Cloud phase identification of Arctic boundary-layer clouds from airborne spectral reflection measurements: test of three approaches
Arctic boundary-layer clouds were investigated with remote sensing and in situ instruments during the Arctic Study of Tropospheric Aerosol, Clouds and Radiation (ASTAR) campaign in March and April 2007. The clouds formed in a cold air outbreak over the open Greenland Sea. Beside the predominant mixe...
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ftcopernicus:oai:publications.copernicus.org:acp5393 2023-05-15T13:11:12+02:00 Cloud phase identification of Arctic boundary-layer clouds from airborne spectral reflection measurements: test of three approaches Ehrlich, A. Bierwirth, E. Wendisch, M. Gayet, J.-F. Mioche, G. Lampert, A. Heintzenberg, J. 2018-01-15 application/pdf https://doi.org/10.5194/acp-8-7493-2008 https://www.atmos-chem-phys.net/8/7493/2008/ eng eng doi:10.5194/acp-8-7493-2008 https://www.atmos-chem-phys.net/8/7493/2008/ eISSN: 1680-7324 Text 2018 ftcopernicus https://doi.org/10.5194/acp-8-7493-2008 2019-12-24T09:58:04Z Arctic boundary-layer clouds were investigated with remote sensing and in situ instruments during the Arctic Study of Tropospheric Aerosol, Clouds and Radiation (ASTAR) campaign in March and April 2007. The clouds formed in a cold air outbreak over the open Greenland Sea. Beside the predominant mixed-phase clouds pure liquid water and ice clouds were observed. Utilizing measurements of solar radiation reflected by the clouds three methods to retrieve the thermodynamic phase of the cloud are introduced and compared. Two ice indices I S and I P were obtained by analyzing the spectral pattern of the cloud top reflectance in the near infrared (1500–1800 nm wavelength) spectral range which is characterized by ice and water absorption. While I S analyzes the spectral slope of the reflectance in this wavelength range, I S utilizes a principle component analysis (PCA) of the spectral reflectance. A third ice index I A is based on the different side scattering of spherical liquid water particles and nonspherical ice crystals which was recorded in simultaneous measurements of spectral cloud albedo and reflectance. Radiative transfer simulations show that I S , I P and I A range between 5 to 80, 0 to 8 and 1 to 1.25 respectively with lowest values indicating pure liquid water clouds and highest values pure ice clouds. The spectral slope ice index I S and the PCA ice index I P are found to be strongly sensitive to the effective diameter of the ice crystals present in the cloud. Therefore, the identification of mixed-phase clouds requires a priori knowledge of the ice crystal dimension. The reflectance-albedo ice index I A is mainly dominated by the uppermost cloud layer (τ<1.5). Therefore, typical boundary-layer mixed-phase clouds with a liquid cloud top layer will be identified as pure liquid water clouds. All three methods were applied to measurements above a cloud field observed during ASTAR 2007. The comparison with independent in situ microphysical measurements shows the ability of the three approaches to identify the ice phase in Arctic boundary-layer clouds. Text albedo Arctic Greenland Greenland Sea Copernicus Publications: E-Journals Arctic Greenland Atmospheric Chemistry and Physics 8 24 7493 7505 |
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Open Polar |
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Copernicus Publications: E-Journals |
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ftcopernicus |
language |
English |
description |
Arctic boundary-layer clouds were investigated with remote sensing and in situ instruments during the Arctic Study of Tropospheric Aerosol, Clouds and Radiation (ASTAR) campaign in March and April 2007. The clouds formed in a cold air outbreak over the open Greenland Sea. Beside the predominant mixed-phase clouds pure liquid water and ice clouds were observed. Utilizing measurements of solar radiation reflected by the clouds three methods to retrieve the thermodynamic phase of the cloud are introduced and compared. Two ice indices I S and I P were obtained by analyzing the spectral pattern of the cloud top reflectance in the near infrared (1500–1800 nm wavelength) spectral range which is characterized by ice and water absorption. While I S analyzes the spectral slope of the reflectance in this wavelength range, I S utilizes a principle component analysis (PCA) of the spectral reflectance. A third ice index I A is based on the different side scattering of spherical liquid water particles and nonspherical ice crystals which was recorded in simultaneous measurements of spectral cloud albedo and reflectance. Radiative transfer simulations show that I S , I P and I A range between 5 to 80, 0 to 8 and 1 to 1.25 respectively with lowest values indicating pure liquid water clouds and highest values pure ice clouds. The spectral slope ice index I S and the PCA ice index I P are found to be strongly sensitive to the effective diameter of the ice crystals present in the cloud. Therefore, the identification of mixed-phase clouds requires a priori knowledge of the ice crystal dimension. The reflectance-albedo ice index I A is mainly dominated by the uppermost cloud layer (τ<1.5). Therefore, typical boundary-layer mixed-phase clouds with a liquid cloud top layer will be identified as pure liquid water clouds. All three methods were applied to measurements above a cloud field observed during ASTAR 2007. The comparison with independent in situ microphysical measurements shows the ability of the three approaches to identify the ice phase in Arctic boundary-layer clouds. |
format |
Text |
author |
Ehrlich, A. Bierwirth, E. Wendisch, M. Gayet, J.-F. Mioche, G. Lampert, A. Heintzenberg, J. |
spellingShingle |
Ehrlich, A. Bierwirth, E. Wendisch, M. Gayet, J.-F. Mioche, G. Lampert, A. Heintzenberg, J. Cloud phase identification of Arctic boundary-layer clouds from airborne spectral reflection measurements: test of three approaches |
author_facet |
Ehrlich, A. Bierwirth, E. Wendisch, M. Gayet, J.-F. Mioche, G. Lampert, A. Heintzenberg, J. |
author_sort |
Ehrlich, A. |
title |
Cloud phase identification of Arctic boundary-layer clouds from airborne spectral reflection measurements: test of three approaches |
title_short |
Cloud phase identification of Arctic boundary-layer clouds from airborne spectral reflection measurements: test of three approaches |
title_full |
Cloud phase identification of Arctic boundary-layer clouds from airborne spectral reflection measurements: test of three approaches |
title_fullStr |
Cloud phase identification of Arctic boundary-layer clouds from airborne spectral reflection measurements: test of three approaches |
title_full_unstemmed |
Cloud phase identification of Arctic boundary-layer clouds from airborne spectral reflection measurements: test of three approaches |
title_sort |
cloud phase identification of arctic boundary-layer clouds from airborne spectral reflection measurements: test of three approaches |
publishDate |
2018 |
url |
https://doi.org/10.5194/acp-8-7493-2008 https://www.atmos-chem-phys.net/8/7493/2008/ |
geographic |
Arctic Greenland |
geographic_facet |
Arctic Greenland |
genre |
albedo Arctic Greenland Greenland Sea |
genre_facet |
albedo Arctic Greenland Greenland Sea |
op_source |
eISSN: 1680-7324 |
op_relation |
doi:10.5194/acp-8-7493-2008 https://www.atmos-chem-phys.net/8/7493/2008/ |
op_doi |
https://doi.org/10.5194/acp-8-7493-2008 |
container_title |
Atmospheric Chemistry and Physics |
container_volume |
8 |
container_issue |
24 |
container_start_page |
7493 |
op_container_end_page |
7505 |
_version_ |
1766246382939668480 |