地形重力波拖曳参数化方案在华南中尺度模式（GRAPES）中的应用试验

在华南中尺度模式GRAPES中发展KA95方案地形重力波拖曳参数化方案(GWDO),并对2012年的2月8—12日影响华南冷空气过程、8月23—24日发生在广东的局地性暴雨和5—8月共4个月的KA95方案预报试验进行检验。结果表明,KA95地形重力波拖曳参数化方案的引入,改善了GRAPES模式对冬、春季低层南风偏强和地面温度偏高的现象,一定程度上纠正了在模式积分过程中出现的南风偏差,改正了在业务预报中因南风偏强而导致温度偏差过大的现象;改善了模式对局地强降水强度和落区的预报,减小了大雨和暴雨的漏报率和预报偏差,提高了GRAPES模式对降水的预报效果。      

GRAPES中地形重力波拖曳物理过程的引进和应用试验

在中国新一代全球中期/区域中尺度同化与预报系统(GRAPES)模式中引进了ECMWF地形重力波拖曳物理过程,填补了GRAPES全球中期数值预报系统中物理过程的空白。重新计算了地形重力波过程需要的地形静态资料数据,并与原ECMWF模式的地形静态参数进行了对比分析,验证了模式地形参数的正确性。利用GRAPES模式,进行了地形重力波拖曳物理过程影响的敏感性数值试验;结果表明:引进地形重力波拖曳过程以后,在存在大地形的区域,风场会发生变化,当纬向风遇到青藏高原时,一部分气流会产生爬坡效应而越过高原,使高原上空的西风气流减弱;另一部分气流会绕过高原,在高原的南侧产生绕流;随着模式积分时间的延长,风场变化会越来越明显,地形越复杂,风场的变化也越复杂;连续的模式积分试验结果显示,引进地形重力波过程,可以延长GRAPES模式的可用预报时效,提高了全球形势预报的准确率。通过对一次降水过程的模拟,对地形重力波过程影响降水预报的原因进行了简单分析。结果显示:引进地形重力波拖曳过程后,改变了大气流场的分布,使预报的流场更接近于大气真实状态,从而提高了降水预报的准确率。     

一个双波地形重力波拖曳参数化方案

当地形次尺度强迫的作用与显式的经典动力作用效应相当时,地形重力波拖曳力对于环流的维持,以及动量和热量通量输送的动力效应变得十分显著。这种地形次尺度拖曳作用项可通过参数化的方法,在动力方程中加入额外的小项而引入数值模式。目前成熟的地形重力波拖曳参数化方法,如第1代基于线性单波理论的参数化方案;以及侧重考虑了临界层作用等因素对拖曳力的额外贡献的第2代参数化方案,都无法有效表达风速垂直变化引起的波动应力随高度变化的特征。基于上述考虑,本文给出了一个双波参数化方案用于计算地形重力波拖曳中由线性自由传播重力波造成的波动应力的垂直分布。通过二阶WKB近似,它对由风速垂直变化引起的对波动应力的选择性临界层吸收过程和经典的临界层吸收过程做了显式处理;而在不发生临界层吸收现象的地区,则用两个单波同时在垂直方向上进行应力的传播,并利用波饱和标准进行应力耗散。进一步地在真实地形(以大别山地区为个例)条件下的测试结果表明,通过在不同理想风速廓线以及北半球冬季中纬度纬向平均风廓线下对波动应力垂直分布的计算,证明该方案确实能有效地给出应力随高度变化的特征。     

包络地形和重力波拖曳对区域气候模拟效果的影响

用NCAR区域气候模式(RegCM2)的数值试验，研究了包络地形和地形重力波拖曳作用对1991年5、6月份中国区域内气候模拟效果的影响。通过试验结果的对比分析发现，在模式中引入地形重力波拖曳作用可在一定程度上改善模式对气候系统和要素的模拟效果，使模拟结果更符合气候实况。包络地形对模拟结果也有一定的改善，但对于细网格的区域气候模式(RCM)来说，其效果不如重力波拖曳明显。不论是地形重力波拖曳还是包络地形，在模式积分的初期，它们的作用并不明显，随着积分时间的增长，它们对模拟结果的影响程度增大。     

包络地形和重力波拖曳对气候模拟效果的影响

该文用Nju-PσM的数值试验, 研究了包络地形和地形重力波拖曳作用对7月气候模拟效果的影响.通过试验结果的对比分析, 发现包络地形和重力波拖曳作用都可在一定程度上改善模式的模拟性能, 使模拟结果更符合气候实况.     

一次大暴雨过程中地形重力波拖曳作用的研究

利用WRFV3.9数值模式,对2011年6月9-10日发生在湘鄂赣交界附近山区的一次江淮气旋大暴雨天气过程进行模拟.进行了地形重力波拖曳作用的控制试验和不考虑地形重力波拖曳作用的敏感性试验.结果表明,控制试验能较好地再现江淮气旋及其产生的强降水;模式引入地形重力波拖曳后能够更好地模拟出地形附近雨带的中心位置和强度;地形...     

青藏高原地形重力波拖曳的初步分析及数值模拟研究

针对目前对青藏高原大地形激发的重力波拖曳相关问题还不十分清楚,在GRAPES_Meso模式中引入次网格地形重力波拖曳参数化方案,通过数值试验初步研究了青藏高原地区次网格地形重力波拖曳的一些相关参数,结果指出:(1)沿30°N地形重力波拖曳的垂直分布显示,阻塞拖曳主要存在于模式的低层(第1—5层),重力波拖曳主要存在于模式的第5—10层;从水平分布看,模式第3层以阻塞拖曳为主,主要位于青藏高原边缘地区,阻塞拖曳大值区沿喜马拉雅山脉走向和青藏高原东坡;模式第5层以重力波拖曳为主,主要位于青藏高原东部地区和云贵高原的北部边缘。(2)弗劳德数和气流绕流高度分析表明,在青藏高原喜马拉雅山脉一带和高原东部边缘地区,气流爬坡能力强,同时在这一地区绕流高度最高;弗劳德数越大的地区绕流高度距离地表越高。(3)采用次网格地形重力波拖曳参数化方案后,对于低层和高层地形重力波破碎的发生有更准确的描述,地形重力波是向上垂直传播的。(4)个例和批量试验检验结果表明,采用次网格地形重力波拖曳参数化方案对于风场和降水模拟有正效果,提高了模式预报的准确率。     

地形重力波拖曳参数化方案在一次陕西极端性暴雨天气过程中的应用

利用中尺度WRF模式进行敏感性试验,分析探讨加入地形重力波拖曳参数化方案(GWDO)后对2013年陕西入夏以来最强的一次暴雨过程的模拟能力和地形影响下强降水的形成机制。本次过程是在高空槽和低涡配合的有利形势下形成的,秦巴山区的地形作用对本次暴雨过程有着重要影响。在引入地形重力波参数化方案后,模式对关中大暴雨中心的模拟能力有所提高,强降水落区及量级与实况更为接近,较为有效地改善了环流形势及主要影响系统的模拟。在引入地形重力波参数化方案后,这一地区环流进行调整,有利的水汽条件和对流不稳定配合强烈的上升运动,是影响关中地区强降水的重要因素。该参数化方案对陕西暴雨预报具有一定的适用性,但是对陕南的暴雨区模拟还具有较大的误差,需要进一步改进。     

青藏高原边坡地形重力波拖曳方案应用的个例研究

本文针对我国西南地区的一次持续性暴雨过程,利用WRF模式引入地形重力波拖曳方案进行120h的模拟,对比结果认为引入地形重力波拖曳的模拟效果总体看来略有优势,并详细分析了不同模拟时段的位势高度场,风场,海平面气压场与降水,其结果认为,引入与未引入地形重力波模拟的差异主要出现在48~72h之后,位势高度场方面,72h之后,在青藏高原主体上引入拖曳方案后的模拟结果相对未引入拖曳方案的结果是正偏差,高原下游地区为负偏差,引入后的模拟相对准确;风场模拟方面同样72h以内的模拟差距较小,72h之后高原上出现一处气旋性涡旋,其中心位置的模拟,引入拖曳方案后的结果相对准确,本次个例中出现的一例西南低涡,两实验都能够较好的模拟出700h Pa的气旋性涡旋;降水模拟的结果表明,在72h之后,对于四川地区降水中心位置的模拟,引入拖曳方案的模拟有所提高,但中心依然过强。这方面主要考虑降水的模拟牵涉模式内部更为复杂的处理过程和其他因素,地形重力波拖曳只是其中一个影响因素而不是核心因素。另外此方案对温度场及海平面气压场模拟的影响不明显。理论上讲引入地形重力波拖曳效应的模拟是物理过程相对更为完善的,在本次个例中模拟效果也略优,但在高原下坡复杂地形处长期应用的模拟效果仍需要更多的测试,将在后续工作中加以完善。     

克拉玛依大风数值预报中的重力波拖曳方案应用研究

新疆克拉玛依地区位于背风坡,长期受翻山气流形成的局地大风影响。该地区日常大风预报业务主要依托克拉玛依气象局的精细化数值预报系统,为进一步完善该系统的预报效果,本文开展了重力波拖曳参数化方案应用试验,对比分析了三组试验方案:不开启重力波拖曳、只开启外层区域重力波拖曳以及两重嵌套设置下均开启重力波拖曳的结果。试验结果表明:在克拉玛依大风预报个例中,对于山区地形背风坡处的克拉玛依站,不启动重力波拖曳会导致风速偏大和起风时间较早;开启外层重力波拖曳方案可以延迟克拉玛依站起风时间,两重区域均开启可以进一步延迟该站的起风时间,使起风时间更接近实况;对于非山区地形背风坡处的站点,在内层开启重力波拖曳会导致一定的负效果;对内层区域的统计检验结果表明不开启重力波拖曳,会使地形复杂区域风场预报存在一定的正偏差,在外层开启重力波拖曳会使正偏差有一定改善,而两重嵌套均开启重力波拖曳方案会导致非地形陡峭区域的负偏差增加。综合全区域内大风预报检验结果表明,只在外层开启重力波拖曳会获得最小的误差和较好的预报效果。     

A Two-Wave Scheme for Orographic Gravity Wave Drag Parameterization

When the magnitude of sub-scale ographic forcing is comparable with explicitly ordinary dynamic forcing, the drag effect reduced by ographic gravity wave is to be significant for maintaining dynamic balance of atmospheric circulation, as well as the momentum and energy transport. Such sub-scale ographic forcing should be introduced into numerically atmospheric model by means of drag being parameterized. Furthermore, the currently mature ographic gravity wave drag （OGWD） parameterization, i.e., the so-called first-generation （based on lineal single-wave theoretical framework） or the second-generation drag parameterization （including an important extra forcing by the contribution of critical level absorption）, cannot correctly and effectly describe the vertical profile of wave stress under the influence of ambient wind shearing. Based on aforementioned consideration, a new two-wave scheme was proposed to parameterize the ographic gravity wave drag by means of freely propagating gravity waves. It starts with a second order WKB approximation, and treats the wave stress attenuations caused by either the selective critical level absorption or the classical critical level absorption explicitly; while in the regions where critical levels are absent, it transports the wave stress vertically by two sinusoidal waves and deposits them and then damps them according to the wave saturation criteria. This scheme is thus used to conduct some sample computations over the Dabie Mountain region of East China, as an example. The results showed that the new two-wave scheme is able to model the vertical distribution of the wave stress more realistically.     

Improved Wind and Precipitation Forecasts over South China Using a Modified Orographic Drag Parameterization Scheme

To improve the wind and precipitation forecasts over South China, a modified orographic drag parameterization(OP) scheme that considers both the gravity wave drag(GWD) and the mountain blocking drag(MBD) effects was implemented in the Global/Regional Assimilation and Prediction System Tropical Mesoscale Model(GRAPES-TMM). Simulations were performed over one month starting from 1200 UTC19 June 2013. The initial and lateral boundary conditions were obtained from the NCEP global forecast system output. The simulation results were compared among a control(CTL) experiment without the OP scheme, a GWDO experiment with the OP scheme that considers only the GWD effect, and an MBD experiment with the modified OP scheme(including both GWD and MBD). The simulation with the modified OP scheme successfully captured the main features of precipitation, including its distribution and intensity,and improved the wind circulation forecast in the lower troposphere. The modified OP scheme appears to improve the wind forecast by accelerating the ascending air motion and reinforcing the convergence in the rainfall area. Overall, the modified OP scheme exerts positive impacts on the forecast of large-scale atmospheric fields in South China.     

GRAPES全球三维变分同化系统--基本设计方案与理想试验

中国气象局数值预报研究中心开发了一个全球和区域统一框架的格点三维变分资料同化系统(GRAPES3D-Var).作者给出全球版本的方案设计,采用单点观测试验检验方案设计的合理性和正确性.全球方案选择流函数、速度势、非平衡高度和相对湿度作为分析求解的控制变量,用线性平衡方程作为质量场和风场的动力约束,通过预调方法解决背景误差协方差矩阵阶数过大和难以求逆的问题,其中垂直变换和物理变换以及观测算子设计等方面与区域方案相同,但预调的水平变换采用球谐函数谱滤波表示背景误差协方差的水平相关模型,避免了递归滤波在高纬和极区因相关尺度过大无法实施的问题.另外,设计了一个使极区插值和差分计算完全闭合的网格以及相应的算法,解决了极点分析问题.单点观测理想试验结果表明,GRAPES 3D-Var系统能够合理给出全球任何地区的分析.     

Effects of Different Initial Fields on GRAPES Numerical Prediction

In this paper,a heavy rainfall process occurring in the Huaihe River Basin during 9-10 July 2005 is studied by the new generation numerical weather prediction model system-GRAPES,from the view of different initial field effects on the prediction of the model.Several numerical experiments are conducted with the initial conditions and lateral boundary fields provided by T213 L31 and NCEP final analyses,respectively. The sensitivity of prediction products generated by GRAPES to different initial conditions,including effects of three-dimensional variational assimilation on the results,is discussed.After analyzing the differences between the two initial fields and the four simulated results,the memonic ability of the model to initial fields and their influences on precipitation forecast are investigated.Analyses show the obvious differences of sub-synoptic scale between T213 and NCEP initial fields,which result in the corresponding different simulation results,and the differences do not disappear with the integration running.It also shows that for the same initial field whether it has data assimilation or not,it only obviously influences the GRAPES model results in the initial 24 h.Then the differences reduce.In addition,both the Iocation and intensity of heavy rain forecasted by GRAPES model Further is very close to the fact,but the forecasting area of strong torrential rain has some differences from the fact.For the same initial field when it has assimilation, the 9-12-,12-24-,and 0-24-h precipitation forecasts of the model are better than those without assimilation. All these suggest that the ability of GRAPES numerical prediction depends on the different initial fields and lateral boundary conditions to some extent,and the differences of initial fields will determine the differences of GRAPES simulated results.     

对流天气系统自动站雨量资料同化对降雨预报的影响

利用GRAPES(Global and Regional Assimilation and Prediction Enhanced System,全球/区域同化预报系统)三维变分同化系统,针对对流天气系统特点,用改进的郭晓岚对流参数化方案作为观测算子,同化广东省自动站记录的对流天气系统的雨量资料,并且与同化探空资料进行了比较.在雨带有明显改进的区域,分别同化这两种资料都可以调整大气低层水汽辐合增加(或辐散),对流层中下层增暖增湿(或变冷变干),从而增加(或减少)降水,表明降水的同化方案对初始场的调整在一定     

Possible sources of forecast errors generated by the global/regional assimilation and prediction system for landfalling tropical cyclones. Part I: Initial uncertainties

This paper investigates the possible sources of errors associated with tropical cyclone (TC) tracks forecasted using the Global/Regional Assimilation and Prediction System (GRAPES). The GRAPES forecasts were made for 16 landfalling TCs in the western North Pacific basin during the 2008 and 2009 seasons, with a forecast length of 72 hours, and using the default initial conditions (“initials”, hereafter), which are from the NCEP-FNL dataset, as well as ECMWF initials. The forecasts are compared with ECMWF forecasts. The results show that in most TCs, the GRAPES forecasts are improved when using the ECMWF initials compared with the default initials. Compared with the ECMWF initials, the default initials produce lower intensity TCs and a lower intensity subtropical high, but a higher intensity South Asia high and monsoon trough, as well as a higher temperature but lower specific humidity at the TC center. Replacement of the geopotential height and wind fields with the ECMWF initials in and around the TC center at the initial time was found to be the most efficient way to improve the forecasts. In addition, TCs that showed the greatest improvement in forecast accuracy usually had the largest initial uncertainties in TC intensity and were usually in the intensifying phase. The results demonstrate the importance of the initial intensity for TC track forecasts made using GRAPES, and indicate the model is better in describing the intensifying phase than the decaying phase of TCs. Finally, the limit of the improvement indicates that the model error associated with GRAPES forecasts may be the main cause of poor forecasts of landfalling TCs. Thus, further examinations of the model errors are required.     

The Impacts of Climate Change on the Autumn North Atlantic Wave Climate

Abstract

In this study, we investigate the impact of global warming induced by possible climate change on the autumn winds, the related storm climate, and the wave climate over the North Atlantic Ocean. These analyses are based on a third-generation wave model, WAVEWATCHIII? and dynamically downscaled winds, obtained from the Canadian Regional Climate Model driven by the third version of the Coupled Global Climate Model (T47) from the Canadian Centre for Climate Modelling and Analysis following the A1B climate change scenario of the Special Report on Emission Scenarios from the Intergovernmental Panel on Climate Change. Compared with the present wave climate, represented as 1970–1999, the significant wave heights in the northeast North Atlantic will increase, whereas in other areas, such as the mid-latitudes, they will decrease, with associated changes in winds in the future climate (2040–2069). An analysis of inverse wave ages is used to suggest that wind-driven wave regimes tend to occur more frequently in the northeast North Atlantic and decrease in the mid-latitudes in the climate change scenario. The dominant North Atlantic storm-track region is estimated to shift northward, especially over the northern Northeast Atlantic, where the frequency of occurrence of the most intense cyclones is estimated to increase. We suggest that changes in storm densities are related to changes in the upper level steering flow in the atmosphere, which are the precursor to changes in the winds and ocean waves.     

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。     

基于PR和VIRS融合资料的东亚台风和非台风降水结构分析

借助JAXA/EORC热带台风数据集资料,实现了台风区和非台风区的分离,在此基础上,利用热带测雨卫星搭载的测雨雷达和可见光/红外扫描仪的融合观测资料,对1998~2007年东亚雨季台风及非台风降水的气候特征和降水云红外信号特征进行了分析。结果表明:1)东亚台风降水强度谱较非台风降水谱更宽,特别是对流降水主要分布在5~20 mm/h之间;强降水更多,主要分布在东亚洋面。2)雨季东亚降水的主要形式是非台风层云降水,但台风降水对局地降水量的贡献也不容忽视,例如台湾以东附近洋面可达20%。3)台风降水云亮温海陆分布差异显著;其雨顶高度在4~9 km(层云)和4.5~12.5 km(对流)之间均有分布,较非台风降水雨顶高度谱更宽。4)不同等级的台风在降水强度、覆盖区域和云顶10.8μm亮温分布上差异大。