Department of Environmental Sciences
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Seminar Abstracts
Environmental Sciences Seminar Abstract            

  Spectral Analysis of A Linearized Land-Atmosphere System: Modeling and Applicatons
Pierre Gentine
Columbia University

This talk will be dedicated to the use and applications of a linearized land-atmosphere model. In an introductory part, the interest of land-atmosphere study will be emphasized. In particular, coupled simple models together form a higher complexity system exhibiting emergent behaviors as well new time and spatial scales. The apparition of these new features will be examined. Moreover the use of simple modeling to understand the main interactions of the land and atmosphere coupling will be further discussed.

The present talk will refresh and improve the work first introduced by Lettau (1951). A linearized land-atmosphere model, forced by times series of incoming radiation at the land-surface, is solved analytically. With this model, the profiles of temperature and heat fluxes in the soil and the Atmospheric Boundary Layer (ABL) can be expressed in terms of temporal Fourier series. Moreover the surface variables (temperature, specific humidity, surface fluxes) are also derived analytically and are expressed as functions of both surface parameters (friction velocity, vegetation height, aerodynamic resistance, stomatal conductance) and frequency of the forcing of incoming radiation. This original approach has several advantages. The model only requires very little data to perform well (time series of incoming radiation at the land-surface, mean daily specific humidity and potential temperature at any given height) and allows theoretically studying the temporal and spectral response of a coupled land-atmosphere system to any forcing of incoming radiation at the land-surface. The diurnal evolution of the ABL and the soil temperature and flux profiles will be emphasized, as well as their dependency on the frequency of the forcing. This will theoretically highlight the existence and diurnal behavior of the Surface and Mixed-Layer. This model will be shown to be helpful for the conception of remote-sensing tools and for the use of data assimilation (filtering) of observed brightness temperature. Moreover guidelines for the collection of remotely sensed data can be obtained through this simple model. The model will also be used to analyze the diurnal and (temporal) spectral dependency of surface variables, as well as the energy partitioning at the land-surface.

In the last part of the presentation, the propagation of an energy budget error at the land-surface in the coupled land-atmosphere system will be discussed. This error is introduced in the form of a Brownian Bridge (conditioned Brownian Motion) and represents the closure error of the land-surface energy-budget, inherent to any modeling or measurement. Our model will be shown to corroborate and explain experimental findings (aircraft measurements and meteorological sondes). Future improvements of the model will be discussed in the conclusion.

Last updated: 10/19/2009