Assessment of snow transport in avalanche terrain
Assessment of snow transport in avalanche terrain
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DOI：
10.1016/j.coldregions.2007.05.012
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发表时间：
2008-02
影响因子：
4.1
通讯作者：
M. Lehning;C. Fierz
中科院分区：
文献类型：
--
作者：
M. Lehning;C. Fierz
在暴风雪或随后的强风期间，对当地到区域的积雪进行评估是可靠地估计雪崩危险的先决条件。尽管几十年来它一直受到关注，但量化雪输送的问题仍然存在。从点测量到全三维模拟的系统都经过了测试，但都有各自的弱点。我们提出了一个新的漂移指数，这已经过测试，并在瑞士取得了一定的成功。该指数需要从一个避风的自动气象站和一个从风暴露的网站缩放风速输入。利用雪盖模式SNOWPACK，将气象资料外推到四个主要方面，并计算了这些方面的雪盖发展。根据测得的风向和风速，在逆风方面的雪侵蚀的阈值条件进行测试：如果风是强大到足以侵蚀目前的雪在这个方面的表面，雪层被侵蚀，运输和沉积到顺风方面。有了这个计划，虚拟的，“代表性的”积雪的四个主要方面在附近的气象站重建的过程中的冬季和质量输送率转换为背风沉积漂移指数。与FlowCapt，声学测量装置，测量当地的质量通量的比较表明，测得的质量通量相关性以及与量的背风坡沉积预测的漂移指数。此外，FlowCapt传感器和SNOWPACK漂移指数都能很好地检测到飘雪期，并与当地观察员报告的飘雪期相对应。当比较区域模式的强和弱的雪运输计算从110多个自动气象站在瑞士阿尔卑斯山与当地观察员的相应报告，也发现了良好的相关性。与早期版本的指数相反，该指数仅基于SNOWPACK的平场模拟，新指数不再高估吹雪事件的强度和持续时间。它的结论是，雪崩预警的目的，FlowCapt传感器和SNOWPACK漂移指数是合适的手段来量化本地区域雪运输。
A local to regional assessment of transported snow during snow storms or subsequent periods of strong winds is a prerequisite to reliably estimate avalanche danger. Despite the fact that it has received continuing attention for decades, the problem of quantifying snow transport persists. Systems from point measurements to full three-dimensional simulations have been tested but all have their respective weaknesses. We present a new drift index, which has been tested and operated with some success in Switzerland. The index requires input from a wind-sheltered automatic weather station and a scaled wind speed from a wind-exposed site. Using the snow cover model SNOWPACK, the meteorological data is extrapolated to the four main aspects and snow cover development is calculated for these aspects. Depending on the measured wind direction and speed, a threshold condition for snow erosion at the upwind aspect is tested: if the wind is strong enough to erode the current snow at the surface of this aspect, the snow layer is eroded, transported and deposited onto the downwind aspect. With this scheme, the virtual, “representative” snow cover on the four main aspects in the vicinity of the meteorological stations are reconstructed for the course of the winter and the mass transport rate is converted to a lee-deposition drift index. A comparison with FlowCapt, an acoustic measurement device, which measures a local mass flux, shows that the measured mass flux correlates well with the amount of lee-slope deposition predicted by the drift index. Also, drifting snow periods are well detected by both the FlowCapt sensor and the SNOWPACK drift index and correspond to drifting snow periods reported by local observers. When comparing regional patterns of strong and weak snow transport as calculated from more than 110 automatic weather stations in the Swiss Alps with corresponding reports from local observers a good correlation is found, too. As opposed to earlier versions of the index, which had been based on flat field simulations of SNOWPACK alone, the new index no longer overestimates intensity and duration of blowing snow events. It is concluded that for the purpose of avalanche warning, the FlowCapt sensor and the SNOWPACK drift index are suitable means to quantify local to regional snow transport.