Statistical analysis of the surface circulation of the California Current
Statistical analysis of the surface circulation of the California Current
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DOI：
10.1029/96jc02008
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发表时间：
1996-10
影响因子：
--
通讯作者：
M. Swenson;P. Niiler
中科院分区：
文献类型：
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作者：
M. Swenson;P. Niiler
我们利用1985-1990年加利福尼亚海流（20°N - 40°N）的一组混合层漂流浮标轨迹，获得了统计上可靠的平均海流、平均方差场和地理上变化的扩散率、积分时间尺度和积分空间尺度的估计。扩散系数的典型值为1.1 ~ 8.7 × 107 cm2 s−1，时间尺度为2.1 ~ 7.1 d，空间尺度为16 ~ 59 km。变异场向125°W方向呈较强的西向梯度，扩散系数向西南方向呈减小趋势。在靠近海岸边界和30°N， 130°W的变化场中，亚北极锋和北亚热带锋靠近加利福尼亚流的区域具有显著的各向异性。扩散度张量的反对称分量表明，气旋涡旋主导了该地区漂流者的中尺度特征。我们通过对κ∞∝u02T和κ∞∝u0L的最小二乘拟合来寻求简单的参数化，将随机速度场的运动尺度与扩散系数联系起来，其中u02为速度方差。我们没有发现可以区分这两种假设的案例。对于经向分量，线性回归是不成功的，这表明，经向偏离速度是由一种流动形式引起的，这种流动形式是由波或相干结构等显著组织起来的。漂移者的一个子集沿着他们的轨迹测量温度，我们使用所得数据来产生基于拉格朗日估计的水平涡热通量散度的第一个直接估计。此外，我们利用我们的扩散系数估计值和海表温度气气学分别计算了涡旋热通量散度的“涡旋扩散系数”参数化：∇·< u ' θ ' > =∇（κ∇Θ）。这两个独立的术语很好地吻合，这为扩散系数估计提供了一定程度的保证。加州海流涡旋热通量散度很小（<5 W m−2），对该地区上层海洋的长期热收支影响不大。
We use a set of mixed-layer drifting buoy trajectories from the California Current (20°N–40°N) during 1985–1990 to obtain statistically reliable estimates of the mean currents, the mean variance field, and the geographically varying diffusivity, integral timescales, and integral space scales. Typical values for the diffusivity are 1.1–8.7 × 107 cm2 s−1, while the timescales and space scales are 2.1–7.1 days and 16–59 km, respectively. The variance field displays a strong westward gradient out to 125°W, and diffusivity shows a tendency to decrease toward the southwest part of the domain. Significant anisotropy is found in the variance field near the coastal boundary and at 30°N, 130°W, which is the region where the subarctic and northern subtropical fronts approach the California Current. The antisymmetric component of the diffusivity tensor indicates that cyclonic eddies dominate the mesoscale signature of drifters in this region. We seek simple parameterizations to relate the scales of motion of the random velocity field to the diffusivity by testing least squares fits to κ∞ ∝ u02T and κ∞ ∝ u0L, where u02 is the velocity variance. We found no cases for which these two hypotheses could be distinguished. For the meridional component the linear regressions are not successful, which suggests that the meridional departure velocities result from a flow regime that is significantly organized by, for example, waves or coherent structures. A subset of the drifters measured temperature along their tracks, and we use the resultant data to produce the first direct estimates of the horizontal eddy heat flux divergence based on Lagrangian estimates. In addition, we separately compute the “eddy diffusivity” parameterization of the eddy heat flux divergence, ∇ · 〈u′θ′〉 = ∇(κ∇Θ), using our diffusivity estimates and a sea surface temperature climatology. The two independent terms agree well, which provides a measure of reassurance about the diffusivity estimates. The eddy heat flux divergence in the California Current is very small (<5 W m−2) and does not appear to be significant in the long-term heat budget of the upper ocean in this region.