High-Resolution 10-micronmeter Spectroscopy of Ammonia and Phosphine Lines on Jupiter

Abstract

High spectral resolution measurements of NH3and PH3lines on Jupiter in the 10.5- to 11.2-μm range are presented. Observations, recorded on January 21–23, 1991, cover the 10°–40°S latitude range and several longitudes including the Great Red Spot (GRS). Information on the temperature in the upper troposphere was retrieved from the continuum radiance at wavelengths around 12.8 and 17.8 μm. At all observed longitudes, the 200-mbar temperature field is minimum at latitudes of 20°–25°S near the location of the South Tropical Zone, in agreement with Voyager infrared retrievals. This minimum temperature is lower over the GRS than at other longitudes. The ammonia mixing ratio at ∼380 mbar is not significantly enhanced over the GRS. The phosphine abundance probed at ∼580 mbar is also not enhanced (within a precision of 10%), suggesting that this molecule is not a precursor of the reddish chromophores. The NH3abundance at 380 mbar varies highly with latitude and longitude, a possible consequence of the active jovian meteorology. At the resolution of our observations (∼8000 km), the NH3humidity at this altitude ranges between 15 and 100% throughout the available data set. Above the cloud tops, the NH3mixing ratio in the 240-mbar region reaches a maximum near 15°–18°S and decreases by a factor of ∼40 at latitudes 30°–35°S. This variation is not correlated with the 200-mbar temperature. It can be explained by a decrease of the eddy mixing coefficient near 240 mbar from ∼4000 to ≤400 cm2sec−1between the two latitude ranges. The PH3mixing ratio near 580 mbar lies between 1.7 and 2.6 × 10−7in the observed regions. At all longitudes, PH3varies smoothly with latitude, decreasing by ∼30% from 10° to 35°S. This variation may also reflect a decrease in the strength of the eddy mixing near 580 mbar or at deeper levels in the atmosphere.