Constraining the Temporal Variability of Neutral Winds in Saturn's Low-Latitude Ionosphere Using Magnetic Field Measurements
Constraining the Temporal Variability of Neutral Winds in Saturn's Low-Latitude Ionosphere Using Magnetic Field Measurements
复制标题
使用磁场测量限制土星低纬度电离层中性风的时间变化
DOI：
10.1029/2020je006578
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发表时间：
2021
期刊：
影响因子：
--
通讯作者：
Agiwal O
中科院分区：
文献类型：
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作者：
Agiwal O
卡西尼号航天器在 5 个月的时间间隔内完成了 22 圈土星轨道，被称为“大结局”，在此期间，航天器穿越了土星及其近点附近的赤道环之间先前未探索的区域。磁场观测揭示了时变低纬度场对准电流的存在，这些电流被认为是由磁共轭热层纬度的中性纬向风中的速度切变驱动的。我们认为大气波是低纬度热层时间变化的合理驱动因素，并根据经验将大气波扰动纬向流的区域限制在±25°纬度之间。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模拟速度切变的时间序列，并与从 Bψ 观测中凭经验推断的角速度切变进行直接比较。假设稳态电离层 Pedersen 电导，我们确定 Grand Finale 区间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，测量的电离层电流必须在~10分钟的时间尺度上处于稳态，并且在近赤道电离层的本地时间~2小时内轴对称。我们的研究说明了使用磁层数据集来限制热层区域大气变化的潜力。
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 theBϕobservations. 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.