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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: g1 and g2 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 g1\leq 1; -1\leq g2\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