Bulletin of the American Meteorological Society, 2017
Editor’s note: For easy download the posted pdf of the State of the Climate for 2017 is a low-res... more Editor’s note: For easy download the posted pdf of the State of the Climate for 2017 is a low-resolution file. A high-resolution copy of the report is available by clicking here. Please be patient as it may take a few minutes for the high-resolution file to download.
Remote Sensing of Clouds and the Atmosphere XI, 2006
Multiband filter radiometers (MBFRs) are extensively used in national networks for UV climate mon... more Multiband filter radiometers (MBFRs) are extensively used in national networks for UV climate monitoring and information to the public about the potential risk of solar UV exposure. In order to provide an international, uniform expression of the Global UV index measurements, a harmonized calibration scale is needed. In this paper we present the results of the first international intercomparison of
The Dutch-Finnish Ozone Monitoring Instrument (OMI) on board the NASA EOS Aura spacecraft is a na... more The Dutch-Finnish Ozone Monitoring Instrument (OMI) on board the NASA EOS Aura spacecraft is a nadir viewing spectrometer that measures solar reflected and backscattered light in a selected range of the ultraviolet and visible spectrum. The instrument has a 2600 km wide viewing swath and it is capable of daily, global contiguous mapping. The Finnish Meteorological Institute and NASA Goddard Space Flight Center have developed a surface ultraviolet irradiance algorithm for OMI that produces noontime surface spectral UV irradiance estimates at four wavelengths, noontime erythemal dose rate (UV index), and the erythemal daily dose. The overpass erythemal daily doses derived from OMI data were compared with the daily doses calculated from the ground-based spectral UV measurements from 18 reference instruments. Two alternative methods for the OMI UV algorithm cloud correction were compared: the plane-parallel cloud model method and the method based on Lambertian equivalent reflectivity. The validation results for the two methods showed some differences, but the results do not imply that one method is categorically superior to the other. For flat, snow-free regions with modest loadings of absorbing aerosols or trace gases, the OMI-derived daily erythemal doses have a median overestimation of 0-10%, and some 60 to 80% of the doses are within ±20% from the ground reference. For sites significantly affected by absorbing aerosols or trace gases one expects, and observes, bigger positive bias up to 50%. For high-latitude sites the satellite-derived doses are occasionally up to 50% too small because of unrealistically small climatological surface albedo.
Multiband filter radiometers (MBFRs) are extensively used in national measurement networks for UV... more Multiband filter radiometers (MBFRs) are extensively used in national measurement networks for UV climate monitoring and for informing the public about potential health risks from excessive solar UV exposure. Results from the first international intercomparison of MBFRs, arranged in Oslo in 2005, are presented. Forty-three radiometers of type GUV, NILU-UV, and UVMFR-7 were assembled, representing monitoring stations on several continents. The first objective was to conduct a blind intercomparison of Global UV Index (UVI) processed by the instrument owners. Eleven independent data sets were compared, eight of which agreed with the reference to within ±5% and ten to within ±10%. The second objective was to provide a harmonized calibration scale for all instruments. When this scale was applied, the UVI agreed to within ±5% (2-sigma) for solar zenith angles (SZAs) up to 90°. The results demonstrate that MBFRs provide accurate UVI measurements for realistic sky conditions and a wide range of SZAs, provided the calibration functions are optimized. The harmonized UVI scale is traceable to the European QASUME reference spectroradiometer.
Photochemical & photobiological sciences : Official journal of the European Photochemistry Association and the European Society for Photobiology, Jan 14, 2018
The Environmental Effects Assessment Panel (EEAP) is one of three Panels of experts that inform t... more The Environmental Effects Assessment Panel (EEAP) is one of three Panels of experts that inform the Parties to the Montreal Protocol. The EEAP focuses on the effects of UV radiation on human health, terrestrial and aquatic ecosystems, air quality, and materials, as well as on the interactive effects of UV radiation and global climate change. When considering the effects of climate change, it has become clear that processes resulting in changes in stratospheric ozone are more complex than previously held. Because of the Montreal Protocol, there are now indications of the beginnings of a recovery of stratospheric ozone, although the time required to reach levels like those before the 1960s is still uncertain, particularly as the effects of stratospheric ozone on climate change and vice versa, are not yet fully understood. Some regions will likely receive enhanced levels of UV radiation, while other areas will likely experience a reduction in UV radiation as ozone- and climate-driven c...
The success of the Montreal Protocol in curbing increases in harmful solar ultraviolet (UV) radia... more The success of the Montreal Protocol in curbing increases in harmful solar ultraviolet (UV) radiation at the Earth’s surface has recently been demonstrated. This study also provided evidence that the UV Index (UVI) measured by SUV-100 spectroradiometers at three Antarctic sites (South Pole, Arrival Heights, and Palmer Station) is now decreasing. For example, a significant (95% confidence level) downward trend of −5.5% per decade was reported at Arrival Heights for summer (December through February). However, it was also noted that these measurements are potentially affected by long-term drifts in calibrations of approximately 1% per decade. To address this issue, we have reviewed the chain of calibrations implemented at the three sites between 1996 and 2018 and applied corrections for changes in the scales of spectral irradiance (SoSI) that have occurred over this period (Method 1). This analysis resulted in an upward correction of UVI data measured after 2012 by 1.7% to 1.8%, plus ...
Cover credit: Scientists acquiring measurements of East Antarctic sea ice and snow cover thicknes... more Cover credit: Scientists acquiring measurements of East Antarctic sea ice and snow cover thickness and properties during the 2003 Australian-led ARISE multidisciplinary field experiment. The photo was taken by Rob Massom (Australian Antarctic Division) on
A ground-based ultraviolet (GUV) multi-filter radiometer was set up at Marambio, 64 • S, 56 • W, ... more A ground-based ultraviolet (GUV) multi-filter radiometer was set up at Marambio, 64 • S, 56 • W, Antarctica, in 2017. The instrument continuously measures ultraviolet (UV) radiation, visible (VIS) radiation and photosynthetically active radiation (PAR). The measurements are designed for providing high-quality longterm time series that can be used to assess the impact of global climate change in the Antarctic region. The quality assurance includes regular absolute calibrations and solar comparisons performed at Marambio and at Sodankylä, Finland. The measurements continue observations at Marambio that were performed with (Norwegian Institute for Air Research UV Radiometer (NILU-UV) radiometers between 2000 and 2010 as part of the Antarctic NILU-UV network. These measurements are ideally suited for assessing the effects of the ongoing stratospheric ozone recovery on the ecosystem, as the data products include information on radiation at various wavelengths ranging from UV to VIS so that changes on biologically effective radiation due to ozone can be separated from those due to other factors. Data products include total ozone, photosynthetically active radiation (PAR), visible (VIS) radiation at 555 nm, UV index, UV irradiance at 5 channels, UVB and UVA dose rate and daily dose, and biologically weighted UV dose rate and daily dose, calculated with 10 different action spectra. The data from the last 5 d and the daily maximum UV index time series are plotted and updated daily on the following web
An SUV-150B spectroradiometer for measuring solar ultraviolet (UV) irradiance was installed at Su... more An SUV-150B spectroradiometer for measuring solar ultraviolet (UV) irradiance was installed at Summit, Greenland, in August 2004. Here we compare the initial data from this new location with similar measurements from Barrow, Alaska and South Pole. Measurements of irradiance at 345 nm performed at equivalent solar zenith angles (SZAs) are almost identical at Summit and South Pole. The good agreement can be explained with the similar location of the two sites on high-altitude ice caps with high surface albedo. Clouds have little impact at both sites, but can reduce irradiance at Barrow by more than 75%. Clear-sky measurements at Barrow are smaller than at Summit by 14% in spring and 36% in summer, mostly due to differences in surface albedo and altitude. Comparisons with model calculations indicate that aerosols can reduce clear-sky irradiance at 345 nm by 4-6%; aerosol influence is largest in April. Differences in total ozone at the three sites have a large influence on the UV Index. At South Pole, the UV Index is on average 20-80% larger during the ozone hole period than between January and March. At Summit, total ozone peaks in April and UV Indices in spring are on average 10-25% smaller than in the summer. Maximum UV Indices ever observed at Summit and South Pole are 6.7 and 4.0, respectively. The larger value at Summit is due to the site's lower latitude. For comparable SZAs, average UV Indices measured during October and November at South Pole are 1.9-2.4 times larger than measurements during March and April at Summit. Average UV Indices at Summit are over 50% greater than at Barrow because of the larger cloud influence at Barrow.
The 19 channel rotating shadow band radiometer GUVis-3511 built by Biospherical Instruments is in... more The 19 channel rotating shadow band radiometer GUVis-3511 built by Biospherical Instruments is introduced as an instrument which is able to provide automated ship borne measurements of the direct, diffuse and global spectral irradiance components without a requirement for stabilization. Several direct sun products, including spectral direct beam transmittance, aerosol optical depth, Ångström exponent, and precipitable water can be derived from these observations. The individual steps of the data analysis are described, and the different sources of uncertainty are discussed. The total uncertainty of the observed direct beam transmittances is estimated to be 4.24% at 95% CI for ship borne operation. The calibration is identified as the dominating contribution to the total uncertainty. A comparison of direct beam transmittance with those obtained from a Cimel sun photometer at a land site and a manually operated Microtops II sun photometer on a ship is presented, yielding relative deviations of less than 3% and 4%, on land and on ship, respectively, for most channels and in agreement with our previous uncertainty estimate. These numbers demonstrate that the instrument is well suited for ship borne operation, and the applied methods for motion correction work accurately. Based on spectral direct beam transmittance, aerosol optical depth at 510 nm can be retrieved with an uncertainty of 0.0032 for a 95% CI. Only minor deviations occur due to the different methods used for estimating Rayleigh scattering and gas absorption optical depths, as implemented by AERONET and in our processing. Relying on the cross-calibration of the 940 nm water vapor channel with the Cimel sun photometer, the column amount of precipitable water has been estimated with an uncertainty of ± 0.034 cm. More research is needed to estimate the accuracy of the instrument for low sun (solar zenith angles larger than 70 •) and during periods with strong swell.
the Montreal protocol on Substances that Deplete the ozone Layer has been hailed as the most succ... more the Montreal protocol on Substances that Deplete the ozone Layer has been hailed as the most successful environmental treaty ever (https://www.unenvironment.org/news-and-stories/story/ montreal-protocol-triumph-treaty). Yet, although our main concern about ozone depletion is the subsequent increase in harmful solar UV radiation at the earth's surface, no studies to date have demonstrated its effectiveness in that regard. Here we use long-term UV Index (UVI) data derived from high-quality UV spectroradiometer measurements to demonstrate its success in curbing increases in UV radiation. Without this landmark agreement, UVi values would have increased at mid-latitude locations by approximately 20% between the early 1990s and today and would approximately quadruple at midlatitudes by 2100. In contrast, an analysis of UVI data from multiple clean-air sites shows that maximum daily UVI values have remained essentially constant over the last ~20 years in all seasons, and may even have decreased slightly in the southern hemisphere, especially in Antarctica, where effects of ozone depletion were larger. Reconstructions of the UVi from total ozone data show evidence of increasing UVI levels in the 1980s, but unfortunately, there are no high-quality UV measurements available prior to the early 1990s to confirm these increases with direct observations. Concern about ozone depletion arose primarily because of its potential to increase UV-B radiation, and the consequent effects on health and the environment 1. Observations of unexpected springtime decrease in stratospheric ozone over Antarctica 2-commonly referred to as the "ozone hole"-led to the rapid adoption of the Montreal Protocol on Substances that Deplete the Ozone Layer in 1987 3. It has been shown that without this treaty and its subsequent Amendments and Adjustments, ozone holes would by now also be occurring over the North Pole, resulting in highly elevated UVI in the Arctic 4. Even at mid-latitudes, the UVI would by now have increased markedly, and would more than double at some latitudes by the middle of the 21 st century 5-7. However, due to the success of the Montreal Protocol, ozone decreases appear to have been brought under control 8 , though any effects on surface UV irradiances have not previously been confirmed by measurements. We attempt to redress this issue by using an analysis of long-term UV measurements from instruments that meet the stringent requirements of the Network for the Detection of Atmospheric Composition Change (NDACC, www.ndacc.org).
We calculate the variation of spectral solar irradiance in the umbral shadow of the total solar e... more We calculate the variation of spectral solar irradiance in the umbral shadow of the total solar eclipse of August 21, 2017 and compare it to observations. Starting from the sun's and moon's positions, we derive a realistic profile of the lunar shadow at the top of the atmosphere, including the effect of solar limb darkening. Subsequently, the Monte-Carlo model MYSTIC is used to simulate the transfer of solar radiation through the earth's atmosphere. Among the effects taken into account are the atmospheric state (pressure, temperature), concentrations of major gas constituents and the curvature of the earth, as well as the reflectance and elevation of the surrounding area. We apply the model to the total solar eclipse on August 21, 2017 at a position located in Oregon, where irradiance observations were performed for wavelengths between 306 nm and 1020 nm. The influence of the surface reflectance, the ozone profile and mountains surrounding the observer is investigated. An increased sensitivity during totality is found for the reflectance and topography, compared to non-eclipse conditions. During the eclipse, the irradiance at the surface does not only depend on the total ozone column (TOC) but also the vertical ozone distribution, which in general complicates derivations of the TOC from spectral surface irradiance. The findings are related to an analysis of the prevailing photon path and its difference compared to non-eclipse conditions. Using the most realistic estimate for each parameter, the model is compared to the irradiance observations. During totality, the relative difference between model and observations is less than 10% in the spectral range from 400 nm to 1020 nm. Slightly larger deviations occur in the ultraviolet range below 400 nm and at 665 nm.
Thirty-three years ago, an unprecedented thinning of stratospheric ozone was reported over Antarc... more Thirty-three years ago, an unprecedented thinning of stratospheric ozone was reported over Antarctica 1. In response to concerns about elevated exposure to solar ultraviolet-B radiation (UV-B; wavelengths 280-315 nm) resulting from ozone depletion, the international community mobilized and worked together to understand the causes and find a solution to this dramatic change in Earth's environment. The policy solution that emerged to address this global environmental problem was the 1985 Vienna Convention for the Protection of the Ozone Layer. In this international agreement the United Nations recognized the fundamental importance of preventing the damaging effects of stratospheric ozone depletion, whether on human health or the environment. This convention was followed by the 1987 Montreal Protocol on Substances that Deplete the Ozone Layer with its subsequent amendments, adjustments, and decisions that were negotiated to control the consumption and production of anthropogenic ozone-depleting substances, including chlorofluorocarbons (CFCs). The Montreal Protocol now has the unique distinction of being the only treaty, ever, of any type, ratified by all 197 countries of the United Nations. The Parties to the Montreal Protocol base their decisions on scientific, environmental, technical, and economic information provided by three assessment Panels (Box 1). All three panels provide full assessment reports to the Parties every four years (quadrennial reports) and shorter, periodic updates in the intervening years as needed. The implementation of the Montreal Protocol has successfully prevented the uncontrolled global depletion of the stratospheric ozone layer 2,3. Concentrations of ozonedepleting substances have been declining in the stratosphere since the late 1990s. While significant seasonal ozone depletion over Antarctica has occurred annually since the 1980s (called the "ozone hole"), there have been small, but significant, positive trends in total column ozone in Antarctica in spring over the period 2001-2013. Global mean total ozone has been projected to recover to pre-1980 levels by about the middle of the 21 st century, assuming full compliance to the Montreal Protocol 2. Many of the chemical compounds controlled by the Montreal Protocol are not only involved in depletion of stratospheric ozone, but are also potent greenhouse gases 4. Modeling studies indicate that, in the absence of the Montreal Protocol, global mean temperatures would have risen by more than 2C by 2070, due to the warming effects from ozone-depleting substances alone 5. The adoption of the Kigali Amendment to the Montreal Protocol in 2016 limits the production and consumption of hydrofluorocarbons (HFCs), powerful greenhouse gases that are used as substitutes to ozone-depleting substances. This amendment has further broadened and strengthened the scope of the Montreal Protocol, creating an effective international treaty that not only addresses stratospheric ozone depletion, but is doing more to mitigate global climate change than any other human actions to date 7-10. One of the important reasons for the success of the Montreal Protocol has been its foundation on high quality science, which not only improves our understanding of the causes and mechanisms of ozone depletion, but also of the environmental effects of these atmospheric changes. The Environmental Effects Assessment Panel (EEAP) is specifically charged with providing regular assessments of the state of the science on the environmental effects of ozone depletion and consequent changes in UV radiation at Earth's surface, and the interactive effects of climate change (Box 1 and Fig. 1). Here, we summarize key findings from the most recent EEAP Quadrennial Assessment, and consider the significant policy and societal implications of these environmental effects. We specifically highlight the multiple ways by which the Montreal Protocol is contributing to environmental sustainability and human health and well-being consistent with many of the United Nations Sustainability Goals (Box 2). More in-depth information on ozone depletion and its environmental effects can be found in the full Assessments published by the Ozone Secretariat of the United Nations Environment Programme (https://ozone.unep.org) and elsewhere (Photochemical & Photobiological Sciences journal) 11-17. By focusing on the interactions between stratospheric ozone dynamics, UV radiation, and climate change, the report from the EEAP complements that of the UN's Intergovernmental Panel on Climate Change (IPCC;https://www.ipcc.ch; summarized by Pachauri, et al. 18) to provide a comprehensive assessment on the environmental effects of global changes in Earth's atmosphere.
Solar ultraviolet (UV) irradiances were measured with NILU-UV multichannel radiometers at Ushuaia... more Solar ultraviolet (UV) irradiances were measured with NILU-UV multichannel radiometers at Ushuaia (54 • S) and Marambio (64 • S) between 2000 and 2013. The measurements were part of the Antarctic NILU-UV network, which was started in cooperation between Spain, Argentina and Finland. The erythemally weighted UV irradiance time series of both stations were analysed for the first time. The quality assurance procedures included a travelling reference instrument to transfer the irradiance scale to the stations. The time series were homogenized and high quality measurements were available for the period 2000-2010. During this period UV indices of 11 or more were measured on 5 and 35 days at Marambio and Ushuaia, respectively. At Marambio, the peak daily maximum UV index of 12 and daily doses of around 7 kJ m −2 were measured in November 2007. The highest UV daily doses at both stations were typically around 6 kJ m −2 and occurred when the stations were inside the polar vortex, resulting in very low total ozone amount. At both stations, daily doses in late November could even exceed those in the summer. At Marambio, in some years, also daily doses in October can be as high as those during the summer. At Ushuaia, the peak daily maximum UV index of 13 was measured twice: in November 2003 and 2009. Also during those days, the station of Ushuaia was inside the polar vortex.
Bulletin of the American Meteorological Society, 2017
Editor’s note: For easy download the posted pdf of the State of the Climate for 2017 is a low-res... more Editor’s note: For easy download the posted pdf of the State of the Climate for 2017 is a low-resolution file. A high-resolution copy of the report is available by clicking here. Please be patient as it may take a few minutes for the high-resolution file to download.
Remote Sensing of Clouds and the Atmosphere XI, 2006
Multiband filter radiometers (MBFRs) are extensively used in national networks for UV climate mon... more Multiband filter radiometers (MBFRs) are extensively used in national networks for UV climate monitoring and information to the public about the potential risk of solar UV exposure. In order to provide an international, uniform expression of the Global UV index measurements, a harmonized calibration scale is needed. In this paper we present the results of the first international intercomparison of
The Dutch-Finnish Ozone Monitoring Instrument (OMI) on board the NASA EOS Aura spacecraft is a na... more The Dutch-Finnish Ozone Monitoring Instrument (OMI) on board the NASA EOS Aura spacecraft is a nadir viewing spectrometer that measures solar reflected and backscattered light in a selected range of the ultraviolet and visible spectrum. The instrument has a 2600 km wide viewing swath and it is capable of daily, global contiguous mapping. The Finnish Meteorological Institute and NASA Goddard Space Flight Center have developed a surface ultraviolet irradiance algorithm for OMI that produces noontime surface spectral UV irradiance estimates at four wavelengths, noontime erythemal dose rate (UV index), and the erythemal daily dose. The overpass erythemal daily doses derived from OMI data were compared with the daily doses calculated from the ground-based spectral UV measurements from 18 reference instruments. Two alternative methods for the OMI UV algorithm cloud correction were compared: the plane-parallel cloud model method and the method based on Lambertian equivalent reflectivity. The validation results for the two methods showed some differences, but the results do not imply that one method is categorically superior to the other. For flat, snow-free regions with modest loadings of absorbing aerosols or trace gases, the OMI-derived daily erythemal doses have a median overestimation of 0-10%, and some 60 to 80% of the doses are within ±20% from the ground reference. For sites significantly affected by absorbing aerosols or trace gases one expects, and observes, bigger positive bias up to 50%. For high-latitude sites the satellite-derived doses are occasionally up to 50% too small because of unrealistically small climatological surface albedo.
Multiband filter radiometers (MBFRs) are extensively used in national measurement networks for UV... more Multiband filter radiometers (MBFRs) are extensively used in national measurement networks for UV climate monitoring and for informing the public about potential health risks from excessive solar UV exposure. Results from the first international intercomparison of MBFRs, arranged in Oslo in 2005, are presented. Forty-three radiometers of type GUV, NILU-UV, and UVMFR-7 were assembled, representing monitoring stations on several continents. The first objective was to conduct a blind intercomparison of Global UV Index (UVI) processed by the instrument owners. Eleven independent data sets were compared, eight of which agreed with the reference to within ±5% and ten to within ±10%. The second objective was to provide a harmonized calibration scale for all instruments. When this scale was applied, the UVI agreed to within ±5% (2-sigma) for solar zenith angles (SZAs) up to 90°. The results demonstrate that MBFRs provide accurate UVI measurements for realistic sky conditions and a wide range of SZAs, provided the calibration functions are optimized. The harmonized UVI scale is traceable to the European QASUME reference spectroradiometer.
Photochemical & photobiological sciences : Official journal of the European Photochemistry Association and the European Society for Photobiology, Jan 14, 2018
The Environmental Effects Assessment Panel (EEAP) is one of three Panels of experts that inform t... more The Environmental Effects Assessment Panel (EEAP) is one of three Panels of experts that inform the Parties to the Montreal Protocol. The EEAP focuses on the effects of UV radiation on human health, terrestrial and aquatic ecosystems, air quality, and materials, as well as on the interactive effects of UV radiation and global climate change. When considering the effects of climate change, it has become clear that processes resulting in changes in stratospheric ozone are more complex than previously held. Because of the Montreal Protocol, there are now indications of the beginnings of a recovery of stratospheric ozone, although the time required to reach levels like those before the 1960s is still uncertain, particularly as the effects of stratospheric ozone on climate change and vice versa, are not yet fully understood. Some regions will likely receive enhanced levels of UV radiation, while other areas will likely experience a reduction in UV radiation as ozone- and climate-driven c...
The success of the Montreal Protocol in curbing increases in harmful solar ultraviolet (UV) radia... more The success of the Montreal Protocol in curbing increases in harmful solar ultraviolet (UV) radiation at the Earth’s surface has recently been demonstrated. This study also provided evidence that the UV Index (UVI) measured by SUV-100 spectroradiometers at three Antarctic sites (South Pole, Arrival Heights, and Palmer Station) is now decreasing. For example, a significant (95% confidence level) downward trend of −5.5% per decade was reported at Arrival Heights for summer (December through February). However, it was also noted that these measurements are potentially affected by long-term drifts in calibrations of approximately 1% per decade. To address this issue, we have reviewed the chain of calibrations implemented at the three sites between 1996 and 2018 and applied corrections for changes in the scales of spectral irradiance (SoSI) that have occurred over this period (Method 1). This analysis resulted in an upward correction of UVI data measured after 2012 by 1.7% to 1.8%, plus ...
Cover credit: Scientists acquiring measurements of East Antarctic sea ice and snow cover thicknes... more Cover credit: Scientists acquiring measurements of East Antarctic sea ice and snow cover thickness and properties during the 2003 Australian-led ARISE multidisciplinary field experiment. The photo was taken by Rob Massom (Australian Antarctic Division) on
A ground-based ultraviolet (GUV) multi-filter radiometer was set up at Marambio, 64 • S, 56 • W, ... more A ground-based ultraviolet (GUV) multi-filter radiometer was set up at Marambio, 64 • S, 56 • W, Antarctica, in 2017. The instrument continuously measures ultraviolet (UV) radiation, visible (VIS) radiation and photosynthetically active radiation (PAR). The measurements are designed for providing high-quality longterm time series that can be used to assess the impact of global climate change in the Antarctic region. The quality assurance includes regular absolute calibrations and solar comparisons performed at Marambio and at Sodankylä, Finland. The measurements continue observations at Marambio that were performed with (Norwegian Institute for Air Research UV Radiometer (NILU-UV) radiometers between 2000 and 2010 as part of the Antarctic NILU-UV network. These measurements are ideally suited for assessing the effects of the ongoing stratospheric ozone recovery on the ecosystem, as the data products include information on radiation at various wavelengths ranging from UV to VIS so that changes on biologically effective radiation due to ozone can be separated from those due to other factors. Data products include total ozone, photosynthetically active radiation (PAR), visible (VIS) radiation at 555 nm, UV index, UV irradiance at 5 channels, UVB and UVA dose rate and daily dose, and biologically weighted UV dose rate and daily dose, calculated with 10 different action spectra. The data from the last 5 d and the daily maximum UV index time series are plotted and updated daily on the following web
An SUV-150B spectroradiometer for measuring solar ultraviolet (UV) irradiance was installed at Su... more An SUV-150B spectroradiometer for measuring solar ultraviolet (UV) irradiance was installed at Summit, Greenland, in August 2004. Here we compare the initial data from this new location with similar measurements from Barrow, Alaska and South Pole. Measurements of irradiance at 345 nm performed at equivalent solar zenith angles (SZAs) are almost identical at Summit and South Pole. The good agreement can be explained with the similar location of the two sites on high-altitude ice caps with high surface albedo. Clouds have little impact at both sites, but can reduce irradiance at Barrow by more than 75%. Clear-sky measurements at Barrow are smaller than at Summit by 14% in spring and 36% in summer, mostly due to differences in surface albedo and altitude. Comparisons with model calculations indicate that aerosols can reduce clear-sky irradiance at 345 nm by 4-6%; aerosol influence is largest in April. Differences in total ozone at the three sites have a large influence on the UV Index. At South Pole, the UV Index is on average 20-80% larger during the ozone hole period than between January and March. At Summit, total ozone peaks in April and UV Indices in spring are on average 10-25% smaller than in the summer. Maximum UV Indices ever observed at Summit and South Pole are 6.7 and 4.0, respectively. The larger value at Summit is due to the site's lower latitude. For comparable SZAs, average UV Indices measured during October and November at South Pole are 1.9-2.4 times larger than measurements during March and April at Summit. Average UV Indices at Summit are over 50% greater than at Barrow because of the larger cloud influence at Barrow.
The 19 channel rotating shadow band radiometer GUVis-3511 built by Biospherical Instruments is in... more The 19 channel rotating shadow band radiometer GUVis-3511 built by Biospherical Instruments is introduced as an instrument which is able to provide automated ship borne measurements of the direct, diffuse and global spectral irradiance components without a requirement for stabilization. Several direct sun products, including spectral direct beam transmittance, aerosol optical depth, Ångström exponent, and precipitable water can be derived from these observations. The individual steps of the data analysis are described, and the different sources of uncertainty are discussed. The total uncertainty of the observed direct beam transmittances is estimated to be 4.24% at 95% CI for ship borne operation. The calibration is identified as the dominating contribution to the total uncertainty. A comparison of direct beam transmittance with those obtained from a Cimel sun photometer at a land site and a manually operated Microtops II sun photometer on a ship is presented, yielding relative deviations of less than 3% and 4%, on land and on ship, respectively, for most channels and in agreement with our previous uncertainty estimate. These numbers demonstrate that the instrument is well suited for ship borne operation, and the applied methods for motion correction work accurately. Based on spectral direct beam transmittance, aerosol optical depth at 510 nm can be retrieved with an uncertainty of 0.0032 for a 95% CI. Only minor deviations occur due to the different methods used for estimating Rayleigh scattering and gas absorption optical depths, as implemented by AERONET and in our processing. Relying on the cross-calibration of the 940 nm water vapor channel with the Cimel sun photometer, the column amount of precipitable water has been estimated with an uncertainty of ± 0.034 cm. More research is needed to estimate the accuracy of the instrument for low sun (solar zenith angles larger than 70 •) and during periods with strong swell.
the Montreal protocol on Substances that Deplete the ozone Layer has been hailed as the most succ... more the Montreal protocol on Substances that Deplete the ozone Layer has been hailed as the most successful environmental treaty ever (https://www.unenvironment.org/news-and-stories/story/ montreal-protocol-triumph-treaty). Yet, although our main concern about ozone depletion is the subsequent increase in harmful solar UV radiation at the earth's surface, no studies to date have demonstrated its effectiveness in that regard. Here we use long-term UV Index (UVI) data derived from high-quality UV spectroradiometer measurements to demonstrate its success in curbing increases in UV radiation. Without this landmark agreement, UVi values would have increased at mid-latitude locations by approximately 20% between the early 1990s and today and would approximately quadruple at midlatitudes by 2100. In contrast, an analysis of UVI data from multiple clean-air sites shows that maximum daily UVI values have remained essentially constant over the last ~20 years in all seasons, and may even have decreased slightly in the southern hemisphere, especially in Antarctica, where effects of ozone depletion were larger. Reconstructions of the UVi from total ozone data show evidence of increasing UVI levels in the 1980s, but unfortunately, there are no high-quality UV measurements available prior to the early 1990s to confirm these increases with direct observations. Concern about ozone depletion arose primarily because of its potential to increase UV-B radiation, and the consequent effects on health and the environment 1. Observations of unexpected springtime decrease in stratospheric ozone over Antarctica 2-commonly referred to as the "ozone hole"-led to the rapid adoption of the Montreal Protocol on Substances that Deplete the Ozone Layer in 1987 3. It has been shown that without this treaty and its subsequent Amendments and Adjustments, ozone holes would by now also be occurring over the North Pole, resulting in highly elevated UVI in the Arctic 4. Even at mid-latitudes, the UVI would by now have increased markedly, and would more than double at some latitudes by the middle of the 21 st century 5-7. However, due to the success of the Montreal Protocol, ozone decreases appear to have been brought under control 8 , though any effects on surface UV irradiances have not previously been confirmed by measurements. We attempt to redress this issue by using an analysis of long-term UV measurements from instruments that meet the stringent requirements of the Network for the Detection of Atmospheric Composition Change (NDACC, www.ndacc.org).
We calculate the variation of spectral solar irradiance in the umbral shadow of the total solar e... more We calculate the variation of spectral solar irradiance in the umbral shadow of the total solar eclipse of August 21, 2017 and compare it to observations. Starting from the sun's and moon's positions, we derive a realistic profile of the lunar shadow at the top of the atmosphere, including the effect of solar limb darkening. Subsequently, the Monte-Carlo model MYSTIC is used to simulate the transfer of solar radiation through the earth's atmosphere. Among the effects taken into account are the atmospheric state (pressure, temperature), concentrations of major gas constituents and the curvature of the earth, as well as the reflectance and elevation of the surrounding area. We apply the model to the total solar eclipse on August 21, 2017 at a position located in Oregon, where irradiance observations were performed for wavelengths between 306 nm and 1020 nm. The influence of the surface reflectance, the ozone profile and mountains surrounding the observer is investigated. An increased sensitivity during totality is found for the reflectance and topography, compared to non-eclipse conditions. During the eclipse, the irradiance at the surface does not only depend on the total ozone column (TOC) but also the vertical ozone distribution, which in general complicates derivations of the TOC from spectral surface irradiance. The findings are related to an analysis of the prevailing photon path and its difference compared to non-eclipse conditions. Using the most realistic estimate for each parameter, the model is compared to the irradiance observations. During totality, the relative difference between model and observations is less than 10% in the spectral range from 400 nm to 1020 nm. Slightly larger deviations occur in the ultraviolet range below 400 nm and at 665 nm.
Thirty-three years ago, an unprecedented thinning of stratospheric ozone was reported over Antarc... more Thirty-three years ago, an unprecedented thinning of stratospheric ozone was reported over Antarctica 1. In response to concerns about elevated exposure to solar ultraviolet-B radiation (UV-B; wavelengths 280-315 nm) resulting from ozone depletion, the international community mobilized and worked together to understand the causes and find a solution to this dramatic change in Earth's environment. The policy solution that emerged to address this global environmental problem was the 1985 Vienna Convention for the Protection of the Ozone Layer. In this international agreement the United Nations recognized the fundamental importance of preventing the damaging effects of stratospheric ozone depletion, whether on human health or the environment. This convention was followed by the 1987 Montreal Protocol on Substances that Deplete the Ozone Layer with its subsequent amendments, adjustments, and decisions that were negotiated to control the consumption and production of anthropogenic ozone-depleting substances, including chlorofluorocarbons (CFCs). The Montreal Protocol now has the unique distinction of being the only treaty, ever, of any type, ratified by all 197 countries of the United Nations. The Parties to the Montreal Protocol base their decisions on scientific, environmental, technical, and economic information provided by three assessment Panels (Box 1). All three panels provide full assessment reports to the Parties every four years (quadrennial reports) and shorter, periodic updates in the intervening years as needed. The implementation of the Montreal Protocol has successfully prevented the uncontrolled global depletion of the stratospheric ozone layer 2,3. Concentrations of ozonedepleting substances have been declining in the stratosphere since the late 1990s. While significant seasonal ozone depletion over Antarctica has occurred annually since the 1980s (called the "ozone hole"), there have been small, but significant, positive trends in total column ozone in Antarctica in spring over the period 2001-2013. Global mean total ozone has been projected to recover to pre-1980 levels by about the middle of the 21 st century, assuming full compliance to the Montreal Protocol 2. Many of the chemical compounds controlled by the Montreal Protocol are not only involved in depletion of stratospheric ozone, but are also potent greenhouse gases 4. Modeling studies indicate that, in the absence of the Montreal Protocol, global mean temperatures would have risen by more than 2C by 2070, due to the warming effects from ozone-depleting substances alone 5. The adoption of the Kigali Amendment to the Montreal Protocol in 2016 limits the production and consumption of hydrofluorocarbons (HFCs), powerful greenhouse gases that are used as substitutes to ozone-depleting substances. This amendment has further broadened and strengthened the scope of the Montreal Protocol, creating an effective international treaty that not only addresses stratospheric ozone depletion, but is doing more to mitigate global climate change than any other human actions to date 7-10. One of the important reasons for the success of the Montreal Protocol has been its foundation on high quality science, which not only improves our understanding of the causes and mechanisms of ozone depletion, but also of the environmental effects of these atmospheric changes. The Environmental Effects Assessment Panel (EEAP) is specifically charged with providing regular assessments of the state of the science on the environmental effects of ozone depletion and consequent changes in UV radiation at Earth's surface, and the interactive effects of climate change (Box 1 and Fig. 1). Here, we summarize key findings from the most recent EEAP Quadrennial Assessment, and consider the significant policy and societal implications of these environmental effects. We specifically highlight the multiple ways by which the Montreal Protocol is contributing to environmental sustainability and human health and well-being consistent with many of the United Nations Sustainability Goals (Box 2). More in-depth information on ozone depletion and its environmental effects can be found in the full Assessments published by the Ozone Secretariat of the United Nations Environment Programme (https://ozone.unep.org) and elsewhere (Photochemical & Photobiological Sciences journal) 11-17. By focusing on the interactions between stratospheric ozone dynamics, UV radiation, and climate change, the report from the EEAP complements that of the UN's Intergovernmental Panel on Climate Change (IPCC;https://www.ipcc.ch; summarized by Pachauri, et al. 18) to provide a comprehensive assessment on the environmental effects of global changes in Earth's atmosphere.
Solar ultraviolet (UV) irradiances were measured with NILU-UV multichannel radiometers at Ushuaia... more Solar ultraviolet (UV) irradiances were measured with NILU-UV multichannel radiometers at Ushuaia (54 • S) and Marambio (64 • S) between 2000 and 2013. The measurements were part of the Antarctic NILU-UV network, which was started in cooperation between Spain, Argentina and Finland. The erythemally weighted UV irradiance time series of both stations were analysed for the first time. The quality assurance procedures included a travelling reference instrument to transfer the irradiance scale to the stations. The time series were homogenized and high quality measurements were available for the period 2000-2010. During this period UV indices of 11 or more were measured on 5 and 35 days at Marambio and Ushuaia, respectively. At Marambio, the peak daily maximum UV index of 12 and daily doses of around 7 kJ m −2 were measured in November 2007. The highest UV daily doses at both stations were typically around 6 kJ m −2 and occurred when the stations were inside the polar vortex, resulting in very low total ozone amount. At both stations, daily doses in late November could even exceed those in the summer. At Marambio, in some years, also daily doses in October can be as high as those during the summer. At Ushuaia, the peak daily maximum UV index of 13 was measured twice: in November 2003 and 2009. Also during those days, the station of Ushuaia was inside the polar vortex.
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Papers by G. Bernhard