1987 Vol. 4, No. 1
Display Method:
1987, 4(1): 1-12.
doi: 10.1007/BF02663607
Abstract:
In order to identify the sensitivity of the numerical simulation to the orography specification in a low resolution spectral model, two sets of numerical experiments for full-mountain and no-mountain cases are performed. By comparing the results, it is possible to determine the effects of mountains on the atmospheric general circulation.This is a global, spectral model incorporating the primitive equations segmented by physical parameteriza-tion and mountains, with five equally-spaced sigma levels in the vertical and a triangular truncation at wavenumber 10 in the horizontal.Analysis of results supports earlier work by demonstrating that the low resolution global spectral model is capable of simulating the major features of global general circulation and indicates that it is necessary to consider the effects of mountains on stationary disturbances in the numerical simulation. The simulations show that topography plays an important role in intensifying heat sources for maintenance of disturbances.All the simulation tests indicate that orography has an important influence on the distribution of heat sources and sinks. It reflects that interaction and interrelation exist between the effects of orography and heat sources and the atmospheric circulation via the dynamical processes of atmosphere. This result confirms the view points proposed by Yeh and Zhu (1958), but differs from those by Kasahara and Washington (1971), Manabe and Terpstra (1974).
In order to identify the sensitivity of the numerical simulation to the orography specification in a low resolution spectral model, two sets of numerical experiments for full-mountain and no-mountain cases are performed. By comparing the results, it is possible to determine the effects of mountains on the atmospheric general circulation.This is a global, spectral model incorporating the primitive equations segmented by physical parameteriza-tion and mountains, with five equally-spaced sigma levels in the vertical and a triangular truncation at wavenumber 10 in the horizontal.Analysis of results supports earlier work by demonstrating that the low resolution global spectral model is capable of simulating the major features of global general circulation and indicates that it is necessary to consider the effects of mountains on stationary disturbances in the numerical simulation. The simulations show that topography plays an important role in intensifying heat sources for maintenance of disturbances.All the simulation tests indicate that orography has an important influence on the distribution of heat sources and sinks. It reflects that interaction and interrelation exist between the effects of orography and heat sources and the atmospheric circulation via the dynamical processes of atmosphere. This result confirms the view points proposed by Yeh and Zhu (1958), but differs from those by Kasahara and Washington (1971), Manabe and Terpstra (1974).
1987, 4(1): 13-23.
doi: 10.1007/BF02656658
Abstract:
The physical effects of topography and heat sources on the formation and maintenance of the summer mon-soon over Asia we discussed in this paper by using the transformed Eularian-mean equations and a quasigeostrophic 34-level spherical coordinate model.The computed results of the divergence of the E-P flux, the induced meridional circulation and the pertur-bation geostrophic wind speed induced by the forcing of topography and heat sources show that the diabatic heating effect over the Tibetan Plateau may play an important role for the formation and maintenance of the summer monsoon over Asia, which is much greater than the dynamical effect of topography.The computed results also show that, of the physical effects of topography and heat sources on the formation and maintenance of the summer monsoon over Asia, the effect of forced meridional circulation is larger than that of the divergence of E-P flux of the induced waves.
The physical effects of topography and heat sources on the formation and maintenance of the summer mon-soon over Asia we discussed in this paper by using the transformed Eularian-mean equations and a quasigeostrophic 34-level spherical coordinate model.The computed results of the divergence of the E-P flux, the induced meridional circulation and the pertur-bation geostrophic wind speed induced by the forcing of topography and heat sources show that the diabatic heating effect over the Tibetan Plateau may play an important role for the formation and maintenance of the summer monsoon over Asia, which is much greater than the dynamical effect of topography.The computed results also show that, of the physical effects of topography and heat sources on the formation and maintenance of the summer monsoon over Asia, the effect of forced meridional circulation is larger than that of the divergence of E-P flux of the induced waves.
1987, 4(1): 24-42.
doi: 10.1007/BF02656659
Abstract:
Experiments using a quasi-geostrophic model and the ECMWF T21 spectral model with and without orography are performed to investigate the effects of mechanical forcing on the mean meridional circulation. Results show that mechanical forcing intensifies the horizontal poleward heat flux and redistributes the eddy angular momentum in the vertical, and that this changes significantly the intensity and location of the mean me-ridional circulation centres.It is shown how the mean meridional circulation is set up in such a way to satisfy both the dynamical and thermodynamical transport requirements of the model atmosphere. Whenever external forcing changes the eddy fluxes, the Coriolis torques from the upper horizontal branches of the mean meridional circulations change to balance the extra divergence of eddy momentum flux, and additional adiabatic heating is produced by the vertical branches of the toroids to balance the extra divergence of eddy heat flux. The mean meridional circula-tion is, therefore, confirmed to be very sensitive to mechanical forcing, and can be used as an efficient tool to quantitatively diagnose the adequacy of the orographic representation of numerical forecasting and general cir-culation models.
Experiments using a quasi-geostrophic model and the ECMWF T21 spectral model with and without orography are performed to investigate the effects of mechanical forcing on the mean meridional circulation. Results show that mechanical forcing intensifies the horizontal poleward heat flux and redistributes the eddy angular momentum in the vertical, and that this changes significantly the intensity and location of the mean me-ridional circulation centres.It is shown how the mean meridional circulation is set up in such a way to satisfy both the dynamical and thermodynamical transport requirements of the model atmosphere. Whenever external forcing changes the eddy fluxes, the Coriolis torques from the upper horizontal branches of the mean meridional circulations change to balance the extra divergence of eddy momentum flux, and additional adiabatic heating is produced by the vertical branches of the toroids to balance the extra divergence of eddy heat flux. The mean meridional circula-tion is, therefore, confirmed to be very sensitive to mechanical forcing, and can be used as an efficient tool to quantitatively diagnose the adequacy of the orographic representation of numerical forecasting and general cir-culation models.
1987, 4(1): 43-54.
doi: 10.1007/BF02656660
Abstract:
In this paper an evolution equation in integral-differential form for finite amplitude Rossby waves on a weak shear is presented and an efficient method for its numerical solution is set up. It is shown that a propa-gation of solitary wave is possible whenever a proper weak shear in basic flows acts with the nonlinear effects and dispersion of the media, both in the atmosphere and in the ocean. To test the numerical method for solving the evolution equation, a series of experiments are carried out. The results indicate that the solitary solutions do exist and interact with each other in quite a succinct, manner. Therefore the method is successful and efficient for solving initial value problems of the above equation. The time decoupling problem arising in the numerical scheme and the related filtering technique are discussed. A variety of interesting phenomena such as the interaction of solitary Rossby waves, damping, dispersion and the development of nonlinear wave train are numerically studied.
In this paper an evolution equation in integral-differential form for finite amplitude Rossby waves on a weak shear is presented and an efficient method for its numerical solution is set up. It is shown that a propa-gation of solitary wave is possible whenever a proper weak shear in basic flows acts with the nonlinear effects and dispersion of the media, both in the atmosphere and in the ocean. To test the numerical method for solving the evolution equation, a series of experiments are carried out. The results indicate that the solitary solutions do exist and interact with each other in quite a succinct, manner. Therefore the method is successful and efficient for solving initial value problems of the above equation. The time decoupling problem arising in the numerical scheme and the related filtering technique are discussed. A variety of interesting phenomena such as the interaction of solitary Rossby waves, damping, dispersion and the development of nonlinear wave train are numerically studied.
1987, 4(1): 55-65.
doi: 10.1007/BF02656661
Abstract:
The definition Tor stability D of standing waves given in this paper is used to denote the relative magnitude of annual variation of the waves. Analysis of the temporal (seasonal) and spatial (meridional) changes of the monthly mean circulation at 500 and 100 hPa shows its temporal and spatial demarcation and the bourdary be-tween the middle-and-low latitude circulation and the middle-aod-high latitude circulation in the wave field. Based on the annual march of D and the position of the boundary, a discussion is made of the seasonal trans-formation of the Northern- Hemisphere mean circulation and Ihe- pattern of its development.
The definition Tor stability D of standing waves given in this paper is used to denote the relative magnitude of annual variation of the waves. Analysis of the temporal (seasonal) and spatial (meridional) changes of the monthly mean circulation at 500 and 100 hPa shows its temporal and spatial demarcation and the bourdary be-tween the middle-and-low latitude circulation and the middle-aod-high latitude circulation in the wave field. Based on the annual march of D and the position of the boundary, a discussion is made of the seasonal trans-formation of the Northern- Hemisphere mean circulation and Ihe- pattern of its development.
1987, 4(1): 66-73.
doi: 10.1007/BF02656662
Abstract:
Based on calculations of data from FGGE Level III b, a discussion is made of the energy balance in the 40－50 day periodic oscillation over the Asian monsoon region during the 1979 summer. It is found that the main source of 40－50 day periodic perturbation is the monsoon region extending from central South Asia to Southeast Asia. In the upper layer over the North Pacific subtropical area (10－20oN, 150oE－150oW) pres-sure work turns into kinetic energy that maintains 40－50 day periodic perturbation associated with the variation in position and intensity of the mid-Pacific trough. The mean energy budget in the three-dimensional space (0－30oE, 30oE－150oW, 100－1000 hPa) indicates that the 40－50 day periodic perturbation transports kinetic energy to a seasonal mean and a transient perturbation wind field.
Based on calculations of data from FGGE Level III b, a discussion is made of the energy balance in the 40－50 day periodic oscillation over the Asian monsoon region during the 1979 summer. It is found that the main source of 40－50 day periodic perturbation is the monsoon region extending from central South Asia to Southeast Asia. In the upper layer over the North Pacific subtropical area (10－20oN, 150oE－150oW) pres-sure work turns into kinetic energy that maintains 40－50 day periodic perturbation associated with the variation in position and intensity of the mid-Pacific trough. The mean energy budget in the three-dimensional space (0－30oE, 30oE－150oW, 100－1000 hPa) indicates that the 40－50 day periodic perturbation transports kinetic energy to a seasonal mean and a transient perturbation wind field.
1987, 4(1): 74-84.
doi: 10.1007/BF02656663
Abstract:
Sea-level pressure variations over the North Pacific Ocean influence the surface climate conditions of China and western North America. Documentary records of precipitation in China data back to the mid-15th century, and a well-replicated network of tree-ring chronologies from western North America dates to the early 17th century. These proxy climate records are used separately and together to estimate sea-level pressure variations over the North Pacific back to 1600 A.D. The models are calibrated over the period 1899 to 1950 and verified over the independent period, 1951 to 1963. The best estimates, derived from predictors in China and western North America, calibrate 44.7% of summer sea-level pressure variance. The study demonstrates the potential of com-bining different prosy data sources to derive estimates of past climate.
Sea-level pressure variations over the North Pacific Ocean influence the surface climate conditions of China and western North America. Documentary records of precipitation in China data back to the mid-15th century, and a well-replicated network of tree-ring chronologies from western North America dates to the early 17th century. These proxy climate records are used separately and together to estimate sea-level pressure variations over the North Pacific back to 1600 A.D. The models are calibrated over the period 1899 to 1950 and verified over the independent period, 1951 to 1963. The best estimates, derived from predictors in China and western North America, calibrate 44.7% of summer sea-level pressure variance. The study demonstrates the potential of com-bining different prosy data sources to derive estimates of past climate.
1987, 4(1): 85-92.
doi: 10.1007/BF02656664
Abstract:
A tropical squall line that passed over the ship array of the Global Atmospheric Research Programme’s Atlantic Tropical Experiment (GATE) on 9－10 August 1974 is analyzed. This squall line was similar to squall systems that passed over the GATE ship array on four other days. It began as a purely convective cloud line, then developed an associated stratiform cloud and precipitation area. The stratiform rain built up to a maxi-mum amount over a period of 8 h, then gradually diminished over a 6 h period. This stratiform rain is esti-mated to have accounted for 32% of the squall system’s total precipitation. As in other GATE squall lines, the upper-level cloud shield from which the stratiform rain fell, was advected slowly forward of the line during the system’s lifetime, the leading line of corrective clouds consisted of transient smaller-scale convective elements, which lent the line an irregular shape and pulsatory movement, and the stratiform portion of the system was characterized by the development of a mid-level mesoscale vortex similar to that seen in other GATE eases.
A tropical squall line that passed over the ship array of the Global Atmospheric Research Programme’s Atlantic Tropical Experiment (GATE) on 9－10 August 1974 is analyzed. This squall line was similar to squall systems that passed over the GATE ship array on four other days. It began as a purely convective cloud line, then developed an associated stratiform cloud and precipitation area. The stratiform rain built up to a maxi-mum amount over a period of 8 h, then gradually diminished over a 6 h period. This stratiform rain is esti-mated to have accounted for 32% of the squall system’s total precipitation. As in other GATE squall lines, the upper-level cloud shield from which the stratiform rain fell, was advected slowly forward of the line during the system’s lifetime, the leading line of corrective clouds consisted of transient smaller-scale convective elements, which lent the line an irregular shape and pulsatory movement, and the stratiform portion of the system was characterized by the development of a mid-level mesoscale vortex similar to that seen in other GATE eases.
1987, 4(1): 93-104.
doi: 10.1007/BF02656665
Abstract:
Starting from the equations of motion and continuity, a theoretical model is deduced in this paper for the variation in wind velocity over water caused by abrupt changes in surface roughness and temperature when air flows from land to water, based on the consideration that the turbulent exchange coefficient varies with height and distance from the upwind edge. According to the computation of this model, the variation in wind velocity over water, as the drift of air is from land to water, occurs mainly in the first few kilometers from the upwind edge. The wind velocity over water increases to a maximum when the air over land is stable, it tends to moderate when neutral condition is reached, and least variation is shown in unstable condition. And when the air over land is unstable the wind velocity is less over water than over land in strong winds, but some-what greater in light winds.
Starting from the equations of motion and continuity, a theoretical model is deduced in this paper for the variation in wind velocity over water caused by abrupt changes in surface roughness and temperature when air flows from land to water, based on the consideration that the turbulent exchange coefficient varies with height and distance from the upwind edge. According to the computation of this model, the variation in wind velocity over water, as the drift of air is from land to water, occurs mainly in the first few kilometers from the upwind edge. The wind velocity over water increases to a maximum when the air over land is stable, it tends to moderate when neutral condition is reached, and least variation is shown in unstable condition. And when the air over land is unstable the wind velocity is less over water than over land in strong winds, but some-what greater in light winds.
1987, 4(1): 105-112.
doi: 10.1007/BF02656666
Abstract:
Meridional and vertical wind velocities of the free atmosphere were observed continuously in mid-latitude summer of 1981 by using Platteville ST radar in the eastern Colorado plains in order to obtain the mesoscale spectra. Power spectra were obtained for both meridional and vertical components at heights of 3.3－7.9 km for meridional and 3.3－17.7 km for vertical. Results show that the “-5/3 law” is a good fit to “meridional” spectra for wave periods ranging from ~3 hr to 2 days which are consistent with other published observations and give further evidence to the existence of a universal -5/3 law in mesoscale atmospheric motions. Results also show that for wave periods shorter than 3 hr (to about 10 min), the spectra obviously depart from the –5/3 law and reflect the significant contribution of thunderstorm activities which frequently happen in the mid-latitude summer. Mesoscale spectra of vertical velocity show some characteristics of gravity waves. The mechanism of the observed spectra is discussed.
Meridional and vertical wind velocities of the free atmosphere were observed continuously in mid-latitude summer of 1981 by using Platteville ST radar in the eastern Colorado plains in order to obtain the mesoscale spectra. Power spectra were obtained for both meridional and vertical components at heights of 3.3－7.9 km for meridional and 3.3－17.7 km for vertical. Results show that the “-5/3 law” is a good fit to “meridional” spectra for wave periods ranging from ~3 hr to 2 days which are consistent with other published observations and give further evidence to the existence of a universal -5/3 law in mesoscale atmospheric motions. Results also show that for wave periods shorter than 3 hr (to about 10 min), the spectra obviously depart from the –5/3 law and reflect the significant contribution of thunderstorm activities which frequently happen in the mid-latitude summer. Mesoscale spectra of vertical velocity show some characteristics of gravity waves. The mechanism of the observed spectra is discussed.
1987, 4(1): 113-118.
doi: 10.1007/BF02656667
Abstract:
Typhoon eye, one of the most outstanding features in the evolution of typhoon, has various complex configurations: circular, elliptic, oval, square, polygonal, or irregular shapes. It is very interesting to note that some typhoons show the concentric double-eyes encircled with two concentric cloud towers.The concentric double-eye structure and intensity of typhoons are investigated and discussed by using reconnaissance aircraft data, radar echo photos and satellite images, 76 double-eye typhoons were observed during 1949－1983. The results indicate that the concentric double-eye structure, generally appearing in intense typhoons over the northwestern Pacific Ocean, is closely related to typhoon’s intensity. This kind of structure has apparent characteristics in geographical and seasonal distributions.Based on the observational data, an idealized structure model for the concentric double-eye typhoons is proposed.
Typhoon eye, one of the most outstanding features in the evolution of typhoon, has various complex configurations: circular, elliptic, oval, square, polygonal, or irregular shapes. It is very interesting to note that some typhoons show the concentric double-eyes encircled with two concentric cloud towers.The concentric double-eye structure and intensity of typhoons are investigated and discussed by using reconnaissance aircraft data, radar echo photos and satellite images, 76 double-eye typhoons were observed during 1949－1983. The results indicate that the concentric double-eye structure, generally appearing in intense typhoons over the northwestern Pacific Ocean, is closely related to typhoon’s intensity. This kind of structure has apparent characteristics in geographical and seasonal distributions.Based on the observational data, an idealized structure model for the concentric double-eye typhoons is proposed.
1987, 4(1): 119-124.
doi: 10.1007/BF02656668
Abstract:
By performing error analysis of the information from the 48-hr forecasting charts of the 500-hPa fields by the B model over eastern Asia in the period of July to September 1982 and expansions of the height fields of westerlies and the subtropical zone by use of the Chebyshev polynomial and EOF, respectively, a scheme is developed for predicting the synchronous STH coefficient (i. e. time coefficient) in terms of the Chebyshev one, thus making possible statistical forecasting of the 500-hPa subtropical field within 48 hr. Tests with independent samples indicate that, to a certain extent, this scheme can be used in operational prediction as a reference.
By performing error analysis of the information from the 48-hr forecasting charts of the 500-hPa fields by the B model over eastern Asia in the period of July to September 1982 and expansions of the height fields of westerlies and the subtropical zone by use of the Chebyshev polynomial and EOF, respectively, a scheme is developed for predicting the synchronous STH coefficient (i. e. time coefficient) in terms of the Chebyshev one, thus making possible statistical forecasting of the 500-hPa subtropical field within 48 hr. Tests with independent samples indicate that, to a certain extent, this scheme can be used in operational prediction as a reference.
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