Radiative-convective models of the atmospheres of Uranus and Neptune: heating sources and seasonal effects

Abstract

The observations made during the Voyager 2 flyby have shown that the stratosphere of Uranus and Neptune are warmer than expected by previous models. In addition, no seasonal variability of the thermal structure has been observed on Uranus since Voyager 2 era and significant subseasonal variations have been revealed on Neptune. In this paper, we evaluate different realistic heat sources that can induce sufficient heating to warm the atmosphere of these planets and we estimate the seasonal effects on the thermal structure. The seasonal radiative-convective model developed by the Laboratoire de Météorologie Dynamique is used to reproduce the thermal structure of these planets. Three hypotheses for the heating sources are explored separately: aerosol layers, a higher methane mole fraction, and thermospheric conduction. Our modelling indicates that aerosols with plausible scattering properties can produce the requisite heating for Uranus, but not for Neptune. Alternatively, greater stratospheric methane abundances can provide the missing heating on both planets, but the large values needed are inconsistent with current observational constraints. In contrast, adding thermospheric conduction cannot warm alone the stratosphere of both planets. The combination of these heat sources is also investigated. In the upper troposphere of both planets, the meridional thermal structures produced by our model are found inconsistent with those retrieved from Voyager 2/IRIS data. Furthermore, our models predict seasonal variations should exist within the stratospheres of both planets while observations showed that Uranus seems to be invariant to meridional contrasts and only subseasonal temperature trends are visible on Neptune. However, a warm south pole is seen in our simulations of Neptune as observed since 2003.

References in corpus (15)

• The habitability of Proxima Centauri b II. Possible climates and Observability
• Is Gliese 581d habitable? Some constraints from radiative-convective climate modeling
• Methane on Uranus: The case for a compact CH4 cloud layer at low latitudes and a severe CH4 depletion at high-latitudes based on re-analysis of Voyager occultation measurements and STIS spectroscopy
• Neptune's Atmospheric Composition from AKARI Infrared Spectroscopy
• Mid-Infrared Spectroscopy of Uranus from the Spitzer Infrared Spectrometer: 1. Determination of the Mean Temperature Structure of the Upper Troposphere and Stratosphere
• Methane depletion in both polar regions of Uranus inferred from HST/STIS and Keck/NIRC2 observations
• Latitudinal variation in the abundance of methane (CH4) above the clouds in Neptune's atmosphere from VLT/MUSE Narrow Field Mode Observations
• Accurate and Approximate Calculations of Raman Scattering in the Atmosphere of Neptune
• A pole to pole pressure temperature map of Saturn's thermosphere from Cassini Grand Finale data
• Uranus in Northern Mid-Spring: Persistent Atmospheric Temperatures and Circulations Inferred from Thermal Imaging
• HST/WFC3 Observations of Uranus' 2014 storm clouds and comparison with VLT/SINFONI and IRTF/SpeX observations
• Mid-Infrared Ethane Emission on Neptune and Uranus
• 1D photochemical model of the ionosphere and the stratosphere of Neptune
• Retrieving Neptune's aerosol properties from Keck OSIRIS observations. I. Dark regions
• Longitudinal Variations in the Stratosphere of Uranus from the Spitzer Infrared Spectrometer

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