On the u☆-U Relationship in the Stable Atmospheric Boundary Layer over Arctic Sea Ice
On the u☆-U Relationship in the Stable Atmospheric Boundary Layer over Arctic Sea Ice
复制标题
北极海冰稳定大气边界层u☆-U关系的研究
DOI：
10.3390/atmos12050591
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发表时间：
2021
期刊：
影响因子：
2.9
通讯作者：
D. Chechin
中科院分区：
文献类型：
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作者：
D. Chechin
研究了北极海冰稳定大气边界层中摩擦速度u☆与平均风速u之间的关系。为此目的，使用了北冰洋表面热收支（SHEBA）实验期间收集的观测数据。观测结果显示了所谓的“曲棍球棒”形状的u☆- u关系，其中u☆随着UUtr风速的增加而缓慢增加，其中Utr是两种状态之间过渡的风速。这种关系在最高观测高度，即9米和14米高度上最为明显，当空气表面温差超过稳定条件下的平均值时，这种关系也更为明显。结果表明，Monin-Obukhov相似理论（MOST）较好地再现了观测到的u☆−u关系。这表明，至少对于SHEBA数据集，MOST与u☆−u关系的“曲棍球棒”形状之间没有矛盾。然而，SHEBA数据以及单列模拟表明，对于稳定性强的情况，由于ABL的浅，u☆随高度显著降低。结果表明，当假设u☆与高度无关时，根据某一水平观测计算的归一化阻力系数，即所谓的动量稳定性修正函数的值可能会被显著低估。为了克服这一问题，在MOST框架中采用局部标度代替表面通量标度来考虑u☆随高度的减小。使用这种扩展的MOST使归一化阻力系数的估计更接近于Businger-Dyer关系。
A relationship between the friction velocity u☆ and mean wind speed U in a stable atmospheric boundary layer (ABL) over Arctic sea ice was considered. To that aim, the observations collected during the Surface Heat Budget of the Arctic Ocean (SHEBA) experiment were used. The observations showed the so-called “hockey-stick” shape of the u☆−U relationship, which consists of a slow increase of u☆ with increasing wind speed for UUtr, where Utr is the wind speed of transition between the two regimes. Such a relationship is most pronounced at the highest observational levels, namely at 9 and 14 m, and is also sharper when the air-surface temperature difference exceeds its average values for stable conditions. It is shown that the Monin–Obukhov similarity theory (MOST) reproduces the observed u☆−U relationship rather well. This suggests that at least for the SHEBA dataset, there is no contradiction between MOST and the “hockey-stick” shape of the u☆−U relationship. However, the SHEBA data, as well as the single-column simulations show that for cases with strong stability, u☆ significantly decreases with height due to the shallowness of the ABL. It was shown that when u☆ was assumed independent of height, the value of the normalized drag coefficient, i.e., of the so-called stability correction function for momentum, calculated using observations at a certain level, can be significantly underestimated. To overcome this, the decrease of u☆ with height was taken into account in the framework of MOST using local scaling instead of the scaling with surface fluxes. Using such an extended MOST brought the estimates of the normalized drag coefficient closer to the Businger–Dyer relation.