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Abstract
An objective analysis scheme developed at the Goddard Laboratory for Atmospheric Sciences (GLAS) to assimilate meteorological data is described. Wind, geopotential height, and relative humidity are analyzed on mandatory pressure levels. Surface pressure and temperature are reduced to sea level and analyzed there. The objective analysis procedure is of the successive correction type, but modified to account for variable data density and quality.
A sample analysis is presented for 1200 GMT 19 January 1979 and shows good agreement with the one produced by the European Centre for Medium Range Weather Forecasts (ECMWF). The present analysis/forecast system demonstrates reasonable forecast skill over the Northern Hemisphere for an ensemble of five-day integrations during the First Special Observing Period (SOP-1) of the First GARP (Global Atmospheric Research Program) Global Experiment (FGGE).
The vertical motion field shows excellent agreement with the large-scale synoptic pattern for the 1200 GMT 19 January case. The mean meridional circulation depicted in the FGGE analysis is in close agreement with observational estimates.
Abstract
An objective analysis scheme developed at the Goddard Laboratory for Atmospheric Sciences (GLAS) to assimilate meteorological data is described. Wind, geopotential height, and relative humidity are analyzed on mandatory pressure levels. Surface pressure and temperature are reduced to sea level and analyzed there. The objective analysis procedure is of the successive correction type, but modified to account for variable data density and quality.
A sample analysis is presented for 1200 GMT 19 January 1979 and shows good agreement with the one produced by the European Centre for Medium Range Weather Forecasts (ECMWF). The present analysis/forecast system demonstrates reasonable forecast skill over the Northern Hemisphere for an ensemble of five-day integrations during the First Special Observing Period (SOP-1) of the First GARP (Global Atmospheric Research Program) Global Experiment (FGGE).
The vertical motion field shows excellent agreement with the large-scale synoptic pattern for the 1200 GMT 19 January case. The mean meridional circulation depicted in the FGGE analysis is in close agreement with observational estimates.
Abstract
Time averages of the latitudinal distribution of kinetic energy and terms of the kinetic energy equation are presented as depicted by the Goddard Laboratory for Atmospheric Science (GLAS) analyses of the First GARP Global Experiment (FGGE) during the First Special Observing Period (SOP-1). Monthly averages display peaks in the stationary wave energy at 30°N and in the tropics. Global decompositions of the streamfunction and velocity potential in spherical harmonics are truncated at the fourth degree. The kinetic energy distribution of the associated wind field displays peaks in the tropics and northern mid-latitudes in January, but only a tropical peak in February.
The Eliassen-Palm relationship for latitudinal momentum and geopotential wave transport appears to have some support in these analyses, particularly in the mid-latitudes. In the deep tropics, latitudinal convergence of the fully resolved stationary wave momentum transport accompanies latitudinal convergence of stationary wave geopotential flux in westerly flow, in contradiction to this relationship.
Such results make it difficult to interpret time averages in terms of idealized wave propagation and linear theories. However, there is an interesting correspondence between observed weekly averages of the global-scale kinetic energy and the zonally averaged wind.
Abstract
Time averages of the latitudinal distribution of kinetic energy and terms of the kinetic energy equation are presented as depicted by the Goddard Laboratory for Atmospheric Science (GLAS) analyses of the First GARP Global Experiment (FGGE) during the First Special Observing Period (SOP-1). Monthly averages display peaks in the stationary wave energy at 30°N and in the tropics. Global decompositions of the streamfunction and velocity potential in spherical harmonics are truncated at the fourth degree. The kinetic energy distribution of the associated wind field displays peaks in the tropics and northern mid-latitudes in January, but only a tropical peak in February.
The Eliassen-Palm relationship for latitudinal momentum and geopotential wave transport appears to have some support in these analyses, particularly in the mid-latitudes. In the deep tropics, latitudinal convergence of the fully resolved stationary wave momentum transport accompanies latitudinal convergence of stationary wave geopotential flux in westerly flow, in contradiction to this relationship.
Such results make it difficult to interpret time averages in terms of idealized wave propagation and linear theories. However, there is an interesting correspondence between observed weekly averages of the global-scale kinetic energy and the zonally averaged wind.
Abstract
The influence of tropical wind data on the numerical prediction of ultralong waves is examined. Two data assimilation experiments are performed using the GLAS fourth-order general circulation model. The two experiments are identical except that one utilizes tropical wind data while the other does not. Six forecasts are generated from the initial conditions provided by each experiment.
After two days, a reduction in the extratropical wind error is found in the assimilation experiment with tropical wind data. For the six pairs of forecasts examined, the effect of tropical wind data on the 72 h planetary wave prediction is positive in four cases and negative in two cases over the western half of the Northern Hemisphere. Also, the 72 h planetary wave error appears in a predominantly barotropic mode.
A detailed examination of the 0000 GMT 15 January 1979 case reveals that the planetary waves are more strongly affected by the wind data in the Northern Hemisphere than in the Southern Hemisphere. Examination of the velocity potential suggests the presence of stronger heating gradients in the no-tropical-wind forecast. The differences present in the initial divergent wind field remain largely restricted to the tropics after 72 h whereas significant differences may be seen in the rotational wind component at all latitudes after 72 h.
Abstract
The influence of tropical wind data on the numerical prediction of ultralong waves is examined. Two data assimilation experiments are performed using the GLAS fourth-order general circulation model. The two experiments are identical except that one utilizes tropical wind data while the other does not. Six forecasts are generated from the initial conditions provided by each experiment.
After two days, a reduction in the extratropical wind error is found in the assimilation experiment with tropical wind data. For the six pairs of forecasts examined, the effect of tropical wind data on the 72 h planetary wave prediction is positive in four cases and negative in two cases over the western half of the Northern Hemisphere. Also, the 72 h planetary wave error appears in a predominantly barotropic mode.
A detailed examination of the 0000 GMT 15 January 1979 case reveals that the planetary waves are more strongly affected by the wind data in the Northern Hemisphere than in the Southern Hemisphere. Examination of the velocity potential suggests the presence of stronger heating gradients in the no-tropical-wind forecast. The differences present in the initial divergent wind field remain largely restricted to the tropics after 72 h whereas significant differences may be seen in the rotational wind component at all latitudes after 72 h.
Abstract
The influence of tropical latent heating on the short-to-medium-range numerical prediction of ultralong waves is examined. Two integrations of the GLAS general circulation model are made from the came initial state. One forecast utilizes the full model physics, the other contains no latent heating in the tropical belt from 20°S to 20°N.
The tropical and subtropical divergence fields react to differences in the latent heating within half a day. Differences in the rotational wind field within these latitudes are noted in about three days, while at mid-latitudes (30°–60°) the influence is not felt until five days. At higher latitudes the five-day predictions of a strong North Atlantic block with and without latent heating are quite similar.
Although the greatest changes in the heating field occur in the Southern Hemisphere, the largest temperature, height and wind change take place in the Northern Hemisphere. It appears that the upper troposheric tropical westerlies are sustained in the model by tropical heat sources, and reverse to easterlies when these sources are removed.
Abstract
The influence of tropical latent heating on the short-to-medium-range numerical prediction of ultralong waves is examined. Two integrations of the GLAS general circulation model are made from the came initial state. One forecast utilizes the full model physics, the other contains no latent heating in the tropical belt from 20°S to 20°N.
The tropical and subtropical divergence fields react to differences in the latent heating within half a day. Differences in the rotational wind field within these latitudes are noted in about three days, while at mid-latitudes (30°–60°) the influence is not felt until five days. At higher latitudes the five-day predictions of a strong North Atlantic block with and without latent heating are quite similar.
Although the greatest changes in the heating field occur in the Southern Hemisphere, the largest temperature, height and wind change take place in the Northern Hemisphere. It appears that the upper troposheric tropical westerlies are sustained in the model by tropical heat sources, and reverse to easterlies when these sources are removed.
Abstract
The vertical and temporal Structure of the global scale flow in the Goddard Laboratory for Atmospheric Sciences analyses of data from the First GARP Global Experiment are presented. The fields are represented in terms of spherical harmonic expansions of the streamfunction, velocity potential and geopotential. The global scale patterns are obtained from triangular truncations of such series, neglecting terms past the fourth degree.
Some modes display prominent high frequency oscillations in the velocity potential and geopotential height that may be related to diurnal cycles of cumulus convection. Such oscillations are not apparent in the streamfunction. Low-order harmonics with nodes only along latitude circles are nearly equivalent barotropic. However, those harmonics that have no nodes between the poles reverse phase with height.
The following conclusions are drawn regarding the global scale patterns: 1) Since the divergent component of the meridional flow is not much smaller than the rotational part, the global scale pattern resembles forced modes of linear tidal theory more closely than it resembles free modes. 2) Because the vertical structure reverses, longitudinal heating gradients are probably important to the forcing. 3) The high frequency oscillations of the velocity potential and height field imply high frequency components in the forcing due to heating. 4) Monthly and weekly averages display suggestive teleconnection patterns.
Abstract
The vertical and temporal Structure of the global scale flow in the Goddard Laboratory for Atmospheric Sciences analyses of data from the First GARP Global Experiment are presented. The fields are represented in terms of spherical harmonic expansions of the streamfunction, velocity potential and geopotential. The global scale patterns are obtained from triangular truncations of such series, neglecting terms past the fourth degree.
Some modes display prominent high frequency oscillations in the velocity potential and geopotential height that may be related to diurnal cycles of cumulus convection. Such oscillations are not apparent in the streamfunction. Low-order harmonics with nodes only along latitude circles are nearly equivalent barotropic. However, those harmonics that have no nodes between the poles reverse phase with height.
The following conclusions are drawn regarding the global scale patterns: 1) Since the divergent component of the meridional flow is not much smaller than the rotational part, the global scale pattern resembles forced modes of linear tidal theory more closely than it resembles free modes. 2) Because the vertical structure reverses, longitudinal heating gradients are probably important to the forcing. 3) The high frequency oscillations of the velocity potential and height field imply high frequency components in the forcing due to heating. 4) Monthly and weekly averages display suggestive teleconnection patterns.
Abstract
The spectral energetics of the Northern Hemisphere circulation during blocking episodes of the FGGE year is investigated with gridded analyses of observational data and Parallel simulation experiments. The purpose of this study is to describe the energetics distinctions of the observed and simulated blockings in the context of the general circulation and to assess the capability of the model to simulate blockings.
In the observed circulation a pronounced winter blocking is developed and maintained by the nonlinear wave-wave interaction L(1) from the kinetic energy source for n = 3–10, where L(n) is the transfer of eddy kinetic energy from all other wavenumbers to wavenumber n. In the case of the. double blocking in the winter, both L(1) and L(2) support the blocking. The kinetic energy source of n=3–10 for upscale input at n = 1 and 2 is supported by the baroclinic conversion at n3–10. The simulated winter circulation shows strong baroclinic conversion at all wavenumbers, including ultralong waves. However, the simulation fails to produce pronounced blocking for the absence of L(1), and the converted energy cascades down to shorter waves. The wave-mean transfer of kinetic energy from the large-scale disturbances to the zonal mean component further prevents the accumulation of the kinetic energy at the ultralong waves.
In contrast to the winter situation, the summer blocking seems to be directly supported by both L(4) and baroclinic conversion at other planetary-scale waves. Consequently, the summer circulation is better simulated than the winter circulation.
Abstract
The spectral energetics of the Northern Hemisphere circulation during blocking episodes of the FGGE year is investigated with gridded analyses of observational data and Parallel simulation experiments. The purpose of this study is to describe the energetics distinctions of the observed and simulated blockings in the context of the general circulation and to assess the capability of the model to simulate blockings.
In the observed circulation a pronounced winter blocking is developed and maintained by the nonlinear wave-wave interaction L(1) from the kinetic energy source for n = 3–10, where L(n) is the transfer of eddy kinetic energy from all other wavenumbers to wavenumber n. In the case of the. double blocking in the winter, both L(1) and L(2) support the blocking. The kinetic energy source of n=3–10 for upscale input at n = 1 and 2 is supported by the baroclinic conversion at n3–10. The simulated winter circulation shows strong baroclinic conversion at all wavenumbers, including ultralong waves. However, the simulation fails to produce pronounced blocking for the absence of L(1), and the converted energy cascades down to shorter waves. The wave-mean transfer of kinetic energy from the large-scale disturbances to the zonal mean component further prevents the accumulation of the kinetic energy at the ultralong waves.
In contrast to the winter situation, the summer blocking seems to be directly supported by both L(4) and baroclinic conversion at other planetary-scale waves. Consequently, the summer circulation is better simulated than the winter circulation.
Abstract
With the increase in the observations data provided by FGGE and the use of global circulation models with full physics for the data assimilation, it is now becoming feasible to attempt to estimate globally the atmospheric diabatic heating. The thermodynamic equation in isobaric coordinates and the data generated by the FGGE III-b analysis of the Goddard Laboratory for Atmospheres (GLA) are employed to serve this purpose.
The results of the present study generally agree with other previous investigations. However, some important difference are also revealed. 1) The diabatic heating obtained in the tropics in the present study is larger than that obtained elsewhere; 2) the relatively large heating over the mountainous areas shown in other studies does not appear; 3) no significant negative values of diabatic heating are found in the polar regions; and 4) unlike other studies cooling is noted over parts of Eurasia in the summer.
Abstract
With the increase in the observations data provided by FGGE and the use of global circulation models with full physics for the data assimilation, it is now becoming feasible to attempt to estimate globally the atmospheric diabatic heating. The thermodynamic equation in isobaric coordinates and the data generated by the FGGE III-b analysis of the Goddard Laboratory for Atmospheres (GLA) are employed to serve this purpose.
The results of the present study generally agree with other previous investigations. However, some important difference are also revealed. 1) The diabatic heating obtained in the tropics in the present study is larger than that obtained elsewhere; 2) the relatively large heating over the mountainous areas shown in other studies does not appear; 3) no significant negative values of diabatic heating are found in the polar regions; and 4) unlike other studies cooling is noted over parts of Eurasia in the summer.
Abstract
The energetics in numerical weather forecast experiments with the NCAR general circulation model have been analyzed. The 6-layer, 5-degree, second-generation global model was used to make two 10-day forecasts with the same initial conditions. The two experiments differed primarily in the methods of convective parameterization.
Hemispheric integrals of the model energies and energy transformations are presented in the context of their approach to a quasi-equilibrium climatology. Spectral and spatial analyses of the eddy energies and transformations provide further insight into the model response to the initial conditions. After the initial adjustment, the eddy kinetic energy appears to lag the conversion from eddy available potential energy to eddy kinetic energy by at least 48 h in the long waves (wavenumbers 1–4) and by approximately 24 h in the baroclinic waves (wavenumbers 5–7), whereas little or no time lag is apparent in the short waves (wavenumbers 8–12).
The sensitivity of the forecast energetics to two different convective parameterizations is also examined. There is little appreciable difference between the two experiments in the eddy kinetic energy integrals during the first 36 h of the forecast, but temporal patterns of the eddy transformations are distinctly different after 12 h.
Abstract
The energetics in numerical weather forecast experiments with the NCAR general circulation model have been analyzed. The 6-layer, 5-degree, second-generation global model was used to make two 10-day forecasts with the same initial conditions. The two experiments differed primarily in the methods of convective parameterization.
Hemispheric integrals of the model energies and energy transformations are presented in the context of their approach to a quasi-equilibrium climatology. Spectral and spatial analyses of the eddy energies and transformations provide further insight into the model response to the initial conditions. After the initial adjustment, the eddy kinetic energy appears to lag the conversion from eddy available potential energy to eddy kinetic energy by at least 48 h in the long waves (wavenumbers 1–4) and by approximately 24 h in the baroclinic waves (wavenumbers 5–7), whereas little or no time lag is apparent in the short waves (wavenumbers 8–12).
The sensitivity of the forecast energetics to two different convective parameterizations is also examined. There is little appreciable difference between the two experiments in the eddy kinetic energy integrals during the first 36 h of the forecast, but temporal patterns of the eddy transformations are distinctly different after 12 h.
Abstract
Four numerical simulations of the global atmosphere for January 1979 are analyzed to study the formation of blocking in terms of Northern Hemisphere energetics. The Goddard Laboratory for Atmospheres (GLA) 4° × 5° latitude-longitude grid general circulation model (GCM) and 2° × 2.5° grid GCM are employed with the GLA and Geophysical Fluid Dynamics Laboratory (GFDL) initial datasets.
The difficulty in simulating a realistic blocking due to inadequate wave–wave interaction can be attributed in part to inadequate grid resolution. Among four simulations, the simulations by the high resolution GCM produce realistically strong blockings with compatible spectral energetics as in the observed blocking episodes. The latitude–height cross sections of the energy variables of wavenumber 1 is presented to describe the dipole structure of blockings. Blocking development is also examined in time series of barotropic and baroclinic components of energy and associated conversions.
Abstract
Four numerical simulations of the global atmosphere for January 1979 are analyzed to study the formation of blocking in terms of Northern Hemisphere energetics. The Goddard Laboratory for Atmospheres (GLA) 4° × 5° latitude-longitude grid general circulation model (GCM) and 2° × 2.5° grid GCM are employed with the GLA and Geophysical Fluid Dynamics Laboratory (GFDL) initial datasets.
The difficulty in simulating a realistic blocking due to inadequate wave–wave interaction can be attributed in part to inadequate grid resolution. Among four simulations, the simulations by the high resolution GCM produce realistically strong blockings with compatible spectral energetics as in the observed blocking episodes. The latitude–height cross sections of the energy variables of wavenumber 1 is presented to describe the dipole structure of blockings. Blocking development is also examined in time series of barotropic and baroclinic components of energy and associated conversions.
Abstract
The global scale divergent and rotational flow components of the Global Weather Experiment (GWE) are diagnosed from three different analyses of the data. The rotational flow shows closer agreement between the analyses than does the divergent flow. Although the major outflow and inflow centers are similarly placed in all analyses, the global kinetic energy of the divergent wind varies by about a factor of 2 between different analyses while the global kinetic energy of the rotational wind varies by only about 10% between the analyses.
A series of real data assimilation experiments has been performed with the GLA general circulation model (GCM) using different amounts of tropical wind data during the First Special Observing Period of the Global Weather Experiment. In experiment 1, all available tropical wind data were used; in the second experiment, tropical wind data were suppressed; while, in the third and fourth experiments, only tropical wind data with westerly and easterly components, respectively, were assimilated.
The rotational wind appears to be more sensitive to the presence or absence of tropical wind data than the divergent wind. It appears that the model, given only extratropical observations, generates excessively strong upper tropospheric westerlies These biases are sufficiently pronounced to amplify the globally integrated rotational flow kinetic energy by about 10% and the global divergent flow kinetic energy by about a factor of 2.
Including only easterly wind data in the tropics is more effective in controlling the model error than including only westerly wind data. This conclusion is especially noteworthy because approximately twice as many upper tropospheric westerly winds were available in these cases as easterly winds.
Abstract
The global scale divergent and rotational flow components of the Global Weather Experiment (GWE) are diagnosed from three different analyses of the data. The rotational flow shows closer agreement between the analyses than does the divergent flow. Although the major outflow and inflow centers are similarly placed in all analyses, the global kinetic energy of the divergent wind varies by about a factor of 2 between different analyses while the global kinetic energy of the rotational wind varies by only about 10% between the analyses.
A series of real data assimilation experiments has been performed with the GLA general circulation model (GCM) using different amounts of tropical wind data during the First Special Observing Period of the Global Weather Experiment. In experiment 1, all available tropical wind data were used; in the second experiment, tropical wind data were suppressed; while, in the third and fourth experiments, only tropical wind data with westerly and easterly components, respectively, were assimilated.
The rotational wind appears to be more sensitive to the presence or absence of tropical wind data than the divergent wind. It appears that the model, given only extratropical observations, generates excessively strong upper tropospheric westerlies These biases are sufficiently pronounced to amplify the globally integrated rotational flow kinetic energy by about 10% and the global divergent flow kinetic energy by about a factor of 2.
Including only easterly wind data in the tropics is more effective in controlling the model error than including only westerly wind data. This conclusion is especially noteworthy because approximately twice as many upper tropospheric westerly winds were available in these cases as easterly winds.
