The interaction between terrestrial ecosystems and the atmosphere continues to be a central research theme within climate, hydrology, and ecology communities. This interest is stimulated by research issues pertinent to both the fundamental laws and the hierarchy of scales. To further explorer such topics over various spatial and temporal domains, in this study, biosphere-atmosphere interactions are studied at two different scales, leaf-to-canopy and canopy-to-atmospheric boundary-layer (ABL) scales, by utilizing both models and long-term measurements collected from the Duke Forest AmeriFlux sites. For the leaf-to-canopy scale, two classical problems motivated by contemporary applications are considered: (1) ‘inverse problem’ – determination of nighttime ecosystem respiration, and (2) forward problem – estimation of two-way interactions between leaves and their microclimate ‘’. An Eulerian inverse approach was developed to separate aboveground respiration from forest floor efflux using mean CO2 concentration and air temperature profiles within the canopy using detailed turbulent transport theories. The forward approach started with the assumption that canopy physiological, drag, and radiative properties are known. The complexity in the turbulent transport model needed for resolving the two-way interactions was then explored. This analysis considered a detailed multi-layer ecophysiological and radiative model embedded in a hierarchy of Eulerian turbulent closure schemes ranging from well-mixed assumption to third order closure schemes with local thermal-stratification within the canopy. For the canopy-to-ABL scale, this study mainly explored problems pertinent to the impact of the ecophysiological controls on the regional environment. First, the possible combinations of water states (soil moisture and atmospheric humidity) that trigger convective rainfall were investigated, and a distinct ‘envelope’ of these combinations emerged from the measurements. Second, an analytical model as a function of atmospheric and ecophysiological properties was proposed to examine how the potential to trigger convective rainfall shifts over different land-covers. The results suggest that pine plantation, whose area is projected to dramatically increase in the Southeastern US (SE), has greater potential to trigger convective rainfall than the other two ecosystems. Finally, the interplay between ecophysiological and radiative attributes on surface temperature, in the context of regional cooling/warming, was investigated for projected land-use changes in the SE region. / Dissertation

This study proposes a stratified approach of drought severity assessment using multi-layer simulated soil moisture. SWAT (Soil and Water Assessment Tool) models are calibrated for 50 watersheds in the South-Atlantic Gulf region of the Southeastern US and a high-resolution daily soil moisture dataset is obtained at Hydrologic Unit Code (HUC-12) resolution for a period of January 1982 through December 2013. A near real-time hydrologic simulation framework by coupling the calibrated SWAT models with the National Centers for Environmental Prediction (NCEP) coupled forecast system model version 2 (CFSv2) weather data is developed to forecast various water balance components including soil moisture (SM), actual evapotranspiration (ET), potential evapotranspiration ET (PET), and runoff (SURQ) for near-real time drought severity assessment, and drought forecasting for a lead of 9-months. A combination of the surface and total rooting depth soil moisture percentiles proves to be an effective increment over conventional drought assessment approaches in capturing both, transient and long-term drought impacts. The proposed real-time drought monitoring approach shows high accuracy in capturing drought onset and propagation and shows a high degree of similarity with the U.S. Drought Monitor (USDM), the long-term (PDSI, PHDI, SPI-9 and SPI-12), and the short-term (Palmer Z index, SPI-1 and SPI-6) drought indices. / Master of Science / Drought, a recurring and worldwide phenomenon, with spatial and temporal characteristics varying significantly from across globe, lead to long-term and cumulative environmental changes. Often referred to as creeping phenomena, droughts are difficult to predict and constant monitoring is required to capture the signs of the onset of drought. Spatial variability in drought severity requires an understanding of the hydrology of the region and a knowledge of the relationship between drought inducing climatic extremes and other regional or local characteristics which help build, sustain and propagate droughts. In the absence of long-term observed hydrologic variables like soil moisture, evapotranspiration, simulated hydrologic variables serve an important purpose in understanding the impact of drought on various components of the water budget. However, several continental scale, physics-based models, and large scale remote sensing products find themselves restricted in explaining the watershed scale and sub-watershed scale variability in relation to drought. This study provides a high-resolution simulation of hydrological variables for 50 watersheds in the South-Atlantic Gulf region of the Southeastern US. The high resolution hydrologic simulations provide bedrock for retrospective drought simulations and understanding the response of various hydrologic variables of these watersheds to drought. It also aids in understanding the spatial variability in the relationship, and understanding the impact of seasonality and hydroclimatology on drought. The understanding of the interplay of various water budget components at watershed scale is used in developing a reliable seasonal drought forecasting framework based on the forecasted hydrologic variables from SWAT-CFSv2 coupled models for application in real time with a lead time of 9 months.

900 archived FRM filters from 15 sites over the southeast during 2007 were analyzed for PM2.5 chemical composition and physical properties. Secondary components (i.e. sulfate aerosol and SOA) were the major contributors to the PM2.5 mass over the southeast, whereas the contribution from biomass burning varied with season and was negligible (2%) during summer. Excluding biomass burning influence, FRM WSOC was spatially homogeneous throughout the region, similar to sulfate, yet WSOC was moderately enhanced in locations of greater predicted isoprene emissions in summer. On smaller spatial scale, a substantial urban/rural gradient of WSOC was found through comparisons of online WSOC measurements at one urban/rural pair (Atlanta/Yorkville) in August 2008, indicating important contribution from anthropogenic emissions. A comparative study between Atlanta and LA reveals a number of contrasting features between two cities. WSOC gas-particle partitioning, investigated through the fraction of total WSOC in the particle phase, Fp, exhibited differing relationships with ambient RH and organic aerosols. In Atlanta, both particle water and organic aerosol (OA) can serve as an absorbing phase. In contrast, in LA the aerosol water was not an important absorbing phase, instead, Fp was correlated with OA mass. Fresh LA WSOC had a consistent brown color and a bulk absorption per soluble carbon mass at 365 nm that was 4 to 6 times higher than freshly-formed Atlanta soluble organic carbon. Interpreting soluble brown carbon as a property of freshly-formed anthropogenic SOA, the difference in absorption per carbon mass between the two cities suggests most WSOC formed within Atlanta is not from an anthropogenic process similar to LA.