In this study we have conducted a survey of westward-propagating mixed Rossby–Gravity (MRG) wave events in the upper troposphere and quantified their association with the intrusions of extratropical disturbances for the period 1979–2019. MRG wave events are identified by imposing the meridional structure of theoretical MRG waves onto the equatorial meridional winds at 200 hPa. In all, 2390 MRG wave events are identified and the majority (61%) of them occurred during the months of May–October, and 65% of the total MRG wave events occurred over the central–east Pacific and Atlantic Ocean domains. Not only the frequency of occurrence but also the amplitude, wavenumber and trapping scale of the MRG wave events are found to exhibit a clear seasonality. MRG wave events associated with intrusions of extratropical disturbances are identified as when the potential vorticity on the 350-K isentropic surface at 15° latitude exceeded 1 Potential Vorticity Unit (PVU) in the vicinity of the MRG wave events. We find that 37% of the MRG wave events are intrusion MRG wave events and a large majority (88%) of such events occurred over the central–east Pacific and Atlantic Ocean domains. It is also noteworthy that nearly 70% of such intrusions occurred in the winter hemisphere where the westerly wind ducts are well developed. Over the central–east Pacific during northern hemispheric (NH) winter, it is observed that the intrusion MRG wave events have a bigger amplitude and have a larger meridional extent compared to non-intrusion MRG wave events. They also exhibit a similar spatial scale as the extratropical disturbances implying that resonant interactions may be a primary mechanism for the genesis of MRG wave events. During NH summer, on the other hand, MRG wave events are primarily triggered by convective processes and the extratropical disturbances may be instrumental in amplifying their amplitude.

中文翻译：

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向西传播的混合罗斯贝重力波的调查及其与温带扰动的关联的量化

在这项研究中，我们对对流层上层向西传播的混合罗斯贝重力（MRG）波事件进行了调查，并量化了它们与 1979 年至 2019 年期间温带扰动入侵的关联。MRG 波事件是通过将理论 MRG 波的经向结构强加到 200 hPa 赤道经向风上来识别的。总共识别出 2390 个 MRG 波事件，其中大多数（61%）发生在 5 月至 10 月期间，并且 65% 的 MRG 波事件发生在中东部太平洋和大西洋地区。MRG波事件不仅发生频率，而且在振幅、波数和捕获尺度上都表现出明显的季节性。当 15°纬度 350-K 等熵表面上的位涡在 MRG 波事件附近超过 1 个位涡单位 (PVU) 时，即可识别与温带扰动侵入相关的 MRG 波事件。我们发现 37% 的 MRG 波事件是入侵 MRG 波事件，其中绝大多数 (88%) 发生在中东部太平洋和大西洋地区。还值得注意的是，近70%的此类入侵发生在西风管发育良好的冬半球。北半球冬季中东太平洋上空，与非入侵MRG波事件相比，入侵MRG波事件具有更大的振幅和更大的经向范围。它们还表现出与温带扰动相似的空间尺度，这意味着共振相互作用可能是 MRG 波事件发生的主要机制。另一方面，在北半球夏季，MRG 波事件主要由对流过程触发，温带扰动可能有助于放大其幅度。