Airborne observations and simulations of three-dimensional radiative interactions between Arctic boundary layer clouds and ice floes
Based on airborne spectral imaging observations, three-dimensional (3-D) radiative effects between Arctic boundary layer clouds and highly variable Arctic surfaces were identified and quantified. A method is presented to discriminate between sea ice and open water under cloudy conditions based on ai...
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ftdoajarticles:oai:doaj.org/article:c7d9663d52f248d2975e431794e16299 2023-05-15T13:10:56+02:00 Airborne observations and simulations of three-dimensional radiative interactions between Arctic boundary layer clouds and ice floes M. Schäfer E. Bierwirth A. Ehrlich E. Jäkel M. Wendisch 2015-07-01T00:00:00Z https://doi.org/10.5194/acp-15-8147-2015 https://doaj.org/article/c7d9663d52f248d2975e431794e16299 EN eng Copernicus Publications http://www.atmos-chem-phys.net/15/8147/2015/acp-15-8147-2015.pdf https://doaj.org/toc/1680-7316 https://doaj.org/toc/1680-7324 1680-7316 1680-7324 doi:10.5194/acp-15-8147-2015 https://doaj.org/article/c7d9663d52f248d2975e431794e16299 Atmospheric Chemistry and Physics, Vol 15, Iss 14, Pp 8147-8163 (2015) Physics QC1-999 Chemistry QD1-999 article 2015 ftdoajarticles https://doi.org/10.5194/acp-15-8147-2015 2022-12-31T15:53:48Z Based on airborne spectral imaging observations, three-dimensional (3-D) radiative effects between Arctic boundary layer clouds and highly variable Arctic surfaces were identified and quantified. A method is presented to discriminate between sea ice and open water under cloudy conditions based on airborne nadir reflectivity γ λ measurements in the visible spectral range. In cloudy cases the transition of γ λ from open water to sea ice is not instantaneous but horizontally smoothed. In general, clouds reduce γ λ above bright surfaces in the vicinity of open water, while γ λ above open sea is enhanced. With the help of observations and 3-D radiative transfer simulations, this effect was quantified to range between 0 and 2200 m distance to the sea ice edge (for a dark-ocean albedo of α water = 0.042 and a sea-ice albedo of α ice = 0.91 at 645 nm wavelength). The affected distance Δ L was found to depend on both cloud and sea ice properties. For a low-level cloud at 0–200 m altitude, as observed during the Arctic field campaign VERtical Distribution of Ice in Arctic clouds (VERDI) in 2012, an increase in the cloud optical thickness τ from 1 to 10 leads to a decrease in Δ L from 600 to 250 m. An increase in the cloud base altitude or cloud geometrical thickness results in an increase in Δ L for τ = 1/10 Δ L = 2200 m/1250 m in case of a cloud at 500–1000 m altitude. To quantify the effect for different shapes and sizes of ice floes, radiative transfer simulations were performed with various albedo fields (infinitely long straight ice edge, circular ice floes, squares, realistic ice floe field). The simulations show that Δ L increases with increasing radius of the ice floe and reaches maximum values for ice floes with radii larger than 6 km (500–1000 m cloud altitude), which matches the results found for an infinitely long, straight ice edge. Furthermore, the influence of these 3-D radiative effects on the retrieved cloud optical properties was investigated. The enhanced brightness of a dark pixel next to an ice edge ... Article in Journal/Newspaper albedo Arctic Sea ice Directory of Open Access Journals: DOAJ Articles Arctic Atmospheric Chemistry and Physics 15 14 8147 8163 |
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Directory of Open Access Journals: DOAJ Articles |
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ftdoajarticles |
language |
English |
topic |
Physics QC1-999 Chemistry QD1-999 |
spellingShingle |
Physics QC1-999 Chemistry QD1-999 M. Schäfer E. Bierwirth A. Ehrlich E. Jäkel M. Wendisch Airborne observations and simulations of three-dimensional radiative interactions between Arctic boundary layer clouds and ice floes |
topic_facet |
Physics QC1-999 Chemistry QD1-999 |
description |
Based on airborne spectral imaging observations, three-dimensional (3-D) radiative effects between Arctic boundary layer clouds and highly variable Arctic surfaces were identified and quantified. A method is presented to discriminate between sea ice and open water under cloudy conditions based on airborne nadir reflectivity γ λ measurements in the visible spectral range. In cloudy cases the transition of γ λ from open water to sea ice is not instantaneous but horizontally smoothed. In general, clouds reduce γ λ above bright surfaces in the vicinity of open water, while γ λ above open sea is enhanced. With the help of observations and 3-D radiative transfer simulations, this effect was quantified to range between 0 and 2200 m distance to the sea ice edge (for a dark-ocean albedo of α water = 0.042 and a sea-ice albedo of α ice = 0.91 at 645 nm wavelength). The affected distance Δ L was found to depend on both cloud and sea ice properties. For a low-level cloud at 0–200 m altitude, as observed during the Arctic field campaign VERtical Distribution of Ice in Arctic clouds (VERDI) in 2012, an increase in the cloud optical thickness τ from 1 to 10 leads to a decrease in Δ L from 600 to 250 m. An increase in the cloud base altitude or cloud geometrical thickness results in an increase in Δ L for τ = 1/10 Δ L = 2200 m/1250 m in case of a cloud at 500–1000 m altitude. To quantify the effect for different shapes and sizes of ice floes, radiative transfer simulations were performed with various albedo fields (infinitely long straight ice edge, circular ice floes, squares, realistic ice floe field). The simulations show that Δ L increases with increasing radius of the ice floe and reaches maximum values for ice floes with radii larger than 6 km (500–1000 m cloud altitude), which matches the results found for an infinitely long, straight ice edge. Furthermore, the influence of these 3-D radiative effects on the retrieved cloud optical properties was investigated. The enhanced brightness of a dark pixel next to an ice edge ... |
format |
Article in Journal/Newspaper |
author |
M. Schäfer E. Bierwirth A. Ehrlich E. Jäkel M. Wendisch |
author_facet |
M. Schäfer E. Bierwirth A. Ehrlich E. Jäkel M. Wendisch |
author_sort |
M. Schäfer |
title |
Airborne observations and simulations of three-dimensional radiative interactions between Arctic boundary layer clouds and ice floes |
title_short |
Airborne observations and simulations of three-dimensional radiative interactions between Arctic boundary layer clouds and ice floes |
title_full |
Airborne observations and simulations of three-dimensional radiative interactions between Arctic boundary layer clouds and ice floes |
title_fullStr |
Airborne observations and simulations of three-dimensional radiative interactions between Arctic boundary layer clouds and ice floes |
title_full_unstemmed |
Airborne observations and simulations of three-dimensional radiative interactions between Arctic boundary layer clouds and ice floes |
title_sort |
airborne observations and simulations of three-dimensional radiative interactions between arctic boundary layer clouds and ice floes |
publisher |
Copernicus Publications |
publishDate |
2015 |
url |
https://doi.org/10.5194/acp-15-8147-2015 https://doaj.org/article/c7d9663d52f248d2975e431794e16299 |
geographic |
Arctic |
geographic_facet |
Arctic |
genre |
albedo Arctic Sea ice |
genre_facet |
albedo Arctic Sea ice |
op_source |
Atmospheric Chemistry and Physics, Vol 15, Iss 14, Pp 8147-8163 (2015) |
op_relation |
http://www.atmos-chem-phys.net/15/8147/2015/acp-15-8147-2015.pdf https://doaj.org/toc/1680-7316 https://doaj.org/toc/1680-7324 1680-7316 1680-7324 doi:10.5194/acp-15-8147-2015 https://doaj.org/article/c7d9663d52f248d2975e431794e16299 |
op_doi |
https://doi.org/10.5194/acp-15-8147-2015 |
container_title |
Atmospheric Chemistry and Physics |
container_volume |
15 |
container_issue |
14 |
container_start_page |
8147 |
op_container_end_page |
8163 |
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1766245263731589120 |