共查询到20条相似文献，搜索用时 593 毫秒
1.
利用大涡模式模拟了对流边界层结构演变以及深对流触发过程。通过改变鲍恩比的敏感性试验研究不同大气初始状况下湿润和干旱下垫面湍流特征及其对深对流触发过程的影响。结果表明:干旱下垫面的混合层干而暖,厚度较大;湿润下垫面相反。由于地表感热通量对热力湍流形成的作用更大,干旱下垫面上湍流混合和夹卷作用更强,使得水汽和相当位温在边界层内分布更均一,而在边界层顶有较大的负扰动;干旱下垫面上对流强度较湿润下垫面大,但均表现为泡状对流,水平方向上呈网状结构。不同下垫面上深对流的发生与大气初始状况有关,当初始时刻1—3 km的逆温强度较弱时（0.15 K/（100 m））,边界层内湍流迅速发展,深对流首先在干旱下垫面发生,但因对流有效位能较小,云层厚度小于湿润下垫面。当1—3 km的逆温强度增加到0.55 K/（100 m）时,云层形成时间较晚,云层厚度明显减小,仅当边界层顶的比湿较大时,有深对流发生,但仍首先发生在干旱下垫面,考虑贯穿对流在边界层顶引起的较强冷却作用,云层厚度大于湿润下垫面。 相似文献
2.
P. Seetaramayya S. S. Parasnis S. G. Nagar K. G. Vernekar 《Boundary-Layer Meteorology》1993,65(3):307-314
Aerological observations carried out on board ORV Sagarkanya at a stationary location (20° N, 89° E) over the Head Bay of Bengal during August 18–21, 1990 were analysed to study the thermodynamic structure of the marine boundary layer in relation to a monsoon depression which formedin situ with its centre at 20° N, 88° E. The q(mixing ratio) reversal observed at 850 hPa prior to formation of the low pressure area shifted to a higher level (h<700 hPa) with the formtion of the low. Positive buoyancy below 850 hPa prior to the formation of the low indicated conditions favourable for deep convection. When the low pressure area intensified into a depression, negative buoyancy was observed at lower levels. 相似文献
3.
本文主要利用第一次“中美热带西太平洋海气相互作用联合调查”所获得的海洋水文、气象及大气探测资料,分析了热带西太平洋暖水区边界层大气层结特征,指出热带西太平洋边界层大气具有多层结构和多层送温现象,边界层内各层厚度及气温、位温、混合比随高度的变化趋势如下:超绝热层位于地面以上50m左右,气温、位温、混合比迅速减小,系绝热不稳定层;第一层为混合层,平均厚度为351m,位温、混合比变化不明显;混合层上又是逆温层大多为30—100m厚,位温迅速增大,混合比迅速减小,系绝对稳定层;700—1000m为浅对流云活跃层, 相似文献
4.
Local variations in the summertime mixing height over metropolitan St. Louis, Missouri, are examined in order to evaluate the dynamical and thermodynamical influences of an urban area. Case studies employing aircraft, lidar, pilot balloon and radiosonde data from Project METROMEX show variations in the height of a temperature inversion which caps a deep mixing layer. A dome-like lifting of the inversion structure occurs over the urban-industrial center with subsidence of the inversion layer at the perimeter of the metropolitan area. The maximum amplitude of the dome occurs shortly after mid-day, suggesting that thermal influences are primarily responsible. 相似文献
5.
穿透性对流是导致北半球夏季平流层低层南亚高压内水汽极值形成的重要机制之一,关于副热带东亚季风区穿透性对流是否对平流层低层水汽等物质分布存在影响目前尚不清楚。本文选取2016年的武汉暴雨事件,采用Cloudsat和Aura Microwave Limb Sounder（MLS）卫星数据,分析了东亚季风区的穿透性对流活动对上对流层/下平流层物质分布的影响。利用CloudSat卫星资料云分类产品和Aura MLS卫星数据联合分析武汉暴雨过程中捕捉到1次穿透性对流事件,该事件发生于2016年7月4日05时（协调世界时）的穿透性对流,中心位于海上梅雨带区域。分析表明,这次对流穿透事件对上对流层/下平流层物质分布有显著影响,穿透性对流活动影响到对流层顶以上的物质分布,具体表现是:首先,穿透性对流显著减少了局地对流层顶附近的臭氧含量,较之气候态对流层顶臭氧含量偏少32.53%;其次,穿透性对流能够增加局地对流层顶附近的水汽混合比含量,它通过更多的云冰粒子蒸发来增强局地平流层水汽含量,同时通过更强的垂直水汽输送来直接加湿平流层。此次穿透性对流事件对水汽变化影响较之对臭氧含量变化的影响更为显著,它使得对流层顶水汽混合比增加近乎一倍（98.15%）。因此,副热带东亚季风区的穿透性对流活动对于对流层向平流层的物质输送起着重要的作用。 相似文献
6.
The thermodynamic structure of the Atmospheric Boundary Layer (ABL) over the Arabian sea region has been studied with the help of 135 aerological observations obtained during MONSOON-77 in the region (10–14° N, 64–68° E) by USSR research vessels. Low-level inversions were observed over the western Arabian sea region (west of 66° E) in association with suppressed convection. The different sublayers of the ABL, viz. the mixed layer, the cloud layer and the inversion/isothermal/stable layer were identified. The low-level stability analysis indicated that in the region east of 66° E, conditions were favourable for deep convection. The thermodynamic transformation of the boundary layer after precipitation was documented. 相似文献
7.
Observations were made of a shallow stratus of upslope origin using an aircraft equipped with insitu probes and with a vertically-pointing radar of 3-mm wavelength. A cloud layer of 300 m thickness was found below the inversion; an additional layer of 100 m thickness was located within the inversion. The coldest temperature within the cloud was -2°C and the cloud contained no ice particles. Drizzle drops up to 180 Am were present in both cloud layers.The observations reveal precipitation and air motion structures of approximately 1 km horizontal dimensions. The origin of this organization appears to be weak convection. In addition, mixing played an important role in forming the cloud droplet and drizzle drop size distributions. 相似文献
8.
In this study,an extreme rainfall event that occurred on 25 May 2018 over Shanghai and its nearby area was simulated using the Weather Research and Forecasting model,with a focus on the effects of planetary boundary layer(PBL)physics using double nesting with large grid ratios(15:1 and 9:1).The sensitivity of the precipitation forecast was examined through three PBL schemes:the Yonsei University Scheme,the Mellor?Yamada?Nakanishi Niino Level 2.5(MYNN)scheme,and the Mellor?Yamada?Janjic scheme.The PBL effects on boundary layer structures,convective thermodynamic and large-scale forcings were investigated to explain the model differences in extreme rainfall distributions and hourly variations.The results indicated that in single coarser grids(15 km and 9 km),the extreme rainfall amount was largely underestimated with all three PBL schemes.In the inner 1-km grid,the underestimated intensity was improved;however,using the MYNN scheme for the 1-km grid domain with explicitly resolved convection and nested within the 9-km grid using the Kain?Fritsch cumulus scheme,significant advantages over the other PBL schemes are revealed in predicting the extreme rainfall distribution and the time of primary peak rainfall.MYNN,with the weakest vertical mixing,produced the shallowest and most humid inversion layer with the lowest lifting condensation level,but stronger wind fields and upward motions from the top of the boundary layer to upper levels.These factors all facilitate the development of deep convection and moisture transport for intense precipitation,and result in its most realistic prediction of the primary rainfall peak. 相似文献
9.
Convective mixing in the monsoon boundary layer 总被引：1，自引：0，他引：1
Surendra S. Parasnis 《Boundary-Layer Meteorology》1991,56(4):395-400
Aerological observations over a tropical inland station collected during different phases of the Indian summer monsoon have been used to study the convective mixing in the monsoon boundary layer. The mixing line (ML) model for the thermodynamic structure of a partially cloudy boundary layer has been used to estimate the mixing by convection. The ML model together with the saturation point approach is able to depict different convective mixing regimes in the monsoon boundary layer. 相似文献
10.
N. Kalthoff B. Adler Ch. Barthlott U. Corsmeier S. Mobbs S. Crewell K. Trumner Ch. Kottmeier A. Wieser V. Smith P. Di Girolamo 《Atmospheric Research》2009,93(4):680-694
During the ‘Convective and Orographically-induced Precipitation Study’ (COPS) performed in summer 2007, deep convection developed on July 15, although convective available potential energy was only moderate and convective inhibition was high. Convection was restricted to an area east of the Black Forest crest. Data analysis revealed that the convection was triggered by different mechanisms. Due to a surface high which was situated east of the Black Forest and a surface low which approached the investigation area from the west, a mesoscale convergence zone was established between the two regions and moved eastwards. Secondly, high insolation favoured the development of slope and valley winds and high evapotranspiration resulted in an increase of moisture in the planetary boundary layer (PBL). The thermally driven circulation systems formed a convergence zone along the mountain crest. When the synoptically induced mesoscale convergence zone reached the Black Forest, the different convergence zones superimposed optimally, such that strong updraughts were observed above the mountain. These updraughts penetrated the PBL-capping inversion and nearly reached the level of free convection. About 15 min after the convergence zone had passed the Black Forest crest, first clouds developed east of it. While moving further eastwards, the convergence zone intensified and became visible as a north-south oriented cloud line in the satellite images. Some deep convective cells with precipitation formed within the cloud line. The dense COPS network allowed the capture of the position and characteristics of the convergence zone and explains why convection developed in some restricted areas only. 相似文献
11.
The spatial variation of the nocturnal urban boundary-layer structure is described and the time variation of the mixing height, and the nocturnal inversion top and strength after sunrise is presented for urban sites located upwind, downwind, and near the center of the heat island, and at an upwind rural site. Observations were derived from high resolution temperature profiles obtained by a helicopter during 35 intensive morning experiments in St. Louis, Missouri.The nocturnal urban boundary layer increased in depth from the upwind edge of the urban area. Far downwind, in suburban and rural areas, a remnant of the urban boundary layer existed between a stable surface-based layer and an upper inversion that resembled the upwind rural inversion.The mixing height (base of the inversion) evolved in a parabolic manner after sunrise at the urban locations. A rise in the inversion top after sunrise at the urban locations is believed to be due to low-level convergence which caused the entire inversion layer to be lifted. Due to large horizontal temperature gradients associated with the urban heat island, cold air advection tended to counteract the urban-induced lifting effect by inhibiting mixing-height growth at urban locations upwind of the heat-island center. Advection also caused the maximum height and fastest growth rate of the urban mixed layer to be shifted downwind of the urban area with time. However, mean mixing-height growth rates at various urban locations did not differ significantly. The rural mixing-height growth rate was about twice as large as urban values for up to 3 hr after sunrise. Spatial differences in the mixing height became small near the time of inversion dissipation, which appeared to occur at about the same time at all locations.On assignment from the National Oceanic and Atmospheric Administration, U.S. Department of Commerce. 相似文献
12.
针对在研仪器——大气辐射超高光谱探测仪的临边探测模式,模拟计算了大气温度和水汽的权重函数。以此为基础,利用信息量和权重函数线性化方法,结合仪器的可探测亮温阈值0.3 K,计算并分析6种大气状态下,大气温度和水汽混合比廓线在不同反演精度条件下可获得的光谱通道数,在满足最佳光谱通道数200的要求下,理论上预估其反演精度。温度廓线整体反演精度为0.6 K,水汽混合比廓线反演精度可达到5%,但热带大气在16~20 km高度的水汽廓线反演精度仅为10%。反演精度预估,仅提供了一种全面认识仪器性能的方法,精度的确定还有赖于真实探测数据的获取和反演方法。 相似文献
13.
《Dynamics of Atmospheres and Oceans》1997,26(2):95-130
A one-dimensional penetrative plume model has been constructed to parameterize the process of deep convection in ocean general circulation models (OGCMs). This research is motivated by the need for OGCMs to better model the production of deep and intermediate water masses. The parameterization scheme takes the temperature and salinity profiles of OGCM grid boxes and simulates the subgrid-scale effects of convection using a one-dimensional parcel model. The model moves water parcels from the surface layer down to their level of neutral buoyancy, simulating the effect of convective plumes. While in transit, the plumes exchange water with the surrounding environment; however, the bulk of the plume water mass is deposited at e level of neutral buoyancy. Weak upwelling around the plumes is included to maintain an overall mass balance. The process continues until the negative buoyant energy of the one-dimensional vertical column is minimized. The parameterized plume entrainment rate, which plays a central role in the parameterization, is calculated using modified equations based on the physics of entraining buoyant plumes. This scheme differs from the convective adjustment techniques currently used in OGCMs, because the parcels penetrate downward with the appropriate degree of mixing until they reach their level of neutral stability. 相似文献
14.
Results of simultaneous balloon and acoustic sounding in the lower troposphere (in the surface layer up to 800 m) carried out in Velikie Luki in May–June 2002 jointly by the Moscow State University (MSU) and Central Aerological Observatory (CAO) are discussed. During the experiment, the tethered (captive) balloon for measuring air temperature and ozone partial pressure was ascended and descended 15 times. Simultaneously, gradient measurements were performed at a 4-m tower. During the intervals between ascents, the temperature stratification was determined by using the Ekho-1 sodar data. A dominating influence of temperature stratification and of some weather events on the ozone distribution with altitude is shown. In case of unstable stratification, its partial pressure is almost unchanged within the entire lower troposphere; in case of surface inversion, the ozone decrease is observed near the surface. In case of elevated inversion the ozone partial pressure is almost the same both below inversion and above it; in the layer of the inversion itself, it increases spasmodically with the altitude. Synoptic conditions largely influence the stratification regime: under conditions of the Arctic air mass, the thermal convection is observed more often and surface inversions are observed more rarely than when the local mass dominates. Artificial dynamic mixing can lead to the surface inversion dissipation in several minutes. 相似文献
15.
P. Martano D. Cava G. Mastrantonio S. Argentini A. Viola 《Boundary-Layer Meteorology》2005,115(1):85-103
Nocturnal convection, originating in a well-mixed marine cloud-topped boundary layer, advected onshore, was observed using a Doppler sodar on the Tyrrhenian coast in Italy. The horizontal and vertical dimensions of the downdrafts were evaluated. The oscillation frequency triggered by the downdrafts at the inversion layer, derived from the harmonic analysis of the sodar measured vertical velocity (w), is compared with the Brunt-Vaisala frequency, obtained from the rawinsonde temperature profile. A similarity function for the 2w vertical profile was used to fit the sodar experimental data and to retrieve the depth of the mixing layer and the sensible heat flux at the top of the cloud layer. The results are in agreement with the convection layer depth observed in the sodar echoes facsimile record, and with the energy budget evaluated at the top of the cloud layer using the rawinsonde profiles. 相似文献
16.
This study examines the processes controlling the diurnal variability of ozone (O3) in the marine boundary layer of the Kwajalein Atoll, Republic of the Marshall Islands (latitude 8° 43′ N, longitude 167°
44′ E), during July to September 1999. At the study site, situated in the equatorial Pacific Ocean, O3 mixing ratios remained low, with an overall average of 9–10 parts per billion on a volume basis (ppbv) and a standard deviation
of 2.5 ppbv. In the absence of convective storms, daily O3 mixing ratios decreased after sunrise and reached minimum during the afternoon in response to photochemical reactions. The
peak-to-peak amplitude of O3 diurnal variation was approximately 1–3 ppbv. During the daytime, O3 photolysis, hydroperoxyl radicals, hydroxyl radicals, and bromine atoms contributed to the destruction of O3, which explained the observed minimum O3 levels observed in the afternoon. The entrainment of O3-richer air from the free troposphere to the local marine boundary layer provided a recovery mechanism of surface O3 mixing ratio with a transport rate of 0.04 to 0.2 ppbv per hour during nighttime. In the presence of convection, downward
transport of O3-richer tropospheric air increased surface O3 mixing ratios by 3–12 ppbv. The magnitude of O3 increase due to moist convection was lower than that observed over the continent (as high as 20–30 ppbv). Differences were
ascribed to the higher O3 levels in the continental troposphere and weaker convection over the ocean. Present results suggest that moist convection
plays a role in surface-level O3 dynamics in the tropical marine boundary layer. 相似文献
17.
During the Atlantic Expedition 1965 and the Atlantic Tradewind Experiment (ATEX) 1969, shipborne aerological measurements were obtained in order to investigate the thermodynamical and kinematic structure of the planetary boundary layer in low latitudes. Under suppressed convection, the subdivision of this layer into five sub-regions was found to be a rather permanent feature. Enhanced cumulus convection effects a smoothing of the thermodynamical discontinuities and leads sometimes to a destruction of the trade inversion. Due to the surface pressure distribution and the thermal wind distribution in the lower atmosphere, the actual wind speed and direction are nearly constant with height below cloud base. In the cloud layer up to the inversion, the wind speed generally decreases and the air flow tends to become more zonal. 相似文献
18.
Diurnal and Seasonal Variations of Thermal Stratification and Vertical Mixing in a Shallow Fresh Water Lake 总被引：1，自引：0，他引：1
Yichen Yang Yongwei Wang Zhen Zhang Wei Wang Xia Ren Yaqi Gao Shoudong Liu Xuhui Lee 《Acta Meteorologica Sinica》2018,32(2):219-232
Among several influential factors, the geographical position and depth of a lake determine its thermal structure. In temperate zones, shallow lakes show significant differences in thermal stratification compared to deep lakes. Here, the variation in thermal stratification in Lake Taihu, a shallow fresh water lake, is studied systematically. Lake Taihu is a warm polymictic lake whose thermal stratification varies in short cycles of one day to a few days. The thermal stratification in Lake Taihu has shallow depths in the upper region and a large amplitude in the temperature gradient, the maximum of which exceeds 5°C m–1. The water temperature in the entire layer changes in a relatively consistent manner. Therefore, compared to a deep lake at similar latitude, the thermal stratification in Lake Taihu exhibits small seasonal differences, but the wide variation in the short term becomes important. Shallow polymictic lakes share the characteristic of diurnal mixing. Prominent differences on the duration and frequency of long-lasting thermal stratification are found in these lakes, which may result from the differences of local climate, lake depth, and fetch. A prominent response of thermal stratification to weather conditions is found, being controlled by the stratifying effect of solar radiation and the mixing effect of wind disturbance. Other than the diurnal stratification and convection, the representative responses of thermal stratification to these two factors with contrary effects are also discussed. When solar radiation increases, stronger wind is required to prevent the lake from becoming stratified. A daily average wind speed greater than 6 m s–1 can maintain the mixed state in Lake Taihu. Moreover, wind-induced convection is detected during thermal stratification. Due to lack of solar radiation, convection occurs more easily in nighttime than in daytime. Convection occurs frequently in fall and winter, whereas long-lasting and stable stratification causes less convection in summer. 相似文献
19.
2013年6—9月在河北省固城站观测到多次夜间对流性天气伴随地面O3混合比快速抬升的过程,并引起次日清晨到中午O3混合比升高。大多数对流过程中,O3混合比在半小时内升高至60×10-9～80×10-9,同时NOx等反应性气体混合比下降,θse值降低,说明下沉气流将高空气团带到地面,造成了O3混合比的升高。通过再分析资料得到下沉气团基本来源于对流层中下层,这一结论与当地进行的一次飞机观测结果吻合。多数对流过程中固城站和北京城区地面O3混合比和θse值有相同的变化趋势和程度。根据观测结果,推测华北地区在夏季和初秋时,对流层中下层存在O3高值区,混合比约为60×10-9～80×10-9。对流性天气对地面O3抬升的影响区域与对流系统的影响范围有关,可达到中尺度范围。华北地区光化学污染严重,对流性天气引起的地面O3混合比抬升程度比较强,对环境的影响值得关注。 相似文献
20.
利用常规观测资料、ERA5再分析资料、闪电定位仪资料、福建龙岩双偏振多普勒天气雷达资料,分析了2020年春季闽西南地区的一次强对流过程。结果表明,此次过程发生在地面锋线北侧冷区内,属于典型的高架雷暴过程,产生的灾害性天气包括冰雹、短时强降水、高山站雷雨大风。500 hPa冷平流、850 hPa暖湿平流、925 hPa闽西南地区的假相当位温高能舌为高架雷暴的发生发展提供了有利的环境条件。探空显示逆温层深厚且逆温层顶温度高,暖湿气流沿着锋面被强迫抬升,至逆温层之上饱和假相当位温随高度递减,存在显著的条件不稳定,对流得到快速发展。雷达分析表明,本次高架雷暴冰雹回波自低层快速倾斜向上发展,具有发展快、强度强、降雹时间长的特征。其双偏振参数演变特征与基于地面抬升的雷暴基本一致,降雹阶段表现为CC谷、ZDR接近零、KDP小于零。降雹前回波单体中存在强ZDR和KDP柱,可以作为冰雹预报的参考,提前量达到半小时。 相似文献