藏北高原夏季典型天气大气边界层特征分析

利用加密探空资料,分析了藏北高原那曲和安多地区夏季典型晴天与阴天边界层风速、位温与比湿时空分布及变化特征.结果发现:在夏季8月,上述地区东西分量风速(切变)晴天均比阴天小,安多地区盛行偏西风,那曲地区盛行偏东风;南北分量风速(切变)晴天比阴天大.边界层晴天和阴天白天(晚上)的对流(稳定)边界层特征明显,阴天稳定边界层的厚度和对流边界层的高度较晴天时的都低;比湿夜间比白天大,阴天比晴天大.在安多地区和那曲地区都出现了逆湿现象,强逆湿主要出现在午夜或正午.     

河套干旱地区夏季边界层结构特征观测分析

利用2013年夏季7月爱尔达K/LLX802J型机动式边界层风廓线雷达获取的三维风场资料和银川站高空气象探测资料,对河套干旱地区夏季边界层日变化特征进行了分析.结果表明:爱尔达K/LLX802J型机动式风廓线雷达能较好的反映并分辨出夏季河套干旱地区边界层内大气湍流和风场的演变过程.夏季7月河套干旱地区边界层高度白天平均为2127.2 m,夜间平均为1760.7 m,白天边界层高度比夜间平均高366.5 m.河套干旱区夏季地表非绝热加热对边界层的影响主要集中在800 m以下,800~2000 m高度边界层则主要受昼夜交替和大尺度天气系统的影响.夏季7月河套干旱地区边界层风速在300 m以下随高度增加而增大,离地500 m以下边界层易在北京时间07:00-11:00和18:00-21:00时段发生风速切变;300 m以下边界层白天盛行西南偏南风、夜间盛行南风,300~2000 m高度边界层白天和夜间均盛行东南风;离地300 m以下边界层易在夜间21:00-23:00时出现风向切变.夏季7月白天河套干旱地区边界层大气垂直速度在300 m高度以下随高度增加而增大,由0.3 m·s^-1增大到0.6 m·s^-1,夜间边界层大气垂直速度在200 m高度以下随高度增大而增大;300 m高度以上边界层大气垂直速度无论昼夜随高度变化均较小.     

西北干旱区和黄土高原大气边界层特征对比及其对气候干湿变化的响应

利用西北干旱区民勤、 黄土高原平凉和榆中3站2006-2009年1、 4、 7月和10月逐日08:00时和20:00时探空资料、 降水和日最高气温, 计算和对比分析了最大混合层厚度(ML)、 逆温层特征和垂直温湿场及其对干湿气候变化形成的影响. 结果表明: 最大混合层厚度与最高地气温差关系较为密切, 呈显著正相关, 干旱区民勤较密切其相关系数达0.92. 最大混合层厚度4月最深厚, 干旱区民勤高达2 871 m, 明显高于黄土区两站200~400 m左右, 平凉最为浅薄, 1月不足1 000 m; 但日降水量≥5 mm的降水发生时榆中较深厚, 高于其他两站300~400 m. 强降水发生前后干旱区湿度变化大, 发生时高低空湿度迅速增大, 而黄土高原变化湿度小, 榆中中低层增湿较明显. 干旱区近地层较干, 但有降水时中高层增湿较黄土高原显著. 干湿气候变化与最大混合层厚度、 逆温层的频数和强度、 近地面层的干湿程度关系密切, 混合层越深厚, 逆温层多而强, 近地层越干, 干旱加剧.     

基于加密探空观测的成都市一次重霾污染过程中大气边界层气溶胶垂直结构分析

基于2017年1月4日至7日成都市一次重霾污染过程的系留汽艇探测的低层大气气象要素和大气颗粒物垂直探空加密观测资料,分析了大气边界层结构及气溶胶垂直分布。结果表明,此次重霾污染期间,大气边界层昼夜变化特征基本消失。稳定边界层结构出现25次,对流边界层结构仅出现3次,大气边界层结构趋于稳定,边界层高度普遍在700 m以下。霾污染发生、维持及消散阶段大气边界层气溶胶垂直结构具有明显差异。霾污染发生阶段,大气边界层气溶胶粗、细粒子主要集中在300m高度以下,近地面层大气气溶胶粒子累积触发霾污染事件;霾维持阶段,大气颗粒物粒子浓度数垂直方向趋于一致,大气边界层稳定结构中存在强的大气垂直混合作用;在霾消散阶段,较高处的气溶胶粒子浓度最先下降,且下降幅度最大,表明对流层自由大气作用对霾污染消散具有影响。大气边界层风速的增大加剧了大气传输扩散。温度与大气颗粒物浓度在近地层呈负相关关系,在100m高度以上呈正相关关系。大气边界层低层偏冷,高层偏暖的稳定大气热力层结减弱了大气污染物的垂直扩散。相对湿度的增加有利于气溶胶粒子的吸湿增长和液相化学反应,加剧了霾污染。     

藏北高原地区干、雨季大气边界层结构的不同特征

利用2004年4月预试验期(PIOP)和8月加强期(IOP)的无线电探空仪观测资料,分析了藏北高原地区干、雨季大气边界层结构的不同特征.结果显示:藏北高原地区边界层虚位温、比湿等日变化大,对流混合层高度较高,高度干季在2 211～4 430 m之间,雨季在1 006～2 212 m之间,干季的对流混合层高度明显高于雨季...     

干旱区陆面过程和大气边界层研究进展

干旱区陆面过程和大气边界层不仅与气候、生态、水资源密切相关,而且影响我国气候格局和东亚大气环流,是一个十分重要的研究领域,近20多年已取得了比较系统的研究进展.从干旱区陆面热力和水分过程特征、干旱区大气边界层结构特征、干旱区陆面过程参数及其参数化公式、非均匀下垫面大气边界层理论、干旱城市大气边界层特征与污染机理等方面归纳总结了干旱区陆面过程和大气边界层领域取得的部分研究进展.并且,认为科学试验的代表性、复杂下垫面的影响、尺度转化、地表能量不平衡、极端天气过程的相互作用、水分过程的复杂性等问题是干旱区陆面过程和大气边界层研究领域的突出问题和未来研究重点.     

玛曲高寒草甸夏季近地层微气象和CO2通量特征分析

利用2015年夏季玛曲高寒草甸观测资料,从中选取7月10个连续完整的观测日,分析了近地层气象要素、地表辐射和能量传输以及CO₂通量日变化特征。结果表明：夏季玛曲地区气温和比湿昼夜差异较大,最大温差为19.2 ℃,平均风速为2.7 m?s^-1,风向以东风为主。晴天条件下向下短波辐射可达1 200 W?m^-2左右,平均地表反照率为0.22,均大于藏北那曲地区。净辐射峰值可达850 W?m^-2左右,陆-气间能量传输以潜热输送为主。10 d能量闭合度平均值为0.61,能量不平衡程度较大。夏季玛曲高寒草甸表现为“碳汇”,CO₂通量平均值为-0.20 mg?m^-2?s^-1,晴天碳吸收最大速率为-14.05 mg?m^-2?s^-1,显著大于阴天,最大碳吸收时长为13 h,CO₂密度平均值为530.7 mg?m^-3。     

泸沽湖水体垂直断面季节性分层

通过2015年1月、4月、7月、10月水温、电导率、溶解氧、pH及叶绿素a监测数据对水体温度的季节动态及其垂直分层结构进行分析,探讨了泸沽湖水体水化学性质的季节性分层特征。结果表明:泸沽湖水体在春、夏、秋季出现明显的热力分层现象,冬季水温在垂向上接近同温状态,夏季温跃层位于10~25 m水深处,而秋季温跃层下移至20~30 m处。均温层水温维持在9.5~10℃与泸沽湖年均温一致,说明均温层水体稳定且处于相对恒温状态,是湖区年均温的反映。热力分层结构对电导率、溶解氧、pH及叶绿素a变化有一定影响,致使水体电导率、溶解氧、pH出现明显的分层现象,尤其在夏季,气温升高,热力分层现象显著,溶解氧和pH在温跃层内出现峰值,自峰值处向上、向下均呈递减趋势,均温层处于缺氧状态且p H值较小。虽然叶绿素a在温跃层以下维持较低水平,整体不高,但在表层有突然增高的现象,应予以高度警示,防止泸沽湖出现大面积藻类繁殖甚至局部性爆发。电导率垂向上呈递减变化,在温跃层内降低幅度较大。泸沽湖水体盐度基本保持恒定(约0.10‰),在不考虑盐度效应的情况下,无论是在垂直断面上还是在变温层、温跃层及均温层中,电导率与水温之间存在一简单线性函数关系,证明泸沽湖仍受自然气候影响,保持自然水体状态。     

绿洲与荒漠背景夏季近地层大气特征的对比分析

利用观测试验资料, 对比分析了夏季典型晴天敦煌绿洲与周围荒漠戈壁背景近地面层大气特征的差异. 结果表明: 绿洲具有降温、保湿、风屏等效应, 地表温度和近地面层大气温度明显要比周围荒漠的低, 近地面层大气湿度要明显比周围荒漠的大, 近地面层大气风速和摩擦速度要比周围荒漠的小, 近地面层感热通量比周围荒漠小1/5, 近地面层潜热通量比周围荒漠大 10 倍左右. 同时, 绿洲与周围荒漠相比有比较可观的下沟运动, 这会对绿洲的能量和水分输送有贡献. 绿洲的 Bowen比大约是周围荒漠戈壁的1/20, 相差一个量级, 这说明绿洲和周围荒漠的气候特征相差十分明显.     

河西走廊不同强度槽型沙尘暴垂直动量传输特征分析

利用河西走廊13个气象站逐时地面气象观测资料和MICAPS高低空资料,对该区2010年4月24～25日、2014年4月23～24日和2018年4月4日3次不同强度槽型沙尘暴过程垂直动量特征进行诊断分析,得到槽型沙尘暴的垂直动量传输特征,更好地为槽型沙尘暴的精细化网格预报预警提供有力技术支撑,增强大风强沙尘暴的防灾减灾能力。结果表明：300 hPa极锋急流是造成河西走廊地区槽型沙尘暴的主要高空动力系统,大风沙尘暴出现在高空偏西风急流（≥32 m/s）、中空急流（≥20 m/s）和低空急流（≥12 m/s）附近。沙尘暴前期,近地层大气干热,当高空冷空气侵入,与中低层暖空气进行剧烈交换,在边界层形成不稳定层结;高空槽后冷空气下沉（冷平流中心强度小于等于-10×10-5K/s）,将强风迅速向下传递到地面产生大风;槽前高空急流加强垂直动力抽吸,深厚的辐合辐散区与地面冷锋增强上升运动,最大上升速度位于500 hPa,强度小于等于-30×10-5Pa/s。沙尘暴区距离高空急流轴中心位置越近,辐合辐散中心差值越大、垂直距离越近,辐合中心位置越低,对流性不稳定层结越厚、所处高度越低,冷平流中心强度越强,...     

A case study of atmospheric boundary layer features during winter over a tropical inland station — Kharagpur (22.32°N, 87.32°E)

The local weather and air quality over a region are greatly influenced by the atmospheric boundary layer (ABL) structure and dynamics. ABL characteristics were measured using a tethered balloon-sonde system over Kharagpur (22.32°N, 87.32°E, 40m above MSL), India, for the period 7 December 2004 to 30 December 2004, as a part of the Indian Space Research Organization-Geosphere Biosphere Program (ISRO-GBP) Aerosol Land Campaign II. High-resolution data of pressure, temperature, humidity, wind speed and wind direction were archived along with surface layer measurements using an automatic weather station. This paper presents the features of ABL, like ABL depth and nocturnal boundary layer (NBL) depth. The sea surface winds from Quikscat over the oceanic regions near the experiment site were analyzed along with the NCEP/NCAR reanalysis winds over Kharagpur to estimate the convergence of wind, moisture and vorticity to understand the observed variations in wind speed and relative humidity, and also the increased aerosol concentrations. The variation of ventilation coefficient (V C), a factor determining the air pollution potential over a region, is also discussed in detail.     

Characteristics of extreme dust events observed over two urban areas in Iran

Determination of dust loading in the atmosphere is important not only from the public health point of view, but also for regional climate changes. The present study focuses on the characteristics of two major dust events for two urban areas in Iran, Kermanshah and Tehran, over the period of 4 years from 2006 to 2009. To detect extreme dust outbreaks, various datasets including synoptic data, dust concentration, reanalysis data and numerical results of WRF and HYSPLIT models were used. The weather maps demonstrate that for these events dusts are mainly generated when wind velocity is high and humidity is low in the lower troposphere and the region is under the influence of a thermal low. The event lasts until the atmospheric stability prevails and the surface wind speed weakens. The thermal low nature of the synoptic conditions of these major events is also responsible for deep boundary layer development with its thermals affecting the vertical dust flux over the region. Trajectory studies show that the dust events originated from deserts in Iraq and Syria and transported towards Iran. The main distinction between the two types of mobilizations seems to affect the dust concentrations in the Tehran urban area.     

Atmospheric boundary layer characteristics during the BOBMEX-Pilot experiment

The atmospheric boundary layer characteristics observed during the BOBMEX-Pilot experiment are reported. Surface meteorological data were acquired continuously through an automatic weather monitoring system and manually every three hours. High resolution radiosondes were launched to obtain the vertical thermal structure of the atmosphere. The study area was convectively active, the SSTs were high, surface air was warm and moist, and the surface air moist static energy was among the highest observed over the tropical oceans. The mean sea air temperature difference was about 1.25‡C and the sea skin temperature was cooler than bucket SST by 0.5‡C. The atmospheric mixed layer was shallow, fluctuated in response to synoptic conditions from 100 m to 900 m with a mean around 500 m.     

The influence of wind speed on surface layer stability and turbulent fluxes over southern Indian peninsula station

Surface to atmosphere exchange has received much attention in numerical weather prediction models. This exchange is defined by turbulent parameters such as frictional velocity, drag coefficient and heat fluxes, which have to be derived experimentally from high-frequency observations. High-frequency measurements of wind speed, air temperature and water vapour mixing ratio (eddy covariance measurements), were made during the Integrated Ground Observation Campaign (IGOC) of Cloud Aerosol Interaction and Precipitation Enhancement Experiment (CAIPEEX) at Mahabubnagar, India (16^°44^′N, 77^°59^′E) in the south-west monsoon season. Using these observations, an attempt was made to investigate the behaviour of the turbulent parameters, mentioned above, with respect to wind speed. We found that the surface layer stability derived from the Monin–Obukhov length scale, is well depicted by the magnitude of wind speed, i.e., the atmospheric boundary layer was under unstable regime for wind speeds >4 m s^?1; under stable regime for wind speeds <2 m s^?1 and under neutral regime for wind speeds in the range of 2–3 m s^?1. All the three stability regimes were mixed for wind speeds 3–4 m s^?1. The drag coefficient shows scatter variation with wind speed in stable as well as unstable conditions.     

古尔班通古特沙漠及周边区域冬季大气边界层高度对地表积雪的响应

古尔班通古特沙漠是中国唯一冬季存在长期积雪的沙漠,在此特殊地理环境下,沙漠及周边区域冬季雪深和边界层高度的时空变化特征和相互关系尚未明确。本文利用1980—2019年SMMR（Scanning Multichannel Microwave Radiometer）、SSM/I（Special Sensor Microwave/Imager）、SSMI/S（Special Sensor Microwave Imager/Sounder）被动微波遥感雪深数据、古尔班通古特沙漠腹地雪深观测数据和ERA5再分析资料（the Fifth Generation ECMWF Reanalysis）边界层高度数据,分析了沙漠及周边区域冬季雪深和边界层高度的时空变化特征与相互关系。结果表明：古尔班通古特沙漠及周边区域冬季雪深年均值为8.45 cm,整体呈现东北部和南部积雪较深,其他区域积雪较浅并呈现出由沙漠中心区域向四周逐渐减少的特点,雪深在古尔班通古特沙漠及其东北、南边的邻近区域呈升高趋势,剩余地区呈下降趋势。古尔班通古特沙漠及周边区域冬季边界层高度年均值为105.54 m,呈现东南部和西北部高,中心沙漠区域、东北部、西南部较低的特点,边界层高度在沙漠及周边区域升高而其他区域降低。古尔班通古特沙漠的冬季雪深和大气边界层高度时空变化整体呈负相关,其中93.17%以上的沙漠区域呈负相关,平均相关系数为-0.32,最大相关系数绝对值为-0.58,空间相关系数为-0.42（P<0.05）。     

Atmospheric surface layer characteristics with MONTBLEX data

Data obtained from the 30m high MONTBLEX tower installed at the Indian Institute of Technology, Kharagpur are described. Data on wind speed and direction, temperature and humidity were recorded during the first week of July 1989 at six levels on the tower. They indicate some of the atmospheric surface layer characteristics. Using two levels of tower data involving wind speed and temperature a profile method was used for computing the surface fluxes of heat and momentum. A method for calculating the surface roughness length using the data was also used to obtain the vertical windspeed profile. The computed wind profile was compared with observations, while the surface roughness length was compared with values obtained by a least square fit. The computed surface fluxes were compared with theoretical values obtained by an energy budget method which uses only wind data at one level. The agreement was reasonably good.     

藏北高原典型季节冻土区和多年冻土区小气候特征对比研究

利用藏北高原位于季节冻土区的那曲BJ站和多年冻土区的唐古拉站2008年气象要素观测资料,对两站点的小气候特征进行了分析和对比,得到以下结论：那曲BJ站最大冻结深度可达1.5m左右;唐古拉站活动层最大融化深度超过了3.0m。两站的气温、比湿、降雨和积雪均有明显的季节变化;降雨和比湿均是5-10月较大,其他时段较小;积雪均基本集中在1-3月和10-12月。各层土壤温度及日变幅、温度的月均值和月最高/低值及月较差、比湿的月均值和瞬时最大值、风速瞬时最大值均是那曲BJ站大于唐古拉站。那曲BJ站与唐古拉站的风速、气温、比湿的年平均值分别是4.73m·s^-1、-1.34℃、3.96g·kg^-1和4.02m·s^-1、-5.80℃、3.25g·kg^-1,年降雨量和积雪日数分别为590.50mm、114d和405.27mm、135d,两站5-10月的降雨量分别占全年降雨量的96.20%和86.55%。两站在2月初和11月初由于较大降雪均出现了气温陡降的现象,最大积雪日均出现在11月,日最大积雪深度BJ站小于唐古拉站。典型晴天日,那曲BJ站在冬季而唐古拉站在冬春季节风速日变化明显;比湿日变化夏秋季节较冬春季节明显。     

Estimation of urban mixed layer height in Zanjan using LIDAR observations and numerical modeling

Air pollution predictions often require the height of atmospheric mixed layer in time especially in big cities. Here, the variation of the height of this layer is estimated from direct measurements and also from a numerical forecast model with a high resolution boundary layer scheme. The height of the daytime mixed layer for the city of Zanjan (48.5°N, 36.7°E, 1700m above sea level) is measured using a LIDAR (532 nm) system, which works based on aerosols scattering of laser light. The mixed layer height (z _i ) for Zanjan city, well above mean sea level compared to other major cities in the world, is found to be between 1.4 km typically in spring and 2.2 km in summer, for synoptic calm conditions. Also, the MM5 forecast model with a proper boundary layer scheme (MRF) is used to estimate z _i which shows rather good agreement with direct observations using the LIDAR system. The entrainment zone of the mixed layer was also found to undergo some occasional temporal growth that may be attributed to shear instability that led to more mixed layer growth.