Evolution of Langmuir circulation during a storm
Evolution of Langmuir circulation during a storm
复制标题
DOI：
10.1029/97jc03611
复制
发表时间：
1998-06
影响因子：
--
通讯作者：
Jerome A. Smith
中科院分区：
文献类型：
--
作者：
Jerome A. Smith
沿沿着离加州Point Arguello 50 ~ 150 km的漂移轨迹测量风应力、波浪、分层、速度剖面和径向速度和声学后向散射强度的表面场。1995年3月8日，东南方向的风速从平静增加到12米/秒，与西北方向的涌浪相反。协调世界时3月9日中午，系统风速增至15米/秒，在接下来的12小时内保持稳定，短暂下降并转向60°，然后又返回。混合层迅速加深至25米，随后在接下来的两天里保持大致稳定，尽管阵风风速持续在15-25米/秒。相控阵多普勒声纳系统以5米乘10米的空间分辨率对250米乘150米的表面进行测量。超过6分钟的衰减去除了表面波，允许连续评估与表面运动相关的特征的强度、取向、间隔和组织程度（例如，朗缪尔循环），即使条件太粗糙，无法进行目视评估。几个结果突出：（1）如前所述，大多数风混合产生于跨温跃层的惯性切变。(2)与朗缪尔环流的风/波强迫一致，Plueddemann等人[1996]认为表面速度变化的尺度类似于（u*Us），其中u* 是摩擦速度，Us是表面斯托克斯漂移;然而，一旦朗缪尔环流建立，这里的测量仅与（Us）1成比例。(3)考虑到风和波浪的大小，这里的速度方差比预期的要弱，导致估计的混合效应较小。(4)LC强度的大波动被认为是在风的短暂转向之前，有人建议，气泡浮力可以发挥动态作用。(5)平均取向和间距可以针对强度与径向速度特征而不同。
Wind stress, waves, stratification, velocity profiles, and surface fields of radial velocity and acoustic backscatter intensity were measured along a drift track 50 to 150 km off Point Arguello, California. On March 8, 1995, the wind increased from calm to 12 m/s from the SE, opposing swell from the NW. It increased to 15 m/s at noon UTC on March 9, remained steady over the next 12 hours, briefly dropped and veered by 60°, then returned. A mixed layer deepened quickly to 25 m, then held roughly steady through the next 2 days, in spite of gusty winds continuing at 15–25 m/s. A phased-array Doppler sonar system took measurements covering 250 m by 150 m of the surface, with 5 m by 10 m spatial resolution. Averages over 6 min removed surface waves, permitting continuous assessment of strength, orientation, spacing, and degree of organization of features associated with surface motion (e.g., Langmuir circulation), even when conditions were too rough for visual assessment. Several results stand out: (1) As found previously, most wind mixing arises from inertial shear across the thermocline. (2) Consistent with wind/wave forcing of Langmuir circulation, Plueddemann et al. [1996] suggest that surface velocity variance scales like (u*Us), where u* is friction velocity and Us is the surface Stokes' drift; however, the measurements here scale with (Us)1 alone, once Langmuir circulation is established. (3) The velocity variance is weaker here than expected, given the magnitudes of wind and waves, leading to a smaller estimated mixing effect. (4) Large vacillations in LC strength are seen just before the brief veering of the wind; it is suggested that bubble buoyancy could play a dynamic role. (5) Mean orientation and spacing can differ for intensity versus radial velocity features.