Influence of the Tibetan Plateau on the Summer Climate Patterns over Asia in the IAP/LASG SAMIL Model

A series of numerical experiments are carried out by using the Spectral Atmospheric Model of State Key Laboratory of Numerical Modeling Atmospheric Sciences and Geophysical Fluid Dynamics/Institute of Atmospheric Physics （SAMIL） to investigate how the Tibetan Plateau （TP） mechanical and thermal forcing affect the circulation and climate patterns over subtropical Asia. It is shown that, compared to mechanical forcing, the thermal forcing of TP plays a dominant role in determining the large-scale circulation in summer. Both the sensible heating and the latent heating over TP tend to generate a surface cyclonic circulation and a gigantic anticyclonic circulation in the mid- and upper layers, whereas the direct effect of the latter is much more significant. Following a requirement of the time-mean quasi-geostrophic vorticity equation for large-scale air motion in the subtropics, convergent flow and vigorous ascending motion must appear to the east of TP. Hence the summer monsoon in East China is reinforced efficiently by TP. In contrast, the atmosphere to the west of TP is characterized by divergent flow and downward motion, which induces the arid climate in Mid-Asia.     

Two modes and their seasonal and interannual variation of the baroclinic waves/storm tracks over the wintertime North Pacific

In this study, a newly developed method, termed moving empirical orthogonal function analysis (MEOF), is applied to the study of midlatitude baroclinic waves over the wintertime North Pacific from 1979 to 2009. It is shown that when the daily, high-pass filtered (2-10 days) meridional wind at 250 hPa is chosen as the variable of the MEOF analysis, typical features of baroclinic waves/storm tracks over the wintertime North Pacific can be well described by this method. It is found that the first two leading modes of the MEOF analysis, MEOF1 and MEOF2, assume quite different patterns. MEOF1 takes the form of a single wave train running in the east-west direction along 40°N, while MEOF2 is a double wave train pattern running in the east-west direction along 50°N and 30°N, respectively. The shift composites of various anomalous fields based on MEOF1 and MEOF2 assume typical baroclinic wave features. MEOF1 represents a primary storm track pulsing with an intrinsic time scale of two days. It shows significant "midwinter suppression" and apparent interannual variability. It is stronger after the mid-1990s than before the mid-1990s. MEOF2 represents a double-branch storm track, also with an intrinsic time scale of approximately two days, running along 50°N and 30°N, respectively. It shows no apparent seasonal variation, but its interannual and decadal variation is quite clear. It oscillates with larger amplitude and longer periods after the mid-1990s than before the mid-1990s, and is heavily modulated by El Niño-Southern Oscillation (ENSO).     

气候系统模式FGOALS-s1.1对热带降水年循环模态的模拟

文中评估了中国科学院大气物理研究所大气科学和地球流体力学数值模拟国家重点实验室（LASG/IAP）新一代耦合气候模式Fgoals-s1.1对热带降水年循环模态的模拟能力。通过与观测表层海温（SST）强迫的大气模式SAMIL试验结果比较,分析了海气耦合过程对年循环模态模拟效果的影响。结果表明Fgoals-s1.1能合理再现热带地区降水年循环模态的基本特征。Fgoals-s1.1模拟出了年平均降水场中的主要降水中心,但模拟的赤道和南太平洋降水偏多,而北太平洋降水则偏少。Fgoals-s1.1的季风模态降水呈现与观测一致的关于赤道反对称的特征,其模拟偏差大部分来自大气分量,尤其是在赤道外。Fgoals-s1.1的主要缺陷在于它对春秋非对称模态模拟能力低于单独大气模式,这主要是由于耦合模式模拟的SST距平的年循环位相与观测相反。SST纬向梯度的位相偏差使得太平洋沃克环流和印度洋的反沃克环流在春季强于秋季,最终导致模拟的春秋非对称模态的偏差。Fgoals-s1.1模拟的季风区范围接近观测,存在的问题在于模拟的西北太平洋季风区、东亚季风区都偏小。本文结果表明,大气模式偏差仅是Fgoals-s1.1在降水年循环模态模拟上的偏差的部分来源,改进模式模拟的SST,特别是赤道地区SST季节循环,是今后Fgoals-s1.1发展过程中急需解决的问题。     

冬季北太平洋海表面热通量异常和海气相互作用的耦合模式模拟

基于中国科学院大气物理研究所大气科学与地球流体力学数值模拟国家重点实验室(LASG/IAP)开发的耦合气候系统模式FGOALS_s1.0控制试验的积分结果,分析了冬季北太平洋海表面湍流热通量(潜热和感热通量之和)异常及其对海表面温度(SST)异常的影响,并通过分析海温倾向方程,比较了各因子对SST变率的相对贡献.结果表...     

The North Atlantic oscillation simulated by versions 2 and 4 of IAP/ LASG GOALS Model

The capabilities of two versions of the Global-Ocean-Atmosphere-Land-System model (i.e. GOALS-2 and GOALS-4) developed at State Key Laboratory of Atmospheric Sciences and Geophysical Fluid Dynamics (LASG), are validated in terms of the simulations of the winter North Atlantic Oscillation (NAO), which is currently the subject of considerable scientific interest. The results show that both GOALS-2 and GOALS-4 exhibit a realistic NAO signal associated with relatively reasonable spatial pat-terns of sea level pressure, surface air temperature, and precipitation. Generally speaking, the associated pat-terns of precipitation in GOALSs match better with the observation in comparison with the case of surface temperature. For the imprint of NAO on the ocean, or perhaps a coupling between the two fluids, the asso-ciated tripole patterns of the North Atlantic SST anomaly are presented distinctly in GOALS-2, for GOALS-4 however, this is not the case. Spatially, the models’ main deficiencies appear to be that the simu-lated Icelandic lows shift northward apparently, which in turn result in the blemish of GOALSs in repro-ducing the accompanied surface wind anomalies. For the interannual and even longer time scale variations of DJF sea level pressure (SLP) over the North Atlantic region. GOALSs reproduce the center with the strongest variability rationally, but the intensities are far weaker than the observation.     

Water Vapor and Cloud Radiative Forcings over the Pacific Ocean Simulated by the LASG/IAP AGCM: Sensitivity to Convection Schemes

Characteristics of the total clear-sky greenhouse effect (GA) and cloud radiative forcings (CRFs), along with the radiative-related water vapor and cloud properties simulated by the Spectral Atmospheric Model developed by LASGIAP (SAMIL) are evaluated. Impacts of the convection scheme on the simulation of CRFs are discussed by using two AMIP (Atmospheric Model Inter-comparison Project) type simulations employing different convection schemes: the new Zhang-McFarlane (NZH) and Tiedtke (TDK) convection schemes. It shows that both the climatological GA and its response to El Nio warming are simulated well, both in terms of spatial pattern and magnitude. The impact of the convection scheme on GA is not significant. The climatological longwave CRF (LWCRF) and its response to El Nio warming are simulated well, but with a prominently weaker magnitude. The simulation of the climatology (response) of LWCRF in the NZH (TDK) run is slightly more realistic than in the TDK (NZH) simulation, indicating significant impacts of the convection scheme. The shortwave CRF (SWCRF) shows large biases in both spatial pattern and magnitude, and the results from the TDK run are better than those from the NZH run. A spuriously excessive negative climatological SWCRF over the southeastern Pacific and an insufficient response of SWCRF to El Nio warming over the tropical Pacific are seen in the NZH run. These two biases are alleviated in the TDK run, since it produces vigorous convection, which is related to the low threshold for convection to take place. Also, impacts of the convection scheme on the cloud profile are discussed.     

The Vertical Structures of Atmospheric Temperature Anomalies Associated with El Nio Simulated by the LASG/IAP AGCM： Sensitivity to Convection Schemes

The vertical structures of atmospheric temperature anomalies associated with El Nio are simulated with a spectrum atmospheric general circulation model developed by LASG/IAP (SAMIL). Sensitivity of the model’s response to convection scheme is discussed. Two convection schemes, i.e., the revised Zhang and Macfarlane (RZM) and Tiedtke (TDK) convection schemes, are employed in two sets of AMIP-type (Atmospheric Model Intercomparison Project) SAMIL simulations, respectively. Despite some deficiencies in the up...     

夏季亚洲-太平洋涛动的耦合模式模拟

亚洲-太平洋涛动是夏季欧亚大陆东部(15°—50°N,60°—120°E)与北太平洋上空(15°—50°N,180°—120°W)温度场反相变化的现象。亚洲-太平洋涛动指数由对流层上层(500—200 hPa)温度定义,反映了亚洲-太平洋纬向热力差异。基于一个全球海-气耦合模式FGOALS_gl的20世纪气候模拟试验结果,讨论了其对20世纪亚洲-太平洋涛动指数变化的模拟能力。结果表明,较之ERA-40再分析资料(1960—1999年),模式很好地刻画出上层温度场的平均态和主导模态的空间型。从趋势上看,模式对北太平洋上空温度的年代际变化和趋势模拟较好,但未能模拟出亚洲东部陆地上空的降温趋势。从频谱分析结果看,模拟的亚洲-太平洋涛动指数2—3,a的年际变率与再分析资料相当,5-7 a周期的变率较弱。模式能够较好地模拟出与亚洲-太平洋涛动指数相关的亚洲季风区气候异常。在20世纪模拟中,外强迫因子会改变耦合系统的年际变率,在自然因子强迫下亚洲-太平洋涛动指数的功率谱向低频方向增强,人为强迫因子的作用则相反。自然强迫因子和人为强迫因子在不同时期对亚洲-太平洋涛动年际和年代际变率的作用不同。在年际变率中人为强迫因子能够控制亚洲-太平洋涛动的变率使其不致过大;在年代际变率中人为强迫因子会增强自然强迫下亚洲-太平洋涛动的变率。模式上层温度的主导模态受ENSO调制,可能影响亚洲-太平洋涛动的年际变率。因此,模式对ENSO模拟能力的缺陷是制约模式对流层上层温度及亚洲-太平洋涛动指数变率的重要因素。     

新旧两个版本GAMIL模式对1997/98强E1 Ni(n)o年西太平洋暖池区独特云辐射强迫特征的数值模拟

1997/98年强E1 Ni(n)o背景下西太平洋暖池区云辐射强迫的变化,表现出诸多不同于以往的特征,已经成为检验气候模式性能的一个重要标准.本文基于卫星资料,分析了大气环流模式GAMIL1.0和2.0版对上述现象的模拟能力.结果表明,GAMIL1.0模式对热带地区云辐射特征分布,尤其对西太平洋暖池区的长(短)波云辐射...     

Annual cycle and interannual variability in the tropical pacific as simulated by three versions of FGOALS

The seasonal cycle and interannual variability in the tropical oceans simulated by three versions of the Flexible Ocean-Atmosphere-Land System (FGOALS) model (FGOALS-g1.0, FGOALS-g2 and FGOALSs2), which have participated in phases 3 and 5 of the Coupled Model Intercomparison Project (CMIP3 and CMIP5), are presented in this paper. The seasonal cycle of SST in the tropical Pacific is realistically reproduced by FGOALS-g2 and FGOALSs2, while it is poorly simulated in FGOALS-g1.0. Three feedback mechanisms responsible for the SST annual cycle in the eastern Pacific are evaluated. The ocean-atmosphere dynamic feedback, which is successfully reproduced by both FGOALS-g2 and FGOALS-s2, plays a key role in determining the SST annual cycle, while the overestimated stratus cloud-SST feedback amplifies the annual cycle in FGOALS-s2. Because of the serious warm bias existing in FGOALS-g1.0, the ocean-atmosphere dynamic feedback is greatly underestimated in FGOALS-g1.0, in which the SST annual cycle is mainly driven by surface solar radiation. FGOALS-g1.0 simulates much stronger ENSO events than observed, whereas FGOALS-g2 and FGOALSs2 successfully simulate the observed ENSO amplitude and period and positive asymmetry, but with less strength. Further ENSO feedback analyses suggest that surface solar radiation feedback is principally responsible for the overestimated ENSO amplitude in FGOALS-g1.0. Both FGOALS-g1.0 and FGOALS-s2 can simulate two different types of El Ni-no events — with maximum SST anomalies in the eastern Pacific (EP) or in the central Pacific (CP) — but FGOALS-g2 is only able to simulate EP El Ni-no, because the negative cloud shortwave forcing feedback by FGOALS-g2 is much stronger than observed in the central Pacific.     

西北太平洋热带气旋潜势分布和年际变率的数值模拟

热带气旋潜势指数是定量表征影响热带气旋生成的大尺度环境条件指标,在不能显式模拟热带气旋的气候系统模式中,常被作为热带气旋的代用指标。基于中国科学院大气物理研究所大气科学和地球流体力学数值模拟国家重点实验室发展的AGCM GAMIL2.0模式在历史海温驱动下的积分结果,评估了该模式对热带气旋潜势气候态、季节循环和年际变率的模拟能力。并分别从影响热带气旋潜势分布的热力因子(相对湿度、热带气旋最大风速)和动力因子(垂直风切变、绝对涡度、垂直抬升速度)的角度,讨论了造成热带气旋潜势模拟误差的原因。结果表明,在西北太平洋地区,模式能够合理再现热带气旋潜势的气候态分布,但由于GAMIL2.0模拟的相对湿度偏大且向东延伸,造成了热带气旋潜势大值区较之再分析资料偏大且偏东10°。由于GAMIL2.0模拟的季风槽位置偏北偏强,导致模拟的热带气旋潜势季节循环北进偏早而南退偏晚。在年际变化方面,GAMIL2.0能合理模拟出热带气旋潜势在ENSO正负位相东西反向的变化特征,但位于20°—30°N的加强和减弱区的分界线偏西,这与模拟的垂直速度和相对湿度的模拟误差有关,进一步分析表明,这是由于模拟中ENSO事件期间的西北太平洋异常上升中心比观测偏西且偏强造成的。     

东亚-太平洋型季节内演变和维持机理研究

利用850hPa的纬向风异常建立一个逐候东亚-太平洋(East Asian Pacific,EAP)型指数,研究其季节内演变特征,发现东亚-太平洋型经向波列是东亚夏季风季节内变化的主要模态.其演变过程为:扰动首先出现在北太平洋中部,并通过正压不稳定过程从基本气流中获得能量而发展,在高层罗斯贝波能量向南频散,激发热带对流异常和赤道罗斯贝波,并相互锁相,因赤道罗斯贝波受β效应影响而共同向西移动.热带对流和环流异常在菲律宾附近达到最强,此时在东亚沿岸出现经向三极型波列,此后中低纬度异常继续向西北方向移动,使降水异常在长江流域能维持较长时间.东亚-太平洋型在东亚发展和维持有以下原因:首先,菲律宾暖水上空的对流和低层环流之间存在正反馈;其次,由于海陆热力差异导致暖大陆和冷海洋之间存在特殊的纬向温度梯度和北风垂直切变,东亚-太平洋型在经向上有向北倾斜的斜压结构,能通过斜压能量转换从平均有效位能中获得能量,同时,也能从经向温度梯度的平均有效位能中获得能量.