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تسجيل مستخدم جديدTropospheric Composition and Circulation of Uranus with ALMA and the VLA
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We present ALMA and VLA spatial maps of the Uranian atmosphere taken between 2015 and 2018 at wavelengths from 1.3 mm to 10 cm, probing pressures from $sim$1 to $sim$50 bar at spatial resolutions from 0.1 to 0.8. Radiative transfer modeling was performed to determine the physical origin of the brightness variations across Uranuss disk. The radio-dark equator and midlatitudes of the planet (south of $sim$50$^circ$ N) are well fit by a deep H$_2$S mixing ratio of $8.7_{-1.5}^{+3.1}times10^{-4}$ ($37_{-6}^{+13}times$ Solar) and a deep NH$_3$ mixing ratio of $1.7_{-0.4}^{+0.7}times10^{-4}$ ($1.4_{-0.3}^{+0.5}times$ Solar), in good agreement with literature models of Uranuss disk-averaged spectrum. The north polar region is very bright at all frequencies northward of $sim$50$^circ$N, which we attribute to strong depletions extending down to the NH$_4$SH layer in both NH$_3$ and H$_2$S relative to the equatorial region; the model is consistent with an NH$_3$ abundance of $4.7_{-1.8}^{+2.1} times 10^{-7}$ and an H$_2$S abundance of $<$$1.9times10^{-7}$ between $sim$20 and $sim$50 bar. Combining this observed depletion in condensible molecules with methane-sensitive near-infrared observations from the literature suggests large-scale downwelling in the north polar vortex region from $sim$0.1 to $sim$50 bar. The highest-resolution maps reveal zonal radio-dark and radio-bright bands at 20$^circ$S, 0$^circ$, and 20$^circ$N, as well as zonal banding within the north polar region. The difference in brightness is a factor of $sim$10 less pronounced in these bands than the difference between the north pole and equator, and additional observations are required to determine the temperature, composition and vertical extent of these features.
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