The potential role of low‐level circulation on the transport of atmospheric moisture towards Central America and northern South America is studied with the Dynamical Recycling Model (DRM) for the period 1981–2015. The net 2D field for advection of moisture in the DRM is estimated based on two different approaches: from the Vertically Integrated Moisture Flux (VIMF) and from a linear combination of low‐level winds (Ueff). The relative importance of low‐level wind structures is inferred from the comparison of both DRM approaches. The Ueff approach yields larger long‐term estimates of transport from the Pacific compared to the VIMF approach, largely associated with the effect of the low‐level circulation over the eastern Pacific, known as the Choco Jet (CJ). Large differences in the transport estimated by both approaches also appear to be associated with different phases of El Niño‐Southern Oscillation (ENSO), when differences in the low‐level circulation take place over the eastern Pacific and the tropical Atlantic. Similar differences are found for anomalous activity of the CJ and the Caribbean Low‐level Jet (CLLJ). The differences in the magnitude of long‐term estimates and anomalies from both 2D approaches show that details in vertical wind shear are important for the estimation of water vapour transport. However, the sign of the anomalies and correlation patterns under different circulation regimes were the same for both methods. Furthermore, with both approaches, it is found that variability in the low‐level circulation over the eastern Pacific and the tropical Atlantic is substantially related to changes in the vapour transport towards Central America and northern South America. In addition, the robustness of this signal suggests that a simple 2D tool like the DRM may be effectively used to study transport changes under different regimes, like different ENSO phases or climate change scenarios.

中文翻译：

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低水平循环在水蒸气向南美中部和北部的输送中的作用：二维拉格朗日方法的见解

利用1981-2015年期间的动态循环模型（DRM），研究了低空循环对大气水分向中美洲和南美洲北部的运输的潜在作用。DRM中水分对流的净二维场是根据两种不同方法估算的：从垂直积分水分通量（VIMF）和低水平风的线性组合（Ueff）。从两种DRM方法的比较可以推断出低层风结构的相对重要性。与VIMF方法相比，Ueff方法对来自太平洋的运输产生了更大的长期估计，这在很大程度上与东太平洋低空环流的影响（称为Choco Jet（CJ））有关。当东太平洋和热带大西洋的低空环流发生差异时，两种方法估计的输运差异也似乎与厄尔尼诺-南方涛动（ENSO）的不同阶段有关。在CJ和加勒比低空急流（CLLJ）的异常活动中发现了类似的差异。两种二维方法的长期估算值和异常值的大小差异表明，垂直风切变的细节对于估算水汽输送非常重要。但是，两种方法在不同循环方式下的异常迹象和相关模式都相同。此外，通过两种方法，研究发现，东太平洋和热带大西洋低空环流的变化与通向中美洲和南美洲北部的蒸气输送的变化密切相关。此外，该信号的鲁棒性表明，像DRM这样的简单2D工具可以有效地用于研究不同制度下的运输变化，例如不同的ENSO阶段或气候变化情景。