In the southwest Pacific, a meandering jet-stream in the upper troposphere is sometimes found at ~30° S during austral winters and is usually treated as a sub-tropical jet (STJ) due to its low latitude. For two contrasting cases, we have conducted analyses from two perspectives to identify the STJ and PFJ: first, using previously published qualitative criteria to identify jet-cores and second, investigating the jet-stream axes of STJ and PFJ identified using 2-PVU curves. The results showed that the chosen meandering jet-stream case at ~30° S was a merged, and for a time, a superposed STJ and PFJ. Downstream of the jet-streak, the PFJ split to the south and the STJ to the east. This is in significant contrast to the horizontally well-separated jet-stream case chosen in this study. Some processes likely contributing to the superposition of the STJ and PFJ were analyzed and discussed. The movement of PFJ that was closely associated with the movement of the low over the Tasman Sea and the convection in and near the tropical region may have played dominant roles.

中文翻译：

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西南太平洋副热带急流与极锋急流合并叠加：案例研究

在西南太平洋，南半球冬季有时会在南纬 30° 处发现对流层上层的蜿蜒急流，由于纬度较低，通常被视为副热带急流 (STJ)。对于两个对比案例，我们从两个角度进行分析来识别 STJ 和 PFJ：首先，使用先前发布的定性标准来识别喷流核心；其次，研究使用 2-PVU 曲线识别的 STJ 和 PFJ 的喷流轴。结果表明，所选的~30°S 蜿蜒急流情况是合并的，并且一度是STJ 和PFJ 的叠加。在急流的下游，PFJ 向南分裂，STJ 向东分裂。这与本研究中选择的水平分离的急流案例形成鲜明对比。分析和讨论了一些可能导致 STJ 和 PFJ 叠加的过程。 PFJ的运动与塔斯曼海上空低压运动以及热带地区及其附近的对流运动密切相关，可能发挥了主导作用。