Disk and circumsolar radiances in the presence of ice clouds
The impact of ice clouds on solar disk and circumsolar radiances is investigated using a Monte Carlo radiative transfer model. The monochromatic direct and diffuse radiances are simulated at angles of 0 to 8° from the center of the sun. Input data for the model are derived from measurements cond...
| Main Authors: | , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2017-06-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | http://www.atmos-chem-phys.net/17/6865/2017/acp-17-6865-2017.pdf |
| _version_ | 1828528630458744832 |
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| author | P. Haapanala P. Räisänen G. M. McFarquhar J. Tiira A. Macke M. Kahnert M. Kahnert J. DeVore T. Nousiainen |
| author_facet | P. Haapanala P. Räisänen G. M. McFarquhar J. Tiira A. Macke M. Kahnert M. Kahnert J. DeVore T. Nousiainen |
| author_sort | P. Haapanala |
| collection | DOAJ |
| description | The impact of ice clouds on solar disk and circumsolar radiances is
investigated using a Monte Carlo radiative transfer model. The monochromatic
direct and diffuse radiances are simulated at angles of 0 to 8° from
the center of the sun. Input data for the model are derived from measurements
conducted during the 2010 Small Particles in Cirrus (SPARTICUS) campaign
together with state-of-the-art databases of optical properties of ice
crystals and aerosols. For selected cases, the simulated radiances are
compared with ground-based radiance measurements obtained by the Sun and
Aureole Measurements (SAM) instrument.
<br><br>
First, the sensitivity of the radiances to the ice cloud properties and
aerosol optical thickness is addressed. The angular dependence of the disk
and circumsolar radiances is found to be most sensitive to assumptions about
ice crystal roughness (or, more generally, non-ideal features of ice
crystals) and size distribution, with ice crystal habit playing a somewhat
smaller role. Second, in comparisons with SAM data, the ice cloud optical
thickness is adjusted for each case so that the simulated radiances agree
closely (i.e., within 3 %) with the measured disk radiances. Circumsolar
radiances at angles larger than ≈ 3° are systematically
underestimated when assuming smooth ice crystals, whereas the agreement with
the measurements is better when rough ice crystals are assumed. Our results
suggest that it may well be possible to infer the particle roughness directly
from ground-based SAM measurements. In addition, the results show the
necessity of correcting the ground-based measurements of direct radiation for
the presence of diffuse radiation in the instrument's field of view, in
particular in the presence of ice clouds. |
| first_indexed | 2024-12-11T21:55:26Z |
| format | Article |
| id | doaj.art-15f2e3e00e8941008cfbb980f97f8356 |
| institution | Directory Open Access Journal |
| issn | 1680-7316 1680-7324 |
| language | English |
| last_indexed | 2024-12-11T21:55:26Z |
| publishDate | 2017-06-01 |
| publisher | Copernicus Publications |
| record_format | Article |
| series | Atmospheric Chemistry and Physics |
| spelling | doaj.art-15f2e3e00e8941008cfbb980f97f83562022-12-22T00:49:19ZengCopernicus PublicationsAtmospheric Chemistry and Physics1680-73161680-73242017-06-01176865688210.5194/acp-17-6865-2017Disk and circumsolar radiances in the presence of ice cloudsP. Haapanala0P. Räisänen1G. M. McFarquhar2J. Tiira3A. Macke4M. Kahnert5M. Kahnert6J. DeVore7T. Nousiainen8Department of Physics, University of Helsinki, P.O. Box 64, 00014 University of Helsinki, FinlandFinnish Meteorological Institute, P.O. Box 503, 00101 Helsinki, FinlandDepartment of Atmospheric Science, University of Illinois at Urbana-Champaign, Urbana, 105 South Gregory St., IL 61801-3070, USADepartment of Physics, University of Helsinki, P.O. Box 64, 00014 University of Helsinki, FinlandLeibniz Institute for Tropospheric Research, Permoserstraße 15, 04318 Leipzig, GermanyResearch Department, Swedish Meteorological and Hydrological Institute, Folkborgsvägen 17, 601 76 Norrköping, SwedenDepartment of Earth and Space Science, Chalmers University of Technology, 412 96 Gothenburg, SwedenVisidyne, Inc., 429 Stanley Drive, Santa Barbara, CA 93105, USAFinnish Meteorological Institute, P.O. Box 503, 00101 Helsinki, FinlandThe impact of ice clouds on solar disk and circumsolar radiances is investigated using a Monte Carlo radiative transfer model. The monochromatic direct and diffuse radiances are simulated at angles of 0 to 8° from the center of the sun. Input data for the model are derived from measurements conducted during the 2010 Small Particles in Cirrus (SPARTICUS) campaign together with state-of-the-art databases of optical properties of ice crystals and aerosols. For selected cases, the simulated radiances are compared with ground-based radiance measurements obtained by the Sun and Aureole Measurements (SAM) instrument. <br><br> First, the sensitivity of the radiances to the ice cloud properties and aerosol optical thickness is addressed. The angular dependence of the disk and circumsolar radiances is found to be most sensitive to assumptions about ice crystal roughness (or, more generally, non-ideal features of ice crystals) and size distribution, with ice crystal habit playing a somewhat smaller role. Second, in comparisons with SAM data, the ice cloud optical thickness is adjusted for each case so that the simulated radiances agree closely (i.e., within 3 %) with the measured disk radiances. Circumsolar radiances at angles larger than ≈ 3° are systematically underestimated when assuming smooth ice crystals, whereas the agreement with the measurements is better when rough ice crystals are assumed. Our results suggest that it may well be possible to infer the particle roughness directly from ground-based SAM measurements. In addition, the results show the necessity of correcting the ground-based measurements of direct radiation for the presence of diffuse radiation in the instrument's field of view, in particular in the presence of ice clouds.http://www.atmos-chem-phys.net/17/6865/2017/acp-17-6865-2017.pdf |
| spellingShingle | P. Haapanala P. Räisänen G. M. McFarquhar J. Tiira A. Macke M. Kahnert M. Kahnert J. DeVore T. Nousiainen Disk and circumsolar radiances in the presence of ice clouds Atmospheric Chemistry and Physics |
| title | Disk and circumsolar radiances in the presence of ice clouds |
| title_full | Disk and circumsolar radiances in the presence of ice clouds |
| title_fullStr | Disk and circumsolar radiances in the presence of ice clouds |
| title_full_unstemmed | Disk and circumsolar radiances in the presence of ice clouds |
| title_short | Disk and circumsolar radiances in the presence of ice clouds |
| title_sort | disk and circumsolar radiances in the presence of ice clouds |
| url | http://www.atmos-chem-phys.net/17/6865/2017/acp-17-6865-2017.pdf |
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