Satellite-based estimates of net radiation and modeling the role of topography and vegetation on inter-annual hydro-climatology

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2010.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Cataloged from student-submitted PDF version of thesis.Includes bibliographical references (p. 229-260).The Fourth Assessment Report of the Intergovernmental Panel on Climate Change acknowledged that the lack of relevant observations in various regions of the world is a crucial gap in understanding and modeling impacts of climate change related to hydrologic cycle. The Surface Radiation Budget (SRB) is an important component in the study of land surface processes. Existing SRB retrieval algorithms generally suffer from two major shortcomings: difficulty in dealing with cloudy sky conditions and reliance on study-site specific ancillary ground data. In this work, a framework of estimating net radiation from the MODerateresolution Imaging Spectroradiometer (MODIS) data is presented that is applicable under all-sky conditions, while solely relying on satellite data. The results from the proposed methodology are compared against several ground measurements within the United States for the entire 2006. Finally, monthly radiation maps for the Continental United States are produced. Modeling, similar to observations, is critical to the Earth Sciences and the second part of this work focuses on the impact of incorporating vegetation dynamics and topography in modeling hydro-climatology over large river basins. Land and atmosphere are coupled with each other through the exchange of heat, momentum and water at the boundary. This work involves coupling of a physically-based, fully distributed ecohydrology model with a numerical atmospheric model, using high performance computing. The ability of the ecohydrology model (in an offline mode) to accurately resolve hydro-climatic signatures and vegetation dynamics is first examined. The ecohydrology model is applied in a highly instrumented catchment, Walnut Gulch Experimental Watershed (WGEW) in Arizona, for a period of 11-years (1997-2007). The ecohydrology model is able to capture the behavior of several key hydrologic variables and vegetation dynamics within the WGEW. A series of three synthetic experiments are conducted with a coupled land-atmosphere model. The anomalies of various simulated quantities between the synthetic experiments are examined within the rainfall-soil moisture feedback hypothesis proposed by Elathir [1998]. The results from the experiments highlight the need to explicitly account for vegetation dynamics and topography within a numerical atmospheric model. The thesis concludes with a discussion of contributions, and future directions for this work.by Gautam Bisht.Ph.D

Nullor Based New Implementation of CDBA Using Current Feedback Operational Amplifier

In this paper, a methodology based on nullors and passive elements to create equivalent circuits for existing building blocks has been presented. This methodology has been used for generating the equivalent nullor circuit for Current Differencing Buffered Amplifier (CDBA) and its implementation through AD844 ICs of Current Feedback Operational Amplifier (CFOA) has been presented. The proposed circuit is further modified by replacing the equivalent nullor sections with smaller blocks. The implemented CDBA (proposed CDBA-I) has been simulated and compared with existing topologies of CDBA to represent its proper functioning using LTSPICE. The proposed CDBA configuration offers a symmetric structure for its 2 differential inputs and offers higher bandwidth. Moreover, the configuration has been modified further to achieve low noise output terminal by the use of another CFOA (proposed CDBA-II). Both of these proposed configurations have been simulated and verified experimentally

Nullor Based New Implementation of CDBA Using Current Feedback Operational Amplifier

163-167In this paper, a methodology based on nullors and passive elements to create equivalent circuits for existing building blocks has been presented. This methodology has been used for generating the equivalent nullor circuit for Current Differencing Buffered Amplifier (CDBA) and its implementation through AD844 ICs of Current Feedback Operational Amplifier (CFOA) has been presented. The proposed circuit is further modified by replacing the equivalent nullor sections with smaller blocks. The implemented CDBA (proposed CDBA-I) has been simulated and compared with existing topologies of CDBA to represent its proper functioning using LTSPICE. The proposed CDBA configuration offers a symmetric structure for its 2 differential inputs and offers higher bandwidth. Moreover, the configuration has been modified further to achieve low noise output terminal by the use of another CFOA (proposed CDBA-II). Both of these proposed configurations have been simulated and verified experimentally

The Community Land Model version 5 : description of new features, benchmarking, and impact of forcing uncertainty

The Community Land Model (CLM) is the land component of the Community Earth System Model (CESM) and is used in several global and regional modeling systems. In this paper, we introduce model developments included in CLM version 5 (CLM5), which is the default land component for CESM2. We assess an ensemble of simulations, including prescribed and prognostic vegetation state, multiple forcing data sets, and CLM4, CLM4.5, and CLM5, against a range of metrics including from the International Land Model Benchmarking (ILAMBv2) package. CLM5 includes new and updated processes and parameterizations: (1) dynamic land units, (2) updated parameterizations and structure for hydrology and snow (spatially explicit soil depth, dry surface layer, revised groundwater scheme, revised canopy interception and canopy snow processes, updated fresh snow density, simple firn model, and Model for Scale Adaptive River Transport), (3) plant hydraulics and hydraulic redistribution, (4) revised nitrogen cycling (flexible leaf stoichiometry, leaf N optimization for photosynthesis, and carbon costs for plant nitrogen uptake), (5) global crop model with six crop types and time‐evolving irrigated areas and fertilization rates, (6) updated urban building energy, (7) carbon isotopes, and (8) updated stomatal physiology. New optional features include demographically structured dynamic vegetation model (Functionally Assembled Terrestrial Ecosystem Simulator), ozone damage to plants, and fire trace gas emissions coupling to the atmosphere. Conclusive establishment of improvement or degradation of individual variables or metrics is challenged by forcing uncertainty, parametric uncertainty, and model structural complexity, but the multivariate metrics presented here suggest a general broad improvement from CLM4 to CLM5