Insights into the Causes and Predictability of the 2022/23 California Flooding

IF 4.8 2区 地球科学 Q1 METEOROLOGY & ATMOSPHERIC SCIENCES
Siegfried D. Schubert, Yehui Chang, Anthony M. DeAngelis, Young-Kwon Lim, Natalie P. Thomas, Randal D. Koster, Michael G. Bosilovich, Andrea M. Molod, Allison Collow, Amin Dezfuli
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Abstract

Abstract In late December of 2022 and the first half of January 2023 an unprecedented series of atmospheric rivers (ARs) produced near record heavy rains and flooding over much of California. Here we employ the NASA GEOS AGCM run in a “replay” mode, together with more idealized simulations with a stationary wave model, to identify the remote forcing regions, mechanisms and underlying predictability of this flooding event. In particular, the study addresses the underlying causes of a persistent positive Pacific/North American (PNA) - like circulation pattern that facilitated the development of the ARs. We show that that pattern developed in late December as a result of vorticity forcing in the North Pacific jet exit region. We further provide evidence that this vorticity forcing was the result of a chain of events initiated in mid-December with the development of a Rossby wave (as a result of forcing linked to the MJO) that propagated from the northern Indian Ocean into the North Pacific. As such, both the initiation of the event and the eventual development of the PNA depended critically on internally-generated Rossby wave forcings, with the North Pacific jet playing a key role. This, combined with contemporaneous SST (La Niña) forcing that produced a circulation response in the AGCM that was essentially opposite to the positive PNA, underscores the fundamental lack of predictability of the event at seasonal time scales. Forecasts produced with the GEOS coupled model suggests that useful skill in predicting the PNA and extreme precipitation over California was in fact limited to lead times shorter than about 3 weeks.
洞察 2022/23 年加州洪灾的原因和可预测性
摘要 2022 年 12 月下旬和 2023 年 1 月上半月,一系列前所未有的大气河流(ARs)在加利福尼亚大部分地区造成了近乎创纪录的暴雨和洪水。在此,我们利用美国宇航局全球地球观测系统 AGCM 以 "重放 "模式运行,并使用静止波模型进行更理想化的模拟,以确定这次洪水事件的遥远强迫区域、机制和潜在的可预测性。这项研究特别探讨了类似太平洋/北美洲(PNA)的持续正向环流模式的根本原因,这种模式促进了 ARs 的发展。我们表明,这种模式是在 12 月下旬形成的,是北太平洋喷流出口区域涡度强迫的结果。我们还进一步提供了证据,证明这种涡度强迫是一连串事件的结果,这些事件始于 12 月中旬,当时出现了从北印度洋传播到北太平洋的罗斯比波(这是与 MJO 有关的强迫的结果)。因此,该事件的开始和 PNA 的最终发展都主要取决于内部产生的罗斯比波作用,其中北太平洋喷流起了关键作用。这一点,再加上当时的 SST(拉尼娜)强迫,在 AGCM 中产生了与正 PNA 基本相反的环流响应,突出表明了该事件在季节时间尺度上缺乏基本的可预测性。利用全球地球观测系统耦合模式进行的预测表明,预测 PNA 和加利福尼亚极端降水的有用技能实际上仅限于短于约 3 周的准备时间。
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来源期刊
Journal of Climate
Journal of Climate 地学-气象与大气科学
CiteScore
9.30
自引率
14.30%
发文量
490
审稿时长
7.5 months
期刊介绍: The Journal of Climate (JCLI) (ISSN: 0894-8755; eISSN: 1520-0442) publishes research that advances basic understanding of the dynamics and physics of the climate system on large spatial scales, including variability of the atmosphere, oceans, land surface, and cryosphere; past, present, and projected future changes in the climate system; and climate simulation and prediction.
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