Moist Adiabat Research Articles

Observations of Moist Adiabatic Ascent in Northeast Colorado Cumulus Congestus Clouds

The characteristics of entrainment in and below 12 developing cumulus congestus clouds in the north-eastern Colorado area were investigated using measurements obtained with the NCAR/NOAA sailplane, supporting aircraft and rawinsondes. A region of moist adiabatic ascent was found in eight of the most vigorous clouds sampled. A gradual increase was noted in the equivalent potential temperature and the ratio of the liquid water content to the adiabatic value from the edge of the updraft region inward to the moist adiabatic core. Previous measurements and conceptual and theoretical models of entrainment are discussed in the context of the present set of measurements. The moist adiabatic core was positioned off-center with respect to the boundaries of the updraft region. The measurements supported previous conceptual cloud models in which the updraft acts as an obstacle to the horizontal wind thereby causing the environmental air to flow around the upshear portion of the cell, protecting that region from entrainment. A turbulent wake would be expected to occur in the down-shear portion of the cell, producing increased turbulence and mixing in that region.

The Parameterization of Tropospheric Lapse Rates in Terms of Surface Temperature

Abstract The relationship between the lapse rate of temperature and the surface temperature is investigated by comparing the zonally averaged temperature structure of the atmosphere to that which is generated by several assumptions concerning the lapse rate. It is found that the value of ∂θ/∂p for any given temperature sounding is essentially constant, but that this value varies with both latitude and season. The ratio of ∂θ/∂p to the value of ∂θ/∂p along a moist adiabat at the surface is found empirically to have a cubic dependence on the surface temperature. This dependence is used to define a relationship between the surface temperature and the lapse rate which can be used to generate a zonally averaged temperature structure for the troposphere which is in good agreement with that which is observed. The parameterization is suitable for use in a climate model based either on radiative equilibrium or zonally averaged energy balance calculations.

On the Dynamics and Energy Transformations in Steady-State Hurricanes

A dynamic model of the inflow layer in a steady mature hurricane is evolved, relating wind speed, pressure gradient, surface shearing stress, mass flow, and convergence. The low-level air trajectories are assumed to be logarithmic spirals. With this hypothesis, properties such as maximum wind and central pressure are determined through choice of a parameter depending on the inflow angle: a moderate hurricane arises with inflow angles of about 20°, while 25° gives an intense or extreme storm. Most of this study treats the moderate storm. In order to maintain its core pressure gradients, an oceanic source of sensible and latent heat is required. As a result, latent heat release in the inner hurricane area occurs at higher heat content (warmer moist adiabats) than mean tropical subcloud air. The heat transfer from the ocean and the release of latent heat in the core determine the pressure gradient along the trajectory, and this prescribes the particular trajectory selected by the air among an infinite number available from the logarithmic spiral family. This selection principle is evolved using recent work on “relative stability” of finite amplitude thermal circulations. Of an infinite number of dynamically possible spirals, the one is realized which maximizes the rate of kinetic energy production under the thermodynamic constraints, here formulated in terms of the relation between heat release and pressure gradient. Finally, rainfall, efficiency of work done by the storm, and kinetic energy budgets are examined in an attempt to understand the difference between the hurricane—a rare phenomenon—and the common sub-hurricane tropical storm. DOI: 10.1111/j.2153-3490.1960.tb01279.x

On the Dynamics and Energy Transformations in Steady-State Hurricanes

A dynamic model of the inflow layer in a steady mature hurricane is evolved, relating wind speed, pressure gradient, surface shearing stress, mass flow, and convergence. The low-level air trajectories are assumed to be logarithmic spirals. With this hypothesis, properties such as maximum wind and central pressure are determined through choice of a parameter depending on the inflow angle: a moderate hurricane arises with inflow angles of about 20°, while 25° gives an intense or extreme storm.
 Most of this study treats the moderate storm. In order to maintain its core pressure gradients, an oceanic source of sensible and latent heat is required. As a result, latent heat release in the inner hurricane area occurs at higher heat content (warmer moist adiabats) than mean tropical subcloud air. The heat transfer from the ocean and the release of latent heat in the core determine the pressure gradient along the trajectory, and this prescribes the particular trajectory selected by the air among an infinite number available from the logarithmic spiral family.
 This selection principle is evolved using recent work on “relative stability” of finite aniplitude thermal circulations. Of an infinite number of dynamically possible spirals, the one is realized which maximizes the rate of kinetic energy production under the thermodynamic constraints, here formulated in terms of the relation between heat release and pressure gradient.
 Finally, rainfall, efficiency of work done by the storm, and kinetic energy budgets are examined in an attempt to understand the difference between the hurricane—a rare phenomenon—and the common sub-hurricane tropical storm.

The Precipitation under the Assumption of Dry Adiabatic Change and Moist Adiabatic Change of the Air

It is the purpose of this paper to make clear the condensation equation. Using this equation and the vertical motion computed from vorticity equation, an amount of heavy rainfall was calculated. In connection with this problem, the author attempts to calculate the amount of condensation of the vapour and vertical velocity under the assumption of not only dry adiabatic change but also moist adiabatic change of the air.