Engineering topics

Ochs, H. T., III

Publications and source records attributed to Ochs, H. T., III.

3 records

NASA NTRS1986

A variational assimilation method for satellite and conventional data: Development of basic model for diagnosis of cyclone systems

A three-dimensional diagnostic model for the assimilation of satellite and conventional meteorological data is developed with the variational method of undetermined multipliers. Gridded fields of data from different type, quality, location, and measurement source are weighted according to measurement accuracy and merged using least squares criteria so that the two nonlinear horizontal momentum equations, the hydrostatic equation, and an integrated continuity equation are satisfied. The model is used to compare multivariate variational objective analyses with and without satellite data with initial analyses and the observations through criteria that were determined by the dynamical constraints, the observations, and pattern recognition. It is also shown that the diagnoses of local tendencies of the horizontal velocity components are in good comparison with the observed patterns and tendencies calculated with unadjusted data. In addition, it is found that the day-night difference in TOVS biases are statistically different (95% confidence) at most levels. Also developed is a hybrid nonlinear sigma vertical coordinate that eliminates hydrostatic truncation error in the middle and upper troposphere and reduces truncation error in the lower troposphere. Finally, it is found that the technique used to grid the initial data causes boundary effects to intrude into the interior of the analysis a distance equal to the average separation between observations.

Achtemeier, G. L.↗

NASA NTRS1986

Evaluation of a multivariate variational assimilation of conventional and satellite data for the diagnosis of cyclone systems

A variational data assimilation method for the study of cyclone-scale weather systems is described. The variational data assimilation method is to incorporate primitive equations for a moist, convectively unstable atmosphere and the radiative transfer equation. The variables to be adjusted include the three-dimensional vector wind, height, temperature, and moisture from rawinsonde data, and cloud-wind vectors, moisture, and radiance from satellite data. The development of variational model 1 which contains two nonlinear horizontal momentum equations, an integrated continuity equation, and a hydrostatic equation is examined. Examples applying the assimilation model to rawinsonde and satellite data are presented.

Achtemeier, Gary L.↗

NASA NTRS1982

Drop rebound in clouds and precipitation

The possibility of rebound for colliding cloud drops was measured by determining the collection efficiency. The collection efficiency for 17 size pairs of relatively uncharged drops in over 500 experimental runs was measured using two techniques. The collection efficiencies fall in a narrow range of 0.60 to 0.70 even though the collection drop was varied between 63 and 326 microns and the size ratio from 0.05 to 0.33. In addition the measured values of collection efficiencies (Epsilon) were below the computed values of collision efficiencies (E) for rigid spheres. Therefore it was concluded that rebound was occurring for these sizes since inferred coalescence (epsilon = Epsilon/E) efficiencies are about 0.6 yo 0.8. At a very small size ratio (r/R = p = 0.05, R = 326 microns) the coalescence efficiency inferred is in good agreement with the experimental findings for a supported collector drop. At somewhat large size ratios the inferred values of epsilon are well above results of supported drop experiments, but show a slight correspondence in collected drop size dependency to two models of drop rebound. At a large size ratio (p = 0.73, R = 275) the inferred coalescence efficiency is significantly different from all previous results.

Ochs, H. T., III↗