斜压模、正压模和异常海温时间变化的位相关系

利用 1958- 1997共 4 0年 NECP/ NCAR再分析大气资料和 GISST海表温度资料集 ,研究了大气斜压模、正压模与海表温度变化这三者之间位相关系 ,并从大气动力学方程组解释了这些位相关系。指出 :大气斜压西风异常时间变化的位相落略微后于 SSTA的变化位相 ,而正压西风异常的变化位相则超前于SSTA变化位相。斜压纬向风异常的变化又超前于正压异常纬向风的变化。斜压纬向风异常与海表温度异常之间存在正相关关系 ,而异常正压纬向风与异常海表温度之间则存在负相关关系。斜压模的产生联系于热力强迫 ,而正压模的产生则归因于斜压扰动间的非线性相互作用。这些由动力和热力过程控制的位相关系包含着ENSO循环的可能机制。

正斜压模演变所揭示的武汉暴雨过程

对 1998年 7月 2 1— 2 2日发生在武汉附近的大暴雨过程的大气正、斜压分量演变过程进行了研究 ,结果表明 :大气流场正压分量的演变与此次大暴雨的酝酿、发展和消亡具有内在的联系 ;正压分量在暴雨区的演变在一定程度上反映高、低空急流耦合形势 ;正、斜压平均相对模的演变与暴雨生命史相吻合。

次天气尺度与中尺度正、斜压模演变揭示的武汉暴雨过程

利用滤波原理提取出大气流场中的次天气尺度和中尺度信息，再把大尺度和中尺度水平风场分别分解为正压分量（垂直平均）和斜压分量（扰动）流场。对1998年7月21～22日发生在武汉附近的强暴雨过程进行了次天气尺度与中尺度流场正、斜压分量演变特征的分析。结果表明：次天气尺度与中尺度流场正压分量的演变与此次强暴雨的酝酿、发展和消亡具有内在的联系；次天气尺度与中尺度流场高层200hPa斜压分量很强，低层850hPa正压分量很强；次天气尺度与中尺度流场斜压性占主导地位，随着暴雨的发展，中尺度流场的正压性减弱而斜压性进一步增强，而次天气尺度流场的正压性增强而斜压性减弱。以上结论对于揭示中尺度暴雨过程发生发展的本质有一定的意义。

ENSO循环与低纬度大气的正压和斜压运动

:利用一个 2层海洋模式和 GISST资料、NCEP再分析资料 ,对大气正压 /斜压运动与 ESNO循环之间的联系进行了研究。结果表明 ,在赤道中、东太平洋地区 ,大气斜压模在 ENSO时间尺度上的变化位相略超前于正压模的变化 ,正压模的变化位相超前于 SSTA变化 ,SSTA变化位相超前斜压模的变化位相。斜压纬向风异常与SSTA具有正相关关系 (西太平洋西部相反 ) ;正压模则与 Nino3区海温异常有负相关关系 (西太平洋西部相反 )。斜压模与海表异常加热相互激励 ,促进异常海温增长 ,是增长模 ;而正压模则抑制斜压模的和海温异常的增长 ,是转换模。正压模的位相超前对预测 El Nino/ L a Nina的发生发展具有参考意义。

亚洲夏季风环流结构与热带印度洋偶极型海温异常

使用T42L28大气环流模式就夏季风时期大气对印度洋海温偶极子型异常的响应进行了数值试验研究,结果表明,印度洋偶极子型海温异常可以引起感热和潜热加热异常并进而形成异常辐合辐散,导致热带印度洋及其邻近地区夏季降水异常。同时此热带扰动可激发或造成中纬度异常波列。通过改变季风区温度场分布,偶极子型海温强迫可以影响大气的正/斜压环流结构和斜压性强弱。强的纬向风垂直切变趋向于靠近海洋异常偏暖的地区。不论是正偶极子型强迫或负偶极子型强迫,西太平洋暖池和东亚地区的大气环流均出现异常并激发出中纬度的异常波列,但异常类型并未显著反相。

基本气流的垂直切变作用下的低纬低频波

在低纬地区 ,风速的垂直切变也是很明显的 ,作者解释了这些纬向气流的垂直切变对低纬长波性质以及对不同模态的相互作用的影响 。

全球海洋高频振荡分布特征

基于1992年10月~2006年6月时间间隔为7 d的卫星高度计海面高度异常(SLA)资料,分析了周期短于165 d的高频波动及其能量的空间分布特征。在功率谱密度计算基础上,分析了各频段所含能量占周期在15~165 d的高频波动总能量的百分比,发现随着最显著波动周期从1个月增大到5个月,其对应的纬度从7°增加到32°,最显著波动周期在全球呈明显的纬向带状分布。由二维方向谱分析上述高频信号主要是第一斜压模Rossby波的信号,并且在每个纬度带上的最显著波动周期与该纬度的Rossby波阈值周期一致。

Impacts of Indonesian Throughflow on seasonal circulation in the equatorial Indian Ocean

Impacts of the Indonesian Throughflow(ITF) on seasonal circulation in the equatorial eastern Indian Ocean are investigated using the ocean-only model LICOM by opening and closing ITF passages. LICOM had daily forcing from NCEP reanalysis data during 2000–2011. It can reproduce vertical profiles of mean density and buoyancy frequency of World Ocean Atlas 2013 data. The model also simulates well annual oscillation in the central Indian Ocean and semiannual oscillation in the eastern Indian Ocean of sea level anomalies(SLA) using satellite altimeter data, as well as the semiannual oscillation of surface zonal equatorial currents of Ocean Surface Current Analyses Real Time current data in the equatorial Indian Ocean. The wave decomposition method is used to analyze the propagation and reflection of equatorial long waves based on LICOM output. Wave analysis suggests that ITF blockage mainly influences waves generated from the Indian Ocean but not the Pacific Ocean, and eastern boundary reflections play an important role in semiannual oscillations of SLA and zonal current dif ferences in the equatorial Indian Ocean associated with ITF. Reconstructed ITF-caused SLA using wave decomposition coefficient dif ferences between closed and open ITF-passage experiments suggest both Kelvin and Rossby waves from the first baroclinic mode have comparable contributions to the semiannual oscillations of SLA diff erence. However, reconstructed ITFcaused surface zonal currents at the equator suggest that the first meridional-mode Rossby wave has much greater contribution than the first baroclinic mode Kelvin wave. Both reconstructed sea level and zonal currents demonstrate that the first baroclinic mode has a greater contribution than other baroclinic modes.

Theoretical study of the effect of topographic height and width on generation of internal tides

Internal tides generated upon two-dimensional Gaussian topographies of different sizes and steepness are investigated theoretically in a numerical methodology.Compared with previous theoretical works,this model is not restricted by weak topography,but provides an opportunity to examine the influence of topography.Ten typical cases are studied using different values of height and/or width of topography.By analyzing the baroclinic velocity fields,as well as their first eight baroclinic modes,it is found that the magnitude of baroclinic velocity increases and the vertical structure becomes increasingly complex as height increases or width decreases.However,when both height and width vary,while parameter s(the ratio of the topographic slope to the characteristic slope of the internal wave ray) remains invariant,the final pattern is influenced primarily by width.The conversion rate is studied and the results indicate that width determines where the conversion rate reaches a peak,and where it is positive or negative,whereas height affects only the magnitude.High and narrow topography is considerably more beneficial to converting energy from barotropic to baroclinic fields than low and wide topography.Furthermore,parameter s,which is an important non-dimensional parameter for internal tide generation,is not the sole parameter by which the baroclinic velocity fields and conversion rate are determined.

A time-dependent baroclinic model on NEC bifurcation

As it is well-known, the North Equatorial Current (NEC) bifurcates into the Kuroshio flowing northward and the equatorward Mindanao Current, which is well depicted by Munk's theory in 1950 in terms of its climatology. However, Munk's theory is unable to tell the NEC bifurcation variability with time. In the present paper, a time-dependent baroclinic model forced by wind, in which temporal and baroclinic terms are added to Munk's equation, is proposed to examine the seasonal variability of the NEC bifurcation latitude. An analytical solution is obtained, with which the seasonal variability can be well described: NEC bifurcation reaches its northernmost position in December and its southernmost position in June with a range of about 1° in latitude, consistent with previous results with observations. The present solution will degenerate to Munk's one in the case of steady and barotropic state.

Vertical Structure of the Tidal Currents on the Continental Shelf of the East China Sea

The available data on tidal currents spanning periods greater than six months for the continental shelf of the East China Sea (26°30.052′N, 122°35.998′E) were analyzed using several methods. Tidal Current Harmonic Analysis results demonstrated that semi-diurnal tides dominated the current movement. The tidal currents of the principal diurnal and semidiurnal rotated clockwise with depth, with the deflection of the major semi-axes to the right in the upper layer and to the left in the lower layer. The vertical structures of two principal semi-diurnal constituents-M2 and S2-were similar, which indicates that the tidal currents are mainly barotropic in this area. The main features of the variation of the four principal tidal constituents with depth demonstrate that the currents in this region are influenced by the upper and lower boundary layers. Therefore, the tidal constituents of the shallow water are similar. Different vertical modes were calculated based on the Empirical Orthogonal Function (EOF) analysis of the Eastern and Northern components of the tidal currents, with a variance contribution for the zero-order model of at least 90%. The variance contribution of the baroclinic model is minimal, which further reveals a strong barotropic character for the tidal currents of this region.

Lie Point Symmetry Algebras and Finite Transformation Groups of Baroclinic Mode for Rotating Stratified Flows

The transformation groups and symmetries of the baroclinic mode for rotating stratified flow can be obtained via the standard approach. Applying the symmetry group on some special solutions, the newly obtained results disprove a known conjecture.

Relationship between cross-equatorial flows over the Bay of Bengal and Australia in boreal summer:Role of tropical diabatic heating

The interannual variability of cross-equatorial flows(CEFs)over the Asian–Australian monsoon(AAM)region during boreal summer was analyzed by applying the empirical orthogonal function(EOF)method to the meridional wind at 925 h Pa.The first mode(EOF1)exhibits an in-phase relationship among different CEF channels over the AAM region,which has received much attention owing to its tight linkage with ENSO.By contrast,the second mode(EOF2)possesses an out-of-phase relationship between the Bay of Bengal(BOB)CEF(90°E)and Australian CEF,among which the New Guinea CEF near 150°E shows the most significant opposite correlation with the BOB CEF.Observational and numerical model results suggest that the equatorially asymmetric heat source(sink)over the western(eastern)Maritime Continent,closely associated with the in-situ sea surface temperature anomaly,can induce cross-equatorial northerly(southerly)flow into the heating hemisphere,which dominates the out-of-phase relationship between the BOB and New Guinea CEFs.Furthermore,an equatorially symmetric heating over the central Pacific may indirectly change the CEFs by modulating the zonal atmospheric circulation near the Maritime Continent.

A STUDY ON THE BAROCLINIC STRUCTURE OF THE ABYSSAL CIRCULATION

In this paper, the linear continuously stratified model of the abyssal circulation proposed by Pedlosky (1992) was extended to include the second order term -(γθ zzz ) in the vertical turbulent mixing parameterization of - (w′θ′) z=k υθ zz -γθ zzz , in which k υ is a vertical diffusion coefficient, and γ is the second order coefficient of turbulent mixing (or simply called γ term and γ<0 is only allowed). The influence of the γ term on the baroclinic structure of the abyssal circulation driven by upwelling out of the abyss was investigated. It was found that the γ term has a noticeable influence on the baroclinic structure of the upwelling driven abyssal circulation. For uniform upwelling, it favors the baroclinic layering of the abyssal circulation in the eastern part of the basin, but prevents the layering in the west. In addition, this parameter was found to decrease the vertically averaging meridional velocity of the abyssal circulation from the west to the east on the southern boundary. For upwelling localized near the eastern boundary, the γ-term favors baroclinic layering of the abyssal circulation in the whole basin. Especially, on the southern boundary the γ-term could strengthen the vertically averaging meridional velocity in the west, but greatly weaken it in the east. The model presented here might be considered as an extension of the Pedlosky baroclinic model of the abyssal circulation.