scholarly journals Measurements of spectral irradiance during the solar eclipse of 21 August 2017: reassessment of the effect of solar limb darkening and of changes in total ozone

2019 ◽  
Vol 19 (7) ◽  
pp. 4703-4719 ◽  
Author(s):  
Germar Bernhard ◽  
Boyan Petkov
Keyword(s):  
Solar Radiation ◽  
Solar Eclipse ◽  
Total Ozone ◽  
Solar Spectrum ◽  
Solar Limb ◽  
Spectral Irradiance ◽  
Visible Range ◽  
Global Irradiance ◽  
Filter Radiometer ◽  
Limb Darkening

Abstract. Measurements of spectral irradiance between 306 and 1020 nm were performed with a GUVis-3511 multi-channel filter radiometer at Smith Rock State Park, Oregon, during the total solar eclipse of 21 August 2017. The radiometer was equipped with a shadowband, allowing the separation of the global (sun and sky) and direct components of solar radiation. Data were used to study the wavelength-dependent changes in solar irradiance at Earth's surface. Results were compared with theoretical predictions using three different parameterizations of the solar limb darkening (LD) effect, which describes the change in the solar spectrum from the Sun's center to its limb. Results indicate that the LD parameterization that has been most widely used during the last 15 years underestimates the LD effect, in particular at UV wavelengths. The two alternative parameterizations are based on two independent sets of observations from the McMath–Pierce solar telescope. When these parameterizations are used, the observed and theoretical LD effects agree to within 4 % for wavelengths larger than 400 nm and occultation of the solar disk of up to 97.8 %. Maximum deviations for wavelengths between 315 and 340 nm are 7 %. These somewhat larger differences compared to the visible range may be explained with varying aerosol conditions during the period of observations. The aerosol optical depth (AOD) and its wavelength dependence was calculated from measurements of direct irradiance. When corrected for the LD effect, the AOD decreases over the period of the eclipse: from 0.41 to 0.34 at 319 nm and from 0.05 to 0.04 at 1018 nm. These results show that AODs can be accurately calculated during an eclipse if the LD effect is corrected. The total ozone column (TOC) was derived from measurements of global irradiance at 306 and 340 nm. Without correction for the LD effect, the retrieved TOC increases by 20 DU between the first and second contact of the eclipse. With LD correction, the TOC remains constant to within natural variability (±2.6 DU or ±0.9 % between first and second contact and ±1.0 DU or ±0.3 % between third and fourth contact). In contrast to results of observations from earlier solar eclipses, no fluctuations in TOC were observed that could be unambiguously attributed to gravity waves, which can be triggered by the supersonic speed of the Moon's shadow across the atmosphere. Furthermore, systematic changes in the ratio of direct and global irradiance that could be attributed to the solar eclipse were not observed, in agreement with results of three-dimensional (3-D) radiative transfer (RT) models. Our results advance the understanding of the effects of solar LD on the spectral irradiance at Earth's surface, the variations in ozone during an eclipse, and the partitioning of solar radiation in direct and diffuse components.

scholarly journals Measurements of spectral irradiance during the solar eclipse of 21 August 2017: reassessment of the effect of solar limb darkening and of changes in total ozone

2018 ◽  
Author(s):  
Germar Bernhard ◽  
Boyan Petkov
Keyword(s):  
Solar Radiation ◽  
Solar Eclipse ◽  
Total Ozone ◽  
Solar Spectrum ◽  
Solar Limb ◽  
Spectral Irradiance ◽  
Visible Range ◽  
Global Irradiance ◽  
Filter Radiometer ◽  
Limb Darkening

Abstract. Measurements of spectral irradiance between 306 and 1020 nm were performed with a GUVis-3511 multi-channel filter radiometer at Smith Rock State Park, Oregon, during the total solar eclipse of 21 August 2017. The radiometer was equipped with a shadowband, allowing to separate the global (sun and sky) and direct components of solar radiation. Data were used to study the wavelength-dependent changes of solar irradiance at Earth's surface. Results were compared with theoretical predictions using three different parameterizations of the solar limb darkening (LD) effect, which describes the change of the solar spectrum from the Sun's center to its limb. Results indicate that the LD parameterization that has been most widely used during the last 15 years underestimates the LD effect, in particular at UV wavelengths. The two alternative parameterizations are based on two independent sets of observations from the McMath-Pierce Solar Telescope. When these parameterizations are used, the observed and theoretical LD effects agree to within 4 % for wavelengths larger than 400 nm and occultation of the solar disk of up to 97.8 %. Maximum deviations for wavelengths between 315 and 340 nm are 7 %. These somewhat larger differences compared to the visible range may be explained with varying aerosol conditions during the period of observations. Aerosol optical depth (AOD) and its wavelength dependence was calculated from measurements of direct irradiance. When corrected for the LD effect, AOD monotonically decreases over the period of the eclipse: from 0.41 to 0.32 at 319 nm and from 0.05 to 0.04 at 1018 nm. These results show that AODs can be accurately calculated during an eclipse if the LD effect is corrected. The total ozone column (TOC) was derived from measurements of global irradiance at 306 and 340 nm. Without correction for the LD effect, the retrieved TOC increases by 20 DU between the 1st and 2nd contact of the eclipse. With LD correction, the TOC remains constant to within natural variability (±2.6 DU or ±0.9 % between 1st and 2nd contact and ±1.0 DU or ±0.3 % between 3rd and 4th contact). In contrast to results of observations from earlier solar eclipses, no fluctuations in TOC were observed that could be attributed to gravity waves, which can be triggered by the supersonic speed of the Moon's shadow across the atmosphere. Furthermore, systematic changes in the ratio of direct and global irradiance that could be attributed to the solar eclipse were not observed. This finding agrees with results of three-dimensional radiative transfer models but contradicts reports from earlier observations, which indicate that the diffuse-to-direct ratio may change by 30 %. Our results advance the understanding of the effects of solar LD on the spectral irradiance at Earth's surface, the variations of ozone during an eclipse, and the partitioning of solar radiation in direct and diffuse components.

scholarly journals Coordinated weather balloon solar radiation measurements during a solar eclipse

2016 ◽  
Vol 374 (2077) ◽  
pp. 20150221 ◽  
Author(s):  
R. G. Harrison ◽  
G. J. Marlton ◽  
P. D. Williams ◽  
K. A. Nicoll
Keyword(s):  
Solar Radiation ◽  
Solar Eclipse ◽  
Solar Limb ◽  
Mean Value ◽  
Radiation Environment ◽  
Atmospheric Effects ◽  
Sensor Platforms ◽  
Solar Eclipses ◽  
Limb Darkening ◽  
Radiation Measurements

Solar eclipses provide a rapidly changing solar radiation environment. These changes can be studied using simple photodiode sensors, if the radiation reaching the sensors is unaffected by cloud. Transporting the sensors aloft using standard meteorological instrument packages modified to carry extra sensors, provides one promising but hitherto unexploited possibility for making solar eclipse radiation measurements. For the 20 March 2015 solar eclipse, a coordinated campaign of balloon-carried solar radiation measurements was undertaken from Reading (51.44°N, 0.94°W), Lerwick (60.15°N, 1.13°W) and Reykjavik (64.13°N, 21.90°W), straddling the path of the eclipse. The balloons reached sufficient altitude at the eclipse time for eclipse-induced variations in solar radiation and solar limb darkening to be measured above cloud. Because the sensor platforms were free to swing, techniques have been evaluated to correct the measurements for their changing orientation. In the swing-averaged technique, the mean value across a set of swings was used to approximate the radiation falling on a horizontal surface; in the swing-maximum technique, the direct beam was estimated by assuming that the maximum solar radiation during a swing occurs when the photodiode sensing surface becomes normal to the direction of the solar beam. Both approaches, essentially independent, give values that agree with theoretical expectations for the eclipse-induced radiation changes. This article is part of the themed issue ‘Atmospheric effects of solar eclipses stimulated by the 2015 UK eclipse’.

scholarly journals Effects of total solar eclipse of 29 March 2006 on surface radiation

2007 ◽  
Vol 7 (22) ◽  
pp. 5775-5783 ◽  
Author(s):  
S. Kazadzis ◽  
A. Bais ◽  
M. Blumthaler ◽  
A. Webb ◽  
N. Kouremeti ◽  
...  
Keyword(s):  
Solar Eclipse ◽  
Total Ozone ◽  
Diffuse Radiation ◽  
Black Body ◽  
Black Body Radiation ◽  
Total Solar Eclipse ◽  
Surface Radiation ◽  
Radiative Transfer Model ◽  
Transfer Model ◽  
Limb Darkening

Abstract. Solar irradiance spectral measurements were performed during a total solar eclipse. The spectral effect of the limb darkening to the global, direct irradiance and actinic flux measurements was investigated. This effect leads to wavelength dependent changes in the measured solar spectra showing a much more pronounced decrease in the radiation at the lower wavelengths. Radiative transfer model results were used for the computation of a correction for the total ozone measurements due to the limb darkening. This correction was found too small to explain the large decrease in total ozone column derived from the standard Brewer measurements, which is an artifact in the measured irradiance due to the increasing contribution of diffuse radiation against the decreasing direct irradiance caused by the eclipse. Calculations of the Extraterrestrial spectrum and the effective sun's temperatures, as measured from ground based direct irradiance measurements, showed an artificial change in the calculations of both quantities due to the fact that radiation coming from the visible part of the sun during the eclipse phases differs from the black body radiation described by the Planck's law.

scholarly journals Effects of total solar eclipse of 29 March 2006 on surface radiation

2007 ◽  
Vol 7 (3) ◽  
pp. 9235-9258 ◽  
Author(s):  
S. Kazadzis ◽  
A. Bais ◽  
M. Blumthaler ◽  
A. Webb ◽  
N. Kouremeti ◽  
...  
Keyword(s):  
Solar Eclipse ◽  
Total Ozone ◽  
Diffuse Radiation ◽  
Total Solar Eclipse ◽  
Surface Radiation ◽  
Radiative Transfer Model ◽  
Transfer Model ◽  
Visible Part ◽  
Planck’S Law ◽  
Limb Darkening

Abstract. Solar irradiance spectral measurements were performed during a total solar eclipse. The spectral effect of the limb darkening to the global, direct irradiance and actinic flux measurements was investigated. This effect leads to wavelength dependent changes in the measured solar spectra showing a much more pronounced decrease in the radiation at the lower wavelengths. Radiative transfer model results were used for the computation of a correction for the total ozone measurements due to the limb darkening. This correction was found too small to explain the large decrease in total ozone column derived from the standard Brewer measurements, which is an artifact in the measured irradiance due to the increasing contribution of diffuse radiation against the decreasing direct irradiance caused by the eclipse. Calculations of the Extraterrestrial spectrum and the effective sun's temperatures, as measured from ground based direct irradiance measurements, showed an artificial change in the calculations of both quantities due to the fact that radiation coming from the visible part of the sun during the eclipse phases differs from the back body radiation described by the Planck's law.

scholarly journals Spectral UV Measurements of Global Irradiance, Solar Radiance, and Actinic Flux in New Zealand: Intercomparison between Instruments and Model Calculations

2008 ◽  
Vol 25 (6) ◽  
pp. 945-958 ◽  
Author(s):  
Mario Blumthaler ◽  
Barbara Schallhart ◽  
Michael Schwarzmann ◽  
Richard McKenzie ◽  
Paul Johnston ◽  
...  
Keyword(s):  
New Zealand ◽  
Total Ozone ◽  
Spectral Irradiance ◽  
Atmospheric Composition ◽  
Radiative Transfer Model ◽  
Transfer Model ◽  
Total Ozone Mapping Spectrometer ◽  
Model Calculations ◽  
Global Irradiance ◽  
Sky Radiance

Abstract Presented here are the results of a short but intense measurement campaign at Lauder, New Zealand, in which spectral irradiance from instruments operated by the National Institute of Water and Atmospheric Research (NIWA) and Austria/Innsbruck (ATI) were traced to different irradiance standards and compared. The observed spectral differences for global irradiance were relatively small (<5%) and were consistent with those expected from observed differences in the radiation standards used by each group. Actinic fluxes measured by both groups were also intercompared and found to agree at the 10% level. The ATI instrument had the additional capability of measuring solar direct beam irradiance and sky radiances. These provided the first series of sky radiance measurements at this pristine Network for the Detection of Atmospheric Composition Change (NDACC) site. The polarization of sky radiance results were compared with estimates from a radiative transfer model without any aerosols and was found to be up to 25% smaller. Total ozone values derived from Total Ozone Mapping Spectrometer (TOMS), Dobson measurements by NIWA, spectral direct sun measurements by ATI, and spectral global irradiance measurements by NIWA agreed generally within 2%–3%.

scholarly journals Restoring the top-of-atmosphere reflectance during solar eclipses: a proof of concept with the UV absorbing aerosol index measured by TROPOMI

2021 ◽  
Vol 21 (11) ◽  
pp. 8593-8614
Author(s):  
Victor Trees ◽  
Ping Wang ◽  
Piet Stammes
Keyword(s):  
Air Quality ◽  
Solar Eclipse ◽  
Solar Irradiance ◽  
Colour Change ◽  
Solar Limb ◽  
Reflectance Spectra ◽  
The Moon ◽  
Solar Eclipses ◽  
Limb Darkening ◽  
Aerosol Index

Abstract. During a solar eclipse the solar irradiance reaching the top of the atmosphere (TOA) is reduced in the Moon shadow. The solar irradiance is commonly measured by Earth observation satellites before the start of the solar eclipse and is not corrected for this reduction, which results in a decrease in the computed TOA reflectances. Consequently, air quality products that are derived from TOA reflectance spectra, such as the ultraviolet (UV) absorbing aerosol index (AAI), are distorted or undefined in the shadow of the Moon. The availability of air quality satellite data in the penumbral and antumbral shadow during solar eclipses, however, is of particular interest to users studying the atmospheric response to solar eclipses. Given the time and location of a point on the Earth's surface, we explain how to compute the obscuration during a solar eclipse, taking into account wavelength-dependent solar limb darkening. With the calculated obscuration fractions, we restore the TOA reflectances and the AAI in the penumbral shadow during the annular solar eclipses on 26 December 2019 and 21 June 2020 measured by the TROPOMI/S5P instrument. We compare the calculated obscuration to the estimated obscuration using an uneclipsed orbit. In the corrected products, the signature of the Moon shadow disappeared, but only if wavelength-dependent solar limb darkening is taken into account. We find that the Moon shadow anomaly in the uncorrected AAI is caused by a reduction of the measured reflectance at 380 nm, rather than a colour change of the measured light. We restore common AAI features such as the sunglint and desert dust, and we confirm the restored AAI feature on 21 June 2020 at the Taklamakan Desert by measurements of the GOME-2C satellite instrument on the same day but outside the Moon shadow. No indication of local absorbing aerosol changes caused by the eclipses was found. We conclude that the correction method of this paper can be used to detect real AAI rising phenomena during a solar eclipse and has the potential to restore any other product that is derived from TOA reflectance spectra. This would resolve the solar eclipse anomalies in satellite air quality measurements in the penumbra and antumbra and would allow for studying the effect of the eclipse obscuration on the composition of the Earth's atmosphere from space.

scholarly journals Accurate 3D radiative transfer simulation of spectral solar irradiance during the total solar eclipse of August 21, 2017

2019 ◽  
Author(s):  
Paul Ockenfuß ◽  
Claudia Emde ◽  
Bernhard Mayer ◽  
Germar Bernhard
Keyword(s):  
Solar Eclipse ◽  
Solar Irradiance ◽  
Monte Carlo Model ◽  
Solar Limb ◽  
Relative Difference ◽  
Total Solar Eclipse ◽  
Ozone Profile ◽  
Increased Sensitivity ◽  
Limb Darkening ◽  
Spectral Solar Irradiance

Abstract. 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.

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