O O M

One theory is that hazes, or smog and aerosols in the stratosphere rain down and are deposited on the upper levels of clouds in the troposphere. We have smog on Earth, much of which is man-made. But, on Jupiter according to Amy Simon-Miller, "In Jupiter's case we likely have incident sunlight/ultraviolet radiation interacting with the aerosols and gases to make hydrocarbon smog. The small particles would then rain down toward the clouds. We are actually seeing the majority of the colored substance above the clouds in a thick hazy layer. The clouds underneath can be white as new ammonia ice wells up and the clouds overturn. In the locations where the clouds shoot higher from convection, they are whiter, since we are looking through less haze and seeing the fresh clouds." (Simon-Miller personal communication.)

According to Simon-Miller et al. (2001), the main differences between the belts and zones, if these areas are assumed to be typical, lies in the color of the tropo-spheric hazes and the optical depth of the variable cloud sheet. In all cases, the cloud sheet at the base of the tropospheric haze shows no evidence of coloration [105]. This generally agrees with the findings of West et al. (1896), and SimonMiller et al. (2000), who find the majority of the coloration is likely to be in diffuse particles above the thick cloud deck. If white ammonia ice crystals are mixed in this layer, the color differences between belts and zones could be entirely due to the proportion of ammonia ice in the mix or riming the colored particles [106].

In the belts, the higher pressure of a thinner cloud sheet, and thicker, redder haze could be produced by downwelling and convergence in cyclonic sheer zones, evaporating the ices in the haze and clouds and increasing the layer thickness of tropospheric haze. A few fresh white clouds are forced up by convective events to replenish the layers as smog likely falls out from above to color them. In zones, small wisps of color could be formed in a similar manner, with weak cyclonic events temporarily evaporating the tropospheric hazes as they subside in the otherwise upwelling, and therefore brighter, surroundings [107].

In the case of the EZ, where a color gradient can sometimes be seen between the northern (EZn) and southern (EZs) sections of the zone (as mentioned previously), there may be an indication that a riming or mixing of ice with the haze caused the EZs to appear whiter than the EZn [108].

The Great Red Spot has its own internal energy driving it and the height and temperature arguments we use to explain color on the rest of the planet do not apply to it! (Simon-Miller, personal communication October 25, 2004). The Great Red Spot has been studied in detail with spacecraft imaging to determine its thermal structure, dynamics, color, and composition [109] (Fig. 4.4). Infrared data suggest that the GRS has a higher, colder cap of haze than other regions [110], and color studies indicate a difference in its color from other red regions [111]. Using data from the Galileo spacecraft SSIduring its nominal mission from December 1995 to December 1997, Simon-Miller et al. (2001), observed that the central core of the GRS was the reddest in color and may be caused by a different coloring agent than other regions on the planet [112]. Indeed, amateur ground based observations have revealed this same appearance. During the 2003-2004 apparition, the center of the GRS gave a distinct dark red condensation appearance at the core in many amateur CCD images. During the nominal mission, the cloud sheet was found to be quite thick at various locations within the GRS. The pressure results confirmed that the cloud sheet is higher (lower in pressure) in the north than in the south,

Fig. 4.4. Comparison of The Great Red Spot at Four different Wavelengths. These images show the appearance of the GRS in violet light (415 nm, upper left), infrared light (757nm, upper right), and infrared light in both a weak (732 nm, lower left) and a strong (886 nm, lower right) methane absorption band. Reflected sunlight at each of these wavelengths penetrates to different depths and is scattered or absorbed by different atmospheric constituents before detection by the Galileo spacecraft. (Credit: Courtesy NASA/JPL-Caltech).

Fig. 4.4. Comparison of The Great Red Spot at Four different Wavelengths. These images show the appearance of the GRS in violet light (415 nm, upper left), infrared light (757nm, upper right), and infrared light in both a weak (732 nm, lower left) and a strong (886 nm, lower right) methane absorption band. Reflected sunlight at each of these wavelengths penetrates to different depths and is scattered or absorbed by different atmospheric constituents before detection by the Galileo spacecraft. (Credit: Courtesy NASA/JPL-Caltech).

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