Marine Atmospheric Boundary Layers Associated with Summer Monsoon Onset over the South China Sea in 1998

The variations of the marine atmospheric boundary layer (MABL) associated with the South China Sea Summer Monsoon were examined using the Global Positioning System (GPS) sounding datasets obtained four times daily during May-June 1998 on board Research Vessels Kexue 1 and Shiyan 3. The MABL height is defined as the height at the lowest level where virtual potential temperature increases by 1 K from the surface. The results indicate that the MABL height decreased over the northern South China Sea (SCS) and remained the same over the southern SCS, as sea surface temperature (SST) fell for the northern and rose for the southern SCS after the monsoon onset. Over the northern SCS, a decrease in both the SST and the surface latent-heat flux after the onset resulted in a reduction of the MABL height as well as a decoupling of MABL from clouds. It was found that MABL height reduction corresponded to rainfall occurrence. Over the southern SCS, a probable reason for the constant increase of SST and surface heat flux was the rainfall and internal atmospheric dynamics.

The Effect of the East China Sea Kuroshio Front on the Marine Atmospheric Boundary Layer

Various satellite data,JRA-25(Japan reanalysis of 25 years) reanalyzed data and WRF(Weather Research Forecast) model are used to investigate the in situ effect of the ESKF(East China Sea Kuroshio Front) on the MABL(marine atmospheric boundary layer).The intensity of the ESKF is most robust from January to April in its annual cycle.The local strong surface northerly/northeasterly winds are observed right over the ESKF in January and in April and the wind speeds decrease upward in the MABL.The thermal wind effect that is derived from the baroclinic MABL forced by the strong SST gradient contributes to the strong surface winds to a large degree.The convergence zone existing along the warm flank of the ESKF is stronger in April than in January corresponding to the steeper SST(sea surface temperature) gradient.The collocations of the cloud cover maximum and precipitation maximum are basically consistent with the convergence zone of the wind field.The clouds develop higher(lower) in the warm(cold) flank of the ESKF due to the less(more) stable stratification in the MABL.The lowest clouds are observed in April on the cold flank of the ESKF and over the Yellow Sea due to the existence of the pronounced temperature inversion.The numerical experiments with smoothed SST are consistent with the results from the ovservations.

Study on Clouds and Marine Atmospheric Boundary Layer

A set of remote sensing instruments of Peking University, which includes mainly a dual-channel(22.235GHz and 35.5GHz) microwave radiometer, a 8mm microwave and a 5mm microwave radiometer, has been developed for the Western North-Pacific Cloud-Radiation Experiment (WENPEX). The instruments were used to observe the cloud and marine atmospheric boundary-layer in the southwest sea area of Japan in winter time from 1989 to 1991.In the weather change process, the characteristics of the marine atmospheric boundary-layer and liquid water content in cloud of this area in winter time are studied from observation data. A one-dimensional mixed layer model is presented for the growth and evolution of a cloud-topped marine boundary-layer. The model is used to study in the WENPEX. The simulation results are in agreement with observation data, especially the integral water in cloud.

The concentration and distribution of dimethyl sulfide in the marine atmospheric boundary layer near the equator

A one-dimensional photochemical model with parameterized vertical eddy diffusion is used to simulate the dimethyl sulfide (DMS) in the marine atmospheric boundary layer near the equator. The boundary condition of theDMS flux over sea surface is assigned from gas exchange models that deped on sea surface wind speed and DMS concentration in surface water. Photolysis rates at various altitudes are calculated as a function of Solar zenith angle, andthe radiation calculation includes ozone absorption,surface reflection and molecular scattering.The simulated results of the DMS diurnal cycle are in good agreement with the observations. Sensitivity tests ofthe model indicate that the concentration of the DMS in the marine surface layer appears to be affected by a combination of chemical processes and meteorological conditions. In addition, photochemical processes are rather important.The reaction of the DMS with OH radical, the heterogeneous conversion of SO2 and the deposition of NSS-SO andthe methanesulfonic acid (MSA) are critical factors of controlling the DMS, SO2, NSS-SO and the MSA concentrations and distributions in the atmosphere.The DMS concentration in air is directly proportional to surface windspeed, but it is inversely proportional to boundary layer height in the convective boundary layer. The distributions ofthe DMS concentrations in air are strongly influenced by atmospheric stratification in stable conditions.

Structures and Characteristics of the Windy Atmospheric Boundary Layer in the South China Sea Region during Cold Surges

An observational analysis of the structures and characteristics of a windy atmospheric boundary layer during a cold air outbreak in the South China Sea region is reported in this paper. It is found that the main structures and characteristics are the same as during strong wind episodes with cold air outbreaks on land. The high frequency turbulent fluctuations （period 〈 1 min） are nearly random and isotropic with weak coherency, but the gusty wind disturbances （1 rain〈period 〈 10 min） are anisotropic with rather strong coherency. However, in the windy atmospheric boundary layer at sea, compared with that over land, there are some pronounced differences： （1） the average horizontal speed is almost independent of height, and the vertical velocity is positive in the lower marine atmospheric boundary layer; （2） the vertical flux of horizontal momentum is nearly independent of height in the low layer indicating the existence of a constant flux layer, unlike during strong wind over the land surface; （3） the kinetic energy and friction velocity of turbulent fluctuations are larger than those of gusty disturbances; （4） due to the independence of horizontal speed to height, the horizontal speed itself （not its vertical gradient used over the land surface） can be used as the key parameter to parameterize the turbulent and gusty characteristics with high accuracy.

Atmospheric mercury over the marine boundary layer observed during the third China Arctic Research Expedition

TGM measurements on board ships have proved to provide valuable complementary information to measurements by a ground based monitoring network.During the third China Arctic Research Expedition （from July 11 to September 24,2008）,TGM concentrations over the marine boundary layer along the cruise path were in-situ measured using an automatic mercury vapor analyzer.Here we firstly reported the results in Japan Sea,North Western Pacific Ocean and Bering Sea,where there are rare reports.The value ranged between 0.30 and 6.02 ng/m 3 with an average of （1.52 ± 0.68） ng/m 3 ,being slightly lower than the background value of Northern Hemisphere （1.7 ng/m 3 ）.Notably TGM showed considerably spatial and temporal variation.Geographically,the average value of TGM in Bering Sea was higher than those observed in Japan Sea and North Western Pacific Ocean.In the north of Japan Sea TGM levels were found to be lower than 0.5 ng/m 3 during forward cruise and displayed obviously diurnal cycle,indicating potential oxidation of gaseous mercury in the atmosphere.The pronounced episode was recorded as well.Enhanced levels of TGM were observed in the coastal regions of southern Japan Sea during backward cruise due primarily to air masses transported from the adjacent mainland reflecting the contribution from anthropogenic sources.When ship returned back and passed through Kamchatka Peninsula TGM increased by the potential contamination from volcano emissions.

Marine-Atmospheric Boundary Layer Characteristics over the South China Sea During the Passage of Strong Typhoon Hagupit

The structures and characteristics of the marine-atmospheric boundary layer over the South China Sea during the passage of strong Typhoon Hagupit are analyzed in detail in this paper. The typhoon was generated in the western Pacific Ocean, and it passed across the South China Sea, finally landfalling in the west of Guangdong Province. The shortest distance between the typhoon center and the observation station on Zhizi Island （10 m in height） is 8.5 km. The observation data capture the whole of processes that occurred in the regions of the typhoon eye, two squall regions of the eye wall, and weak wind regions, before and after the typhoon’s passage. The results show that： （a） during the strong wind （average velocityˉu≧10 m s？1） period, in the atmospheric boundary layer below 110 m, ˉu is almost independent of height, and vertical velocity ˉw is greater than 0, increasing with ˉu and reaching 2–4 m s？1 in the squall regions;（b） the turbulent fl uctuations （frequency＆gt;1/60 Hz） and gusty disturbances （frequency between 1/600 and 1/60 Hz） are both strong and anisotropic, but the anisotropy of the turbulent fl uctuations is less strong;（c） ˉu can be used as the basic parameter to parameterize all the characteristics of fl uctuations;and （d） the vertical fl ux of horizontal momentum contributed by the average fl ow （ˉu＆#183; ˉw） is one order of magnitude larger than those contributed by fl uctuation fl uxes （u＆#39;w＆#39; and v＆#39;w＆#39;）, implying that strong wind may have seriously disturbed the sea surface through drag force and downward transport of eddy momentum and generated large breaking waves, leading to formation of a strongly coupled marine-atmospheric boundary layer. This results in ˉw ＆gt; 0 in the atmosphere, and some portion of the momentum in the sea may be fed back again to the atmosphere due to ˉu ＆#183; ˉw＆gt;0.

一次层积云发展过程对黑潮延伸体海洋锋强迫的响应研究——观测与机制分析

由于缺乏海上现场观测,对天气尺度扰动下,海表面温度锋(海洋锋)对海洋大气边界层(MABL)垂直结构和MABL内海洋性低云(marine stratus)的影响研究较少。2014年4月12日,中国海洋大学东方红2号科学考察船在黑潮延伸体海区的海洋锋附近捕捉到一次层积云的迅速发展。在比较稳定的天气形势下,由暖水侧向北穿越海洋锋时,云底和云顶高度升高,云区范围迅速扩大。本文利用多种大气—海洋联合观测数据,结合卫星观测和再分析资料,对此次层积云迅速发展的机理进行了综合分析。结果表明,在海上低压后部西北风控制下,在海洋锋的暖水侧(下风方)形成热通量大值中心和低压槽,有助于高空西风动量下传,进而又使得海气界面热通量增加,这种正反馈效应为MABL内混合层厚度加大和云底/顶高度在海洋锋的下风方升高提供有利背景条件。4月12日09:00~12:00(协调世界时),来自日本本州岛陆地的低空暖平流到达该热通量中心上空,暖平流与热通量中心的共同作用,导致该时段近海面暖中心强度异常增加,MABL中静力不稳定层加深和低压槽发展,综合作用的结果使得混合层厚度明显加深,云底高度升高,云区迅速发展。本研究有助于理解在复杂大气背景扰动下MABL对海洋强迫的响应机理。

蒸发波导模型特征及其适用性研究

蒸发波导是海面上经常出现的大气结构,实时获取蒸发波导环境下的大气折射率剖面,对于海上运作的雷达、通信、导航等系统效能发挥具有重要意义。通常通过测量近海面高度上的空气温度、湿度、风速和气压,以及海面温度,采用蒸发波导模型来确定蒸发波导环境下的大气折射率剖面。针对目前不同蒸发波导模型在相同大气条件下波导高度预测结果存在差异的问题,对5种蒸发波导模型进行了模型误差敏感性分析,同时基于铁塔平台实测水文气象数据计算的蒸发波导高度与不同模型预测的高度进行了比较,给出了不同大气稳定性条件下蒸发波导模型使用建议,所得结果对海上蒸发波导环境下的电波传播特性计算以及蒸发波导的预报具有一定的指导意义。

一次春季黄海海雾和东海层云关系的研究

结合多种观测数据和数值模拟结果对2011年3月12—13日的一次黄海海雾过程进行分析。观测数据分析表明:此次黄海海雾过程与东海层云之间存在密切的联系。地面高低压位置为水汽从层云区向北输送提供了有利的环流条件;黄海上空天气尺度下沉运动,加强了海洋大气边界层(MABL)层结的稳定性,MABL顶自南向北高度降低,有利于水汽在向北输送过程中不断向海面聚集;下沉导致的干层以及逆温层对海雾的发生发展起重要作用。模式结果进一步证明天气尺度下沉运动与MABL内的下沉在29°—30°N附近同位相叠加,使得该海区上空的下沉运动明显增强,边界层高度迅速下降。下沉可能会导致气块温度升高,云滴蒸发,来自层云区的水汽随流场向北向下输送逐渐接近冷海面凝结成雾,近海面水汽的平流输送使海雾进一步向北发展。本研究为海雾预报提供新的参考思路。

一次层积云发展过程对黑潮延伸体海洋锋强迫的响应研究——数值模拟和试验

2014年4月12日,中国海洋大学东方红2号调查船在黑潮延伸体海区由暖水侧向北穿越海洋锋时,捕捉到了一次层积云云底和云顶高度升高的过程。本文利用船测数据结合WRF模式进行数值模拟和试验,对此次层积云迅速发展的机理进行了综合分析。结果显示,在黑潮延伸体区域,西北风控制下,海洋锋和来自日本本州岛陆地的低空暖平流共同作用使得层积云发展。通过数值试验发现,海洋锋作为背景场,为该区域提供了200W·m^(-2)的潜热通量并导致气压下降,从而在暖水侧产生了0.05m·s^(-1)的上升运动。同时,来自日本本州岛陆地的暖平流作为日尺度扰动,在09-12UTC到达潜热通量中心,导致该时段该区域2~3℃的增温和0.5hPa的降压。但两者并非单纯线性叠加,而是在海洋锋提供背景条件的前提下,暖平流产生触发作用,通过局地海气相互作用,使得该时段该区域垂直运动异常增强,进而造成云的异常发展。本研究有助于理解在复杂大气背景扰动扰动下MABL对海洋强迫的响应机理,同时对于理解海洋对边界层的影响又反馈到海洋的过程有一定帮助。

1998年季风爆发期南海大气边界层的日变化

在南海尚未有关于海洋大气边界层结构日变化方面的研究。研究海洋大气边界层,有利于我们更好地研究海洋表层结构变化影响机制,对发生在海洋大气边界层上的过程进行预测预报。因此了解南海海洋大气边界层的结构特征,对于我们进一步了解南海天气尺度海气相互作用有非常重要的意义。通过对1998年在南海南部(6°15′N,110°E)和南海北部(20°29′39″N,116°57′48″E)的南海季风试验中定点科考船释放一天四次的探空观测资料分析得出,季风爆发前海洋大气边界层存在规则的日变化,在中午达到深厚。季风爆发后南海北部大气边界层日变化消失,南海南部依然明显。分析表明对其日变化起重要影响的是短波辐射;潜热输送对大气边界层高度日变化影响不大。与大气边界层厚度日变化相对应,南海南部边界层内水汽日变化明显,而南海北部较不明显。

黄海夏季海雾的边界层结构特征及其与春季海雾的对比

利用海上浮标站、高分辨率数字式探空仪等多种观测手段和三维中尺度模式，对2008年7月7-11日1次夏季黄海海雾过程的边界层结构特征进行了观测分析与数值模拟，并将结果与春季的黄海海雾个例进行对比。结果表明：（1）夏季海洋大气边界层（MABI，）中无强逆温层，静力稳定度较春季下降，有利于湍流的发展。加之水汽量较大，容易形成比较厚的雾（500m）；春季低空有明显逆温层，水汽供应量较少，但强稳定的层结可以使水汽局限于比较低的空中，形成比较薄的雾层（200m）。（2）在夏季风控制下，青岛近海海洋大气边界层（MABL）中高、低层气块均来自海洋上空，温湿属性差异不大，使得温度垂直差异较小；春季MABL中高、低层气块分别来自陆地和海洋，来自陆地的暖、干气流和海洋的冷却效应导致强逆温层和雾区上方干层的出现。（3）夏季海雾的含水量大，水汽在凝结成雾的过程中放出更多的凝结潜热，雾中的海表面气温（SAT）明显高于海表面水温（SST）；春季雾顶强烈的长波辐射冷却和湍流混合使雾中气温明显下降，雾中SAT与SST更加接近，甚至出现SAT小于SST。以上结果有助于对海雾形成机制的认识。

湍流影响下的近海面大气折射率剖面

海上近地层大气折射剖面是影响海上舰船雷达低空探测的主要因素,通常不考虑大气湍流的影响往往导致雷达探测误差较大。基于海洋大气近地层相似理论,给出了利用近海面气象参数和海面温度确定平均大气折射指数和脉动折射率剖面的方法,建立了考虑湍流影响的近海面大气折射率剖面模型,并进行了数值模拟和初步的试验验证。建立的近海面大气折射率剖面模型对于近海面电波传播的准确预测和提高雷达系统的性能具有一定的指导意义。

大气对黑潮延伸区中尺度海洋涡旋的响应——冬季暖、冷涡个例分析

采用动态合成、带通滤波等方法,通过对冬季黑潮延伸区暖、冷两个中尺度海洋涡旋的分析,研究了大气对中尺度海洋涡旋的响应特征。结果表明,海表温度(SST)与近海面风速的正相关关系在涡旋的动态合成图上清晰可见,暖(冷)涡上空对应10 m风速的极大(小)值,即海洋对大气的强迫作用在日时间尺度上表现显著;SST高低值中心基本对应10 m风无辐散区,暖(冷)涡上空为异常正(负)涡度分布;暖(冷)涡上空潜热、感热通量增大(减小),降低(增大)大气稳定度,从而加强(减弱)边界层垂直混合作用,使得海洋大气边界层增厚(变薄)。暖(冷)涡旋上空对应摩擦速度极大(小)值,反映了湍流粘性力在高(低)海温中心增大(减小)的特征,表明动量垂直混合机制在中小尺度海气相互作用中起着主要作用。中尺度海洋涡旋能够影响大气瞬变扰动,大气瞬变扰动强度在暖(冷)涡下游上空出现极大(小)值,该影响不仅表现在海洋大气边界层,在自由大气中低层也有较为清晰的反映。此外,从能量转换的角度入手,发现斜压能量转换在中尺度海洋涡旋影响大气瞬变扰动强度中贡献明显。

海上大气折射率的相似性研究

基于边界层相似理论,通过数值模拟的方法研究了大气折射率的相似性,数值模拟结果显示大气折射率在不稳定大气条件和近中性条件下大气折射率近似满足相似理论,在稳定大气条件下大气折射率不满足相似理论假设。其次通过气象梯度塔测量的水文气象参数计算的大气折射率剖面和开路涡度系统测量的数据计算的相似性特征量,实验研究了大气折射率的相似性,研究也表明大气折射率在稳定大气条件下不满足相似性。

海面状态参数化对海上大气边界层数值模拟的影响研究

由于海上大气边界层的下垫面是复杂多变的海面,因此海面状态的参数化对海上大气边界层数值模拟起到十分关键的作用。采用高分辨的大气边界层模式进行敏感性试验研究,讨论了不同海面参数化方案对海上大气边界层数值模拟产生的影响。结果表明:几种海面粗糙度参数化方案在中低风速下模拟垂直结构主要的差异出现在边界层和自由大气分界面上;考虑到波浪的等海面状况的影响,应使用包含海面状况的参数化方案来模拟海上大气边界层。

浪花和飞沫水滴在海面大风边界层中的垂直传输

对我们在南海海域建立的大气边界层观测站的资料进行分析表明,在冷涌和热带气旋(包括强台风)过境的大风期间,在边界层底层10 min平均的水平风速ū基本不随高度而变,甚至大都伴随有明显的上升气流。而且风场脉动中含有强相干性的阵风扰动(vg,频率位于1/60~1/600 Hz频段),以及近于随机性的高频湍流脉动(v_t,频率大于1/60 Hz),它们的特性以及都可以很好地用水平风速ū来参数化表示。取实测的(ū,)和脉动v′=v_g+v_t,或取实测的ū与参数化的v_g、v_t和,应用拉格朗日随机模式作数值模拟,结果表明:由破头浪发射出来的浪花和飞沫水滴(半径r_p为10~500μm)有相当大的一部分可以飞离大气底层而进入100 m高以上的大气中,继而对进入大气中的海盐气溶胶通量有重要贡献,不可以被忽略。在水滴的垂直传输过程中,阵风扰动起了极重要的作用,而在>0且较显著时更起重要作用。我们对上扬率(可上升至100 m以上高度的水滴数与由海面发射出的水滴数之比)作出了初步的参数化公式,有很高的精度,主要的参量是无量纲量ū~2/(r_gp),其中r_p和g分别是水滴半径和重力加速度。

星载SAR在海气边界层气象学中的应用研究

SAR(Synthetic Aperture Radar,合成孔径雷达)作为一种现代高空间分辨率成像侧视雷达,对地球表面海洋所成的图像中蕴含了极为丰富的中尺度及亚中尺度海洋大气边界层的信息,因此对边界层气象学研究有着非常重要的意义。但是,使用SAR研究海气边界层这一涵盖微波遥感、气象学及海洋学等学科的科学前沿课题在国内却少有文献报道。在此背景下,首先介绍了SAR反演海洋大气边界层的研究概况,回顾了SAR反演海气边界层参数的原理和方法。然后以2002年5月7日当地时间10时53分ERS-2卫星获取的香港地区(22.097°N,E 114.300°E)SAR海洋图像为例,进行了反演风向风速的初步试验,最终获得了较高精度的风矢量。具体过程如下:先对SAR图像进行预处理,包括ADC(Analog Digital Converter,模数转换器)补偿、精确校准及斑点滤波等过程;然后利用经典的谱分析方法求得具有180°模糊度的风向,再用香港天文台气象浮标实测资料消除这一不确定性得到了真实的相对风向;紧接着利用CMOD4地球物理模式函数计算得到了海面上10 m高的风速。与气象浮标站所记录的平均风速和风向比较,两个20 km×20 km大小的试验区域求得的风向误差分别为23.71°和7.00°,平均风速误差分别为0.18 m/s和-0.12 m/s。结果表明,如果对SAR预先进行严格的预处理,结合经典的谱分析方法和CMOD4模型,即可获取高精度的风矢量。这一结果为今后海洋大气边界层的研究奠定了良好的基础。

南海季风试验期间海面低层大气过程的初步数值模拟试验

采用一维高分辨率大气边界层模式(OSUPBL),模拟了南海海面低层大气,得到高分辨率的海面低层大气的各种气象要素及界面通量和能量平衡关系,并将模拟结果和南海季风试验(SCSMEX)观测结果和日本气象厅(J MA)再分析资料进行对比分析。结果指出,OSUPBL模式模拟得到的海面大气边界层的风速、温、湿垂直廓线,大气边界层高度以及海表面短波辐射、长波辐射、感热、潜热通量、净辐射和海面热收支等与实际观测结果基本一致。