Evolution of Entropy and Mediation of the Solar Wind by Turbulence
Evolution of Entropy and Mediation of the Solar Wind by Turbulence
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DOI：
10.3847/1538-4357/ab7010
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发表时间：
2020-03
期刊：
影响因子：
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通讯作者：
L. Adhikari;G. Zank;L.-L. Zhao-L.;G. M. Webb
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文献类型：
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作者：
L. Adhikari;G. Zank;L.-L. Zhao-L.;G. M. Webb
基于太阳风和湍流输运模型方程的守恒形式，我们研究了太阳风熵的演化，并将模型结果与旅行者2号的测量结果进行了比较。对于γ=5/3(>；1)的多变指数，由于湍流的耗散，熵随距离增加，在75Au时比在1Au时高约12.84%。然而，如果多变指数满足γ<；1，则熵减小。我们发现，不仅拾取离子的产生，而且流的切变也会导致太阳风速的降低。结果表明，太阳风的流动能(动能加热能)和湍动能(磁能)之和是恒定的，说明太阳风的动能通过切变和拾离子各向同性作用转化为湍动能，湍动能通过湍动的耗散作用来加热太阳风。将太阳风熵、太阳风密度、热气压强、太阳风质子温度和脉动磁能的理论解与旅行者2号的测量结果进行了比较，结果表明理论结果与观测结果吻合较好。
We study the evolution of solar wind entropy based on a conservative formulation of solar wind and turbulence transport model equations, and compare the model results to Voyager 2 measurements. For a polytropic index of γ = 5/3 (>1), entropy increases with distance due to the dissipation of turbulence, being about 12.84% higher at 75 au than at 1 au. However, if the polytropic index satisfies γ < 1, entropy decreases. We show that not only the creation of pickup ions, but also stream-shear leads to a decrease of the solar wind speed. We show that the sum of the solar wind flow energy (kinetic plus enthalpy) and turbulent (magnetic) energy is constant, indicating that kinetic solar wind energy is transferred into turbulent energy via stream-shear and pickup ion isotropization, which then in turn heats the solar wind via the dissipation of turbulence. We compare the theoretical solutions of the solar wind entropy, the solar wind density, the thermal gas pressure, the solar wind proton temperature, and the fluctuating magnetic energy with those measured by Voyager 2. The results show that the theoretical results are in good agreement with the observed results.