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All sourcesNASA NTRSDOE OSTI
NASA NTRS2019

Saturn Atmospheric Dynamics One Year After Cassini: Long-Lived Features and Time Variations in the Drift of the Hexagon

We examine Saturn's atmospheric dynamics with observations in the visible range from ground-based telescopes and Hubble Space Telescope (HST). We present a detailed analysis of observations acquired during 2018 obtaining drift rates of major meteorological systems from the equator to the North polar hexagon. A system of polar storms that appeared in the planet in March 2018 and remained active with a complex phenomenology at least until September is analyzed elsewhere [Sanchez-Lavega et al., 2019]. Many of the regular cloud features visible in 2018 are long-lived and can be identified in Saturn images in 2017, and in some cases, for up to a decade using also Cassini ISS images. Without considering the polar storms, the most interesting long-lived cloud systems are: i) A bright white spot in the Equatorial Zone that can be tracked continuously since 2014 with minimal changes in its zonal velocity, which was 444:3 +or- 3:1 ms(exp -1) in 2014 and 452:4 + or - 1:7 ms(exp -1) in 2018. This velocity is remarkably different from the zonal winds at the cloud level at its latitude during the Cassini mission, and is closer to zonal winds obtained at the time of the Voyagers flybys and to zonal winds from Cassini VIMS infrared images of the lower atmosphere. ii) A large long-lived Anticyclone Vortex, here AV, that formed after the Great White Spot of 2010-2011. This vortex has changed significantly in visual contrast, drift rate and latitude with minor changes in size over the last years. iii) A system of subpolar vortices at latitudes 60-65N present at least since 2011. These vortices and additional atmospheric features here studied follow drift rates consistent with zonal winds obtained by Cassini. We also present a study of the positions of the vertices of Saturn's North polar hexagon from 2015 to 2018. These measurements are compared with previous analyses during the Cassini mission (2007-2014), observations with HST in the 90s, and data from the Voyagers in 1980-1981 to explore the long term variability of the hexagon's drift rate. We find variations in the drift rate of the hexagon through these epochs that can not be fit by seasonal changes in the polar area. Instead, the different drift rates reinforce the role of the North Polar Spot that was present in the Voyager epoch and in the early 90s to cause a faster drift rate of the hexagon at that time compared with the current slower one.

R Hueso↗
NASA NTRS1982

Parameterization of IR cooling in a middle atmosphere dynamics model. I - Effects on the zonally averaged circulation

A computationally efficient two-stream parameterization of IR cooling is developed for a middle atmosphere dynamics model. The parameterization combines the monochromatic feature of an emissivity formulation with the computational simplicity of a single spatial integral to evaluate the monochromatic transfer equation. Calculations show strong radiative control of the mesopause region and the need for substantial deceleration of the mean zonal winds. Calculated temperatures show good agreement in the summer hemisphere where planetary wave activity is negligible, but in the polar night of the winter hemisphere they are about 30 K too cold, which suggests planetary wave heating must make up the deficit. With observed ozone densities, globally averaged radiative equilibrium temperatures in the 65-75 km region are too cold and an additional heat source about 1 K/day is required.

Apruzese, J. P.↗
NASA NTRS2019

Constraining Stellar Parameters and Atmospheric Dynamics of the Carbon AGB star V Oph

Molecules and dust produced by the atmospheres of cool evolved stars contribute to a significant amount of the total material found in the interstellar medium. To understand the mechanism behind the mass loss of these stars, it is of pivotal importance to investigate the structure and dynamics of their atmospheres. Our goal is to verify if the extended molecular and dust layers of the carbon-rich asymptotic giant branch (AGB) star V Oph, and their time variations, can be explained by dust-driven winds triggered by stellar pulsation alone, or if other mechanisms are in play. We model V Oph mid-infrared interferometric VLTI-MIDI data (8–13 μm), at phases 0.18, 0.49, and 0.65, together with literature photometric data, using the latest-generation self-consistent dynamic atmosphere models for carbon-rich stars: DARWIN. We determine the fundamental stellar parameters: T(eff) = 2600 K, L(bol) = 3585 L⊙, M = 1.5 M⊙, C/O = 1.35, Mass flow rate= 2.50 x 10(exp -6) M⊙/yr. We calculate the stellar photospheric radii at the three phases: 479, 494, 448 R⊙; and the dust radii: 780, 853, 787 R⊙. The dynamic models can fairly explain the observed N-band visibility and spectra, although there is some discrepancy between the data and the models, which is discussed in the text. We discuss the possible causes of the temporal variations of the outer atmosphere, deriving an estimate of the magnetic field strength, and computing upper limits for the Alfvén waves velocity. In addition, using period–luminosity sequences, and interferometric modeling, we suggest V Oph as a candidate to be reclassified as a semi-regular star.

Gioia Rau↗
NASA NTRS1987

Atmosphere dynamic processes structure at 80-105 km altitude

Determination of wind velocity by means of Doppler meteor radars is based on the assumption that an ionized meteor trail drifts together with the neutral atmosphere. From the Doppler frequency shift it is possible to estimate the radial velocity of the trail drift. Conversion of the recorded radial velocity to the true wind velocity vector in the given space region depends both on the radar technical parameters and the chosen atmospheric motion model. The atmospheric dynamic processes structure is considered.

Kalchenko, B. V.↗
NASA NTRS2019

Impact of Assimilating AIRS Cloud-Cleared Radiances on Atmospheric Dynamics and Boundary Layer Height at High Latitudes

High latitude weather forecasts, on scales ranging from mesoscale to synoptic, present difficulties due, in part, to the sparsity of conventional observations. In addition, the prevalence of extended low-level stratus cloud cover limits the use of infrared data, which are operationally assimilated only in areas unaffected by clouds. Use of cloud-cleared AIRS (Atmospheric Infrared Sounder) radiances (AIRS CCR), allows the assimilation of infrared information in cloudy regions, permitting data ingestion in regions usually undersampled. This study explores the sensitivity of planetary boundary layer height and related atmospheric dynamics to the assimilation of these data in the Goddard Earth Observing System (GEOS, version 5) data assimilation and forecast system during the boreal fall 2014 season using observing system experiments (OSEs). Examined here are comparisons between the current, operational approach of assimilating AIRS clear-sky radiances against the assimilation of CCR. Assimilation of hyperspectral infrared information from AIRS over the Arctic region slightly modifies the lower midtropospheric temperature structure, which in turn contributes to adjustments in geopotential height, affecting the baroclinic instability properties over the entire hemisphere and explaining the overall improvement in global forecast skill.

McGrath-Spangler, E. L.↗
NASA NTRS1992

Variable oxygen airglow on Venus as a probe of atmospheric dynamics

High-resolution images are presented of an oxygen airglow that arises during downwelling at an altitude of about 95 km on the nightside of Venus. Oxygen atoms are formed by photolysis of CO2 on the sunlit hemisphere and are then transported to the nightside, where they recombine during descent. The newly formed molecular oxygen emits radiation to produce the airglow. Localized, short-lived regions of emission and neighboring dark areas are observed, demonstrating the potential of such observations to constrain atmospheric dynamics at this little-studied and important altitude in the Venusian mesosphere.

Allen, David↗
NASA NTRS2010

Middle Atmosphere Dynamics with Gravity Wave Interactions in the Numerical Spectral Model: Tides and Planetary Waves

As Lindzen (1981) had shown, small-scale gravity waves (GW) produce the observed reversals of the zonal-mean circulation and temperature variations in the upper mesosphere. The waves also play a major role in modulating and amplifying the diurnal tides (DT) (e.g., Waltersheid, 1981; Fritts and Vincent, 1987; Fritts, 1995a). We summarize here the modeling studies with the mechanistic numerical spectral model (NSM) with Doppler spread parameterization for GW (Hines, 1997a, b), which describes in the middle atmosphere: (a) migrating and non-migrating DT, (b) planetary waves (PW), and (c) global-scale inertio gravity waves. Numerical experiments are discussed that illuminate the influence of GW filtering and nonlinear interactions between DT, PW, and zonal mean variations. Keywords: Theoretical modeling, Middle atmosphere dynamics, Gravity wave interactions, Migrating and non-migrating tides, Planetary waves, Global-scale inertio gravity waves.

Mayr, Hans G.↗
NASA NTRS1984

Geomagnetic Disturbances Caused by Internal Atmospheric Dynamics

It is commonly believed that geomagnetic disturbances are caused by external influences connected with the solar wind. The 27-day recurrence of perturbations seems to be a strong hint for this interaction. But frequently geomagnetic disturbances occur without any relation to sunspot numbers or radiowave fluxes. This was one of the reasons for introducing hypothetical M-regions on the Sun and their relation to solar wind activities. Only one half of the variance of the geomagnetic AL-index could be related to the solar wind. Therefore it is concluded that internal processes of the magnetosphere were responsible for additional geomagnetic activity. Arguments, which might lead to the suggestion of geomagnetic disturbances as being caused by internal atmospheric dynamics are discussed and a rather preliminary scenario of those processes is proposed.

Sonneman, G.↗
NASA NTRS1982

Solar atmospheric dynamics. II - Nonlinear models of the photospheric and chromospheric oscillations

The one-dimensional, nonlinear dynamics of the solar atmosphere is investigated, and models of the observed photospheric (300 s) and chromospheric (200 s) oscillations are described. These are resonances of acoustic wave cavities formed by the variation of the temperature and ionization between the subphotospheric, hydrogen convection zone and the chromosphere-corona transition region. The dependence of the oscillations upon the excitation and boundary conditions leads to the conclusion that for the observed amplitudes, the modes are independently excited and, as trapped modes, transport little if any mechanical flux. In the upper photosphere and lower chromosphere, where the two modes have comparable energy density, interference between them leads to apparent vertical phase delays which might be interpreted as evidence of an energy flux.

Leibacher, J.↗
NASA NTRS1986

The Vega balloons - A tool for studying atmosphere dynamics on Venus

The Vega balloon experiment, designed to measure the dynamics of the Venus atmosphere, comprised the balloons themselves, their gondolas with on-board sensors and radio transmitters, and the radio telescope network on the earth. The structures and the physical parameters of the balloon probe are described, together with the instruments on the gondola, designed for the measurements of the atmospheric pressure, temperature, and vertical wind flows, and illumination, as well as possible flashes of lightning. Consideration is also given to the formatting of the information flow for the individual parameters measured.

Kremnev, R. S.↗
NASA NTRSDate not supplied

3D Radiative MHD Modeling of the Solar Atmospheric Dynamics and Structure

Dramatic dynamical phenomena accompanied by strong thermodynamic and magnetic structuring are the primary drivers of great interest in studying the solar atmosphere with high spatial and temporal resolutions. Using current computational capabilities, it has become possible to model the magnetized solar plasma in different regimes with a high degree of realism. To study the fine structuring of the solar atmosphere and dynamics, we use 3D MHD radiative models covering all layers from the upper convection zone to the corona. Realistic 3D radiative MHD modeling of the solar magnetoconvection and atmosphere allows us to generate synthetic observables that directly link the physical properties of the solar plasma to spectroscopic observables. In the presentation, we discuss qualitative and quantitative changes of the atmospheric structure and dynamics at different layers of the solar atmosphere, properties of acoustic and surface gravity waves, sources of local heating in the chromosphere-corona transition region, formation of shocks, and high-frequency oscillations in the corona, as well as manifestation of these phenomena in the modeled observables.

SMD↗
NASA NTRS1989

Subtropical middle atmosphere dynamics observed by the Chung Li radar

The Chung Li Radar (24.91 N; 121.24 E) has been operating since 1986. A five beam observational configuration was used on a regular basis to study the various dynamics processes in the atmosphere-lower stratosphere height region. Due to its geographical location, the annual Typhoon and Mei-Yu seasons provide good opportunities to study the various interesting dynamic processes such as instabilities, generation of gravity waves, wave mean field interaction, etc. Three dimensional air motions due to these fronts are presented. Special cases of gravity wave generation, propagation and their effects on the turbulent layers are discussed.

Fu, I. J.↗
NASA NTRS1987

Atmospheric dynamics

The paper presents an overview of U.S. contributions in the period of 1983-1986, to the analysis and study of the atmosphere's motion and of the role of this motion in the thermodynamics and chemistry of the atmosphere. Special attention is given to the linear and quasi-linear studies of the dynamics of atmospheric disturbances; studies of the wave breaking phenomenon; and investigations of various long-lived features, ranging from climatological stationary waves to long-period oscillations in the tropics. Consideration is also given to diagnostics for the interactions among disturbances and the mean flow, nontraditional approaches to instability and disturbance growth, and dynamical systems and multiple equilibria.

Lindzen, Richard S.↗
NASA NTRS1978

Some properties of upper atmosphere dynamics

A unifying description is provided of some important dynamic properties of the upper atmosphere in composition and temperature characteristic of a variety of phenomena, including diurnal and seasonal tides, magnetic storms, and momentum coupling with the magnetosphere. A theoretical multiconstituent model is used which can link the large-scale variations of composition and temperature to the dynamics and energetics of the thermosphere. Global mean properties of the thermosphere are reviewed, and an attempt is made to convey some understanding of the dynamic properties of energy and diffusive mass transport in the thermosphere. Attention is given to sources of energy for the thermosphere, the transport processes involved in the solar diurnal tide of the thermosphere, energy and particle sources for the annual tide, feedback from composition changes to wind-field and temperature variations, energy deposition in the thermosphere during magnetic storms and substorms, and momentum source signatures in the thermosphere.

Mayr, H. G.↗
NASA NTRS1980

Theoretical and experimental investigations of upper atmosphere dynamics

A brief overview of the significant contributions made to the understanding of the dynamics of the Earth's upper atmosphere is presented, including the addition of winds and diffusion to the semi-empirical Global Reference Atmospheric Model developed for the design phase of the Space Shuttle, reviews of turbulence in the lower thermosphere, the dynamics of the equatorial mesopause, stratospheric warming effects on mesopause level dynamics, and the relevance of these studies to the proposed Middle Atmosphere Program (1982-85). A chronological bibliography, with abstracts of all papers published, is also included.

Roper, R. G.↗
NASA NTRS1985

Future possibilities in objective analysis and data assimilation for atmospheric dynamics

The role that dynamics plays in estimating the state of the atmosphere from incomplete and noisy data is reviewed. Objective analysis represents an attempt at relying mostly on the data and minimizing the role of dynamics in the estimation. Data assimilation tries to balance properly the roles of dynamical and observational information. Sequential estimation is presented as the proper framework for understanding this balance, and the Kalman filter as the ideal, optimal procedure for data assimilation. The optimal filter computes forecast error covariances of a given atmospheric model exactly, and hence data assimilation should be closely connected with predictability studies. This connection is described, and consequences drawn for currently active areas of the atmospheric and related sciences, namely, mesoscale meteorology, long range forecasting, and upper ocean dynamics. Possibilities offered by judicious data assimilation in understanding barotropic adjustment, a phenomenon that appears to play a crucial role in atmospheric behavior on the scale of weeks to months, and hence in long range forecasting are addressed.

Ghil, M.↗
NASA NTRS1987

Atmosphere dynamics in the equatorial meteor zone

The study of the atmospheric circulation of the Earth from its surface to the altitudes of 100 to 110 km is essential for establishing atmospheric motion regularities with a view toward perfecting weather forecasting. The main results of the Soviet equatorial meteor expedition (SEME) are presented. A continuous cycle of measurements was carried out. Considerable interdiurnal variation of the zonal component was observed. Importantly, in the meridional component, the prevalence of a two day component was established in the equatorial meteor zone for the first time. The pronounced westward motion of the atmosphere over the equator is noted. The SEME data analysis has shown that the meteor zone is characterized by flashes of intensity of the internal gravity waves and turbulence at highest instability moments of atmosphere due to tidal motion.

Kascheev, B. L.↗