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At least 325 records · Page 18
All sourcesNASA NTRSDOE OSTI
NASA NTRS1989

Biases and nonsystematic errors in NMC MRF predictions of momentum and zonal winds

The period of study considered by Rosen et al. (1987) for M forecasts is extended and the source of errors in these forecasts is examined. Time series of daily values of MRF forecasted minus the observed M are presented for forecast lead times of 2, 5, and 10 days from December 1985 through November 1988. A graph is presented of the covariance between errors in the angular momentum per unit mass forecasted at a 10-day lag, and those in the forecasted global angular momentum for the same period.

Rosen, Richard D.↗
NASA NTRS1991

Effects of large zonal plasma drifts on the subauroral ionosphere

A model of the earth's ionosphere and plasmasphere is used to investigate the effects of an imposed westward plasma drift of maximum velocity 2 km/s. A closed subauroral tube of plasma is considered and the velocity spike persists for 10 min. Ion-neutral frictional heating causes rapid elevation of the F-region O(+) temperature. The F-layer O(+) concentration is decreased due to increased O(+) loss rate and rapid ion flows both upward and downward from the F-region. The upward flux of O(+) through the topside ionosphere can each 5 x 10 exp 9/sq cm/s; when the velocity spike ceases there is a return flow of O(+) that tends to replenish the F-layer. Most of the features revealed by the model for the F-region and topside ionosphere are in accord with observations of subauroral ion drifts. Downward flows that are predicted to be persistently present around the 300 km altitude level appear to agree with observations only occasionally; suggestions are made to resolve this discrepancy.

Sellek, R.↗
NASA NTRS1992

Instability of the zonal jets and longitudinal thermal waves in a Jovian atmosphere

Jupiter atmosphere observations conducted during the Voyager 1 and 2 encounters indicate slowly moving large-scale features; ground-based measurements with the NASA IR Telescope Facility have noted large scale waves that are either fixed or slowly moving relative to system III. These observations suggest features originating deep in the atmosphere. The present suggestion of an alternative source proceeds from a model of the jets which views the observed waves as due to the quasigeostrophic instability of the jets in the upper troposphere; these are of sufficient duration to give the impression of permanence under observational conditions.

Pirraglia, Joseph A.↗
NASA NTRS1993

A relationship between potential vorticity and zonal wind on Jupiter

We present evidence from analysis of Voyager data and numerical experiments that in Jupiter's troposphere at midlatitudes the potential vorticity is given simply by the reciprocal of the streamfunction. This relationship agrees with the results of a vortex-tube stretching analysis of the Voyager wind-field data of the Great Red Spot and White Oval BC, whereas other published models do not. The derivative of streamfunction with respect to potential vorticity is negative definite, and in the quasigeostrophic limit the relationship is neutrally stable with respect to Arnold's second stability theorem. Numerical experiments indicate that the relationship is also neutrally stable in the primitive shallow-water system. This resolves a long-standing question as to how Jupiter's cloud-top winds are able to violate the Rayleigh-Kuo stability criterion, and constrains the two-layer model to a single free parameter.

Dowling, Timothy E.↗
NASA NTRS1993

Energy transports by ocean and atmosphere based on an entropy extremum principle. I - Zonal averaged transports

The maximum entropy production principle suggested by Paltridge (1975) is applied to separating the satellite-determined required total transports into atmospheric and oceanic components. Instead of using the excessively restrictive equal energy dissipation hypothesis as a deterministic tool for separating transports between the atmosphere and ocean fluids, the satellite-inferred required 2D energy transports are imposed on Paltridge's energy balance model, which is then solved as a variational problem using the equal energy dissipation hypothesis only to provide an initial guess field. It is suggested that Southern Ocean transports are weaker than previously reported. It is argued that a maximum entropy production principle can serve as a governing rule on macroscale global climate, and, in conjunction with conventional satellite measurements of the net radiation balance, provides a means to decompose atmosphere and ocean transports from the total transport field.

Sohn, Byung-Ju↗
NASA NTRS1993

Intercomparison of observed cloud radiative forcing - A zonal and global perspective

Cloud radiative forcing determined by the Earth Radiation Budget Experiment (ERBE) scene identification method and two regression methods is compared using identical data sources and the same analysis periods. Results confirm that from the global perspective the increased reflection of SW radiation induced by clouds is greater than outgoing longwave energy trapped by clouds. The estimates of net effect obtained from the three methods are found to be in good agreement (within 3.5 W/sq m). It is concluded that differences in published global mean values of net cloud radiative forcing are mainly due to different data sources and analysis periods. The best estimated annual mean among all previous estimates is considered to be the ERBE measurement (-17.3 W/sq m).

Sohn, Byung-Ju↗
NASA NTRS1993

A zonal CFD method for three-dimensional wing simulations

The primary objective of this work is to demonstrate the feasibility of a 3D potential/viscous flow coupling procedure for reducing computational effort while maintaining solution accuracy. The closed-loop, overlapped, velocity-coupling concept has been developed in a new code, ZAP3D, that couples a potential flow panel code with a Navier-Stokes method. The current ZAP3D calculation for an aspect ratio 5 wing with an outer domain radius of about 1.2 chords represents a speed-up in CPU time over the ARC3D large domain calculation by about a factor of 2.5. This improvement is achieved for less than a 0.5 percent deviation in C(L), 10 counts change in C(D), and 0.0015 variation in C(My). Additional reductions in the required computational domain for ZAP3D are expected as the method is further developed and refined.

Summa, J. M.↗
NASA NTRS1993

Multi-zonal Navier-Stokes code with the LU-SGS scheme

The LU-SGS (lower upper symmetric Gauss Seidel) algorithm has been implemented into the Compressible Navier-Stokes, Finite Volume (CNSFV) code and validated with a multizonal Navier-Stokes simulation of a transonic turbulent flow around an Onera M6 transport wing. The convergence rate and robustness of the code have been improved and the computational cost has been reduced by at least a factor of 2 over the diagonal Beam-Warming scheme.

Klopfer, G. H.↗
NASA NTRS1993

Zonal Two Equation Kappa-Omega Turbulence Models for Aerodynamic Flows

Two new versions of the kappa-omega two-equation turbulence model will be presented. The new Baseline (BSL) model is designed to give results similar to those of the original kappa-omega model of Wilcox, but without its strong dependency on arbitrary freestream values. The BSL model is identical to the Wilcox model in the inner 50% of the boundary-layer but changes gradually to the standard kappa-epsilon model (in a kappa- omega formulation) towards the boundary-layer edge. The free shear layers. The second version of the model is called Shear-Stress Transport (SST) model. It is a variation of the BSL model with the additional ability to account for the transport of the principal turbulent shear stress in adverse pressure gradient boundary-layers. The model is based on Bradshaw's assumption that the principal shear-stress is proportional to the turbulent kinetic energy, which is introduced into the definition of the eddy-viscosity. Both models are tested for a large number of different flowfields. The results of the BSL model are similar to those of the original kappa-omega model, but without the undesirable freestream dependency. The predictions of the SST model are also independent of the freestream values but show better agreement with experimental data for adverse pressure gradient boundary-layer flows.

Menter, Florian R.↗
NASA NTRS1997

Zonal and Meridional Mass Redistribution in the Tropical Pacific During El Nino Southern Oscillation Events

This note aims at documenting the ENSO-related sea level changes for the whole tropical Pacific, and for the 1979-1996 period which covers numerous El Nino and La Nina events. For this purpose, we rely on (a) 0/450 dbar surface dynamic height anomaly (an alias for sea level) derived from XBT and TOGA-TAO measurements during 1979-1996, (b) TOPEX/Poseidon derived sea level anomaly during 1993-1996, and (c) Murtugudde et al. [1996] model sea level output during 1979-1995.

Delcroix, Thierry↗
NASA NTRS2004

Zonal Flows Below the Sun's Convection: Analytic Approximation

We have derived a simple analytic solution showing how the Sun's global oscillations (g-modes) can drive east-west flows at low latitude deep inside the Sun. This flow is analogous to the Quasi Biennial Oscillation in the Earth s upper atmosphere. It has an observed period of 1.3 years in the solar case but its cause was not known until we published an explanation in a Letter to the Editor a few months ago. Now we give full details of the model and show how it can be used to limit the range of g-modes that can be actively driving the reversing flows. A nonlinear feedback feature of the model is that the flow itself creates the turbulent dissipation that extracts momentum from the g-modes that, in turn, drives the flow.

Wolff, Charles L.↗