Landfalling atmospheric rivers (ARs) frequently trigger heavy and sometimes prolonged precipitation, especially in regions with favored orographic enhancement. The presence and strength of ARs are often described using the integrated water vapor (IWV) and the integrated vapor transport (IVT). However, the associated precipitation is not directly correlated with these two variables. Instead, the intensity of precipitation is mainly determined by the net convergence of moisture flux and the initial degree of saturation of the air column. In this study, a simple algorithm is proposed for estimating the heavy precipitation attributable to the IVT convergence. Bearing a strong resemblance to the Kuo-Anthes parameterization scheme for cumulus convection, the proposed algorithm calculates the large-scale primary condensation rate (PCR) as a proportion of the IVT convergence, with a reduction to account for the general moistening in the atmosphere. The amount of reduction is determined by the column relative humidity (CRH), which is defined as the ratio of IWV to its saturation counterpart. Our analysis indicates that the diagnosable PCR compares well to the forecast precipitation rate given by a numerical weather prediction model. It is also shown that the PCR in an air column with CRH 0.50 is negligibly small. The usefulness of CRH and PCR as two complements to standard AR analysis is illustrated in three case studies. The potential application of PCR to storm classification is also explored.

中文翻译：

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柱相对湿度和一次冷凝率作为大气河流分析的两个有用补充

登陆大气河流 (AR) 经常引发强降水，有时甚至是长时间降水，尤其是在有利于地形增强的地区。AR 的存在和强度通常使用综合水蒸气 (IWV) 和综合蒸气传输 (IVT) 来描述。然而，相关降水与这两个变量并不直接相关。相反，降水强度主要由湿气通量的净收敛和气柱的初始饱和度决定。在这项研究中，提出了一种简单的算法来估计归因于 IVT 收敛的强降水。与积云对流的 Kuo-Anthes 参数化方案非常相似，所提出的算法将大规模一次冷凝率 (PCR) 计算为 IVT 收敛的比例，并减少以考虑大气中的一般润湿。减少量由色谱柱相对湿度 (CRH) 决定，CRH 定义为 IWV 与其饱和对应物的比率。我们的分析表明，可诊断的 PCR 与数值天气预报模型给出的预测降水率相当。还表明，在带有 CRH 的空气柱中的 PCR 我们的分析表明，可诊断的 PCR 与数值天气预报模型给出的预测降水率相当。还表明，在带有 CRH 的空气柱中的 PCR 我们的分析表明，可诊断的 PCR 与数值天气预报模型给出的预测降水率相当。还表明，在带有 CRH 的空气柱中的 PCR0.50 小到可以忽略不计。三个案例研究说明了 CRH 和 PCR 作为标准 AR 分析的两个补充的有用性。还探讨了 PCR 在风暴分类中的潜在应用。