Sensitivity of the Simulated Tropical Intraseasonal Oscillation to Cumulus Parameterizations

The sensitivity of the simulated tropical intraseasonal oscillation or MJO (Madden and Julian oscilla tion)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 axe more prone to be produced when the maximum heating appears very high.     

Sensitivity of the Simulated Tropical Intraseasonal Oscillation to Cumulus Parameterizations

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     

IAP AGCM4.0模式对热带大气季节内振荡的模拟评估

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。     

Comparison of seasonal and intraseasonal variation of tropical climate in NCAR CCM2 GCM with two different cumulus schemes

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     

IMPACTS OF CUMULUS PARAMETERIZATION AND RESOLUTION ON THE MJO SIMULATION

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.     

Analysis on the 10-yr Simulation of the Meiyu Precipitation and Its Associated Circulation with the GAMIL Model

The major features of Meiyu precipitation and associated circulation systems simulated by the grid-point atmospheric model of IAP LASG (GAMIL) with Zhang-McFarlane and Tiedtke cumulus parameterization schemes are examined in this paper. The results show that the model with both schemes can reproduce the heavy precipitation center over the Yangtze-Huai River Basin (YHRB) during the Meiyu period. The horizontal and vertical structures of the circulation systems during the Meiyu period are also well simulated,such as the intensive meridional gradients of moisture and μse (pseudo-equivalent temperature), the strong low-level southwesterly flow in the lower troposphere over East China, the location of the westerly jet stream in the upper troposphere, the strong ascending motion in heavy precipitation zone, and compensation downward motion on the northern and southern sides of the heavy precipitation belt. However, obvious discrepancies occur in the simulated temperature field in the mid-lower troposphere,especially with the Zhang-McFarlane scheme. In addition, the simulated Meiyu period (onset and duration) is found to be associated with the temperature difference in the lower atmosphere over the land and ocean, and with the cumulus parameterization schemes. The land-sea thermal contrast (LSTC) simulated by the Zhang-McFarlane scheme increases faster than that in the reanalysis from April to July, and changes from negative to positive at the end of May. Consequently, the simulated Meiyu onset begins in May, one month earlier than the observation. On the other hand, since the LSTC simulated by the Tiedtke scheme is in agreement with the reanalysis during June and July, the simulated Meiyu period is similar to the observation. The different LSTCs simulated by the GAMIL model with the two cumulus parameterization schemes may affect the Meiyu period simulations. Therefore, it is necessary to refine the cumulus parameterization scheme in order to improve the Meiyu precipitation simulation by the GAMIL model.     

Sensitivity of MJO simulations to diabatic heating profiles

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.     

The Madden-Julian oscillation in the Canadian Climate Centre general circulation model

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     

Impacts of cumulus momentum transport on MJO simulation

Vertical cumulus momentum transport is an important physical process in the tropical atmosphere and plays a key role in the evolution of the tropical atmospheric system. This paper focuses on the impact of the vertical cumulus momentum transport on Madden-Julian Oscillation (MJO) simulation in two global climate models (GCMs). The Tiedtke cumulus parameterization scheme is applied to both GCMs [CAM2 and Spectral Atmospheric general circulation Model of LASG/IAP (SAMIL)]. It is found that the MJO simulation ability might be influenced by the vertical cumulus momentum transport through the cumulus parameterization scheme. However, the use of vertical momentum transport in different models provides different results. In order to improve model's MJO simulation ability, we must introduce vertical cumulus momentum transport in a more reasonable way into models. Furthermore, the coherence of the parameterization and the underlying model also need to be considered.     

IMPACT OF TROPICAL INTRASEASONAL OSCILLATIONS ON THE PRECIPITATION OF GUANGDONG IN JUNES

The impact of tropical intraseasonal oscillations on the precipitation of Guangdong in Junes and its physical mechanism are analyzed using 30-yr (1979 to 2008), 86-station observational daily precipitation of Guangdong and daily atmospheric data from NCEP-DOE Reanalysis. It is found that during the annually first rainy season (April to June), the modulating effect of the activity of intraseasonal oscillations propagating eastward along the equator (MJO) on the June precipitation in Guangdong is different from that in other months. The most indicative effect of MJO on positive (negative) anomalous precipitation over the whole or most of the province is phase 3 (phase 6) of strong MJO events in Junes. A Northwest Pacific subtropical high intensifies and extends westward during phase 3. Water vapor transporting along the edge of the subtropical high from Western Pacific enhances significantly the water vapor flux over Guangdong, resulting in the enhancement of the precipitation. The condition is reverse during phase 6. The mechanism for which the subtropical high intensifies and extends westward during phase 3 is related to the atmospheric response to the asymmetric heating over the eastern Indian Ocean. Analyses of two cases of sustained strong rainfall of Guangdong in June 2010 showed that both of them are closely linked with a MJO state which is both strong and in phase 3, besides the effect from a westerly trough. It is argued further that the MJO activity is indicative of strong rainfall of Guangdong in June. The results in the present work are helpful in developing strategies for forecasting severe rainfall in Guangdong and extending, combined with the outputs of dynamic forecast models, the period of forecasting validity.     

Experimental Dynamical Forecast of an MJO Event Observed during TOGA-COARE Period

With a hybrid atmosphere-ocean coupled model we carried out an experimental forecast of a well documented Madden-Julian Oscillation (MJO) event that was observed during the period of Tropical Ocean Global Atmosphere Coupled Ocean-Atmosphere Response Experiment (TOGA-COARE). The observed event, originated in the western Indian Ocean around 6 January 1993, moved eastward with a phase speed of about 6.2 m s-1 and reached the dateline around February 1. The hybrid coupled model reasonably forecasts the MJO initiation in the western Indian Ocean, but the predicted MJO event propagates too slow (~ 4.4 m s-1). Results from previous observational studies using unprecedented humidity profiles obtained by NASA Aqua/AIRS satellite suggested that two potential physical processes may be responsible for this model caveat. After improving the cumulus parameterization scheme based on the observations, the model is able to forecast the same event one month ahead. Further sensitivity experiment confirms that the speed-up of model MJO propagation is primarily due to the improved convective scheme. Further, air-sea coupling plays an important role in maintaining the intensity of the predicted MJO. The results here suggest that MJO prediction skill is sensitive to model cumulus parameterization and air-sea coupling. Citation: Fu, X., B. Wang, Q. Bao, et al., 2008: Experimental dynamical forecast of an MJO event observed during TOGA-COARE period, Atmos. Oceanic Sci. Lett., 1, 24-28     

Interannual spring Wyrtki jet variability and its regional impacts

The role of spring Wyrtki jets in modulating the equatorial Indian Ocean and the regional climate is an unexplored problem. The source of interannual variability in the spring Wyrtki jets is explored in this study. The relationship between intraseasonal and interannual variability from 1958 to 2008 and its relation with Indian Summer Monsoon is further addressed. Analysis reveals that the interannual variability in spring Wyrtki jets is controlled significantly by their intraseasonal variations. These are mostly defined by a single intraseasonal event of duration 20 days or more which either strengthens or weakens the seasonal mean jet depending on its phase. The strong spring jets are driven by such intraseasonal westerly wind bursts lasting for 20-days or more, whereas the weak jets are driven by weaker intraseasonal westerlies. During the years of strong jets, the conventional westward phase propagation of Wyrtki jets is absent and instead there is an eastward phase propagation indicating the possible role of Madden Julian Oscillation (MJO) in strengthening the spring Wyrtki jets. These strong intraseasonal westerly wind bursts with eastward phase propagation during strong years are observed mainly in late spring and have implications on June precipitation over the Indian and adjoining land mass. Anomalously strong eastward jets accumulate warm water in the eastern equatorial Indian Ocean (EIO), leading to anomalous positive upper ocean heat content and supporting more local convection in the east. This induces subsidence over the Indian landmass and alters monsoon rainfall by modulating monsoon Hadley circulation. In case of weak current years such warm anomalies are absent over the eastern EIO. Variations in the jet strength are found to have strong impact on sea level anomalies, heat content, salinity and sea surface temperature over the equatorial and north Indian Ocean making it a potentially important player in the north Indian Ocean climate variability.     

积云参数化方案对热带降水年循环模态模拟的影响

本文利用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)发展的大气环流模式(SAMIL),采用Zhang-McFarlane (ZM)和Tiedtke (TDK)两种积云对流参数化方案,讨论了积云对流参数化方案对热带降水年循环模态模拟的影响.结果表明,两种积云对流参数化方案均能合理再现...     

Madden–Julian Oscillation simulated in BCC climate models

This study evaluates the ability of four versions BCC (Beijing Climate Center or National Climate Center) models (BCC_AGCM2.1, BCC_AGCM2.2, BCC_CSM1.1 and BCC_CSM1.1m) in simulating the MJO phenomenon using the outputs of the AMIP (Atmospheric Model Intercomparison Project) and historical runs. In general, the models can simulate some major characteristics of the MJO, such as the intensity, the periodicity, the propagation, and the temporal/spatial evolution of the MJO signals in the tropics. There are still some biases between the models and the observation/reanalysis data, such as the overestimated total intraseasonal variability, but underestimated MJO intensity, shorter significant periodicity, and excessive westward propagation. The differences in the ability of simulating the MJO between AMIP and historical experiments are also significant. Compared to the AMIP runs, the total intraseasonal variability is reduced and more realistic, however the ratio between the MJO and its westward counterpart decreases in the historical runs. This unrealistic simulation of the zonal propagation might have been associated with the greater mean precipitation over the Pacific and corresponded to the exaggeration of the South Pacific Convergence Zone structure in precipitation mean state. In contrast to the T42 versions, the improvement of model resolution demonstrate more elaborate topography, but the enhanced westward propagation signals over the Arabia Sea followed. The underestimated (overestimated) MJO variability over eastern Indian Ocean (Pacific) was assumed to be associated with the mean state. Three sets of sensitive experiments using BCC_CSM1.1m turn out to support this argument.     

Tropical intraseasonal rainfall variability in the CFSR

While large-scale circulation fields from atmospheric reanalyses have been widely used to study the tropical intraseasonal variability, rainfall variations from the reanalyses are less focused. Because of the sparseness of in situ observations available in the tropics and strong coupling between convection and large-scale circulation, the accuracy of tropical rainfall from the reanalyses not only measures the quality of reanalysis rainfall but is also to some extent indicative of the accuracy of the circulations fields. This study analyzes tropical intraseasonal rainfall variability in the recently completed NCEP Climate Forecast System Reanalysis (CFSR) and its comparison with the widely used NCEP/NCAR reanalysis (R1) and NCEP/DOE reanalysis (R2). The R1 produces too weak rainfall variability while the R2 generates too strong westward propagation. Compared with the R1 and R2, the CFSR produces greatly improved tropical intraseasonal rainfall variability with the dominance of eastward propagation and more realistic amplitude. An analysis of the relationship between rainfall and large-scale fields using composites based on Madden-Julian Oscillation (MJO) events shows that, in all three NCEP reanalyses, the moisture convergence leading the rainfall maximum is near the surface in the western Pacific but is above 925?hPa in the eastern Indian Ocean. However, the CFSR produces the strongest large-scale convergence and the rainfall from CFSR lags the column integrated precipitable water by 1 or 2?days while R1 and R2 rainfall tends to lead the respective precipitable water. Diabatic heating related to the MJO variability in the CFSR is analyzed and compared with that derived from large-scale fields. It is found that the amplitude of CFSR-produced total heating anomalies is smaller than that of the derived. Rainfall variability from the other two recently produced reanalyses, the ECMWF Re-Analysis Interim (ERAI), and the Modern Era Retrospective-analysis for Research and Applications (MERRA), is also analyzed. It is shown that both the ERAI and MERRA generate stronger rainfall spectra than the R1 and more realistic dominance of eastward propagating variance than R2. The intraseasonal variability in the MERRA is stronger than that in the ERAI but weaker than that in the CFSR and CMORPH.     

WRF模式不同云参数化方案的暴雨预报能力检验及集成试验

利用WRFV3. 6的8种微物理方案和6种积云参数化方案对湖北及其周边地区夏季12次暴雨过程进行回报,分析各种方案对暴雨预报的影响。结果显示,各种方案均能较好地预报出降水过程,但其降水强度和范围存在一定差异。当积云参数化方案为KF方案时,对Lin、WSM6、Thompson、Morrison 2-mom、CAM5. 1、WDM5、WDM6、NSSL 2-mom微物理方案做敏感性试验,发现CAM 5. 1方案优于其他7种微物理方案,M orrison 2-mom次之。当微物理方案为CAM 5. 1时,对KF、BM J、GD、SAS、G3D、Tiedtke积云参数化方案做敏感性试验,发现在不同量级降水预报中,6种积云参数化方案各有优劣。综合考虑,GD、SAS、Tiedtke积云参数化方案优于其他3种方案。在此基础上开展多方案集成试验,结果表明集合平均(ensemble mean,EMN)在一定程度上可以减少预报误差,降低单个成员预报的不确定性。     

基于WRF的积云对流参数化方案对中国夏季降水预报的影响研究

为了研究WRF(Weather Research and Forecasting)中尺度模式中积云对流参数化方案对夏季降水预报的影响,基于水平分辨率为9 km的WRF模式,采用Kain-Fritsch(KF)、尺度适应的KF、Tiedtke、new Tiedtke和尺度适应的new Tiedtke方案等5种积云对流参数...     

积云对流参数化方案对东亚夏季环流和降水模拟的影响

利用WRF（Weather Research and Forecasting）模式对东亚夏季区域气候模拟中最常选用的两种积云对流参数化方案进行对比分析,研究积云对流参数化方案选用对大尺度环流模拟的影响。结果表明:Kain-Fritsch（KF）方案对西太平洋副热带高压（简称副高）及环流的模拟效果较好,虽然KF方案模拟降水偏多,但是时空分布与TRMM降水分布接近;Grell-Freitas（GF）方案对流加热率过大,从而模拟的南海—菲律宾区域对流异常增强,在南海—菲律宾洋面上的垂直输送异常增大,非绝热加热的范围偏大,导致副高南侧下沉区辐散减弱,抑制了副高北抬西伸,进而影响到水汽输送和季风环流,最终对东亚夏季降水的模拟产生不利影响。修改GF方案对流加热率和干燥率的敏感性试验表明,减小对流加热率和干燥率参数能有效抑制南海—菲律宾区域过强的对流,东亚大尺度环流的模拟得到明显改进。     

Impacts of a GCM＇s Resolution on MJO Simulation

Long-term integrations are conducted using the Spectral Atmospheric Model （referred to as SAMIL）, which was developed in the Laboratory for Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics （LASG） in the Institute of Atmospheric Physics （IAP）, with different resolutions to inves-tigate sensitivity of the Madden-Julian Oscillation （MJO） simulations to the model＇s resolution （horizontal and vertical）. Three resolutions of the model, R15L9, R42L9 and R42L26, with identical physical processes, all produced the basic observed features of the MJO, including the spatiotemporal space-time spectra and eastward propagation. No fundamental differences among these simulations were found. This indicates that the model resolution is not a determining factor for simulating the MJO. Detailed differences among these modeling results suggest, however, that model resolution can substantially affect the simulated MJO in certain aspects. For instance, at a lower horizontal resolution, high frequency disturbances were weaker and the structures of the simulated MJO were better defined to a certain extent. A higher vertical resolution led to a more realistic spatiotemporal spectrum and spatial distribution of MJO precipitation. Meanwhile, increasing the model＇s resolution improved simulation of the climatology. However, increasing the resolution should be based on improving the cumulus parameterization scheme.     

Performance of FGOALS-s2 in simulating intraseasonal oscillation over the south Asian monsoon region

The capability of the current version of the air-sea coupled climate model, the Flexible Global Ocean-Atmosphere-Land System model, Spectral Version 2 (FGOALS-s2), in simulating the boreal summer intraseasonal oscillation (ISO) over the south Asian monsoon (SAM) region is diagnosed, in terms of dominant period, propagation direction, and vertical structure. Results show that the coupled model can reasonably simulate the main features of observed ISO propagation compared to the chosen AGCM. These features include the eastward movement of intraseasonal 850-hPa zonal wind over the Arabian Sea and Bay of Bengal, the vertical structure in active phases, and the realistic phase relationship between ISO and underlying SST. However, the eastward propagation cannot be reproduced in the uncoupled model. This suggests that air-sea interaction is important in generating intraseasonal variability over the SAM region. Nevertheless, some deficiencies remain in the coupled model, which may relate to physical processes depicted by the cumulus parameterization and PBL schemes within its atmospheric component.