Modelling perturbations propagating through the mesopause into the earth's upper atmosphere

Global oscillations formed in the terrestrial troposphere, stratosphere and mesosphere propagate into the thermosphere and ionosphere where they change the dynamics, energy and composition. This thesis presents a series of studies which examine in detail the nature and influence of solar tides and the planetary 2-day wave above 80 km altitude. The Coupled Thermosphere-Ionosphere Model (CTIM) calculates self-consistently the dynamics, energy and composition of the terrestrial thermosphere and ionosphere in three dimensions and is used as the main tool in these studies. In order to simulate the upwardly propagating perturbations which are formed outside the height range of the model, the lower boundary of the CTIM at 80 km height was modified to allow the global profiles of pressure-, wind- and temperature oscillations to be specified. In principle, following the modification, any such profile can be used for the external forcing as long the parameters at the lower boundary' are self-consistent. One effective method of achieving this is to specify global perturbations of geopotential height, using Hough functions for the latitudinal structure, and calculating the simultaneous wind- and temperature oscillations at the lower boundary analytically with expressions from Classical Tidal Theory. The necessary formalism for this has been fully implemented. For validation of the new code a series of comparisons with other numerical models and Incoherent Scatter Radar measurements at equinox and solstice are presented and show that CTIM is capable of reproducing many tidal features found in the "real" thermosphere. A further study is presented which investigates processes causing planetary' wave signatures in the ionosphere. It is found not only that CTIM reproduces some key properties of upwards propagating planetary waves found in other theoretical and modelling studies, but also that upwards propagating tides may, through modulation of their amplitudes, carry planetary wave signatures into the 200 km height regime where they are transferred into the ionosphere by chemical processes. The new CTIM thus offers the possibility of carrying out many unprecedented studies exploring the nature of the Earth's upper atmosphere

Upper atmospheres and ionospheres of planets and satellites

The upper atmospheres of the planets and their satellites are more directly exposed to sunlight and solar wind particles than the surface or the deeper atmospheric layers. At the altitudes where the associated energy is deposited, the atmospheres may become ionized and are referred to as ionospheres. The details of the photon and particle interactions with the upper atmosphere depend strongly on whether the object has anintrinsic magnetic field that may channel the precipitating particles into the atmosphere or drive the atmospheric gas out to space. Important implications of these interactions include atmospheric loss over diverse timescales, photochemistry and the formation of aerosols, which affect the evolution, composition and remote sensing of the planets (satellites). The upper atmosphere connects the planet (satellite) bulk composition to the near-planet (-satellite) environment. Understanding the relevant physics and chemistry provides insight to the past and future conditions of these objects, which is critical for understanding their evolution. This chapter introduces the basic concepts of upper atmospheres and ionospheres in our solar system, and discusses aspects of their neutral and ion composition, wind dynamics and energy budget. This knowledge is key to putting in context the observations of upper atmospheres and haze on exoplanets, and to devise a theory that explains exoplanet demographics.Comment: Invited Revie

Phosphine gas in the cloud decks of Venus

Measurements of trace gases in planetary atmospheres help us explore chemical conditions different to those on Earth. Our nearest neighbour, Venus, has cloud decks that are temperate but hyperacidic. Here we report the apparent presence of phosphine (PH3) gas in Venus’s atmosphere, where any phosphorus should be in oxidized forms. Single-line millimetre-waveband spectral detections (quality up to ~15σ) from the JCMT and ALMA telescopes have no other plausible identification. Atmospheric PH3 at ~20 ppb abundance is inferred. The presence of PH3 is unexplained after exhaustive study of steady-state chemistry and photochemical pathways, with no currently known abiotic production routes in Venus’s atmosphere, clouds, surface and subsurface, or from lightning, volcanic or meteoritic delivery. PH3 could originate from unknown photochemistry or geochemistry, or, by analogy with biological production of PH3 on Earth, from the presence of life. Other PH3 spectral features should be sought, while in situ cloud and surface sampling could examine sources of this gas

Sunlight refraction in the mesosphere of Venus during the transit on June 8th, 2004

Many observers in the past gave detailed descriptions of the telescopic aspect of Venus during its extremely rare transits across the Solar disk. In particular, at the ingress and egress, the portion of the planet's disk outside the Solar photosphere has been repeatedly perceived as outlined by a thin, bright arc ("aureole"). Those historical visual observations allowed inferring the existence of Venus' atmosphere, the bright arc being correctly ascribed to the refraction of light by the outer layers of a dense atmosphere. On June 8th, 2004, fast photometry based on electronic imaging devices allowed the first quantitative analysis of the phenomenon. Several observers used a variety of acquisition systems to image the event -- ranging from amateur-sized to professional telescopes and cameras -- thus collecting for the first time a large amount of quantitative information on this atmospheric phenomenon. In this paper, after reviewing some elements brought by the historical records, we give a detailed report of the ground based observations of the 2004 transit. Besides confirming the historical descriptions, we perform the first photometric analysis of the aureole using various acquisition systems. The spatially resolved data provide measurements of the aureole flux as a function of the planetocentric latitude along the limb. A new differential refraction model of solar disk through the upper atmosphere allows us to relate the variable photometry to the latitudinal dependency of scale-height with temperature in the South polar region, as well as the latitudinal variation of the cloud-top layer altitude. We compare our measurements to recent analysis of the Venus Express VIRTIS-M, VMC and SPICAV/SOIR thermal field and aerosol distribution. Our results can be used a starting point for new, more optimized experiments during the 2012 transit event.Comment: Icarus, in pres

Composition of Titan's ionosphere

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/94758/1/grl21212.pd

Comparing managerial work practices and values in nationally homogeneous versus heterogeneous groups Examining German, British and French work teams

SIGLEAvailable from British Library Document Supply Centre-DSC:DX199467 / BLDSC - British Library Document Supply CentreGBUnited Kingdo

Global characteristics of gravity waves in the upper atmosphere of Mars as measured by MAVEN/NGIMS

We present an analysis of gravity waves in Mars' upper atmosphere above 120 km. Using in-situ data from NGIMS onboard MAVEN we have been able to characterise waves from nearly 4000 orbits. We have used temperature and density profiles to extract perturbations and interpret these as vertically propagating gravity waves which we characterise by their amplitude and wavelength. In this region of the atmosphere gravity waves have amplitudes of around 10%. Vertical wavelengths are found to be around 10–30 km. We observe an increase in gravity wave amplitudes with increasing solar zenith angle. Gravity wave amplitudes appear invariant in altitude on the dayside, however increase with altitude on the nightside