197 research outputs found
Shallow water simulations of Saturn's giant storms at different latitudes
Shallow water simulations are used to present a unified study of three major storms on Saturn (nicknamed as Great White Spots, GWS) at different latitudes, polar (1960), equatorial (1990), and mid-latitude (2010) (SĂĄnchez-Lavega, 2004; SĂĄnchez-Lavega et al., 2011). In our model, the three GWS are initiated by introducing a Gaussian function pulse at the latitude of the observed phenomena with controlled horizontal size and amplitude. This function represents the convective source that has been observed to trigger the storm. A growing disturbance forms when the pulse reacts to ambient winds, expanding zonally along the latitude band of the considered domain. We then compare the modeled potential vorticity with the cloud field, adjusting the model parameters to visually get the closest aspect between simulations and observations. Simulations of the 2010 GWS (planetographic latitude ~+40Âș, zonal velocity of the source ~-30 m s-1) indicate that the Coriolis forces and the wind profile structure shape the disturbance generating, as observed, a long region to the east of the convective source with a high speed peripheral anticyclonic circulation, and a long-lived anticyclonic compact vortex accompanied by strong zonal advection on the southern part of the storm forming a turbulent region. Simulations of the equatorial 1990 GWS (planetographic latitude +12Âș-+5Âș, zonal velocity of the source 365-400 m s-1) show a different behavior because of the intense eastward jet, meridional shear at the equatorial region, and low latitude dynamics. A round shaped source forms as observed, with the rapid growth of a Kelvin-Helmholtz instability on the north side of the source due to advection and to the strong meridional wind shear, whereas at the storm latitude the disturbance grows and propagates eastward. The storm nucleus is the manifestation of a Rossby wave, while the eastward propagating planetary-scale disturbance is a gravity-Rossby wave trapped around the equator. The simulated 1960 GWS disturbance (planetographic latitude +56Âș, zonal velocity 4 m s-1) formed a chain of periodic oval spots that mimic the few available observations of the phenomenon. For the mid and high latitude storms, simulations predict a strong injection of negative relative vorticity due to divergence of the upwelling storm material, which may produce large anticyclones on the anticyclonic side of the zonal profile, and a quick turbulent expansion on the background cyclonic regions. In general, simulations indicate that negative relative vorticity injected by storms determines the natural reaction to zonal winds at latitudes where Coriolis forces are dominant.Peer ReviewedPostprint (published version
Dynamics and clouds in planetary atmospheres from telescopic observations
This review presents an insight into our current knowledge of the atmospheres of the planets Venus, Mars, Jupiter, Saturn, Uranus and Neptune, the satellite Titan, and those of exoplanets. It deals with the thermal structure, aerosol properties (hazes and clouds, dust in the case of Mars), chemical composition, global winds, and selected dynamical phenomena in these objects. Our understanding of atmospheres is greatly benefitting from the discovery in the last 3 decades of thousands of exoplanets. The exoplanet properties span a broad range of conditions, and it is fair to expect as much variety for their atmospheres. This complexity is driving unprecedented investigations of the atmospheres, where those of the solar systems bodies are the obvious reference. We are witnessing a significant transfer of knowledge in both directions between the investigations dedicated to Solar System and exoplanet atmospheres, and there are reasons to think that this exchange will intensity in the future. We identify and select a list of research subjects that can be conducted at optical and infrared wavelengths with future and currently available ground-based and space-based telescopes, but excluding those from the space missions to solar system bodies
Ohmic Dissipation in the Atmospheres of Hot Jupiters
Hot Jupiter atmospheres exhibit fast, weakly-ionized winds. The interaction
of these winds with the planetary magnetic field generates drag on the winds
and leads to ohmic dissipation of the induced electric currents. We study the
magnitude of ohmic dissipation in representative, three-dimensional atmospheric
circulation models of the hot Jupiter HD 209458b. We find that ohmic
dissipation can reach or exceed 1% of the stellar insolation power in the
deepest atmospheric layers, in models with and without dragged winds. Such
power, dissipated in the deep atmosphere, appears sufficient to slow down
planetary contraction and explain the typically inflated radii of hot Jupiters.
This atmospheric scenario does not require a top insulating layer or radial
currents that penetrate deep in the planetary interior. Circulation in the
deepest atmospheric layers may actually be driven by spatially non-uniform
ohmic dissipation. A consistent treatment of magnetic drag and ohmic
dissipation is required to further elucidate the consequences of magnetic
effects for the atmospheres and the contracting interiors of hot Jupiters.Comment: Accepted to the Astrophysical Journa
Practical study of optical stellar interferometry
In this work we present an observational technique and a detailed analysis of
the stellar interferograms produced by three bright stars: Betelgeuse, Rigel
and Sirius. It is shown that the atmospheric turbulence is responsible for the
reduction of the long-exposure fringe visibility of the obtained interference
patterns. By using different baselines in our interferometer, we are able to
distinguish the decay of the visibility with the baseline, how different
parameters such us the diameter of the holes in our interferometer or their
distribution affects the pattern, and to measure the turbulence with the
estimation of the Fried parameter r0. The work and methodology are presented as
a method for postgraduate students that targets practical learning of optical
interferometry in astronomy and how it is affected by several causes, such as
the atmospheric turbulence.Comment: 11 pages, 6 figures, paper submitted and accepted to AJ
Mechanisms of jet formation on the giant planets
The giant planet atmospheres exhibit alternating prograde (eastward) and
retrograde (westward) jets of different speeds and widths, with an equatorial
jet that is prograde on Jupiter and Saturn and retrograde on Uranus and
Neptune. The jets are variously thought to be driven by differential radiative
heating of the upper atmosphere or by intrinsic heat fluxes emanating from the
deep interior. But existing models cannot account for the different flow
configurations on the giant planets in an energetically consistent manner. Here
a three-dimensional general circulation model is used to show that the
different flow configurations can be reproduced by mechanisms universal across
the giant planets if differences in their radiative heating and intrinsic heat
fluxes are taken into account. Whether the equatorial jet is prograde or
retrograde depends on whether the deep intrinsic heat fluxes are strong enough
that convection penetrates into the upper troposphere and generates strong
equatorial Rossby waves there. Prograde equatorial jets result if convective
Rossby wave generation is strong and low-latitude angular momentum flux
divergence owing to baroclinic eddies generated off the equator is sufficiently
weak (Jupiter and Saturn). Retrograde equatorial jets result if either
convective Rossby wave generation is weak or absent (Uranus) or low-latitude
angular momentum flux divergence owing to baroclinic eddies is sufficiently
strong (Neptune). The different speeds and widths of the off-equatorial jets
depend, among other factors, on the differential radiative heating of the
atmosphere and the altitude of the jets, which are vertically sheared. The
simulations have closed energy and angular momentum balances that are
consistent with observations of the giant planets.Comment: 21 pages, 10 figure
An Analytic Radiative-Convective Model for Planetary Atmospheres
We present an analytic 1-D radiative-convective model of the thermal
structure of planetary atmospheres. Our model assumes that thermal radiative
transfer is gray and can be represented by the two-stream approximation. Model
atmospheres are assumed to be in hydrostatic equilibrium, with a power law
scaling between the atmospheric pressure and the gray thermal optical depth.
The convective portions of our models are taken to follow adiabats that account
for condensation of volatiles through a scaling parameter to the dry adiabat.
By combining these assumptions, we produce simple, analytic expressions that
allow calculations of the atmospheric pressure-temperature profile, as well as
expressions for the profiles of thermal radiative flux and convective flux. We
explore the general behaviors of our model. These investigations encompass (1)
worlds where atmospheric attenuation of sunlight is weak, which we show tend to
have relatively high radiative-convective boundaries, (2) worlds with some
attenuation of sunlight throughout the atmosphere, which we show can produce
either shallow or deep radiative-convective boundaries, depending on the
strength of sunlight attenuation, and (3) strongly irradiated giant planets
(including Hot Jupiters), where we explore the conditions under which these
worlds acquire detached convective regions in their mid-tropospheres. Finally,
we validate our model and demonstrate its utility through comparisons to the
average observed thermal structure of Venus, Jupiter, and Titan, and by
comparing computed flux profiles to more complex models.Comment: 57 pages, 1 table, 13 figures; journal-formatted version at:
http://dx.doi.org/10.1088/0004-637X/757/1/10
PlanetCam UPV/EHU: a two-channel lucky imaging camera for solar system studies in the spectral range 0.38-1.7 ”m
This is an author-created, un-copyedited version of an article published in Publications of the Astronomical Society of the Pacific. IOP Publishing Ltd is not responsible for any errors or omissions in this version of the manuscript or any version derived from it.We present PlanetCam UPV/EHU, an astronomical camera designed fundamentally for high-resolution imaging of Solar System planets using the âlucky imagingâ technique. The camera observes in a wavelength range from 380 nm to 1.7 ”m and the driving science themes are atmosphere dynamics and vertical cloud structure of Solar System planets. The design comprises two configurations that include one channel (visible wavelengths) or two combined channels (visible and short wave nfrared) working simultaneously at selected wavelengths by means of a dichroic beam splitter. In this paper the camera components for the two configurations are described, as well as camera performance and the different tests done for the precise characterization of its radiometric and astrometric capabilities at high spatial resolution. Finally, some images of solar system objects are presented as well as photometric results and different scientific cases on astronomical targets.Peer ReviewedPostprint (author's final draft
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