Other
Scientific paper
Sep 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011ess.....2.1306s&link_type=abstract
American Astronomical Society, ESS meeting #2, #13.06
Other
Scientific paper
To date, the exotic meteorology of hot Jupiters has primarily been characterized with thermal measurements, providing only indirect clues to the wind regime. Recently, however, Snellen et al. (2010) presented high-resolution groundbased transit spectra of HD209458b containing an apparent 2 km/sec blueshift, which they interpreted as a signature of atmospheric winds flowing from dayside to nightside toward Earth along the planet's terminator. Motivated by these observations, we describe the types of Doppler signatures generated by the atmospheric circulation and show how Doppler measurements can place powerful constraints on the meteorology. We show that, depending on parameters, the atmospheric circulation--and Doppler signature--of hot Jupiters splits into two regimes. At moderate stellar insolation, the day-night thermal forcing generates fast east-west jet streams from the interaction of standing planetary-scale waves with the mean flow. In this regime, air along the terminator (as seen during transit) flows toward Earth in some regions and away from Earth in others, leading to a bimodal Doppler signature exhibiting distinct, superposed blue- and redshifted velocity peaks. Under more intense stellar insolation, however, the thermal forcing is so strong that it damps these planetary-scale waves, inhibiting their ability to generate jet streams. As a result, this second regime exhibits a circulation dominated primarily by high-altitude, day-to-night airflow along both terminators rather than longitudinally symmetric jets. This causes air to flow toward Earth along most of the terminator, leading to a predominantly blueshifted Doppler signature during transit. We present state-of-the-art 3D circulation models including nongrey radiative transfer to quantify this regime shift and the resulting Doppler signatures; these models suggest that HD189733b lies in the first regime while HD209458b lies in the second regime. Moreover, we show how the amplitude of the Doppler shifts place strong constraints on the strength of frictional drag in the upper atmospheres of hot Jupiters.
Fortney Jonathan J.
Lewis Nikole K.
Shabram Megan
Showman Adam P.
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