The Cassini spacecraft completed 22 orbits around Saturn known as the “Grand Finale” over a 5 months interval, during which time the spacecraft traversed the previously unexplored region between Saturn and its equatorial rings near periapsis. The magnetic field observations reveal the presence of temporally variable low‐latitude field‐aligned currents which are thought to be driven by velocity shears in the neutral zonal winds at magnetically conjugate thermospheric latitudes. We consider atmospheric waves as a plausible driver of temporal variability in the low‐latitude thermosphere, and empirically constrain the region in which they perturb the zonal flows to be between ±25° latitude. By investigating an extensive range of hypothetical wind profiles, we present and analyze a timeseries of the modeled velocity shears in thermospheric zonal flows, with direct comparisons to empirically inferred angular velocity shears from the B_ϕ observations. We determine the maximum temporal variability in the peak neutral zonal winds over the Grand Finale interval to be ∼350 m/s assuming steady‐state ionospheric Pedersen conductances. We further show that the ionospheric currents measured must be in steady‐state on ∼10 min timescales, and axisymmetric over ∼2 h of local time in the near‐equatorial ionosphere. Our study illustrates the potential to use of magnetospheric datasets to constrain atmospheric variability in the thermosphere region.

中文翻译：

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使用磁场测量约束土星低纬电离层中性风的时间变化

卡西尼号飞船在5个月的时间间隔内完成了绕土星的22个轨道，即“大结局”，在此期间，飞船穿越了土星与其赤道环附近的未开挖区域之间的先前未开发区域。磁场观测表明存在时变的低纬度磁场对准的电流，该电流被认为是由在磁共轭热层纬度的中性纬向风中的速度剪切驱动的。我们认为大气波是低纬度热圈中时间变化的合理推动因素，并根据经验将它们扰动纬向流的区域限制在纬度为±25°之间。通过研究广泛的假设风廓线，我们提出并分析了热层纬向流中速度剪切模型的时间序列，乙_φ观察。假设稳态电离层Pedersen电导，我们确定在Grand Finale间隔内峰值中性纬向风的最大时间变化为〜350 m / s。我们进一步表明，所测量的电离层电流必须在约10分钟的时标上处于稳态，并且在近赤道电离层中约2 h的当地时间轴对称。我们的研究表明了利用磁层数据集来限制热圈地区大气变化的潜力。