Meteorological Problems Research Articles

A new contouring algorithm

An algorithm is developed to obtain the contour plot of principal scalar, vector and tensor valued fields in areas of engineering such as elevations of a terrain, deflections or stresses varying within the domain. This can be applied to scalar field problems in meteorology as well. An isoparametric style of interpolation is used to obtain such contours in two as well as in three dimensions. Computer programs have been developed to plot the contours, the surfaces as well as the deformed shapes and viewed from any point in any direction.

EVALUATION AND LIMITS OF PROTECTIVE BOOM PLANS FOR HIGH TIDAL RANGE AND STRONG CURRENT AREAS

ABSTRACT The French organization of onshore oil spill response is defined by specific intervention plans (Polmar plans), established for every coastal department. One of the main elements of these plans consists of detailed plans for deploying booms to protect sensitive areas. The Ministry of the Sea, with assistance from CEDRE, carries out exercises every year in different coastal locations to test the feasibility and efficiency of the boom deployment plans and also to train local personnel in handling antipollution equipment. Lessons learned from these exercises enable the improvement of deployment plans and help define new research areas. Within this framework, CEDRE has undertaken a feasibility study for the installation of booms in high tidal range and strong current areas. This experimental study involved a 15-day period, during the autumn of 1993, of on-site observations on the behavior of booms installed in one of the most difficult sites on the Atlantic shoreline. The main parameters observed were resistance, containment efficiency, and mechanical behavior of booms during the tide cycle, particularly when booms are stranded at low tide. In spite of successful boom installation, the experiment encountered difficulties due to meteorological and instrumentation problems. Nevertheless, important lessons have been learned.Static boom protection seems to be difficult for such sites, which leads us to question the validity of numerous Polmar plans. We should test alternative response techniques such as dynamic recovery systems set up at the openings to sensitive areas, which will necessitate good coordination between at-sea and on-shore response authorities.Mooring systems design and installation are jobs for specialists and should be prepared in advance.Various local means, such as fishing vessels or oyster farm barges, can be used for deploying protective booms.

Forecasting for a Large Field Program: STORM-FEST

Abstract Stormscale Operational and Research Meteorology-Fronts Experimental Systems Test (STORM-FEST) was held from 1 February to 15 March 1992 in the central United States as a preliminary field systems test for an eventual larger-scale program. One of the systems tested was a remote operations center, located in Boulder, Colorado, which was significantly displaced from the main field concentration of scientists and research aircraft. In concert with the remote operations center test was a test of remote forecasting support, also centered in Boulder. The remote forecasting for STORM-FEST was the first major cooperative effort for the Boulder-Denver Experimental Forecast Facility (EFF), a cooperative effort between operations and research aimed at finding more effective ways of addressing applied meteorological problems. Two other newly formed EFF's, at Norman, Oklahoma, and Kansas City, Missouri, also played key roles in the forecasting/nowcasting support. A description of the design and function of thi...

The Application of a Technique for Vector Correlation to Problems in Meteorology and Oceanography

Abstract In a recent study, Crosby et al. proposed a definition for vector correlation that has not been commonly used in meteorology or oceanography. This definition has both a firm theoretical basis and a rather complete set of desirable statistical properties. In this study, the authors apply the definition to practical problems arising in meteorology and oceanography. In the first of two case studies, vector correlations were calculated between subsurface currents for five locations along the southeastern shore of Lake Erie. Vector correlations for one sample size were calculated for all current meter combinations, first including the seiche frequency and then with the seiche frequency removed. Removal of the seiche frequency, which was easily detected in the current spectra, had only a small effect on the vector correlations. Under reasonable assumptions, the vector correlations were in most cases statistically significant and revealed considerable fine structure in the vector correlation sequences. ...

GEMTM: a general model for energy and mass transfer of land surfaces and its application at the FIFE sites

A general energy and mass transport model (GEMTM) was developed to predict the dynamic interactions between land surfaces and the atmosphere. In contrast to other landsurface models, the present model successfully linked leaf-level processes, canopy microclimate, soil abiotic processes, plant growth and biomass production dynamics. The plant canopy was divided into shaded leaf and sunlit leaf sublayers in a canopy microclimate submodel. Stomatal conductance and photosynthesis of shaded and sunlit leaves were simulated separately. The leaf photosynthesis submodel distinguished C 1 and C 4 pathways. The multi-reflection of radiation within canopy and soil-surface system was considered in calculations of surface albedo and energy balance. A unique feature of the present model is that the interaction between soil-canopy and the atmosphere in energy transfer was implemented by coupling the energy balance of the canopy and soil surface with soil thermal dynamics. A second unique feature is that iterative determinations of plant water potential based upon plant water balance enabled the model to explicitly represent the interaction between the above-ground and the below-ground processes. A third unique feature is that explicit coupling between land-surface processes and plant growth dynamics enabled the model to simulate short-term as well as long-term (annual and seasonal) interactions between land surfaces and the atmosphere. Thus, the model has the capability to represent the dynamic and two-way interactions between land surfaces and the atmosphere. The model was validated using energy flux and biomass production data from two sites of the First ISLSCP Field Experiment (FIFE). The simulated sensible heat flux, latent heat flux, and soil-surface heat flux matched the measured data well. Simulated green leaf and live stem dry weights also agreed well with the field data. The model simulated realistically the diurnal and seasonal change of net CO 2 flux, canopy resistance, plant water potential, canopy and soil-surface temperature. Live root dry weight and root-zone spatial distribution dynamics were also simulated. The general nature of this model framework enables its application to a wide range of problems in terrestrial ecology, climatology, agricultural meteorology and hydrology. It can readily be adapted to different vegetation types.

Wind and wind forces in a plantation spruce forest

Observations have been made of the tubulent structure within and above a dense (LAI=10.2) plantation spruce forest along with measurements of the movement of individual trees. The mean statistics of the turbulence and the turbulence spectra are compared with observations in other crops and complementary wind-tunnel studies using 1∶75 scale plastic trees. The measurements show that momentum transport and the subsequent motion of the trees is dominated by intermittent sweep/ejection events associated with ‘honami’ waves moving across the forest. The trees themselves act as forced damped harmonic oscillators and appear to short circuit the normal turbulent energy dissipation process by efficiently absorbing energy at their resonant frequencies. It is argued that understanding the nature and formation of ‘honami’ waves over forests and crops is a crucial problem in agricultural and forest meteorology because of their important role both in turbulent transport and in causing wind damage.

Spaceborne Radar Sensing of Precipitation above an Ocean Surface: Polarization Contrast Study

This feasibility study explores the potential benefits of polarization adjustment for spaceborne radar sensing of precipitation. More specifically, the role of the wave polarization in separating or “distinguishing” ocean surface return from the hydrometeor echoes of a “chirped” signal is examined. To that end, experimental as well as computational data for the polarization scattering matrices of hydrometeors and ocean surfaces are obtained and used to calculate ocean and precipitation “response” to the transmitted pulse for various rain rates and incidence angles. The analysis is restricted to X and C bands, but simulations are performed for several signal-to-noise ratios, rain rates, and ocean surfaces. The problem is further restricted to the monostatic case (same polarizations for transmitter and receiver). Even when the ocean and hydrometeor echoes are mixed throughout the entire radar resolution volume, the results appear promising. It is found that polarization, which provides the best contrast between rain and ocean returns, varies from almost circular near nadir to elliptical at large off-nadir look angles of incidence (ellipticity of 23° at a 40° incidence angle). Calculations show an order of magnitude improvement in the ratio of the returns when compared with the traditional choice of HH (horizontal transmit and receive polarization). The improvement is largest for the range of angles between 15° and 20° but depends on the assumed rain rate and, in particular, on the ocean surface roughness. The general method described in this paper can be applied to many problems of radar and lidar meteorology, while the specific results reported here may have relevance for future precipitation measurement missions such as Tropical Rainfall Measuring Mission 2.

An Adjoint Sensitivity Study of Blocking in a Two-Layer Isentropic Model

This paper presents a new methodology for adjoint sensitivity analysis, previously developed in general terms by Cacuci, into a form directly applicable 10 meteorological problems. This technique is illustrated by examining the sensitivity of a blocking index in a two-layer isentropic model. The index represents a response function for the sensitivity analysis that unlike previous meteorological applications, is an operator and not a functional, and thus extends the scope of adjoint sensitivity to general operator-type responses depending on time and/or space. The sensitivity of the blocking index to perturbations introduced into the model atmosphere, as well as to model parameters, is discussed. The methodology of generalized adjoint sensitivity analysis described in this paper constitutes a prototype for further applications in the atmospheric and/or oceanic sciences.

Numerical Experience with Limited-Memory Quasi-Newton and Truncated Newton Methods

Computational experience with several limited-memory quasi-Newton and trun- cated Newton methods for unconstrained nonlinear optimization is described. Comparative tests were conducted on a well-known test library (J. J. Mor, B. S. Garbow, and K. E. Hillstrom, ACM Trans. Math. Software, 7 (1981), pp. 17-41), on several synthetic problems allowing control of the clustering of eigenvalues in the Hessian spectrum, and on some large-scale problems in oceanography and meteorology. The results indicate that among the tested limited-memory quasi-Newton methods, the L-BFGS method (D. C. Liu and J. Nocedal, Math. Programming, 45 (1989), pp. 503-528) has the best overall performance for the problems examined. The numerical performance of two truncated Newton methods, differing in the inner-loop solution for the search vector, is competitive with that of L-BFGS.

A New Set of Orthonormal Modes for Linearized Meteorological Problems

Abstract A new orthogonal decomposition based on the Schmidt decomposition approach has been applied to the barotropic equation linearized around the January 300-mb climatological flow. The Schmidt decomposition can be computed numerically performing a singular value decomposition of the numerical representation of the equation. The decomposition provides a set of positive real numbers whose minimum is linked to the singularity of the linear equation. A nonzero minimum singular value guarantees nonsingularity. Within the limits of the numerical precision and resolution used (R15 and R30) the nondivergent, global, barotropic equation linearized around the winter climatology is not singular, but it is very badly conditioned. The Schmidt decomposition gives two sets of orthonormal basis functions, and a possible interpretation is offered by expressing the covariance matrix of forced responses in terms of Schmidt modes. An interpretation of the basis is obtained by showing that one set corresponds to the EOF ...

Regularizing the Satellite Temperature-Retrieval Problem through Singular-Value Decomposition of the Radiative Transfer Physics

A new method is derived for retrieving atmospheric temperature profiles from satellite-measured spectral radiance that appears, in first tests, to effectively circumvent certain difficulties of other well-known and implemented methods. In particular, the new method provides an elective way to avoid numerical instability without having to force the algorithm toward adherence to a priori statistics not dependent on the radiance measurements. This provides the opportunity to extract more information from satellite sounding instruments, without encountering instabilities owing to overlapping weighting functions. BY implication, this means that retrievals can be obtained without the typically strong external constraints of smoothing or cohesion to historical characteristics of the thermal or moisture structure. The new retrieval method is derived from a singular-value decomposition (SVD) of the radiative transfer physics governing the satellite measurements. The basis is an orthogonal one depending only on the characteristics of the sounding radiometer and not on a priori statistics. The SVD procedure allows one to efficiently structure and extract the information content of satellite observations and to rationally control the numerical, algorithmic instability. This is accomplished by discarding those singular vectors that adversely transform small radiometer errors into large retrieval errors, while retaining those vectors that transform radiance information reliably and unproblematically into thermal information. It is hoped that this new SVD methodology will find useful application for improving the impact of satellite observations on satellite retrievals and thereby improve the impact of retrievals on meteorological problems varying from short-range forecasting to long-range assessment of global change.

A Climatic Classification for Citrus Winter Survival in China

The citrus tree is susceptible to frost damage. Winter injury to citrus from freezing weather is the major meteorological problem in the northern pail of citrus growing regions in China. Based on meteorological data collected at 120 stations in southern China and on the extent of citrus freezing injury, five climatic regions for citrus winter survival in China were developed. They were: 1) no citrus tree injury. 2) light injury to mandarins (citrus reticulate) or moderate injury to oranges (citrus sinensis), 3) moderate injury to mandarins or heavy injury to oranges, 4) heavy injury to mandarins, and 5) impossible citrus tree growth. This citrus climatic classification was an attempt to provide guidelines for regulation of citrus production, to effectively utilize land and climatic resources, to chose suitable citrus varieties, and to develop methods to prevent injury by freezing.

A Simple Technique for Multiple-Parameter Pattern Recognition with an Example of Locating Fronts in Model Output

Abstract A statistical pattern recognition technique called IREW is described. IREW has several strengths, such as fast execution, small storage requirements, and increments learning, that may make the technique useful for many meteorological pattern recognition problems. A weakness of IREW is that it may not recognize complex patterns as well as more sophisticated pattern recognition techniques do. IREW analyzes data by using a derivative of Bayes' rule to multiplicatively combine the influence of predictors. The weight assigned to each predictor is determined empirically from a training dataset containing the data and verifications for multiple cases. IREW uses several methods to select useful subsets of a large set of predictors. The objective identification of surface fronts in Nested Grid Model forecasts is described to illustrate how IREW can be applied to a typical pattern recognition problem. The work consisted of identifying factors related to fronts and using some of those factors to make analys...

Nonlinear adaptive regression predictors based on singular decomposition

The paper deals with a non-linear regression model, linear in parameters. The least-squares adaptation method has been used to determine the model parameters. The conditionality problem in solving equations, which follows from the dependent predictors, has been suppressed by singular decomposition. This model is especially suitable for treating meteorological problems because non-linear processes, e.g. changes of air masses, changes of circulation patterns, etc., can be treated. The model has been tested in connection with the forecast of daily maximum and minimum temperatures. The RMS error lies in the range of 1–2°C, if the principal PPM is supposed.

Transient Development in Confluent and Diffluent Flow

Explaining the growth of disturbances superimposed on mean flows is a central problem in meteorology. Most widely studied models of the development process involve perturbations to shear flows with shear restricted to the meridional direction. Recently the importance of zonal variation of the mean flow was recognized and the study of shear flows extended to include zonal variation in shear. These studies found that the eigenfunctions associated with unstable modes in the simple shear problem are highly sensitive to zonal variation of the mean flow. However, there also exists another mechanism for development in a zonally inhomogeneous flow field: transient growth not associated with exponential instability. Properly configured perturbations exhibit transient growth in deformation fields associated with regions of confluence and diffluence at rates comparable to development in shear flow. In this work analytic solution of the linear initial value problem for the barotropic vorticity equation in deformation flow is used to construct local perturbations that undergo rapid transient development. Implications for cyclogenesis and block formation are discussed.

An application of GMRES to indefinite linear problems in meteorology

A preliminary investigation of a Krylov subspace method (GMRES) has been performed on a set of representative problems that can be encountered in geophysical fluid dynamics. Though in the majority of the numerical experiments practical convergence was correlated with the confinement of the eigenvalue spectrum to one complex half plane, it appears that there are cases in which this fact may not be enough to guarantee a practical rate of convergence. However, in the cases that did converge, results seem to indicate that convergence of the iterative GMRES can be obtained when the eigenvalues of the linear operator are all confined to a complex half plane (in agreement with Saad and Schultz). Simple shifts and scale selective dissipation are very effective in controlling convergence. A substantial improvement can be achieved by using preconditioning suggested by the physical nature of the problem. It appears that this is the best way to accelerate convergence. Even with preconditioning, however, it remains important that most of the eigenvalues be confined to one half plane.

Main meteorological problems of rice production and protective measures in China

China is one of the largest rice producers in the world. Since 1949, the rice production in China has increased considerably. The strong monsoon and continental climate and the varied topography provide suitable conditions for rice growth. However, cold, drought, water logging injury and other meteorological disasters happen frequently, resulting in unstable yield. This paper briefly introduces natural conditions in China that are favourable for rice production. Attention is focused on the main meteorological disasters and the protective measures adopted in rice production. Finally, some profitable suggestions for China's future rice production are given.

A four-layer model for the heat budget of homogeneous land surfaces

The model is an explicit solution of the equations which define the conservation of heat and water vapour in the system consisting of uniform vegetation and soil. The vegetation has two layers, the first extending from a reference height in the atmosphere to the virtual sink for momentum and the second from the virtual sink to the soil surface. Soil between the surface and the damping depth is divided into an upper, completely dry layer and a lower wet layer. Throughout the system, differences of potential per unit flux are specified by resistances, notably the conventional surface resistance governing the loss of vapour from foliage and a new soil resistance, assumed proportional to the accumulated loss of water by evaporation from the soil surface, which is proportional to the square root of elapsed time. Since the total energy available to the system is limited by absorption of radiation, the increase of transpiration from foliage as it expands decreases evaporation from the soil. Conversely, as soil dries, transpiration rate per unit of foliage area increases. This interaction of vapour fluxes is governed by the behaviour of the saturation vapour pressure deficit within the vegetation, identified as a major variable. General implications of the model are consistent with observations and estimates of evaporation rate from a stand of wheat grown in Arizona agree well with measurements from lysimeters. The model is applicable to a wide range of problems in agricultural meteorology and hydrology. With simplification, it could be used to obtain surface exchanges of sensible and latent heat in atmospheric general circulation models.

A four‐layer model for the heat budget of homogeneous land surfaces

AbstractThe model is an explicit solution of the equations which define the conservation of heat and water vapour in the system consisting of uniform vegetation and soil. The vegetation has two layers, the first extending from a reference height in the atmosphere to the virtual sink for momentum and the second from the virtual sink to the soil surface. Soil between the surface and the damping depth is divided into an upper, completely dry layer and a lower wet layer. Throughout the system, differences of potential per unit flux are specified by resistances, notably the conventional surface resistance governing the loss of vapour from foliage and a new soil resistance, assumed proportional to the accumulated loss of water by evaporation from the soil surface, which is proportional to the square root of elapsed time. Since the total energy available to the system is limited by absorption of radiation, the increase of transpiration from foliage as it expands decreases evaporation from the soil. Conversely, as soil dries, transpiration rate per unit of foliage area increases. This interaction of vapour fluxes is governed by the behaviour of the saturation vapour pressure deficit within the vegetation, identified as a major variable.General implications of the model are consistent with observations and estimates of evaporation rate from a stand of wheat grown in Arizona agree well with measurements from lysimeters. The model is applicable to a wide range of problems in agricultural meteorology and hydrology. With simplification, it could be used to obtain surface exchanges of sensible and latent heat in atmospheric general circulation models.

Conjugate-Gradient Methods for Large-Scale Minimization in Meteorology

Abstract During the last few years new meteorological variational analysis methods have evolved, requiring large-scale minimization of a nonlinear objective function described in terms of discrete variables. The conjugate-gradient method was found to represent a good compromise in convergence rates and computer memory requirements between simpler and more complex methods of nonlinear optimization. In this study different available conjugate-gradient algorithms are presented with the aim of assessing their use in large-scale typical minimization problems in meteorology. Computational efficiency and accuracy are our principal criteria. Four different conjugate-gradient methods, representative of up-to-date available scientific software, were compared by applying them to two different meteorological problems of interest using criteria of computational economy and accuracy. Conclusions are presented as to the adequacy of the different conjugate algorithms for large-scale minimization problems in different met...