Numerical Study On Cloud Lines Over An Urban Street In Tokyo

`Kanpachi Street Cloud (KSC)' is an unusual small-scalecumulus cloud line visible during calm summer conditions over a major street in the Tokyo metropolitanarea. In order to understand the mechanism leading to the formation of this cloud line,numerical simulations have been performed using the Regional Atmospheric Modelling System.The general characteristics of the simulated KSC agree well with observations. On alarge-scale view, the KSC can be characterized as a cumulus cloud line generated at the convergenceline of two sea breezes on the western side of Tokyo Bay, while on the microscale view, it resemblesBenard-type thermal convection modified longitudinally by wind shear.The location of the convergence line leading to the KSCformation coincides withthe Kanpachi street location, although the street itself does notmake any direct effect on the KSC formation. Additional numerical experiments were performed toidentify causes of the KSC formation in accordance with urbanization, by changing anthropogenicheat impact, land-cover and grid resolution.They confirmed that the formation of the KSC requirestwo meteorological processes at the same time:(1) the convergence of two sea breezes – the localsouth-eastern sea breeze from Tokyo Bay andan extended southern sea breeze from thePacific Ocean, respectively; (2) Forcing due to an urban heat island. It is shown that urbanization couldchange the intensity and position of the KSC through enhancement of local upward motions and changesin the near-surface horizontal pressure gradient between urban and sub-urban areas. Further,fine horizontal grid resolution is needed to be able to resolve these local thermal convection issues.     

Numerical Modelings of the Climatic Effects of the Land-Sea Distribution and Topography

The effects of the land-sea contrast and the topography on the climatic properties are simulated in this paper by use of a p- σ incorporated coordinate system model in a zonal domain. In this paper we firstly discuss the statistical features of the model and find that the capability of the model is stable, with the same land-sea distribution and to-pography seven monthly mean climate states are close to one another, their variance is even less than the initial one. Secondly, we focally discuss the effects of the land-sea contrast and the topography on the modeled climate fields, It is pointed out that the land-sea contrast and the topography influence the atmosphere mainly through the heating ef-fect and the former has larger influences on the simulated large scale climate fields than the latter.     

祁连山南麓夏季地形云特征及山谷风影响分析

利用门源、祁连气象站2004—2013年6—8月逐时常规观测资料,分析了地形云的日变化特征,结果表明:两站夏季总、低云量的日变化呈现双峰型特征;层积云和积雨云的日变化呈反相特征。层积云出现频率最高在清晨,积雨云在午后至傍晚出现频率最高;门源站层积云出现频率高于祁连站,而祁连站积雨云出现频率高于门源站。两站山谷风环流特征明显,风速最大值出现在午后,最小值出现在清晨;门源站谷风控制时间长于山风,祁连站山风控制时间长于谷风。两站积雨云出现时间与山谷风风速最大值出现时间之间具有对应关系;有天气系统影响时形成的积雨云,持续时间较长,降水较多;仅由地形风及热力、湍流作用形成的积雨云,持续时间较短,降水较少。层积云的形成有3种类型:第1种由高层云演变而来;第2种由积雨云对流发展受到抑制而形成;第3种由局地山谷风环流形成,云的形成与山谷风环流以及边界层日变化特征相关。     

海南岛海风演变特征的观测分析

本文利用2012年海南岛19个常规气象站、5个海岛站的逐时资料以及海口站的探空资料,对海南岛海风的时空演变特征及在不同天气条件下海风发展的特征进行了统计分析,结果表明:2012年全年海南岛的海风多发生于春、秋季,频率分别为40%和33%,冬季最少(约为19%),尤其是一月,大部分站点均不足10%。夏季海风出现时刻较早;南部沿海海风结束时间晚于北部沿海;冬季海风开始得较晚,南部海风结束时间早于北部沿海。海风平均持续时间约为10 h。沿海站的海风风速主要集中在3~6 m·s~(-1),且最大风速值出现在春季,除琼山、海口站外,最大海风强度多出现于春夏季。内陆站中部山区附近海风出现频率较高、开始时刻较早、持续时间较长、强度也较大。海风向内陆的传播距离至少为70 km;海风易发生在阴天,其次为多云天气,少云日的海风最少。     

High Resolution Deterministic Prediction System (HRDPS) Simulations of Manitoba Lake Breezes

The Effects of Lake Breezes On Weather–Manitoba (ELBOW-MB) field project, conducted around Lakes Manitoba and Winnipeg in July 2013, was the first in-depth field study of lake breezes in Manitoba, Canada. Using observational data collected during ELBOW-MB and output from the 2.5?km Canadian High Resolution Deterministic Prediction System (HRDPS), comparisons were made between HRDPS output and observational data to determine whether the HRDPS can simulate Manitoba lake breezes. The model comparisons considered various lake-breeze characteristics, such as depth, inland penetration distance, and initiation and dissipation time. In addition, cross-sections of lake-breeze circulations were analyzed. The results show that the HRDPS was able to correctly simulate lake breezes, or lack thereof, in 78% of cases on Lake Winnipeg and 68% of cases on Lake Manitoba. Modelled lake-breeze initiation and dissipation times were found to be too early in some cases and too late in others when compared with observations. Overall, it was found that the HRDPS was able to simulate most aspects of lake breezes, although inland penetration distance was one characteristic that the HRDPS was not able to simulate realistically.     

2006年8月青岛国际帆船赛期间海陆风特征及三维结构分析

利用2006年青岛国际帆船赛期间(2006年8月9~31日)的观测资料,对赛场附近的海陆风特征进行了分析,并根据激光雷达和多普勒雷达资料分析了海风的三维结构,结果发现:(1)青岛国际帆船赛期间海陆风发生的频率非常高;陆风时间一般在03:00~09:00时;在副高控制下,赛场全天风速较弱,一般在2.5 m.s-1以下,风向也不集中,陆风多为东北北方向,海风的方向则以东-东南风为主。海风形成的时间较迟,而副高边缘的海陆风较明显,海风形成时间相对较早。海风形成后,风速一般在3~4 m.s-1,为一天中风速最大的时段;风向也较集中,陆风以北-西北北风向为主,海风以东南风为主;(2)海陆风消亡时,风速往往迅速减小,海陆风越强,风速减小得越厉害。(3)海陆温差不是决定海风强弱的唯一因子。(4)海风在垂直方向一般比较浅薄,多在300 m以下。发展强盛的海风垂直高度可达1.5 km左右,向内陆推进100 km左右。多普勒雷达风廓线产品却可以较好地反映赛场附近海风风向的转变和垂直结构。     

青岛近海夏季海风特征及其预报方法研究

采用2003～2006年7～9月青岛以及沿海地区自动站资料、探空资料对青岛近海海风进行了统计分析.平均而言,青岛近海7～8月海风发生频率为30%～35%,9月海风发生频率为25%;海风开始时间平均为10:00～12:00,结束时间可以持续到18:00～19:00;海风在垂直方向上厚度为500～600 m左右.青岛近海海风的发生与否取决于青岛上空低层925 hPa风速大小、低层大气稳定度、海陆温差以及海平面气压差四方面的综合效应.通常,925 hPa风速达到8 m/s,系统风较强时不利于海风建立;当低层大气不稳定时,有利于触发海风环流的建立;海陆温差达到4 ℃以上时,青岛近海易出现海风;此外,当地转风为离岸风时,海阳站或日照站与青岛本站08:00时海平面气压差>1 hPa时,当日一般不会出现海风.综合以上预报因子及其指标,通过建立逻辑回归模型,初步实现了夏季青岛近海海风能否发生的客观预报,并在2007年举行的国际帆船赛期间得到了应用.     

四川盆地西部一次典型连续夜雨的数值模拟

利用中尺度模式WRF研究了2017年7月15-17日发生在四川盆地西部的一次典型连续性夜雨过程的形成机制,重点讨论了"山谷风"局地环流对此次夜雨过程的作用.研究表明:(1)此次降水天气过程主要发生在500 hPa"北高南低"的环流形势背景下,这种背景有利于北方冷空气向南输送;850 hPa上台风东侧的偏南气流和副热带高...     

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.