Water Vapor Variability Across Spatial Scales: Insights for Theory, Parameterization, and Model Assessment

The subject of this dissertation is the scale dependence of water vapor variability as observed by remote sensing and in situ measurements, and predicted by aqua-planet simulation. Global observations of the water vapor field from the Atmospheric Infrared Sounder (AIRS) are used to show that the first order structure function of the water vapor field exhibits power law behavior for scales between 50 km and 500 km throughout much of the troposphere. The power law scaling exponents are shown to vary between the boundary layer and free troposphere, with first order structure function scaling exponents of approximately 1/3 in the boundary layer and less than 1/2 in the free troposphere. Observations from the 396 m level of the WLEF television broadcast tower are used to show that the convective mixed layer layer and nocturnal residual layer exhibit power law behavior of first order structure functions and first order detrended fluctuation functions for scales between 1 km and 100 km. The power law scaling exponents computed from the tower observations of the convective mixed layer are shown to be consistent with the AIRS boundary layer regime exponents, while the exponents computed from the tower observations of the residual layer are shown to be consistent with AIRS free tropospheric regime scaling exponents. Finally, structure functions of the instantaneous water vapor field are computed from aqua-planet simulations performed at T85 and T340 spectral resolutions. Free tropospheric structure function scaling exponents for scales less than 500 km computed from the T340 spectral resolution simulation are shown to agree very well with free tropospheric scaling exponents computed from AIRS. Boundary layer structure function scaling exponents from the T340 spectral resolution are shown to be generally larger than boundary layer scaling exponents from AIRS.