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1.
Sensitivity of the Simulated Tropical Intraseasonal Oscillation to Cumulus Parameterizations 
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下载免费PDF全文 The sensitivity of the simulated tropical intraseasonal oscillation or MJO （Madden and Julian oscillation） to different cumulus parameterizations is studied by using an atmospheric general circulation model （GCM）--SAMIL （Spectral Atmospheric Model of IAP LASG）. Results show that performance of the model in simulating the MJO alters widely when using two different cumulus parameterization schemes-the moist convective adjustment scheme （MCA） and the Zhang-McFarlane （ZM） scheme. MJO simulated by the MCA scheme was found to be more realistic than that simulated by the ZM scheme. MJO produced by the ZM scheme is too weak and shows little propagation characteristics. Weak moisture convergence at low levels simulated by the ZM scheme is not enough to maintain the structure and the eastward propagation of the oscillation. These two cumulus schemes produced different vertical structures of the heating profile. The heating profile produced by the ZM scheme is nearly uniform with height and the heating is too weak compared to that produced by the MCA, which maybe contributes greatly to the failure of simulating a reasonable MJO. Comparing the simulated MJO by these two schemes indicate that the MJO simulated by the GCM is highly sensitive to cumulus parameterizations implanted in. The diabatic heating profile plays an important role in the performance of the GCM. Three sensitivity experiments with different heating profiles are designed in which modified heating profiles peak respectively in the upper troposphere （UH）, middle troposphere （MH）, and lower troposphere （LH）. Both the LH run and the MH run produce eastward propagating signals on the intraseasonal timescale, while it is interesting that the intraseasonal timescale signals produced by the UH run propagate westward. It indicates that a realistic intraseasonal oscillation is more prone to be excited when the maximum heating concentrates in the middle-low levels, especially in the middle levels, while westward propagating disturbances 相似文献
2.
Xiaolong Jia Chongyin Li Ningfang Zhou Jian Ling 《Dynamics of Atmospheres and Oceans》2010,49(2-3):141-163
The Madden–Julian oscillation (MJO) is simulated using an AGCM with three different cumulus parameterization schemes: a moist convective adjustment (MCA) scheme, the Zhang–McFarlane (ZM) mass-flux scheme, and the Tiedtke scheme. Results show that the simulated MJO is highly dependent on the cumulus parameterization used. Among the three cumulus parameterizations, only the MCA scheme produces MJO features similar to observations, including the reasonable spatial distribution, intraseasonal time scales and eastward propagation. Meanwhile, the amplitude is too large and the eastward propagation speed too fast than observations and the relationship between precipitation and low-level wind anomaly is unrealistic with enhanced convection occurring within easterly anomalies instead of westerly anomalies as in observations. The over-dependence of precipitation on boundary convergence produced by the MCA scheme is presumably responsible for this unrealistic phase relation in the simulation. The other two schemes produce very poor simulations of the MJO: spectral power of westward propagation is larger than that of eastward propagation in zonal wind and precipitation, indicating a westward propagation of the intraseasonal variability.The mean state and vertical profile of diabatic heating are perhaps responsible for the differences in these simulations. The MCA scheme produces relatively realistic climate background. When either ZM or Tiedtke scheme is used, the observed extension of westerly winds from the western Pacific to the dateline is missing and precipitation over the equatorial region and SPCZ is dramatically underestimated. In addition, diabatic heating produced by both ZM and Tiedtke schemes are very weak and nearly uniform with height. The heating profile produced by the MCA scheme has a middle-heavy structure with much larger magnitude than those produced by the other two schemes. In addition, a very unrealistic boundary layer heating maximum produced by the MCA scheme induces too strong surface convergence, which perhaps contributes to the too strong intraseasonal variability in the simulation. 相似文献
3.
Sensitivity of MJO simulations to diabatic heating profiles 总被引：2，自引：0，他引：2
The difficulty for global atmospheric models to reproduce the Madden–Julian oscillation (MJO) is a long-lasting problem. In an attempt to understand this difficulty, simple numerical experiments are conducted using a global climate model. This model, in its full paramterization package (control run), is capable of producing the gross features of the MJO, namely, its planetary-scale, intraseasonal, eastward slow propagation. When latent heating profiles in the model are artificially modified, the characteristics of the simulated MJO changed drastically. Intraseasonal perturbations are dominated by stationary component over the Indian and western Pacific Oceans when heating profiles are top heavy (maximum in the upper troposphere). In contrast, when diabatic heating is bottom heavy (maximum in the lower troposphere), planetary-scale, intraseasonal, eastward propagating perturbations are reproduced with a phase speed similar to that of the MJO. The difference appears to come from surface and low-level moisture convergence, which is much stronger and more coherent in space when the heating profile is bottom heavy than when it is top heavy. These sensitivity experiments, along with other theoretical, numerical, and observational results, have led to a hypothesis that the difficulty for global models to produce the MJO partially is rooted in a lack of sufficient diabatic heating in the lower troposphere, presumably from shallow convection. 相似文献
4.
IAP AGCM4.0模式对热带大气季节内振荡的模拟评估 总被引：1，自引：1，他引：0
基于中国科学院大气物理所大气环流模式IAP AGCM4.0总共30年(1979~2008年)的模拟结果,评估了IAP AGCM4.0模式对热带大气季节内振荡的模拟能力。分析结果表明IAP AGCM4.0模式可以在一定程度上模拟出热带大气季节内振荡的主要时空谱结构特征,在周期30~80天处存在明显的谱能量中心;模式模拟的季节内振荡东传的主要特征与观测基本一致,东移波的能量远大于西移波。基于RMM指数(All-season Real-time Multivariate MJO Index)的分析表明,模式模拟的850 h Pa和200 h Pa季节内尺度风场和对流活动在赤道地区的空间分布与观测基本一致。但与观测相比,模式模拟的热带大气季节内振荡的周期较短,东传速度快于观测,虚假的西传特征过强,对流活跃区域范围较小、强度较弱。就非绝热加热而言,模式模拟结果与再分析资料比较接近,但最大加热在印度洋和西太平洋地区出现的位相较晚。进一步分析表明,模式中影响对流触发的相对湿度阈值(RHc)的不同取值(RHc分别取为85%、90%、95%和100%),可以显著影响热带大气非绝热加热垂直廓线,从而影响模式对热带大气季节内振荡的模拟;当对流触发相对湿度阈值取为90%时,IAP AGCM4.0模式对热带大气季节内振荡模拟的能力相对最好,非绝热加热垂直廓线在不同位相的分布特征也与再分析资料最为接近。这说明模式对流参数化方案中不同参数的合适选取,可以改进模式对热带大气季节内振荡的模拟能力。 相似文献
5.
本文从赤道β平面近似下的线性化扰动方程组出发,基于第二类条件不稳定(CISK)理论,研究了热带对流层大气准40天低频振荡的动力机制。研究发现,当对流层中、上层存在较大的对流凝结加热时可激发出纬向波数为1、周期为40天左右的不稳定Kelvin波,它以每天8到11个经度的相速缓慢向东移动。由此指出,观测到的热带对流层大气30—50天的低频振荡可能正是这种由对流凝结加热所驱动的缓慢东移的Kelvin波的具体表现。这可对热带对流层大气30—50天低频振荡现象的动力机制给以初步的物理解释。 相似文献
6.
Jian Sheng 《Climate Dynamics》1995,12(2):125-140
The Madden-Julian oscillation (MJO) simulated by the Canadian Climate Centre general circulation model (CCC GCM) is identified
by a principal oscillation pattern (POP) analysis and compared with that observed in the real atmosphere. The results are
based upon two integrations of the CCC GCM, one with a parameterization of penetrative cumulus convection (EXP1) and the other
with a moist convective adjustment scheme (EXP2). The signal of MJO can be detected in both integrations as the first POP
of the 200 hPa velocity potential along the equator. The disturbances show a distinctive wave number one structure with the
strongest local amplitude found in the longitudes corresponding to the region of the Asian monsoon. The phase speed of the
eastward wave propagation is higher in the eastern Pacific and lower in the monsoon region where the convective activities
are strongest. These features are in good agreement with the observations. The energy spectrum of the velocity potential peaks
at the frequency corresponding to a period of about 38 days for EXP1, which is somewhat shorter compared to the observed periods
of 40–50 days. On the other hand, two spectral peaks can be clearly identified for EXP2, one with a period of 24 days and
the other with a much longer period, somewhere near 112 days. Both peaks appear statistically significant at 95% level. Long
term data of the observed atmosphere show little indication of such spectral separation. The horizontal patterns identified
by the POP analysis resemble to some extent the baroclinic response of tropical flow to a heat source travelling with the
speed of MJO. At the upper level, Rossby wave energy propagates westward with winds generally following the height contours,
whereas Kelvin wave energy propagates to the east from the heat source with strong cross-contour flow near the equator. At
the lower level, the patterns are essentially reversed. The model-generated precipitation and diabatic heating are examined
by compositing against the moving MJO. It is found in EXP2 that the composite heating distribution is coherent with the flow
pattern only in a certain sector of the equator, depending on whether the fast or slow mode is used to determine the reference
point. The composite vertical heating profile of a slower mode tends to have a maximum found at a lower level. The sensitivity
of simulated MJO to the cumulus convection scheme in the model is discussed.
Received: 19 December 1994 / Accepted: 11 July 1995 相似文献
7.
Comparison of seasonal and intraseasonal variation of tropical climate in NCAR CCM2 GCM with two different cumulus schemes 总被引：4，自引：0，他引：4
K. Rajendran Ravi S. Nanjundiah J. Srinivasan 《Meteorology and Atmospheric Physics》2002,79(1-2):57-86
Summary
The seasonal and intraseasonal variation of tropical climate in National Center for Atmospheric Research (NCAR) Community
Climate Model Version 2 (CCM2) General Circulation Model (GCM) has been examined using two different cumulus parameterization
schemes, the moist convective adjustment scheme of Manabe et al. (1965) and the mass-flux scheme of Hack (1994). Ten-year
simulations have been undertaken with each of these schemes with SST prescribed according to the monthly mean climatology.
The seasonal mean rainfall in the tropics simulated by the moist convective adjustment scheme (MCA) scheme was found to be
more realistic than the mass-flux (Hack) scheme. The more realistic simulation by the MCA scheme was found to be on account
of the fact that the mean moist static energy of the lower troposphere in the MCA scheme was closer to the observations than
in the Hack scheme. In both the schemes, the precipitation in the tropics increases montonically with precipitable water vapour
when the precipitable water vapour is above 40 mm. This is consistent with relationship between precipitation and precipitable
water in the observations. The Hack scheme tends to simulate lower precipitation (for a given amount of precipitable water)
when compared to observations.
The MCA scheme simulates the eastward migration of convective systems along the equator quite well, although the speed of
propagation is somewhat low. The poleward migration of convective systems in the Indian region is more realistically simulated
by the MCA scheme than the Hack scheme. This is because the latitudinal gradient of the mean moist static energy in the MCA
scheme is more realistic than in the Hack scheme. Over most of the tropics, simulation by the MCA scheme is more realistic
on both seasonal and intraseasonal timescales.
Received November 1, 2000 Revised June 20, 2001 相似文献
8.
Madden-Julian Oscillations (MJO) in six integrations using an AGCM with different cumulus
parameterization schemes and resolutions are examined to investigate their impacts on the MJO simulation.
Results suggest that the MJO simulation can be affected by both resolution and cumulus parameterization,
though the latter, which determines the fundamental ability of the AGCM in simulating the MJO and the
characteristics of the simulated MJO, is more crucial than the former. Model resolution can substantially
affect the simulated MJO in certain aspects. Increasing resolution cannot improve the simulated MJO
substantially, but can significantly modulate the detailed character of the simulated MJO; meanwhile, the
impacts of resolution are dependent on the cumulus parameterization, determining the basic features of the
MJO. Changes in the resolution do not alter the nature of the simulated MJO but rather regulate the
simulation itself, which is constrained by cumulus parameterization schemes. Therefore, the vertical
resolution needs to be increased simultaneously. The vertical profile of diabatic heating may be a crucial
factor that is responsible for these different modeling results. To a large extent, it is determined by the
cumulus parameterization scheme used. 相似文献
9.
Based on the aqua-planet experiments, the wavenumber-frequency characteristics of tropical waves and their influencing factors in SST distribution and the convective parameterization scheme are investigated using the spectral atmospheric general circulation model （SAMIL）. Space-time spectral analysis is used to obtain the variance of convectively coupled tropical waves. In the Control experiment with maximum SST located at the equator the simulated tropical-wave behaviors are in agreement with those in observations and theoretical solutions. When the maximum SST is located at 5°N, the symmetric and antisymmetric waves are much weaker than those in the control experiment, suggesting that tropical wave activities are very sensitive to the SST distributions. Importantly, the variance maximum of Madden-Julian oscillation （MJO） is found to occur around 5°N, which suggests that the development of the MJO depends largely on the latitude of maximum SST. Furthermore, the seasonal variations of MJO may be mainly caused by the seasonal variations of the maximum SST. The experiment results with two different cumulus schemes the Manabe moist convective adjustment and Zhang-McFarlane （ZM） convective scheme, were also compared to examine the impacts of convective parameterization. Weakened variances of each individual tropical wave when the ZM scheme is used suggest that the ZM scheme is not favorable for the tropical wave activities. However, the wave characteristics are different when the ZM scheme is used in different models, which may imply that the simulated basic state is important to the meridional distributions of the waves. The MJO signals suggest that the parameterization scheme may have great influence on the strength, but have less direct impact on the MJO distribution. The frequency of the tropical waves may be associated with the moisture control of convection and the large-scale condensation scheme used in the model. 相似文献
10.
An atmospheric general circulation model is used in a series of three experiments to simulate the intraseasonaloscillation in the tropical atmosphere.Analyses of the model daily data show that various physical variables,from sever-al different regions,exhibit fluctuations with a spectral peak between 30 and 60 days.This represents a 30—60 dayoscillation in the tropical atmosphere and possesses several features which are consistent with observations.These in-clude a horizontal structure dominated by zonal wavenumber 1 and a vertical structure which is predominantlybaroclinic.The effect of warm SST (sea surface temperature) anomalies on the 30—60 day oscillation in the tropical atmos-phere is also simulated by prescribing global SST as observed in 1983.This has the effect of weakening the oscillationwhile at the same time the vertical structure becomes less baroclinic.The importance of cumulus convection to the propagational characteristics of this oscillation is demonstrated by acomparison of results based on different parameterizations for convection.In one case,where the maximum convectionover the Pacific is simulated to be too far east,the simulated 30—60 day oscillation shows evidence of westward propa-gation.In the second case,where the convection maximum is located near the observed position in the western Pacific,there is more clearly evidence of eastward propagation.Both results suggest that the location of maximum convection in the Pacific can have an important influence on thestrength,structure and propagation of the 30—60 day oscillation. 相似文献