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1.
Kyu-Myong Kim William K.-M. Lau Yogesh C. Sud Gregory K. Walker 《Climate Dynamics》2010,35(1):115-126
Effects of aerosol radiative forcing on the diurnal and seasonal cycles of precipitation over West Africa and eastern Atlantic
Ocean are investigated for the boreal summer season: June–July–August. An eight year (2000–2007) average of GCM simulated
rainfall data is compared with the corresponding TRMM rainfall data. The comparison shows that the amplitude of the diurnal
cycles of rainfall over land and ocean are reasonably well simulated. Over land, the phase of the simulated diurnal cycle
of precipitation peaks several hours earlier than that of the TRMM data. Corresponding differences over the ocean(s) are relatively
smaller. Some of the key features of the aerosol induced model simulated field anomalies are: (a) aerosol direct radiative
forcing which increases the atmospheric stability and reduces the daytime moist convection and convective precipitation; (b)
the aerosol induced changes in the diurnal cycle of precipitation are out of phase with those of the TRMM data over land,
but are in-phase over the ocean; (c) aerosols reduce the amplitude of the diurnal cycle of precipitation over land and enhance
it over ocean. However, the phase of the diurnal cycle is not affected much by the aerosol radiative forcing both over land
and ocean. During the boreal summer, aerosol radiative forcing and induced circulation and precipitation cool the Sahel and
the southern part of Sahara desert more than the adjacent areas to the north and south, thereby shifting the peak meridional
temperature gradient northward. Consequently, an anomalous easterly jet is found north of its climatological location. This
anomalous jet is associated with increased cyclonic circulation to the south of its axis, resulting in an anomalous monsoon
rain belt in the Sahel. 相似文献
2.
Sun-Seon Lee Ye-Won Seo Kyung-Ja Ha Jong-Ghap Jhun 《Asia-Pacific Journal of Atmospheric Sciences》2013,49(2):171-182
The western North Pacific subtropical high (WNPSH) is a crucial component of the East Asian summer monsoon (EASM) system and significantly influences the precipitation in East Asia. In this study, distinguished role of WNPSH on the EASM and Indian Ocean monsoon (IOM) are investigated. Based on the boreal summer mean field of 850-hPa geopotential height and its interannual variability, the WNPSH index (WNPSHI) is defined by the areaaveraged geopotential height over the region [110°–150°E, 15°–30°N]. The WNPSHI is significantly related to the precipitation over the East Asian monsoon (EAM) region [105°–150°E, 30°–40°N] and IOM region [70°–105°E, 5°–15°N]. Rainfalls over these two regions have good correlation with WNPSH developments and the geopotential height fields at 850 hPa related to the EAM precipitation and IOM precipitation have remarkably different teleconnection patterns in boreal summer. These features exhibit that EAM and IOM precipitations have different type of development processes associated with different type of WNPSH each other. Focusing on the relationships among the EAM precipitation, IOM precipitation, and the WNPSH variabilities, we assume that WNPSH and EAM precipitation are usually fluctuated simultaneously through the sea surface temperature (SST)-subtropical ridge-monsoon rainfall feedback, whereas the IOM precipitation varies through the different process. To clarify the relationships among WNPSH, EAM, and IOM, two cases are selected. The first one is the case that all of WNPSH, EAM, and IOM are in phase (WE(+)I(+)), and the second one is the case that WNPSH and EAM are in phase and WNPSH/EAM and IOM is out of phase (WE(+)I(?)). These two cases are connected to the thermal forcing associated with SST anomalies over the eastern Pacific and Indian Ocean. This different thermal forcing induces the change in circulation fields, and then anomalous circulation fields influence the moisture convergence over Asian monsoon regions interactively. Therefore, the monsoon rainfall may be changed according to the thermal conditions over the tropics. 相似文献
3.
The reproducibility of boreal summer intraseasonal variability (ISV) and its interannual variation by dynamical models are
assessed through diagnosing 21-year retrospective forecasts from ten state-of-the-art ocean–atmosphere coupled prediction
models. To facilitate the assessment, we have defined the strength of ISV activity by the standard deviation of 20–90 days
filtered precipitation during the boreal summer of each year. The observed climatological ISV activity exhibits its largest
values over the western North Pacific and Indian monsoon regions. The notable interannual variation of ISV activity is found
primarily over the western North Pacific in observation while most models have the largest variability over the central tropical
Pacific and exhibit a wide range of variability in spatial patterns that are different from observation. Although the models
have large systematic biases in spatial pattern of dominant variability, the leading EOF modes of the ISV activity in the
models are closely linked to the models’ El Nino-Southern Oscillation (ENSO), which is a feature that resembles the observed
ISV and ENSO relationship. The ENSO-induced easterly vertical shear anomalies in the western and central tropical Pacific,
where the summer mean vertical wind shear is weak, result in ENSO-related changes of ISV activity in both observation and
models. It is found that the principal components of the predicted dominant modes of ISV activity fluctuate in a very similar
way with observed ones. The model biases in the dominant modes are systematic and related to the external SST forcing. Thus
the statistical correction method of this study based on singular value decomposition is capable of removing a large portion
of the systematic errors in the predicted spatial patterns. The 21-year-averaged pattern correlation skill increases from
0.25 to 0.65 over the entire Asian monsoon region after applying the bias correction method to the multi-model ensemble mean
prediction. 相似文献
4.
Tropical cyclone genesis frequency over the western North Pacific simulated in medium-resolution coupled general circulation models 总被引：4，自引：0，他引：4
This study examines the tropical cyclone (TC) genesis frequency over the western North Pacific simulated in atmosphere–ocean
coupled general circulation models from the World Climate Research Programme’s Coupled Model Intercomparison Project phase
3. We first evaluate performances of eight models with atmospheric horizontal resolution of T63 or T106 by analyzing their
daily-mean atmospheric outputs of twentieth-century climate simulations available from the Program for Climate Model Diagnosis
and Intercomparison database. The genesis frequency is validated against the best-track data issued by the Japan Meteorological
Agency. Five of the eight models reproduce realistic horizontal distribution of the TC genesis with a large fraction over
the 10°–20°N, 120°–150°E area. These five high-performance models also realistically simulate the summer–winter contrast of
the frequency. However, detailed seasonal march is slightly unrealistic; four of the models overestimate the frequency in
the early season (May–June) while all of them underestimate the frequency in the mature season (July–September). Reasons for
these biases in the seasonal march for the five high-performance models are discussed using the TC genesis potential (GP)
index proposed by Emanuel and Nolan (in Am Meteor Soc, pp 240–241, 2004). The simulated GP has seasonal biases consistent with those of the TC genesis frequency. For all five models, the seasonal
biases in GP are consistent with those in environmental lower-tropospheric vorticity, vertical wind shear, and relative humidity,
which can be attributed to the simulated behavior of monsoon trough. The observed trough migrates northward from the equatorial
region to reach the 10°–20°N latitudinal band during the mature season and contributes to the TC frequency maximum, whereas
the simulated trough migrates northward too rapidly and reaches this latitude band in the early season, leading to the overestimation
of the TC genesis frequency. In the mature season, the simulated trough reaches as far as 15°–25°N, accompanied by a strong
vertical shear south of the trough, providing an unfavorable condition for TC genesis. It is concluded that an adequate simulation
of the monsoon trough behavior is essential for a better reproduction of the TC frequency seasonal march. 相似文献
5.
Shortwave cloud radiative forcing on major stratus cloud regions in AMIP-type simulations of CMIP3 and CMIP5 models 总被引：1，自引：0，他引：1
Cloud and its radiative effects are major sources of uncertainty that lead to simulation discrepancies in climate models. In this study, shortwave cloud radiative forcing (SWCF) over major stratus regions is evaluated for Atmospheric Models Intercomparison Project (AMIP)-type simulations of models involved in the third and fifth phases of the Coupled Models Intercomparison Project (CMIP3 and CMIP5). Over stratus regions, large deviations in both climatological mean and seasonal cycle of SWCF are found among the models. An ambient field sorted by dynamic (vertical motion) and thermodynamic (inversion strength or stability) regimes is constructed and used to measure the response of SWCF to large-scale controls. In marine boundary layer regions, despite both CMIP3 and CMIP5 models being able to capture well the center and range of occurrence frequency for the ambient field, most of the models fail to simulate the dependence of SWCF on boundary layer inversion and the insensitivity of SWCF to vertical motion. For eastern China, there are large differences even in the simulated ambient fields. Moreover, almost no model can reproduce intense SWCF in rising motion and high stability regimes. It is also found that models with a finer grid resolution have no evident superiority than their lower resolution versions. The uncertainties relating to SWCF in state-of-the-art models may limit their performance in IPCC experiments. 相似文献
6.
An evaluation of the simulated water balance of Eurasia and northern Africa at 6000 y BP using lake status data 总被引：1，自引：0，他引：1
Changes in the water balance of Eurasia and northern Africa in response to insolation forcing at 6000 y BP simulated by five
atmospheric general circulation models have been compared with observations of changes in lake status. All of the simulations
show enhancement of the Asian summer monsoon and of the high pressure cells over the Pacific and Central Asia and the Middle
East, causing wetter conditions in northern India and southern China and drier conditions along the Chinese coast and west
of the monsoon core. All of the models show enhancement of the African monsoon, causing wetter conditions in the zone between
ca 10–20 °N. Four of the models show conditions wetter than present in southern Europe and drier than present in northern
Europe. Three of the models show conditions similar to present in the mid-latitude continental interior, while the remaining
models show conditions somewhat drier than present. The extent and location of each of the simulated changes varies between
the models, as does the mechanism producing these changes. The lake data confirm some features of the simulations, but indicate
discrepancies between observed and simulated climates. For example, the data show: (1) conditions wetter than present in central
Asia, from India to northern China and Mongolia, indicating that the simulated Asian monsoon expansion is too small; (2) conditions
wetter than present between ca. 10–30 °N in Africa, indicating that the simulated African monsoon expansion is too small;
(3) that northern Europe was drier, but the area of significantly drier conditions was more localized (around the Baltic)
than shown in the simulations; (4) that southern Europe was wetter than present, apparently consistent with the simulations,
but pollen data suggest that this reflects an increase in summer rainfall whereas the models show winter precipitation, and
(5) that the mid-latitude continental interior was generally wetter than present.
Received: 29 March 1996 / Accepted: 31 May 1996 相似文献
7.
Lei WANG Qing BAO Wei-Chyung WANG Yimin LIU Guo-Xiong WU Linjiong ZHOU JiANDong LI Hua GONG Guokui NIAN Jinxiao LI Xiaocong WANG Bian HE 《大气科学进展》2019,(7):697-710
Cloud dominates influence factors of atmospheric radiation, while aerosol–cloud interactions are of vital importance in its spatiotemporal distribution. In this study, a two-moment(mass and number) cloud microphysics scheme, which significantly improved the treatment of the coupled processes of aerosols and clouds, was incorporated into version 1.1 of the IAP/LASG global Finite-volume Atmospheric Model(FAMIL1.1). For illustrative purposes, the characteristics of the energy balance and cloud radiative forcing(CRF) in an AMIP-type simulation with prescribed aerosols were compared with those in observational/reanalysis data. Even within the constraints of the prescribed aerosol mass, the model simulated global mean energy balance at the top of the atmosphere(TOA) and at the Earth's surface, as well as their seasonal variation, are in good agreement with the observational data. The maximum deviation terms lie in the surface downwelling longwave radiation and surface latent heat flux, which are 3.5 W m-2(1%) and 3 W m-2(3.5%), individually. The spatial correlations of the annual TOA net radiation flux and the net CRF between simulation and observation were around 0.97 and 0.90, respectively. A major weakness is that FAMIL1.1 predicts more liquid water content and less ice water content over most oceans. Detailed comparisons are presented for a number of regions, with a focus on the Asian monsoon region(AMR). The results indicate that FAMIL1.1 well reproduces the summer–winter contrast for both the geographical distribution of the longwave CRF and shortwave CRF over the AMR. Finally, the model bias and possible solutions, as well as further works to develop FAMIL1.1 are discussed. 相似文献
8.
在中国西部的青藏高原和新疆地区的若干条冰川区域采集雪和冰芯样品,分析了雪冰样品中的黑碳,并模拟了雪冰黑碳产生的辐射强迫。我国西部雪冰黑碳的平均浓度为63 ng/g,高于北半球其他地区的实测结果。影响雪样黑碳浓度空间分布格局的主因是周边的排放源。模拟结果显示,黑碳在中国西部冰川雪表的沉降产生的平均辐射强迫为（+4.0±2.0) W/m2。喜马拉雅山中段的东绒布冰芯记录揭示黑碳主要来源于南亚,经印度夏季风输送;1951年以来黑碳的平均浓度为16 ng/g,产生的月平均辐射强迫在2001年夏季超过了+4.5 W/m2。南亚排放的黑碳可能抵达青藏高原南部腹地,对青藏高原的冰川表面能量平衡有一定影响。 相似文献
9.
青藏高原感热气泵影响亚洲夏季风的机制 总被引：6，自引：1，他引：5
本文回顾了二十年来关于青藏高原感热驱动气泵(TP-SHAP)及其影响亚洲夏季风的研究进展,并从能量(θ)、位涡—加热(PV–Q)、和角动量守恒(AMC)的不同角度阐述其影响机制。指出高原斜坡上的表面感热加热改变了移向高原的大气质块的能量从而出现垂直抽吸的重要性。强调了高原加热产生的位涡强迫在近地层制造了强度大范围广的、环绕高原的气旋式环流,把丰沛的水汽从海洋输运到大陆,为季风对流降水提供充足的水汽条件。证明高原加热还通过改变其上空的温、压场的结构从而制造出高原上空近对流层顶的绝对涡度和位涡的最小值,在角动量平衡约束下,在亚洲季风区激发出与Hadley环流反向的季风经圈环流,从而为季风发生发展提供了大范围上升运动的背景。文中还对近年来有关青藏高原影响亚洲夏季风机制的讨论进行概述,并展望了未来的研究方向。 相似文献
10.
1 INTRODUCTION In the recent years, more and more researches have shown that the effect of Tropical Ocean is very evident in the process of ocean-air interaction; Sea-Surface Temperature Anomaly (SSTA) takes on global configuration and SSTA in different areas are interrelated and also have their respective characteristics. The SSTA over Indian Ocean and Pacific Ocean are interrelated. WU et al.[1] and MENG et al.[2] indicated that the evident positive correlation of inter-annual… 相似文献
11.
Propagation and mechanisms of the quasi-biweekly oscillation over the Asian summer monsoon region 
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下载免费PDF全文 The propagation and underlying mechanisms of the boreal summer quasi-biweekly oscillation (QBWO) over the entire Asian monsoon region are investigated, based on ECMWF Interim reanalysis (ERA-Interim) data, GPCP precipitation data, and an atmospheric general circulation model (AGCM). Statistical analyses indicate that the QBWO over the Asian monsoon region derives its main origin from the equatorial western Pacific and moves northwestward to the Bay of Bengal and northern India, and then northward to the Tibetan Plateau (TP) area, with a baroclinic vertical structure. Northward propagation of the QBWO is promoted by three main mechanisms: barotropic vorticity, boundary moisture advection, and surface sensible heating (SSH). It is dominated by the barotropic vorticity effect when the QBWO signals are situated to the south of 20°N. During the propagation taking place farther north toward the TP, the boundary moisture advection and SSH are the leading mechanisms. We use an AGCM to verify the importance of SSH on the northward propagation of the QBWO. Numerical simulations confirm the diagnostic conclusion that the equatorial western Pacific is the source of the QBWO. Importantly, the model can accurately simulate the propagation pathway of the QBWO signals over the Asian monsoon region. Simultaneously, sensitivity experiments demonstrate that the SSH over northern India and the southern slope of the TP greatly contributes to the northward propagation of the QBWO as far as the TP area. 相似文献
12.
人为气溶胶的直接辐射效应及其对南亚冬季风的影响 总被引：2，自引：0，他引：2
运用区域气候模式RegCM4.0(Regional Climate Model Verson 4.0)耦合入一个化学过程,对硫酸盐、黑碳、有机碳这3种人为气溶胶的时空分布特征和直接辐射效应进行了数值模拟,进而研究了气溶胶对南亚冬季风的影响。结果表明:光学厚度和地表短波辐射强迫的时空变化可能主要受硫酸盐气溶胶的影响。在南亚夏季风向冬季风转换时期和南亚冬季风盛行时期,大气层顶和地表的负短波辐射强迫分布与气溶胶分布基本一致,地表辐射强迫强度绝对值比大气层顶辐射强迫强度绝对值大得多。相关分析和合成分析表明:在南亚夏季风向冬季风转换时期和南亚冬季风盛行时期,南亚人为气溶胶主要分布区中的气溶胶柱浓度含量与南亚冬季风的建立和强度有反相关关系。这与气溶胶吸收太阳辐射,从而引起气温和位势高度的变化有关。 相似文献
13.
Summary The East Asian (China, Korea and Japan) summer monsoon precipitation and its variability are examined from the outputs of
the coupled climate models performing coordinated experiments leading to the Intergovernmental Panel on Climate Change Fourth
Assessment Report (IPCC AR4). Out of the 22 models examined, 14 reproduce the observed shape of the annual cycle well with
peak during the boreal summer (June through August), but with varying magnitude. Three models simulate the maximum a month
later and with lower magnitudes. Only one model considerably underestimates the magnitude of the annual cycle. The remaining
4 models show some deviations from the observed. Models are unable to simulate the minimum in July with peaks in June and
August associated with northward shifts of the Meiyu-Changma-Baiu precipitation band. The realistic simulation of the annual cycle does not appear to depend on the model resolution. The inter-model
variation is slightly larger during summer, implying larger diversity of the models in simulating summer monsoon precipitation.
The spatial rainfall patterns are reasonably well simulated by most of the models, with several models able to simulate the
precipitation associated with the Meiyu-Changma-Baiu frontal zone and that associated with the location of the subtropical high over the north Pacific. Simulated spatial distribution
could be sensitive to model resolution as evidenced by two versions of MIROC3.2 model. The multi-model ensemble (MME) pattern
reveals an underestimation of seasonal precipitation over the east coast of China, Korea-Japan peninsular and the adjoining
oceanic regions. This may be related with the mass-flux based scheme employed for convective parameterization by majority
of the models. Further the inter-model variation of precipitation is about 2 times stronger south of 30° N, than north of
this latitude, indicating larger diversity of the coupled models in simulating low latitude precipitation. The simulated inter-annual
variability is estimated by computing the mean summer monsoon seasonal rainfall and the coefficient of variability (CV). In
general the mean observed seasonal precipitation of 542 mm and CV of 6.7% is very well simulated by most of the models. Except
for one model mean seasonal precipitation varies from 400 to 650 mm. However the CV varies from 2 to 9%.
Future projections under the radiative forcing of doubled CO2 scenario are examined for individual models and by the MME technique. Changes in mean precipitation and variability are tested
by the t-test and F-ratio respectively to evaluate their statistical significance. The changes in mean precipitation vary from −0.6% (CNRM-CM3)
to about 14% (ECHO-G; UKMO-HadCM3). The MME technique reveals an increase varying from 5 to 10%, with an average of 7.8% (greater
than the observed CV of 6.7%) over the East Asian region. However the increases are significant over the Korea-Japan peninsula
and the adjoining north China region only. The increases may be attributed to the projected intensification of the subtropical
high, Meiyu-Changma-Baiu frontal zone and the associated influx of moist air from the Pacific inland. The projected changes in the amount of precipitation
are directly proportional to the projected changes in the strength of the subtropical high. Further the MME suggests a possible
increase in the length of the summer monsoon precipitation period from late spring through early autumn. The changes in precipitation
could be stabilized by controlling the CO2 emissions. 相似文献
14.
AMIP model simulations of the east China (5–50°N; 105–122°E) monsoon system are analyzed to study coherent relationships
between rainfall and wind annual cycle biases. A comparison with observed interannual variability patterns is carried out
to identify the physical processes that explain the biases. The analyses show that poleward displacement of the simulated
east Asian jet stream causes the ascending branch of the jet-induced transverse circulation to move north and, as a consequence,
produces negative (positive) rainfall biases occur in central (northeast) China. The model simulations show decreased southwesterly
flow and ITCZ rainfall over the South China Sea when weaker (versus observations) summer Hadley and Walker circulations are
present. This results from diminished model tropical disturbance activity, and highlights the importance of air-sea interactions.
In addition, during October–January, intensified model low-level easterlies enhance moisture transport and produce positive
local rainfall biases over central and northeast China. Biases in the east China monsoon system are concurrently reflected
in the planetary circulation. Enhanced northeast China rainfall results from increased surface pressure over the North Pacific
and an amplified zonal pressure gradient along the east China coast. This bias pattern is associated with differences in model
representations of topography. On the other hand, the South China Sea experiences an extensive elongated meridional rainfall
bias dipole structure that straddles the equator. This is accompanied by a baroclinic vertical pattern over the tropics as
well as a barotropic wave train that extends from Australia to the Antarctic, where the teleconnection is likely a direct
atmospheric response to tropical convective heating.
Received: 20 June 2000 / Accepted: 17 September 2000 相似文献
15.
A physically based cloud nucleation parameterization was introduced into an optical properties/radiative transfer module incorporated with the off-line air quality modeling system Regional Atmospheric Modeling System (RAMS)-Models-3 Community Multi Scale Air Quality (CMAQ) to investigate the distribution features of the first indirect radiative effects of sulfate, nitrate, and ammonium-sulfate-nitrate (ASN) over East Asia for the years of 2005, 2010, and 2013. The relationship between aerosol particles and cloud droplet number concentration could be properly described by this parameterization because the simulated cloud fraction and cloud liquid water path were generally reliable compared with Moderate Resolution Imaging Spectroradiometer (MODIS) retrieved data. Simulation results showed that the strong effect of indirect forcing was mainly concentrated in Southeast China, the East China Sea, the Yellow Sea, and the Sea of Japan. The highest indirect radiative forcing of ASN reached ?3.47 W m?2 over Southeast China and was obviously larger than the global mean of the indirect forcing of all anthropogenic aerosols. In addition, sulfate provided about half of the contribution to the ASN indirect forcing effect. However, the effect caused by nitrate was weak because the mass burden of nitrate was very low during summer, whereas the cloud fraction was the highest. The analysis indicated that even though the interannual variation of indirect forcing magnitude generally followed the trend of aerosol mass burden from 2005 to 2013, the cloud fraction was an important factor that determined the distribution pattern of indirect forcing. The heaviest aerosol loading in North China did not cause a strong radiative effect because of the low cloud fraction over this region. 相似文献
16.
An extensive set of boreal summer seasonal hindcasts from a two tier system is compared with corresponding seasonal hindcasts from two other coupled ocean–atmosphere models for their seasonal prediction skill (for precipitation and surface temperature) of the Asian summer monsoon. The unique aspect of the two-tier system is that it is at relatively high resolution and the SST forcing is uniquely bias corrected from the multi-model averaged forecasted SST from the two coupled ocean–atmosphere models. Our analysis reveals: (a) The two-tier forecast system has seasonal prediction skill for precipitation that is comparable (over the Southeast Asian monsoon) or even higher (over the South Asian monsoon) than the coupled ocean–atmosphere. For seasonal anomalies of the surface temperature the results are more comparable across models, with all of them showing higher skill than that for precipitation. (b) Despite the improvement from the uncoupled AGCM all models in this study display a deterministic skill for seasonal precipitation anomalies over the Asian summer monsoon region to be weak. But there is useful probabilistic skill for tercile anomalies of precipitation and surface temperature that could be harvested from both the coupled and the uncoupled climate models. (c) Seasonal predictability of the South Asian summer monsoon (rainfall and temperature) does seem to stem from the remote ENSO forcing especially over the Indian monsoon region and the relatively weaker seasonal predictability in the Southeast Asian summer monsoon could be related to the comparatively weaker teleconnection with ENSO. The uncoupled AGCM with the bias corrected SST is able to leverage this teleconnection for improved seasonal prediction skill of the South Asian monsoon relative to the coupled models which display large systematic errors of the tropical SST’s. 相似文献
17.
Recent work has shown the dominance of the Himalaya in supporting the Indian summer monsoon(ISM),perhaps by surface sensible heating along its southern slope and by mechanical blocking acting to separate moist tropical flow from drier midlatitude air.Previous studies have also shown that Indian summer rainfall is largely unaffected in sensitivity experiments that remove only the Tibetan Plateau.However,given the large biases in simulating the monsoon in CMIP5 models,such results may be model dependent.This study investigates the impact of orographic forcing from the Tibetan Plateau,Himalaya and Iranian Plateau on the ISM and East Asian summer monsoon(EASM) in the UK Met Office's Had GEM3-GA6 and China's Institute of Atmospheric Physics FGOALS-FAMIL global climate models.The models chosen feature oppositesigned biases in their simulation of the ISM rainfall and circulation climatology.The changes to ISM and EASM circulation across the sensitivity experiments are similar in both models and consistent with previous studies.However,considerable differences exist in the rainfall responses over India and China,and in the detailed aspects such as onset and retreat dates.In particular,the models show opposing changes in Indian monsoon rainfall when the Himalaya and Tibetan Plateau orography are removed.Our results show that a multi-model approach,as suggested in the forthcoming Global Monsoon Model Intercomparison Project(GMMIP) associated with CMIP6,is needed to clarify the impact of orographic forcing on the Asian monsoon and to fully understand the implications of model systematic error. 相似文献
18.
BCC_AGCM2.1对中国东部地区云辐射特征模拟的偏差分析 总被引：2，自引：0，他引：2
通过与观测及再分析资料的对比,评估了中国国家气候中心大气环流模式BCC_AGCM 2.1对中国东部地区云辐射特征的模拟性能,并着重分析了模拟偏差的原因.在云辐射特征的基本气候态模拟方面,模式能大致再现中国东部中纬度层状云大值带,以及层状云冷季多、暖季少的季节特征,模拟的短波云辐射强迫也具有与观测相对应的季节变化特征.在云辐射强迫和地面温度相互影响过程的模拟方面,模式也能模拟出与观测相近的相互作用过程,即地面温度降低伴随着层状云云量增多以及负的净云辐射强迫加强,升温时层状云云量减少和净云辐射强迫减弱.但模式模拟的大陆层状云云量系统性偏少(尤其在冷季),使得模式在该处的短波云辐射强迫明显偏弱.初步分析表明,造成层状云模拟差异的主要原因是在中国西南地区对流层低层模式模拟的偏南气流明显偏弱以及陆-气潜热通量偏小.偏南气流偏弱导致低层散度和垂直运动条件不利于中层云的形成.同时偏南气流偏弱也不利于向西南地区的水汽输送,再加上模式模拟地表向上潜热通量偏小,这二者都使得模式模拟中国西南区域对流层低层的水汽含量严重偏少,相对湿度偏低,同样不利于层状云生成和发展.水汽偏少进一步导致在冷异常情况下青藏高原下游云辐射-地表温度反馈模拟偏弱,即呈现冷异常时,水汽条件偏弱限制了云量增加,弱化了进一步降低温度的反馈过程. 相似文献
19.
Cloud-radiative forcing(CRF) at the top of the atmosphere(TOA) over the western Pacific warm pool(WP) shows unique characteristics in response to El Ni?o events. In this region, the responses of CRF to El Ni?o events have been a useful metric for evaluating climate models. Satellite data are used to analyze the CRF anomalies to El Ni?o events simulated by the new and old versions of the Climate System Model of the Chinese Academy of Meteorological Sciences(CAMS-CSM), which has participated in the Atmospheric Model Intercomparison Project(AMIP). Here, simulations for super El Ni?o years, El Ni?o years, and normal years are compared with observations. The results show that the mean values of both longwave CRF(LWCRF) and shortwave CRF(SWCRF) in CAMS-CSM are weaker than the observations for each category of El Ni?o events. Compared with the old version of CAMS-CSM, the decrease in LWCRF during El Ni?o events is well simulated by the new version of CAMS-CSM. However, both new and old models cannot reproduce the anomalous SWCRF in El Ni?o events. The biases in the CRF response to El Ni?o events are attributed to the biases in the cloud vertical structure because of a weaker crash of the Walker circulation in CAMS-CSM. Due to the modification of the conversion rate from cloud droplets to raindrops in the cumulus convection scheme, the new version of CAMS-CSM has better CRF skills in normal years, but biases in El Ni?o events still exist in the new version. Improving the response of the Walker circulation to El Ni?o events is key to higher skills in simulating the cloud radiative responses. 相似文献
20.
The temperature biases of 28 CMIP5 AGCMs are evaluated over the Tibetan Plateau(TP) for the period 1979–2005. The results demonstrate that the majority of CMIP5 models underestimate annual and seasonal mean surface 2-m air temperatures(T_(as)) over the TP. In addition, the ensemble of the 28 AGCMs and half of the individual models underestimate annual mean skin temperatures(T_s) over the TP. The cold biases are larger in T_(as) than in T_s, and are larger over the western TP. By decomposing the T_s bias using the surface energy budget equation, we investigate the contributions to the cold surface temperature bias on the TP from various factors, including the surface albedo-induced bias, surface cloud radiative forcing, clear-sky shortwave radiation, clear-sky downward longwave radiation, surface sensible heat flux, latent heat flux,and heat storage. The results show a suite of physically interlinked processes contributing to the cold surface temperature bias.Strong negative surface albedo-induced bias associated with excessive snow cover and the surface heat fluxes are highly anticorrelated, and the cancelling out of these two terms leads to a relatively weak contribution to the cold bias. Smaller surface turbulent fluxes lead to colder lower-tropospheric temperature and lower water vapor content, which in turn cause negative clear-sky downward longwave radiation and cold bias. The results suggest that improvements in the parameterization of the area of snow cover, as well as the boundary layer, and hence surface turbulent fluxes, may help to reduce the cold bias over the TP in the models. 相似文献