Journal cover Journal topic
Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
Journal topic

Journal metrics

Journal metrics

  • IF value: 5.509 IF 5.509
  • IF 5-year value: 5.689 IF 5-year 5.689
  • CiteScore value: 5.44 CiteScore 5.44
  • SNIP value: 1.519 SNIP 1.519
  • SJR value: 3.032 SJR 3.032
  • IPP value: 5.37 IPP 5.37
  • h5-index value: 86 h5-index 86
  • Scimago H index value: 161 Scimago H index 161
Discussion papers
https://doi.org/10.5194/acp-2018-1048
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/acp-2018-1048
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 02 Nov 2018

Research article | 02 Nov 2018

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Atmospheric Chemistry and Physics (ACP).

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

Germar Bernhard1 and Boyan Petkov2 Germar Bernhard and Boyan Petkov
  • 1Biospherical Instruments Inc., San Diego, CA 92110, USA
  • 2Institute of Atmospheric Sciences and Climate (ISAC) of th e Italian National Research Council (CNR), I-40129 Bologna, Italy

Abstract. Measurements of spectral irradiance between 306 and 1020nm 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 400nm and occultation of the solar disk of up to 97.8%. Maximum deviations for wavelengths between 315 and 340nm 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 319nm and from 0.05 to 0.04 at 1018nm. 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 340nm. Without correction for the LD effect, the retrieved TOC increases by 20DU between the 1st and 2nd contact of the eclipse. With LD correction, the TOC remains constant to within natural variability (±2.6DU 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.

Germar Bernhard and Boyan Petkov
Interactive discussion
Status: open (until 28 Dec 2018)
Status: open (until 28 Dec 2018)
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
[Subscribe to comment alert] Printer-friendly Version - Printer-friendly version Supplement - Supplement
Germar Bernhard and Boyan Petkov
Germar Bernhard and Boyan Petkov
Viewed
Total article views: 211 (including HTML, PDF, and XML)
HTML PDF XML Total Supplement BibTeX EndNote
177 31 3 211 8 1 2
  • HTML: 177
  • PDF: 31
  • XML: 3
  • Total: 211
  • Supplement: 8
  • BibTeX: 1
  • EndNote: 2
Views and downloads (calculated since 02 Nov 2018)
Cumulative views and downloads (calculated since 02 Nov 2018)
Viewed (geographical distribution)
Total article views: 211 (including HTML, PDF, and XML) Thereof 211 with geography defined and 0 with unknown origin.
Country # Views %
  • 1
1
 
 
 
 
Cited
Saved
No saved metrics found.
Discussed
No discussed metrics found.
Latest update: 15 Nov 2018
Publications Copernicus
Download
Short summary
Solar radiation at ultraviolet, visible, and infrared wavelengths was measured during the total solar eclipse of 21 August 2017. Data were used to study the wavelength-dependent changes of solar radiation at Earth's surface and to validate parameterizations of solar limb darkening (LD), which describes the change of the Sun's brightness between its center and its edge. The study highlights the importance of the LD effect when calculating total ozone and aerosol optical depth during an eclipse.
Solar radiation at ultraviolet, visible, and infrared wavelengths was measured during the total...
Citation
Share