关于亚洲中高纬区极端气候的研究——国家自然科学基金重大项目内容及阶段进展简介

近年来极端气候的发生频率和强度有明显增强的趋势,在我国尤为突出(Yin et al., 2023b),造成了越来越大的对经济社会和人民生命安全的威胁。我国科学家也越来越关注我国及东亚区域的极端气候问题。对比而言,亚洲中高纬区虽然也是气候变化的高敏感区,受到的关注却相当少,可能是源于气候资料的相对欠缺,也可能和亚洲高纬度区域(特别是西伯利亚地区)人口少、经济社会发展滞后有关。实际上,随着对于北极放大效应的研究的深入,极其有必要开展对整个亚洲中高纬区开展气候变化影响和极端气候研究,把我国科学家高度关注的研究区域从东亚区向北延伸。其中有很多关键科学问题需要研究,特别是该区域极端气候的形成与变异过程、机制以及可预测性,极端气候对生态系统的影响,极端气候的未来演变趋势,等等。因此,国家自然科学基金委地学部在择优的基础上以重大项目的方式支持了这个方面的研究(项目执行期为2020~2024年)。本文概要介绍了该项目的框架和若干初步研究进展。

青藏高原隆起及海陆分布变化对亚洲大陆气候的影响

我们利用经过改进的NCARCCMI动力气候模式并综合出一个40～50MaB．P．的下垫面情景，进行了海陆分布和SST分布由古代到现代、青藏高原由隆起初期、隆起到现代高原一半和现代高度共5个情景的数值试验。结果表明，从古代到现代，模拟的中国气候是变冷的并且东部变湿而西北部变干。青藏高原的隆起是模拟出来的中国变冷的主要原因。青藏高原从隆起初期到隆起到现代高度一半时期中国地区降水是增加的，但当继续隆起后降水却有所减少，尤其是中国西北地区。本文还对海陆分布和SST分布变化以及青藏高原隆起对手风环流的影响作了分析。

轨道尺度亚洲气候演化机理的数值模拟:历史与展望

轨道尺度亚洲气候演化是古气候热点问题之一,其变化过程和机理对理解当前全球变暖下亚洲气候变化具有重要参考意义。最近几十年,基于黄土、石笋、湖泊等载体的轨道尺度亚洲气候重建研究获得显著进展,气候演化历史的基本框架已被构建,不同区域和指标记录之间的差异暗示了气候演化机理的复杂性。数值模拟作为研究气候动力学的重要工具之一,在轨道尺度亚洲气候变化中也得到广泛应用和快速发展。基于此,本文尝试对最近十数年轨道尺度亚洲气候演化机理的数值模拟研究做一简单总结和梳理。目前的数值模拟尚未对地质记录给出的各种变化特征、区域差异等现象,尤其是东亚夏季风的黄土和石笋差异、季风和干旱气候的耦合关系等,给出合理解释。因此,在未来工作中亟须涵盖多轨道旋回的高分辨率瞬变试验,结合良好定年的重建记录,以期对轨道尺度亚洲气候变化机理获得更深入完整的认识。

Holocene Climate Cycles in Northwest Margin of Asian Monsoon

In the mid-latitude regions of the Asian continent, Zhuye Lake is located in the northwest margin of the Asian monsoon, where the modem climate is affected by the Asian monsoon and Westerlies. In this study, we investi- gated the absolutely dated Holocene records in Zhuye Lake for detecting the Holocene climate cycles. Totally, 14 14C dates and 6 optically simulated luminescence （OSL） dates are obtained from the QTH01 and QTH02 sections. The proxies of grain-size, total organic carbon content （TOC）, C/N and 813C are used for wavelet analysis, and the results show obvious -256, -512 and -1024-year climate cycles, which are consistent with the Holocene millennial and cen- tennial scale climate cycles in the typical Asian summer monsoon domain. In different parts of the Zhuye Lake, the Holocene sediments show variable climate cycles that are affected by the lake basin topography. In the Zhuye Lake, the Holocene climate cycles are mainly correlated with the solar-related Asian summer monsoon variability and the North Atlantic ice-rafting events.

SIMULATION OF PRESENT CLIMATE OVER EAST ASIA BY A REGIONAL CLIMATE MODEL

A 15-year simulation of climate over East Asia is conducted with the latest version of a regional climate model RegCM3 nested in one-way mode to the ERA40 Re-analysis data. The performance of the model in simulating present climate over East Asia and China is investigated. Results show that RegCM3 can reproduce well the atmospheric circulation over East Asia. The simulation of the main distribution patterns of surface air temperature and precipitation over China and their seasonal cycle/evolution, are basically agree with that of the observation. Meanwhile a general cold bias is found in the simulation. As for the precipitation, the model tends to overestimate the precipitation in northern China while underestimate it in southern China, particularly in winter. In general, the model has better performance in simulating temperature than precipitation.

Asian climate change under 1.5-4 ℃ warming targets

Based on simulations of 18 CMIP5 models under three RCP scenarios, this article investigates changes in mean temperature and precipitation and their extremes over Asia in the context of global warming targets of 1.5-4 ℃, and further compares the differences between 1.5 ℃ and 2 ℃ targets. Results show that relative to the pre-industrial era, the mean temperature over Asia increases by 2.3 ℃, 3.0 ℃, 4.6 ℃, and 6.0 ℃ at warming targets of 1.5 ℃, 2 ℃, 3 ℃, and 4 ℃, respectively, with stronger warming in high latitudes than in low latitudes. The corresponding enhancement in mean precipitation over the entire Asian region is 4.4%, 5.8%, 10.2%, and 13.0%, with significant regional differences. In addition, an increase in warm extremes, a decrease in cold extremes, and a strengthening in the variability of amounts of extreme precipitation are projected. Under the 1.5 ℃ target, compared with the climate under the 2 ℃ target, the mean temperature will be lower by 0.5-1 ℃ over Asia; the mean precipitation will be less by 5%-20% over most of Asia, but will be greater by about 10%-15% over West Asia and western South Asia; extreme high temperatures will be uniformly cooler throughout the Asian region, and the warming in extreme low temperatures will decrease significantly in high latitudes of Asia; extreme precipitation will be weaker over most of Asia but will be stronger over West Asia and western South Asia. Under the 1.5 ℃ and 2 ℃ warming targets, the probability of very hot weather （anomalies greater than 1σ, σ is standard deviation）, extremely hot weather （anomalies greater than 3or）, and extremely heavy precipitation （anomalies greater than 3σ） occurring will increase by at least once, 10%, and 10%, respectively, compared to the reference period （1861-1900）.

CLIMATIC CHARACTERISTICS OF THE ONSET OF SOUTH CHINASEA SUMMERMONSOON II.INTER-DECADAL VARIATION

By using the 40-year NCEP (1958-1997) grid point reanalysis meteorological data, we analyzed the inter-decadal variation on the climatic characteristics of the onset of South China Sea summer monsoon. The results are as follows. (1) There was great difference on the onset date of the SCS summer monsoon between the first two decades and the last two decades. It was late on the 6th pentad of May for the first two decades and was on the 4th and 5th pentad of May for the next two decades. (2) Except for the third decade (1978-1987), the establishment of the monsoon rainfall was one to two pentads earlier than the onset of the summer monsoon in all other three decades. (3) The onset of the SCS monsoon is the result of the abrupt development and eastward advancement of the southwesterly monsoon over the Bay of Bengal. The four-decade analysis shows that there were abrupt development of the southwesterly monsoon over the Bay of Bengal between the 3rd and 4th pentad of May, but there was great difference between its eastward movement and its onset intensity. These may have important effect to the earlier or later onset of the SCS summer monsoon. (4) During the onset of the SCS summer monsoon, there were great difference in the upper and lower circulation feature between the first two and the next two decades. At the lower troposphere of the first two decades, the Indian-Burma trough was stronger and the center of the subtropical high was located more eastward. At the upper troposphere, the northward movement of the center of subtropical high was large and located more northward after it landed on the Indo-China Peninsula. After comparison, we can see that the circulation feature of the last two decades was favorable to the establishment and development of the SCS summer monsoon.

Impact of European Black Carbon on East Asian Summer Climate

The remote response of the East Asian summer monsoon （EASM） to European black carbon （EUBC） aerosols was studied by using an ensemble of sensitivity experiments with the Geophysical Fluid Dynamics Laboratory （GFDL） atmospheric general circulation model （AGCM） Atmospheric Model version 2.1 （AM2.1）.The results show that EUBC causes an enhanced EASM.The resulted enhanced southwesterly brings more moisture supply from the Bay of Bengal,which causes an increase in precipitation over the Yangtze River valley,northeastem China,the eastern part of the Yellow River valley,and the Tibetan Plateau.Diagnostic examination suggests that EUBC induces enhanced tropospheric heating over most of the Eurasian Continent through a propagating wave train and horizontal air temperature advection.This phenomenon results in intensified thermal contrast between land and ocean,which accounts for the enhanced EASM.Moreover,reductions in EUBC emission in 1992 may have contributed to decadal weakening of the EASM in the early 1990s.

亚洲季风演化、北半球大冰期的发展与喜马拉雅—青藏高原隆升

青藏高原对亚洲季风气候的形成和发展有着重要的影响。通过综合最新的研究成果,本文对高原的阶段性隆升及其气候效应、北半球大冰期形成的可能原因和对亚洲气候的影响进行了初步讨论。并指出,高原的隆升可以划分为3个主要阶段,也就是10—9百万年的有意义隆升,亚洲季风开始形成;3.6—2.6百万年,高原加速隆升,亚洲冬、夏季风同时加强;2.6百万年以来,高原持续隆升,亚洲季风冬夏季风变率加大,冬季风加强。

A survey on pollen dispersal in the western Pacific Ocean and its paleoclimatological significance as a proxy for variation of the Asian winter monsoon

Pollen grains deposited in marine sediments are transported from land to sea by wind or surface water flows.We analyzed pollen collected from the air and seawater from the coast of the Yellow Sea near China and into the western Pacific Ocean between December 2008 and January 2009 during the cruise "KX08-973".Results showed that abundant pollen grains of Artemisia and Chenopodiaceae were probably transported to the continental shelf of the East China Sea,the East Philippine Sea and the equatorial regions of the Pacific Ocean by the winter monsoon.Some pollen may have even traveled over 2000 km from the East Asia continent to the tropical Pacific Ocean.However,a gradual decline of temperate components and an increase in tropical components was observed towards the tropical regions.Fern spores were rare in the air samples,but much more abundant in seawater samples,even though they were collected in nearly the same areas,which indicates that most fern spores were carried to the ocean by flowing water.These results suggest that the winter monsoon may be the major pollen carrier and transporter in the study area during winter.