Challenges in Modeling Turbulent Heat Fluxes to Snowpacks in Forest Clearings
Challenges in Modeling Turbulent Heat Fluxes to Snowpacks in Forest Clearings
复制标题
模拟森林空地积雪湍流热通量的挑战
DOI：
10.1175/jhm-d-18-0050.1
复制
发表时间：
2018
影响因子：
3.8
通讯作者：
N. Kinar
中科院分区：
文献类型：
--
作者：
J. Conway;J. Pomeroy;W. Helgason;N. Kinar
森林空地是万年青森林的共同特征，产生不同于邻近森林和开阔地形的积雪堆积和融化。本研究调查的挑战，在指定湍流通量的显热和潜热积雪在森林空地。在加拿大落基山脉的两个森林空地积雪模拟使用一维（1D）积雪模型。在选择如何指定湍流通量时，发现优化对测得的雪表面温度或融雪之间的权衡。使用莫宁-奥布霍夫相似理论的计划往往会产生负偏差的表面温度，而计划，增强湍流通量，以减少表面温度偏差，导致过多的熔体。从蒙特卡罗实验的不确定性估计表明，没有现实的参数集可以成功地消除表面温度和熔体的偏差。为了成功模拟低风速条件下的地表温度，需要一个不包括大气稳定度修正的简单方案。非湍流平流通量和/或湍流的非本地源被认为是占低风条件下的热交换的维护。通过在低风速条件下允许增强潜热通量，改进了融雪的模拟。当积雪模型在表面温度上进行优化时，需要谨慎，因为模型调整可以补偿雪表面和积雪内的辐射，传导和湍流热交换的概念和数值模型中的缺陷。在水文和气象模型中，这种模型调整可能会对森林砍伐模拟中的融化速度和无雪过渡时间产生很大影响。
Forest clearings are common features of evergreen forests and produce snowpack accumulation and melt differing from that in adjacent forests and open terrain. This study has investigated the challenges in specifying the turbulent fluxes of sensible and latent heat to snowpacks in forest clearings. The snowpack in two forest clearings in the Canadian Rockies was simulated using a one-dimensional (1D) snowpack model. A trade-off was found between optimizing against measured snow surface temperature or snowmelt when choosing how to specify the turbulent fluxes. Schemes using the Monin–Obukhov similarity theory tended to produce negatively biased surface temperature, while schemes that enhanced turbulent fluxes, to reduce the surface temperature bias, resulted in too much melt. Uncertainty estimates from Monte Carlo experiments showed that no realistic parameter set could successfully remove biases in both surface temperature and melt. A simple scheme that excludes atmospheric stability correction was required to successfully simulate surface temperature under low wind speed conditions. Nonturbulent advective fluxes and/or nonlocal sources of turbulence are thought to account for the maintenance of heat exchange in low-wind conditions. The simulation of snowmelt was improved by allowing enhanced latent heat fluxes during low-wind conditions. Caution is warranted when snowpack models are optimized on surface temperature, as model tuning may compensate for deficiencies in conceptual and numerical models of radiative, conductive, and turbulent heat exchange at the snow surface and within the snowpack. Such model tuning could have large impacts on the melt rate and timing of the snow-free transition in simulations of forest clearings within hydrological and meteorological models.