Jupiter's Deep Cloud Structure Revealed Using Keck Observations of Spectrally Resolved Line Shapes

TL;DR

This study introduces a novel spectroscopic method to determine the depth and composition of Jupiter's deep clouds, revealing variations across latitudes and identifying water clouds at specific pressure levels.

Contribution

The paper presents a new technique combining Fraunhofer line analysis and pressure-broadened CH3D profiles to map Jupiter's deep cloud structure and water vapor distribution.

Findings

Deep cloud tops vary with latitude, with some regions lacking clouds above 2 bars.

The South Tropical Zone has a water cloud between 4 and 5 bars.

Hot Spots are relatively dry below 4.5 bars, matching Galileo data.

Abstract

Technique: We present a method to determine the pressure at which significant cloud opacity is present between 2 and 6 bars on Jupiter. We use: a) the strength of a Fraunhofer absorption line in a zone to determine the ratio of reflected sunlight to thermal emission, and b) pressure-broadened line profiles of deuterated methane (CH3D) at 4.66 microns to determine the location of clouds. We use radiative transfer models to constrain the altitude region of both the solar and thermal components of Jupiter's 5-micron spectrum. Results: For nearly all latitudes on Jupiter the thermal component is large enough to constrain the deep cloud structure even when upper clouds are present. We find that Hot Spots, belts, and high latitudes have broader line profiles than do zones. Radiative transfer models show that Hot Spots in the North and South Equatorial Belts (NEB, SEB) typically do not have opaque clouds at pressures greater than 2 bars. The South Tropical Zone (STZ) at 32 degrees S has an opaque cloud top between 4 and 5 bars. From thermochemical models this must be a water cloud. We measured the variation of the equivalent width of CH3D with latitude for comparison with Jupiter's belt-zone structure. We also constrained the vertical profile of water in an SEB Hot Spot and in the STZ. The Hot Spot is very dry for P<4.5 bars and then follows the water profile observed by the Galileo Probe. The STZ has a saturated water profile above its cloud top between 4 and 5 bars.