“4·23”南疆翻山型强沙尘暴动力结构特征分析

利用2014年4月22日-23日高空、地面、区域自动气象站加密观测和1°×1°NCEP/NCAR再分析资料,分析4月23日南疆翻山型强沙尘暴天气的高低空环流及动力结构特征。结果表明:巴尔喀什湖低槽引导极地干冷空气爆发性南下进入南疆,造成4×10-2h Pa·km-1剧烈的气压梯度和地面冷锋,引发了大风、强沙尘暴,盆地中尺度低压辐合使尉犁加强为"黑风";300 h Pa极锋急流快速南下至南疆盆地,动量下传形成低空急流,高低空急流是此次强沙尘暴形成的动力条件;急流附近高空辐散、低层辐合及层结不稳定,有利于沙尘暴发生。本次强沙尘暴动力结构特征:干冷与干暖空气剧烈交绥,激发热力不稳定,产生热力对流;高空辐散、低层辐合与高低空急流、地面冷锋配合,加强上升运动,使地面沙尘卷入空中并输送;高低空急流抽吸加强冷暖空气垂直运动,位能向动能转化,引起了地面大风,驱动沙尘暴发生。     

Review of the Atmospheric Response to the Ocean Mesoscale Eddies

As one of the most important mesoscale ocean features, the mesoscale eddies are omnipresent and have significant impact on the overlying atmosphere. Based on the comprehensive review of the influence of mesoscale eddies on the atmospheric boundary layer and the local circulation, the corresponding physical mechanisms and their impacts on weather systems were presented systematically. ①Eddy-induced SST anomalies may modify the surface wind speed, horizontal divergence, cloud and precipitation through turbulence heat flux anomalies. Meanwhile, additional secondary circulations arise over the eddies. What is more, there are obvious regional and seasonal differences for atmospheric responses. ② Studies in the South China Sea, the Kuroshio Extension region and the Southern Ocean indicate that atmospheric responses to mesoscale eddies can be explained by the changes of sea level pressure or the vertical momentum transport. These two mechanisms can be distinguished by the phase relationship between the atmospheric anomaly center and the eddy core. Diagnosis on the inner dynamical processes may draw better conclusions. ③The energy conversions are affected by mesoscale eddies, which may affect storm tracks and jet streams, and finally result in distant influences on weather patterns. Moreover, sea temperature anomalies from sea surface to the thermocline associated with mesoscale eddies have significant impacts on the intensification and the maintenance of tropical cyclones.     

On meteotsunamis around Tsushima Strait generated by the Baiu front

On July 15, 2009, a meteotsunami occurred over Tsushima Strait and flood damage was recorded on the west coast of Tsushima Island. This study investigated the meteorological systems related to that meteotsunami event using surface observation data, grid-point value data, and a mesoscale meteorological model. The mid-latitude trough in the mid-troposphere approached the moist air of the Baiu precipitation system, and a cold downdraft occurred over a wide area of western Japan. In the western Tsushima Strait, the warm, moist air of the lower atmosphere kept the front of the cold downdraft stationary. Around this area, an atmospheric gravity wave was generated continuously with the wave-conditional instability of the second kind mechanism and propagated toward Tsushima Island. The atmospheric gravity wave generated a pressure disturbance at sea level, which produced the meteotsunami. The frequency of the pressure disturbance using the numerical model had a peak in the 5- to 20-min period range, which corresponded with the peak frequency range of the observed tidal records.     

Climatological Characteristics of the East Asian Winter Monsoon Simulated by CWRF Regional Climate Model

Based on the ERA-Interim atmospheric reanalysis data from the European Medium-Term Weather Forecast Center from 1979 to 2016 and the ERSSTv4 sea surface temperature data from the US National Oceanic and Atmospheric Administration, the regional climate model CWRF was used to simulate the climate characteristics in East Asia. The results show that the CWRF model can well reproduce the average characteristics of the East Asian winter monsoon circulation, including the location and intensity of the low-level continental cold high pressure and variation characteristics of wind field in high and low levels. The occurrence area and frequency of the north wind in the simulation and the reanalysis data were further calculated and compared. It is shown that they are basically consistent. The distribution of air temperature and precipitation over China are well represented by the model. The water vapor transport is also in good agreement with the reanalysis data. The water vapor from the Bay of Bengal plays a vital role in the precipitation over South China. The simulation results of apparent heat source and apparent moisture sink show that the model can well simulate the thermal difference between the East Asian continent and the adjacent sea area. The analysis results indicate that CWRF model has the ability to simulate the main characteristics of the East Asian winter monsoon.     

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.     

Simulation of atmospheric states for a storm surge on the west coast of Korea: model comparison between MM5, WRF and COAMPS

High-quality informations on sea level pressure and sea surface wind stress are required to accurately predict storm surges over the Korean Peninsula. The storm surge on 31 March 2007 at Yeonggwang, on the western coast, was an abrupt response to mesocyclone development. In the present study, we attempted to obtain reliable surface winds and sea level pressures. Using an optimal physical parameterization for wind conditions, MM5, WRF and COAMPS were used to simulate the atmospheric states that accompanied the storm surge. The use of MM5, WRF and COAMPS simulations indicated the development of high winds in the strong pressure gradient due to an anticyclone and a mesocyclone in the southern part of the western coast. The response to this situation to the storm surge was sensitive. A low-level warm advection was examined as a possible causal mechanism for the development of a mesocyclone in the generating storm surge. The low-level warm temperature advection was simulated using the three models, but MM5 and WRF tended to underestimate the warm tongue and overestimate the wind speed. The WRF simulation was closer to the observed data than the other simulations in terms of wind speed and the intensity of the mesocyclone. It can be concluded that the magnitude of the storm surge at Yeonggwang was dependent, not only on the development of a mesocyclone but on ocean effects as well.     

中国西北地区水汽的平流输送和辐合输送

分析了中国西北地区上空的水汽汇聚过程———平流输送与辐合输送,为西北地区降水过程数值模拟的参数化提供依据.分析表明:中国西北大部分地区为负的水汽平流输送,从上风方向得到的水汽输入小于水汽输出,是水汽的净流失区;中国西北地区中部为大范围负的水汽辐合输送,当地的水汽由风场向外扩散,加剧了当地的水分流失,是水汽扩散区;在水汽净输送的年际变化中,中国西北地区小于华北地区,平流输送呈上升趋势,辐合输送下降,平流的相对贡献在增加;在与大气环流系统的关系中,中国西北地区水汽的平流输送主要受西风带影响,辐合输送与南亚夏季风有显著相关.变化趋势表明西风的作用在加强.     

Norwegian sea‐surface palaeoenvironments of marine oxygen‐isotope stage 3: the paradoxical response of dinoflagellate cysts

High‐resolution marine palynological data have been obtained from two very long sediment cores (MD952009 and MD952010) retrieved from the southern Norwegian Sea. The dinoflagellate cyst assemblages show pronounced fluctuations in composition, which correlate strongly with magnetic susceptibility records and also mimic the δ¹⁸O signal of the GISP2 Greenland ice‐core. If focusing on the period from 48 to 30 cal. kyr BP, this correlation suggests a paradoxical response of the sea‐surface environments to the atmospheric conditions over Greenland: when the Greenland δ¹⁸O signal reflects warm interstadial conditions, the Norwegian Sea depicts cold sea‐surface temperatures with quasi‐perennial sea‐ice cover (based on dinoflagellate cysts). In contrast, when the Greenland δ¹⁸O records cold stadial periods, the Norwegian Sea‐surface temperatures are warm (based on dinoflagellate cysts), probably linked to inflow of the North Atlantic Drift. These results, similar in both cores, are contrary to those of previous studies and shed light on a possible decoupling of Norwegian sea surface‐water conditions and atmospheric conditions over Greenland. This decoupling could be linked to an atmosphere–ocean system behaving similar to that which the Northern Hemisphere is experiencing at present, i.e. strongly variable owing to the North Atlantic Oscillation. Copyright © 2002 John Wiley & Sons, Ltd.     

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.     

Study on Water Internal Recycle Process and Mechanism in Typical Mountain Areas of Inland Basins,Northwest China: Progress and Challenge

The water resource and its change of mountainous area are very important to the oasis economic system and ecosystem in the arid areas of northwest China. Accurately understanding the water transfer and circulation process among vegetation, soil, and atmosphere over different hydrological units in mountainous areas such as snow and ice, cold desert, forest and grassland is the basic scientific issue of water research in cold and arid regions, which is also the basis of water resource delicacy management and regulation. There are many research results on the hydrological function of different land covers in mountain areas, basin hydrological processes, however, there are only very limited studies on the water internal recycle at basin scale. The quantitative study on the mechanism of water internal recycle is still at the starting stage, which faces many challenges. The key project “Study on water internal recycle processes and mechanism in typical mountain areas of inland basins, Northwest China” funded by National Natural Science Foundation of China will select the Aksu River and Shule River Basin, which have better observation basis, as study area. The internal mechanism of moisture transfer and exchange process of different land cover and atmosphere, the internal mechanism of water cycle in the basin, and water transfer paths in atmosphere will be studied through enhancing runoff plot experiments on different land cover, analyzing the mechanism of water vapor transfer and exchange between different land covers in the watershed by isotope tracing on the water vapor flux of vegetation water, soil moisture and atmospheric moisture, improving the algorithms of remote sensing inversion and ground verification on land surface evapotranspiration on different land cover, and analyzing the water vapor flux from reanalysis data, and the coupling modeling of regional climate model and land surface process model. At last, the effect of different land cover in hydrological process of mountain area, and the impact of land cover on downstream oasis will be systematically analyzed.     

基于Polar WRF模型的南极冰盖气温、风速和气压数值模拟北大核心CSCD

在全球变暖的背景下,南极已成为全球气候变化研究的热点,然而其区域内的观测站点稀疏且缺乏较长的时间序列,限制了人们对南极气候变化机制的分析与理解。Polar WRF作为目前最先进的极地区域气候模型之一,有力弥补了观测资料不足的缺陷,然而模式存在误差,在应用之前有必要对其定量评估。本文利用Polar WRF3.9.1对2004-2013年南极冰盖2m气温、10m风速和地表气压进行了数值模拟,并与28个气象站数据进行了对比分析,结果表明:模式对气温的模拟值在东南极沿岸偏低,在内陆偏高,在南极半岛既存在冷偏差也存在暖偏差,而对风速和气压的模拟整体呈高估。而从均方根误差和平均绝对误差的空间分布来看,模式对气温和气压的模拟结果在东南极沿岸的精度高于内陆和南极半岛,而风速则在内陆的精度要高于沿岸地区。但总体来说模拟效果较为理想,在2004-2013年间气温、风速、气压的模拟值的变化趋势与实测值的变化趋势相同。模式模拟的年平均2m气温和近地面气压在所有站点都通过了α=0.1的显著性检验,季节误差和月误差整体较小,且所有月份的相关系数都分别大于0.90与0.79。模式对10m风速的模拟精度要略低,部分沿岸站点的年平均误差超过了7.5m·s^(-1),但整体而言其在四季和各个月份的相关性均大于0.5且误差小于4.5m·s^(-1)。虽然Polar WRF作为天气模式,但在模拟长时间尺度的气候方面仍然表现较好。     

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.     

Weekly cycle of meteorological parameters over Moscow region

Analysis of aerological radiosonde data in the period of 2000–2009 shows that, in the warm period of the year, the air temperature over Moscow region is higher in the first half of the week than in the second half. The statistically significant (at the α = 0.05 significance level) air temperature differences between Tuesday and Friday, as well as between Wednesday and Friday, reach 0.8°C and are manifested in the atmospheric boundary layer (according to nighttime observations) and in the middle troposphere (according to daytime observations). In the upper troposphere, the weekly temperature cycle positively correlates with the weekly cycle of air pressure, while in the lower troposphere, it positively correlates with the weekly cycle of water vapor content. In the upper troposphere, the southerly wind is strengthened in the middle of the week, and northerly wind is strengthened on the weekend. In the boundary layer, the temperature changes induce the weekly cycle of the static stability of the atmosphere.     

内蒙古干旱半干旱带2012年“7·20”极端暴雨事件的特征及成因

2012年7月下旬, 处于内陆干旱-半干旱地带的内蒙古中-西部地区出现了有气象记录以来的极端降水事件, 使该区气象与气候预测面临新问题. 7月20日河套地区出现大范围暴雨天气, 其中两个台站日降水量超历史极值, 一个台站超历史阈值, 属极端天气事件. 利用常规及精细化监测资料和NCEP再分析资料对此次极端降水天气事件进行分析. 结果表明: 从天气背景看, 贝加尔湖低槽内冷空气侵入副高西侧的暖空气中, 在对流层低层激发出低涡系统, 低涡前侧的南风急流使南来水汽到达41°N以北, 并在河套地区聚集. 对流层低层水汽通量维持在8~10g·cm^-1·hPa^-1·s^-1, 大气比湿达12~17 g·kg^-1, 为极端降水事件提供了丰沛的水汽. 该事件是通过MCC强烈发展形成的, 河套西北部不断有中尺度对流系统MCS发展东移, 河套南部新生的β中尺度系统发展并入MCS中, MCS系统发展为中尺度对流复合体MCC, MCC中心的TBB值达-40~-83 ℃. 近地面雷达监测显示, 河套东北部、中部存在强雷达回波群, 回波群内对流单体中心的反射率因子均达到50~55 dbz, 构成超级对流单体. 地面上, 不断新生的中尺度辐合线长时间存在于河套东北部并促发对流性暴雨. 暴雨前期对流层低层增温作用显著, 中高层"干侵入"使大气不稳定能量进一步增加. 冷锋前暖空气强烈的上升运动促发了大气不稳定能量释放. 该事件很可能与当前全球变暖密切相关, 随着全球变暖, 北极冰量减少, 夏季风增强, 雨带北移, 使得中纬度内陆干旱-半干旱带发生前所未有的极端降水事件过程.     

季节性海冰驱动的冰期北大西洋“电容器”效应

第四纪冰期的千年尺度气候突变事件——Dansgaard-Oeschger Event (D-O事件),一直是古气候学领域关注的重点。近年来,数值模拟的研究发现,北大西洋副极地地区年际-年代际气候变率的振幅在D-O事件中的冰阶冷期远大于间冰阶暖期,这一现象为理解该区域海温代理指标的气候学意义提供了重要参考价值,但其动力机制尚不清晰。本文利用海气耦合气候模型(COSMOS),通过模拟氧同位素(MIS)3阶段的一个典型D-O事件过程,探讨了冰阶冷期北大西洋气候变率的放大机制。结果显示,北大西洋副极地海域的季节性海冰通过调控海气间热量交换,影响当地气候变率的幅度。冰阶期,热带暖水向北输送导致海洋次表层逐渐升温,削弱了表层-次表层海水的密度层结,有利于次表层暖水上涌,促进海冰融化及海表温度升高。这将激发出海平面气压的负异常,引起气旋式风切变,并通过Ekman抽吸作用加速表层-次表层海水的垂直混合,进一步促进次表层暖水的上涌。这一正反馈机制造成海洋次表层热量的迅速释放,海表温度快速升高。当次表层热量释放结束后,海表将无暖水补充,导致海表温度下降,海冰增多。该过程激发的海表气压正异常(即反气旋式风切变)将抑制垂直混合发生,促进次表层热量积累,为下一次放热过程提供条件。在间冰阶暖期,随着北大西洋季节性海冰消失,海气间热交换不再受海冰变化影响,海洋次表层与大气间的热交换始终处于准平衡态,气候变率的振幅显著下降。本研究结果显示,北大西洋季节性海冰的存在可以调控海洋次表层热量积累-释放的过程,产生“电容器”效应,这对理解冰期年际-年代际气候变率放大现象有重要启示意义。     

2009/2010年我国西南秋冬春连旱特征及其大气环流异常分析

利用中国逐日站点降水资料、逐日季风监测指数及逐日副热带高压指数、74项环流指数及NCEP/NCAR再分析资料, 分析了2009年秋季至2010年春季的秋冬春西南特大干旱过程中各指数及大气环流异常特征.结果表明: 自2009年10月底东亚冬季风建立以来, 至2010年春季, 东亚冬季风强度持续偏强, 加之西太平洋副热带高压较常年偏西偏南, 西南地区长期受副高控制, 气温持续偏高, 加之冷空气虽然总体偏强, 但主要控制我国北方地区, 造成冷暖空气在西南地区少有交汇, 致使降水偏少, 干旱发生发展. 印缅槽强度较常年偏弱, 来自印度洋、孟加拉湾以及南海的水汽条件不足, 向西南地区输送的来自南海和孟加拉湾两条水汽通道的水汽通量均较常年偏弱很多, 加之西南地区、特别是云南地区自2009年秋季以来, 长期处于下沉运动的正距平区, 造成这段时间西南地区干旱少雨, 旱情持续. 2009年9月El Niño事件全面爆发, 南海-西太平洋地区形成异常反气旋流场, 该反气旋流场较常年偏西偏南, 造成副高位置偏西偏南, 从而使得云贵高原及其周边的印度季风区的降雨量明显偏少;高原地区及南海、菲律宾附近及热带辐合带地区OLR异常对西太平洋副热带高压的变化有一定影响, 进而影响西南地区降水, 其内在机制还有待深入研究.     

中纬度海气相互作用研究进展

回顾了中纬度海气相互作用的研究现状,分析了长期以来该项研究进展缓慢的原因和近十几年来的研究成果,结果指出:中纬度海洋在全球气候变化中有着重要的作用;冬季中纬度海气相互作用的强信号是冷空气强度;中纬度海洋强暖流区海气能量交换异常对同期和后期(半年至一年)北半球范围内的大气环流型有重要影响;当冬季黑潮和湾流海域海洋对大气同时异常多或异常少加热时,易形成夏季长江中下游偏旱或偏涝的环流形势。最后还提出,深入研究中纬度海气能量系统异常对大气环流影响及其物理机制,是今后海气相互作用研究的重要内容,其结果将为短期气候预测提供理论依据。     

Inertial-Dissipation flux measurements over south Bay of Bengal during BOBMEX-Pilot experiment

This paper describes measurement of air-sea parameters and estimation of sensible and latent heat fluxes by the “Inertial-Dissipation” technique over south Bay of Bengal. The data were collected on ORV Sagar Kanya during BOBMEX-Pilot cruise during the period 23rd October 1998 to 12th November 1998 over south Bay of Bengal. The fluxes are estimated using the data collected through fast response sensors namely Gill anemometer, Sonic anemometer and IR Hygrometer. In this paper the analyses carried out for two days, one relatively cloud free day on November 3rd and the other cloudy with rain on November 1st, are presented. Sea surface and air temperatures are higher on November 3rd than on November 1st. Sensible heat flux for both the days does not show any significant variation over the period of estimation, whereas latent heat flux is more for November 3rd than November 1st. An attempt is made to explain the variation of latent heat flux with a parameter called thermal stability on the vapor transfer from the water surface, which depends on wind speed and air to sea surface temperature difference.     

Evolving ideas about the Cretaceous climate and ocean circulation

The Cretaceous is a special episode in the history of the Earth named for a unique rock type, chalk. Chalk is similar to modern deep-sea calcareous ooze and its deposition in epicontinental seas occurred as these areas became an integral part of the ocean. The shelf-break fronts that today separate inshore from open-ocean waters cannot have existed during the Late Cretaceous probably because the higher sea level brought the base of the wind-mixed Ekman layer above the sea floor on the continental margins.A second peculiarity of the Cretaceous is its warm equable climate. Tropical and polar temperatures were warmer than today. Meridional and ocean-continent temperature gradients were lower. The warmer climate was a reflection of higher atmospheric levels of greenhouse gasses, CO₂ and possibly CH₄, reinforced by higher water vapor content in response to the warmer temperatures. Most of the additional energy involved in the meridional heat transport system was transported as latent heat of vaporization of H₂0 by the atmosphere. Poleward heat transport may have been as much as 1 Petawatt (20%) greater than it is today. C₃ plants provided for more efficient energy transport into the interior of the continents.Circulation of the Cretaceous ocean may have been very different from that of today. It is impossible for large areas of the modern ocean to become anoxic, but episodes of local anoxia occurred during the earlier Cretaceous and became regional to global during the middle of the Cretaceous. The present ocean structure depends on constant wind systems, which in turn depend on stability of the atmospheric pressure systems forced by polar ice. During most of the Cretaceous the polar regions were ice free. Without polar ice there were seasonal reversals of the high-latitude atmospheric pressure systems, resulting in disruption of the mid- and high latitude wind systems. Without constant mid-latitude westerly winds, there would be no subtropical and polar fronts in the ocean, no well-developed ocean pycnocline, and no tropical subtropical gyres dominating ocean circulation. Instead the ocean circulation would be accomplished through mesoscale eddies which could carry warmth to the polar regions.Greater knowledge and understanding of the Cretaceous is critical for learning how the climate system operates when one or both polar regions are ice free.     

中国水汽输送年际和年代际变化研究进展

大气中的水汽输送对于全球的水分循环、气候系统、生态环境等具有重要意义。水汽输送是影响中国旱涝空间分布的重要因素，其年际和年代际变化与厄尔尼诺-南方涛动、海温、北大西洋涛动、太平洋年代际涛动等因素对东亚大气环流的调控作用有关。本文就近期关于中国地区水汽输送年际和年代际变化的部分研究工作进行了回顾和评述，包括影响中国东部降水年际和年代际变化的水汽输送机制、影响梅雨特征年代际变化的水汽输送机制、热带海温对中国上空水汽输送的影响机制等问题。此外，本文回顾了近期与青藏高原地区水汽输送机制有关的研究进展。