东中国海黑潮海洋锋的季节变化特征及其成因

利用高分辨率海洋和大气再分析资料研究了东中国海黑潮海洋锋的季节变化特征及其成因。研究表明,东海黑潮海洋锋存在明显的季节变化,从冬季到次年春季逐渐增强,并在春季达到最强,初夏以后强度逐渐减弱,9—10月达到全年最弱。通过诊断混合层热流量方程发现,东海黑潮区一年四季均表现为暖的温度平流,有利于海洋锋的形成和维持,该暖平流也存在季节变化并在春季达到最大,对海洋锋在春季达到最强起了重要作用。海气界面净热通量在秋冬季对海洋锋的形成有促进作用,有利于海洋锋增强,而在春夏季则起抑制作用,促进海洋锋消亡。温度垂直输送全年对海洋锋起一定程度的抑制作用。总之,在海温水平平流和海表净热通量的共同作用下导致海洋锋春季达到最强,而夏秋季海表净热通量和温度垂直输送作用的共同作用致使海洋锋减弱并最后消失。因此,海洋的动力和热力共同作用导致了东海黑潮海洋锋的季节变化,其中海温水平平流和海表净热通量对海洋锋的季节变化起主要作用,而温度垂直输送项对海洋锋的发展起抑制作用,但影响相对较小。     

两例强海洋气旋的诊断分析

本文介绍了北美东海岸两例(1972年11月16—18日和1982年1月9—11日)强海洋气旋的诊断分析。这两例气旋都沿一强低层斜压带生成,而且它们也都随一接近的对流层高空短波槽而加深。1972年11月16—18日的风暴沿卡罗来纳海岸线,在低层辐合加强和气旋性涡旋的形成有利于早期气旋生成医前方发展起来,在气旋的东北部有效的海洋加热和水汽通量有助于低层斜压性的加强和气旋路径上暖湿气团的不稳定。当地面低压上游大约300公里处有一普通的对流层中部低槽存在时,气旋开始爆发性加深(35百帕/12小时)。应注意的是,在气旋开始加深阶段,其中心附近有很强的对流和内部特别大的气压梯度,表明非绝热过程在其急剧发展阶段的作用。1982年1月9—11日气旋的形成和加深对对流层中上部旺盛的低压槽/较强的急流系统以及大尺度斜压性的反应,比1972年11月的气旋要强一些。除气旋后部,海洋热通量一般都很小。当气旋爆发性加深时,没有大范围的对流和对流不稳定。1982年的风暴强度达到峰值时是在冷水区,而1972年的风暴达到最大强度时,是在墨西哥湾流的暖水区。在1982年的个例中,上层锋生可以有助于对流层上部低压槽加强和使在下游发展。     

利用一个海气耦合模式对台风Krovanh的模拟

采用中尺度大气模式MM5和区域海洋模式POM构造了中尺度海气耦合模式, 模拟了Krovanh (0312) 台风过程中台风－海洋相互作用, 分析了台风引起的海面降温影响台风强度的机制和海洋对台风响应的特征。试验结果显示: 考虑台风引起的海面降温使台风强度模拟有了较大改进, 模拟的台风中心气压和近中心最大风速均与实况较符合。POM模拟的海表面温度与TRMM/TMI观测的海表面温度也较为一致, 台风Krovanh在其路径右侧95 km处引起较大的海面降温, 最大降温幅度达5.8℃。与海表面温度降低相对应的是混合层深度的增加, 较大的海面降温对应较大的混合层加深, 表明大风夹卷在海表面温度的降低中起主要作用。分析表明, 台风引起的海面降温降低海洋向大气输送的潜热通量和感热通量, 特别是在台风内核区, 平均总热通量减少了32.1%。热通量的减少使得湿静力能及湿静力能径向梯度减小, 削弱了台风强度。     

一次黑潮海洋锋强迫下的蒸发波导突变性与非均匀性的观测与模拟研究

蒸发波导是影响海上雷达系统探测性能的主导机制,海表温度（SST）锋带来的蒸发波导非均匀性和突变性具有重要的研究价值。2018年春季航次“海气相互作用观测试验”,曾两次穿越黑潮海域获取了珍贵的观测资料。在此基础上,结合欧洲中期天气预报中心（ECMWF）再分析资料（ERA-Interim）和HYSPLIT（Hybrid Single Particle Lagrangian Integrated Trajectories）气块轨迹溯源,分离出两个重要的走航观测时段。S1段（持续约21 h）气流从暖海水区吹向冷海水区,以稳定层结为主,其间因黑潮海洋锋的存在,气流由黑潮主体的暖水区吹向大陆冷海区时,形成具有强逆温层的海洋边界层,并伴随海雾的生成,导致此处蒸发波导高度突降为0。此后为持续近66 h的S2段,气流由冷海水区吹向暖海水区,以近中性弱不稳定层结为主,蒸发波导高度基本维持在12 m高度。数值模拟结果表明,模拟时段内的黑潮海洋锋区,蒸发波导高度突变性和非均匀性始终存在,且伴随暖海水吹向冷海水的锋区突变性更强。黑潮海洋锋对蒸发波导的这种天气尺度强迫作用的加强与层结稳定度的突变和海雾的生成有关。      

海表面盛行风背景下大气对黑潮海洋锋的响应特征

采用一系列高分辨率的卫星资料,应用高通滤波等方法,研究了春季不同海表面盛行风背景下,东海黑潮海洋锋区附近的海气关系。观测分析表明:在东海,春季3种不同海表面盛行风条件下海表面温度与海表面风速之间都存在明显的正相关关系,表现为海洋对大气的强迫作用。大气对海洋锋的响应在3种不同盛行风条件下也存在明显的差异。在西北盛行风和东南盛行风背景下,即当风向垂直于海洋锋由冷侧(暖侧)吹向暖侧(冷侧)时,海表面风的辐散(辐合)出现在海洋锋上空。同时,海洋锋对海平面气压(SLP)、降水和对流活动的影响较弱,表明大气对海洋锋的响应主要局限在大气边界层内。在东北盛行风背景下,即当风平行于海洋锋时,在海洋锋的暖(冷)水侧上空为海表面风的辐合(辐散),并与SLP的异常低(高)值相对应,主要雨带出现在黑潮暖舌上空。无论从总降水还是层云、对流降水频次的空间分布来看,盛行东北风时,海表面温度对其上雨带的影响最为明显。分析结果还表明,在不同盛行风背景下,海洋锋附近的海气关系由不同的物理机制在起主导作用。当盛行平行于海洋锋的东北风时,主要由SLP调整机制起作用;而盛行垂直于海洋锋的西北风时则主要由垂直混合机制起作用。     

台风"凤凰"强降水过程中的波作用诊断分析

介绍了“扰动热力切变平流参数”的概念,并基于此概念及波流相互作用的理论,对登陆台风“凤凰”2008年7月27日00:00－31日00:00(世界时)的暴雨过程进行了诊断分析.通过采用ARPS模式的资料,对波作用密度M和波作用通量散度▽·F进行计算,分析其与6h累积地面降水的关系.结果表明,波作用密度的异常值区始终覆盖观测雨区,二者在水平分布和时间演变趋势上比较相似,该波作用密度能够比较准确地综合表征强降水系统典型的动力场和热力场扰动的垂直结构,因而与降水系统的发生演变密切相关,其正高值区与观测的6h累积地面降水具有良好的对应关系.同时对波作用通量散度▽·F的分析表明,在登陆台风引发的暴雨过程中,非地转风位涡扰动和一阶扰动平流与动力场和热力场扰动梯度耦合项是影响扰动热力切变平流异常变化的主要强迫项.进一步分析表明扰动与基本态的交换主要是扰动热量平流交换,而扰动动量平流交换非常弱.     

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。     

Ocean-to-Atmosphere Forcing in the Vicinity of the Sea Surface Temperature Front in the East China Sea—Seasonal Variations

采用一系列高分辨率的卫星资料研究了我国东部海区的海洋温度锋对局地大气的强迫作用及其季节变化.分析表明,当春季海洋锋增强时,海温与海表面风速之间存在明显的正相关关系,并且在海洋锋的暖(冷)侧形成海表风的辐合(辐散),表现为海洋对大气的强迫作用.海温对表面风场的影响程度与海洋锋的强度成正比,春季影响程度最大,夏、秋季最小.海洋锋对其附近的总降水、对流、层云降水均有影响,尤其在春季海洋锋暖侧的降水强度增大,对流降水的频次增多,“雨顶”高度也有明显的抬升.暖流对大气的影响不仅局限在边界层,其影响可达整个对流层.另外,分析发现对流降水对海温的响应比层云降水更加敏感.研究还表明,暖流上空高、低云呈现相反的年循环特点,冬季多0.5～2 km的边界层云,夏季多云底在10 km以上的高云.深对流云集中出现在3～6月,从冬季到初夏,30％以上的云量中心抬高了接近8km.春季和初夏在海洋锋的暖侧频繁地出现深对流活动.     

我国东部海洋温度锋区对大气的强迫作用——季节变化

采用一系列高分辨率的卫星资料研究了我国东部海区的海洋温度锋对局地大气的强迫作用及其季节变化。分析表明, 当春季海洋锋增强时, 海温与海表面风速之间存在明显的正相关关系, 并且在海洋锋的暖 (冷) 侧形成海表风的辐合 (辐散), 表现为海洋对大气的强迫作用。海温对表面风场的影响程度与海洋锋的强度成正比, 春季影响程度最大, 夏、秋季最小。海洋锋对其附近的总降水、对流、层云降水均有影响, 尤其在春季海洋锋暖侧的降水强度增大, 对流降水的频次增多, "雨顶" 高度也有明显的抬升。暖流对大气的影响不仅局限在边界层, 其影响可达整个对流层。另外, 分析发现对流降水对海温的响应比层云降水更加敏感。研究还表明, 暖流上空高、低云呈现相反的年循环特点, 冬季多0.5~2 km的边界层云, 夏季多云底在10 km以上的高云。深对流云集中出现在3~6月, 从冬季到初夏, 30%以上的云量中心抬高了接近8 km。春季和初夏在海洋锋的暖侧频繁地出现深对流活动。     

春季东海黑潮锋影响强对流的个例分析

利用卫星观测和再分析资料,研究了2018 年 4 月 30 日东海黑潮海面温度锋(黑潮锋)影响低云突破边界层发展为对流云团,并导致强降水的过程。结果表明：(1)29 日 12 时东海 500 hPa 上受短波槽控制,低空处于高低压之间的偏南气流中;黑潮锋大气边界层稳定,有利于低云发展。 (2)黑潮锋的暖水侧向大气不断输送热量和水汽,稳定性减弱;而冷水侧对大气的冷却作用显著, 大气稳定性增加。(3)经过约12 h 的调整,黑潮锋通过垂直混合机制强迫表层风速发生变化,在黑潮锋上空形成风速辐合,叠加背景辐合场,导致辐合明显增强。(4)受平流效应影响,黑潮锋上空大气增湿增温,抬升凝结高度降低。(5)潜热释放与低空辐合之间形成正反馈,最终导致对流云团发展,降水强度显著增强。     

The breakup of marine boundary-layer clouds over an inhomogeneous sea surface temperature field

This numerical study examines the breakup of marine atmospheric boundary-layer (MABL) clouds through various physical processes over an inhomogeneous sea surface temperature (SST) field. Three regimes are identified under which the cloud layer will break up. (A) advection of drier air into the MABL for the California case. (B) daytime absorption of solar radiation, occurring most easily over the cold water. (C) mesoscale fluctuations in the flow, producing holes in the cloud layer.The budget study of these three situations concludes that large-scale subsidence, solar radiation, local mesoscale advection, and inhomogeneous surface fluxes cannot be neglected in modeling cloud breakup. This study also confirms the belief that the mixing process alone induced by evaporative entrainment is generally insufficient to predict the breakup of the cloud layer.Sections of this paper are based on an extended abstract by the author and Dr. Steven Stage for the Ninth Symposium on Turbulence and Diffusion held at Riso, Denmark, 1990.     

1998年南海夏季风爆发前后的海洋上空大气边界层

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.     

Heat fluxes and roll circulations over the western Gulf Stream during an intense cold-air outbreak

Turbulence and heat fluxes in the marine atmospheric boundary layer (MABL) for the roll vortex regime, observed during the Genesis of Atlantic Lows Experiment (GALE) over the western Gulf Stream, have been studied. The spectral analysis suggests that cloud streets (roll vortices) are vertically organized convection in the MABL having the same roll scale for both the cloud layer and subcloud layer, and that the roll spacing is about three times the MABL depth. The roll circulations contribute significantly to the sensible (temperature) and latent heat (moisture) fluxes with importance increasing upward. Near the MABL top, these fluxes are primarily due to roll vortices which transfer both sensible heat and moisture upward in the lower half of the convective MABL. Near the MABL top, the roll circulations transfer sensible heat downward and moisture upward in the clear thermal-street region, but roll vortices influenced by evaporative cooling can transfer sensible heat upward and moisture downward in the cloud-street region. Near the cloud-top, the upward buoyancy flux due to evaporative cooling is highly related to the roll circulations near the inversion.For the lower half of the MABL, the normalized temperature flux decreases upward more rapidly than the humidity flux, which is mainly because potential temperature () increases slightly upward while humidity (q) decreases slightly upward above the unstable surface layer. The gradient production (associated with the gradient) is a source for the temperature flux in the unstable surface layer but changes to a sink in the mixed layer, while the gradient production (associated with the q gradient) acts as a source for the humidity flux in both the unstable surface and mixed layers. The results suggest that the entrainment at the MABL top might affect the budgets of temperature and humidity fluxes in the lower MABL, but not in the unstable surface layer.Caelum Research Corporation, Silver Spring, MD, 20901, U.S.A.     

2019年台风利奇马引发山东特大暴雨成因分析

利用地面观测资料、雷达资料、FY-2G卫星云图资料及欧洲中心细网格资料,对台风利奇马登陆北上引发山东特大暴雨的成因进行分析。发现:利奇马登陆北上过程中,冷空气先后从台风的西部、西南部与南部侵入至台风中心内部,使其暖心结构逐渐减弱,其变性时段发生在10日20:00至11日08:00。山东的特大暴雨主要出现在台风变性前12h至台风变性后6h。变性之前的暴雨主要是由于台风螺旋云带与高空槽尾部云系相叠加造成的,变性之后的暴雨则是由于冷空气侵入致使台风外围云系演变成强对流复合体造成的。变性之前,对流层内800～500hPa风速小,500～250hPa风速大,气层内有暖平流,整层的上升运动,降水以暖区对流降水为主;变性之后800～500hPa风速大,500～250hPa风速小,500hPa至地面是上升运动,以上为下沉运动,降水以斜压锋区附近的对流降水为主。当500hPa至地面气层内出现冷平流时,湿层变薄,降水趋于减弱。特大暴雨区出现在台风中心西北方向,与850hPa假相当位温锋区与水汽通量散度辐合大值区相吻合。     

Air mass modification over Lake Michigan

The modification of a relatively cold air mass over the warm water of Lake Michigan is studied by using a two-dimensional nonlinear mesoscale model. Considerable amounts of heat and water vapor are supplied from the water surface to the lower atmosphere by turbulent eddies. A convective mixed layer develops and grows toward the downwind region with stratocumulus clouds over the lake.The model simulates the warming and moistening of the mixed layer, the development of a boundary layer, the divergence and convergence of wind near the coastlines, and the turbulent fluxes.The model warming of the mixed layer across the lake was about 2.2 °K and the moistening of the mixed layer was about 0.8 g kg^–1, which are comparable to 2.7 °K and 0.8 g kg^–1 observed by Lenschow (1973). The convective boundary layer, which includes the cloud layer, subcloud layer, and superadiabatic layer near the water surface, is well simulated. The tilt of the inversion which coincides with the cloud top is also well reproduced. When a prescribed cooling rate is applied at the cloud top, stronger turbulence and a deeper cloud layer are generated. Without the cooling, the cloud is shallow and the shape of the cloud base is determined by surface conditions. The rise of the inversion is due to upward vertical motion, and deepening of the convective layer in the downwind region.     

河北省冬季低槽冷锋层状云结构特征和可播性分析

2018年1月6日河北省出现一次低槽冷锋天气系统,利用两次云粒子垂直探测资料分析层状云结构特征和演化规律,探讨冬季低槽冷锋系统层状云催化条件和催化时机。结果表明：天气系统初期西南风风速中心发生在6500 m高空时,风速随高度呈不连续分布,层状云云顶温度为-29.2℃,中低云层稀薄;3000 m以上云层粒子基本被冰化,云内过冷水含量小于0.05 g·m^-3,固态含水量为0.1 g·m^-3左右,3000 m以下云层有大量自然冰晶,过冷水低于0.15 g·m^-3,不具备催化条件。700—3000 m高度层西南风加强,云内过冷水含量普遍大于0.1 g·m^-3;2200 m风速中心风速达16 m·s^-1,该高度最大液态水含量达0.38 g·m^-3,冰晶浓度为6 L^-1,温度为-9℃,适宜催化。低槽冷锋天气系统层状云结构特征和催化条件受槽前西南风强弱和风速中心高度影响,天气系统初期层状云云顶过高、温度过低时,层状云为不可播云。随槽线东移,风速中心高度降低,3000 m以下西南风加强,层状云转变为可播云。     

基于北京多源资料的云宏观特征判识北大核心CSCD

获取准确的云高及其变化特征,对于揭示天气系统的演变以及改进气候模式具有重要作用。由于不同设备观测云高的不确定性,将锋区要素不连续变化理论引入云高分析中,将云底部、云顶部大气的交界过渡带区域视为云锋区,研究探空、毫米波雷达、风廓线雷达等不同类型设备观测要素在云锋区及云外环境大气的变化特征。对流云和层状云个例研究表明:在云锋区,温湿度及雷达反射率因子随高度的一阶、二阶导数均呈不连续现象(即一阶、二阶导数值在云内外和云锋区表现为不相等),风廓线雷达信噪比垂直梯度也出现突变,因此不同设备观测云高具有较好空间一致性,并得到云底和云顶高度的合理范围和相应判据;相对于层状云,对流云内外温度梯度差异以及云体内反射率因子二阶导数的脉动变化幅度均偏大,因此可作为区分二者的参考指标。     

Observed response of marine boundary layer cloud to the interannual variations of summertime Oyashio extension SST front

Active roles of both sea surface temperature (SST) and its frontal characteristics to the atmosphere in the mid-latitudes have been investigated around the western boundary current regions, and most studies have focused on winter season. The present study investigated the influence of the variation of the summertime Oyashio extension SST front (SSTF) in modulating low-level cloud properties (i.e., low-level cloud cover [LCC], cloud optical thickness [COT], and shortwave cloud radiative effect [SWCRE]) on inter-annual timescales, based on available satellite and Argo float datasets during 2003–2016. First, we examined the mechanism of summertime SSTF variability itself. The strength of the SSTF (S_SSTF), defined as the maximum horizontal gradient of SST, has clear inter-annual variations. Frontogenesis equation analysis and regression analysis for subsurface temperature indicated that the inter-annual variations of the summertime S_SSTF in the western North Pacific are closely related to the variations of not surface heat flux, but western boundary currents, particularly the Oyashio Extensions. The response of low-level cloud to intensified S_SSTF is that negative SWCRE with positive COT anomaly in the northern flank of the SSTF can be induced by cold SST anomalies. The spatial scale of the low-level cloud response was larger than the SST frontal scale, and the spatial distribution of the response was mainly constrained by the pathways of Kuroshio and Oyashio Extensions. Multi-linear regression analysis revealed that the local SST anomaly played largest role in modulating the SWCRE and COT anomalies among the cloud controlling factors (e.g., estimated inversion strength, air-temperature advection) accounting for more than 50% of the variation. This study provides an observational evidence of the active role of local SST anomalies in summertime associated with the western boundary currents to the oceanic low-level cloud.