Vertical Heat Transport Research Articles

大気モデルのパラメーターとしての垂直安定度の役割について

It is shown that two-parameter geostrophic models are not consistent system for certain type of disturbance in view of baroclinic development. Static stability field as a third parameter has significant roles on dynamical properties such as wave velocity, growth rate, meridional and vertical heat transport and instability of the wave disturbances in a baroclinic atmosphere.

On the Maintenance of Zonal Mean Flow

Assuming that the longitudi n al phase of each wave component of disturbance takes random values, relations which hold among mean eddy transports have been found in the case of stationary mean. In the middle latitudes, where the horizontal eddy transport of heat is northward, the vertical eddy transport of heat is expected to be upward from one of these relations, causing the transformation from eddy potential energy to eddy kinetic energy. As to the vertical eddy transport of momentum, it seems to be upward not only in low latitudes but also in middle latitudes. This suggests, from the balance requirement of angular momentum, that the downward transport of angular momentum by the frictional effects, in addition to the indirect meridional circulation, cannot be so small in magnitude as hitherto been considered.Combining these relations among eddy transports with the equations for the balance of angular momentum and thermal energy, it has been found possible to express the relation between the distributions of mean zonal flow and heat source. Detailed discussions for this expression are left for future studies, but the observed relation between them can be thus explained at least qualitatively.

Eddy diffusion of momentum, water vapour, and heat near the ground

An account is given of an experimental study of the factors which control the vertical turbulent transport of momentum, water vapour, and heat in the first 2 m of air above a short grass surface. The results of fifty-one observations, each of which extended over 30 min, are presented. Measurements were made of the vertical profiles of wind speed, temperature and humidity, and of the rate of evaporation and the aerodynamic drag of the surface. Measurement of the heat-balance components was also attempted. On any one occasion it was not generally possible to observe all the desired quantities. It is found that the wind speed and temperature profiles always have the same form, and that this form is shared on the majority of occasions by the humidity profile. The profiles depart from the logarithmic form found in adiabatic conditions in the manner suggested by Deacon. In near adiabatic conditions as defined by small numerical values of the Richardson number the established laboratory law relating the surface drag to the fluid velocity over a rough surface in turbulent flow is found to hold over the site and a value is deduced for von Kármán's constant. In conditions other than adiabatic it is shown that the explicit wind profile law suggested by Deacon holds in unstable but not in stable conditions. In the latter conditions equations proposed by Rossby & Montgomery and by Holtzman are found to represent the observations with reasonable precision. The friction coefficient of the surface is computed and found to be independent of wind speed but to increase in value in unstable conditions. Values of the eddy diffusivity for momentum, water vapour and heat are obtained on a direct observational basis from the expressions from which the diffusivities are normally defined, and it is found that the diffusivities for momentum and vapour are identical over the range of stability experienced. The magnitude of the diffusivity for heat often appears to be approximately the same as that for momentum or vapour, but exceptions occur when it is much larger than the other two. The exceptions do not appear to be related to stability.

Vertical transport of heat by turbulence in the atmosphere

A necessary consequence of the classical theory of the turbulent transfer of heat in the atmosphere is that the flux of heat is in the direction from high to low potential temperature, and this normally involves the flux being from low to high actual temperature. On examination this is shown to be consistent with the second law of thermodynamics. However, the theory assumes that an eddy may be regarded as a normal sample of the population at its level of origin; but when account is taken of buoyancy effects in a necessarily heterogeneous atmosphere it is clear that this assumption is incorrect. It also becomes apparent in the discussion that a definition of the concept ‘level of origin’ of an eddy more rigid than that given in the classical theory is necessary, and this has been given. It is shown that a component of heat flux, here called ‘convective turbulence’, must result from the buoyancy forces. This is always directed upwards and is thus opposed to the general downward transfer of mechanical turbulence. Records of the fluctuations in temperature at fixed levels show amplitudes which cannot be explained by mechanical turbulence. The traces further indicate that convective turbulence may at times completely dominate the direction of the flow of heat, a conclusion which is supported by reference to some synoptic examples. This result helps to explain the normal increase of potential temperature with height. Dimensional considerations provide a rough measure of the dependence of the buoyancy flux on the lapse rate and amplitude of fluctuations, and also allow the total flux to be written in the classical form pc p K '(gT/gz + Γ). K ', which may be positive or negative, will depend upon the synoptic situation. Some of the implications in synpotic and general theoretical meteorology are discussed in detail. The turbulent transfer of physical quantities other than heat is briefly considered.