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- Author or Editor: G. D. Hembree x
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Abstract
Two-week experimental forecasts were carried for 12 July Cases with a nine vertical level, 270 km grid-size hemispheric model, and the results were examined statistically. The solutions studied were the stationary (10-day average) and transient components of the general circulation; in particular, the ensemble mean of temperature, zonal wind and eddy kinetic energy; and the hemispheric maps of ensemble mean height fields. The predictive ability of this model was examined by comparing the results with observation and calculating statistical scores such as standard deviation, correlation coefficient and horizontal gradient (S1) score for 1000, 500 and 50 mb geopotential height verified against the NMC (National Meteorological Center) analysis. The results were also analyzed in terms of zonal wavenumbers of geopotential. So far as this model (1967 version) is concerned, the predictability in the lower atmosphere seems to decay more rapidly in July than in January. However, the predictability of the middle and upper troposphere is greater in July than in January; the planetary-scale waves were better predicted. The simulation of the summer stratosphere is very poor with the nine-level vertical resolution. The prediction was also compared with that of a spectral model of comparable horizontal and vertical resolution.
Abstract
Two-week experimental forecasts were carried for 12 July Cases with a nine vertical level, 270 km grid-size hemispheric model, and the results were examined statistically. The solutions studied were the stationary (10-day average) and transient components of the general circulation; in particular, the ensemble mean of temperature, zonal wind and eddy kinetic energy; and the hemispheric maps of ensemble mean height fields. The predictive ability of this model was examined by comparing the results with observation and calculating statistical scores such as standard deviation, correlation coefficient and horizontal gradient (S1) score for 1000, 500 and 50 mb geopotential height verified against the NMC (National Meteorological Center) analysis. The results were also analyzed in terms of zonal wavenumbers of geopotential. So far as this model (1967 version) is concerned, the predictability in the lower atmosphere seems to decay more rapidly in July than in January. However, the predictability of the middle and upper troposphere is greater in July than in January; the planetary-scale waves were better predicted. The simulation of the summer stratosphere is very poor with the nine-level vertical resolution. The prediction was also compared with that of a spectral model of comparable horizontal and vertical resolution.
Abstract
A two-week prediction was made, applying a general circulation model on Kurihara's global grid to an observed data set. The maps for the basic meteorological elements at 10 vertical levels for 5 days in March 1965 were analyzed manually with the aid of nephanalysis charts. This report discusses the forecast results selectively for the tropical areas only. The predicted wind, temperature, and precipitation were compared, whenever possible, with the observed data including satellite cloud pictures. The main objective was to attempt a tropical forecast for a case study, and to obtain a crude idea, based on one sample, about the feasibility of predicting tropical weather systems. Some capability in the prediction of the tropical atmosphere is evident for about 3 days, in particular for the upper troposphere, but the prediction needs considerable improvement for the lower troposphere as well as for the stratosphere.
Abstract
A two-week prediction was made, applying a general circulation model on Kurihara's global grid to an observed data set. The maps for the basic meteorological elements at 10 vertical levels for 5 days in March 1965 were analyzed manually with the aid of nephanalysis charts. This report discusses the forecast results selectively for the tropical areas only. The predicted wind, temperature, and precipitation were compared, whenever possible, with the observed data including satellite cloud pictures. The main objective was to attempt a tropical forecast for a case study, and to obtain a crude idea, based on one sample, about the feasibility of predicting tropical weather systems. Some capability in the prediction of the tropical atmosphere is evident for about 3 days, in particular for the upper troposphere, but the prediction needs considerable improvement for the lower troposphere as well as for the stratosphere.
Abstract
A series of 2-week predictions were made with a general circulation model for 12 winter cases selected from the period 1964–69. All were January cases. The same prediction model—the most sophisticated and probably the most realistic model of those we tested in 1967—was used throughout. The model was hemispheric and had an N = 40 grid (grid size of about 270 km at mid-latitudes) with nine vertical levels. A detailed description of the model's performance is attempted by making statistical analyses of the forecast results compared with observed data. The analyses also provide useful insight into the dynamical behavior of the long waves in the middle latitude zone. The verification study reveals the practical limit of predictability with the 1967 version of the Geophysical Fluid Dynamics Laboratory model. For example, the correlation coefficient between prediction and observation of the 500-mb geopotential deviation from January normal stays above zero until the 10th day. A spectral study of the planetary and cyclone waves was also made. The behavior of the ultralong wave in this model is disappointing, but cyclone waves are reasonably well predicted until the eighth day.
Abstract
A series of 2-week predictions were made with a general circulation model for 12 winter cases selected from the period 1964–69. All were January cases. The same prediction model—the most sophisticated and probably the most realistic model of those we tested in 1967—was used throughout. The model was hemispheric and had an N = 40 grid (grid size of about 270 km at mid-latitudes) with nine vertical levels. A detailed description of the model's performance is attempted by making statistical analyses of the forecast results compared with observed data. The analyses also provide useful insight into the dynamical behavior of the long waves in the middle latitude zone. The verification study reveals the practical limit of predictability with the 1967 version of the Geophysical Fluid Dynamics Laboratory model. For example, the correlation coefficient between prediction and observation of the 500-mb geopotential deviation from January normal stays above zero until the 10th day. A spectral study of the planetary and cyclone waves was also made. The behavior of the ultralong wave in this model is disappointing, but cyclone waves are reasonably well predicted until the eighth day.
Abstract
Two-week predictions were made for two winter cases by applying the Geophysical Fluid Dynamics Laboratory high-resolution, nine-level, hemispheric, moist general circulation model. Three versions of the model are discussed: Experiment 1 includes the orography but not the radiative transfer or the turbulent exchange of heat and moisture with the lower boundary; Experiment 2 accounts for all of these effects as well as land-sea contrast; Experiment 3 allows, in addition, the difference in thermal properties between the land-ice and sea-ice surfaces, as well as an 80% relative humidity condensation criterion reduced from the 100% criterion in Experiments 1 and 2.
The computed results are compared with observed data in terms of the evolution of individual cyclonic and anticyclonic patterns, the zonal mean structure of temperature, wind, and humidity, the precipitation over the United States, and the hemispheric energetics.
The forecast near sea level was considerably improved in Experiments 2 and 3 over Experiment 1. The experiment succeeded in forecasting the birth of second and third generation extratropical cyclones and their behavior thereafter. The hemispheric sum of precipitation was increased five times in Experiment 2 over that in Experiment 1, and even more in Experiment 3, the greatest contribution occurring in the Tropics. Two winter cases were considered. The correlation coefficients between the observed and the forecast patterns for the change of 500-mb geopotential height from the initial time remained above 0.5 for 13 days in one case and for 9 days in the other.
There are, however, several defects in the model. The forecast temperature was too low. In the flow pattern the intensities of the Highs and Lows weakened appreciably after 6 or 8 days, reflecting the fact that the forecast of eddy kinetic energy was less than the observed. On the other hand, the intensity of the tropospheric westerlies was too great.
Abstract
Two-week predictions were made for two winter cases by applying the Geophysical Fluid Dynamics Laboratory high-resolution, nine-level, hemispheric, moist general circulation model. Three versions of the model are discussed: Experiment 1 includes the orography but not the radiative transfer or the turbulent exchange of heat and moisture with the lower boundary; Experiment 2 accounts for all of these effects as well as land-sea contrast; Experiment 3 allows, in addition, the difference in thermal properties between the land-ice and sea-ice surfaces, as well as an 80% relative humidity condensation criterion reduced from the 100% criterion in Experiments 1 and 2.
The computed results are compared with observed data in terms of the evolution of individual cyclonic and anticyclonic patterns, the zonal mean structure of temperature, wind, and humidity, the precipitation over the United States, and the hemispheric energetics.
The forecast near sea level was considerably improved in Experiments 2 and 3 over Experiment 1. The experiment succeeded in forecasting the birth of second and third generation extratropical cyclones and their behavior thereafter. The hemispheric sum of precipitation was increased five times in Experiment 2 over that in Experiment 1, and even more in Experiment 3, the greatest contribution occurring in the Tropics. Two winter cases were considered. The correlation coefficients between the observed and the forecast patterns for the change of 500-mb geopotential height from the initial time remained above 0.5 for 13 days in one case and for 9 days in the other.
There are, however, several defects in the model. The forecast temperature was too low. In the flow pattern the intensities of the Highs and Lows weakened appreciably after 6 or 8 days, reflecting the fact that the forecast of eddy kinetic energy was less than the observed. On the other hand, the intensity of the tropospheric westerlies was too great.
Abstract
With a 9-level general circulation model, all attempt was made to simulate numerically the breakdown of the circumpolar vortex in the winter stratosphere for the case of March 1965. The marching computations were started 2 and 5 days prior to the breakdown. The simulation of the vortex elongation and destruction was, to a certain extent, successful, but the split vortex in the prediction erroneously merged again after 8 days. The sudden warming was not simulated at all. The development of the Aleutian high associated with the vortex breakdown was not well computed. Studies are made on zonally averaged quantities pertaining to the tropospheric and stratospheric circulations and their coupling. The increase of eddy kinetic energy at the time of the amplification of zonal wavenumber 2 is discussed both for the numerical simulation and for the observed fields. It is reconfirmed that the eddy kinetic energy in the stratosphere is primarily supplied from below in the form of vertical flux of geopotential. The propagation of wave energy takes place through a rather narrow zonal belt at high latitude. A possible relation between the stratospheric vortex destruction and the tropospheric process of meandering westerlies is discussed in terms of vertical transmission of wave energy.
Abstract
With a 9-level general circulation model, all attempt was made to simulate numerically the breakdown of the circumpolar vortex in the winter stratosphere for the case of March 1965. The marching computations were started 2 and 5 days prior to the breakdown. The simulation of the vortex elongation and destruction was, to a certain extent, successful, but the split vortex in the prediction erroneously merged again after 8 days. The sudden warming was not simulated at all. The development of the Aleutian high associated with the vortex breakdown was not well computed. Studies are made on zonally averaged quantities pertaining to the tropospheric and stratospheric circulations and their coupling. The increase of eddy kinetic energy at the time of the amplification of zonal wavenumber 2 is discussed both for the numerical simulation and for the observed fields. It is reconfirmed that the eddy kinetic energy in the stratosphere is primarily supplied from below in the form of vertical flux of geopotential. The propagation of wave energy takes place through a rather narrow zonal belt at high latitude. A possible relation between the stratospheric vortex destruction and the tropospheric process of meandering westerlies is discussed in terms of vertical transmission of wave energy.
Abstract
Truncation error of the numerical solution in a circulation model is still one of the most serious sources of error for the extended-period prediction. Different grid intervals are taken and the behavior of the solution is studied empirically. The meshes for the hemispheric domain are N=20, 40 and 80, where N is the number of grid points between the pole and the equator on the stereographic projection map. Analysis revealed that finer meshes provide clearly better solutions even for the planetary-scale mode, and the N=80 solution is definitely different from the N=40 beyond about 6 days. Further comparisons were made to see if the N=80 solution is actually closer to observation. The results were encouraging. Promise is seen for improvement in the forecast to about 10 days. The inclusion of subgrid-scale eddy viscosity, which seems to be necessary when applying a grid to the flow field, is also examined.
Abstract
Truncation error of the numerical solution in a circulation model is still one of the most serious sources of error for the extended-period prediction. Different grid intervals are taken and the behavior of the solution is studied empirically. The meshes for the hemispheric domain are N=20, 40 and 80, where N is the number of grid points between the pole and the equator on the stereographic projection map. Analysis revealed that finer meshes provide clearly better solutions even for the planetary-scale mode, and the N=80 solution is definitely different from the N=40 beyond about 6 days. Further comparisons were made to see if the N=80 solution is actually closer to observation. The results were encouraging. Promise is seen for improvement in the forecast to about 10 days. The inclusion of subgrid-scale eddy viscosity, which seems to be necessary when applying a grid to the flow field, is also examined.
