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.     

中南半岛与南海热力差异对南海季风爆发的影响

利用1958-1998年NCEP/NCAR再分析资料和1975-1998年OLR资料,分析了中南半岛与南海热力差异的季节和年际变化特征,以及这种热力差异对南海季风爆发的影响.结果表明,中南半岛与南海热力差异存在明显的季节变化,从第3候歼始,感热加热的作用使中南半岛地表温度高于南海并一直持续到第25候,之后,中南半岛与南海热力差异发生逆转,这种逆转是由于第22-23候出现在中南半岛的对流及降水造成中南半岛地表温度降低所致.进一步研究指出,中南半岛与南海热力差异的上述季节变化特征还表现出最著的年际差异,这种年际差异对南海季风的爆发有着重要影响.首先,上述热力差异的逆转是南海季风爆发的一个必要条件:1958-1998年,逆转时间均早于(或等于)南海季风爆发时间;其次,中南半岛地表温度高于南海的持续时间与南海季风爆发日期之间呈显著正相关,即中南半岛地表温度高于南海的时间越早、转为低于南海的时间越迟,则南海季风爆发越迟.     

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.     

Observations and Numerical Simulations of Urban Heat Island and Sea Breeze Circulations over New York City

Observations from two SOund Detection And Ranging (SODAR) units, a 10 m micrometeorological tower and five Automated Surface Observing Stations (ASOS) were examined during several synoptic scale flow regimes over New York City after the World Trade Center disaster on September 11, 2001. An ARPS model numerical simulation was conducted to explore the complex mesoscale boundary layer structure over New York City. The numerical investigation examined the urban heat island, urban roughness effect and sea breeze structure over the New York City region. Estimated roughness lengths varied from 0.7 m with flow from the water to 4 m with flow through Manhattan. A nighttime mixed layer was observed over lower Manhattan, indicating the existence of an urban heat island. The ARPS model simulated a sea-breeze front moving through lower Manhattan during the study period consistent with the observations from the SODARs and the 10-m tower observations. Wind simulations showed a slowing and cyclonic turning of the 10-m air flow as the air moved over New York City from the ocean. Vertical profiles of simulated TKE and wind speeds showed a maximum in TKE over lower Manhattan during nighttime conditions. It appears that this TKE maximum is directly related to the influences of the urban heat island.     

Numerical Modelling of the Effects of Vegetation and Environmental Conditions on the Lake Breeze

The influence of vegetation and environmental conditions on the lake breeze and associated boundary-layer turbulence structure has been studied using a two-dimensional nonhydrostatic, compressible mesoscale model coupled with the SiB2 land-surface scheme. The results show that the impacts of vegetation on the lake effects are dependent on the environmental conditions, such as soil wetness and background wind, as well as vegetation characteristics. Both soil wetness and background wind play important roles in modifying lake effects on boundary-layer turbulence and the lake breeze, while the effects of vegetation type are secondary compared to the other factors. Without background wind, and under the same soil wetness, the maximum horizontal windspeed of the lake breeze is insensitive to the type of vegetation. Soil wetness can greatly affect both the maximum horizontal windspeed and the maximum vertical velocities of the lake breeze. With background wind, the lake-breeze circulations, upward motion regions, and boundary-layer turbulence structure all change markedly. A weaker background wind can strengthen the lake breeze, while stronger background wind suppresses the lake breeze circulations. The distribution of sensible and latent heat fluxes is also very sensitive to the soil wetness and background wind. However, for the same soil wetness (0.25 and 0.4 were chosen), there is only a small difference in the distribution of sensible and latent heat fluxes between the bare soil and vegetated soil or between the types of vegetated soils.     

长江三角洲夏季海陆风与热岛环流的相互作用及城市化的影响

用三维中尺度模式研究长江三角洲夏季海陆风与城市热岛环流的相互作用,白天由于东海海风和太湖湖风环流与上海市热岛环流相互增强,最大垂直速度可达６．２ｃｍ／ｓ;夜间则相反,由于海风（包括长江江风）与湖风的对撞,因而在上海到江阴市沿江出现一条水平辐合带,如果上海周围地区随着经济发展,大片农田被城市下垫面所取代,而使绿地覆盖率下降到１５％以下,则睡季夜间地面气温可上升３℃,两个增温中心分别在苏州和嘉兴附近,