Engineering topics

Farrell, B.

Publications and source records attributed to Farrell, B..

10 records

NASA NTRS1995

Evaluation of high temperature polymers

The purpose of this paper is to identify and develop arc-track resistant insulation materials that can operate reliably at 300 C. In the first phase, high performance polymers are evaluated based on structure, thermal stability and electrical properties. Next, the polymers are ranked according to performance and experimental characterization. Then, experimental evaluations in wire configuration are conducted. And selection is made based on performance and commerical potential.

Jayaraj, K.↗

NASA NTRS1985

Transient growth of damped baroclinic waves

A solution of the linear initial value problem for the model of Eady with the inclusion of Ekman damping is presented. This model exhibits large transient growth of perturbations for synoptic cyclone spatial scales and a realistic value of the vertical turbulent viscosity coefficient despite the fact that all normal modes are exponentially decaying. Similar results are found for the model of Charney, implying that exponential instability cannot, in general, serve to explain the occurrence of cyclone scale disturbances in midlatiudes. Rather these are seen to arise additionally and perhaps predominantly from the release of mean flow potential energy by favorably configured initial perturbations. The Petterssen criterion for midlatitude cyclogenesis results naturally from this development as does its extension to the formation of subtropical monsoon depressions. Implications for the maintenance of midlatitude temperature gradients are discussed.

Farrell, B.↗

NASA NTRS1985

Rossby waves in opposing currents

A barotropic Rossby wave incident to a region of increasing mean flow velocity opposing the wave group velocity undergoes a reversal of direction at a stopping point where the mean flow velocity and local wave group velocities are equal and opposite. Incident wave amplitude increases approaching this stopping point, which may be referred to as a group velocity critical layer, but eventually suffers a decrease along its trajectory so that the reflected wave amplitude and energy tend to zero on approach to a phase velociy critical layer located where the opposing flow vanishes. Some applications of this process to observations of synoptic scale Rossby waves are suggested and an axample of the interaction of an incident wave with a barotropic model of the Hadley circulation is presented to illustrate these ideas.

Farrell, B.↗

NASA NTRS1984

Modal and non-modal baroclinic waves

Solution of the initial-value problem for the Eady model is presented. In the presence of boundaries, normal mode waves as well as non-modal waves exist. Energy extracted from the mean flow during the initial development of a perturbation is found to excite the persistent normal modes. It is suggested that this process may be important to cyclogenesis and in providing energy to neutral or near-neutral normal modes. In particular, the Petterssen criterion for cyclogenesis is clarified.

Farrell, B.↗

NASA NTRS1983

Absolute barotropic instability and monsoon depressions

Monsoon depressions over the Bay of Bengal develop almost entirely in July and August. After studies conducted by Lindzen et al. (1980) and Stevens and Lindzen (1978), only barotropic instability remains as a mechanism for the development of the wave disturbances associated with monsoon depressions. The present investigation has the objective to show that barotropic instability is able to explain the wave aspects of monsoon depressions, but that normal mode analysis is inadequate. It is found that the local barotropically unstable response to regional perturbations in the Bay of Bengal during July and August will be dominated by the lower troposphere. The analysis clearly identifies the features of the mean flow which lead to monsoon depressions in July. The features include the development of an easterly jet as opposed to semijet structure in the mean flow, and the development of a modest easterly flow at the jet center as opposed to westerly flow.

Lindzen, R. S.↗

NASA NTRS1983

Charney's problem for baroclinic instability applied to barotropic instability

If barotropically unstable easterly jets may be approximated by broken line profiles, it becomes possible to use the solutions of the Charney (1947) problem for baroclinic instabilithy in order to solve the barotropic problem. Results are presented for easterly jets having an arbitrary degree of symmetry, and it is noted that the convenient calculation obtained for the growth of both localized and normal mode perturbations is important in the study of monsoon depressions over India.

Lindzen, R. S.↗

NASA NTRS1982

Vacillations due to wave interference - Applications to the atmosphere and to annulus experiments

It is noted that vacillations in zonally averaged flows can arise from wave interference between coexisting waves with the same zonal wavenumber but different phase speeds. It is shown that the appropriate baroclinic instability problem for the annulus does yield multiple instabilities which can produce vacillations via interference. It is also shown that the interference of traveling Rossby waves with stationary forced waves can lead to vacillations whose amplitudes and periods are consistent with the observed index cycle.

Lindzen, R. S.↗

NASA NTRS1980

The role of polar regions in global climate, and a new parameterization of global heat transport

The effects of the transport of heat between polar regions and other latitudes on climate sensitivity and stability are examined within the framework of simple energy balance models. New heat transport parameterizations adjust radiative equilibrium distributions of temperature with latitude on the basis of Hadley cells and baroclinically unstable eddies; including the effects of static stability changes with latitude eliminates the possible error in estimating the pole-equator temperature difference. It is found that climate sensitivity and stability for the new transport parameterizations can differ from other models, and is capable of simulating the sensitivity required by existing climate data.

Lindzen, R. S.↗

NASA NTRS1980

A simple approximate result for the maximum growth rate of baroclinic instabilities

The Charney problem for baroclinic instability involves the quasi-geostrophic instability of a zonal flow on a beta plane where the zonal flow is characterized by a constant vertical shear. The atmosphere is non-Boussinesq and continuous. The solution of this problem involves confluent hypergeometric functions, and the mathematical difficulty of the problem has precluded extracting simple results of generality. It is shown that there exists very simple, powerful approximate result for the growth rate of the most rapidly growing instability, viz., that this growth rate is linearly proportional to the surface meridional temperature gradient. The coefficient of proportionality is also easily determined. The result extends to substantially more general profiles than those in the Charney problem.

Lindzen, R. S.↗

NASA NTRS1980

The concept of wave overreflection and its application to baroclinic instability

The paper reviews the concept of wave overreflection and its application to baroclinic instability. The instabilities associated with overreflection are likely to be identical to critical layer instabilities; the baroclinic instability is examined in terms of overreflection of vertically propagating Rossby waves which leads to rapid estimates of growth rates and phase speeds of unstable modes for arbitrary distributions of zonal velocities in models with and without lids. It was found that Charney and Green modes are essentially critical-layer instabilities and that baroclinic instability can be eliminated by stretching the transition region from zero shear at the ground to the interior shear. Finally, it is shown that the potential vorticity flux of baroclinically unstable modes is confined to a layer between the ground and the neighborhood of the steering level.

Lindzen, R. S.↗