Doppler wind measurements in Neptune’s stratosphere with ALMA. (arXiv:2305.06787v1 [astro-ph.EP])
<a href="http://arxiv.org/find/astro-ph/1/au:+Carrion_Gonzalez_O/0/1/0/all/0/1">Óscar Carrión-González</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Moreno_R/0/1/0/all/0/1">Raphael Moreno</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Lellouch_E/0/1/0/all/0/1">Emmanuel Lellouch</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Cavalie_T/0/1/0/all/0/1">Thibault Cavalié</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Guerlet_S/0/1/0/all/0/1">Sandrine Guerlet</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Milcareck_G/0/1/0/all/0/1">Gwenaël Milcareck</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Spiga_A/0/1/0/all/0/1">Aymeric Spiga</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Clement_N/0/1/0/all/0/1">Noé Clément</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Leconte_J/0/1/0/all/0/1">Jérémy Leconte</a>
Neptune’s tropospheric winds are among the most intense in the Solar System,
but the dynamical mechanisms that produce them remain uncertain. Measuring wind
speeds at different pressure levels may help understand the atmospheric
dynamics of the planet. The goal of this work is to directly measure winds in
Neptune’s stratosphere with ALMA Doppler spectroscopy. We derived the Doppler
lineshift maps of Neptune at the CO(3-2) and HCN(4-3) lines at 345.8 GHz
($lambda$~0.87 mm) and 354.5 GHz (0.85 mm), respectively. For that, we used
spectra obtained with ALMA in 2016 and recorded with a spatial resolution of
~0.37″ on Neptune’s 2.24″ disk. After subtracting the planet solid rotation, we
inferred the contribution of zonal winds to the measured Doppler lineshifts at
the CO and HCN lines. We developed an MCMC-based retrieval methodology to
constrain the latitudinal distribution of wind speeds. We find that CO(3-2) and
HCN(4-3) lines probe the stratosphere of Neptune at pressures of
$2^{+12}_{-1.8}$ mbar and $0.4^{+0.5}_{-0.3}$ mbar, respectively. The zonal
winds at these altitudes are less intense than the tropospheric winds based on
cloud tracking from Voyager observations. We find equatorial retrograde
(westward) winds of $-180^{+70}_{-60}$ m/s for CO, and $-190^{+90}_{-70}$ m/s
for HCN. Wind intensity decreases towards mid-latitudes, and wind speeds at
40$^circ$S are $-90^{+50}_{-60}$ m/s for CO, and $-40^{+60}_{-80}$ m/s for
HCN. Wind speeds become 0 m/s at about 50$^circ$S, and we find that the
circulation reverses to a prograde jet southwards of 60$^circ$S. Overall, our
direct stratospheric wind measurements match previous estimates from stellar
occultation profiles and expectations based on thermal wind equilibrium. These
are the first direct Doppler wind measurements performed on the Icy Giants,
opening a new method to study and monitor their stratospheric dynamics.
Neptune’s tropospheric winds are among the most intense in the Solar System,
but the dynamical mechanisms that produce them remain uncertain. Measuring wind
speeds at different pressure levels may help understand the atmospheric
dynamics of the planet. The goal of this work is to directly measure winds in
Neptune’s stratosphere with ALMA Doppler spectroscopy. We derived the Doppler
lineshift maps of Neptune at the CO(3-2) and HCN(4-3) lines at 345.8 GHz
($lambda$~0.87 mm) and 354.5 GHz (0.85 mm), respectively. For that, we used
spectra obtained with ALMA in 2016 and recorded with a spatial resolution of
~0.37″ on Neptune’s 2.24″ disk. After subtracting the planet solid rotation, we
inferred the contribution of zonal winds to the measured Doppler lineshifts at
the CO and HCN lines. We developed an MCMC-based retrieval methodology to
constrain the latitudinal distribution of wind speeds. We find that CO(3-2) and
HCN(4-3) lines probe the stratosphere of Neptune at pressures of
$2^{+12}_{-1.8}$ mbar and $0.4^{+0.5}_{-0.3}$ mbar, respectively. The zonal
winds at these altitudes are less intense than the tropospheric winds based on
cloud tracking from Voyager observations. We find equatorial retrograde
(westward) winds of $-180^{+70}_{-60}$ m/s for CO, and $-190^{+90}_{-70}$ m/s
for HCN. Wind intensity decreases towards mid-latitudes, and wind speeds at
40$^circ$S are $-90^{+50}_{-60}$ m/s for CO, and $-40^{+60}_{-80}$ m/s for
HCN. Wind speeds become 0 m/s at about 50$^circ$S, and we find that the
circulation reverses to a prograde jet southwards of 60$^circ$S. Overall, our
direct stratospheric wind measurements match previous estimates from stellar
occultation profiles and expectations based on thermal wind equilibrium. These
are the first direct Doppler wind measurements performed on the Icy Giants,
opening a new method to study and monitor their stratospheric dynamics.
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