冬季菲律宾周围对流活动与北太平洋风暴轴联系的数值模拟

通过利用IAP 2-L AGCM进行的数值模拟,进一步揭示了冬季菲律宾周围对流活动异常对北太平洋风暴轴变化的影响及其二者联系的物理机制和物理过程。结果表明:当菲律宾周围对流活动增强时,在500 hPa等压面图上强迫产生一个自赤道西太平洋开始,经我国东部、堪察加半岛、白令海,到美国西海岸的异常波列;位于西太平洋的经向三圈环流增强,位置北移;在风暴轴的西半部和东端斜压性增强;从而导致了北太平洋风暴轴增强、北抬、东伸。     

热带太平洋-印度洋海温异常综合模对南亚高压的影响

从综合考虑热带太平洋和印度洋海温异常特征出发,研究了热带太平洋-印度洋海温异常综合模对南亚高压的影响.当热带太平洋-印度洋海温异常综合模为正位相(西印度洋和东太平洋海温距平为正,东印度洋-西太平洋海温距平为负),南亚高压偏弱,位置偏东偏南;当热带太平洋-印度洋海温异常综合模为负位相(西印度洋和东太平洋海温距平为负,东印度洋-西太平洋海温距平为正),南亚高压偏强,位置偏西偏北.热带太平洋-印度洋海温异常综合模影响南亚高压主要通过三种机制:一是通过影响亚洲季风从而影响了降水潜热形成的大气加热场分布,在正(负)位相年,青藏高原大气热源为负(正)异常,因此青藏高原上空空气上升减弱(加强),南亚高压偏弱(偏强);南海季风和热带辐合带加强(减弱),菲律宾附近的大气热源加强(减弱),有利于上空青藏高原东南侧反气旋(气旋)式的距平环流,因此南亚高压偏东偏南(偏西偏北).二是热带太平洋-印度洋海温的纬向热力对比引起赤道纬向垂直(Walker)环流异常,必将引起高空纬向风异常,在正(负)位相年,南亚高压南部的印度洋高空会出现西(东)风异常,导致南亚高压偏弱(偏强).三是综合模的正(负)异常加强(减小)西印度洋经度范围的区域Hadley环流,其北侧伊朗高原上的异常下沉(上升)支,造成南亚高压偏弱(偏强),位置偏东偏南(偏西偏北).     

黑潮延伸体中尺度涡年代际变化与北太平洋风暴轴变化之间的关系

利用18年带通滤波的卫星高度计资料,通过引入黑潮延伸体中尺度涡能量(EKE)的面积指数,分析了黑潮延伸体中尺度涡EKE的强度和位置的年代际变化特征,并使用回归分析等方法分析了它们与北太平洋风暴轴之间的关系。结果表明,黑潮延伸体中尺度涡增强与北太平洋风暴轴的增强相对应,而EKE位置偏北(南)时对应的北太平洋风暴轴也偏北(南),同时当EKE的位置偏东(偏西)时北太平洋风暴轴则西退(东移)。此外,北太平洋风暴轴的变化对黑潮延伸体也可能有一定的反馈作用,黑潮延伸体中尺度涡EKE强度的变化与北太平洋风暴轴EOF第一和第三个模态(第二个模态)回归的海表面高度距平模态有明显的3~4年滞后的正(负)相关,而黑潮延伸体中尺度涡EKE位置的变化则相反。这种滞后相关可能是通过北太平洋风暴轴驱动的遥相关型环流改变海表面风应力旋度并强迫出的海表面高度距平的西传导致的。     

冬季北极涛动异常对北太平洋风暴轴的可能影响

基于美国国家海洋和大气局气候预测中心公报的北极涛动（Arctic Oscillation,AO）指数逐月数据以及美国国家环境预报中心和大气研究中心的1986—2017年逐日再分析资料等,运用回归和合成分析等方法,分析了北极涛动与北太平洋地区风暴轴的时间演变特征、两者之间的联系及AO异常影响风暴轴的可能机制。结果表明：1）风暴轴经度指数与纬度指数有显著正相关性,两者具有同步变化的特征,而这两者与风暴轴强度指数都呈负相关,但不显著。AO指数与北太平洋风暴轴强度呈显著正相关,且AO指数与风暴轴经度、纬度指数也呈正相关,但并不显著。2）在北极涛动强正（负）位相年份,风暴轴区域天气尺度滤波方差强（弱）、500 hPa高度场上东亚大槽减弱（加深）、急流偏北偏强（偏南偏弱）、扰动动能增强（减弱）、斜压性增强（减弱）。可能影响机制是,异常变化的AO影响东亚大槽,改变急流强度,使斜压性发生变化,进而对风暴轴产生影响。     

冬季北太平洋风暴轴的年际型态及其与大气环流的关系

利用NCEP/NCAR再分析资料,运用31点带通数字滤波、线性相关和合成分析方法,研究了1961/1962—2010/2011年冬季北太平洋风暴轴西部、东部区域强度指数的年际演变特征,划分了风暴轴的典型型态,并进一步探讨了与同期北半球500 hPa位势高度场和SLP的关系。结果表明:风暴轴气候态的极大值区域位于中纬度北太平洋中西部,最大值点的频数集中区域和均方差分布的异常中心都有两个。风暴轴西部和东部区域强度指数(WI和EI)的年际演变具有独立性,典型型态可分为单、双中心型两类。WI(EI)指数与北半球500 hPa位势高度场的相关分布类似于WP(PNA)遥相关型;单中心型风暴轴偏强时,极涡南扩,平均槽加深;呈双中心型时,极涡明显偏西。WI(EI)指数与SLP的相关分布类似于NPO(NAO)遥相关型;单中心型风暴轴偏强(弱)时,SLP距平场呈AO遥相关型的正(负)异常位相。     

卑尔根气候模式中亚洲—太平洋涛动和影响西北太平洋热带气旋频数的环流背景的关系

利用挪威卑尔根的全球大气-海洋-海冰耦合模式的300年气候态数值积分结果,结合观测资料,分析了夏季亚洲-太平洋涛动(APO)的年际变化对与西北太平洋热带气旋生成频数相关联的大尺度环流背景的影响。模式结果表明,当夏季APO异常偏强(弱)时,西太平洋副热带高压位置偏东(西)偏北(南),南亚高压位置偏北(南),西北太平洋低层大气异常辐合(辐散),高层大气异常辐散(辐合),对流活动加强(减弱)。这种环流背景条件有(不)利于西北太平洋热带气旋的发生发展,西北太平洋热带气旋频数因而偏多(少)。     

ENSO事件对冬季北半球太平洋风暴轴维持的影响

利用欧洲中期天气预报中心（ＥＣＭＷＦ）每日客观分析资料及美国大气研究中心（ＮＣＡＲ）再分析资料研究ＥＮＳＯ事件对简报北半球太平洋风暴轴维持的影响,结果表明,Ｅｌ、Ｎｉｎｏ（Ｌａ Ｎｉｎａ）年,风暴轴区域斜压性强（弱）,风暴轴位置向东（西）扩展（收缩）且强度强（弱）,与风暴轴发展有关的涡动热量通量和运量通量也同时增强（减弱）,由此揭示出ＥＮＳＯ事件对太平洋风暴轴的维持和发展有重要影响．     

夏季亚洲-太平洋涛动与中国近海热带气旋活动的关系

采用联合台风警报中心的台风最伟路径资料和NCEP/NCAR再分析资料,分析了夏季亚洲-太平洋涛动(Asian-Pacif-ic Oscillation,简称APO)与东亚近海-西北太平洋大气环流的关系,并进一步探讨了APO与中国近海热带气旋(tropical cy-clone,简称TC)活动的关系.研究表明:(1)夏季APO强弱与同期西北太平洋及中国东部近海TC活动存在密切关系,即在APO强(弱)年,西北太平洋TC活动偏西(东)和偏北(南),中国东部近海TC明显增多(减少);(2)当APO偏强(弱)时,中国东部近海大气环流有(不)利于TC的维持和发展,表现为低层存在异常气旋性(反气旋性)环流,对流层高低层纬向风垂直切变减小(增大),且对流加强(减弱);(3)APO强弱也影响着TC引导气流的方向:在APO强(弱)年,西北太平洋副热带高压(以下简称副高)偏北和偏东(偏南和偏西),副高南侧偏东气流减弱(加强),有利于TC的向西北行或在偏北(南)纬度西行,进入中国东部近海的TC增多(减少);(4)APO强弱也影响着南海-热带西太平洋TC源地上空的大气环流,在APO强(弱)年,南海-热带西太平洋季风槽偏北、偏西(偏南、偏东),热带西太平洋TC活动偏北和偏西(偏南和偏东),有利于进入中国东部近海TC的增多(减少).     

热带偶极型对流活动与东亚夏季风的联系

采用１９７９～１９９４年ＮＣＥＰ／ＮＣＡＲ再分析风场资料和ＯＬＲ资料,研究了热带对流的变化特征,讨论了热带对流年际变化与东亚夏季风的关联。指出：夏季热带对流存在以西太平洋暖池附近和赤道中太平洋附近中心的年际变化方差大值区,且这两个中心的充变化呈偶极型反位相振荡,这种偶极型对流活动与东亚夏季风有密切关系。当暖池附近对流偏强（弱）,赤道中太平洋附近对流偏弱（强）时,东亚夏季风偏强（弱）,雨带偏北（南）     

冬季北太平洋风暴轴异常及其与东亚大气环流的关系

利用NCEP/NCAR逐日再分析资料,应用滤波方差、相关分析、合成分析等研究了1963年冬季至2011年冬季北太平洋风暴轴的时空演变特征,并探讨了风暴轴活动强弱与东亚—北太平洋大气环流的关系。结果表明：与1980s后期风暴轴活动显著增强相比,近10 a来风暴轴活动又进入较气候平均水平偏低的阶段,且风暴轴主体位置有着向东北、西南两侧的振荡现象。风暴轴活动强（弱）年,东亚地区近地面温度偏高（低）、对流层低层阿留申低压和西伯利亚高压偏弱（强）、中国东部及日本上空850 hPa北风减弱（加强）;对流层中层东亚大槽减弱北缩（加深南进）、对流层高层西风急流减弱（加强）。风暴轴活动与冬季影响中国的冷空气活动次数相关关系显著。     

Future climate in the Pacific Northwest

Climate models used in the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4) on the whole reproduce the observed seasonal cycle and twentieth century warming trend of 0.8°C (1.5°F) in the Pacific Northwest, and point to much greater warming for the next century. These models project increases in annual temperature of, on average, 1.1°C (2.0°F) by the 2020s, 1.8°C (3.2°F) by the 2040s, and 3.0°C (5.3°F) by the 2080s, compared with the average from 1970 to 1999, averaged across all climate models. Rates of warming range from 0.1°C to 0.6°C (0.2°F to 1.0°F) per decade. Projected changes in annual precipitation, averaged over all models, are small (+1% to +2%), but some models project an enhanced seasonal cycle with changes toward wetter autumns and winters and drier summers. Changes in nearshore sea surface temperatures, though smaller than on land, are likely to substantially exceed interannual variability, but coastal upwelling changes little. Rates of twenty-first century sea level rise will depend on poorly known factors like ice sheet instability in Greenland and Antarctica, and could be as low as twentieth century values (20 cm, 8^″) or as large as 1.3 m (50^″).     

Salinity minimum in the tropical Pacific

It is shown that the salinity minimum at subsurface depths of the tropical Pacific is a local phenomenon. Characteristics of the salinity minimum are relative by absolute values and variable in time. It appears and disappears in the intertropical convergence zone according to variability of the freshwater budget sign. The salinity minimum appears during the negative phase of the freshwater budget on the background of the previous freshening of the sea surface. The salinity minimum at intermediate depths in both hemispheres is a single phenomenon of climatic time scale. At present, it exists at intermediate layers in the arid zones of both hemispheres due to the negative phase of the freshwater budget. This minimum is related to the Earth climate system variability at the geological time scale. Differences in its properties in the Northern and Southern hemispheres reflect differences in the freshwater budget values and the duration of their influence at the geological time scale.     

Salinity minimum in the North Pacific

Analyzed is the variability of seasonal salinity in the North Pacific. It is demonstrated that the formation and disappearance of salinity minimum in subsurface layers depends on the freshwater budget variability of different time scales. In general, the salinity minimum is a temporary phenomenon formed during the negative phase of freshwater budget, when the evaporation exceeds the precipitation. Seasonal variability of fresh water budget leads to the seasonal formation of salinity minimum on the boundary between the climatic zones. The existence of salinity minimum at intermediate depths in the tropics is caused by the negative phase of long-period variability of freshwater budget.     

Decadal atmosphere-ocean variations in the Pacific

Considerable evidence has emerged of a substantial decade-long change in the north Pacific atmosphere and ocean lasting from about 1976 to 1988. Observed significant changes in the atmospheric circulation throughout the troposphere revealed a deeper and eastward shifted Aleutian low pressure system in the winter half year which advected warmer and moister air along the west coast of North America and into Alaska and colder air over the north Pacific. Consequently, there were increases in temperatures and sea surface temperatures (SSTs) along the west coast of North America and Alaska but decreases in SSTs over the central north Pacific, as well as changes in coastal rainfall and streamflow, and decreases in sea ice in the Bering Sea. Associated changes occurred in the surface wind stress, and, by inference, in the Sverdrup transport in the north Pacific Ocean. Changes in the monthly mean flow were accompanied by a southward shift in the storm tracks and associated synoptic eddy activity and in the surface ocean sensible and latent heat fluxes. In addition to the changes in the physical environment, the deeper Aleutian low increased the nutrient supply as seen through increases in total chlorophyll in the water column, phytoplankton and zooplankton. These changes, along with the altered ocean currents and temperatures, changed the migration patterns and increased the stock of many fish species. A north Pacific (NP) index is defined to measure the decadal variations, and the temporal variability of the index is explored on daily, annual, interannual and decadal time scales. The dominant atmosphere-ocean relation in the north Pacific is one where atmospheric changes lead SSTs by one to two months. However, strong ties are revealed with events in the tropical Pacific, with changes in tropical Pacific SSTs leading SSTs in the north Pacific by three months. Changes in the storm tracks in the north Pacific help to reinforce and maintain the anomalous circulation in the upper troposphere. A hypothesis is put forward outlining the tropical and extratropical realtionships which stresses the role of tropical forcing but with important feed-backs in the extratropics that serve to emphasize the decadal relative to interannual time scales. The Pacific decadal timescale variations are linked to recent changes in the frequency and intensity of El Niño versus La Nina events but whether climate change associated with global warming is a factor is an open question.The National Center for Atmospheric Research is sponsored by the National Science Foundation     

Scale interaction in the Western Pacific Monsoon

Summary The lower-tropospheric scale interactions occurring in the summer monsoon of the western North Pacific are reviewed and summarised in a conceptual model. Diabatic heating produces a circulation with similar characteristics to those that are observed. In the lower troposphere the advection of vorticity by the divergent wind produces a compact, and more intense response than in the upper levels. Subsequent phase dispersion westward, and group propagation eastwards, lead to a monsoon depression in convectively suppressed conditions, a westerly jet with cross-equatorial flow, and a strong confluence region to the east of the monsoon depression.I suggest that this confluence zone traps tropical waves in the mid-lower troposphere in a similar manner to the accumulation and emanation mechanisms described by Chang and Webster. The details of the convection in the confluence zone are of little direct consequence to the monsoon circulation, which is similar in scale to the deformation radius for the undisturbed tropics. However, mesoscale convective systems can both self organise into larger coherent structures and produce vortices of horizontal scale 100–200 km, which are long-lived and potentially have considerable indirect influence on both the monsoon and embedded systems, such as tropical cyclones. The confluence zone provides an excellent environment for tropical cyclone formation, which is enhanced by the presence of a previously developed tropical cyclone. Scale-interaction arising from the merger of developing vortices and the large monsoon depression can lead to development of a very large typhoon and rapid breakdown of the total monsoon circulation. The interaction of tropical cyclones with the mid-latitude systems is complex and not well understood, but recurving tropical cyclones may provide a major component of the emanation of energy to higher latitudes.With 16 Figures     

Latent ice-forming nuclei in the Pacific Northwest

Some cloud condensation nuclei (CCN) constitute a reservoir of latent ice-forming nuclei (IFN) active by condensation-followed-by-freezing and by sorption. Evaporated droplets occasionally left aerosol particles that acted as sorption IFN at temperatures as high as −5°C and water vapor supersaturation over ice of 0.2%. The newly formed aerosol particles (residues of evaporated droplets) are all mixed particles. The discovery of IFN produced from CCN promotes new insights into the process of ice formation in clouds; in an evaporating parcel of a cloud the rate of formation of ice particles will be enhanced by continuous production of IFN. Aerosol particles left behind after evaporation of a cloud may provide a source of IFN for formation of some of the cirrus clouds.     

Dynamic Linkage between the North Pacific and the Tropical Pacific: Atmosphere-Ocean Coupling

In this study, dynamic linkage of atmosphere-ocean coupling between the North Pacific and the tropical Pacific was demonstrated using a large number of ensemble perturbed initial condition experiments in a fully coupled fast ocean-atmosphere model (FOAM). In the FOAM model, an idealized mixed layer warming was initiated in the Kuroshio-Oyashio extension region, while the ocean and atmosphere remained fully coupled both locally and elsewhere. The modeling results show that the warm anomalies are associated with anomalous cyclonic winds, which induce initial warming anomalies extending downstream in the following winter. Then, the downstream warming spreads southwestward and induces SST warming in the equatorial Pacific via surface wind-evaporation-SST feedback. Warming in the tropical Pacific is further reinforced by Bjerknes’ feedback.     

A multidecadal oscillation in the northeastern Pacific

研究表明北太平洋海洋内部模态能够通过海气相互作用导致气候系统振荡和全球气候响应。最好的例子就是太平洋年代际振荡(PDO),但是以往的研究中发现很多气候年代际变化现象用PDO没法给与很好的解释。本研究通过分析过去140年的资料发现北太平洋区域另外一个多年代际振荡模态,并将其定义为太平洋多年代际振荡(以下简称PMO),其表现为北太平洋白令海峡以南和阿拉斯加湾流区域海表面温度存在60年左右周期的异常偏高或者异常偏低。随着海温这一低频振荡的发生,全球气温、降水都表现出显著的年代际异常。更重要的是,PMO超前全球气温2–3年和海温3–7年发生转变。与此同时,北极涛动形态和大气环流随着PMO正负位相的转变也发生改变。由于PMO与全球温度有着很好的关系,因此PMO的发现对全球变暖趋势长时间尺度预报的改进有着重要作用。     

Impacts of the central and eastern Pacific types of ENSOon sea surface temperature in the South Pacific

The present study examines the relationship between two types of El Niño–Southern Oscillation (ENSO), the central Pacific (CP) ENSO and the eastern Pacific (EP) ENSO, and the sea surface temperature (SST) variability over the South Pacific (SP) (20° S–60° S, 145° E–70° W) using NOAA OI SST for the period 1982–2006. The SP SST variability associated with the two types of ENSO varies with season. These two types of ENSO can excite different atmospheric patterns associated with the Pacific–South American mode, through which they influence the SP SST variability. Both the surface turbulent air–sea heat fluxes and the heat advection by Ekman currents (i.e., Ekman heat fluxes) have an important impact on the SST variability. An analysis of the surface mixed layer heat budget indicates that the heat fluxes (the sum of turbulent heat fluxes and Ekman heat fluxes) can effectively explain much of the SST variability related to the two types of ENSO.     

Decadal change in relationship between western North Pacific tropical cyclone frequency and the tropical Pacific SST

In this study, we examine the relationship between the number of tropical cyclones (TCs) in the western North Pacific and the tropical Pacific sea surface temperature (SST) during the main TC season (July–November) for the period of 1965–2006. Results show that there are periods when TC frequency and the tropical Pacific SST are well correlated and periods when the relationship breaks down. Therefore, decadal variation is readily apparent in the relationship between the TC frequency and the SST variations in the tropical Pacific. We further examine the oceanic and atmospheric states in the two periods (i.e., 1979–1989 vs. 1990–2000) when the marked contrast in the correlation between the TC frequency and the tropical Pacific SST is observed. Before 1990, the analysis indicates that oceanic conditions largely influenced anomalous TC frequency, whereas atmospheric conditions had little impact. After 1990, there the reverse appears to be the case, i.e., atmospheric conditions drive anomalous TC frequency and oceanic conditions are relatively unimportant. A role of atmosphere and ocean in relation to the TC development in the western North Pacific changes, which is consistent with the change of the correlations between the TC frequency and the tropical Pacific SST.