The thermal field of the terminator mesosphere of Venus using solar transit data

Description

We exploit the solar transits of Venus in 2004 and 2012, to derive useful constraints on the mesosphere of the planet by the observation of the so-called "aureole" resulting from direct sunlight refraction. In 2012 we organized an extensive campaign, involving observations through both space- and ground- based telescopes. A specific design adapted from the Lyot coronograph was developed and replicated in several copies to improve the SNR in proximity of the solar disk (Venus Twilight Experiment).we report on the different data sets collected during the 2012 transit, and present lightcurve analyses based on imaging from NASA's Solar Dynamic Observatory (SDO), JAXA's Hinode, and by the instruments of the Venus Twilight Experiment.We explored different approaches to model the variation of the aureole brightness, ranging from simple isothermal modeling to multi-layer.Although less resolved than the local measurements obtained by Venus Express (SOIR experiment), aureole modeling has the advantage of being able to cover simultaneously a wide range of latitudes. We were able to compare the aureole-derived vertical refractivity profiles to density profiles obtained simultaneously by SOIR during the transit itself. Our inverse model, constraining the vertical temperature profiles at all latitudes, detects a cold layer (at ~86-94 km altitude on average) whose vertical extent depends on latitude (thicker towards the N pole than at the Equator), and a latitude-dependent aerosol slanted-opacity altitude (tau=1).Eventually our model shows that a relevant contribution to the aureole flux comes from deep layers where aerosol absorption cannot be neglected, allowing us to put some constraints on the scale height of aerosol dispersion.

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