The ocean general circulation model developed at the Institute of Numerical Mathematics, Russian Academy of Sciences, is briefly described. The model is based on a complete system of nonlinear (primitive) equations describing ocean hydro- and thermodynamics in the Boussinesq approximation and written in a spherical sigma-coordinate system. The main feature of the model is that its numerical implementation makes use of splitting with respect to physical processes and spatial coordinates. This allows the use of efficient implicit algorithms. The annual mean regime produced in a 121-year model run with a realistic climatic annual cycle of atmospheric forcing specified from the NCEP reanalyses is analyzed and compared with observations. The simulated ocean circulation patterns and thermohaline fields are shown to accord, on the whole, with observations and to agree well with results of other models. The sensitivity of the global thermohaline circulation to variations in wind stress is examined. To this end, two experiments with different wind stresses specified from NCEP and ECMWF reanalyses are compared. The response of the thermohaline structure and ocean circulation to this wind variation is analyzed. In turn, this response leads to noticeable variations in meridional heat and freshwater transport, which is important in climate formation.
A method proposed recently for remote monitoring of currents in coastal regions of the ocean is discussed and compared to alternative approaches. The new method, which is referred to as the method of matched nonreciprocity (MMN), represents further development of conventional acoustic tomography of currents as applied to shallow-sea conditions. In measurements of currents, low-frequency acoustic waves are employed as sounding signals. The MMN makes it possible to obtain real-time current charts in a region extending horizontally to tens or hundreds of kilometers and covering the whole depth of the water from the surface of the ocean to its bottom. Such charts are important in solving major scientific problems, in particular, monitoring of climate changes and verification of global-circulation models. It is shown that the MMN is free of limitations inherent in the monitoring methods proposed previously. The MMN is based on recent advances in the theory and mathematical modeling of acoustic propagation in inhomogeneous moving media and also in the use of the matched-field method for solving tomographic inverse problems. The physical basis of the MMN is a choice of an acoustic-field characteristic for measurements, which must be sensitive to current profiles and insensitive to both acoustic-speed variations and bottom topography. As a result, the MMN leads to a stable solution of the inverse problem for the vertical distribution of current velocity. The development of methods for current acoustic tomography is considered from the standpoint of their applicability to monitoring ocean dynamics in coastal regions. Possible applications of the MMN to solving other oceanographic problems are also discussed.
An approximate computational model is proposed for the ocean surface irradiance due to the open sun under broken-cloud conditions. The model takes into consideration an additional irradiance produced at the sunlit observation point by the radiation scattered within clouds and emerging from them through their lower and lateral boundaries. The cloud cover is introduced as a plane-parallel homogeneous layer covering the nth part of the sky with equal probability, and the cloud sizes are taken to be small in comparison with the size of the entire cloud layer causing the additional irradiance. Computations of the irradiance against the cloud amount and optical thickness, the sun elevation, and the received radiation wavelength show that almost always, except for short wavelengths at low sun elevations, as n increases, the irradiance increases amounting to as much as 150% of its value under cloudless conditions.
A study of 105-year series of the parameters of the Honolulu and Canadian highs has revealed neither significant trends nor significant long-period oscillations similar to those observed in the parameters of the Azores and Siberian highs. For the period 1958-1997, the coefficients of correlation between the total ozone content (TOC) and meteorological parameters and also their linear and quadratic trends are computed for different regions of North America. Quadratic TOC trends are reliably established. This fact counts in favor of long-period ozone oscillations, i.e., in favor of a natural origin of the TOC trends. A clearly pronounced pole ward trend of the tropopause discontinuity is established. This trend is one of the causes for the negative ozone trend observed over southeastern North America.
Statistical relationships between sea surface temperature (SST) in the equatorial Pacific (NINO3.4 region), zonal wind circulation L-phi around a latitude circle, and wind circulation L-S around contours enclosing various atmospheric centers of action and cyclone-active regions were studied depending on the time scale of averaged circulation time series. For this purpose, simultaneous correlation coefficients between a series of monthly mean SST in NINO3.4 and series of circulation around a latitude circle and contours were calculated using different time scales of averaged data. This allowed the estimation of an optimal time scale (or scales) on which the tropical ocean and the atmosphere interact. Regularities, similarities, and differences in the variation of correlations depending on the averaging interval applied to circulation series were found for various regions, latitudes, and pressure levels.
Solar-radiation propagation in the ocean-atmosphere system (OAS) is modeled as radiative transfer in a two-medium layer with an air-water interface reflecting and transmitting radiation by the Fresnel law. The contributions of the direct solar radiation and the background solar radiation multiply scattered in the atmosphere are resolved. The effects of both the reflecting interface and the ocean regarded as a scattering medium are estimated by the influence-function method. Several models are proposed for taking into account radiative transfer between the atmosphere and the ocean. These models correspond to different approximations for the optical transfer operator of the OAS.
The chaotic advection in a background now [5] is considered using a barotropic model of a semicircular basin with a linear bottom topography and a source-sink system located at the corners of the basin boundary. With the use of numerical experiments, the outflow of passive tracers (markers) from the vortex region into the flawing region due to periodic oscillations of flow rate is studied. The rate and degree of marker outflow are studied as functions of oscillation parameters (frequency amplitude, and phase). An approach based on studying the distribution of marker outflow times over the whole basin is proposed for investigating the mechanism and parameters of chaotic advection in open systems with a finite lifetime of trajectories, The chaotic regions revealed using this approach are compared to those obtained using the Lyapunov exponents and Poincare sections calculated for a finite time.
Simultaneous measurements of temperature fluctuations are taken at six heights z = 1, 2, 5, 10, 18, and 36 m under the conditions of unstable stratification. A procedure to separate out an organized component of the temperature field is proposed. The organized component is defined as a synchronous positive deviation of temperature from its mean value for each of the above heights expressed in the Oboukhov length scales \L\ from z = 0.1\L\ to z = \L\. The probability of occurrence of such convective structures, their role in forming the time correlation function, and their contribution to the vertical heat flux are estimated. The notion of organized convective structures is used for a physical interpretation of data on empirical orthogonal functions (EOFs) calculated from the covariance matrices for the indicated heights of measurements and presented In the form of universal functions of the dimensionless height zeta = z/\L\.
This work analyzes the known numerical and experimental results concerning the characteristics of quasi-two-dimensional turbulence in flows subject to bottom friction. According to theoretical predictions, bottom friction limits the inverse energy cascade from large scales. This fact is confirmed by both numerical and experimental results. At a moderate supercriticality of flows and an actual spatial resolution, bottom friction significantly or even completely suppresses the energy flux toward small wave numbers. In this case, the inertial range of energy turns out to be destroyed; however, the energy spectra can be close to -5/3 power-law spectra in a bounded range of wave numbers near the forcing wave number.
Monte Carlo calculations of individual components of the outgoing solar radiation in the spherical atmosphere are used to study the spectral distributions of deviations of the total radiation intensity, radiances of the zero- and first-order scattering components, and atmospheric haze radiance from the corresponding characteristics for an average atmosphere. Four types of natural targets and different conditions of solar Illumination are considered, The features of formation of these components are described as functions of the atmosphere turbidity, which makes it possible to estimate the variability of the atmospheric effect as clutter during observation of these targets from space.
The concept of atmospheric centers of action (ACAs) viewed as characteristics of the atmospheric general circulation and the climate an the whole is discussed. The variability of ACAs is analyzed using 105-year (1891-1995) time series of monthly mean coordinates and intensities of all eight ACAs occurring in the Northern Hemisphere. Climate theory is regarded as the statistical dynamics of an oscillating system with a very large number of strongly interacting degrees of freedom. Specific features of the system are external forcings with one-day and one-year periods, as well as with an 11.86-year Jupiter period and a 60-year main period of revolution of the Sun, Jupiter, and Saturn around the center of inertia of the solar system, etc.; a parametric resonant strengthening of disturbances on doubled periods; and transformation of periods into cycles. Evidence for cycle occurrence in climatic series is given.
This paper reports the results of studies of the seasonal variability of the world ocean climate based an diagnostic and adaptation calculations by a model of the ocean general circulation with the use of the seasonal climatic arrays of temperature and salinity from the World Ocean Atlas 1994 and Hellerman's climatic arrays of the fields of tangential wind stress (1983), The calculations were carried our on a one-degree grid and at 32 levels. The calculations, resulted in balanced seasonal climatic fields of temperature, salinity, density, sea-surface height, and currents. The seasonal variability of circulation and: integral characteristics of the world ocean climate, such as the dynamic sea-surface height and meridional transport of mass and heat, it discussed. An analysis of calculation results has shown that the seasonal variability of the fields of sea-surface height and currents is most clearly defined in the equatorial and tropical regions of the world ocean, The seasonal variability of the sea-surface height gradients largely determines the seasonal circulation regime: in the Northern Hemisphere summer season, the subsurface equatorial Lomonosov and Cromwell currents are intensified, and the Somali current is intensified sharply. In winter, the equatorial Tareev countercurrent appears. The maximum variability of integral meridional heat transports is typical of the equatorial and tropical zones, where heat transports in winter and summer are opposite in sign, In the Northern Hemisphere winter season, the meridional transport is directed northward, and in the Southern Hemisphere winter season, it is directed southward.
The dynamics of the optical parameters of stratospheric aerosol produced by the Mt. Pinatubo eruption is given. Measurements were carried out using a two-wavelength lidar with operating wavelengths of 532 and 1064 nm. The processing procedure of the data obtained with two-wavelength polarization laser sounding is described. The aerosol backscattering coefficient and depolarization coefficient at a wavelength of 532 nm and the ratio of the backscattering coefficients taken at two wavelengths are given in the form of isolines in the height-time plane. Possible temporal transformations of stratospheric-aerosol microphysical characteristics governing variations in the optical parameters are discussed.
A two-dimensional turbulent incompressible flow over the rough surface of a gently sloping hill is considered, The system of hydrodynamic equations is written in the natural curvilinear coordinate system related to streamlines. A modified Prandtl model, which is free of new empirical parameters, is used for turbulence. The solution is constructed as an expansion in terms of two small parameters h = H-0/H much less than 1 and mu(0) = 1/ln(H/Z(0)) much less than 1, where H is the height of the logarithmic layer, H-0 is the height of the hill, and Z(0) is the height of roughness. In the upper layers of the flow, the velocity components and pressure are expressed through a single harmonic function Psi, which is determined from the solution of the Dirichlet problem for a half-plane. For hills whose shapes are described by a rational function, a parabola, a Gaussian function, a hyperbolic cosine, or some others, the solution is expressed through elementary functions. The velocity in the boundary layer is found in the form of a logarithmic profile with the roughness parameter depending on the longitudinal coordinate. With the method of integral relations, a first-order differential equation is derived for the function of the roughness parameter. The solution of this equation is represented in the form of a simple integral of a function depending on the boundary normal derivative of Psi. The solution obtained converts asymptotically to the expansion for the outer region and thus represents a combined solution in the entire flow. A detailed comparison with experimental data obtained in wind-tunnel modeling points to a good agreement of the theoretical results with these data [2, 3].
A discrete spectrum of seismic oscillations was obtained in the range of periods 1-2 h. These oscillations were recorded in St. Petersburg (60 degrees N, 30 degrees E) by a seismometer with a vertical pendulum. The frequency distances between the harmonics of this spectrum are in agreement with the theory of short-period free oscillations of the atmosphere of the Lamb-wave type.
The amplitude phase characteristics (APC) or surface air temperature (SAT) annual cycle (AC) in the Northern Hemisphere are analyzed. From meteorological observations for the 20th century and meteorological reanalyses for its second half, it is found that over land negative correlation of SAT AC amplitude with annual mean SAT dominates. Nevertheless, some exceptions exist. The positive correlation between these two variables is found over the two desert regions: in northern Africa and in Central America. Areas of positive correlations are also found for the northern Pacific and for the tropical Indian and Pacific Oceans. Southward of the characteristic annual mean snow ice boundary (SIB) position, the shape of the SAT AC becomes more sinusoidal under climate warming. In contrast, northward of it, this shape becomes less sinusoidal. The latter is also found for the above-mentioned two desert regions. In the Far East (southward of about 50°N), the SAT AC shifts as a whole: here its spring and autumn phases occur earlier if the annual mean SAT increases. From energy balance climate considerations, those trends for SAT AC APC in the middle and high latitudes are associated with the influence of the albedo SAT feedback due to the SIB movement. In the Far East the trends are attributed to the interannual cloudiness variability, and in the desert regions, to the influence of a further desertification and/or scattering aerosol loading into the atmosphere. In the north Pacific, the exhibited trends could only be explained as a result of the influence of the greenhouse-gases loading on atmospheric opacity. The trends for SAT AC APC related to the SIB movement are simulated reasonably well by the climate model of intermediate complexity (IAP RAS CM) in the experiment with greenhouse gases atmospheric loading. In contrast, the tendencies resulting from the cloudiness variability are not reproduced by this model. The model also partly simulates the tendencies related to the desertification processes.
The stability of internal gravity waves (IGWs) propagating at small angles to the vertical is studied, These waves are presented by a periodic (in both velocity and density deviation from its standard value) plane-parallel stationary flow. The general form of dissipation is taken into consideration. Neutral-stability curves are obtained for a periodic velocity profile, and analytic stability criteria are formulated for a periodic buoyancy profile. From the results obtained, it is inferred that IGW instability is possible in the middle and the upper atmosphere.
The mathematical theory of design of optical experiments developed by V.P. Kozlov is applied to an optimal design of an experiment on remote sensing of the concentration of optically active substances in the ocean. An experimental design includes the number of spectral channels of the optical receiver, their positions in the spectrum, and the widths of spectral windows in each channel. Algorithms of searching for optimal channels and retrieving substance concentrations from measurements of the ocean radiance in optimal channels are presented. The implementation of such algorithms requires the statistical relationship between the ocean radiance spectrum and the concentration of the substance in question. This relationship is obtained by mathematical modeling. An optimal design is calculated for remote sensing of chlorophyll concentration in the world ocean oh board ships or low-flying aircraft. It is shown that the accuracy of concentration retrieval in the optimal experiment is significantly higher than that in algorithms based on color-index measurements and factor analysis. The robustness of the optimal design to changes in experimental conditions and models used for optical properties of water is tested.
Midlatitude wintertime ocean-atmosphere interactions were studied. To this end, a series of numerical experiments were carried our with the atmospheric general circulation model of the Institute of Numerical Mathematics, Russian Academy of Sciences, in the regime of perpetual January for 360 months of model time. In one of the experiments, a model of die upper ocean for the midlatitude Northern Hemisphere was combined wish the model of the atmosphere. It was shown that the coupled model pf the atmosphere and upper ocean is closer to observations in the pattern of the leading empirical orthogonal functions (EOFs) of interannual anomalies in the 500-mb surface height (H-500) than the model of the atmosphere with a prescribed climatic sea surface temperature (SST). This result may indicate that the coupled model is better in describing the low-frequency variability of the atmosphere. Two experiments, one with a time-independent positive and the other with an alternating (with a definite temporal pattern) (SST) anomaly in the North Atlantic, were performed. The spatial monopole pattern of SST anomaly and its temporal behavior were chosen to be consistent with atmospheric model dynamics according to the results of the experiment with the coupled model. It was shown that a localized response of the atmospheric model to SST anomaly has a baroclinic structure and is clearly defined as a response to time-dependent SST anomaly. The spatial pattern of this response to a monopole SST anomaly in the North Atlantic is such that die induced atmospheric circulation tends to suppress the SST anomaly. Thus, a negative feedback occurs in the model. It was found that a stationary response of the atmosphere in the 500-mb geopotential height to a time-independent SST anomaly can contain, together with a localized response in H-500 a global response with the spatial pattern determined by the low-frequency EOFs with the largest contributions to the variance.
