| In this dissertation, I present an improved multilayer radiative seasonal climate model for the study of giant-planet stratospheric temperatures with primary application to Saturn. Motivated by current Cassini and ground-based observations of a persistent enhancement of hydrocarbon emission from equator to south pole on Saturn (Greathouse et al. 2005a,b Orton et al. 2005 Flasar et al. 2005 and Howett et al. 2007), and the need to disentangle radiative and dynamical contributions to seasonal climate change, this work details the sensitivity of the stratosphere towards seasonal changes in insolation and chemistry. Until this research, the seasonal stratospheric responsivity was found to be slow and minimally pressure-dependent. Despite the fact that methane is the dominant absorber in giant planet atmospheres, current knowledge of shortwave near-infrared spectral transitions are limited to laboratory fitted band-models, which are not generated with optimal giant-planet atmospheric conditions (Tomasko et al. 2007). Summer thermal trends in the stratosphere are heavily dependent upon shortwave CH4 near-infrared parameterization. Observational trends in 2002 and 2004 are reproduced.This model incorporates stratospheric heating due to CH4 absorption of sunlight in the near infrared and visible regime and by C2H 2, C2H6, and C2H4 in the ultraviolet over the spectral region 2000 to 105 cm-1. Stratospheric cooling is due to CH4, C2H2, and C2 H6 line emission along with H2-H2, H2-He, and H2-CH4 collision induced continuum emissions within the spectral range of 0 to 1600 cm-1. The inclusion of seasonally variable photochemical hydrocarbon abundances produces seasonal trends comparable to observations. The choice of near-infrared (2000 - 9500 cm-1) CH4 absorption parameterization dramatically influences stratospheric heating and largely determines the seasonal responsivity of the stratosphere. This work has been funded by the Lunar and Planetary Institute in Houston. |
