Browsing by Subject "Convection (Meteorology)"
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Item A case study of a derecho (windstorm) in the central plains(Texas Tech University, 1988-12) Kleyla, Robert PatrickDuring the afternoon of 29 July 1986 three separate supercell thunderstorms developed over central and eastern South Dakota. In their mature stages each storm produced numerous tornadoes; furthermore, one tornado reached F4 status and eventually devastated a power plant near Sioux City, Iowa. Other reports included large hail and an unusually high number of reports of strong winds exceeding 50 knots. During the period, the three supercells eventually merged into one convective complex, and shortly thereafter reached mesoscale convective complex (MCC) status over northwest Iowa. An extremely large area of the Central Plains was affected by this system including South Dakota, Minnesota, Nebraska, Iowa, Illinois, and Missouri. This system had similar characteristics to previous MCC events. However, it was different in some respects since many MCC systems have been known to become heavy-rain producers while this system continued to produce severe weather many hours after it had reached MCC status (especially involving straight-line winds which exceeded 90 knots in some places). To analyze this event (termed a derecho), the system has been considered from the perspectives of the synoptic and sub-synoptic scales. The information used includes upper-air data, surface observations, satellite pictures, and radar data. Since this system basically occurred between rawinsonde sites the thermodynamic structure of the system itself would be difficult to ascertain without a true mesoscale network; however, since the magnitude of this system was not forecasted by the NWS or NSSFC, a detailed synoptic and sub-synoptic scale analysis of the pre-storm, storm, and post-storm conditions was performed to determine how similar this event was to other systems studied by other researchers. On the sub-synoptic scale, surface observations and radar data were used to determine how the system propagated throughout its history. Although this convective system caused no deaths and only a few injuries, extensive crop and property damage followed in its wake. Climatology shows that during the summer months the most favorable regions for derecho storms are over the Central Plains.Item A high-resolution radar analysis of a tropical cloud cluster(Texas Tech University, 1985-05) Desrochers, Paul RIn this study, a high-resolution radar analysis of a tropical cloud cluster was conducted. A number of computer programs were designed which organized the radar data into various analysis formats, such as PPIs, RHIs and EPRHIs (End Point Range Height Indicator). Each of the analysis methods was found to be useful for a specific task. For example, the high-resolution composite PPI was useful for tracking precipitation features of the cloud cluster. In general, the horizontal resolution of the high-resolution analysis schemes was 1 km. This was found to be sufficient to define the structure of small convective cells, and to detect convective cells as small as 1 km in horizontal extent. Scale interactions between convection and the anvil of the tropical cloud cluster were observed through the high-resolution analysis. Anvil development during the cluster's intensifying stage was observed to be dependent upon blowoff from convective towers. This was a favorable interaction for the anvil. However, convection did not always interact advantageously with the anvil. A line of convection that moved under the anvil associated with another line of convection was seen to cause partial destruction to the anvil. Later, during the cloud cluster's mature and dissipating stages, small scale convection developed inside the anvil. This convection was not destructive to the anvil.Item Doppler radar analysis of a tropical Pacific convective event(Texas Tech University, 2001-05) Marsalek, David J.Determining moisture and heat budgets for the entire atmosphere remains one of the biggest challenges in modem day meteorology. In order to accurately determine these values, it is important for meteorologists to gain insight into the convective and stratiform activity occurring over the world's oceans, which cover approximately threefourths of the surface. Little is known about such tropical events due to the lack of data collection because of its associated difficulties over the oceans. This thesis examines a signifícant precipitation event over the central Pacific slightly north of the equator. The purpose is to compare the nature of the convective and stratiform events to past research in this area. By determining the specifics of this event and its similarities and differences to past events over the tropical oceans, researchers can more accurately speculate as to whether or not tropical oceanic precipitation can be treated as the same throughout or if it differs from region to region. This case differs in many aspects in its evolution from past research, prompting a simple, new model to be created based solely on the observations of the event.Item Dual Doppler analysis of an oceanic tropical mesoscale convective system during the Kwajalein experiment (KWAJEX)(Texas Tech University, 2001-08) Spooner, Catherine LynnNot availableItem Evolution of a mesoscale convective system(Texas Tech University, 1990-12) Tesmer, Jeffrey RansdellThis thesis presents a description of the evolution of the second of three mesoscale convective systems that passed over the PRE-ST0RM mesonetwork on 3-4 June 1985 Three NC-^JK CP-3 and CP-4 Doppler radar volume scans along with Wichita (NWS) WSR-57 radar scans were analyzed with surface wind and pressure data to explain the complex precipitation structure from 2100 to 0200 GMT The precipitation pattern contained a convective line, a northeastward extension of convection called the northeast band, stratiform precipitation m the northern half of the system, and smaller precipitation structures in the eastern portion of the system Detailed analysis of this system shows that the intersection of the convective line and the northeast band produced strong upward motion within an area of intense convection that influenced the surface pressure pattern and the internal circulation generated by the mesoscale convective system.Item Initiation, evolution, and demise of derecho producing mesoscale convective systems(Texas Tech University, 2004-08) Liebl, Shawn MNot availableItem Mesoscale convective systems: structure, development and storm-environment interactions(Texas Tech University, 1988-05) Rappaport, Edward NeilThis study describes Mesoscale Convective Systems (MCSs), clusterings of thunderstorms associated with significant weather events. Analyses focused on several objectives: a documentation of the conditions in which MCSs form; an elucÃdation of the life cycle and internal structure of a mid-latitude Mesoscale Convective Complex (MCC); and a systematic comparison of the precipitation structures and environments of many MCSs. In meeting the objectives the evolution of an episode of f ive MCSs over West Texas was investigated using as a principal source data collected by Texas Tech University as a participant in the Texas High Plains Cooperative Program (HIPLEX). Results of the study show that the first MCS formed near a cold front where lifting along an elevated dew-point front released instability. Surface outflows from the MCSs advanced the surface baroclinic zone associated with the cold front and helped initiate subsequent convection. Convection in the mature MCSs was uncoupled from the surface layer and occurred just ahead of mid-level short-wave perturbations. The third MCS in the sequence formed from isolated echoes over the mountains which merged and grew into an MCC with a low-level precipitation pattern whose organization resembled that of tropical MCSs, extended about 500 km across and had a lifetime of about 24 hours. Behind a squall line and a transition zone near the leading edge occurred an extensive region of precipitation that was organized during the system's mature stage as a set of curved rainbands. A composite wind analysis shows a center of cyclonic inflow at 500 mb near the common center of curvature of the rainbands. Upward motion in the middle- and upper-level cloud and a mesoscale unsaturated downdraft below are diagnosed. MCSs consisting of a squall line followed by a wide region of lighter rain develop in an environment where the relative flow at 300 mb Is moist and directed from front to rear. Rainbands embedded in the trailing stratiform area are a common element of the wide systems. Narrow squall-line MCSs tend to occur in an environment having at 300 mb a rear-to-front flow, or a front-to-rear flow of dry air.Item Multiscale study of a convectively driven high wind event(Texas Tech University, 2003-08) Midgley, Caleb JThe purpose of this study is to investigate a convectively-driven high wind event which affected the Texas Panhandle during the late afternoon/early evening hours of 30 May 2001. This storm was characterized by a feature referred to as a bow echo, a phenomenon that has typically been associated with straight-line winds. To accomplish the analysis, WSR-88D level II radar data from the Lubbock, Texas, radar site was used to diagnose storm structure based upon reflectivity and radial velocity data. Also, West Texas Mesonet data, along with the standard surface observing network, was obtained to identify storm-scale features in the low levels and investigate how these features may have affected the fransition from a supercellular convective mode to a linear bow echo mode. To complement the sparse upper-air network, an MM5 simulation was run for the event to diagnose features in the near-storm environment that may have had an organizing influence.Item Topographic influences on Amarillo radar echo climatology(Texas Tech University, 1980-08) Marshall, Timothy P.A radar climatology within 185 km (100 nm) surrounding Amarillo, Texas, has been assembled for the spring convective season (May and June) from 1975 through 1978. The objective has been to obtain significant evidence supporting the importance of the Caprock escarpment in initiating convection. Included is a data extraction technique that accounts, in part, for range bias effects. Conditions favoring convection were identified in terms of synoptic patterns and use of daily sounding data from Amarillo. Semi-quantitative correlations of initial echo occurrences with topographic roughness has revealed four potential source regions favorable for convective development.