@article{ccb9580f37a74043888896202929b220,
title = "Temporal characteristics of cloud radiative effects on the Greenland Ice Sheet: Discoveries from multiyear automatic weather station measurements",
abstract = "The impact of clouds on Greenland's surface melt is difficult to quantify due to the limited amount of in situ observations. To better quantify cloud radiative effects (CRE), we utilize 29 automatic weather stations and provide the first analysis on seasonal and hourly timescales in both accumulation and ablation zones. Seasonal CRE shows opposing cycles across geographical regions. CRE generally increases during melt season in the north of Greenland, mainly due to longwave CRE enhancement by cloud fraction and liquid water. CRE decreases from May to July and increases afterwards in the middle and south of Greenland, mainly due to strengthened shortwave CRE caused by surface albedo reduction. This finding resolves the contrasting seasonal distributions in previous studies at different Arctic locations. Longwave seasonal cycle also shifts from increasing in the north to decreasing in the south, implying spatial variations in cloud and atmospheric conditions. On hourly timescales, longwave downwelling radiation exhibits a bimodal distribution peaking at ∼−70 W/m 2 (i.e., clear state) and ∼0 W/m 2 (i.e., cloudy state), suggesting that Greenland alternates between fairly clear and overcast. In the cloudy state, CRE strongly correlates with the combined influence of solar zenith angle and albedo (r = 0.85, p < 0.01) probably because clouds are thick enough for CRE to become saturated. The close relationship between CRE and albedo over dark surfaces suggests a stabilizing feedback: Net CRE is negative at low albedo caused by snow melt and snow metamorphism and thus tends to increase albedo and decelerate surface melt. ",
keywords = "automatic weather stations, cloud, Greenland, radiation",
author = "Wenshan Wang and Zender, {Charles S.} and {van As}, Dirk",
note = "Funding Information: The authors acknowledge the GC-Net (http://cires1.colorado.edu/science/groups/steffen//gcnet/order/admin/station.php) and PROMICE (http://www.promice.org/DataDownload.html) teams for providing AWS measurements, and thank Dr. Nathaniel B. Miller and Dr. David Longenecker for providing the NOAA GMD radiation measurements at Summit, Greenland (https://www.esrl.noaa.gov/gmd/dv/data/index.php?category=Radiation&site=SUM) and patiently answering all our questions. We thank Mr. Clive Lee from Kipp & Zonen for helping us investigate the window overheating problem of unshaded and unventilated pyrgeometers. The KAN stations from PROMICE are funded by the Greenland Analogue Project (GAP). The AIRS level 3 atmospheric profiles were obtained from the Goddard Earth Sciences Data and Information Services Center provided by the Jet Propulsion Laboratory, California Institute of Technology (https://disc.gsfc.nasa.gov/datasets/AIRX3STD_V006 /summary?keywords=AIRX3STD). The ICECAPS radiosonde data at Summit, Greenland were obtained from the data ftp of the Earth System Research Laboratory, the National Oceanic and Atmospheric Administration (ftp://ftp1.esrl.noaa.gov/psd3 /arctic/summit/radiosonde/processed/). The radiation, meteorology and atmospheric profile data at Barrow, Alaska, USA, were obtained from the Atmospheric Radiation Measurement (ARM) Program sponsored by the U.S. Department of Energy, Office of Science, Office of Biological and Environmental Research, Climate and Environmental Sciences Division (http://www.archive.arm.gov/discovery/\#v/results/s/fsite::nsa.P/ffac::nsa.C1). Supported by NASA ACCESS NNX14AH55A, NASA AIST 80NSSC17K0540, and DOE ACME DE-SC0012998. Funding Information: The authors acknowledge the GC-Net (http://cires1.colorado.edu/science/ groups/steffen//gcnet/order/ admin/station.php) and PROMICE (http://www.promice.org/ DataDownload.html) teams for providing AWS measurements, and thank Dr. Nathaniel B. Miller and Dr. David Longenecker for providing the NOAA GMD radiation measurements at Summit, Greenland (https://www.esrl.noaa.gov/gmd/dv/ data/index.php?category=Radiation&site =SUM) and patiently answering all our questions. We thank Mr. Clive Lee from Kipp & Zonen for helping us investigate the window overheating problem of unshaded and unventilated pyrgeometers. The KAN stations from PROMICE are funded by the Greenland Analogue Project (GAP). The AIRS level 3 atmospheric profiles were obtained from the Goddard Earth Sciences Data and Information Services Center provided by the Jet Propulsion Laboratory, California Institute of Technology (https://disc.gsfc.nasa.gov/ datasets/AIRX3STD_V006 /summary? keywords=AIRX3STD). The ICECAPS radiosonde data at Summit, Greenland were obtained from the data ftp of the Earth System Research Laboratory, the National Oceanic and Atmospheric Administration (ftp://ftp1.esrl.noaa.gov/psd3 /arctic/summit/radiosonde/processed/). The radiation, meteorology and atmospheric profile data at Barrow, Alaska, USA, were obtained from the Atmospheric Radiation Measurement (ARM) Program sponsored by the U.S. Department of Energy, Office of Science, Office of Biological and Environmental Research, Climate and Environmental Sciences Division (http://www.archive.arm.gov/discovery/ \#v/results/s/fsite::nsa.P/ffac::nsa.C1). Supported by NASA ACCESS NNX14AH55A, NASA AIST 80NSSC17K0540, and DOE ACME DE-SC0012998. Publisher Copyright: {\textcopyright}2018. American Geophysical Union. All Rights Reserved.",
year = "2018",
month = oct,
day = "27",
doi = "10.1029/2018JD028540",
language = "English",
volume = "123",
pages = "11,348--11,361",
journal = "Journal of Geophysical Research: Atmospheres",
issn = "2169-8996",
publisher = "Wiley",
number = "20",
}
