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1.
Simulation of China Summer Precipitation Using a Regional Air-Sea Coupled Model 总被引：1，自引：0，他引：1 
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下载免费PDF全文 A regional air-sea coupled model based on the regional climate model(RegCM3)and the regional oceanic model POM(Princeton Ocean Model)is developed and a series of experiments are performed to verify the ability of the coupled model in simulating the summer precipitation over China from 1963 to 2002.The results show that the space correlation coefficients between the GISST(Global Ice and Sea Surface Temperature)data and the simulated SST by RegCM3-POM exceed 0.9.Compared with the uncoupled experiments,the coupled model RegCM3-POM has a better performance in simulating the mean summer(June to August)precipitation over China,and the distribution of the rainband in the coupled model is more accurate.The improvement of the rainfall simulation is significant over the Yangtze River Valley and in South China.The rainbelt intraseasoaal evolution over eastern China in summer indicates that the simulation ability of RegCM3-POM is improved in comparison with the uncoupled model.The interannual summer rainfall variation over eastern China simulated by RegCM3-POM is in accordance with observation,while the spatial pattern of the interannual summer rainfall variation in the uncoupled model is inaccurate.The simulated correlation coefficient between the summer rainfall in the uncoupled model RegCM3 and observation is0.30 over the Yangtze River Valley and 0.29 in South China.The coefficient between the rainfall in the coupled RegCM3-POM and observation is 0.48 over the Yangtze River Valley and 0.61 in South China.The RegCM3-POM has successfully simulated the correlation coefficients between summer rainfall in the Yangtze River Valley and SST anomalies of the Bay of Bengal,South China Sea,and the Kuroshio area,whereas the uncoupled model RegCM3 fails to reproduce this relationship.The study further shows that the monsoon circulation and the path of the moisture transport flux simulated by RegCM3-POM are in good agreement with the NCEP/NCAR data. 相似文献
2.
区域海气耦合模式对中国夏季降水的模拟 总被引：8，自引：0，他引：8
以区域气候模式RegCM3和普林斯顿海洋模式POM为基础,建立了一个区域海气耦合模式,对1963-2002年中国夏季气候进行模拟,重点分析该耦合模式对中国夏季降水的模拟性能以及降水模拟改进的可能原因.结果表明:耦合模式对中国夏季雨带分布的模拟明显优于控制试验(单独的大气模式),对长江流域以及华南降水的模拟性能改进尤为明显,同时耦合模式能够更为真实地刻画中国东部地区汛期雨带的移动.对降水的年际变化分析发现,耦合模式模拟的1963-2002年中国夏季降水年际变率与观测吻合,模拟的夏季长江流域降水与观测降水相关系数达到0.48,模拟的华南夏季降水与观测的相关系数达到0.61,而控制试验结果与观测降水的相关系数均较小.对中国东部长江流域夏季降水与近海海温的相关分析表明,用给定海温驱动的大气模式,并不能正确模拟出中国东部夏季降水与海温的关系,而耦合模式能够较好地模拟出长江流域与孟加拉湾、南海以及黑潮区海温的关系,与GISST(全球海冰和海表温度)和观测降水相关关系一致.对水汽输送通量的分析发现,控制试验模拟的水汽输送路径与NCEP/NCAR再分析资料相比差别较大,耦合模式模拟的来自海洋上的水汽输送强度和路径与NCEP/NCAR再分析资料一致,提高了耦合模式对水汽输送的模拟能力,从而改善了模式对华南以及长江流域降水的模拟. 相似文献
3.
应用广西壮族自治区国家气象站降水,NCEP/NCAR逐日再分析资料,NOAA逐日向外长波辐射(OLR)等逐日资料,NOAA-CPC热带大气季节内振荡(MJO)指数等,使用经验正交函数分解方法分析了广西冬季降水的气候特征;用功率谱、带通滤波、相关分析和滞后线性回归等方法,以及定义MJO相关降水事件,研究了广西冬季降水异常偏多年的降水低频特征及其与MJO的联系。(1)广西冬季降水特征以全区一致型分布为主;冬季降水异常偏多年份的逐日降水具有14~26 d的低频周期。(2) MJO强对流在赤道印度洋东部发展并东传到西太平洋热带地区时,广西可出现冬季持续强降水。(3)当MJO异常对流在印度洋东部热带地区产生,中南半岛地区到华南地区上空为异常低频偏南和偏西南气流,有利于降水形成;当印度洋东部热带地区为MJO对流抑制区,华南地区上空为异常低频偏东气流控制,不利于降水产生。(4)华南地区上空大气环流的异常是由热带印度洋地区的MJO对流激发的Rossby波列造成。 相似文献
4.
The performance of a regional air-sea coupled model, comprising the Regional Integrated Environment Model System (RIEMS) and the Princeton Ocean Model (POM), in simulating the seasonal and intraseasonal variations of East Asian summer monsoon (EASM) rainfall was investigated. Through comparisons of the model results among the coupled model, the uncoupled RIEMS, and observations, the impact of air-sea coupling on simulating the EASM was also evaluated. Results showed that the regional air-sea coupled climate model performed better in simulating the spatial pattern of the precipitation climatology and produced more realistic variations of the EASM rainfall in terms of its amplitude and principal EOF modes. The coupled model also showed greater skill than the uncoupled RIEMS in reproducing the principal features of climatological intraseasonal oscillation (CISO) of EASM rainfall, including its dominant period, intensity, and northward propagation. Further analysis indicated that the improvements in the simulation of the EASM rainfall climatology and its seasonal variation in the coupled model were due to better simulation of the western North Pacific Subtropical High, while the improvements of CISO simulation were owing to the realistic phase relationship between the intraseasonal convection and the underlying SST resulting from the air-sea coupling. 相似文献
5.
采用一种基于降水异常追踪MJO（Madden–Julian Oscillation）东传的MJO识别方法（MJO Tracking）评估了参与MJOTF/GASS（MJO Task Force/Global Energy and Water Cycle Experiment Atmospheric System Study）全球模式比较计划的全海气耦合模式（CNRM-CM）、半海气耦合模式（CNRM-ACM）和大气模式（CNRM-AM）1991～2010年模拟MJO的能力,探究了海气耦合过程对模式模拟MJO能力的影响机理。CNRM-CM模式模拟的MJO结构更加接近观测,该模式不仅具有最高的MJO生成频率,也能够模拟较强的MJO强度以及较远的传播距离。海气耦合过程会造成CNRM-CM和CNRM-ACM模式中印度洋—太平洋暖池区域海温气候态的冷偏差。但是这种海温气候态的偏差基本没有改变模式模拟MJO的能力。CNRM-CM中MJO对流中心东（西）侧存在较强的季节内尺度海温暖（冷）异常,纬向梯度明显,而CNRM-ACM和CNRM-AM中不存在这样的海温东西不对称结构。结果表明在CNRM模式中海气耦合过程调控模式海温季节内尺度变率对模式MJO模拟能力的影响比调控模式海温气候态更加重要。 相似文献
6.
Kenneth R. Sperber Silvio Gualdi Stephanie Legutke Veronika Gayler 《Climate Dynamics》2005,25(2-3):117-140
The Madden-Julian oscillation (MJO) dominates tropical variability on timescales of 30–70 days. During the boreal winter/spring,
it is manifested as an eastward propagating disturbance, with a strong convective signature over the eastern hemisphere. The
space–time structure of the MJO is analyzed using simulations with the ECHAM4 atmospheric general circulation model run with
observed monthly mean sea-surface temperatures (SSTs), and coupled to three different ocean models. The coherence of the eastward
propagation of MJO convection is sensitive to the ocean model to which ECHAM4 is coupled. For ECHAM4/OPYC and ECHO-G, models
for which ~100 years of daily data is available, Monte Carlo sampling indicates that their metrics of eastward propagation
are different at the 1% significance level. The flux-adjusted coupled simulations, ECHAM4/OPYC and ECHO-G, maintain a more
realistic mean-state, and have a more realistic MJO simulation than the nonadjusted scale interaction experiment (SINTEX)
coupled runs. The SINTEX model exhibits a cold bias in Indian Ocean and tropical West Pacific Ocean sea-surface temperature
of ~0.5°C. This cold bias affects the distribution of time-mean convection over the tropical eastern hemisphere. Furthermore,
the eastward propagation of MJO convection in this model is not as coherent as in the two models that used flux adjustment
or when compared to an integration of ECHAM4 with prescribed observed SST. This result suggests that simulating a realistic
basic state is at least as important as air–sea interaction for organizing the MJO. While all of the coupled models simulate
the warm (cold) SST anomalies that precede (succeed) the MJO convection, the interaction of the components of the net surface
heat flux that lead to these anomalies are different over the Indian Ocean. The ECHAM4/OPYC model in which the atmospheric
model is run at a horizontal resolution of T42, has eastward propagating zonal wind anomalies and latent heat flux anomalies.
However, the integrations with ECHO-G and SINTEX, which used T30 atmospheres, produce westward propagation of the latent heat
flux anomalies, contrary to reanalysis. It is suggested that the differing ability of the models to represent the near-surface
westerlies over the Indian Ocean is related to the different horizontal resolutions of the atmospheric model employed. 相似文献
7.
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
8.
Summary The Regional Climate Model RegCM3 has been used to examine its suitability in simulating the Indian summer monsoon circulation
features and associated rainfall. The model is integrated at 55 km horizontal resolution over a South Asia domain for the
period April–September of the years 1993 to 1996. The characteristics of wind at 850 hPa and 200 hPa, temperature at 500 hPa,
surface pressure and rainfall simulated by the model over the Indian region are examined for two convective schemes (a Kuo-type
and a mass flux scheme). The monsoon circulation features simulated by RegCM3 are compared with those of the NCEP/NCAR reanalysis
and the simulated rainfall is validated against observations from the Global Precipitation Climatology Centre (GPCC) and the
India Meteorological Department (IMD). Validation of the wind and temperature fields shows that the use of the Grell convection
scheme yields results close to the NCEP/NCAR reanalysis. Similarly, the Indian Summer Monsoon Rainfall (ISMR) simulated by
the model with the Grell convection scheme is close to the corresponding observed values. In order to test the model response
to land surface changes such as the Tibetan snow depth, a sensitivity study has also been conducted. For such sensitivity
experiment, NIMBUS-7 SMMR snow depth data in spring are used as initial conditions in the RegCM3. Preliminary results indicate
that RegCM3 is very much sensitive to Tibetan snow. The model simulated Indian summer monsoon circulation becomes weaker and
the associated rainfall is reduced by about 30% with the introduction of 10 cm of snow over the Tibetan region in the month
of April. 相似文献
9.
Using the regional air-sea coupled climate model RegCM3-POM,a series of numerical experiments are performed to simulate the summer climate in 1997 and 1998 with different coupling time steps.The results show that the coupled model has good performance on the simulation of the summer sea surface temperature(SST) in 1997 and 1998,and the simulation results of CPL1(with the coupling time step at 1 hour) are similar to those of CPL6(with the coupling time step at 6 hours).The coupled model can well simulate SST differences between 1997 and 1998.As for the simulation of the drought in 1997 and the flood in 1998,the results of CPL6 are more accurate.The coupled model can well simulate the drought in 1997 over North China,and compared with the results of the atmosphere model RegCM3,the simulation ability of the coupled model is improved.The coupling model has better ability in the simulation of the circulation in the middle and low levels,and the water vapor transportation in the coupling model is reasonable in both 1997 and 1998.RegCM3(an uncoupled model) cannot correctly simulate the transportation path differences between 1997 and 1998,but the coupled model can simulate the differences well. 相似文献
10.
The influence of ocean–atmosphere coupling on the simulation and prediction of the boreal winter Madden–Julian Oscillation
(MJO) is examined using the Seoul National University coupled general circulation model (CGCM) and atmospheric—only model
(AGCM). The AGCM is forced with daily SSTs interpolated from pentad mean CGCM SSTs. Forecast skill is examined using serial
extended simulations spanning 26 different winter seasons with 30-day forecasts commencing every 5 days providing a total
of 598 30-day simulations. By comparing both sets of experiments, which share the same atmospheric components, the influence
of coupled ocean–atmosphere processes on the simulation and prediction of MJO can be studied. The mean MJO intensity possesses
more realistic amplitude in the CGCM than in AGCM. In general, the ocean–atmosphere coupling acts to improve the simulation
of the spatio-temporal evolution of the eastward propagating MJO and the phase relationship between convection (OLR) and SST
over the equatorial Indian Ocean and the western Pacific. Both the CGCM and observations exhibit a near-quadrature relationship
between OLR and SST, with the former lagging by about two pentads. However, the AGCM shows a less realistic phase relationship.
As the initial conditions are the same in both models, the additional forcing by SST anomalies in the CGCM extends the prediction
skill beyond that of the AGCM. To test the applicability of the CGCM to real-time prediction, we compute the Real-time Multivariate
MJO (RMM) index and compared it with the index computed from observations. RMM1 (RMM2) falls away rapidly to 0.5 after 17–18
(15–16) days in the AGCM and 18–19 (16–17) days in the CGCM. The prediction skill is phase dependent in both the CGCM and
AGCM. 相似文献
11.
为检验区域气候模式与沙尘模式耦合模式RegCM Dust的性能,以2006年东亚地区一次沙尘暴过程为例,将模拟结果与观测资料进行对比,以检验模式对沙尘天气过程的模拟能力。结果表明：模式对沙尘暴过程的地面风场特征模拟效果较好,总体上重现了大风区的分布;地面沙尘浓度和沙尘光学厚度模拟结果与观测分布总体吻合。模式虽然是区域气候模式与沙尘模式耦合模式,但由于其内核是建立在中尺度数值模式MM4基础上,因此对天气过程尤其是沙尘天气过程具备较好的把握能力,对于沙尘天气过程预测具有良好的应用前景。 相似文献
12.
区域海气耦合模式模拟的2003年东亚夏季风季节内振荡 总被引：1，自引：0，他引：1
评估了一个区域海气耦合模式(由区域环境系统集成模式RIEMS和普林斯顿海洋模式POM组成)对2003年东亚夏季风季节内振荡(ISO)的模拟性能。通过与观测海温驱动单独大气模式结果的比较,分析了海气耦合过程对东亚夏季大气ISO模拟性能的影响。结果表明:耦合模式能够模拟出2003年中国东部地区夏季降水的气候态分布,模拟的中国东部尤其是江淮地区大气ISO活动较单独大气模式更为显著。同时,耦合模式能够较好地再现大气ISO经向上北传的传播特征,模拟的江淮流域降水处于活跃和中断期时西北太平洋地区低频降水和环流异常在强度和空间分布上较单独大气模式都更为合理。相比于单独大气模式,耦合模式对大气ISO模拟的改善,一方面与其对气候态西北太平洋副热带高压和相关对流层底层风场模拟的改善有关,另一方面与其包含海气相互作用,因而对低频降水与海温和水汽辐合位相关系模拟的改善有关。 相似文献
13.
积云参数化方案对夏季东亚季风区海气系统位相关系模拟的影响 总被引：1，自引：0，他引：1
本文利用区域海气耦合模式RegCM-POM,分别选取Grell积云参数化方案和Emanuel积云参数化方案对北半球夏季(5—10月)的东亚气候进行模拟,研究不同积云对流参数化方案(CPS)对东亚夏季季风区海气系统位相关系模拟的影响。结果表明:不同CPS模拟的陆地降水具有一定的不确定性,而海洋降水和海温的模拟受CPS选择的影响更大。其中,Emanuel方案对海洋降水和海温的分布形势模拟总体上要好于Grell方案,且可以更好的模拟中国近海各海区的海气系统位相关系,特别是大气对海温的负反馈过程。原因在于Emanuel方案模拟的对流降水与海温的位相关系更接近观测总降水与海温的位相关系;而Grell方案对南海和孟加拉湾的对流降水模拟偏少,对黑潮对流降水的模拟偏多,错误地模拟了这几个海区积云对流过程发挥的作用,故其模拟的海气系统位相关系不如Emanuel方案。 相似文献
14.
The Madden–Julian oscillation (MJO) produced by a mesoscale model is investigated using standardized statistical diagnostics. Results show that upper- and lower-level zonal winds display the correct MJO structure, phase speed (8 m s?1) and space–time power spectrum. However, the simulated free atmosphere moisture, outgoing longwave radiation and precipitation do not exhibit any clear MJO signal. Yet, the boundary layer moisture, moist static energy and atmospheric instability, measured using a moist static energy instability index, have clear MJO signals. A significant finding is the ability of the model to simulate a realistic MJO phase speed in the winds without reproducing the MJO wind-convection coupling or a realistic propagation in the free atmosphere water vapor. This study suggests that the convergence of boundary layer moisture and the discharge and recharge of the moist static energy and atmospheric instability may be responsible for controlling the speed of propagation of the MJO circulation. 相似文献
15.
将区域海气耦合模式RegCM3-POM和区域气候模式RegCM3 40年(1963-2002年)的模拟结果与NCEP/NCAR再分析资料进行对比,检验区域海气耦合模式对中国华北地区夏季大气水汽含量和水汽输送特征的模拟能力,比较耦合模式与单独区域气候模式的差异.结果表明,区域海气耦合模式RegCM3-POM的模拟性能相对于单独区域气候模式RegCM3,大气水汽输送特征的模拟能力有了较大的改进.分析显示两种模式都能够较好地再现东哑地区气候平均夏季大气水汽储量浅红和水汽输送的空间分布特征,而耦合模式对大气水汽输送的模拟更为合理.在对流层中低层更接近观测;耦合模式对中国华北地区夏季平均大气水汽输送通量在垂直方向卜的分布型及水平4个边界水汽输送收支的模拟,相对于单独大气模式有了一定的改进;耦合模式对伴随华北地区夏季早涝的大气水汽异常输送也具有较好的模拟能力,其模拟的水汽输送异常的来源与观测基本一致,尤其是在20°N以北地区,耦合模式结果相对于单独区域气候模式有了很大的改进.但同时耦合模式在低纬度海洋上对气候平均夏季大气水汽含量模拟的偏差比区域气候模式显著;与观测相比,耦合模式对来自孟加拉湾地区的大气水汽输送模拟偏弱,而对西太平洋副热带高压西侧水汽输送模拟偏强,与华北夏季旱涝相联系的水汽输送异常的模拟在低纬度海洋上也存在明显偏差. 相似文献
16.
In this research the dynamic downscaling method by Regional Climate Model (RegCM4.5) was used to assess the performance and sensitivity of seasonal simulated North and West of Iran (NI&WI) climate factors to different convection schemes, and transforms the large-scale simulated climate variables into land surface states over the North of Iran (NI) and West of Iran (WI). A 30-year (1986–2015) numerical integration simulation of climate over NI&WI was conducted using the regional climate model RegCM4.5 nested in one-way ERA-Interim reanalysis data. The Grell, Kuo and MIT-Emanuel cumulus convection with Holtslag and University of Washington (UW) planetary boundary layer (PBL) parameterization schemes were applied in the running of RegCM4.5 to test their capability in simulating precipitation and temperature in winter-spring (January–April) over NI and WI. The results demonstrated that the RegCM4.5 model has a good potential for simulating the variables and trend of surface temperature over the NI and WI region. Magnitude of the model bias for land surface temperature over different regions of Iran varies by convection parameterization schemes. In most cases, the root mean square error between post-processed simulated seasonal average temperature and observation value was less than 1 °C, but there is a systematic “cold bias”. In general, with respect to land surface temperature simulations, a better performance is obtained when using post-processing model’s data with Holtslag PBL-Grell and Holtslag PBL-Kuo configuration schemes, compared to the other simulations, over the NI&WI region. Also, the UW PBL convection schemes show a relatively excellent spatial correlations and normalized standard deviations closer to 1 for thirty-year seasonal land surface temperature anomalies over the entire NI&WI region. However, the simulation accuracy of model for precipitation is not as optimal as for temperature. The dominant feature in model simulations is a dry bias with the largest average value (∼1.04 mm/day) over NI region, while the lowest mean bias precipitation (∼−0.47 mm/day), mainly located in WI region. In the comparison of six configuration convection schemes, the Emanuel scheme has been proven to be the most accurate for simulating winter-spring seasonal mean precipitation over NI&WI region. The accuracy of the scheme also showed great difference in simulated station interpolation of precipitation, which urges the improvement for the simulation capability of spatial distribution of precipitation. In general, for seasonal variation of precipitation, the Emanuel convection with two (Holtslag, UW) PBL configuration schemes outperforms with a good correlation score between 0.7−0.8 and normalized standard deviations closer to 1. 相似文献
17.
利用热带大气季节内振荡(MJO)指数、向外长波辐射(OLR)资料和NCEP/NCAR全球逐日再分析资料以及中国南方地区降水资料,应用合成分析等探讨了MJO与2008年初南方雪灾的关系,进而从MJO角度研究雪灾过程成因。结果表明：雪灾过程中,MJO存在明显的东传现象,即由西太平洋向东传送至印度洋附近。伴随着MJO的向东传播,中国南方降水强度及集中区也在随之变化,MJO在一定程度上对雪灾过程有调制作用。通过对OLR的分析,表明2008年初中国南方4次异常降水(雪)过程受到了MJO两次东传的影响,第一次导致西太平洋副热带高压持续偏强,第二次导致南支槽活跃;副热带高压西侧偏南风带来的暖湿气流,以及南支槽带来的印度洋和孟加拉湾的暖湿气流不断向中国输送,为中国南方强降水过程提供了水汽条件。 相似文献
18.
BCC大气环流模式对亚澳季风年际变率主导模态的模拟 总被引：8，自引：3，他引：5
利用观测海温驱动下的北京气候中心大气环流模式(BCC-AGCM)1979-2000年的模拟数据,从亚澳季风(A-AM)年际变率的角度,对该模式的性能进行了分析.通过季节依赖的EOF分析方法(SEOF)得到观测第1模态,与ENSO从暖位相向冷位相的转变相联系,并伴随东南印度洋和西北太平洋的降水异常随季节变化.该模态具有准2a和4-6a周期的谱峰.分析结果显示,BCC模式可以很好地模拟出第1模态的时间变化特征,及其与ENSO位相的同步关系.但是,模式模拟的降水空间型与观测存在偏差,这主要是由于模式对环流场模拟的偏差造成的,具体表现在西北太平洋(WNP)反气旋和南印度洋(SIO)反气旋的季节锁相模拟偏差.前者与模式模拟的环流场整体偏东有关,后者是由于SIO反气旋的发展和衰亡过程受印度洋局地海气相瓦作用影响,而单独大气模式则无法合理地反映这一过程.另外,模式模拟的第一模态降水空间型在夏季效果较差,原因在于模式模拟的夏季平均降水量存在偏差,尤其是东南印度洋的降水量模拟偏少.进一步分析表明,这可能与对流参数化方案的选择有关. 相似文献
19.
Jian Ling Chongyin Li Wen Zhou Xiaolong Jia 《Theoretical and Applied Climatology》2014,115(1-2):231-241
Mechanisms for convective initiation of the Madden–Julian oscillation (MJO) remain poorly understood. During recent years, <50 % of large-scale convectively active episodes over the tropical Indian Ocean have led to MJO initiation. This study explores the structure and evolution of precipitation, diabatic heating, and potential vorticity (PV) that might be used to tell whether an MJO event will be initiated once such a convection episode occurs. Three different cases are studied. As convection becomes active in a large area over the tropical Indian Ocean, early signs favorable for MJO initiation are apparent: a persistent basin-scale coverage in the zonal direction by positive anomalies in precipitation and diabatic heating (in a swallowtail pattern), a persistent vertical dipole of PV generation with cyclonic (anticyclonic) PV generation in the lower (upper) troposphere covering a zonally extended area, and a cyclonic PV anomaly in the midtroposphere with a cyclonic PV pair straddling the equator immediately west of the diabatic heating center. All these signs are robust in the MJO composite but rarely occur all together in a given MJO case. The likelihood of an MJO event following a convective episode over the tropical Indian Ocean depends on how many of these signs occur and how persistent they are. While a preexisting MJO signal is neither a necessary nor a sufficient sign for MJO initiation, an active convective episode over the tropical Indian Ocean is necessary but insufficient for MJO initiation. MJO initiation depends on detailed convective behaviors over the tropical Indian Ocean. 相似文献
20.
通过对贵州省主汛期季节内振荡(Intra-Seasonal Oscillation,ISO)活跃年进行低频对流场和降水的合成分析,确定了影响贵州主汛期ISO和降水的热带印度洋(Indian Ocean,IO)低频对流关键区和南海(South China Sea,SCS)低频对流关键区,并利用MJO活动轨迹对贵州区域强降水过程开展了延伸期预报试验。将贵州省主汛期ISO位相划分为发展、峰值、减弱、抑制、谷值和恢复6个位相,发现贵州主汛期ISO活跃年的降水与本地区低频对流具有较好的对应关系,即在峰值位相时低频对流最强、降水正异常强度最强;在谷值位相时低频对流最弱、降水负异常强度最强。同时,热带和副热带低频对流场在贵州主汛期ISO波动的第1、4位相、第2、5位相及第3、6位相均呈反位相特征。在热带印度洋低频对流发展、并东传的过程中,有两条传播路径分别激发了孟加拉湾西南季风ISO活跃和南海热带季风ISO活跃共同影响贵州主汛期降水;在贵州主汛期有3个低频对流活跃期,IO关键区和SCS关键区ISO都有3次提前的低频对流加强。基于上述研究,分析MJO活动轨迹对贵州主汛期区域强降水过程的影响,发现热带印度洋MJO活动中心强度在贵州区域强降水过程发生前15 d~前3 d具有较好的持续性预报信号,提前9 d时正相关性最好。与延伸期预报业务规定的预报时段(未来11~30 d)相结合,通过确定贵州典型区域强降水过程发生前(提前量为10 d)至过程结束时段的MJO活动轨迹在历年中的最相似时段,发现MJO活动中心轨迹和强度对贵州区域强降水过程的趋势预报具有较好的指示意义。 相似文献