Models of the ISO 3-μm Reflection Spectrum of Jupiter

Precipitating Condensation Clouds in Substellar Atmospheres

“…Carlson et al (H p /H g (1994) retrieve ratios of 0.35 and 0.40 (^0.10) for ammonia clouds in the Equatorial and Northern Tropical Zones, respectively, which are seen in Figure 3 to span a range of values between D1 and 3. Retrievals of ammonia cloud f rain properties for the Jovian tropics from ISO (Infrared Space Observatory) measurements by Brooke et al (1998) indicate a scale height ratio of 0.3, which is consistent with our model results for f rain D 2.…”

“…1) using the Jovian temperature proÐle from V oyager (Lindal et al 1981), the relation for vapor pressure given in Appendix A, and a subcloud mole fraction of 3 ] 10~5 (a wide range of abundances below the expected base of the Jovian ammonia cloud have been reported ; we adopt the value at 0.6 bars retrieved by Kunde et al [1982] for the Northern Equatorial Belt, which also agrees with the best-Ðt values of Carlson, Lacis, & Rossow [1993] and Brooke et al [1998]). The cloud base appears at 0.42 bars, where the temperature is 129 K. Although absent in the Ðgures of Lewis (1969 ; likely caused by reduced vertical resolution), in our interpretation of that model, the vapor is not entirely depleted in the lowest reaches of the cloud (where hence, increases above the cloud q c \ q t ) ; q c base.…”

“…In their analysis, a Ðt for 10 km particles indicates a superior Ðt in comparison to those for 1 and 30 km particles, which we interpret as allowing a size range of 5 to 20 km. Recalling from the discussion of Figure 3 that the Brooke et al (1998) condensate scale height (a single value with no uncertainty) is consistent with Figure 5b indicates that mutual f rain \ 2. consistency with the e †ective radii retrieved by Brooke et al (1998) requires increasing the width of our size distributions and/or reducing our eddy di †usion coefficients. Simultaneously matching the Brooke et al (1998) optical depths requires a substantial reduction of the subcloud ammonia abundance.…”

“…To compare our model with observations averaged over a wider area, we next consider measurements of the Jovian tropics obtained from Earth orbit. Brooke et al (1998) use a 3 km ISO spectrum to retrieve microphysical properties of the Jovian ammonia cloud and Ðnd best Ðts for two possibilities : Ðrst, a monomodal distribution of 10 km ammonia particles with a visible optical depth of 1.1 ; second, a bimodal distribution of 1 and 10 km ammonia particles with an optical depth of 1.3 (equivalent to an e †ective radius of 7 km). Both Ðts include an additional optical depth of 0.1 from gray particles.…”

“…A narrower size distribution results in larger droplet e †ective radii and therefore smaller optical depths ; for the monodisperse case, the data mutually overlap at to r eff D 30 50 km. The darkest gray region corresponds to the range of observations given by West et al (1986) (equivalent to BanÐeld et al 1998, as described in the text), the medium gray region corresponds to the retrievals from V oyager IRIS 5È45 km observations by Carlson et al (1994), and the light gray region corresponds to retrievals from ISO 3 km observations by Brooke et al (1998). The lines correspond to variation of model results as ranges f rain from 0.1 to 10, with results at of 1, 3, and 5 marked by symbols as f rain denoted in (a).…”