**DPS Meeting, Madison, October 1998**

*Session 30P. Jupiter I*

Contributed Poster Session, Wednesday, October 14, 1998, 5:10-6:10pm, Hall of Ideas
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## [30P.20] Phase function of Jovian cloud deduced from reanalysis of Pioneer data

*S. Itoh, N. Kakikura, T. Satoh, K. Kawabata (SUT)*

Scattering phase functions of Jovian clouds are
reconsidered, so that their accuracy may match the needs of
recent Jupiter data obtained with high spatial resolution
and high photometric accuracy by modern instruments, such as
Galileo, HST, and ground-based telescopes. We are able to
explore a huge volume in a parameter space to obtain
suitable combinations of model parameters with a highly
efficient computer code running on today's high-performance
computers.

We analyze a set of photometric measurements (limb darkening
curves) along the STrZ of Jupiter taken at 14 solar phase
angles (12^{\circ}~150^{\circ}) from Pioneer 10 and
11, the same data set as those previously analyzed by
Tomasko et al. (1978) and by Smith and Tomasko (1984). An
adding-doubling computer code is used with Tomasko et al's
(1978) Type 1 model: a cloud layer of infinite optical
thickness is placed beneath a thin layer of Rayleigh
scattering gas. The cloud scattering phase function is
specified with three parameters: g_{1} and g_{2} are the
anisotropy parameter of the Henyey-Greenstein function
(forward and backward scattering) and f is the fraction of
forward scattering. For each grid point in a
three-dimensional volume (0\leq g_{1}\leq 1; -1\leq
g_{2}\leq 0; 0\leq f\leq 1), the Rayleigh optical
depth and the cloud scattering albedo are optimized using a
simplex method. A scattering phase function, with steeper
forward scattering and less prominent backward scattering
compared to Tomasko et al's, reproduces the data very well.

An application was made to Galileo G1 images of the GRS and
its vicinity. A limb darkening curve of the STrZ has been
constructed, in which the solar phase angle ranges between
70^{\circ}~120^{\circ}, well-covered by the Pioneer
data. Our preliminary data analysis indicates that the
optical thickness of the stratospheric haze is ~ 0.1,
thinner than that in the methane band data analyses (West
and Tomasko 1980, etc). Application to other data sets, and
interpretation of a new phase function (in terms of Mie
parameters) will be discussed.

The author(s) of this abstract have provided an email address
for comments about the abstract: j1298607@ed.kagu.sut.ac.jp

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