The Arctic is changing more rapidly than lower latitudes in response to climate change. One measure of that change is the impact of rising temperatures on snowpack. A long-term record of the date of spring snowmelt and the onset of fall snowpack at the Barrow Observatory is an indicator of that change. Daily albedo measurements are used to determine those dates. Albedo from the current year is shown below in its historical context.
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The albedo ratio is calculated using the ratio of the measured daily mean downwelling shortwave radiation and upwelling shortwave radiation at the NOAA Global Monitoring Laboratory (GML) Barrow Observatory (BRW) (Shown as the blue line in figure 1).
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The 1998-2022 mean is shown as the solid gray line with ± one standard deviation of the mean represented by the shaded area.
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The day of snowmelt is determined when the measured daily mean surface albedo drops below 0.3 (represented in the solid red line). While fresh snow has a high albedo (0.8-0.9), the tundra beneath has a very low albedo (0.15-0.25). This ratio of 0.3 gives an indication of when the underlying tundra has been exposed [Stone et al. 2002, Cox et al. 2017]. Although it is possible for the ratio to rise above this threshold for a few days, when the albedo falls below this 0.3, it often does not rise above this value until the following snow season [Cox et al. 2017].
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The Snow-in date (represented by the dotted red line) is determined when the albedo ratio rises above 0.6 or when snow depth persists above 2.54cm (> 1 inch) [Cox et al. 2017]. Compared to the melt-date, the snow-in date is more subjectively determined. In the spring, melt is generally uniform across the region, while the autumn often provides a spatially scattered onset where snowfall can melt before snow cover persists through the winter [Cox et al. 2017].
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Data used to generate this plot (updated daily) is available here. Live cameras of the Barrow Observatory are available here. A more extensive study of albedo (with data up to 2016) can be found here. This study utilizes albedo, soil temperature, and even bird nesting trends.
Additional Information
Barrow's Annual Snow Cycle; Ecological Responses to a Lengthening Snow-free Season
References
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Cox, C. J., R. S. Stone, D. C. Douglas, D. M. Stanitski, G. J. Divoky, G. S. Dutton, C. Sweeney, J. C. George; D. U. Longenecker, 2017: Drivers and environmental responses to the changing annual snow cycle of northern Alaska ; Bull. Am. Meteor. Soc., doi:10.1175/BAMS-D-16-0201.1.
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Stone, R. S., E. G. Dutton, J. M. Harris, and D. Longenecker, 2002: Earlier spring snowmelt in northern Alaska as an indicator of climate change , J. Geophys. Res., 107(D10), 4089, doi:10.1029/2000JD000286.
Detailed Methodology
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Calculated Downwelling Shortwave using the (Direct * Cos(sza))+Diffuse where sza is the Solar Zenith Angle.
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Hourly data is averaged into daily values and then the albedo is calculated (Shortwave upwelling/Shortwave downwelling).
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Used albedo ratios > 0.92 or < 0.08.
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Used data between sunrise and sunset.
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Upwelling measurements less than 10 W/m2 are not used.
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Zenith angles greater than 85° are removed.
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Negative downwelling measurements are not used.
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Adjusted the time zones to local time to account for UTC differences.
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“The snow-in date is defined as the day when > 1 inch (2.54 cm) of snow persists or when albedo exceeds 60% (Cox et al. 2016).”
