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
-
Published:2019-04-09
Issue:7
Volume:19
Page:4703-4719
-
ISSN:1680-7324
-
Container-title:Atmospheric Chemistry and Physics
-
language:en
-
Short-container-title:Atmos. Chem. Phys.
Author:
Bernhard GermarORCID, Petkov Boyan
Abstract
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.
Publisher
Copernicus GmbH
Subject
Atmospheric Science
Reference43 articles.
1. Adams, C., McLinden, C. A., Strong, K., and Umlenski, V.: Ozone and NO2
variations measured during the 1 August 2008 solar eclipse above Eureka,
Canada with a UV-visible spectrometer, J. Geophys. Res., 115, D19310, https://doi.org/10.1029/2010JD014424, 2010. 2. Antón, M., Serrano, A., Cancillo, M. L., Vaquero, J. M., and Vilaplana
J. M.: Solar irradiance and total ozone over El Arenosillo (Spain) during
the solar eclipse of 3 October 2005, J. Atmos. Sol.-Terr. Phy., 72,
789–793, https://doi.org/10.1016/j.jastp.2010.03.025, 2010. 3. Basher, R. E.: Review of the Dobson spectrophotometer and its accuracy, WMO
Global Ozone Res. Monit. Proj. Rep. 13, World Meteorol. Organ., Geneva,
Switzerland, 1982. 4. Bass, A. and Paur, R. J.: The ultraviolet cross sections of ozone: The
measurement, in: Atmospheric Ozone, edited by: Zerefos, C., Ghazi, A., and Reidel, D., Norwell, Mass, 606–616, 1985. 5. Bernhard, G., Booth, C. R., and McPeters, R. D.: Calculation of total column
ozone from global UV spectra at high latitudes, J. Geophys. Res., 108,
4532, https://doi.org/10.1029/2003JD003450, 2003.
Cited by
10 articles.
订阅此论文施引文献
订阅此论文施引文献,注册后可以免费订阅5篇论文的施引文献,订阅后可以查看论文全部施引文献
|
|