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球调和函数和相应的大气环流拓扑模型

Spherical Harmonics and Corresponding Atmospheric Circulation Topological Model

  • 摘要: 球调和函数的Nodal 集(零集)将球面剖分成许多小块。剖分出的顶点数v,边数E ,面数F和球面拓扑的欧拉示性数 χ 之间的关系为 χ = V - E + F = 2 。若球面上流场为有旋场,则Nodal集的物理意义为球面的垂直涡度为零,Nodal集将球面分成正负涡度相间的小块,分别代表气旋,反气旋。对仅有纬向气流的有旋场,则Nodal集既是垂直涡度为零也是纬度加权纬向气流的最大值集。若球面上流场为无旋梯度场,则纬向的Nodal集则是等位势线或等压线,南北的经向环流就和Nodal集相垂直,Nodal集是水平散度为零,剖分球面成正负水平散度相间的小块。据此球面上的纬向环流,经向环流,Hadley环流,三圈环流与行星风带等大气环流,从拓扑上定性地就知道它们的模型。然后再从流场临界点性质加以验证。

     

    Abstract: The nodal sets (zero sets) of spherical harmonics divide the spherical surface into numerous small regions through their intersections and result in the emergence of vertices (V), edges (E), and faces (F). The relationship between these elements and the Euler characteristic (χ) of the spherical topology is given by χ = V - E + F = 2. If the flow field on the spherical surface is vortical, the physical interpretation of nodal sets is that the vertical vorticity on the sphere is zero. And Nodal sets divide the sphere into alternating regions of positive and negative vorticity, representing cyclones and anticyclones, respectively. For vortical fields consisting solely of zonal flow, the nodal sets coincide with both the locations of zero vertical vorticity and the latitude weighted maxima of the zonal flow. If the flow field on the spherical surface is a non-vortical gradient field, the zonal nodal set represents lines of constant potential or isobars. The meridional circulation, such as the north-south meridional flow, is perpendicular to the nodal set. The nodal set corresponds to regions of zero horizontal divergence, dividing the spherical surface into alternating patches of positive and negative horizontal divergence. Based on these considerations, the qualitative models of atmospheric circulations, such as meridional and zonal flows, Hadley circulation, and the three?cell circulation system with its associated planetary wind belts on the sphere can be inferred from a topological perspective. Subsequently, the models can be further validated through the properties of critical points in the flow field.

     

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