P2C2: Role of Westerly Jet Transitions in East Asian Paleoclimate

古气候证据表明，东亚人口稠密地区的降雨量容易发生变化。 中国距今25万年的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，从几百年到几万年不等，它们与地球气候历史期间全球气候系统的不同和不同的强迫有关。 对洞穴沉积记录的标准解释是，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，并没有考虑到今天东亚气候的复杂行为，随着季节的推移，特别是从春季到梅雨期，东亚气候表现出突然的时空变化，从梅雨期到夏季降水期，本研究探讨了北移的假说--南向急流冲击青藏高原是过去气候突变的潜在原因。 对现代东亚气候的动力学研究表明，急流相对于高原的纬度位置决定了降水的季节性，当急流位于高原南部时，它处于春季降水状态;当急流向北移动时，它处于梅雨期;当急流向北移动时，它处于夏季降水状态。该假设提供了具体的预测，可以测试不同的过去的气候情景，特别是在所谓的Dansgaard-Oeschger事件记录在冰芯记录在格陵兰岛;和太阳辐射的变化，从地球的轨道配置的变化。将使用三种互补的方法来检验急流过渡假说：i）在对过去两种特定气候情景的最新模拟中，（全新世中期和末次冰期最大期），由世界各地的各种建模组;二）使用高分辨率大气环流模式进行理想化气候模式模拟，这是解决东亚气候精细尺度特征所必需的; iii）调查现代气候数据和20世纪世纪气候的高分辨率模拟，以了解类似的急流-降雨关系是否适用于这一历史时期的气候变化。该项目涉及与台湾和中国科学家的国际合作，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的公开讲座（重点是东亚），使用“球体上的科学”（SOS）设置气候数据可视化。

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.