气候变化领域集成服务门户(CCPortal): Sensitivity of active-layer freezing process to snow cover in Arctic Alaska

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DOI	10.5194/tc-13-197-2019
	Sensitivity of active-layer freezing process to snow cover in Arctic Alaska
	Yi Y.; Kimball J.S.; Chen R.H.; Moghaddam M.; Miller C.E.
发表日期	2019
ISSN	19940416
EISSN	13
起始页码	197
结束页码	218
卷号	13 期号:1 页码:197-218
英文摘要	The contribution of cold-season soil respiration to the Arctic-boreal carbon cycle and its potential feedback to the global climate remain poorly quantified, partly due to a poor understanding of changes in the soil thermal regime and liquid water content during the soil-freezing process. Here, we characterized the processes controlling active-layer freezing in Arctic Alaska using an integrated approach combining in situ soil measurements, local-scale (~50m) longwave radar retrievals from NASA airborne P-band polarimetric SAR (PolSAR) and a remote-sensing-driven permafrost model. To better capture landscape variability in snow cover and its influence on the soil thermal regime, we downscaled global coarse-resolution (0.5°) MERRA-2 reanalysis snow depth data using finer-scale (500 m) MODIS snow cover extent (SCE) observations. The downscaled 1 km snow depth data were used as key inputs to the permafrost model, capturing finer-scale variability associated with local topography and with favorable accuracy relative to the SNOTEL site measurements in Arctic Alaska (mean RMSE = 0.16m, bias =-m). In situ tundra soil dielectric constant (ϵ) profile measurements were used for model parameterization of the soil organic layer and unfrozen-water content curve. The resulting model-simulated mean zero-curtain period was generally consistent with in situ observations spanning a 2° latitudinal transect along the Alaska North Slope (R: 0.6±0.2; RMSE: 19±6 days), with an estimated mean zero-curtain period ranging from 61±11 to 73±15 days at 0.25 to 0.45 m depths. Along the same transect, both the observed and model-simulated zero-curtain periods were positively correlated (R 0.55, p 0.01) with a MODIS-derived snow cover fraction (SCF) from September to October. We also examined the airborne P-band radar-retrieved μ profile along this transect in 2014 and 2015, which is sensitive to near-surface soil liquid water content and freeze-thaw status. The μ difference in radar retrievals for the surface (~>0.1 m) soil between late August and early October was negatively correlated with SCF in September (R=0.77, p 0.01); areas with lower SCF generally showed larger μ reductions, indicating earlier surface soil freezing. On regional scales, the simulated zero curtain in the upper ( 0.4m) soils showed large variability and was closely associated with variations in early cold-season snow cover. Areas with earlier snow onset generally showed a longer zero-curtain period; however, the soil freeze onset and zero-curtain period in deeper ( 0.5m) soils were more closely linked to maximum thaw depth. Our findings indicate that a deepening active layer associated with climate warming will lead to persistent unfrozen conditions in deeper soils, promoting greater cold-season soil carbon loss. © Author(s) 2019.
语种	英语
WOS研究方向	Physical Geography ; Geology
scopus关键词	active layer; carbon cycle; dielectric property; freezing; integrated approach; MODIS; parameterization; permafrost; sensitivity analysis; snow cover; soil respiration; synthetic aperture radar; thermal regime; tundra soil; water content; Alaska; Arctic; North Slope; United States
来源期刊	The Cryosphere
文献类型	期刊论文
条目标识符	http://gcip.llas.ac.cn/handle/2XKMVOVA/92219
作者单位	Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA, United States; Numerical Terradynamic Simulation Group, University of Montana, Missoula, MT, United States; Department of Electrical Engineering, University of Southern California, Los Angeles, CA, United States
推荐引用方式 GB/T 7714	Yi Y.,Kimball J.S.,Chen R.H.,et al. Sensitivity of active-layer freezing process to snow cover in Arctic Alaska[J],2019,13(1):197-218.
APA	Yi Y.,Kimball J.S.,Chen R.H.,Moghaddam M.,&Miller C.E..(2019).Sensitivity of active-layer freezing process to snow cover in Arctic Alaska.The Cryosphere,13(1),197-218.
MLA	Yi Y.,et al."Sensitivity of active-layer freezing process to snow cover in Arctic Alaska".The Cryosphere 13.1(2019):197-218.