大气河
2022 年 12 月中旬至 2023 年 1 月中旬，由于连续多日的暴雨，加利福尼亚州发生了特大洪水，造成大面积交通中断和停电，2,600 万人处于洪水警戒状态，而所有这些自然灾害都是由强大的大气河一手造成的。大气河是一种特殊的自然现象，可以从数千公里外输送水汽。大气河流的概念是由朱勇和雷金纳德-E-纽厄尔于 1994 年首次提出的，他们发现大气中存在一种细长的带状结构，其输水能力堪比亚马逊河。这太不可思议了！你能想象一条世界上排水量最大的河流从你头顶流过吗？这条天河让我居住的城市西雅图下了大约一周的雨！那一周，我不得不一直打着伞，所有有坡度的都街道变成了一条河流！
2023年12月5日大气河事件卫星图片 (图源 Windy.com)
根据美国国家海洋和大气管理局（NOAA）的数据，美国西海岸每年约有 30% 至 50% 的降水量是由大气河流事件造成的。大气河流将大量水汽从夏威夷一路输送到美国西海岸，造成卡斯卡特德山脉和洛基山脉西侧的暴雨。由于夏威夷地区盛产菠萝，所以这条大气河流有一个有趣的名字：菠萝快车。当人们意识到大气河流的重要性后，美国国家海洋和大气管理局开始对其进行研究和预测。1998 年，拉尔夫和他为国家海洋和大气管理局工作的研究团队飞入大气河以收集重要的气象数据。
2023年12月5日大气河事件850hPa云中水汽含量 (图源 EarthNullSchool)
大气河事件同样导致了西雅图市西部的奥林匹克山区降下大雪。我在华盛顿大学西雅图分校了解到，奥林匹亚山项目的气象学家在奥林匹亚山上设立了气象观测站，以跟踪巨大的降水量，并与卫星数据进行比较。
奥林匹亚项目示意图
中国也有大气河事件，在副热带高压和南支槽的共同作用下，长江中下游地区经常出现“暴力梅雨”事件。例如，2021 年 7 月 20 日，郑州出现暴雨。据中国气象局统计，当日下午4时至5时降水量为201.9毫米，造成292人死亡。因此，大气河流已成为当今学术界重要的研究方向，在这个气候多变的世界，对大气河流发展的精确预测可以挽救更多的生命。
Atmospheric River
From mid-December 2022 to mid-January 2023, California experienced a huge flood due to consecutive days of heavy rain, causing widespread traffic disruptions and power outages, and twenty-six million people were under flood alert. All these natural disasters were caused by the strong atmospheric river, a special natural phenomenon that can transport water from thousands of kilometers away. The concept of an atmospheric river was first proposed by Yong Zhu and Reginald E. Newell in 1994, and they found that there is a long and thin ribbon structure in the atmosphere, and its water-carrying capacity can be compared to the Amazon River. That's incredible! Can you imagine a river with the highest discharge in the world flowing over your head? And this sky river made the city where I live, Seattle, rain for about a week! I had to carry an umbrella all the time that week, and the hilly street turned into a river.
Satellite Picture of Atmospheric River on 5 Dec. 2023 (From Windy.com)
According to NOAA, about 30 to 50 percent of the annual precipitation on the West Coast of the United States is caused by atmospheric river events. The atmospheric river delivers a huge amount of moisture from Hawaii all the way to the west coast of the United States, causing heavy rains on the west side of the Cascades and Rocky Mountains. Since the Hawaiian area produces pineapples, this atmospheric river has a funny name: Pineapple Express. Once people realized the importance of atmospheric rivers, NOAA began researching and predicting them. Ralph and his team of researchers working for NOAA flew into the atmospheric river in 1998 to collect important data.
Cloud Moisture on 850hPa of atmospheric river on 5 Dec. 2023 (From EarthNullSchool)
The atmospheric river caused the Olympic Mountain areas on the west of Seattle city to receive heavy snowfall. I learned in class that meteorologists in the OLYMPEX program set up meteorological observation stations on Olympic Mountain to track the huge precipitation amount and compare it with the satellite data.
The OLYMEPEX Program
The atmospheric river also occurred in China and worked with the subtropical high and the southern trough to cause heavy rains in the middle and lower reaches of the Yangtze River. For example, Zhengzhou experienced heavy rainfall on July 20, 2021. According to the China Meteorological Administration, the amount of precipitation from 4 p.m. to 5 p.m. on that day was 201.9 mm, causing 292 deaths. Therefore, the atmospheric river has become an important research direction nowadays, and precise prediction of the development of the atmospheric river could save more lives in this climate-changing world.