Formula for a baroclinic adjustment theory of climate

Recently, a theory relating baroclinic neutrality and midlatitudes tropopause height has been proposed. However, GCM results have shown that the dependence of the theory on external parameters is not consistent with that displayed by these numerical experiments. In the present paper we suggest an analytic formula for baroclinic adjustment to the neutrality of Eady waves through tropopause modification. This formula extends considerably the abovementioned theory by taking into account both a simple representation of the stratosphere and the topography. These modifications alter the tropopause condition for a baroclinically neutral state and its sensitivity to the external parameters. In particular, the topography introduces a dependence on the tropospheric vertical wind shear of the neutrality condition. This feature is not present in other models that assume a background state with a zero potential vorticity gradient in the troposphere. We show, furthermore, that the modified neutrality condition has sensitivities that may resemble those displayed by GCM simulations, with respect to the parameters defining the background flow.     

Deep-circulation flow at mid-latitude in the western North Pacific

Direct current measurements with five moorings at 27–35°N, 165°E from 1991 to 1993 and with one mooring at 27°N, 167°E from 1989 to 1991 revealed temporal variations of deep flow at mid-latitude in the western North Pacific. The deep-circulation flow carrying the Lower Circumpolar Deep Water from the Southern Ocean passed 33°N, 165°E northwestward with a high mean velocity of 7.8 cm s⁻¹ near the bottom and was stable enough to continue for 4–6 months between interruptions of 1- or 2-months duration. The deep-circulation flow expanded or shifted intermittently to the mooring at 31°N, 165°E but did not reach 35°N, 165°E although it shifted northward. The deep-circulation flow was not detected at the other four moorings, whereas meso-scale eddy variations were prominent at all the moorings, particularly at 35°N and 29°N, 165°E. The characteristics of current velocity and dissolved oxygen distributions led us to conclude that the deep-circulation flow takes a cyclonic pathway after passing through Wake Island Passage, passing 24°N, 169.5–173°E and 30°N, 168–169°E northward, proceeds northwestward around 33°N, 165°E, and goes westward through the south of the Shatsky Rise. We did not find that the deep-circulation flow proceeded westward along the northern side of the Mid-Pacific Seamounts and eastward between the Hess Rise and the Hawaiian Ridge toward the Northeast Pacific Basin.     

On the largest wave height in water of constant depth

Experimental evidence of the fact that, both in the laboratory and in the field, the largest wave height to water depth ratio realisable for oscillatory waves propagating in water of constant depth is about 0.55, has been published recently (Nelson, 1985); (Nelson, 1987); (Nelson, 1994). This paper presents various theoretical approaches to estimate this maximum value. In particular, the higher approximations of the Stokes and cnoidal theories give a much higher limiting wave height, close to 0.78 h, which is commonly used in engineering practice.However, the inclusion of higher harmonics, generated by a wave-maker paddle, into the analysis provides maximum wave height less than ≈ 0.6 h, which is in good agreement with observations.     

On the theory of hailstone growth

Analysis of the existing theories of hailstone growth has shown that there are two different approaches to the explanation of the layered structure of hailstones. L.G. Kachurin showed that the layered structure of ice on the surface of an object placed into the flux of supercooled water aerosol is controlled by the equilibrium film thickness. Another approach is based on the equation of heat balance at the hailstone surface and on the introduction of the critical water content. This paper elucidates the meaning of the critical equilibrium film thickness and establishes the relation between the two existing criteria controlling the transition from the dry regime of hailstone growth to the wet regime.     

On the joint estimation of model and satellite sea surface height anomaly errors

We describe a technique to estimate the error field in the sea surface height (SSH) anomaly field of an ocean model through the joint use of SSH anomaly fields measured from two satellites, Topex/Poseidon (T/P) and ERS-2. The joint error maps for the model, T/P and ERS-2 show distributions distinctly different from one another and globally inhomogeneous. Both sampling errors and instrument errors are represented in the mapped fields. Additionally, we compare the joint error estimation method to a technique using the model and only one satellite, and show the importance of the cross covariance between the measured SSH and the true SSH field in the estimation of the error field. Finally, we look at the distribution of the error versus the variance of the SSH at a location. This logged distribution suggests that the model errors are generally proportional to the model's variance (regression coefficient of 0.99, globally) while the satellites' errors do not exhibit this linear relationship (regression coefficients on the average of 0.60). The comparison of the two satellite distributions implies that ERS-2 has a lower sampling error than the T/P instrument except in the tropical region.     

On the long-term joint distribution of characteristic wave height and period and its application

By analysing the scatter diagrams of characteristic the wave height H and the period T on the basis of instrumental data from various ocean wave stations, we found that the conditional expectation and standard deviation of wave period for a given wave height can be better predicted by using the equations of normal linear regression rather than by those based on the log- normal law. The latter was implied in Ochi' s bivariate log-normal model(Ochi. 1978) for the long-term joint distribution of H and T. With the expectation and standard deviation predicted by the normal linear regression equations and applying proper types of distribution, we have obtained the conditional distribution of T for given H. Then combining this conditional P(T / H) with long-term marginal distribution of the wave height P(H) we establish a new parameterized model for the long-term joint distribution P(H,T). As an example of the application of the new model we give a method for estimating wave period associated with an extreme w     

Consideration for the tropopause’s displacements in the problem of flow over mountains

Within the framework of a two-dimensional, inviscid, stationary model, the problem of an unbounded (in height) two-layer quasi-static airflow over mesoscale mountains is considered. The airflow is characterized by a constant velocity and a discontinuity of temperature stratification at the inner interface (tropopause). The conjugation conditions for the flow fields at the boundary between the layers are formulated exactly, without the standard assumption of small perturbations. According to calculations, partial reflection of wave energy from the tropopause is substantially controlled by nonlinear effects associated with a finite height and shape of terrain. The tropopause’s displacement from the initial (equilibrium) level has a stabilizing effect on the flow, thus interfering with the development of anomalously strong disturbances. As a result, the flow field remains statically stable within a considerably wider range of flow parameters and for a larger mountain heights than predicted in the context of the conventional linear theory. The results obtained in this study are indicative of the importance of a correct consideration of the dynamic interaction between the troposphere and the overlying layers during both simulation of the process of flow and analysis of real atmospheric situations over mountains.     

世界海洋蒸发波导时空统计规律研究

The statistical features of the evaporation duct over the global ocean were comprehensively investigated with reanalysis data sets from the National Centers for Environmental Prediction.These data sets have time and spatial resolutions of 1 h and 0.313°×0.312°,respectively.The efficiency of the analysis was evaluated by processing weather buoy data from the Pacific Ocean and measuring propagation loss in the Yellow Sea of China.The distribution features of evaporation duct height(EDH) and the related meteorological factors for different seas were analyzed.The global EDH is generally high and demonstrates a latitudinal distribution for oceans at low latitudes.The average EDH is approximately 11 m over oceans beside the equator with a latitude of less than 20°.The reasons for the formation of the global EDH features were also analyzed for different sea areas.     

On the theory of rising convective jets

Some new results related to the theory of rising convective jets over heat and momentum sources are presented. The consideration is not restricted to free convective or forced jets—mixed situations are also possible. A known model is generalized to the case of a noticeable contribution of the effects of water-vapor buoyancy. It is established that a universal conservation law that is valid for any entrainment hypotheses exists. A simple approximate criterion of the possibility that jets “break” through barrier layers is derived. An analytic solution that describes a moist-adiabatic rise of a jet above the condensation level is found. The influence of jets on the transport of passive admixtures is assessed. A model is proposed for the horizontal spreading of the warm air transported by a jet below an intense barrier layer.     

On the theory of convective jets and thermals in the atmosphere

In traditional theoretical models of convection from isolated sources, results usually depend little on their sizes: convective jets and isolated thermals rapidly “forget” the source geometry. However, new problems in which the sizes of a source are relatively large and can significantly influence results have recently become important. These are, for example, problems of the dynamics of intensive methane emissions of geologic origin. The paper generalizes some well-known integral models of thermals and jets. Although these simple schemes cannot compete with complicated numerical models in describing the spatial structure of the currents, they are shown to be able to reproduce a number of important numerical results rather well (the height and time of the rise of convective elements) and, moreover, to find clear physical laws and determine explicit dependences on parameters of the problem.     

Route height connection across the sea by using the vertical deflections and ellipsoidal height data

Distance between the main land and island is so long that it is very difficult to precisely connect the height datum across the sea with the traditional method like the trigonometric leveling,or it is very expensive and takes long time to implement the height transfer with the geopotential technique.We combine the data of GPS surveying,astro-geodesy and EGM2008 to precisely connect the orthometric height across the sea with the improved astronomical leveling method in the paper.The Qiongzhou Strait is selected as the test area for the height connection over the sea.We precisely determine the geodetic latitudes,longitudes,heights and deflections of the vertical for four points on both sides across the strait.Modeled deflections of the vertical along the height connecting routes over the sea are determined with EGM2008 model based on the geodetic positions and heights of the sea segmentation points from DNSC08MSS model.Differences of the measured and modeled deflections of the vertical are calculated at four points on both sides and linearly change along the route.So the deflections of the vertical along the route over the sea can be improved by the linear interpolation model.The results are also in accord with those of trigonometirc levelings.The practical case shows that we can precisely connect the orthometric height across the Qiongzhou Strait to satisfy the requirement of order 3 leveling network of China.The method is very efficient to precisely connect the height datum across the sea along the route up to 80 km.     

On the choice of data transformation for modelling time series of significant wave height

Autoregressive models have been shown to adequately model the time series of significant wave height. However, since this series exhibits a seasonal component and has a non-gaussian nature, it is necessary to transform the series before a model can be fit to the data. Two different transformations that have been used in earlier work are shown not to be appropriate for all types of applications. A third transformation is proposed here, which combines the better features of the two earlier ones and which is appropriate for simulation work. This is demonstrated with an example of a series from Figueira da Foz, a location of the Portuguese Coast.     

On the theory of internal waves under ice cover

A theoretical model is contrived that describes the propagation of internal waves under ice cover. According to the results obtained in the study, the flexures of the ice surface with a frequency close to but smaller than the Brunt-Väisälä frequency can gain amplitudes sufficient for recording internal waves. A comparison of the theory with observations showed a satisfactory agreement.     

On the theory of internal surges in shallow basins

On the basis of well-known solutions, we analyse an internal surge, i.e. a sharp step-like variation of the pycnocline depth in a shallow basin. According to results obtained, in those cases where the pycnocline is situated approximately at mid-depth of the basin, the surge may have the form of a steadily moving non-linear wave (kink) governed by the combined Korteweg-de Vries equation with quadratic and cubic non-linearities. The vertical velocity component in such a wave has the form of a pulse and represents a soliton. Estimates of surge parameters obtained from real hydrologic data are in good agreement with the experimentally measured data.Translated by Vladimir A. Puchkin.     

北欧海比容高度及其与卫星高度计海表面高度异常的比较

In this study the steric height anomaly which is calculated from the hydrological data(EN3) is compared with the sea level anomaly derived from satellite altimetry in the Nordic Seas. The overall pattern of steric height is that it is higher in the margin area and lower in the middle area. The extreme values of steric height linear change from1993 to 2010 occur in the Lofoten Basin and off the Norwegian coast, respectively. Such a distribution may be partly attributed to the freshening trend of the Nordic Seas. The correlation between SLA(sea level anomaly) and SHA(steric height anomaly) is not uniform over the Nordic Seas. The time series of SLA and SHA agree well in the Lofoten Basin and northern Norwegian Basin, and worse in the northern Norwegian Sea, implying that the baroclinic effect plays a dominant role in most areas in the Norwegian Sea and the barotropic effect plays a dominant role in the northern Norwegian Sea. The weaker correlations between SLA and SHA in the Greenland and Iceland Seas lead a conclusion that the barotropic contribution is significant in these areas. The area-mean SHA over the entire Nordic Seas has similar amplitudes compared with the SLA during 1996–2002, but SHA has become lower than SLA, being less than half of SLA since 2006.     

Effect that jet streams have on the vertical ozone distribution and characteristics of tropopause inversion layer in the far east region

The paper describes a lidar and presents the results of lidar sensing of the vertical ozone distribution (VOD); the lidar measurements are analyzed together with data from a network of meteorological stations situated along the 132° E meridian. VODs over Primorye and Japan in the winter period are compared. An analysis showed that an interrelation exists between the subtropical jet stream and the structures of VOD and tropopause inversion layer. Specifically, the region of the VOD local maximum above the tropopause is in the upper part of the tropopause inversion layer and the width of the maximum depends on the distance from the core of the subtropical jet stream. It is found that the local ozone minimum in the lower stratosphere corresponds to the local minimum of the squared Brunt-Vaisala frequency within this same altitude range in the winter season, when two tropopauses frequently overlap. It is conjectured that the local ozone maximum and tropopause inversion layer may be associated with mixing processes in the layer where stratospheric and tropospheric circulation cells come into contact near the core of the subtropical jet stream.