Search Results
Abstract
The design of an optimized computation scheme for kinematic vertical motion fields with an upper air network is discussed with a scheme that incorporates 14 degrees of optimization in the evaluation of divergence. The provided range of optimization enables the computation scheme to suit wide varieties of data dispostion in the observation network, and the well-known problem of bias error accumulation in the kinematic ω profiles seems to have been practically overcome. The discussions include the general construction of the scheme in terms of the sequential flow of the computation, the quality of the vertical motion field over the synoptic network through the depth of the atmosphere, and the utilization and application of the scheme under various circumstances.
Abstract
The design of an optimized computation scheme for kinematic vertical motion fields with an upper air network is discussed with a scheme that incorporates 14 degrees of optimization in the evaluation of divergence. The provided range of optimization enables the computation scheme to suit wide varieties of data dispostion in the observation network, and the well-known problem of bias error accumulation in the kinematic ω profiles seems to have been practically overcome. The discussions include the general construction of the scheme in terms of the sequential flow of the computation, the quality of the vertical motion field over the synoptic network through the depth of the atmosphere, and the utilization and application of the scheme under various circumstances.
Abstract
Various aspects of our studies of the kinetic energy balance are discussed, using an improved scheme of computing the horizontal and vertical transports of the kinetic energy with the observed wind and geopotential data over North America. On a firmer basis than before, it has been shown that there is a considerable amount of kinetic energy dissipated outside the planetary boundary layer, particularly at the jet-stream level. This also may imply that intensity of the atmospheric general circulation is significantly higher than is being assumed in most of the numerical models of the atmosphere.
Abstract
Various aspects of our studies of the kinetic energy balance are discussed, using an improved scheme of computing the horizontal and vertical transports of the kinetic energy with the observed wind and geopotential data over North America. On a firmer basis than before, it has been shown that there is a considerable amount of kinetic energy dissipated outside the planetary boundary layer, particularly at the jet-stream level. This also may imply that intensity of the atmospheric general circulation is significantly higher than is being assumed in most of the numerical models of the atmosphere.
Abstract
The latitude-height distributions of the kinetic energy generation and dissipation over North America are presented in a series of cross sections from 25° to 70° N, and from the surface to the 50-mb level. The generation was computed using the twice-daily observed wind and geopotential data for a 1-yr period. The dissipation was obtained for a 3-mo summer period as the residual term of the kinetic energy equation. Throughout all latitudes, the generation and dissipation have a maximum in the planetary boundary layer. They gradually reach a minimum in the mid-troposphere, then increase to another maximum at the jet stream level except in middle latitudes. In the upper troposphere, there seems to be a characteristic meridional distribution both for generation and dissipation. The generation is significantly large north and south of the middle latitude where the kinetic energy is adiabatically destroyed. Those latitudes of large generation in the upper troposphere are also characterized by high frictional dissipation values. Reference is also made to the results in available numerical experiments for comparison and discussion.
Abstract
The latitude-height distributions of the kinetic energy generation and dissipation over North America are presented in a series of cross sections from 25° to 70° N, and from the surface to the 50-mb level. The generation was computed using the twice-daily observed wind and geopotential data for a 1-yr period. The dissipation was obtained for a 3-mo summer period as the residual term of the kinetic energy equation. Throughout all latitudes, the generation and dissipation have a maximum in the planetary boundary layer. They gradually reach a minimum in the mid-troposphere, then increase to another maximum at the jet stream level except in middle latitudes. In the upper troposphere, there seems to be a characteristic meridional distribution both for generation and dissipation. The generation is significantly large north and south of the middle latitude where the kinetic energy is adiabatically destroyed. Those latitudes of large generation in the upper troposphere are also characterized by high frictional dissipation values. Reference is also made to the results in available numerical experiments for comparison and discussion.
Abstract
The diurnal variation and long-term variation of the kinetic energy generation and dissipation are investigated with the wind and geopotential data observed twice a day at 00 and 12 gmt over North America during a 5-yr. period. The generation from the work done by the horizontal pressure force and the dissipation are significantly and consistently greater at 00 gmt than at 12 gmt. The diurnal variation is especially pronounced during the summer. The annual march of the seasons and the year-to-year variation of the kinetic energy parameters are also significant.
By the use of twice-a-day observations for an extended period, the study over North America is increased in generality as an approximation to hemispherical features. However, some uncertainty remains in this respect because of the possible effects of the semidiurnal variations and unconfirmed radiation errors in the radiosonde observations. The previously reported double maxima of the generation and dissipation in the planetary boundary layer and at the jet stream level derived from limited data are confirmed in this study. The multi-annual mean of the dissipation is estimated as 4.12 watts/m.2 About half of the estimated dissipation takes place in the boundary layer, and the other half takes place in the free atmosphere.
Abstract
The diurnal variation and long-term variation of the kinetic energy generation and dissipation are investigated with the wind and geopotential data observed twice a day at 00 and 12 gmt over North America during a 5-yr. period. The generation from the work done by the horizontal pressure force and the dissipation are significantly and consistently greater at 00 gmt than at 12 gmt. The diurnal variation is especially pronounced during the summer. The annual march of the seasons and the year-to-year variation of the kinetic energy parameters are also significant.
By the use of twice-a-day observations for an extended period, the study over North America is increased in generality as an approximation to hemispherical features. However, some uncertainty remains in this respect because of the possible effects of the semidiurnal variations and unconfirmed radiation errors in the radiosonde observations. The previously reported double maxima of the generation and dissipation in the planetary boundary layer and at the jet stream level derived from limited data are confirmed in this study. The multi-annual mean of the dissipation is estimated as 4.12 watts/m.2 About half of the estimated dissipation takes place in the boundary layer, and the other half takes place in the free atmosphere.
Abstract
The vertical distribution and seasonal variation of the kinetic energy balance of the atmosphere are studied. From 11 months' daily wind and geopotential data during 1962 and 1963 over North America, the generation due to the work done by the horizontal pressure force, the local change, the horizontal outflow, and the vertical transport, are evaluated for 20 pressure layers from the surface to 50 mb. The dissipation is then obtained as the residual to balance the kinetic energy equation.
The generation and dissipation are at a maximum in the planetary boundary layer. They decrease gradually to a minimum in the mid-troposphere, increase again to the second maximum in the upper part of the atmosphere, then decrease again farther upward. The generation and dissipation are approximately balanced in the lower troposphere, particularly in the boundary layer, for the large-scale domain of analysis.
The generation and dissipation of the kinetic energy are significantly large both in the lower troposphere and in the upper part of the atmosphere. However, in view of the amount of the kinetic energy contained in different portions of the atmosphere, the energy generation and dissipation are most intense in the lower troposphere, especially in the boundary layer. The efficiency of the dissipation in different portions of the atmosphere is also examined in terms of the depletion time. The depletion time is orders of magnitude shorter in the boundary layer than in the mid-troposphere.
A seasonal change of the energetics is depicted for the one-year period by means of the pressure-time cross sections.
Abstract
The vertical distribution and seasonal variation of the kinetic energy balance of the atmosphere are studied. From 11 months' daily wind and geopotential data during 1962 and 1963 over North America, the generation due to the work done by the horizontal pressure force, the local change, the horizontal outflow, and the vertical transport, are evaluated for 20 pressure layers from the surface to 50 mb. The dissipation is then obtained as the residual to balance the kinetic energy equation.
The generation and dissipation are at a maximum in the planetary boundary layer. They decrease gradually to a minimum in the mid-troposphere, increase again to the second maximum in the upper part of the atmosphere, then decrease again farther upward. The generation and dissipation are approximately balanced in the lower troposphere, particularly in the boundary layer, for the large-scale domain of analysis.
The generation and dissipation of the kinetic energy are significantly large both in the lower troposphere and in the upper part of the atmosphere. However, in view of the amount of the kinetic energy contained in different portions of the atmosphere, the energy generation and dissipation are most intense in the lower troposphere, especially in the boundary layer. The efficiency of the dissipation in different portions of the atmosphere is also examined in terms of the depletion time. The depletion time is orders of magnitude shorter in the boundary layer than in the mid-troposphere.
A seasonal change of the energetics is depicted for the one-year period by means of the pressure-time cross sections.
Abstract
The kinetic energy budget and dissipation are studied in their various partitionings, using daily aerological (wind and geopotential) data from the network over North America for six months.
The total kinetic energy dissipation is partitioned into vertical mean flow and shear flow and also into planetary boundary layer and free atmosphere. Furthermore, the dissipations in the vertical mean flow and shear flow are partitioned separately into components contributed by the boundary layer and free atmosphere. Two important terms in the total kinetic energy equation in determining the total dissipation are the generation and outflow. Two important terms in the mean flow kinetic energy equation in determining the mean flow dissipation are the conversion between the vertical shear and mean flows and the outflow. The mean flow and shear flow dissipations seem to have numerical values of the same order of magnitude. The evaluated boundary layer dissipation and free atmosphere dissipation indicate that the latter is at least, as important as the former. It is also shown that the mean flow dissipation is mainly contributed from the free atmosphere while the shear flow dissipation is contributed from the boundary layer and free atmosphere in the same order of magnitude. The evaluated dissipation values and related kinetic energy parameters are presented and examined in detail.
Of special interest in this study is the direct evaluation of the kinetic energy generation due to the work done by the horizontal pressure force. Daily variation of the generation at different pressure levels seems to suggest three different modes of the generation cycle in the upper, mid, and lower troposphere. Clear vertical profiles of the generation from the surface to the 100-mb. level are obtained; it is shown that strong generation takes place in the upper and lower troposphere while the generation in the mid troposphere is very weak. It is also suggested that there may be an approximate balance of the kinetic energy generation and dissipation in the boundary layer.
Abstract
The kinetic energy budget and dissipation are studied in their various partitionings, using daily aerological (wind and geopotential) data from the network over North America for six months.
The total kinetic energy dissipation is partitioned into vertical mean flow and shear flow and also into planetary boundary layer and free atmosphere. Furthermore, the dissipations in the vertical mean flow and shear flow are partitioned separately into components contributed by the boundary layer and free atmosphere. Two important terms in the total kinetic energy equation in determining the total dissipation are the generation and outflow. Two important terms in the mean flow kinetic energy equation in determining the mean flow dissipation are the conversion between the vertical shear and mean flows and the outflow. The mean flow and shear flow dissipations seem to have numerical values of the same order of magnitude. The evaluated boundary layer dissipation and free atmosphere dissipation indicate that the latter is at least, as important as the former. It is also shown that the mean flow dissipation is mainly contributed from the free atmosphere while the shear flow dissipation is contributed from the boundary layer and free atmosphere in the same order of magnitude. The evaluated dissipation values and related kinetic energy parameters are presented and examined in detail.
Of special interest in this study is the direct evaluation of the kinetic energy generation due to the work done by the horizontal pressure force. Daily variation of the generation at different pressure levels seems to suggest three different modes of the generation cycle in the upper, mid, and lower troposphere. Clear vertical profiles of the generation from the surface to the 100-mb. level are obtained; it is shown that strong generation takes place in the upper and lower troposphere while the generation in the mid troposphere is very weak. It is also suggested that there may be an approximate balance of the kinetic energy generation and dissipation in the boundary layer.
Abstract
This is an attempt to employ a pertinent boundary layer model and proper frictional parameters in the numerical analysis of the angular momentum budget of the atmosphere. The mean zonal surface stress due to friction is examined utilizing Lettau's boundary layer model and the earth's roughness study by the writer and Lettau for the period 1945–1955. The meridional and seasonal variations of the mean zonal surface stress are described; the mountain effect is derived indirectly; the stresses over the continent and ocean are compared; and finally the sensitivity of the numerical analysis to the prescribed frictional parameters is briefly discussed.
Abstract
This is an attempt to employ a pertinent boundary layer model and proper frictional parameters in the numerical analysis of the angular momentum budget of the atmosphere. The mean zonal surface stress due to friction is examined utilizing Lettau's boundary layer model and the earth's roughness study by the writer and Lettau for the period 1945–1955. The meridional and seasonal variations of the mean zonal surface stress are described; the mountain effect is derived indirectly; the stresses over the continent and ocean are compared; and finally the sensitivity of the numerical analysis to the prescribed frictional parameters is briefly discussed.
Abstract
Energetics characteristics of the Asian winter monsoon are studied with twice-daily upper air data during a 20-year period over its source region. It is found that the energetics features over Siberia, North-eastern Asia, China Main and the Japan Sea, are distinctly different reflecting the different roles and characteristic flow patterns of these regions in the system of the winter monsoon.
Siberia, under the dominance of the anticyclonic flow, shows a general adiabatic destruction of kinetic energy through cross-isobaric motion. Northeastern Asia, under the influence of a major cyclonic system, is dominated by typical patterns of energy transformations as observed in most areas of transient synoptic disturbances. The strong westerlies dominate over the general area of the China Main, East China Sea and Japan Sea and the kinetic energy is intensely generated in this portion of the flow. Most of the kinetic energy generated over China Main is exported. Over the Japan Sea area where the series of cyclonic disturbances develops, a strong dissipation takes place.
During the cold air outbreaks, which are recognized with the intrusion of a strong cyclonic upper level flow into China Main, the kinetic energy generation and dissipation are drastically increased in the general area of the China Main, East China Sea and Japan Sea. However, basic energetics features of different regions in the prevailing systems of the Asian winter monsoon remain unchanged. A case study of a cold air outbreak is also presented.
Abstract
Energetics characteristics of the Asian winter monsoon are studied with twice-daily upper air data during a 20-year period over its source region. It is found that the energetics features over Siberia, North-eastern Asia, China Main and the Japan Sea, are distinctly different reflecting the different roles and characteristic flow patterns of these regions in the system of the winter monsoon.
Siberia, under the dominance of the anticyclonic flow, shows a general adiabatic destruction of kinetic energy through cross-isobaric motion. Northeastern Asia, under the influence of a major cyclonic system, is dominated by typical patterns of energy transformations as observed in most areas of transient synoptic disturbances. The strong westerlies dominate over the general area of the China Main, East China Sea and Japan Sea and the kinetic energy is intensely generated in this portion of the flow. Most of the kinetic energy generated over China Main is exported. Over the Japan Sea area where the series of cyclonic disturbances develops, a strong dissipation takes place.
During the cold air outbreaks, which are recognized with the intrusion of a strong cyclonic upper level flow into China Main, the kinetic energy generation and dissipation are drastically increased in the general area of the China Main, East China Sea and Japan Sea. However, basic energetics features of different regions in the prevailing systems of the Asian winter monsoon remain unchanged. A case study of a cold air outbreak is also presented.
Abstract
Eigenvector and harmonic analyses have been performed with monthly mean values of upper air parameters of the Northern Hemispheric circulation for the period from April 1955 to December 1974. The parameters used involve the 700 and 500 mb temperatures, the 700–500 mb thickness, the 300 mb kinetic and eddy kinetic energies, and the 700, 500 and 300 mb zonal/meridional flow indicators. The zonal/meridional flow indicator is defined as the ratio
The first eigenvectors of the normalized parameters are associated with the annual variation of the basic patterns. For the temperature field the first eigenvector overwhelmingly dominates. It reflects the annual variation of temperature in the mid and higher latitudes with an effect of the land-ocean configuration. The second eigenvector shows a land-ocean contrast. The long-term variation of temperature in the lower latitudes also stands out. For the kinetic energy and zonal/meridional flow indicator the first eigenvectors are not as dominant as that of temperature. They reflect the subtropical jet and other hemispherical-scale circulations. The third eigenvector of kinetic energy and second eigenvector of the zonal/meridional flow indicator appear to be associated with the semiannual oscillations of the large-scale wind systems including summer and winter monsoons. It also appears that high-numbered eigenvectors of kinetic energy and zonal/meridional flow indicators are associated with long-term variations in the lower latitudes and short-term variations in the mid to high latitudes.
Abstract
Eigenvector and harmonic analyses have been performed with monthly mean values of upper air parameters of the Northern Hemispheric circulation for the period from April 1955 to December 1974. The parameters used involve the 700 and 500 mb temperatures, the 700–500 mb thickness, the 300 mb kinetic and eddy kinetic energies, and the 700, 500 and 300 mb zonal/meridional flow indicators. The zonal/meridional flow indicator is defined as the ratio
The first eigenvectors of the normalized parameters are associated with the annual variation of the basic patterns. For the temperature field the first eigenvector overwhelmingly dominates. It reflects the annual variation of temperature in the mid and higher latitudes with an effect of the land-ocean configuration. The second eigenvector shows a land-ocean contrast. The long-term variation of temperature in the lower latitudes also stands out. For the kinetic energy and zonal/meridional flow indicator the first eigenvectors are not as dominant as that of temperature. They reflect the subtropical jet and other hemispherical-scale circulations. The third eigenvector of kinetic energy and second eigenvector of the zonal/meridional flow indicator appear to be associated with the semiannual oscillations of the large-scale wind systems including summer and winter monsoons. It also appears that high-numbered eigenvectors of kinetic energy and zonal/meridional flow indicators are associated with long-term variations in the lower latitudes and short-term variations in the mid to high latitudes.
Abstract
The maintenance of large-scale tropical disturbances has been examined with the source terms of kinetic energy generation utilizing the special 1958 upper-air observations in the Marshall Islands area. An optimized objective analysis scheme for the computation of kinematic vertical velocity as well as the method for evaluation of energy variables is presented.
The time mean budgets of kinetic energy source terms are presented in terms of vertical profiles and intensity of processes represented by each term. The eddy conversion of available potential energy has its primary maximum in the layer between 400 and 200 mb, whereas the eddy kinetic energy generation shows maxima in the lower boundary and upper troposphere between 200 and 100 mb. In terms of the time mean budget only a fraction of the released energy by eddy conversion contributes to the eddy generation of kinetic energy in the area.
Through examination of the time series of energy variables, it is revealed that horizontal eddy flux convergence of potential energy is the dominant term in determining the local generation of eddy kinetic energy. The migration pattern of the ITCZ further suggests that this horizontal eddy flux term is closely associated with the position of the ITCZ, with a significant divergence of eddy flux of potential energy when the ITCZ is located to the south of the area.
Abstract
The maintenance of large-scale tropical disturbances has been examined with the source terms of kinetic energy generation utilizing the special 1958 upper-air observations in the Marshall Islands area. An optimized objective analysis scheme for the computation of kinematic vertical velocity as well as the method for evaluation of energy variables is presented.
The time mean budgets of kinetic energy source terms are presented in terms of vertical profiles and intensity of processes represented by each term. The eddy conversion of available potential energy has its primary maximum in the layer between 400 and 200 mb, whereas the eddy kinetic energy generation shows maxima in the lower boundary and upper troposphere between 200 and 100 mb. In terms of the time mean budget only a fraction of the released energy by eddy conversion contributes to the eddy generation of kinetic energy in the area.
Through examination of the time series of energy variables, it is revealed that horizontal eddy flux convergence of potential energy is the dominant term in determining the local generation of eddy kinetic energy. The migration pattern of the ITCZ further suggests that this horizontal eddy flux term is closely associated with the position of the ITCZ, with a significant divergence of eddy flux of potential energy when the ITCZ is located to the south of the area.
