Analyzing Ecohydrology of Subirrigated Meadow, Dry Valley and Upland Dune Ecosystems using Remote Sensing and In-Situ Estimations in the Semiarid Sand Hills Region of Nebraska, USA - Nathan Healey

• Dissertation Defense
• 11/30/2011

Nebraska,s dependence upon the High Plains (Ogallala) Aquifer for agricultural production is vital to the state,s economy, ecology and hydrology. The Sand Hills region (58,000 km2) of Nebraska is a unique system of lakes, (~5%) wetlands, (~10%) subirrigated meadows, (~20%) dry valleys and (~65%) upland sand dune ecosystems. Understanding how each of these land cover types reacts to climate conditions of different water limitations is vital to regional water resource management. This research explores the ecohydrological behavior of different land cover types at the Gudmundsen Sand Hills Research Laboratory (GSRL) near Whitman, Nebraska in the heart of the Sand Hills region of Nebraska by using remote sensing and in-situ estimations of energy partitioning. By employing satellite technology and micrometeorological instrumentation this research establishes a better understanding how energy partitioning, and resulting evapotranspiration (ET), differs between different vegetative communities. We present findings of diurnal and seasonal estimates of energy partitioning as well as daily estimations of ET from both satellite image processing and in-situ observations by Bowen ratio energy balance systems (BREBS). This research also employed different techniques to estimate energy partitioning via remote sensing by adjusting radiation, wind speed, and stability parameters to better represent areas with high topographic relief. The last focal point of this research was to analyze how energy partitioning and ET varied both spatially and temporally under different climate conditions between 2004 (normal year), 2006 (dry year), and 2009 (wet year).

Spatial Accuracy of Climate Networks in Nebraska - Andrea Coop

• Thesis Defense
• 7/6/2011

Climate data has become increasingly scrutinized for its accuracy because of the need for reliable predictions about climate change. The U.S. has taken great strides to keep up with the demand for accurate climate data. Over the last thirty years, vast improvements to instrumentation, data collection, and station siting have created more accurate data records. This study is to explore the accuracy of existing networks.

This study analyzes three climate networks used in Nebraska: the U.S. Historical Climatology Network (HCN), the Automated Weather Data Network (AWDN), and the newest network, the U.S. Climate Reference Network (CRN). Each of these networks has its own instrumentation, collection methods and station sites. Maximum and minimum surface temperature from the three networks and the spatial structure of temperature variations at the surface are compared. Two different timeframes, 2005-2009 and 1985-2005, were used to include the newest network, CRN, in the analysis. Daily data was collected from each of these networks within the specified timeframe. Root mean square error (RMSE) between each candidate station and the surrounding stations within 500 kilometers were calculated and evaluated to determine spatial accuracy of the network. This study found that in the 5 year analysis, CRN versus AWDN, the two networks were not significantly different enough to denote the network with high spatial accuracy. For the 21 year analysis, HCN versus AWDN, AWDN stations showed higher spatial accuracy (smaller error) than HCN stations for the variable of maximum temperature. The error for the two networks were not significantly different enough to decipher the network with the higher spatial accuracy.

Propagating and Non-propagating Interseasonal Oscillations in the Tropical Atmosphere: Their Vertical and Horizontal Structures and Developing Mechanisms - Zhaoning Liang

• Dissertation Defense
• 11/30/2010

A fixed beamformer is proposed and designed to identify source regions of Intra-Seasonal Oscillations (ISO) in the tropical atmosphere. After tested by simulations of single and complex sources of waves, the fixed beamformer is applied to the ECMWF interpolated data grids to detect and identify source regions of the ISO in the tropical Indian and Pacific Ocean region. Results show that the fixed beamforming technique can uniquely identify the source region of the ISO, and the source regions of all major ISO in the tropical Indian and western equatorial Pacific region during the 29 yr from 1974 to 2002 have been identified.

Examinations of ISO development in the source regions indicate that besides the eastward propagating ISO, there were non-propagating ISO during this 29-year period. To understand why some ISO propagate while others are stationary, statistical analyses are used to examine the vertical and horizontal structures of these two types of ISO. Results show very different structures during the development and evolution of these two different types of ISO. For the propagating ISO, both moisture and temperature processes/disturbances are very important for the development of the ISO. This type of ISO is developed in a relatively warm and wet large-scale environment, and wind enhanced surface evaporation is a major mechanism. For the non-propagating ISO, temperature process is not as important as the moisture process in the development of ISO. Temperature anomalies remained weak before the onset of major convection in the ISO and reached peak intensity afterward peak convection. Both temperature and moisture anomalies developed but confined within the source region. The non-propagating ISO develop in a relatively cool and dry environment. Although weak low-level easterly anomalies and surface evaporation existed before the onset of major convection in these ISO, radiation-convection interaction mechanism seems playing an important role in triggering the non-propagating ISO. A key support for this notion is that relatively cold temperature anomalies persisted in the middle troposphere during the development of the ISO. This radiative cooling destabilized the troposphere profile and favored convection development.