Grid Point Values Research Articles

Interpolation of 1961–97 Daily Temperature and Precipitation Data onto Alberta Polygons of Ecodistrict and Soil Landscapes of Canada

Soil quality models developed for ecodistrict polygons (EDP) and the polygons of the soil landscapes of Canada (SLC) to monitor the concentration of soil organic matter require daily climate data as an important input. The objectives of this paper are (i) to provide a method that interpolates the daily station data onto the 894 SLC polygons and 150 EDP in the province of Alberta, Canada, so that the interpolated data fit not only climate mean but also climate variability, especially for the precipitation field, and hence can be used as realistic climate input to soil quality models and (ii) to understand the variability of the Alberta daily climate, such as precipitation frequency. The procedure interpolates the station data onto a dense network of grid points and then averages the gridpoint values inside polygons. The procedure and results for maximum temperature, minimum temperature, and precipitation are reported in detail. The interpolation uses the observed daily data for the period 1 January 1961–31 December 1997 (13 514 days) within the latitude–longitude box (45°–64°N, 116°–124°W). Because the precipitation field can have a short spatial correlation length scale and large variability, a hybrid of the methods of inverse-distance weight and nearest-station assignment is developed for interpolating the precipitation data. This method can reliably calculate not only the number of precipitation days per month, but also the precipitation amount for a day. The temperature field has a long spatial correlation scale, and its data are interpolated by the inverse-distance-weight method. Cross-validation shows that the interpolated results on polygons are accurate and appropriate for soil quality models. The computing algorithm uses all the daily observed climate data; despite that, some stations have a very short time record or only summer records.

A 40 year objective climatology of surface cyclones in the Mediterranean region: spatial and temporal distribution

AbstractA climatological analysis of the synoptic scale cyclones that occur in the Mediterranean region is carried out for an extended period of 40 years (1958–1997). The cyclones are identified with the aid of an objective method based on grid point values, available every 6 h. The study of the seasonal and diurnal variations of the frequency of cyclonic occurrences, with respect to the value of the central pressure, revealed that the major cyclonic centres appear to be different in frequency and location, reflecting the different triggering mechanisms. In the western Mediterranean region, the frequency of occurrence is higher in winter, more so for the intense cyclones, with no substantial diurnal difference in the Gulf of Genoa, and with a preference during the night in southern Italy. The Cyprus centre reveals diurnal variability in location, especially in the cold period, in accordance with the triggering mechanism, being associated principally with weak and moderate cyclones. In northwestern Africa, there appears to be two marked regions of high cyclonic frequency, not only in spring, but also in summer and autumn. The extremely high frequency of cyclonic occurrences in summer in the Mediterranean basin is attributed mainly to the generation of weak thermal lows. The number of rapidly deepening cyclones within 12 h and 24 h increases from the south to the north part of Mediterranean, being mostly favoured near the lee of Alps and the Gulf of Venice, occurring mainly after 06:00 co‐ordinated universal time (UTC). Copyright © 2001 Royal Meteorological Society

Global statistical space‐time scales of oceanic variability estimated from the TOPEX/POSEIDON altimeter data

Four years of the TOPEX/POSEIDON altimeter data are used to produce estimates of statistical space‐time scales of ocean variabilities for the sea surface height. A three‐dimensional (space‐time) correlation function with an anisotropic directional dependence is assumed. The function has Gaussian distributions in radial directions in the space‐time coordinates and ellipsoidal contour surfaces. The function can reveal the space‐time scales and propagations of the variabilities and statistical errors in the altimeter data. We evaluated the space‐time scales using the best fit correlation function to the altimeter data. The scales show geographical differences. This means that dominant variabilities depend on regions. We show an optimum interpolation (OI) method as an example of the application of the fitted correlation function. The OI is applied to the altimeter data in the space‐time domain to make grid point data with higher accuracy than those obtained from a usual spatial (two‐dimensional) OI (2‐D OI). The values of the correlation function are used for the correlation coefficients of the first guess error in the OI. A propagation diagram obtained from the space‐time OI (3‐D OI) shows clear propagations of planetary disturbances with larger amplitude. The grid point values from the 3‐D OI show better correspondences with sea levels from tide gauges than those from the 2‐D OI. The advantage is due to the data of the different cycles being additionally adopted and the correlation function reflecting propagation of the ocean variabilities.

470大規模風場推定における気象衛星雲画像からの雲移動ベクトルの利用可能性の検討

Now, the acid rain has become one of the environmental problems of global scales. In many cases, the cause substances of the acid rain are transported through a long distance. Therefore, the acid rain is not considered as domestic problems only. The long distance transportation model has been developed as one technique for solving the long distance transportation problems of the cause substances of such acidifying. In this model, presumption of a wind field is the most important factor.In order to apply this model to the East Asia area, we tried the presumption of the wind field using the cloud picture obtained from the GMS (Geostational Meteorological Satellite, Himawari by name.) We verified the accuracy of this wind field presumption technique by comparing mutually between the presumed technique of this wind field, the wind vector obtained by the Meteorological Agency Japan, upper-layers weather data, and the GPV (Grid Point Value) data.

STUDY ON AVERAGING THE DISTRIBUTED HYDROLOGICAL CONDITIONS FOR ESTIMATION OF REGIONAL EVAPOTRANSPIRATION

Regional evapotranspiration in the East-Japan is estimated by using NOAA/AVHRR data and GPV (Grid Point Values of meteorological conditions) data based on the heat balance method. Spatial resolutions of those data are different each other.In or order to get the estimated value of evapotranspiration, following two ways of data arrangement are examined and the results computed from the both ways are compared. At first in the paper, GPV data is interpolated to the scale of NOAA/AVHRR data. In the next, NOAA/AVHRR data is averaged to the scale of GPV data. At last, the authors make discussions on the scale averaging the hydrological conditions for getting more reasonable estimation of regional evapotranspiration.

The Semi-Lagrangian Method for the Numerical Resolution of the Vlasov Equation

The numerical resolution of kinetic equations and, in particular, of Vlasov-type equations is performed most of the time using particle in cell methods which consist in describing the time evolution of the equation through a finite number of particles which follow the characteristic curves of the equation, the interaction with the external and self-consistent fields being resolved using a grid. Another approach consists in computing directly the distribution function on a grid by following the characteristics backward in time for one time step and interpolating the value at the feet of the characteristics using the grid point values of the distribution function at the previous time step. In this report we introduce this last method, which couples the Lagrangian and Eulerian points of view and its use for the Vlasov equation and equations derived from it.

Forecast‐observation pattern relationships in NCEP medium range forecasts of non‐winter northern hemisphere 500‐mb height fields: Research note

Empirical orthogonal function (EOF) and singular value decomposition (SVD) analyses are applied to the Dynamical Extended Range Forecasting 90 (DERF90) dataset to find the most predictable areas and patterns in the non‐winter Northern Hemisphere 500‐mb height fields. Global 500‐mb height forecast and analysis fields covering 4 months of 1990 are used. The EOF method is applied to the forecast and analysis fields separately. A close correspondence between the forecast and analysis modes is found for 1‐day lead time. The correlation relations between these modes rapidly decrease with increasing forecast lead time. At 10‐day lead, the projections of the forecasts and corresponding analyses onto the strongest Northern Hemisphere EOF mode of the analyses correlate at 0.65, which is much higher than the general forecast‐analysis correlation of about 0.20. This particularly predictable mode consists of a Pacific/North America‐like pattern. Joint forecast vs. analysis correlation matrices were used to apply the SVD method to forecast and analysis fields. By design, the correlations between the forecast and analysis SVD modes are stronger than between the forecast and analysis EOF modes. Maps of temporal correlations between gridpoint values of analysis fields and the first and second EOF as well as SVD expansion coefficients of the forecast fields (i.e., heterogeneous EOF and SVD correlation maps) are used to find the regions of the best prediction skill. It is shown that the Pacific/North American, western and southeastern Pacific, the southern Atlantic and Indian ocean areas have relatively better prediction skill.

Spatial–Temporal Analysis of Temperature Using Smoothing Spline ANOVA

A new method, smoothing spline ANOVA, for combining station records of surface air temperature to get the estimates of regional averages as well as gridpoint values is proposed. This method is closely related to the optimal interpolation (also optimal averaging) method. It may be viewed as a generalization of these methods from spatial interpolation methods to a method interpolating in both spatial and temporal directions. The connection of this method to the commonly used anomaly approach is discussed in the context of correcting biases resulting from incomplete sampling. A main strength of this new method is its ability to borrow information across both space and time just like optimal interpolation does across space. This increases not only the accuracy of estimates but also the ability to correct various biases resulting from incomplete sampling. Some of these biases are ignored by the anomaly approach.

Easy to use Global and Regional Ionospheric Models — A Report on Approaches Used in Graz

Out of the necessity to provide quick access to ionospheric model data from various computer programs written in different languages (PASCAL, FORTRAN, IDL, etc.) we developed a “data box” approach in the following way: grid point values are calculated from an existing global or regional model and written into a data file. Good values for grid point distances are 5 degrees in latitude, 10 degrees in longitude and 10 km in height. Third order interpolation is used in all grid variables to find the model value where needed. For ray tracing applications splines can be used over the region of interest instead of simple interpolation.

Potential of continental-scale circulation for the determination of local daily surface variables

This study deals with one aspect of statistical downscaling, viz. links between the continental-scale upper-air circulation and surface weather variables on a daily scale. The circulation-to-weather links are expressed in terms of multiple regression between either grid point values or intensities of circulation variability modes and weather elements, including temperature variables, relative humidity, cloudiness, sunshine duration, zonal and meridional wind components, precipitation, and atmospheric pressure. The upper-air circulation influences the surface pressure, temperature and zonal wind most strongly. The relative humidity, cloudiness and sunshine duration appear not to be connected with circulation in winter at all. The low-frequency part of circulation (i.e. processes with periods longer than 10 days) is most efficient in specifying surface weather variables. The circulation-to-weather links manifest considerable intra- and interdecadal variations, posing doubts on the applicability of the ‘downscaling-from-circulation’ method of constructing climate change scenarios.

ANNUAL SEA LEVEL VARIABILITY INDUCED BY CHANGES IN SEA ICE EXTENT AND ACCUMULATION ON ICE SHEETS: AN ASSESSMENT BASED ON REMOTELY SENSED DATA

Changes of mean annual net accumulation at the surface on the grounded ice sheets of East Antarctica, West Antarctica and Greenland in response to variations in sea ice extent are estimated using grid-point values 100 km apart. The data bases are assembled principally by bilinear interpolation of remotely sensed brightness temperature (Nimbus-5 ESMR, Nimbus-7 SMMR), surface temperature (Nimbus-7 THIR), and surface elevation (ERS-1 radar altimeter). These data, complemented by field data where remotely sensed data are not available, are used in multivariate analyses in which mean annual accumulation (derived from firn emissivity) is the dependent variable; the independent variables are latitude, surface elevation, mean annual surface temperature, and mean annual distance to open ocean (as a source of energy and moisture). The last is the shortest distance measured between a grid point and the mean annual position of the 10% sea ice concentration boundary, and is used as an index of changes in sea ice extent as well as of mean concentration. Stepwise correlation analyses indicate that variations in sea ice extent of ± 50 km would lead to changes in accumulation inversely of ± 4% on East Antarctica, ± 10% on West Antarctica, and ±4% on Greenland. These results are compared with those obtained in a previous study using visually interpolated values from contoured compilations of field data; they substantiate the findings for the Antarctic ice sheets (±4% on East Antarctica, ±9% in West Antarctica), and suggest a reduction by one half of the probable change of accumulation on Greenland (from ±8%). The results also suggest a reduction of the combined contribution to sea level variability to ±0.19 mm a-1 (from ±0.22 mm a-1).

Short‐term rainfall prediction method using a volume scanning radar and grid point value data from numerical weather prediction

A physically based short‐term rainfall prediction method, which uses a volume scanning radar, is extended so that it utilizes grid point values from a numerical weather prediction model as supplementary information. The original short‐term prediction method mainly consists of a conceptual rainfall model that can predict rainfall distribution, particularly over mountainous regions, in a qualitative sense. On the other hand, the grid point values from the numerical weather prediction model, the Japan Spectral Model developed by the Japan Meteorological Agency, are operationally distributed as the grid point value (GPV) data. In the original short‐term prediction method the three‐dimensional wind field as well as initial distributions of the air temperature and water vapor were identified using topography and upper air observations. In the extended method, however, in identifying those initial values, the information from the GPV data is used instead of the upper air observations in order to accommodate large differences in temporal and spatial resolution between radar information and upper air observations. It is noted that this extended method does not use predicted GPV rainfall data. The conceptual rainfall model plays the role of bridging the gap between radar information and numerical weather prediction scales. This extended method is applied to a rainfall event which occurred in the bai‐u season (one of the rainy seasons of Japan) in July 1994. Results show that for the extended lead time of three and four hours, prediction of the expanding rainfall area was improved.

CLIMATOLOGICAL CHARACTERISTICS OF SPRINGTIME LOWER TROPOSPHERIC AIRFLOW OVER CENTRAL AND EASTERN NORTH AMERICA

A climatology of springtime lower tropospheric airflow, as represented by 850 hPa observed winds and 1000 hPa geostrophic winds, is presented for central and eastern North America. The climatology is based on twice-daily grid-point values for 1969–1989 from the operational analyses for the Northern Hemisphere prepared by the USA National Weather Service's National Meteorological Centre. Sixteen-point wind roses are used to show the spatial and temporal distributions by direction category of wind frequency, average speed, and wind run. These analyses are supplemented by resultant wind vector and streamline maps for each month. Evident in the climatological distributions is the declining strength of the circulation from March to May, the northward migration and strengthing of the North Atlantic subtropical anticyclone in late spring, and the nocturnal strengthening and veering of southerly airflow over the southern Great Plains. Additionally, areas of cyclonic and/or anticyclonic resultant flow correspond well with earlier identified centres of cyclogenesis and anticyclogenesis. The results presented here may provide a useful climatological baseline for future studies involving lower tropospheric airflow.

Cyclogenesis over the Aegean Sea: Identification and synoptic categories

AbstractAn attempt is made to identify and investigate the structure, behaviour and synoptic characteristics of cyclogenesis over the Aegean Sea. A simple, realistic and easily used methodology of identification, in an analytical form, was established. This combines two types of criteria: synoptic and dynamic/thermodynamic. Six synoptic categories that could favour cyclogenesis over the Aegean Sea are distinguished according to the synoptic criteria. Grid‐point values of geopotential height and temperature are used to calculate the dynamic/thermodynamic criteria, which are used to identify potential cases of cyclogenesis with respect to the thermodynamic prerequisites and the time continuance. It is demonstrated that cyclogenesis over the Aegean Sea is not as rare as was believed. The majority of cases result from the prevalence of a south‐westerly flow, a long‐wave trough and a closed system over the Aegean Sea. The cyclogenesis appears to occur primarily in the cold period of the year, mainly from October to May, and to have a small intensity and lifetime.

Short-term Rainfall Prediction Method Using a Volume Scanning Radar and GPV data

A physically-based short-term rainfall prediction method, which uses a volume scanning radar, is extended so that it utilizes grid point values from a numerical weather prediction, namely GPV data, as supplementary information. It is noted that this extended method does not use predicted GPV rainfall data The conceptual rainfall model in the prediction method plays the role of bridging a gap between radar information and the numerical-weather prediction. This extended method is applied to a rainfall event which occurred in the Baiu season, in July of 1994. Results shows that for extended lead time of three and four hours, the prediction of expanding rainfall area was greatly improved.

Wind observation in view of meteorological services

In the present paper wind observation was discussed in view of meteorological services in Japan. The main purpose of the wind observations at meteorological observatories is to collect data for numerical weather prediction use as initial values. Collected data arc processed by quality checks, initialization and 4-dimensional assimilation technique, and then converted to 3-dimensional grid point values. In spite of some concerns of representativity of the meteorological stations, therefore the present surface observational system is suitable for collecting these data.For calculating design wind speed by using wind data collected at meteorological stations we should adopt some correction techniques for evaluating effects of changes of anemometers and observational conditions. For this purpose wind tunnel test and numerical simulation techniques will be considered.

Recent Climatology of Kinematic Variables in the TOGA-COARE Region

Abstract The importance of the “warm pool” region of the western Pacific on in situ and global-scale circulations has gained wide recognition in the last decade with the advent of TOGA and, more recently, with the field experiment TOGA-COARE. The objectives of this study are two fold: 1)to provide a climatology of the kinematic properties of the atmosphere over the tropical western Pacific and adjacent areas, based on 1985–90 analyses., and 2) to focus on a detailed diagnosis of the four-month period, November–February, since the intensive observing period of TOGA-COARE occurred during those months. The dataset used in this study is the WCRP/TOGA archive II analyses produced by ECMWF. The analyses contain uninitialized gridpoint values of several variables at 2.5° lat/long and at 14 mandatory pressure levels. The dataset also includes a full surface package at the same horizontal resolution. The variables examined are mean sea level pressure, zonal and meridional wind components, vertical velocity, and re...

A Class of Semi-Lagrangian Integrated-Mass (SLM) Numerical Transport Algorithms

A class of conservative numerical transport algorithms is developed based on the concept of Lagrangian mass transport between fixed cells in which density distribution is estimated on the basis of local and adjacent gridpoint values. Upstream and downstream variants of the proposed class of semi-Lagrangian integrated-mass (SLIM) schemes are presented; the upstream form corresponds in essence to the scheme developed by Rancic. Both variants of SLIM are compared with the traditional semi-Lagrangian scheme in two spatial dimensions in Cartesian geometry: on canonical tests, as well as in a bubble convection experiment.

Degrees of freedom in Northern Hemisphere circulation data

Estimates of the number of degrees of freedom (dof) of the 700 hPa Northern Hemisphere extratropical wintertime daily and time average circulation patterns are presented using two statistical methods. In the first method, it is assumed that the distribution of the mean square distances between the circulation patterns and the climate mean follows a χ2 distribution. The number of dof of the best χ2 fit to the empirical data is the most probable number of dof of the circulation data. The other, newly developed hyperspheres method compares the local density properties in the empirical data to density in independently and identically distributed (iid) normal distributions with different number of dof. The best fit, again, determines the most probable number of dof for the observed data. Though the hyperspheres method uses the smallest scales available in the data, just as the Grassberger-Procaccia method (GPM) and other “local” dimension estimation methods, it has distinct features. Most importantly, the GPM assumes that the empirical data is unbounded and distributed uniformly in the multivariate space. In contrast, the hyperspheres method, in accordance with many geophysical applications, assumes a bounded distribution in which density is a strong function of distance from the mean. Additionally, the hyperspheres method directly uses density information, that is neglected by GPM. The advantages of the hyperspheres method as compared to GPM are: (1) no systematic negative bias is present in the dof estimates; (2) the edge effect is eliminated; (3) no scaling is necessary. The results from the two methods overlap, thus indicating that at the 10% significance level the number of dof of the daily circulation data set is 24. This result pertains to a finite dataset in which the definitional requirement for dynamical dimension that the scales measured go to zero is not satisfied. We interpret our dof results as the dimension of a hypothetical subset of the atmospheric circulation that governs the large scale motions. Since the database of this study covers only part of the global atmosphere, the dimension of the whole atmosphere would be larger than our estimate. Our qualitative dimension estimate for the global circulation (60–90) refers to the minimum number of independent variables needed to model the large scale, low frequency variability of the atmosphere. In the present study grid point values served to describe the dynamical system of the atmosphere (spatial embedding, instead of time-delay or temporal embedding.) An argument is made that due to weak coupling between remote processes, estimates with temporal embedding measure only the dimension of a regional subset of the large-scale global circulation DOI: 10.1034/j.1600-0870.1995.t01-3-00005.x

Non-Linear Inversion Travel-Time Tomography: Imaging High-Contrast Inhomogeneities

An iterative and constrained non-linear travel-time tomographic scheme is developed for imaging high-contrast inhomogeneities. The technique has been successfully tested using synthetic data. We have investigated the influence upon the image quality of the random errors in travel times for a cross-hole survey configuration. In the forward problem, the ray path is traced by finding the minimal travel time of each shot-receiver pair in the updated model. For non-linear inversion, we approximate the velocity distribution with a specific first-order surface function so that the analytical derivatives with respect to each grid-point value of the velocity variation can be calculated. A constrained inversion from an arbitrary starting model is implemented in an iterative fashion. Our results indicate that with 180° symmetric angular coverage and a cell size comparable to the minimum dimension of the target, it is possible to get a resolvable image of a high-contrast target only in the direction parallel to the boreholes, even without a priori information. Constraints from knowledge about the velocity distribution along the boreholes or along the surface are very important in overcoming the poor directional resolution. The combination of cross-hole data with VSP data substantially improves travel-time tomography as a means of imaging high-contrast inhomogeneities. The results also show that if the relative travel-time random errors in data exceed an estimated expected value of about 2.5% the fine detail in the shape of a reconstructed target could be severely distorted.