Thermal structure and dynamics of Neptune's atmosphere from Voyager measurements

Abstract

Spatially resolved Voyager infrared spectra from a global mapping sequence are used to characterize the thermal structure of the atmosphere of Neptune between approximately 50 and 100 mbar. A zonal mean meridional temperature cross section is obtained, which shows a minimum in the upper tropospheric and lower stratospheric temperatures at southern mid latitudes with maxima at the equator and high southern latitudes. This is qualitatively similar to the structure observed on Uranus, even though the obliquities and internal heat fluxes of the two planets are quite different. Thermal wind calculations show zonal wind speeds decreasing with altitude at all latitudes. Within the framework of a linear radiative‐dynamical model, the thermal structure and cloud top winds together imply a frictional damping time comparable in magnitude to the radiative relaxation time; similar results have previously been obtained for the other three giant planets. Periodogram techniques for used to search the observed longitude variations of temperature for possible planetary‐scale wave features. Data from two latitude bins are analyzed; one of the bins includes the Great Dark Spot, and the other is centered on the southern mid‐latitude minimum in the zonal mean temperature. A weakly significant feature near planetary wavenumber 4 is identified at the latitude of the spot. The rest of the variance can be attributed to instrument noise and possibly a broadband meteorological spectrum indistinguishable from white noise.