Yoshi-Yuki Hayashi - Academia.edu (original) (raw)
Papers by Yoshi-Yuki Hayashi
Journal of the Atmospheric Sciences, Jul 1, 1992
Journal of the Meteorological Society of Japan, 1991
The results of `aqua planet' GCM experiments are analyzed, concentrating on the planetary scale s... more The results of `aqua planet' GCM experiments are analyzed, concentrating on the planetary scale structure and the structure of precipitating areas around the ITCZ region. The 30 day oscillations, that is, eastward-moving structures on the planetary scale, appear in a similar way regardless of the cumulus parameterization utilized. These structures are considered to be maintained by the dependence of evaporation on wind speed, i, e., the evaporation-wind feedback mechanism. For the maintenance of the disturbances on the synoptic scale, this mechanism is considered to be less effective and other mechanisms such as wave-CISK are more important. It is suggested that the coexistence of two different maintenance mechanism of disturbances is relevant to the existence of hierarchical structure of cumulus activity in the model. At the double ITCZ latitudes in the experiments with Kuo's cumulus parameterization, there are areas of high cumulus activity on the grid scale, which are moving eastward continuously. In the experiment with moist convective adjustment, on the other hand, westward-moving areas of high cumulus activity associated with vorticity, which correspond well to the easterly wave disturbances in the real tropics, are observed. It is revealed that a process which can be called 'evaporation-wind feedback for the zonal mean field' exists and contributes to the separation of the ITCZ into double bands in the experiments with Kuo's parameterization.
Journal of Fluid Mechanics, Nov 1, 1987
This article considers the instabilities of rotating, shallow-water, shear flows on an equatorial... more This article considers the instabilities of rotating, shallow-water, shear flows on an equatorial 8-plane. Because of the free surface, the motion is horizontally divergent and the energy density is cubic in the field variables (i.e. in standard notation the kinetic energy density is $(u2+w2)). Marinone & Ripa (1984) observed that as a consequence of this the wave energy is no longer positive definite (there is a cross-term Uh'u'). A wave with negative wave energy can grow by transferring energy to the mean flow. Of course total (mean plus wave) energy is conserved in this process. Further, when the basic state has constant potential vorticity, we show that there are no exchanges of energy and momentum between a growing wave and the mean flow. Consequently when the basic state has no potential vorticity gradients an unstable wave has zero wave energy and the mean flow is modified so that its energy is unchanged. This result strikingly shows that energy and momentum exchanges between a growing wave and the mean flow are not generally characteristic of, or essential to, instability. A useful conceptual tool in understanding these counterintuitive results is that of disturbance energy (or pseudoenergy) of a shear mode. This is the amount of energy in the fluid when the mode is excited minus the amount in the unperturbed medium. Equivalently, the disturbance energy is the sum of the wave energy and that in the modified mean flow. The disturbance momentum (or pseudomomentum) is defined analogously. For an unstable mode, which grows without external sources, the disturbance energy must be zero. On the other hand the wave energy may increase to plus infinity, remain zero, or decrease to minus infinity. Thus there is a tripartite classification of instabilities. We suggest that one common feature in all three cases is that the unstable shear mode is roughly a linear combination of resonating shear modes each of which would be stable if the other were somehow suppressed. The two resonating constituents must have opposite-signed disturbance energies in order that the unstable alliance has zero disturbance energy. The instability is a transfer of disturbance energy from the member with negative disturbance energy to the one with positive disturbance energy.
Japan Geoscience Union, Mar 10, 2016
Journal of the Meteorological Society of Japan, 1986
Numerical experiments using a general circulation model (GCM) were performed for the purpose of i... more Numerical experiments using a general circulation model (GCM) were performed for the purpose of investigating the possibility of the generation of a long period (30-40 days) oscillation as a collective motion of cumulus activity (so-called wave-CISK) along the equator of an ocean covered globe ("aqua planet"). In our model, the SST distribution was symmetric about the equator and uniform in the longitudinal direction. The results of a 90 day integration exhibited the spontaneous appearance of a collective motion of convective activity together with an east-west wavenumber one circulation (the "30 day oscillation"). The characteristics of this east-west circulation resemble those of the observed 30-60 day oscillation in the actual atmosphere. The 30 day oscillation is characterized by a superposition of two different scales: the scale of precipitation patterns ("super clusters") which is nearly equal to the equatorial radius of deformation, and the scale observed as the modulation of precipitation patterns and the east-west circulation with a wavenumber one. The whole structure moves eastward at a slow phase speed (15m/s). The results also exhibited the spontaneous formation of double ITCZs around the equator. Thus the production of the double ITCZ structure does not necessarily require a minimum SST at the equator. In the equatorial region between the north and south ITCZs, active convection forms super clusters, while in the regions poleward of the ITCZs, active convection forms tropical cyclones. Another experiment without the moist processes resulted in the abrupt disintegration of the 30 day oscillation into Kelvin and Rossby waves. This indicates that strong mode coupling between the equatorial free waves is required in order to maintain the 30 day oscillation. The slow phase speed, the strong mode coupling and the double structure in scale indicate that the collective motion of convective activity along the equator cannot be explained simply as a Kelvin wave mode of the linear equatorial wave-CISK theory presented so far. The 30 day oscillation should be regarded as a new type solution of the equatorial wave-CISK problem.
Journal of the Meteorological Society of Japan, 1984
The amplitudes of stationary Rossby wave packets propagating in a super-rotational zonal flow are... more The amplitudes of stationary Rossby wave packets propagating in a super-rotational zonal flow are studied with the non-divergent linear barotropic vorticity equation. Discussions are made concerning various pitfalls in determining wave amplitudes on the basis of ray theory. It is recalled that the change of wave amplitude along a ray in a slowly varying medium can be calculated by ray theory only by specifying the ray configuration neighbouring the ray considered (owing to the * Cg term). The poleward increase of stream function amplitude of stationary Rossby wavetrains as emphasized by Hoskins and Karoly (1981) is a consequence of a particular ray configuration implicitly assumed (all longitudinally neighbouring rays pointing the same direction). In their problem, a caustic forms at each turning latitude where northward-directed rays turn southward or vice versa. Although *Cg is important for amplitude calculation in general, a spherical harmonic solution cos*'ei*', which is often referred to as a wavetrain along a great circle (*'=0 in a tilted spherical coordinate system), is shown to be an exception. It is suggested that this solution should be interpreted to consist of an isolated single great circle ray. The direct application.of ray theory is impossible in this case so that a slight modification of the method is suggested. It is also noted that attention must be paid to zonally symmetric components (k=0) of solutions, especially when the total wave number of stationary wave is small. This is because steady state solutions of the linearized vorticity equation with basic zonal flows contain an ambiguity of arbitrary function of latitude. A physical consideration that the zonal mean flows do not change at the first order of wave amplitude leads to a modification of spherical harmonic solution.
Japan Geoscience Union, Mar 14, 2018
Computer simulations have been recognized as one of the fundamental tools in understanding planet... more Computer simulations have been recognized as one of the fundamental tools in understanding planetary formation, evolution and diversity of surface environment. However, is may be notified that the
EPSC-DPS Joint Meeting 2011, Oct 1, 2011
ABSTRACT We numerically investigate general circulation of moist atmosphere on synchronously rota... more ABSTRACT We numerically investigate general circulation of moist atmosphere on synchronously rotating planets to examine the dependence of the atmospheric structure on planetary rotation rate. Three representative surface temperature patterns associated with different structure of heat transport appear. However, total amount of energy transport from dayside to nightside has only weak dependence on planetary rotation rate.
Japan Geoscience Union, Mar 10, 2017
Japan Geoscience Union, Mar 14, 2019
EPSC-DPS Joint Meeting 2011, Oct 1, 2011
We perform a numerical simulation of cloud convection by using two-dimensional nonhydrostatic mod... more We perform a numerical simulation of cloud convection by using two-dimensional nonhydrostatic model for the purpose of investigating the structure of cloud convection with condensation of the major component when significant high supersaturation is not allowed. In quasi-equilibrium state, horizontally uniform cloud layer is formed above the condensation level, and the dry adiabatic layer is formed below the level. The updraft and downdraft associated with convection extends from near the surface to the top of the model atmosphere. The updraft and downdraft in the cloud layer seem to be maintained by buoyancy in the dry adiabatic layer.
Japan Geoscience Union, Mar 10, 2016
Dust devils are one of the key elements in the Martian atmospheric circulation. In order to exami... more Dust devils are one of the key elements in the Martian atmospheric circulation. In order to examine their statistics, we conducted high-resolution (up to 5 m) and wide-domain (about 20 × 20 km 2) large-eddy simulations of the Martian daytime convective layer. Large numbers of dust devils developed spontaneously in the simulations, which enabled us to represent a quantitative consideration of Martian dust devil frequency distributions. We clarify the distributions of size and intensity, a topic of debate, and conclude that the maximum vertical vorticity of an individual dust devil has an exponential distribution, while the radius and circulation have power law distributions. A grid refinement experiment shows that the rate parameter of the vorticity distribution and the exponent of the circulation distribution are robust. The mode of the size distribution depends on the resolution, and it is suggested that the mode is less than 5 m. Recently, the characteristics of Martian and terrestrial dust devils have been examined using observational data [e.g., Lorenz, 2011; Fenton and Lorenz, 2015]. These data suggest several possibilities for the distribution of dust devil size. However, the number of samples has not been statistically sufficient to clarify the distribution. Additionally, there may be an observational bias in detection efficiency that depends on dust devil size, and there are some dust devil characteristics that are difficult to represent using only observable quantities. Numerical studies of dust devils are needed to reduce the statistical uncertainty in such observational studies and to conduct further detailed analysis in order to understand the statistical characteristics of dust devils. Numerical investigation of Martian dust devils began with studies of convection in the Martian PBL [e.g.,
Journal of the Atmospheric Sciences, Oct 1, 2016
Cloud convection of a CO 2 atmosphere where the major constituent condenses is numerically invest... more Cloud convection of a CO 2 atmosphere where the major constituent condenses is numerically investigated under a setup idealizing a possible warm atmosphere of early Mars, utilizing a two-dimensional cloudresolving model forced by a fixed cooling profile as a substitute for a radiative process. The authors compare two cases with different critical saturation ratios as condensation criteria and also examine sensitivity to number mixing ratio of condensed particles given externally. When supersaturation is not necessary for condensation, the entire horizontal domain above the condensation level is continuously covered by clouds irrespective of number mixing ratio of condensed particles. Horizontal-mean cloud mass density decreases exponentially with height. The circulations below and above the condensation level are dominated by dry cellular convection and buoyancy waves, respectively. When 1.35 is adopted as the critical saturation ratio, clouds appear exclusively as intense, short-lived, quasiperiodic events. Clouds start just above the condensation level and develop upward, but intense updrafts exist only around the cloud top; they do not extend to the bottom of the condensation layer. The cloud layer is rapidly warmed by latent heat during the cloud events, and then the layer is slowly cooled by the specified thermal forcing, and supersaturation gradually develops leading to the next cloud event. The periodic appearance of cloud events does not occur when number mixing ratio of condensed particles is large.
Japan Geoscience Union, Mar 14, 2019
Japan Geoscience Union, Mar 14, 2018
Japan Geoscience Union, Mar 10, 2016
Japan Geoscience Union, Mar 14, 2018
We call for general interest papers for Planetary Sciences. Planetary Sciences consist of a varie... more We call for general interest papers for Planetary Sciences. Planetary Sciences consist of a variety of studies on the past, present, and future of our solar system and exoplanetary systems. Discussions based on various backgrounds are encouraged.
Journal of the Atmospheric Sciences, Jul 1, 1992
Journal of the Meteorological Society of Japan, 1991
The results of `aqua planet' GCM experiments are analyzed, concentrating on the planetary scale s... more The results of `aqua planet' GCM experiments are analyzed, concentrating on the planetary scale structure and the structure of precipitating areas around the ITCZ region. The 30 day oscillations, that is, eastward-moving structures on the planetary scale, appear in a similar way regardless of the cumulus parameterization utilized. These structures are considered to be maintained by the dependence of evaporation on wind speed, i, e., the evaporation-wind feedback mechanism. For the maintenance of the disturbances on the synoptic scale, this mechanism is considered to be less effective and other mechanisms such as wave-CISK are more important. It is suggested that the coexistence of two different maintenance mechanism of disturbances is relevant to the existence of hierarchical structure of cumulus activity in the model. At the double ITCZ latitudes in the experiments with Kuo's cumulus parameterization, there are areas of high cumulus activity on the grid scale, which are moving eastward continuously. In the experiment with moist convective adjustment, on the other hand, westward-moving areas of high cumulus activity associated with vorticity, which correspond well to the easterly wave disturbances in the real tropics, are observed. It is revealed that a process which can be called 'evaporation-wind feedback for the zonal mean field' exists and contributes to the separation of the ITCZ into double bands in the experiments with Kuo's parameterization.
Journal of Fluid Mechanics, Nov 1, 1987
This article considers the instabilities of rotating, shallow-water, shear flows on an equatorial... more This article considers the instabilities of rotating, shallow-water, shear flows on an equatorial 8-plane. Because of the free surface, the motion is horizontally divergent and the energy density is cubic in the field variables (i.e. in standard notation the kinetic energy density is $(u2+w2)). Marinone & Ripa (1984) observed that as a consequence of this the wave energy is no longer positive definite (there is a cross-term Uh'u'). A wave with negative wave energy can grow by transferring energy to the mean flow. Of course total (mean plus wave) energy is conserved in this process. Further, when the basic state has constant potential vorticity, we show that there are no exchanges of energy and momentum between a growing wave and the mean flow. Consequently when the basic state has no potential vorticity gradients an unstable wave has zero wave energy and the mean flow is modified so that its energy is unchanged. This result strikingly shows that energy and momentum exchanges between a growing wave and the mean flow are not generally characteristic of, or essential to, instability. A useful conceptual tool in understanding these counterintuitive results is that of disturbance energy (or pseudoenergy) of a shear mode. This is the amount of energy in the fluid when the mode is excited minus the amount in the unperturbed medium. Equivalently, the disturbance energy is the sum of the wave energy and that in the modified mean flow. The disturbance momentum (or pseudomomentum) is defined analogously. For an unstable mode, which grows without external sources, the disturbance energy must be zero. On the other hand the wave energy may increase to plus infinity, remain zero, or decrease to minus infinity. Thus there is a tripartite classification of instabilities. We suggest that one common feature in all three cases is that the unstable shear mode is roughly a linear combination of resonating shear modes each of which would be stable if the other were somehow suppressed. The two resonating constituents must have opposite-signed disturbance energies in order that the unstable alliance has zero disturbance energy. The instability is a transfer of disturbance energy from the member with negative disturbance energy to the one with positive disturbance energy.
Japan Geoscience Union, Mar 10, 2016
Journal of the Meteorological Society of Japan, 1986
Numerical experiments using a general circulation model (GCM) were performed for the purpose of i... more Numerical experiments using a general circulation model (GCM) were performed for the purpose of investigating the possibility of the generation of a long period (30-40 days) oscillation as a collective motion of cumulus activity (so-called wave-CISK) along the equator of an ocean covered globe ("aqua planet"). In our model, the SST distribution was symmetric about the equator and uniform in the longitudinal direction. The results of a 90 day integration exhibited the spontaneous appearance of a collective motion of convective activity together with an east-west wavenumber one circulation (the "30 day oscillation"). The characteristics of this east-west circulation resemble those of the observed 30-60 day oscillation in the actual atmosphere. The 30 day oscillation is characterized by a superposition of two different scales: the scale of precipitation patterns ("super clusters") which is nearly equal to the equatorial radius of deformation, and the scale observed as the modulation of precipitation patterns and the east-west circulation with a wavenumber one. The whole structure moves eastward at a slow phase speed (15m/s). The results also exhibited the spontaneous formation of double ITCZs around the equator. Thus the production of the double ITCZ structure does not necessarily require a minimum SST at the equator. In the equatorial region between the north and south ITCZs, active convection forms super clusters, while in the regions poleward of the ITCZs, active convection forms tropical cyclones. Another experiment without the moist processes resulted in the abrupt disintegration of the 30 day oscillation into Kelvin and Rossby waves. This indicates that strong mode coupling between the equatorial free waves is required in order to maintain the 30 day oscillation. The slow phase speed, the strong mode coupling and the double structure in scale indicate that the collective motion of convective activity along the equator cannot be explained simply as a Kelvin wave mode of the linear equatorial wave-CISK theory presented so far. The 30 day oscillation should be regarded as a new type solution of the equatorial wave-CISK problem.
Journal of the Meteorological Society of Japan, 1984
The amplitudes of stationary Rossby wave packets propagating in a super-rotational zonal flow are... more The amplitudes of stationary Rossby wave packets propagating in a super-rotational zonal flow are studied with the non-divergent linear barotropic vorticity equation. Discussions are made concerning various pitfalls in determining wave amplitudes on the basis of ray theory. It is recalled that the change of wave amplitude along a ray in a slowly varying medium can be calculated by ray theory only by specifying the ray configuration neighbouring the ray considered (owing to the * Cg term). The poleward increase of stream function amplitude of stationary Rossby wavetrains as emphasized by Hoskins and Karoly (1981) is a consequence of a particular ray configuration implicitly assumed (all longitudinally neighbouring rays pointing the same direction). In their problem, a caustic forms at each turning latitude where northward-directed rays turn southward or vice versa. Although *Cg is important for amplitude calculation in general, a spherical harmonic solution cos*'ei*', which is often referred to as a wavetrain along a great circle (*'=0 in a tilted spherical coordinate system), is shown to be an exception. It is suggested that this solution should be interpreted to consist of an isolated single great circle ray. The direct application.of ray theory is impossible in this case so that a slight modification of the method is suggested. It is also noted that attention must be paid to zonally symmetric components (k=0) of solutions, especially when the total wave number of stationary wave is small. This is because steady state solutions of the linearized vorticity equation with basic zonal flows contain an ambiguity of arbitrary function of latitude. A physical consideration that the zonal mean flows do not change at the first order of wave amplitude leads to a modification of spherical harmonic solution.
Japan Geoscience Union, Mar 14, 2018
Computer simulations have been recognized as one of the fundamental tools in understanding planet... more Computer simulations have been recognized as one of the fundamental tools in understanding planetary formation, evolution and diversity of surface environment. However, is may be notified that the
EPSC-DPS Joint Meeting 2011, Oct 1, 2011
ABSTRACT We numerically investigate general circulation of moist atmosphere on synchronously rota... more ABSTRACT We numerically investigate general circulation of moist atmosphere on synchronously rotating planets to examine the dependence of the atmospheric structure on planetary rotation rate. Three representative surface temperature patterns associated with different structure of heat transport appear. However, total amount of energy transport from dayside to nightside has only weak dependence on planetary rotation rate.
Japan Geoscience Union, Mar 10, 2017
Japan Geoscience Union, Mar 14, 2019
EPSC-DPS Joint Meeting 2011, Oct 1, 2011
We perform a numerical simulation of cloud convection by using two-dimensional nonhydrostatic mod... more We perform a numerical simulation of cloud convection by using two-dimensional nonhydrostatic model for the purpose of investigating the structure of cloud convection with condensation of the major component when significant high supersaturation is not allowed. In quasi-equilibrium state, horizontally uniform cloud layer is formed above the condensation level, and the dry adiabatic layer is formed below the level. The updraft and downdraft associated with convection extends from near the surface to the top of the model atmosphere. The updraft and downdraft in the cloud layer seem to be maintained by buoyancy in the dry adiabatic layer.
Japan Geoscience Union, Mar 10, 2016
Dust devils are one of the key elements in the Martian atmospheric circulation. In order to exami... more Dust devils are one of the key elements in the Martian atmospheric circulation. In order to examine their statistics, we conducted high-resolution (up to 5 m) and wide-domain (about 20 × 20 km 2) large-eddy simulations of the Martian daytime convective layer. Large numbers of dust devils developed spontaneously in the simulations, which enabled us to represent a quantitative consideration of Martian dust devil frequency distributions. We clarify the distributions of size and intensity, a topic of debate, and conclude that the maximum vertical vorticity of an individual dust devil has an exponential distribution, while the radius and circulation have power law distributions. A grid refinement experiment shows that the rate parameter of the vorticity distribution and the exponent of the circulation distribution are robust. The mode of the size distribution depends on the resolution, and it is suggested that the mode is less than 5 m. Recently, the characteristics of Martian and terrestrial dust devils have been examined using observational data [e.g., Lorenz, 2011; Fenton and Lorenz, 2015]. These data suggest several possibilities for the distribution of dust devil size. However, the number of samples has not been statistically sufficient to clarify the distribution. Additionally, there may be an observational bias in detection efficiency that depends on dust devil size, and there are some dust devil characteristics that are difficult to represent using only observable quantities. Numerical studies of dust devils are needed to reduce the statistical uncertainty in such observational studies and to conduct further detailed analysis in order to understand the statistical characteristics of dust devils. Numerical investigation of Martian dust devils began with studies of convection in the Martian PBL [e.g.,
Journal of the Atmospheric Sciences, Oct 1, 2016
Cloud convection of a CO 2 atmosphere where the major constituent condenses is numerically invest... more Cloud convection of a CO 2 atmosphere where the major constituent condenses is numerically investigated under a setup idealizing a possible warm atmosphere of early Mars, utilizing a two-dimensional cloudresolving model forced by a fixed cooling profile as a substitute for a radiative process. The authors compare two cases with different critical saturation ratios as condensation criteria and also examine sensitivity to number mixing ratio of condensed particles given externally. When supersaturation is not necessary for condensation, the entire horizontal domain above the condensation level is continuously covered by clouds irrespective of number mixing ratio of condensed particles. Horizontal-mean cloud mass density decreases exponentially with height. The circulations below and above the condensation level are dominated by dry cellular convection and buoyancy waves, respectively. When 1.35 is adopted as the critical saturation ratio, clouds appear exclusively as intense, short-lived, quasiperiodic events. Clouds start just above the condensation level and develop upward, but intense updrafts exist only around the cloud top; they do not extend to the bottom of the condensation layer. The cloud layer is rapidly warmed by latent heat during the cloud events, and then the layer is slowly cooled by the specified thermal forcing, and supersaturation gradually develops leading to the next cloud event. The periodic appearance of cloud events does not occur when number mixing ratio of condensed particles is large.
Japan Geoscience Union, Mar 14, 2019
Japan Geoscience Union, Mar 14, 2018
Japan Geoscience Union, Mar 10, 2016
Japan Geoscience Union, Mar 14, 2018
We call for general interest papers for Planetary Sciences. Planetary Sciences consist of a varie... more We call for general interest papers for Planetary Sciences. Planetary Sciences consist of a variety of studies on the past, present, and future of our solar system and exoplanetary systems. Discussions based on various backgrounds are encouraged.