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NASA NTRS1993

Quasi-decadal variability of the stratosphere: Influence of long-term solar ultraviolet variations

A multiple regression statistical model is applied to investigate the existence of upper-stratospheric ozone, temperature, and zonal wind responses to long-term (solar cycle) changes in solar ultraviolet radiation using 11.5 years of reprocessed Nimbus-7 Solar Backscattered Ultraviolet (SBUV) data and 12.4 years of National Meteorological Center (NMC) data. A positive solar cycle variation of independently measured ozone and temperature occurs with maximum amplitude near the low-latitude stratopause. The seasonal solar regression coefficients near 1 mb for both ozone and temperature occur at low latitudes supporting a role for photochemical and radiative forcing in their origin. Zonal wind perturbations that correlate with long-term solar ultraviolet variations are a strong function of season and pressure level. Above approximately 2 mbar, the largest solar-correlated zonal wind enhancements occur at middle winter latitudes near the time of winter solstice in both hemispheres. The Northern Hemisphere December enhancement at 1 mb was especially large, 23 +/- 9 m/s from solar minimum to maximum during the last solar cycle. The derived ozone, temperature, and zonal wind increases with increasing solar ultraviolet flux near the stratopause are larger than predicted by models that consider primarily photochemical and radiative processes. The higher ozone and temperature response amplitudes at low latitudes may be due to modified ozone transport and adiabatic temperature changes induced by the dynamical response. If the midlatitude winter solstice wind enhancements are solar induced, their high amplitudes require a positive feedback due to wave-mean flow interaction such that the planetary wave drag on the flow is reduced under solar maximum conditions.

Hood, L. L.↗

NASA NTRS1990

Measurements of CH4, N2O, CO, H2O, and O3 in the middle atmosphere by the Atmospheric Trace Molecule Spectroscopy Experiment on Spacelab 3

The volume mixing ratios of five minor gases (CH4, N2O, CO, H2O, and O3) have been retrieved through the middle atmosphere from the analysis of 0.01/cm resolution infrared solar occultation spectra recorded near 28 deg N and 48 deg S latitudes with the Atmospheric Trace Molecule Spectroscopy instrument, flow on board Spacelab 3 (April 30 through May 6, 1985). The results are in general agreement with reported measurements from ground-, balloon-, and satellite-based instruments for the same seasons. In detail, the vertical profiles of these gases show the effects of the upper and middle atmospheric transport patterns dominant during the season of these observations. The profiles inferred at different longitudes around 28 deg N suggest a near-uniform zonal distribution of these gases, for conditions corresponding to late spring. The sunrise occultation measurements point to a larger longitudinal variability in the vertical distribution of these gases at 48 deg S.

Gunson, M. R.↗

NASA NTRS1987

Cluster analysis of multiple planetary flow regimes

A modified cluster analysis method was developed to identify spatial patterns of planetary flow regimes, and to study transitions between them. This method was applied first to a simple deterministic model and second to Northern Hemisphere (NH) 500 mb data. The dynamical model is governed by the fully-nonlinear, equivalent-barotropic vorticity equation on the sphere. Clusters of point in the model's phase space are associated with either a few persistent or with many transient events. Two stationary clusters have patterns similar to unstable stationary model solutions, zonal, or blocked. Transient clusters of wave trains serve as way stations between the stationary ones. For the NH data, cluster analysis was performed in the subspace of the first seven empirical orthogonal functions (EOFs). Stationary clusters are found in the low-frequency band of more than 10 days, and transient clusters in the bandpass frequency window between 2.5 and 6 days. In the low-frequency band three pairs of clusters determine, respectively, EOFs 1, 2, and 3. They exhibit well-known regional features, such as blocking, the Pacific/North American (PNA) pattern and wave trains. Both model and low-pass data show strong bimodality. Clusters in the bandpass window show wave-train patterns in the two jet exit regions. They are related, as in the model, to transitions between stationary clusters.

Mo, Kingtse↗

NASA NTRS1982

Jovian winds from Voyager 2. Part II - Analysis of eddy transports

Previous Voyager 1 and 2 Jovian circulation measurements exhibit a large positive correlation between eddy momentum transports and the meridional shear of the zonal wind component, implying a very large rate of conversion of eddy kinetic energy of the zonal jets. Examination of the vectors mainly responsible for the correlation in our recent Voyager 2 global measurements indicates that it is probably caused by a biased sampling of prominent cloud features associated with circulating eddies. Intensive diagnostic measurements with more nearly uniform spatial sampling show no significant correlation in regions where our original measurements showed strong correlations. If the sampling bias mechanism is fully accounted for in all Jovian circulation measurements, the estimated eddy-to-mean-flow kinetic energy conversion rate may be reduced significantly.

Sromovsky, L. A.↗

NASA NTRS1992

Navier-Stokes prediction of large-amplitude delta-wing roll oscillations characterizing wing rock

High-incidence vortical flow about a 65-deg sweep delta wing undergoing static roll and large-amplitude, high-rate-of-roll oscillations is simulated numerically using the time-dependent, three-dimensional, Reynolds-averaged, Navier-Stokes equations. Turbulent computations are presented for static roll angles up through 42 degrees. The effects of roll angle on the vortex aerodynamics are discussed, and the solution accuracy is evaluated by comparison with experimental data. The effects of grid refinement and zonal boundary condition treatment on solution accuracy are assessed at zero roll angle. Numerical simulation of a forced periodic roll motion is also presented.

Chaderjian, Neal M.↗

NASA NTRS2013

Constraints on Saturn's Tropospheric General Circulation from Cassini ISS Images

An automated cloud tracking algorithm is applied to Cassini Imaging Science Subsystem high-resolution apoapsis images of Saturn from 2005 and 2007 and moderate resolution images from 2011 and 2012 to define the near-global distribution of zonal winds and eddy momentum fluxes at the middle troposphere cloud level and in the upper troposphere haze. Improvements in the tracking algorithm combined with the greater feature contrast in the northern hemisphere during the approach to spring equinox allow for better rejection of erroneous wind vectors, a more objective assessment at any latitude of the quality of the mean zonal wind, and a population of winds comparable in size to that available for the much higher contrast atmosphere of Jupiter. Zonal winds at cloud level changed little between 2005 and 2007 at all latitudes sampled. Upper troposphere zonal winds derived from methane band images are approx. 10 m/s weaker than cloud level winds in the cores of eastward jets and approx. 5 m/s stronger on either side of the jet core, i.e., eastward jets appear to broaden with increasing altitude. In westward jet regions winds are approximately the same at both altitudes. Lateral eddy momentum fluxes are directed into eastward jet cores, including the strong equatorial jet, and away from westward jet cores and weaken with increasing altitude on the flanks of the eastward jets, consistent with the upward broadening of these jets. The conversion rate of eddy to mean zonal kinetic energy at the visible cloud level is larger in eastward jet regions (5.2x10(exp -5) sq m/s) and smaller in westward jet regions (1.6x10(exp -5) sqm/s) than the global mean value (4.1x10(ep -5) sq m/s). Overall the results are consistent with theories that suggest that the jets and the overturning meridional circulation at cloud level on Saturn are maintained at least in part by eddies due to instabilities of the large-scale flow near and/or below the cloud level.

DelGenio, Anthony D.↗

NASA NTRS1988

Equatorial semiannual oscillation in zonally averaged temperature observed by the Nimbus 7 SAMS and LIMS

Zonally averaged equatorial temperatures obtained aboard Nimbus 7 by the stratospheric and mesospheric sounder (SAMS) are compared to comparable data obtained from the limb IR monitor of the stratosphere. The SAMS data are shown to confirm the seasonal asymmetry in semiannual wind regimes previously noted in rocketsonde observations near the equator. Two explanations for the asymmetry are considered: (1) an improved Kelvin and gravity wave transmissivity in stronger equatorial easterlies (resulting from planetary Rossby wave momentum transport), implying stronger westerly mean flow acceleration in the first cycle than in the second; and (2) evidence of strong polar-tropical coupling in the northern winter indicating that mean meridional circulations are present on a global scale.

Delisi, Donald P.↗

NASA NTRS1985

Three-dimensional baroclinic instability of a Hadley cell for small Richardson number

A three-dimensional, linear stability analysis of a baroclinic flow for Richardson number, Ri, of order unity is presented. The model considered is a thin horizontal, rotating fluid layer which is subjected to horizontal and vertical temperature gradients. The basic state is a Hadley cell which is a solution of the complete set of governing, nonlinear equations and contains both Ekman and thermal boundary layers adjacent to the rigid boundaries; it is given in a closed form. The stability analysis is also based on the complete set of equations; and perturbation possessing zonal, meridional, and vertical structures were considered. Numerical methods were developed for the stability problem which results in a stiff, eighth-order, ordinary differential eigenvalue problem. The previous work on three-dimensional baroclinic instability for small Ri was extended to a more realistic model involving the Prandtl number, sigma, and the Ekman number, E, and to finite growth rates and a wider range of the zonal wavenumber.

Antar, B. N.↗

NASA NTRS1979

Thermal contrast in the atmosphere of Venus - Initial appraisal from Pioneer Venus probe data

The altitude profiles of temperature and pressure were measured during the descent of four Pioneer Venus probes, showing small contrasts below the clouds, but significant differences within the clouds at altitudes from 45 to 61 km. Measurements of pressure differences were found to be consistent with the cyclostrophic balance of zonal winds ranging from 110 to 150 m/sec at 60 km and from 43 to 77 m/sec at 40 km. The clouds were 10 to 20 K warmer than the extended profiles of the lower atmosphere and the middle cloud is convectively unstable. Both phenomena are due to thermal radiation from below. Meridional wind velocities were studied, concluding that significant planetary scale non-axisymmetric motions were present at latitudes below 30 degrees. This result was consistent with the day-night pressure difference. Indications of flow oscillations in the lower atmosphere were noted and the inference of wave motions in the lower atmosphere was supported by analysis of oscillations in the Doppler residuals.

Seiff, A.↗

NASA NTRS2010

Lasers and the Dynamic Mesosphere/Thermosphere of Venus

A review of ground based mid-infrared uniquely high spectral. resolution measurements of Venus dynamics, temperature, and chemistry will be presented. The described studies will focus on the use of CO2 absorption features and the discovery- and use of CO2 thermospheric non-thermal emission: lines as probes of Venus' atmosphere, from the cloud tops to approx.120 km in the thermosphere. The first investigations using infrared heterodyne spectroscopy with resolving power lambda/Delta(lambda) approx. 10(exp 6) to measure true emission line profiles and to determine their non-thermal nature and lasing component will be described. The use of the thermospheric non-thermal CO2 emission to directly measure sub-solar to anti-solar winds and zonal circulation near 110 km altitudes on Venus to approx.2 m/s accuracy will also be described. The measured emission lures are also used to obtain global maps of mesospheric/thermospheric kinetic and rotational temperatures as well as to obtain evidence of the natural lasing phenomena. Carbon dioxide absorption features globally probe lower altitudes in the atmosphere and can be used to determine nightside temperatures. Isotopic 13 CO2 absorption lines are used to probe deeper in the atmosphere to measure the sub-solar to anti-solar return flow at altitudes just above the cloud tops. These results provided a model for global circulation in the 65 - 120 km altitude region first proposed by Goldstein (1989, PhD.Thesis, U. Pennsylvania, Philadelphia, USA). Results of similar wind and temperature measurements made in recent years will be compared to earlier results to investigate changes in the circulation and temperatures since approx.1990. The high resolution infrared heterodyne technique was also used to investigate chemical processes above the cloud tops, specifically evidence and constraints on oxygen-based chemistry. Described measurements were made by infrared heterodyne spectroscopy using the Goddard Space Flight Center Infrared Heterodyne Spectrometer (IRHS) the GSFC Heterodyne Instrument for Planetary wind And Composition (HIPWAC) and the University of Cologne Tuneable Heterodyne Infrared Spectrometer (THIS).

Kostiuk, Theodor↗

NASA NTRS1982

Prospects for prediction of zonal wind oscillations

The existence of an index cycle, a quasi-periodic oscillation in the strength of the zonal wind intensity, would offer the possibility of predicting an important atmospheric feature over the period of at least one oscillation. To determine whether such a cycle exists, daily time series of several different atmospheric variables for the period November 1-April 30 for 1974-1977 were assembled. Here, the height of the 500 mb surface at latitudes 60 N and 30 N is considered. It is shown that (1) there is evidence that an index cycle exists, (2) there is theoretical reason to expect multiply periodic atmospheric flow patterns, and (3) a relatively simple, dynamically sound prediction scheme can be proposed.

Dutton, J. A.↗

NASA NTRS1979

Theoretical regime diagrams for thermally driven flows in a beta-plane channel

It is noted that thermally driven flows in rotating laboratory containers with cylindrical geometry can be axially symmetric or wavelike depending on the experimental parameters. In anticipation that rotating fluid experiments might soon be done in spherical shell geometry, Barcilon's model has been extended to a beta-plane channel in order to gain a rough understanding of the effects of rotating spherical geometry. An incompressible fluid version of the Charney (1947) model of baroclinic instability, modified to include Ekman pumping at rigid horizontal boundaries is used. With this model, stability boundaries are mapped out for individual zonal wavenumbers in the parameter space used by Barcilon.

Geisler, J. E.↗

NASA NTRS1977

On the theory of solitary Rossby waves

The evolution of long, finite amplitude Rossby waves in a horizontally sheared zonal current is studied. The wave evolution is described by the Korteweg-de Vries equation or the modified Korteweg-de Vries equation depending on the atmospheric stratification. In either case, the cross-stream modal structure of these waves is given by the long-wave limit of the neutral eigensolutions of the barotropic stability equation. Both non-singular and singular eigensolutions are considered and the appropriate analysis is developed to yield a uniformly valid description of the motion in the critical-layer region where the wave speed matches the flow velocity. The analysis demonstrates that coherent, propagating, eddy structures can exist in stable shear flows and that these eddies have peculiar interaction properties quite distinct from the traditional views of turbulent motion.

Redekopp, L. G.↗

NASA NTRS1993

Radiatively driven interactions between stratocumulus and synoptic waves

Quasi-geostrophic disturbances on a midlatitude beta-plane channel forced by radiative heating perturbations due to synoptic-scale variations of low-level stratiform cloud are considered. The longitudinal phase of the cloud is linked to that of the low-level streamfunction. Cloudiness is wavelike with cooling above cloudy areas that decreases exponentially with height. No perturbation cooling occurs above cloud-free areas. Two background flows are considered: one is constant and the other has a jet centered near the tropopause. Forced linear steady waves are found. Though infinitesimal amplitude disturbances are considered, the problem is nonlinear because of the coupling between cloud and winds. The resulting structures are sensitive to the phase shift between cloud and streamfunction with strongest coupling for cloud to the west of surface troughs. The waves have vertical scales on the order of the troposphere depth. The stationary structures capture the summertime pattern of stratocumulus off California and its linkage to the mid-Pacific ridge. When zonal-mean cloud cooling is allowed, the mean westerlies are strengthened in the northern half of the channel near the lower boundary. Synoptic-scale amplitudes respond to the mean cloud cooling by increasing (decreasing) just above the cloud in the northern (southern) part of the channel.

Clark, John H. E.↗

NASA NTRS1981

The rigid shell component for superrotation in planetary atmospheres: Angular momentum budget, mechanical analog and simulation of the spin up process

An analysis of superrotation in the atmosphere of planets, with rotation axis perpendicular to the orbital plane is presented. As the atmosphere expands, Hadley cells develop producing a redistribution of mass and angular momentum. A three dimensional thermally driven zonally symmetric spectral model and Laplace transformation simulate the time evolution of a fluid leading from corotation under globally uniform heating to superrotation under globally nonuniform heating. For high viscosities the rigid shell component of atmospheric superrotation can be understood in analogy with a pirouette. During spin up angular momentum is transferred to the planet. For low iscosities, the process is reversed. A tendency toward geostrophy, combined with increase of surface pressure toward the poles (due to meridional mass transport), induces the atmosphere to subrotate temporarily at lower altitudes. Resultant viscous shear near the surface permits angular momentum to flow from the planet into the atmosphere propagating upwards to produce high altitude superrotation rates.

Mayr, H. G.↗

NASA NTRS1989

An interactive grid generation procedure for axial and radial flow turbomachinery

A combination algebraic/elliptic technique is presented for the generation of three dimensional grids about turbo-machinery blade rows for both axial and radial flow machinery. The technique is built around use of an advanced engineering workstation to construct several two dimensional grids interactively on predetermined blade-to-blade surfaces. A three dimensional grid is generated by interpolating these surface grids onto an axisymmetric grid. On each blade-to-blade surface, a grid is created using algebraic techniques near the blade to control orthogonality within the boundary layer region and elliptic techniques in the mid-passage to achieve smoothness. The interactive definition of bezier curves as internal boundaries is the key to simple construction. This procedure lends itself well to zonal grid construction, an important example being the tip clearance region. Calculations done to date include a space shuttle main engine turbopump blade, a radial inflow turbine blade, and the first stator of the United Technologies Research Center large scale rotating rig. A finite Navier-Stokes solver was used in each case.

Beach, Timothy A.↗

NASA NTRS1990

An interactive grid generation procedure for axial and radial flow turbomachinery

Beach, T. A.↗

NASA NTRS1981

The secondary flow near a baroclinic planetary wave critical line

A critical line (CL) is the surface where the phase speed of a wave in a fluid is equal to the speed of the background flow. The considered investigation is concerned with one aspect of the simplest model of a CL in which the CL is assumed to totally absorb energy from steady, stationary, planetary waves. The aspect of interest is the secondary mean circulation near a CL in a baroclinic atmosphere. The motivation for this study is the observation of the nearly vertical CL by O'Neill and Taylor (1979) which appeared during the sudden warming of 1976/77. Even though the treatment of the CL is highly idealized in the investigation, there is evidence which indicates a very large rate of change in the zonally averaged temperature along a CL may occur. The Lagrangian-mean properties of an idealized baroclinic CL are also examined. It is found that the Lagrangian jets may provide an important transport process for exchange of stratospheric and tropospheric air.

Schoeberl, M. R.↗