Browsing by Subject "Mesonet"
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Item Analysis of rear-flank downdrafts and their evolution during project WIRL(Texas Tech University, 2005-08) Hirth, Brian D.; Schroeder, John L.; Peterson, Richard E.; Weiss, Christopher C.The existence of hook echoes and rear-flank downdrafts (RFDs) in supercell thunderstorms has been well documented over the past several decades (Stout and Huff 1953; van Tassell 1955; Fujita 1958, 1973, 1975; Browning and Donaldson 1963, Browning 1964, 1965; Lemon 1977; Burgess et al. 1977; Brandes 1977; Barnes 1978a,b). The identification of these features has played a vital role in severe thunderstorm research as supercell thunderstorms account for a large percentage of severe weather occurrences each year. Initial investigations have attempted to directly link hook echoes with tornado occurrences; however recent research has shown that a variety of supercell thunderstorms possessing hook echoes fail to produce low-level circulations (Markowski 2002). A recent study using WSR-88D radar data over a seven year period from 1992-1999 found that roughly 15% of mid-level mesocyclones and 40% of low-level mesocyclones actually produced tornadic circulations at the surface (Trapp and Stumpf 2002). Nonetheless hook echoes and their associated RFDs are still thought to play key roles in the development of rotation near the ground. The development of mobile mesonet instrumented vehicles by the National Severe Storms Laboratory propelled supercell thunderstorm research forward in the mid-1990s (Straka et al. 1996). These instrumented suites were produced as a response to the scientific demands of very high spatial and temporal resolution datasets. Since it would be unlikely for a given storm to pass over a fixed network, the practical alternative was to make the network mobile. This new ability to sample supercell characteristics directly at the surface allowed for the direct investigation of RFD surface thermodynamics and kinematics during the Verification of the Origins of Rotation in Tornadoes Experiment (VORTEX; Rasmussen et al. 1994). Markowski et al. (2002) encountered consistent relationships between RFD thermodynamics and tornadogenesis and tornadogenesis failure in a study using 18 tornadic and 12 nontornadic cases from VORTEX. Though an unprecedented study, the near instantaneous nature of these observations did not take into consideration the evolution of an entire RFD lifecycle. Embedded features within a broad RFD circulation could potentially play their own individually significant roles in the generation of tornadoes. The principle objective of this investigation is to document the progression of thermodynamic and kinematic features as they potentially move cyclonically through the RFD region. In doing so, the following questions will be examined: 1. Do RFD equivalent potential temperature and virtual potential temperature values trend colder with time compared to those values measured in the storm-relative inflow? This trend would suggest that RFD air is descending from progressively higher levels allowing for more ambient environmental air to be entrained into the RFD. This result may also suggest that the efficiency of evaporation is increasing as the drier environmental air mixes with the RFD parcels during this entrainment process. 2. Though the equivalent potential temperature and virtual potential temperature perturbations within a particular RFD may be relatively small compared to that of the storm-relative inflow, what effects may weak surface flow have on tornadogenesis and its resulting intensity and longevity? This will be examined to see if any relationships between strong inflow/RFD winds and more significant tornadic episodes can be distinguished. It is now well understood that the mid-level rotation comprising a supercell is obtained through the vertical titling of ambient environmental streamwise vorticity. This component of vorticity is maximized when environmental flow both increases in magnitude and veers with height (Davies-Jones 1984). However the production of low-level vorticity is not as well understood. Solenoidally generated vorticity likely exists along the baroclinic boundaries that define both the forward-flank and rear-flank downdrafts. A secondary aspect of this research will be to investigate the implications that thermodynamic gradients have on the generation of this vorticity.Item Analysis of rear-flank downdrafts and their evolution during project WIRL(2005-08) Hirth, Brian D.; Schroeder, John L.; Peterson, Richard E.; Weiss, Christopher C.The existence of hook echoes and rear-flank downdrafts (RFDs) in supercell thunderstorms has been well documented over the past several decades (Stout and Huff 1953; van Tassell 1955; Fujita 1958, 1973, 1975; Browning and Donaldson 1963, Browning 1964, 1965; Lemon 1977; Burgess et al. 1977; Brandes 1977; Barnes 1978a,b). The identification of these features has played a vital role in severe thunderstorm research as supercell thunderstorms account for a large percentage of severe weather occurrences each year. Initial investigations have attempted to directly link hook echoes with tornado occurrences; however recent research has shown that a variety of supercell thunderstorms possessing hook echoes fail to produce low-level circulations (Markowski 2002). A recent study using WSR-88D radar data over a seven year period from 1992-1999 found that roughly 15% of mid-level mesocyclones and 40% of low-level mesocyclones actually produced tornadic circulations at the surface (Trapp and Stumpf 2002). Nonetheless hook echoes and their associated RFDs are still thought to play key roles in the development of rotation near the ground. The development of mobile mesonet instrumented vehicles by the National Severe Storms Laboratory propelled supercell thunderstorm research forward in the mid-1990s (Straka et al. 1996). These instrumented suites were produced as a response to the scientific demands of very high spatial and temporal resolution datasets. Since it would be unlikely for a given storm to pass over a fixed network, the practical alternative was to make the network mobile. This new ability to sample supercell characteristics directly at the surface allowed for the direct investigation of RFD surface thermodynamics and kinematics during the Verification of the Origins of Rotation in Tornadoes Experiment (VORTEX; Rasmussen et al. 1994). Markowski et al. (2002) encountered consistent relationships between RFD thermodynamics and tornadogenesis and tornadogenesis failure in a study using 18 tornadic and 12 nontornadic cases from VORTEX. Though an unprecedented study, the near instantaneous nature of these observations did not take into consideration the evolution of an entire RFD lifecycle. Embedded features within a broad RFD circulation could potentially play their own individually significant roles in the generation of tornadoes. The principle objective of this investigation is to document the progression of thermodynamic and kinematic features as they potentially move cyclonically through the RFD region. In doing so, the following questions will be examined: 1. Do RFD equivalent potential temperature and virtual potential temperature values trend colder with time compared to those values measured in the storm-relative inflow? This trend would suggest that RFD air is descending from progressively higher levels allowing for more ambient environmental air to be entrained into the RFD. This result may also suggest that the efficiency of evaporation is increasing as the drier environmental air mixes with the RFD parcels during this entrainment process. 2. Though the equivalent potential temperature and virtual potential temperature perturbations within a particular RFD may be relatively small compared to that of the storm-relative inflow, what effects may weak surface flow have on tornadogenesis and its resulting intensity and longevity? This will be examined to see if any relationships between strong inflow/RFD winds and more significant tornadic episodes can be distinguished. It is now well understood that the mid-level rotation comprising a supercell is obtained through the vertical titling of ambient environmental streamwise vorticity. This component of vorticity is maximized when environmental flow both increases in magnitude and veers with height (Davies-Jones 1984). However the production of low-level vorticity is not as well understood. Solenoidally generated vorticity likely exists along the baroclinic boundaries that define both the forward-flank and rear-flank downdrafts. A secondary aspect of this research will be to investigate the implications that thermodynamic gradients have on the generation of this vorticity.Item Characteristics of the quiescent dryline from a case study perspective(2005-05) Conder, Mark R.; Peterson, Richard E.; Schroeder, John L.; Chang, Chia-Bo; Smith, Douglas A.The dryline is a low-level atmospheric boundary that is characterized by a strong horizontal moisture gradient across a narrow zone. Numerous previous studies have already established the dryline’s role of producing lift and convergence necessary for the development of thunderstorms. One of the many forecasting challenges facing the operational meteorologist is determining the evolution of the high plains dryline. This dissertation examines a type of dryline called the "quiescent" dryline. The quiescent dryline exists in a synoptic environment characterized by relatively weak environmental wind. This dryline is observed to advance eastward during the day and retreat westward at night, often repeating this cycle for several days. The exact nature of the motion and evolution of the quiescent dryline is dependent on many factors that occur at different scales in the atmosphere-land/soil system. In order to perform the study, a field experiment was designed to investigate the mesoscale (~10 to 100 km) structure and evolution of the quiescent drylines. The West Texas Mesonet, a network of instrumented towers centered on Lubbock, Texas was utilized along with several additional towers deployed for the experiment. Data was collected and analyzed for several drylines that occurred across the South Plains of West Texas during the spring of 2002. A framework was created to identify and characterize advancing and retreating drylines through the objective analysis of several meteorological quantities. The results showed that the dryline could be identified through strong gradients of moisture, along with moisture advection and convergence, in agreement with previous studies. Relatively high values of moisture advection and convergence were observed in conjunction with retreating drylines. Mobile instrumented platforms were also utilized to examine a quasi-stationary dryline, obtaining detailed measurements of moisture gradients in the vicinity of the dryline at scales less than one kilometer. Additionally, the drylines were simulated by two common meteorological mesoscale models and their forecast skill was evaluated. The results show that simulations with higher horizontal resolutions are not necessarily more accurate in forecasting the dryline evolution.Item Characteristics of the quiescent dryline from a case study perspective(Texas Tech University, 2005-05) Conder, Mark R.; Peterson, Richard E.; Schroeder, John L.; Chang, Chia-Bo; Smith, Douglas A.The dryline is a low-level atmospheric boundary that is characterized by a strong horizontal moisture gradient across a narrow zone. Numerous previous studies have already established the dryline’s role of producing lift and convergence necessary for the development of thunderstorms. One of the many forecasting challenges facing the operational meteorologist is determining the evolution of the high plains dryline. This dissertation examines a type of dryline called the “quiescent” dryline. The quiescent dryline exists in a synoptic environment characterized by relatively weak environmental wind. This dryline is observed to advance eastward during the day and retreat westward at night, often repeating this cycle for several days. The exact nature of the motion and evolution of the quiescent dryline is dependent on many factors that occur at different scales in the atmosphere-land/soil system. In order to perform the study, a field experiment was designed to investigate the mesoscale (~10 to 100 km) structure and evolution of the quiescent drylines. The West Texas Mesonet, a network of instrumented towers centered on Lubbock, Texas was utilized along with several additional towers deployed for the experiment. Data was collected and analyzed for several drylines that occurred across the South Plains of West Texas during the spring of 2002. A framework was created to identify and characterize advancing and retreating drylines through the objective analysis of several meteorological quantities. The results showed that the dryline could be identified through strong gradients of moisture, along with moisture advection and convergence, in agreement with previous studies. Relatively high values of moisture advection and convergence were observed in conjunction with retreating drylines. Mobile instrumented platforms were also utilized to examine a quasi-stationary dryline, obtaining detailed measurements of moisture gradients in the vicinity of the dryline at scales less than one kilometer. Additionally, the drylines were simulated by two common meteorological mesoscale models and their forecast skill was evaluated. The results show that simulations with higher horizontal resolutions are not necessarily more accurate in forecasting the dryline evolution.Item Development of the West Texas Mesonet and supporting instrumentation(2005-05) Weinbeck, Stephen W.; Peterson, Richard E.; Smith, Douglas; Chang, Chia-Bo; Mulligan, KevinIn the last several years, the Wind Science and Engineering Center (WISE) at Texas Tech University has acquired a collection of new atmospheric sensing platforms. The most important of these is the West Texas Mesonet, an array of 40 automated surface observation systems. The purpose of the Mesonet is the acquisition of high spatial and temporal measurements of the atmosphere in West Texas. This provides an order of magnitude increase in the spatial resolution of atmospheric phenomena. The primary focus of WISE research is to understand the surface layer effects of high wind events. The addition of the mesonet allows for substantially better understanding of the resolution of the environment in which these damaging windstorms form and propagate. Despite the improvement of the resolution of the atmosphere, many important physical processes in the storm environment cannot be resolved directly through mesonet observations. In order to provide the high spatial resolution that is necessary, additional observations need to be utilized in conjunction with the Mesonet. Short portable towers and mobile mesonet vehicles allow researchers to capture very high spatial and temporal scales in the atmosphere. To supplement the additional data density at the surface , there is a new WISE boundary layer tower at the Reese technology center; co-located there are a boundary layer wind profiler and Doppler Sodar, as well as the nearby KLBB Doppler radar operated by the National Weather Service is located nearby. Together, these sensing platforms provide observational data of dramatically improved resolution for the Researchers at WISE as well as others. In order to highlight the advantages at the greater density, observations of the damaging wind events of 11 June 2000 and 30 May 2001 will be presented.Item Development of the West Texas mesonet and supporting instrumentation(Texas Tech University, 2005-05) Weinbeck, Stephen W.; Peterson, Richard E.; Smith, Douglas; Chang, Chia-Bo; Mulligan, KevinIn the last several years, the Wind Science and Engineering Center (WISE) at Texas Tech University has acquired a collection of new atmospheric sensing platforms. The most important of these is the West Texas Mesonet, an array of 40 automated surface observation systems. The purpose of the Mesonet is the acquisition of high spatial and temporal measurements of the atmosphere in West Texas. This provides an order of magnitude increase in the spatial resolution of atmospheric phenomena. The primary focus of WISE research is to understand the surface layer effects of high wind events. The addition of the mesonet allows for substantially better understanding of the resolution of the environment in which these damaging windstorms form and propagate. Despite the improvement of the resolution of the atmosphere, many important physical processes in the storm environment cannot be resolved directly through mesonet observations. In order to provide the high spatial resolution that is necessary, additional observations need to be utilized in conjunction with the Mesonet. Short portable towers and mobile mesonet vehicles allow researchers to capture very high spatial and temporal scales in the atmosphere. To supplement the additional data density at the surface , there is a new WISE boundary layer tower at the Reese technology center; co-located there are a boundary layer wind profiler and Doppler Sodar, as well as the nearby KLBB Doppler radar operated by the National Weather Service is located nearby. Together, these sensing platforms provide observational data of dramatically improved resolution for the Researchers at WISE as well as others. In order to highlight the advantages at the greater density, observations of the damaging wind events of 11 June 2000 and 30 May 2001 will be presented.Item Forecast verification: A dispersion modeling perspective(2008-05) Rogers-Van Nice, Rachel G.; Basu, Sukanta; Mulligan, Kevin; Schroeder, John L.The Environmental Protection Agency currently uses AERMOD, an air quality dispersion model to aid in the forecasting of transport and dispersion of air pollution for the U.S. Typically, NWS-ASOS observations (post-processed by EPA-AERMET model) are used as input to the AERMOD model. This traditional framework of running a dispersion model based on point observations is quite problematic from a variety of theoretical standpoints (e.g., lack of representativeness of meteorological data). An alternative viable framework would be to use prognostic meteorological models in conjunction with AERMOD. Indeed, contemporary research shows that the use of prognostic models as a substitute for NWS-ASOS observations alleviates some of the longstanding dispersion modeling problems, but at the same time creates new concerns. I will elaborate on several questions that need to be adequately addressed before prognostic models can be reliably utilized in operational dispersion applications. Most of these questions are rooted in prognostic models’ (in) ability to accurately represent the boundary layer variables of interest to the dispersion modeling community (e.g., wind speed, wind direction, temperature). I will compare the potential of a new generation prognostic meteorological model called the Weather Research and Forecasting (WRF) model in capturing wind speed variable versus data from the West Texas Mesonet by statistical analysis for verification. One year of ARW WRF output is analyzed. The WRF is a 36/12 km two-way nested run using the YSU PBL scheme. With use of innovative strategies for verification of complex spatio-temporal forecast fields and novel verification measures will make this study distinct.Item The effect of rainfall rate on latent and sensible heat fluxes in West Texas(Texas Tech University, 2006-05) Kook, David RichardAn understanding of local changes and relationships of meteorological parameters in the atmospheric boundary layer can be very useful when working with numerical models. A better understanding of these relationships can lead to a better parameterization of the models in the planetary boundary layer thus increasing the accuracy of the models. Using the West Texas Mesonet data from 2003 for all 40 of the sites, I looked into the effects that variable amounts of rainfall had on the amounts of latent and sensible heat fluxes during different periods. Calculations of fluxes from the mesonet data were used to compare dry periods and periods of rainfall throughout the year in hopes that some valuable relationships could be determined. Comparisons were also made between environmentally stable and unstable atmospheres, as well as station location being on or off the Caprock to get a better feeling for how these parameters relate. Linear analysis was then done to show the effect that increasing amounts of precipitation has on the fluxes in an attempt to quantify any possible relationships. Eventually the goal is to be able to accurately partition these fluxes on the small scale and input them as a grid of data into mesoscale numerical modelsItem The observed effects of mesoscale and storm-scale vortices on west Texas heat bursts(2010-12) Boucher, Trevor M.; Leary, Colleen; Weiss, Christopher C.; Basu, SukantaSince the implementation of mesoscale surface observation networks over the past 20 years, heat bursts have evolved from being considered a rare phenomenon to a fairly common one. They can range from hardly noticeable to severely damaging to property. Although theories explaining these heat bursts have been introduced in literature over the last 30 years, the forcing mechanisms that transport warm air to the surface are still unclear. Heat bursts are defined as rapid increases in temperature with corresponding rapid decreases in dewpoint temperature. The low dewpoint and potential temperature values observed in these bursts suggest that dry air is being transported to the surface from some point aloft. As these phenomena are typically found in mature nocturnal mesoscale convective systems, the rear inflow jet has been speculated to be the origin of this low theta-e air. Additionally, mesoscale convective vortices in recent literature have been observed developing in late stages of mature mesoscale convective systems in close proximity to the rear inflow jet. This study will investigate nocturnal mesoscale convective systems which contain either a mesoscale convective vortex or storm-scale vortices and have also produced heat bursts observed by the Texas Tech West Texas Mesonet. The purpose of the study will be to observe the role that the vortices play on the evolution of a heat burst, if any. Any relationship observed between the vortices, rear inflow jet, and surface heat bursts will be observed and discussed as an outcome.