Initial Guess Field Research Articles

Validating INSAT-3D atmospheric temperature retrievals over india using radiosonde measurements and other satellite observations

Atmospheric temperature profiles retrieved from a geostationary INSAT-3D (Indian National Satellite System) sounder level-2 physical retrieval data are evaluated with respect to radiosonde observations, Atmospheric Infrared Sounder (AIRS), and National Centers for Environmental Prediction and Department of Energy (NCEP-DOE) reanalysis-2 data sets over India and adjoining area. This evolution was carried out in the terms of correlation coefficients, bias, and root-mean-square error (RMSE) at each pressure level from surface 1000 to 100 hPa during a one year period in 2016.The initial validation of INSAT-3D temperature profiles with AIRS and NCEP-DOE reanalysis-2 data were taken as reference and computed for the spatial distribution of correlation coefficient, bias, and RMSE at each pressure level over the Indian region. In addition to that, we also compared the INSAT-3D temperature retrievals with 12 selected IMD (India Meteorological Department) radiosonde observations at different geographical features over the Indian subcontinent during the one year period in 2016. In this analysis, for each station at all pressure levels, the correlation coefficients, biases and their corresponding root-mean-square errors (RMSEs) were carried out between INSAT-3D and radiosonde observations. The results of the inter-comparison reveal that temperature retrievals from the INSAT-3D are a good agreement with AIRS and NCEP-DOE reanalysis-2 over the land region and a slight degradation performance over the ocean- and coastal regions of Arabian Sea and Bay of Bengal below 850 hPa. The degradation performance over the ocean- and coastal areas associated with maybe possibility of undetected clouds and uncertainty in surface emissivity and also it might be attributed to improper bias correction coefficients used for brightness temperature of clear-sky pixels before physical retrievals in INSAT-3D algorithm or inherent deficiency in the retrieval algorithm which mainly depends on initial guess field from NWP models. Furthermore, an evaluation of INSAT-3D with 12 IMD radiosonde observation results reveals that temperature retrievals for each station shows very good agreement at all pressure levels, except slight degradation in performance over the coastal regions (GOA, MDS) and island (AMN, PBL) stations possibly the same reason as that of AIRS/NCEP. Overall, the results show that INSAT-3D temperature retrievals over land are a good agreement with AIRS/NCEP and RSRW then over the ocean- and coastal regions which need to be analyzed.

Identifying arbitrary parameter zonation using multiple level set functions

In this paper, we extended the analytical level set method [1,2] for identifying a piece-wisely heterogeneous (zonation) binary system to the case with an arbitrary number of materials with unknown material properties. In the developed level set approach, starting from an initial guess, the material interfaces are propagated through iterations such that the residuals between the simulated and observed state variables (hydraulic head) is minimized. We derived an expression for the propagation velocity of the interface between any two materials, which is related to the permeability contrast between the materials on two sides of the interface, the sensitivity of the head to permeability, and the head residual. We also formulated an expression for updating the permeability of all materials, which is consistent with the steepest descent of the objective function. The developed approach has been demonstrated through many examples, ranging from totally synthetic cases to a case where the flow conditions are representative of a groundwater contaminant site at the Los Alamos National Laboratory. These examples indicate that the level set method can successfully identify zonation structures, even if the number of materials in the model domain is not exactly known in advance. Although the evolution of the material zonation depends on the initial guess field, inverse modeling runs starting with different initial guesses fields may converge to the similar final zonation structure. These examples also suggest that identifying interfaces of spatially distributed heterogeneities is more important than estimating their permeability values.

Optimal control of vibrational transitions of HCl

Control of fundamental and overtone transitions of a vibration are studied for the diatomic molecule, HCl. Specifically, the results of the effect of variation of the penalty factor on the physical attributes of the system (i.e., probabilities) and pulse (i.e., amplitudes) considering three different pulse durations for each value of the penalty factor are shown and discussed. We have employed the optimal control theory to obtain infrared pulses for selective vibrational transitions. The optimization of initial guess field with Gaussian envelope, phrased as maximization of cost functional, is done using the conjugate gradient method. The interaction of the field with the molecule is treated within the semiclassical dipole approximation. The potential and the dipole moment functions used in the calculations of control dynamics are obtained from high level ab-initio calculations.

지역규모 분석 모델을 이용한 서울 도시열섬 특성 연구

A very high resolution weather analysis system (VHRAS) of 50 m horizontal resolution is established based on LAPS. VHRAS utilizes the 3 hourly forecast data of the Unified Model (UM) of the Korea Meteorological Administration (KMA) with the horizontal resolution of 12 km as initial guess fields. The analysis system ingests the automatic weather station (AWS) data as input observations. The analysis system operates every hour for Seoul, Korea region in real time basis. It takes less than 10 minutes for one analysis cycle. The size of grid of the analysis domain is , respectively. The analysis results from December 2010 to February 2011 showed that the mean biases of temperature, maximum and minimum temperature were -0.07, 1.6, , respectively. The temperature in the central part of the city revealed relatively higher value than that of the surrounding mountainous areas, which showed a heat island feature. The heat island appears in zonal direction since the central city region is developed along a large river. Along the heat island, the eastern region was warmer than the western region. The warmer temperature in the western part of the heat island was caused by anthropogenic heat change in conjunction with the change of land use. This system will provide more reliable weather data and information in Seoul.

Selective creation of maximum coherence in multi-level Λ system

We consider the creation of the maximum Raman coherence in the six-level Λ system using optimal control theory. Optimal fields are designed for different initial conditions, resonant, and off-resonant, using the Krotov method including a reference field into the cost functional. Suppression of the population transfer to the intermediate level is achieved via an additional functional constraint which depends on the system dynamics. We demonstrate that the spectrum of the optimised fields has major contribution from the corresponding resonant frequencies independently of the choice of carrier frequency of the initial guess field. We also indicate that the pulse train emerges as a solution of the control problem of coherence optimisation in multi-level quantum systems.

A vertically resolved, global, gap-free ozone database for assessing or constraining global climate model simulations

Abstract. High vertical resolution ozone measurements from eight different satellite-based instruments have been merged with data from the global ozonesonde network to calculate monthly mean ozone values in 5° latitude zones. These ''Tier 0'' ozone number densities and ozone mixing ratios are provided on 70 altitude levels (1 to 70 km) and on 70 pressure levels spaced ~ 1 km apart (878.4 hPa to 0.046 hPa). The Tier 0 data are sparse and do not cover the entire globe or altitude range. To provide a gap-free database, a least squares regression model is fitted to the Tier 0 data and then evaluated globally. The regression model fit coefficients are expanded in Legendre polynomials to account for latitudinal structure, and in Fourier series to account for seasonality. Regression model fit coefficient patterns, which are two dimensional fields indexed by latitude and month of the year, from the N-th vertical level serve as an initial guess for the fit at the N + 1-th vertical level. The initial guess field for the first fit level (20 km/58.2 hPa) was derived by applying the regression model to total column ozone fields. Perturbations away from the initial guess are captured through the Legendre and Fourier expansions. By applying a single fit at each level, and using the approach of allowing the regression fits to change only slightly from one level to the next, the regression is less sensitive to measurement anomalies at individual stations or to individual satellite-based instruments. Particular attention is paid to ensuring that the low ozone abundances in the polar regions are captured. By summing different combinations of contributions from different regression model basis functions, four different ''Tier 1'' databases have been compiled for different intended uses. This database is suitable for assessing ozone fields from chemistry-climate model simulations or for providing the ozone boundary conditions for global climate model simulations that do not treat stratospheric chemistry interactively.

Comparison of ozone simulations using MM5 and CALMET/MM5 hybrid meteorological fields for the July/August 2000 CCOS episode

Two sets of meteorological fields were prepared for the July/August 2000 Central California Ozone Study (CCOS) episode. The first set was generated using the MM5 prognostic model. The second set was generated using the CALMET model in which the MM5-generated output was used as the initial guess field and objective analysis was used to improve agreement between simulated fields and observed air temperatures and wind speed components. The resulting CALMET/MM5 hybrid meteorological fields and those generated using MM5 alone were also used as inputs for the CAMx/SAPRC99 air quality model to simulation ozone concentrations for the July/August 2000 episode. Ozone concentrations simulated using the CALMET meteorological inputs resulted in better agreement with observed concentrations than those simulated using the MM5 generated inputs throughout the modeling domain. This analysis suggested that hybrid meteorological fields, developed by merging the results of objective analysis and prognostic models, can improve episodic air quality model performance over using prognostic meteorological fields alone.

Stabilization of ultracold molecules using optimal control theory

In recent experiments on ultracold matter, molecules have been produced from ultracold atoms by photoassociation, Feshbach resonances, and three-body recombination. The created molecules are translationally cold, but vibrationally highly excited. This will eventually lead them to be lost from the trap due to collisions. We propose shaped laser pulses to transfer these highly excited molecules to their ground vibrational level. Optimal control theory is employed to find the light field that will carry out this task with minimum intensity. We present results for the sodium dimer. The final target can be reached to within $99%$ provided the initial guess field is physically motivated. We find that the optimal fields contain the transition frequencies required by a good Franck-Condon pumping scheme. The analysis identifies the ranges of intensity and pulse duration which are able to achieve this task before any other competing processes take place. Such a scheme could produce stable ultracold molecular samples or even stable molecular Bose-Einstein condensates.

Adjoint assimilation of altimetric, surface drifter, and hydrographic data in a quasi‐geostrophic model of the Azores Current

The flow characteristics in the region of the Azores Current are investigated by assimilating TOPEX/POSEIDON and ERS 1 altimeter data into the multilevel Harvard quasigeostrophic (QG) model with open boundaries (Miller et al., 1983) using an adjoint variational scheme (Moore, 1991). The study site lies in the path of the Azores Current, where a branch retroflects to the south in the vicinity of the Madeira Rise. The region was the site of an intensive field program in 1993, SEMAPHORE. We had two main aims in this adjoint assimilation project. The first was to see whether the adjoint method could be applied locally to optimize an initial guess field, derived from the continous assimilation of altimetry data using optimal interpolation (OI). The second aim was to assimilate a variety of different data sets and evaluate their importance in constraining our QG model. The adjoint assimilation of surface data was effective in optimizing the initial conditions from OI. After 20 iterations the cost function was generally reduced by 50–80%, depending on the chosen data constraints. The primary adjustment process was via the barotropic mode. Altimetry proved to be a good constraint on the variable flow field, in particular, for constraining the barotropic field. The excellent data quality of the TOPEX/POSEIDON (T/P) altimeter data provided smooth and reliable forcing; but for our mesoscale study in a region of long decorrelation times O(30 days), the spatial coverage from the combined T/P and ERS 1 data sets was more important for constraining the solution and providing stable flow at all levels. Surface drifters provided an excellent constraint on both the barotropic and baroclinic model fields. More importantly, the drifters provided a reliable measure of the mean field. Hydrographic data were also applied as a constraint; in general, hydrography provided a weak but effective constraint on the vertical Rossby modes in the model. Finally, forecasts run over a 2‐month period indicate that the initial conditions optimized by the 20‐day adjoint assimilation provide more stable, longer‐term forecasts.

Use of INSAT winds for better depiction of monsoon depressions over the Indian region

AbstractThis study is aimed at evaluating the impact of non‐conventional winds using data obtained by INSAT satellites over the Indian region. The emphasis is on whether the satellite‐derived wind data improve the depiction of monsoon system, flow patterns, the centre of the system, etc. in the objective analysis of the wind field. For this purpose, monthly climatological normals of the wind field are considered as the initial guess field and then objective analyses of the wind field are performed, first using only conventional winds over the land areas and subsequently including winds constructed from cloud‐motion vectors at 850 and 700 hPa. This experiment was performed for the period of 19–21 September, 1991, when a monsoon depression formed over the Bay of Bengal. Verification of these analyses were made by comparing them with carefully drawn subjective analyses. It is inferred that INSAT winds have a positive impact on the objective analysis, and improvement in the analysis is more marked over the data‐void regions of the Arabian sea and the Bay of Bengal. The results presented in the study reveal that INSAT winds are of potential use in the objective analysis of the wind field, thus giving a better depiction of monsoon depression over the Indian region.

Energy Transports by Ocean and Atmosphere Based on an Entropy Extremum Principle. Part 1: Zonal Averaged Transports

The maximum entropy production principle suggested by Paltridge (1975) is applied to separating the satellite-determined required total transports into atmospheric and oceanic components. Instead of using the excessively restrictive equal energy dissipation hypothesis as a deterministic tool for separating transports between the atmosphere and ocean fluids, the satellite-inferred required 2D energy transports are imposed on Paltridge's energy balance model, which is then solved as a variational problem using the equal energy dissipation hypothesis only to provide an initial guess field. It is suggested that Southern Ocean transports are weaker than previously reported. It is argued that a maximum entropy production principle can serve as a governing rule on macroscale global climate, and, in conjunction with conventional satellite measurements of the net radiation balance, provides a means to decompose atmosphere and ocean transports from the total transport field.

On the use of outgoing longwave radiation data in incorporating divergent part of the wind in analysis

In the present study, kinematic divergence computed using ECMWF grid point data at 850 hPa is enhanced by using the relationship between OLR and divergence. This new enhanced divergence is used to compute the velocity potential and then, the divergence part of the wind is obtained from velocity potetial. To obtain the rotational part of wind, we computed the vorticity from wind data, and subsequently stream function and obtained and the rotational part of the wind from the stream function. The total wind is the combination of divergent part obtained from modified velocity potential (using OLR data) and rotational part from unmodified stream function. This total wind field is used as initial guess for univariate objective analysis by optimum interpolation scheme so that Initial Guess field contained the more realistic divergent part of the wind. Consequently, the analysed field also will contain the divergent part of the wind.

Direct Computation of Geostrophic Winds from Observed Winds Using the Balance Equation

Abstract In certain meteorological problems it is desirable to make a grid-point analysis of observed winds. In order to combine a wind analysis with other quantities, or to use the wind analysis in a numerical model, one may wish to know the geostrophic winds (or the heights) that conform to the analyzed winds. Many previous studies have shown that the balance equation accurately describes relationships between winds and the height field. In this paper the balance equation is used to equate geostrophic vorticity at each grid point to a sum of terms evaluated from the wind analysis. Then the geostrophic winds are found by altering an initial guess field of zonal and meridional wind components until the geostrophic vorticity and divergence required at each point are met within a close tolerance. The final wind vectors are a geostrophic field that conforms to the original wind analysis according to the balance equation. Typical examples are shown of geostrophic wind vectors computed by this method in a slop...

The Analysis of Upper-Level Humidity

The incorporation of diagnostic data obtained from surface observations into a humidity analysis at the 850-, 700- and 500-mb levels is tested using European surface and upper-air data for 22 observation times in February 1962. Sparse data conditions are simulated by withholding a portion of both surface and upper-air data. The rms errors and contingency table per cent correct scores indicate that an improved analysis is obtained in data sparse areas by weighting the diagnostic data relative to the radiosonde data. The most appropriate weighting is a function of the reliability of the diagnosis and the data density. The effects of using different initial guess fields, varying the application of the successive approximation technique (SAT) to these fields, and applying smoothing were also considered.

Mean meridional circulations in the Northern Hemisphere lower stratosphere during 1964 and 1965

AbstractZonally‐averaged mean monthly circulations in the meridional plane, which have been forced from momentum and heat sources, are presented for the 100–50 mb, 50–30 mb and 30–10 mb pressure layers, between 25°N latitude and 80°N latitude, during 1964 and 1965. The zonal momentum and continuity equations, written in spherical coordinates, are combined, using an iteration process, to compute mean meridional and vertical motions.Fixed boundary values are required for the vertical component at 10 mb where the downward vertical integration starts and for both components at 22·5°N and 82·5°N latitudes. These values are computed from the initial guess fields, which are based on approximate thermodynamic balance for the vertical component and a momentum balance for the meridional component. The effects of these boundary conditions on the interior motions are discussed.The results of the computed velocity components show a reasonable and consistent pattern, both in time and space. In winter months, motions are much more intense than in summer months and the flow patterns are characterized by cell‐like structures, having upward motions over the pole and downward motions over middle latitudes. It appears as though the lower stratospheric motions over mid‐latitudes are an extension of the tropospheric indirect mean cell. There is a poleward shift in the motions as winter progresses into spring and an equatorward shift as autumn progresses into winter. In summer, the motions are small and not too well organized.In the January and July 1964 momentum budgets, it is shown that a near balance exists between the Coriolis torque and the convergence of eddy momentum flux, which gives an approximate expression for calculating mean meridional velocities. In the January 1964 heat budget, at middle latitudes, a near balance is shown between adiabatic subsidence and heat sources due to radiation and eddy heat‐flux convergence. This balance implies an approximate solution for mean vertical motions. However, this approximation does not appear to be valid near the latitudinal boundaries during January or in certain regions during July.

A direct method of stream-function computation

An iterative method is described that fits a stream function (Ψ) to wind observations. The technique was designed for use in tropical regions where errors in height data and other difficulties preclude use of the geostrophic or balance equations to obtain y; however, the technique is believed to be sufficiently general to have other applications. Since the calculations may be carried out rapidly by an electronic computer, the technique might serve as a replacement for the laborious streamline-isotach method of tropical analysis.
 The equations basic to the computations are given. If the stream function is defined to have the units of height (i.e., meters), it is convenient to use observed heights as the initial-guess field. Several iterations are made until the computed values of Ψ stabilize within a pre-determined limit. Explicit calculations of vorticity and of boundary values of Ψ, as required in a stream function obtained by solution of a Poisson equation, are not needed. Analyses of computed values of Ψ in the Caribbean are compared with independent, subjective analyses of the same data, and show excellent agreement. Autocorrelations show that computed values of stream function were considerably more persistent than height data for the period studied.