Engineering topics

Reeder, Michael J.

Publications and source records attributed to Reeder, Michael J..

7 records

NASA NTRS1988

On air motion trajectories in cold fronts

This paper examines air parcel trajectories in the two-dimensional model for a cold front by Reeder and Smith (1987). These are found to be in close agreement with trajectories deduced from analyses of summertime 'cool changes' in southeastern Australia, adding further support to the applicability of the numerical model to this kind of cold front. The favorable comparison points also to the dynamical consistency of the conceptual model for the cool change, which has evolved from the analysis of data from observational experiments.

Reeder, Michael J.↗

NASA NTRS1988

Balanced and unbalanced upper-level frontogenesis

The impacts of vertical shear in the cross-front component of the geostrophic wind, and of its implied along-front temperature gradient, on frontogenesis at upper levels were investigated using a hierarchy of three dynamical models based on the Keyser and Pecnick (1985) primitive-equation model. The three models are (in order of decreasing sophistication) the anelastic (AN), the geostrophic momentum (GM), and the quasi-geostsrophic (QG) approximations to the primitive equations. Intercomparison of the broad-scale structure of the upper-level jet-fronts as described by the AN and GM models showed close agreement. In contrast, the QG model exhibited marked differences with its AN counterpart, which became more pronounced with increased geostrophic wind.

Reeder, Michael J.↗

NASA NTRS1988

On the movement and low-level structure of cold fronts

Factors that are pertinent to the cold-front motion were examined using the results from previous studies of the low-level structure of cold fronts. Observational studies indicate the existence of two different types of behavior for a cold front. These types of behavior were related to the results of recent theoretical studies, and the mechanism responsible for front propagation was elucidated. It is shown that a necessary requirement for propagation is the existence of an alongfront temperature gradient.

Smith, Roger K.↗

NASA NTRS1988

A generalization of Petterssen's frontogenesis function and its relation to the forcing of vertical motion

The classic Peterssen frontogenesis function, defined as the Lagrangian rate of change of the magnitude of the potential temperature gradient, is generalized to apply to the vector potential temperature gradient. The derivation of vector frontogenesis in natural coordinates is shown, and analytical examples of frontal evolution in nondivergent horizontal velocity fields are given which suggest that both the frontogenetic and rotational components of the vector frontogenesis function F may be comparable in developing frontal zones observed in nature. The relative importance of the magnitude and direction contributions to F is quantitatively investigated, and it is found that the Lagrangian rates of change of the magnitude and direction of the potential temperature gradient are comparable. The frontal circulation is found to be related to the magnitude component of the Q vector, whereas the background circulation is related to the direction component.

Keyser, Daniel↗

NASA NTRS1988

On the horizontal resolution of fronts in numerical weather prediction models

A two-dimensional model is used to study the ability of current numerical weather prediction models to capture frontogenesis and to determine frontal motion. Particular attention is given to the ability of a simulation with a very coarse grid to represent the dynamics of a frontogenetically-active model cold front in a simulation with a relatively fine grid. A resolution between 50 and 100 km is satisfactory for capturing frontal scale motions.

Reeder, Michael J.↗

NASA NTRS1987

A study of frontal dynamics with application to the Australian summertime 'cool change'

The dynamics of frontal evolution is examined in terms of the Australian summertime cool change using a two-dimensional numerical model. The model is synthesized from observational data on surface cold fronts obtained during the Australian Cold Fronts Research Program, and the model develops a quasi-steady surface cold front during the 24 hours of integration. The characteristics of this model are compared with those of a kinematic model; it is observed that the features of the two models correspond. The two-dimensional and kinematic models are also compared with a 24-hour prediction of the cold front of February 1983 using the three-dimensional nested-grid model of the Australian Numerical Meteorology Research Center, developed by Gauntlett et al. (1984). Good correlation between these models is detected.

Reeder, Michael J.↗

NASA NTRS1986

The interaction of a surface cold front with a prefrontal thermodynamically well-mixed boundary layer

The dynamics of a surface cold front as it proceeds from sea to shore and interacts with a thermodynamically well-mixed boundary layer are investigated by means of numerical simulations using a modified version of the two-dimensional model of Reeder and Smith (1987). The theoretical basis of the model is explained, and the results are presented graphically and characterized in detail. Good agreement is found with observational data on Australian summer cold fronts, and the transverse frontal circulation is shown to be significantly affected by diabatic heating.

Reeder, Michael J.↗