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Massachusetts Institute of Technology (1995)

Nonlinear dynamics of water and energy balance in land-atmosphere interaction

Brubaker, Kaye L.

Titre : Nonlinear dynamics of water and energy balance in land-atmosphere interaction

Auteur : Brubaker, Kaye L. (Kaye Lorraine)

Université de soutenance : Massachusetts Institute of Technology

Grade : Doctor of Philosophy (Ph. D.) 1995

The energy and moisture states in the soil and near-surface atmosphere evolve due to fluxes that are themselves a function of these states. The resultant nonlinear dynamical system has modes of variability and statistical signatures that depend on the full coupling of all components of heat and moisture balance. A conceptual land-atmosphere model - consisting of a 1-D (in the vertical), 4- state balance for a soil layer and a turbulently-mixed atmospheric boundary layer - is subjected to stochastic forcing. The statistics of the moisture and energy states are computed ; the covariability structure evolves through the state-dependent turbulent and radiative fluxes in the land-atmosphere system and is not prescribed a priori. The mathematical construct is exploited to explore several land-atmosphere interaction processes and to identify and quantify their influence on regional hydroclimate. Because the soil moisture and temperature are negatively correlated (dry-warm or cool-moist), physical mechanisms that tend to restore each state individually (soilmoisture control of evaporation and temperature dependence of saturation specific humidity) act as anomaly-enhancing (positive) feedback mechanisms for the other state. Dry anomalies are found to persist longer than moist anomalies, when evaporation efficiency is formulated to switch between soil and atmospheric control. Twoway interaction between the land and atmosphere is seen to be critical in establishing the memory and covariability of the moisture and temperature states of the soil. Although usually triggered by large-scale circulation anomalies (decreased precipitation), dry soil anomalies may persist and intensify due to local land-atmosphere interactions. These interactions may, in turn, form feedback mechanisms that reinforce the large-scale anomaly. Thus, the explorations with the 1-D model are relevant to the persistence of hydrologic anomalies on both the local and the larger scale.

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