The interaction of upper-tropospheric water vapor and the earth's infrared radiation field.

摘要

fundamental problem in predicting the response of the climate to anthropogenic perturbations to the atmospheric radiation field is understanding the role of water vapor. Water can provide a positive feedback to a temperature perturbation that is easily understood since a warmer atmosphere can contain more water and be more opaque. This feedback almost certainly occurs in the lower troposphere where shallow convection quickly transports water vapor into the boundary layer from the sea surface and maintains constant high relative humidity. The upper troposphere, however, is isolated from the underlying sea surface over large regions of the globe that are characterized by persistent sinking motion. Given the lack of a comprehensive long-term record of global upper-tropospheric water vapor, its role in climate processes is an unesolved question and is the underlying motivation for the work in this dissertation.;In Chapter Four, regional and seasonal characteristics of upper tropospheric moisture and the ability of a circulation model to capture them is examined. Large-scale variability of moisture in the upper troposphere in 1989 is examined using ECMWF model analyses and TOVS satellite radiances. Radiances computed from the ECMWF analyses reproduce the general locations and seasonal cycle of the TOVS-observed moisture features, but lack the moisture gradients and seasonal contrasts than indicated by the TOVS observations. Dynamically, the TOVS-observed regions of significant subtropical dryness are correlated with persistent subsidence indicated by ECMWF 300mb vertical velocity analyses.;In Chapter Five, the impact of infra-red radiative heating on the evolution of observed atmospheric profiles and the vertical distribution of water vapor is considered. Gravity wave motions are explored as a mechanism to produce vertical layering of moisture and infra-red cooling is shown to slightly amplify the gravity wave. The static and dynamic stability of moist layers is explored.;The first two chapters present introductory material. In Chapter Three, the ability to measure moisture and to model the radiation field in the upper-troposphere is examined. Radiances observed by the GOES-VAS 6.7