Theses and Dissertations from UMD
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Item THE DIURNAL AND SEASONAL RADIATIVE EFFECTS OF CIRRUS CLOUDS UTILIZING LARGE AIRBORNE AND SPACE-BORNE LIDAR DATASETS(2019) Ozog, Scott; Dickerson, Russell R; Yorks, John E; Atmospheric and Oceanic Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Cirrus clouds are globally the most common cloud type, however, their radiative impact on the Earth remains a large source of uncertainty in global climate models. Cirrus are unique in that they are absorptive to terrestrial outgoing longwave radiation, while also relatively transmissive to incoming solar radiation. The interactions of this greenhouse and albedo effect determine the sign and magnitude of cirrus radiative effects. Cirrus are microphysically complex, and can exhibit a variety of different ice crystal shapes and sizes depending on the thermodynamic environment in which they form, and their dynamic formation mechanism. Our ability to reliably model cirrus radiative effects is dependent upon accurate observations and parameterizations incorporated into radiative transfer simulations. Laser lidar instruments provide valuable measurements of cirrus clouds unavailable by other radar systems, passive remote sensors, or in-situ instruments alone. In this dissertation I developed and tested an improved calibration technique for the ACATS lidar instrument, and its impact on the direct retrieval of cirrus HSRL optical properties. HSRL retrievals theoretically have reduced uncertainty over those from a standard backscatter lidar. ACATS flew on two field campaigns in 2012 and 2015 where it was unable to consistently calibrate its etalon. It has been operating from the lab in NASA GSFC collecting zenith pointing data of cirrus layers where the improved calibration has resulted in consistent and reliable separation of the particulate and Rayleigh signal components. The diurnal trend of cirrus influence on the global scale has primarily been limited to data provided by satellites in sun-synchronous orbit, which provide only a snapshot of conditions at two times a day. Utilizing data from the CATS lidar aboard the ISS I investigated cirrus at four periods throughout the day in morning, afternoon, evening, and night across all seasons. Cirrus radiative effects were found to have a large latitudinal dependence, and have a greater potential to cool than many studies suggest with their primary warming contributions skewed towards the nighttime hours. Constrained lidar retrievals reduce the assumptions made in retrieving cirrus optical properties. Utilizing the expansive airborne CPL dataset from six flight campaigns I model the radiative effects of over twenty thousand constrained cirrus observations. Mid-latitude cirrus were found to have a mean positive daytime forcing equivalent to that of the CO2 greenhouse effect. However, synoptic cirrus were found to have a greater warming effect than convective cirrus, which were more likely to have a cooling effect.Item THE MEASUREMENT OF SCHOOL CLIMATE USING SURVEYS: EXPLORING UNIT OF ANALYSIS(2009) Burkhouse, Katie Lynn Sutton; Gottfredson, Gary D; Counseling and Personnel Services; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)School climate researchers have used different units of analysis when assessing school climate features. Overall, there is little research available to understand how different levels of analysis, individual or aggregated, influence the psychometric properties of a survey instrument. The purpose of the current research was to explore the use of different unit of analysis choices in instrument development. Further, the present study sought to replicate findings that the wording of survey instruments may influence the conceptualization of school climate by survey informants. Results indicate that unit of analysis affects on the factor structure, but that there is some overlap in the factors that emerge. Further, the present research confirmed past findings that the wording of climate items appears to affect the perception of items by respondents. Limitations and future directions are discussed. Unit of analysis remains an important theoretical and methodological concept in school climate research.Item ON THE SUMMER TIME DEVELOPMENT OF THE NORTH PACIFIC SEA-LEVEL PRESSURE ANTICYCLONE(2008-04-16) Chan, Steven C; Nigam, Sumant; Atmospheric and Oceanic Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)With the exception of the North Indian Ocean, subtropical ocean basins are dominated by climatological planetary-scale sea-level pressure (SLP) anticyclones. The seasonal variability of the North Pacific subtropical SLP anticyclone is examined here. The largest ERA-40 and linear diagnostic modeled Northern Hemisphere SLP seasonal variabilities are found in the mid-latitudes with relatively less change in the subtropics; this leads to the poleward boreal summer development of the North Pacific and Atlantic subtropical SLP high. Unlike the Northern Hemisphere, the Southern Hemisphere subtropical SLP highs develop equatorward. The zonal-mean Northern Hemisphere subtropical SLP and seasonal variabilities are dominated by continental seasonality - a uniform boreal winter descent changing to a zonally asymmetric continental monsoon ascent and heat lows with relatively little change over the oceans. A linear diagnostic model is used to examine the forcing of the SLP seasonal cycle. The modeled North Pacific SLP seasonal variability is forced mainly by winter stormtracks, extra-tropical North Pacific diabatic cooling, and boreal winter ITCZ. Asian monsoon forces a SLP ridge downstream, but the monsoon response is cancelled significantly by East Pacific diabatic heating and transients. North American diabatic heating and transients are also found to have a limited upstream effect. Boreal summer ITCZ forcing has limited North Pacific SLP response, and that is possibly linked to the prescribed tropical zonal-mean easterlies. ERA-40 and TRMM CSH diabatic heating is inter-compared with other independent measures of diabatic and latent heating. Zonal-mean ERA-40 ITCZ diabatic heating is nearly twice that of NCEP and ERA-15 reanalyses, which indicates a much stronger ERA-40 Hadley Circulation. The ERA-40 Walker Circulation is also stronger than of NCEP Reanalysis, which is consistent with excessive Maritime Continent diabatic heating. Largest differences are also found in the Tropical East Pacific and Atlantic. Vertically integrated TRMM CSH heating is too weak even compare with other TRMM products. However, TRMM CSH mid-tropospheric tropical heating compares well with other datasets. The largest differences appear in the upper and lower troposphere, which implies CSH limitations in handling shallow convection (a known issue) and stratiform precipitation in deep convection.Item Leadership and Safety Climate in High-Risk Military Organizations(2007-04-25) Adamshick, Mark Henry; Gansler, Jacques S; Public Policy; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Preventable accidents and mishaps continue to degrade the readiness of U.S. military forces. In 2006, the National Safety Council reported an annual rate of over 30 accidental fatalities per 100,000 Department of Defense members and estimated that preventable injuries and illnesses cost the department approximately $21 billion per year. Reducing these occurrences was the policy mandate of the Secretary of Defense in 2003. He challenged the military service secretaries to reduce their mishap rates by 50 percent over a two-year period ending September 30, 2005. While each of the military services formulated its own compliance strategy, none of them met the reduction goal. In some cases, the mishap rate actually increased. The purpose of this dissertation is to evaluate the Department of the Navy's (DON) policy compliance strategy and to assess its shortcomings and areas for future improvements. The Navy focused their efforts on leadership-intervention best practices designed to elevate the safety climate in their high-risk units, primarily their aviation components. These units contribute almost 90 percent of the annual mishap cost due to preventable accidents. DON policy-makers theorized that certain leadership interventions would improve safety climate thereby reducing the likelihood that unit members would engage in unsafe behavior both on and off the job. This dissertation evaluates the validity of that general theory, and the appropriateness of the specific leadership interventions chosen, in two distinct data collection and analysis phases. In the first phase, statistical analysis is conducted on a safety-climate survey database maintained by the Naval Post-Graduate School containing 20,000 Navy and Marine Corps military survey respondents assigned to F/A-18 aircraft squadrons completed over the past 5 years. In Phase 2, Commander, Naval Air Forces Atlantic Fleet authorized climate research in four Navy F/A-18 squadrons located at Oceana Naval Air Station. Upon analysis, the intervention methods implemented in the Navy's mishap reduction strategy showed little correlation with safety climate improvement. Phase 2 analysis identified several organizational programs and specific leadership qualities that correlate with elevated safety climate and revealed a preliminary causal relationship between safety climate and safety performance.