Similar to Earth, Saturn’s largest moon, Titan, possesses a system of high-altitude zonal winds (or jets) that encircle the globe. Using the Atacama Large Millimeter/submillimeter Array (ALMA) in 2016 August, Lellouch et al. discovered an equatorial jet at much higher altitudes than previously known, with a surprisingly fast speed of up to ∼340m s⁻¹; however, the origin of such high velocities is not yet understood. We obtained spectrally and spatially resolved ALMA observations in 2017 May to map Titan’s 3D global wind field and compare our results with a re-analysis of the 2016 August data. Doppler wind velocity maps were derived in the altitude range ∼300–1000 km (from the upper stratosphere to the thermosphere). At the highest thermospheric altitudes, a 47% reduction in the equatorial zonal wind speed was measured over the 9 month period (corresponding to L _s = 82–90 on Titan). This is interpreted as being due to a dramatic slowing and loss of confinement (broadening) of the recently discovered thermospheric equatorial jet, as a result of dynamical instability. These unexpectedly rapid changes in the upper-atmospheric dynamics are consistent with strong variability of the jet’s primary driving mechanism.

与土星相似，土星最大的卫星土卫六拥有环绕地球的高空纬向风（或喷气流）系统。Lellouch等人在2016年8月使用阿塔卡马大型毫米/亚毫米阵列（ALMA）。发现了一个赤道喷流，其高度比以前已知的高得多，其出奇的快速速度高达340m s ^-1; 然而，如此高速的起源尚不清楚。我们在2017年5月获得了光谱和空间解析的ALMA观测值，以绘制Titan的3D全球风场图，并将我们的结果与2016年8月数据的重新分析进行了比较。多普勒风速图是在海拔约300-1000 km（从平流层上部到热层）范围内得出的。在最高的热层高度，在9个月的时间内测得的赤道纬向风速降低了47％（对应于L _s = Titan上的82–90）。这被解释为是由于动态不稳定性而导致最近发现的热层赤道射流急剧减慢并失去了限制（扩大）。上层大气动力学中这些出乎意料的快速变化与喷气机主要驱动机构的强烈变化相一致。