热带气旋的结构对其移动影响的动力分析

视热带气旋(以下简称TC)为半径等于R的圆形涡旋,对其水平运动方程作在整个TC区域的平均,进而得到了TC风场结构引起的TC移动方程,求出其解析解,并据此讨论TC风场结构对TC路径的影响,结果表明:即使是轴对称的TC,其路径也有周期性的正(余)弦摆动,且摆动周期不仅与TC所在纬度有关,还受TC的尺度、最大风速及其半径等影响,在半周期和整周期附近移向有突然左折的趋势;而TC的1波非对称分量,并不对TC的移动产生直接影响;只有当TC的非对称分量为多波(如2波)形式时,才对TC的移动产生直接的显著影响,且与非对称分量的初始位相有关.此外,TC的径向风对其移动也有显著影响     

热带风暴热力非对称结构对其运动的影响

研究了热力非对称结构对0421号热带风暴"海马(Haima)"的移动和强度变化的影响。通过物理量场诊断分析发现,热带风暴(气旋)的热力结构在垂直、水平方向均呈非对称分布。热力因子对热带风暴的影响,主要体现在低层。热带风暴朝其移向前方的风暴内部的非绝热增温中心偏折,并有向此方向加速的趋势。了解热带风暴的热力结构分布特征及其对热带风暴移动的影响,对短期预报热带风暴的移动有一定的指示意义。     

Intrusive layering of the Antarctic slope front

Cascading of cold Antarctic shelf water (ASW) initiates compensatory isopycnic upwelling of the warm Circumpolar Deep Water (CDW). The baroclinic/thermoclinic Antarctic slope front (ASF) is formed, and a mesoscale intrusive structure develops on the shelf edge and slope. Mesoscale processes when the ASF peaks are periodically accompanied by local baroclinic instability, which forms a smaller-scale intrusive structure. Therefore, the ASF is naturally subdivided into two layers according to the intrusion scales (vertical δН and horizontal L) and the horizontal parameters of the front (thermoclinity (T_L)_ρ and baroclinity γ_ρ). Analysis of ASF intrusive layering due to the baroclinic factor supports the following conclusion: the higher the (T_L)_ρ of the ASF, the greater the intrusion intensity |δθ| (temperature anomaly amplitude), while an increase in γ_ρ of the ASF leads to a decrease in intrusion scales δН and L. Frontal intrusions can be distinguished by a development degree. Regardless of the degree of development, all warm intrusions are characterized by vertical density stratification, while cold intrusions are characterized by density quasihomogeneity. According to field data, the ASF instability process is subdivided into four stages. When theASF is baroclinically unstable, the local baroclinic deformation radius Rd_L of the front is close in magnitude to the horizontal scale L of the intrusions that form, and their characteristic vertical scale δH is close to the typical vertical scale of front instability.     

热带气旋卫星遥感客观定位方法研究进展

首次从云系形态识别、风场结构分析、云体温湿反演、时空运动匹配等4个崭新角度梳理归纳了热带气旋卫星遥感客观定位方法研究进展,分别介绍此4类方法的实现原理与过程,比较分析各种方法的优缺点与适用性。总结认为,上述方法虽大多仍处于探索研究阶段,但其优于传统人工目视判读定位法的诸多特点将使之成为发展应用的必然;同时综合比较指出,结合运动特征的混合智能算法将是热带气旋中心定位的未来方向;此外建立集成多种资料和算法的热带气旋综合客观定位系统,也有利于提高热带气旋中心定位的稳健性和准确率。     

Waves and diffusion on the sea surface

The frequency spectrum of surface elevations in the presence of wind waves is well known. On this basis, one can estimate the frequency spectrum of vertical velocities in sea-surface waves. Owing to liquid incompressibility, the spectrum of horizontal velocities should have the same frequency dependence. The use of the dispersion equation for waves on the surface of a heavy liquid allows one to obtain to the spatial spectrum of velocities. Therefore, one can estimate the spatial structure function of the velocity field. For short waves and large depths, the structure function increases as r ^1/2, where r is the distance between the points of observations. For long waves and shallow depths h, this increase is proportional to r. The coefficient of turbulent mixing K(r) of pollution spots of size r on the sea surface is now estimated as the product of the spot size and the rms difference of velocities. As a result, depending on r and h, the exponent in the r ⁿ dependence of K(r) may vary between 1.25 and 1.5. This outcome provides an explanation for a scatter in the values of the exponent n, a phenomenon that has been observed by many experimentalists.     

Geometry of scour hole around, and the influence of the angle of attack on the burial of finite cylinders under combined flows

Experiments were conducted to investigate the geometry of the scour hole and flow structure around short cylinders under the action of waves alone (WA) and combined flows (CF). The study is aimed at better understanding the dynamics of isolated objects on a sandy floor under oscillatory flows as occurs in shallow water regions in coastal areas. Flow velocities within the fluid core were recorded and 3D mapping of the bottom was performed with sub-aquatic acoustic sensors. Experiments were conducted for cylinder Reynolds wave number and Keulegan-Carpenter number within the ranges 10⁴R_e1.7×10⁵ and 2KC71, respectively. The present experimental evidence shows that the geometric characteristics of the scour hole (length and width) depend primarily on the Keulegan-Carpenter number (KC) and the cylinder aspect ratio (a_r=L_c/D). The effect of variation in the angle of attack of the flow with respect to the cylinder main axis was also investigated. Initial orientations of zero and ninety degrees were found to be stable while cylinders with intermediate initial orientations tended to orientate their main axes perpendicular to the flow direction. The final angle of orientation was found to be primarily a function of the Shields parameter, θ, and the initial angle of attack, α_i.     

北太平洋夏季热带海区大气运动的平衡关系

利用1998~2003年6~8月的NCEP/NCAR再分析资料(1.0°×1.0°经纬度网格),以对流层中部500 hPa高度层为重点,利用北半球夏季(6~8月)低纬度(0°~30°N)太平洋地区(160°E-120°W)各物理量(水平速度u,v,P-坐标垂直速度ω等)计算了水平运动方程中各分量的大小,通过比较对热带大尺度运动方程进行了简化,并给出了相应的简化方程,认为纬向风在除了赤道这一奇异带以外都是满足地转平衡的,而经向风则在离开赤道30°以外达到地转.由于热带太平洋地区是台风的重要发源地之一,因此弄清此地区的大气运动基本平衡关系有助于台风形成机制的研究.     

Response of a two-layer ocean with a baroclinic current to a moving storm,part I

A storm moves with a constant speed parallel to a stationary geostrophic current which flows only in the upper layer of a two-layer, infinite ocean. It is assumed that the lower layer is motionless. The quasi-geostrophic approximation is valid for a moving speed less than 4 ms^–1 for a storm radius of 100 km. The primary change of the upper layer thickness is caused by the wind stress divergence and the time integral of the wind stress curl. A cyclonic storm generates upwelling in its wake. The effect of the stationary flow similar to a western boundary current is minor by an order of magnitude and noticeable only on the left edge of the flow. Scaling of equations of motion and continuity for a more general upper geostrophic flow leads to expansion with a parametera ²=gH _m(fL)^–2, whereg is reduced gravity,H _m is the maximum thickness of the upper layer,f is Coriolis' parameter andL is the storm radius. The zeroth order perturbations of transport and thickness do not include the stationary flow which appears only in the first order perturbations ina ². When there is a coast, the change of the interface near the coast is dependent on the time integral of the wind stress component parallel to the coast, thus leading to upwelling or downwelling according to the center being to the left or right of the coastline.     

Respiration rates of copepod larvae and a ciliate from a tropical sea

The respiration rates of copepod larvae and a ciliate (Placus sp.) from a tropical sea were measured with an oxygen electrode method. The general range of body size of these animals was 40–161m (diameter equivalent to a sphere), and the respiration rate measured was 0.00076–0.00176l O₂ (animal)^–1h^–1 (or 2.02–9.05l O₂ (mg wet weight)^–1h^–1) at 25.5–29.2C. There was no marked difference observed between the respiration rates of copepod larvae and the ciliate. The respiration rates obtained here are relatively higher than the rates of other similar sized protozoans found in the literature, but lower than the rate extrapolated from larger planktonic copepods in tropical seas.The present results and other information available on microzooplankton biomass suggest that microzooplankton respiration is of near equal importance to that of net zooplankton in the study of energy flow through tropical, pelagic ecosystems.     

Analysis of the global relationship of biennial variation of sea surface temperature and air-sea heat flux using satellite data

We investigated the phase difference and the cross correlation coefficient between the band-pass filtered biennial variations of sea surface temperature (SST) and air-sea heat flux estimated by the monthly mean 2°×2° satellite data of Advanced Very High Resolution Radiometer (AVHRR) and Special Sensor Microwave/Imager (SSM/I) from July 1987 to June 1991. Judging from the phase difference, it can be determined whether the biennial variation of SST is controlled by local thermal air-sea interaction or oceanic processes of horizontal transport. When the local air-sea heat flux controls the biennial variation of SST, the phase of SST advances /2 (6 months) against that of the air-sea heat flux. In contrast, when the biennial variation of SST is controlled by the oceanic process, the phase difference between the SST and the air-sea heat flux becomes 0 or (12 months). In this case, two types of the phase differences are determined, depending on which variability of SST and air-sea heat flux is larger. The close thermal air-sea interaction is noticeable in the tropics and in the western boundary current region. The phase difference of /2 appears mainly in the north Pacific, the southeast Indian Ocean, and the western tropical Pacific; zero in the eastern tropical Pacific and the northeast and equatorial Atlantic; and that of in the central equatorial Pacific and north of the intertropical convergence zone (ITCZ) of the Atlantic. Phase differences of 0, , or /2 are possible in the western boundary current regions. This fact indicates that each current plays a different role to the biennial variation of SST. It is inferred that SST anomalies in the tropics are mutually correlated, and the process in which marked SST anomalies in the tropics are transferred to the remote area was probed. In the equatorial Pacific, the SST anomaly is transferred by the long planetary wave. On the other hand, it is found from the phase relationship and the horizontal correlation of SST that the SST anomaly in the central and western equatorial Pacific is connected through atmospheric mediation. It is suggested that the biennial variation of SST in the eastern Indian Ocean is affected by heat transport due to the Indonesian throughflow from the western tropical Pacific. It is found that the mentioned pattern of the interannual variation of SST in the tropical Atlantic as a dipole is not tenable.     

一个新的热带气旋参数调整方案

基于前人的统计经验公式和现有的实测资料,尤其是详实的热带气旋中心气压资料,对热带气旋的最大风速半径的确定提出一个新的调整方案,使之能较好反映热带气旋风场.比较结果表明,所计算的海浪场与实测资料吻合较好.     

Topographic Effect of Izu Ridge on the Distribution of the North Pacific Intermediate Water South of Japan

The topographic effect of the Izu Ridge on the horizontal distribution of the North Pacific Intermediate Water (NPIW) south of Japan has been studied using observational data obtained by the Seisui-Maru of Mie University (Mie Univ. data) and those compiled by Japan Oceanographic Data Center (JODC data). Both data sets show that water of salinity less than 34.1 psu on potential density () surface of 26.8 is confined to the eastern side of the Izu Ridge, while water of salinity less than 34.2 psu is confined to the southern area over the Izu Ridge at a depth greater than 2000 m and to the southeastern area in the Shikoku Basin. It is also shown by T-S analysis of Mie Univ. data over the Izu Ridge that water of salinity less than 34.2 psu dominates south of 30°N, where the depth of the Izu Ridge is deeper than 2000 m and NPIW can intrude westward over the Izu Ridge. JODC data reveal that relatively large standard deviations of the salinity on surface of 26.7, 26.8 and 26.9 are detected along the mean current path of the Kuroshio and the Kuroshio Extension. Almost all of the standard deviations are less than 0.05 psu in other area with the NPIW, which shows that the time variation in the salinity can be neglected. This observational evidence shows that the topographic effect of the Izu Ridge on the horizontal distribution of the NPIW, which is formed east of 145°E by the mixing of the Kuroshio water and the Oyashio water, is prominent north of 30°N with a depth shallower than 2000 m.     

Primary production and chlorophyll distributions in the subtropical and tropical waters of the Atlantic Ocean in the autumn of 2002

In October and November 2002, high and relatively high values of the chlorophyll a concentration at the sea surface (C _chl) were observed in the English Channel (0.47 mg/m³), in the waters of the North Atlantic Current (0.25 mg/m³), in the tropical and subtropical anticyclonic gyres (0.07–0.42 mg/m³), and also in the southwestern region of the southern subtropical anticyclonic gyre (usually 0.11–0.23 mg/m³). The central regions of the southern subtropical anticyclonic gyre (SATG) and the North Atlantic tropical gyre (NATR) were characterized by lower values of C _chl (0.02–0.08 mg/m³ for the SATG and 0.07–0.14 mg/m³ for the NATR). At most of the SATG stations, the values of the surface primary production (C _phs) varied from 2.5 to 5.5 mg C/m³ per day and were mainly defined by the fluctuations of C _chl (r = +0.78) rather than by those of the assimilation number (r = +0.54). The low assimilation activity of phytoplankton in these waters (1.3–4.6 mg chl a per hour) pointed to a lack of nutrients. An analysis of the variability of their concentration and the composition of photosynthetic pigments showed that, in the waters north of 30° N, the growth of phytoplankton was mostly restricted by the deficiency of nitrogen, while, in more southern areas, at the majority of stations (about 60%), the phosphorus concentrations were the minimum. At the low concentrations of nitrates and nitrites, ammonium represented itself as a buffer that prevented planktonic algae from extreme degrees of nitric starvation. In the tropical waters and in the waters of the SATG, the primary production throughout the water column varied from 240 to 380 mg C/m² 30° per day. This level of productivity at stations with low values of C _chl (<0.08 mg/m³) was provided by a well-developed deep chlorophyll maximum and a high transparency of the water. The light curves of photosynthesis based on in situ measurements point to the high efficiency of utilizing the penetrating solar radiation by phytoplankton on cloudy days.     

Examination of wind-wave interaction source term in WAVEWATCH III with tropical cyclone wind forcing

Results of drag coefficient(CD) from field observations and laboratory wave tank experiments indicate that the operational wave model can overestimate wind energy input under high wind conditions. The wind-wave interaction source term in WAVEWATCH Ⅲ has been modified to examine its behavior with tropical cyclone wind forcing. Using high resolution wind input,numerical experiments under idealized wind field and tropical cyclone Bonnie(1998) were designed to evaluate performance of the modified models. Both experiments indicate that the modified models with reduced CD significantly decrease wind energy input into the wave model and then simulate lower significant wave height(SWH) than the original model. However,the effects on spatial distribution of SWH,mean wavelength,mean wave direction,and directional wave spectra are insignificant. Due to the reduced wind energy input,the idealized experiment shows that the modified models simulate lower SWH than the original model in all four quadrants. The decrease in the front quadrants is significantly larger than that in the rear quadrants;it is larger under higher winds than lower winds. The realistic experiment on tropical cyclone Bonnie shows that the modified model with the various downward trends of CD in high winds creates a simulation that agrees best with scanning radar altimeter observations.     

Dissociation constants of protonated methionine species in seawater media

The dissociation constants (pK₁ and pK₂) for methionine have been measured in artificial seawater as a function of salinity (S = 5 to 35) and temperature (5 to 45 °C). The seawater pK₂ values were lower than the values in NaCl at the same ionic strength while the pK₁ values in seawater were lower only at S = 35. In an attempt to understand these differences, we have made measurements of the constants in Na–Mg–Cl solutions at 25 °C. The measured values have been used to determine the formation of Mg²⁺ complexes and Pitzer interaction parameters for Mg²⁺ with methionine. The seawater model with the interaction parameters accounts for the differences between the value of pK₁ and pK₂ between NaCl and seawater. This study demonstrates that it is important to consider all of the ionic interactions in natural waters when examining the dissociation of organic acids.     

海洋对热带气旋风应力响应的准平衡解析解

为考察海洋上层各物理量对热带气旋风应力的响应问题,本文利用海洋线性化约化重力方程组开展了解析研究,所得主要结论如下:求解该问题使用跟随热带气旋中心移动的极坐标较为方便,当热带气旋风应力在热带气旋云墙内即热带气旋眼中为静止,在云墙处及之外随该极坐标半径增加而成反比衰减时,可求得该问题在此极坐标系中的定常解析解,该解强度与风应力成正比;解的流场在热带气旋云墙内为静止,在云墙处及之外呈现有向外流出的气旋式涡旋形态,且随极坐标半径增加而衰减。在云墙之外离云墙较近处,解的切向流速大于径向流速,在更远处则反之。解的径向流与热带气旋切向风应力平衡,切向流是梯度流,流动呈水平无辐散状态。在热带气旋眼中以及云墙处,海洋上层的厚度不变,且达到最小值。从云墙向外则厚度值逐渐增加。厚度值的变化反映了密度跃层的变化,在厚度值最小处附近,跃层位置有明显抬升,这会造成跃层附近海水涌升,从而海洋上层的响应涡旋是冷性的。略去海洋上层对热带气旋移动的响应,将此移动极坐标系中的解返回到固定坐标系后,则解的空间分布形态不变,但由定常解转变为非定常解,且随热带气旋一起移动;此解最重要的物理性质是其具有准平衡性,这与非平衡的近惯性振荡与重力惯性内波有本质区别。     

Dissociation constants of protonated cysteine species in seawater media

The dissociation constants (pK₁, pK₂ and pK₃) for cysteine have been measured in seawater as a function of temperature (5 to 45 °C) and salinity (S = 5 to 35). The seawater values were lower than the values in NaCl at the same ionic strength. In an attempt to understand these differences, we have made measurements of the constants in Na–Mg–Cl solutions at 25 °C. The measured values have been compared to those calculated from the Pitzer ionic interaction model. The lower values of pK₃ in the Na–Mg–Cl solutions have been attributed to the formation of Mg²⁺ complexes with Cys²⁻ anions

Mg²⁺ + Cys²⁻ = MgCys

The stability constants have been fitted to

after corrections are made for the interaction of Mg²⁺ with H⁺.The pK₁ seawater measurements indicate that H₃Cys⁺ interacts with SO₄²⁻. The Pitzer parameters β⁰(H₃CysSO₄), β¹(H₃CysSO₄) and C(H₃CysSO₄) have been determined for this interaction. The formation of CaCys as well as MgCys are needed to account for the values of pK₂ and pK₃ in seawater.The consideration of the formation of MgCys and CaCys in seawater yields model calculated values of pK₁, pK₂ and pK₃ that agree with the measured values to within the experimental error of the measurements. This study shows that it is important to consider all of the ionic interactions in natural waters when examining the dissociation of organic acids.