EPIC Simulations of Time-Dependent, Three-Dimensional Vortices with Application to Neptune's Great Dark Spot
EPIC Simulations of Time-Dependent, Three-Dimensional Vortices with Application to Neptune's Great Dark Spot
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对随时间变化的三维涡流进行 EPIC 模拟并应用于海王星大黑斑
DOI：
10.1006/icar.1998.5918
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发表时间：
1997
期刊：
影响因子：
3.2
通讯作者：
T. Dowling
中科院分区：
文献类型：
--
作者：
R. LeBeau;T. Dowling
本文采用了Dowlinget al.（1998）在其合著论文中描述的EPIC总环流模型。icarus132,221 - 238)，以模拟类似于海王星条件下的大漩涡。涡旋是反气旋，横截面大致为椭圆形，其运动类似于海王星大黑斑（GDS）的行为，包括赤道漂移，纵横比和方向角的振荡，以及尾部的形成。涡旋也表现出三维运动，这可能解释了GDS偶尔出现的两个重叠的椭圆。我们发现涡旋的经向漂移与背景绝对涡度β*的经向梯度有关。这一结果补充了对飓风漂移的研究。这种相关性表明，海王星上gds型漩涡的漂移率可以通过哈勃太空望远镜（HST）长期监测，这是对行星上涡度梯度的诊断。在我们的模拟中，最适合旅行者GDS漂移率的值为β*≈2 × 10−12m−1s−1。这大约是纬向风廓线给出的值的13倍，纬向风廓线是通过对云跟踪数据拟合一个纬度偶多项式而确定的（Sromovskyet .1993）。用球面谐波（勒让德多项式）重新调整数据，得到的β*值约为Sromovskyet .值的12倍，更符合我们的涡移结果。我们证明，在β* = 0的情况下（对应于Kida（1981）的解析模型）和β* >的情况下，涡旋形状振荡都发生。形状振荡的解释比解释经向漂移更为复杂，因为形状振荡对涡旋和环境中的涡度分布很敏感。ross - by-wave频散对离赤道太近的模式涡旋影响很大。涡旋在到达赤道之前就中断了，分散成波，在几周内在南半球和北半球传播。
Abstract We use the EPIC general circulation model, described in the companion paper by Dowlinget al.(1998.Icarus132, 221–238), to simulate large vortices under conditions similar to those found on Neptune. The vortices are anticyclones with roughly elliptical cross sections and exhibit motions that resemble the behavior of Neptune's Great Dark Spot (GDS), including equatorward drift, oscillations in aspect ratio and orientation angle, and tail formation. The vortices also exhibit three-dimensional motions that may explain the occasional appearance of the GDS as two overlapping ellipses. We find that the meridional drift of the vortices is correlated with the meridional gradient of the background absolute vorticity, β*. This result complements studies of hurricane drift. The correlation suggests that the drift rate of GDS-type vortices on Neptune, which can be monitored over the long term by the Hubble Space Telescope (HST), is diagnostic of the vorticity gradient on the planet. The best fit to the Voyager GDS drift rate in our simulations corresponds to β* ≈ 2 × 10−12m−1s−1. This is about 1 3 of the value given by the zonal-wind profile determined by fitting an even polynomial in latitude to the cloud-tracking data (Sromovskyet al.1993). Refitting the data with spherical harmonics (Legendre polynomials) yields a value for β* that is about 1 2 of the Sromovskyet al.value, and more in line with our vortex-drift results. We show that vortex shape oscillations occur both in the case β* = 0, corresponding to the analytical model of Kida (1981), and for β* > 0. Interpreting the shape oscillations is more complicated than interpreting meridional drift because shape oscillations are sensitive to the distribution of vorticity in the vortex as well as in the environment. Rossby-wave dispersion strongly affects the model vortices that drift too close to the equator. The vortices disrupt before reaching the equator, dispersing into waves that propagate in both the southern and northern hemispheres over the course of a few weeks.