the composite time series when the instrument source data changes and (ii) artificial sub-decadal trends in the underlying instrument data. These artefacts introduce features that can alias with regressors in multiple linear regression (MLR) analysis; both can lead to inaccurate trend estimates. Here, we aim to remove these artefacts using Bayesian methods to infer the underlying ozone time series from a set of composites by building a joint-likelihood function using a Gaussian-mixture density to model outliers introduced by data artefacts, together with a data-driven prior on ozone variability that incorporates knowledge of problems during instrument operation. We apply this Bayesian self-calibration approach to stratospheric ozone in 10° bands from 60° S to 60° N and from 46 to 1 hPa (∼ 21–48 km) for 1985–2012. There are two main outcomes: (i) we independently identify and confirm many of the data problems previously identified, but which remain unaccounted for in existing composites; (ii) we construct an ozone composite, with uncertainties, that is free from most of these problems – we call this the BAyeSian Integrated and Consolidated (BASIC) composite. To analyse the new BASIC composite, we use dynamical linear modelling (DLM), which provides a more robust estimate of long-term changes through Bayesian inference than MLR. BASIC and DLM, together, provide a step forward in improving estimates of decadal trends. Our results indicate a significant recovery of ozone since 1998 in the upper stratosphere, of both northern and southern midlatitudes, in all four composites analysed, and particularly in the BASIC composite. The BASIC results also show no hemispheric difference in the recovery at midlatitudes, in contrast to an apparent feature that is present, but not consistent, in the four composites. Our overall conclusion is that it is possible to effectively combine different ozone composites and account for artefacts and drifts, and that this leads to a clear and significant result that upper stratospheric ozone levels have increased since 1998, following an earlier decline.

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