MM5 Simulations of the China Regional Climate During the LGM.Ⅱ: Influence of Change of Land Area, Vegetation, and Large-scale Circulation Background

Using a regional climate model MM5 nested to an atmospheric global climate model CCM3, a series of simulations and sensitivity experiments have been performed to investigate the relative LGM climate response to changes of land-sea distribution, vegetation, and large-scale circulation background over China.Model results show that compared with the present climate, the fluctuations of sea-land distribution in eastern Asia during the LGM result in the temperature decrease in winter and increase in summer. It has significant impact on the temperature and precipitation in the east coastal region of China. The impact on precipitation in the east coastal region of China is the most significant one, with 25%-50% decrease in the total precipitation change during the LGM. On the other hand, the changes in sea-land distribution have less influence on the climate of inland and western part of China. During the LGM, significant changes in vegetation result in temperature alternating with winter increase and summer decrease, but differences in the annual mean temperature are minor. During the LGM, the global climate, i.e., the large-scale circulation background has changed significantly. These changes have significant influences on temperature and precipitation over China. They result in considerable temperature decreases in this area, and direct the primary patterns and characteristics of temperature changes. Results display that, northeastern China has the greatest temperature decrease, and the temperature decrease in the Tibetan Plateau is larger than in the eastern part of China located at the same latitude. Moreover, the change of large-scale circulation background also controls the pattern of precipitation change. Results also show that, most of the changes in precipitation over western and northeastern parts of China are the consequences of changing large-scale circulation background, of which 50%-75% of precipitation changes over northern and eastern China are the results of changes in large-scale circulation background. Over China, the LGM climate responses to different mechanisms in order of strength from strong to weak are, the large-scale circulation pattern, sea-land distribution, vegetation, CO2 concentration, and earth orbital parameters.     

青藏高原纳木错湖区大气边界层结构分析

利用2007年8月8~19日期间系留气球低探空和GPS无线电探空资料,分析了纳木错湖区大气边界层高度、风、温、湿等要素的垂直结构。结果表明:纳木错湖的冷湖效应推迟了边界层湍流混合及对流边界层出现的时间,边界层高度日变化非常明显,对流边界层高度最高可达1750 m;在晴天条件下,边界层内湖陆风日变化非常明显,湖陆风控制范围常超过边界层高度,可达对流层中部;边界层内比湿变化呈V型变化,白天减小,夜间增大,早晨08:00出现峰值。     

WSR/98D与WSR-81S天气雷达应用对比分析

通过对两次冰雹天气过程的两部天气雷达产品的对比分析,表明WSR/98D产品精细、准确,对弱回波探测能力强,在揭示由海风锋造成的强对流冰雹天气的生成演变机制上明显优于WSR-81S.文章还从信息获取原理以及资料加工等方面剖析了WSR/98D的优越性.将新一代天气雷达与旧的业务雷达进行对比分析,比较其探测的优越性.     

Wind-Tunnel and Numerical Simulations of the Coastal Thermal Internal Boundary Layer

Wind-tunnel experiments in a thermally stratified wind tunnel and direct numerical simulations were performed to simulate the thermal internal boundary layer (TIBL) that developed over a coastal area in a sea-breeze flow. The results of the simulations were analyzed to investigate turbulence structure in the TIBL. To study the effects of the atmospheric stability over the sea on the TIBL, two vertical profiles of temperature were created in the upstream portion of the wind-tunnel experiment and the direct numerical simulation. Turbulence statistics of the TIBL changed significantly according to the temperature profile over the sea, indicating that the stability of the flow over the sea has a significant effect on the structure and turbulence characteristics of the TIBL. Furthermore, the TIBL heights were estimated from the vertical profiles of the local Richardson number. The estimated TIBL heights agreed with those predicted by a pre-existing relation, suggesting that both the wind-tunnel experiment and the direct numerical simulation accurately reproduced the growth of the TIBL.     

东半球夏季低空越赤道气流的年际变化

利用1948—2006年NECP/NCAR的风场、高度场、海平面气压场以及地表温度再分析资料,采用相关分析、合成分析及回归分析等方法,探讨了东半球夏季低空越赤道气流的年际变化特征以及越赤道气流强度与环流系统和前期海陆热力差异的关系。结果表明,越赤道气流强度的年际变化和同期南北半球低纬环流系统,特别是亚澳大陆气压差关系密切。此外,索马里急流和孟加拉湾越赤道气流受海陆热力差异的影响,而东亚越赤道气流则主要受海温影响。     

渤海湾地区一次碰撞型海风锋天气过程的数值模拟分析

利用WRF(Weather Research and Forecasting)模式对渤海湾地区2009年9月26日一次碰撞型海风锋天气过程进行了数值模拟分析,模拟结果较好地重现了这次天气过程以及海风锋的结构和特征。结果显示,海风锋锋后是较为深厚的对流不稳定能量和水汽高值区,锋后水汽高值区的形成源于海风的堆积和往高空输送,而锋后对流不稳定能量的产生归因于抬升凝结高度和自由对流高度的降低以及平衡高度的升高,这些高度变化则源于冷湿海风给低层大气带来的降温和增湿,其中给低层大气带来的增湿是主要影响因子。对流系统与海风锋相向碰撞时,对流系统容易进入海风锋锋后触发强对流不稳定能量形成强对流运动,同时弱对流抑制为对流运动的触发提供了有利的条件,强对流运动把海风锋锋后充沛的水汽往上输送,从而造成强降水天气。另外,对流系统与海风锋碰撞后沿着海风锋锋后移动可能更有利于对流运动的发展和维持。     

山东半岛的海陆风环流及其影响

利用山东半岛３２个气象站１９８７￣１９９１年自记风资料，分析了山东半岛海陆风环流的特征。包括：海陆风的强度和频数、生消时间、水平及垂直伸展距离等。结果表明，白天山东半岛有海风生成时，半岛中部常存在一条辐合线，在夏秋季节常伴随阵雨与雷暴的生成，有时可诱发强对流天气。     

海南一次冰雹天气过程成因分析

利用海南岛上常规观测资料,雷达、葵花卫星等非常规观测资料,欧洲中心再分析资料和NCEP全球实时海温,对比分析了2018年3月3日海南冰雹的环境条件及其中尺度特征。结果表明:(1)3月2—4日,大尺度环流特征为中层干冷的W—SW急流、低层SW暖气流及地面西南低压槽。(2)3日的区域大气层结处于稳定转变为不稳定的状态,局地增长的不稳定能量在海风锋的触发下强烈释放,适宜的0～6km垂直风切变,0℃、20℃高度有利于对流单体发展成雹暴单体。(3)2日海南岛附近区域层结稳定,CAPE值偏低;4日海南岛处于低层大风核入口前侧,水汽辐散,海风锋垂直环流被抑制,这些都不利于强对流的发展。(4)此次降雹单体具有多个雷达回波特征,当移入多普勒雷达静锥区后,利用风廓线雷达资料可监测到高层急流脉动下传,0～5km、0～3km垂直风切变相继增大的特征,对判断风暴的演变具有重要参考意义。(5)初生对流单体在地面辐合线和儋州中部露点锋交界处生成,在海风锋北端和海口-澄迈北部露点锋重叠区发展为雹暴单体,雹暴单体前沿的露点锋有新生单体的传播。     

贺兰山区气候若干问题

本文主要利用宁夏区农业厅和区气象局气候资料中心于1985年3月,组织的贺兰山中部剖面考察期间11个气象站点的观测资料,在国内首次对贺兰山的气候特征进行了较为系统的研究。本文主要阐述了贺兰山东麓的冷湖效应,东坡磷矿点典型的山谷风现象,雨季的最大降水高度,以及研究确定了剖面上西坡日照百分率随高度的真实分布。     

Metropolitan-scale Transport and Dispersion from the New York World Trade Center Following September 11, 2001. Part II: An Application of the CALPUFF Plume Model

Following the collapse of the New York World Trade Center (WTC) towers on September 11, 2001, Local, State, and Federal agencies initiated numerous air monitoring activities to better understand the ongoing impacts of emissions from the disaster. The collapse of the World Trade Center towers and associated fires that lasted for several weeks resulted at times in a noticeable plume of material that was dispersed around the Metropolitan New York City (NYC) area. In general, the plume was only noticeable for a short period of time following September 11, and only apparent close to the World Trade Center site. A study of the estimated pathway which the plume of WTC material would likely follow was completed to support the United States Environmental Protection Agency’s 2002 initial exposure assessments. In this study, the WTC emissions were simulated using the CALMET-CALPUFF model in order to examine the general spatial and temporal dispersion patterns over NYC. This paper presents the results of the CALPUFF plume model in terms of plume dilution and location, since the exact source strength remains unknown. Independent observations of PM_2.5 are used to support the general dispersion features calculated by the model. Results indicate that the simulated plume matched well with an abnormal increase (600–1000% of normal) in PM_2.5 two nights after the WTC collapse as the plume rotated north to southeast, towards parts of NYC. Very little if any evidence of the plume signature was noted during a similar flow scenario a week after September 11. This leads to the conclusion that other than areas within a few kilometers from the WTC site, the PM_2.5 plume was not observable over NYC’s background concentration after the first few days.