P2C2: Role of Westerly Jet Transitions in East Asian Paleoclimate

P2C2：西风急流转变在东亚古气候中的作用

• 批准号: 1405479
• 负责人: John Chiang
• 金额: $ 46.41万
• 依托单位: University of California-Berkeley
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2014
• 资助国家: 美国
• 起止时间: 2014-07-01 至 2020-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1405479&HistoricalAwards=false
• 关键词: P2C2; Role; Westerly; Jet; Transitions

Paleoclimate evidence shows that rainfall over heavily-populated regions of East Asia is susceptible to change. Recent cave speleothem records from China going back a quarter of a million years convincingly show that the climate over East Asia underwent large and abrupt swings during this time period. These oscillations occur at multiple timescales, from a few hundred to tens of thousands of years, and they are tied to distinct and varied forcings on the global climate system during Earth's climate history. The standard interpretation of the speleothem records is that the East Asian summer monsoon intensified or diminished during these oscillations. However, this description is qualitative, and does not factor in the complex behavior of today's East Asian climate which exhibiting both abrupt temporal and spatial shifts as it progresses through the season, in particular from Spring to Meiyu rains, and from Meiyu to Summer rains.This research explores the hypothesis that changes to the north-south position jet stream impinging on the Tibetan Plateau are the underlying cause of the abrupt climate changes in the past. Emerging dynamical studies of the modern East Asian climate suggest that it is the latitudinal position of the jet relative to the Plateau that determines the rainfall seasonality -- when the jet is South of the Plateau, it is in a Spring rainfall regime; when it goes just North, then Meiyu; and when the jet goes well North of the Plateau, Summer. The hypothesis provides specific predictions that can be tested for different past climate scenarios, in particular during the so-called Dansgaard-Oeschger events recorded in ice core records over Greenland; and changes to insolation from changes to the Earth's orbital configuration. The jet transition hypothesis will be tested using three complementary approaches: i) Examination of the association between jet streams and East Asian rainfall changes in state-of-the art simulations of two particular past climate scenarios (mid-Holocene and Last Glacial Maximum) by various modeling groups around the world;ii) Idealized climate model simulations using a high-resolution atmospheric general circulation model necessary for resolving the fine-scale features of East Asian climate;iii) Investigating the modern climate data and high-resolution simulations of 20th century climate to see if similar jet-rainfall relationships hold for climate changes over this historical period.This project involves international collaborations with scientists from Taiwan and China, and supports a graduate student at UC Berkeley. Public lectures on paleoclimate changes (with focus on East Asia) will be offered at the Lawrence Hall of Science, using the "Science on a Sphere" (SOS) setup for climate data visualization.

古气候证据表明，东亚人口稠密地区的降雨量很容易发生变化。最近中国的洞穴洞穴记录令人信服地表明，在这段时间里，东亚的气候经历了巨大而突然的波动。这些振荡发生在多个时间尺度上，从几百年到数万年，它们与地球气候历史上对全球气候系统的不同强迫有关。对洞穴记录的标准解释是东亚夏季风在这些振荡期间增强或减弱。然而，这种描述是定性的，没有考虑今天东亚气候的复杂行为，它在整个季节的发展过程中表现出突变的时间和空间变化，特别是从春季到梅雨，从梅雨到夏季。本研究探索了南北位置急流的变化是过去气候突变的根本原因的假说。对现代东亚气候的新的动力学研究表明，急流相对于高原的纬度位置决定了降水的季节性--当急流在高原以南时，它处于春季降雨状态；当急流刚刚向北移动时，则是梅雨；当急流在高原以北时，则是夏季。该假说提供了特定的预测，可以针对过去不同的气候情景进行测试，特别是在格陵兰岛冰芯记录中记录的所谓丹斯加德-奥施格事件期间；以及地球轨道配置变化对太阳辐射的影响。急流转换假说将用三种互补的方法进行检验：i)在世界各地不同的建模小组对过去两种特殊气候情景(中全新世和末次冰期最大值)的最新模拟中，检验急流与东亚降水变化之间的联系；ii)使用高分辨率大气环流模式进行理想化的气候模式模拟，以解决东亚气候的精细特征；Iii)研究现代气候数据和20世纪气候的高分辨率模拟，以确定类似的急流-降雨关系是否适用于这一历史时期的气候变化。该项目涉及与台湾科学家和中国的国际合作，并支持加州大学伯克利分校的一名研究生。将在劳伦斯科学馆举办关于古气候变化(重点是东亚)的公开讲座，利用“球体上的科学”(SOS)装置实现气候数据可视化。