The Sun has a near-surface shear layer (NSSL), within which the angular velocity decreases rapidly with radius. We provide an explanation of this layer based on the thermal wind balance equation. Since convective motions are not affected by solar rotation in the top layer of the convection zone, we argue that the temperature falls at the same rate at all latitudes in this layer. This makes the thermal wind term very large in this layer and the centrifugal term has also to become very large to balance it, giving rise to the NSSL. From the values of differential rotation Ω(r < rc, θ) at radii less than a radius rc, we can calculate the temperature difference ΔT(r, θ) with respect to the standard solar model at different points of the convection zone by making use of the thermal wind balance equation. Then, we again use this equation in the top layer to calculate Ω(r > rc, θ) there from ΔT(r, θ). We carry on this exercise using both an analytical expression of the differential rotation and the actual data provided by helioseismology. We find that our theoretical results of the NSSL match the observational data reasonably well for rc ≈ 0.96R⊙, giving an estimate of the radius till which the convective motions are affected by the solar rotation.

中文翻译：

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太阳近地表剪切层的理论模型

太阳有一个近地表剪切层（NSSL），其中角速度随半径迅速减小。我们根据热风平衡方程对这一层进行了解释。由于对流运动不受对流层顶层太阳自转的影响，我们认为该层所有纬度的温度下降速度相同。这使得该层的热风项非常大，离心项也必须变得非常大以平衡它，从而产生 NSSL。根据半径小于半径 rc 的微分旋转 Ω(r < rc, θ) 的值，我们可以计算出对流区不同点相对于标准太阳模型的温差 ΔT(r, θ)：利用热风平衡方程。然后，我们再次在顶层使用这个等式从 ΔT(r, θ) 计算 Ω(r > rc, θ)。我们使用差分旋转的解析表达式和日震学提供的实际数据来进行这项工作。我们发现我们的 NSSL 理论结果与 rc ≈ 0.96R⊙ 的观测数据相当吻合，从而估计了太阳自转影响对流运动的半径。