{"id":{"repo_id":"ttu","oai_identifier":"oai:ttu-ir.tdl.org:2346/90007"},"canonical_url":"https://search.dev.ndltd.org/etd/ttu/oai:ttu-ir.tdl.org:2346/90007","repository":{"repo_id":"ttu","name":"Texas Technology University","base_url":"https://ttu-ir.tdl.org/server/oai/request"},"display":{"title":"Insights into tornadogenesis and tornado dynamics from idealized simulations","abstract":"Research over the last decades has resulted in a robust understanding of many aspects of tornadoes, such as the environmental conditions necessary for storms with tornado potential and the complex dynamics of mature tornadoes. However, the detailed processes during tornadogenesis are still less understood. One reason for this might be the difficulty to investigate the complex interactions of the tornado-scale and the storm-scale processes. A deeper understanding of these dynamics during tornadogenesis seems necessary to better predict which storm in an environment with tornado potential will produce a tornado, which is arguably one of the largest challenges for operational tornado warnings. This dissertation presents a collection of three journal articles with different research questions related to tornadogenesis on the interface between tornado-scale and storm-scale dynamics. The main tool is numerical simulation with the Bryan Cloud Model (CM1), configured in highly-idealized setups to focus on the specific research question. The first article is motivated by recent studies which suggest that all supercells have vertical vorticity maxima which could be intensified to tornado strength, but that the presence of a robust and strong low-level mesocyclone is the critical factor deciding about tornadogenesis success. To test this conclusion, the relative importance of vertical vorticity generation in the cold pool to the intensification by the low-level updraft is systematically evaluated in CM1. It is found that small changes in both of these parameters can cause a bifurcation between the tornadic and nontornadic cases, demonstrating the nonlinearity of tornadogenesis. The relative importance of the updraft and cold pool intensities depends on the position within the 2D spectrum spanned by the two parameters, with e.g., intensification of the updraft being most important in the moderate cold pool strength range. In the second article, the vorticity dynamics during tornadogenesis is more formally investigated to answer the question of what mechanism is responsible for large near-ground vertical vorticity in parcels during and after tornadogenesis. The simulations suggest that pre-tornadic vortex patches are predominantly generated by downdrafts (downdraft mechanism) but that once a corner flow has formed in a tornado, abrupt tilting of near-ground horizontal vorticity into the vertical begins to dominate (in-and-up mechanism). This result unifies the extant literature, in which both mechanisms have been shown to be important, depending on when the vorticity maximum was analyzed. The third study seeks to better understand why supercell-external factors such as other storms or airmass boundaries frequently seem to instigate tornadogenesis, a notion which is shown to be consistent with a statistical analysis of radar data of 136 supercell tornadoes. In the CM1 simulations, a longer residence time of vorticity maxima in the updraft region is favorable for tornado formation. The residence time is largely controlled by the near-ground flow speed of the supercell outflow relative to the updraft. In cases in which external outflow impacts but not undercuts the supercell from the southwest, the high pressure perturbation within and ahead of the external outflow can decelerate the updraft-relative flow, and hence serve as a catalyst for tornadogenesis. The results of the three studies are combined to form an updated conceptual model of tornadogenesis, which takes both the tornado-scale and storm-scale processes into account.","abstract_html":"Research over the last decades has resulted in a robust understanding of many aspects of tornadoes, such as the environmental conditions necessary for storms with tornado potential and the complex dynamics of mature tornadoes. However, the detailed processes during tornadogenesis are still less understood. One reason for this might be the difficulty to investigate the complex interactions of the tornado-scale and the storm-scale processes. A deeper understanding of these dynamics during tornadogenesis seems necessary to better predict which storm in an environment with tornado potential will produce a tornado, which is arguably one of the largest challenges for operational tornado warnings. This dissertation presents a collection of three journal articles with different research questions related to tornadogenesis on the interface between tornado-scale and storm-scale dynamics. The main tool is numerical simulation with the Bryan Cloud Model (CM1), configured in highly-idealized setups to focus on the specific research question. The first article is motivated by recent studies which suggest that all supercells have vertical vorticity maxima which could be intensified to tornado strength, but that the presence of a robust and strong low-level mesocyclone is the critical factor deciding about tornadogenesis success. To test this conclusion, the relative importance of vertical vorticity generation in the cold pool to the intensification by the low-level updraft is systematically evaluated in CM1. It is found that small changes in both of these parameters can cause a bifurcation between the tornadic and nontornadic cases, demonstrating the nonlinearity of tornadogenesis. The relative importance of the updraft and cold pool intensities depends on the position within the 2D spectrum spanned by the two parameters, with e.g., intensification of the updraft being most important in the moderate cold pool strength range. In the second article, the vorticity dynamics during tornadogenesis is more formally investigated to answer the question of what mechanism is responsible for large near-ground vertical vorticity in parcels during and after tornadogenesis. The simulations suggest that pre-tornadic vortex patches are predominantly generated by downdrafts (downdraft mechanism) but that once a corner flow has formed in a tornado, abrupt tilting of near-ground horizontal vorticity into the vertical begins to dominate (in-and-up mechanism). This result unifies the extant literature, in which both mechanisms have been shown to be important, depending on when the vorticity maximum was analyzed. The third study seeks to better understand why supercell-external factors such as other storms or airmass boundaries frequently seem to instigate tornadogenesis, a notion which is shown to be consistent with a statistical analysis of radar data of 136 supercell tornadoes. In the CM1 simulations, a longer residence time of vorticity maxima in the updraft region is favorable for tornado formation. The residence time is largely controlled by the near-ground flow speed of the supercell outflow relative to the updraft. In cases in which external outflow impacts but not undercuts the supercell from the southwest, the high pressure perturbation within and ahead of the external outflow can decelerate the updraft-relative flow, and hence serve as a catalyst for tornadogenesis. The results of the three studies are combined to form an updated conceptual model of tornadogenesis, which takes both the tornado-scale and storm-scale processes into account.","abstract_has_math":false,"creators":["Fischer, Jannick"],"institution":"Texas Tech University","degree_name":"Doctor of Philosophy","degree_level":"Doctoral","degree_discipline":"Atmospheric Science","degree_department":null,"school":null,"contributors":[],"advisors":[],"committee_chairs":["Dahl, Johannes"],"committee_members":["Bruning, Eric","Parker, Matthew","Weiss, Christopher"],"year":2022,"date_issued":"2022-08","date_published":"2022-08","updated_at":"2026-07-24T05:04:51Z","subjects":["Tornado","Supercell","Tornadogenesis","Thunderstorm","Parcels","Trajectories","Simulation","Radar","Fluid Dynamics"],"languages":["eng"],"rights":[],"rights_urls":[],"identifier_entries":[]},"links":{"outbound_url":"https://hdl.handle.net/2346/90007","outbound_label":"Handle","outbound_source":"dc:identifier.uri"},"metadata_groups":[{"id":"people","label":"People","entries":[{"key":"dc:contributor.committeechair","label":"Committee Chair","values":["Dahl, Johannes"]},{"key":"dc:contributor.committeemember","label":"Committee Member","values":["Bruning, Eric","Parker, Matthew","Weiss, Christopher"]},{"key":"dc:creator","label":"Author","values":["Fischer, Jannick"]}]},{"id":"academic_context","label":"Academic Context","entries":[{"key":"dc:date.accessioned","label":"Dc Date Accessioned","values":["2022-08-25T20:02:51Z"]},{"key":"dc:date.available","label":"Dc Date Available","values":["2022-08-25T20:02:51Z"]},{"key":"dc:date.issued","label":"Date","values":["2022-08"]},{"key":"dc:type","label":"Dc Type","values":["Dissertation"]},{"key":"thesis:degree_discipline","label":"Discipline","values":["Atmospheric Science"]},{"key":"thesis:degree_level","label":"Degree Level","values":["Doctoral"]},{"key":"thesis:degree_name","label":"Degree Name","values":["Doctor of Philosophy"]},{"key":"thesis:institution_name","label":"Thesis Institution Name","values":["Texas Tech University"]}]},{"id":"subjects_keywords","label":"Subjects and Keywords","entries":[{"key":"dc:subject","label":"Dc Subject","values":["Tornado","Supercell","Tornadogenesis","Thunderstorm","Parcels","Trajectories","Simulation","Radar","Fluid Dynamics"]}]},{"id":"language_rights","label":"Language and Rights","entries":[{"key":"dc:language.iso","label":"Language (ISO)","values":["eng"]}]},{"id":"identifiers","label":"Identifiers","entries":[{"key":"dc:identifier.uri","label":"Identifier URI","values":["https://hdl.handle.net/2346/90007"]}]},{"id":"additional","label":"Additional Metadata","entries":[{"key":"dc:description.abstract","label":"Abstract","values":["Research over the last decades has resulted in a robust understanding of many aspects of tornadoes, such as the environmental conditions necessary for storms with tornado potential and the complex dynamics of mature tornadoes. However, the detailed processes during tornadogenesis are still less understood. One reason for this might be the difficulty to investigate the complex interactions of the tornado-scale and the storm-scale processes. A deeper understanding of these dynamics during tornadogenesis seems necessary to better predict which storm in an environment with tornado potential will produce a tornado, which is arguably one of the largest challenges for operational tornado warnings. This dissertation presents a collection of three journal articles with different research questions related to tornadogenesis on the interface between tornado-scale and storm-scale dynamics. The main tool is numerical simulation with the Bryan Cloud Model (CM1), configured in highly-idealized setups to focus on the specific research question. The first article is motivated by recent studies which suggest that all supercells have vertical vorticity maxima which could be intensified to tornado strength, but that the presence of a robust and strong low-level mesocyclone is the critical factor deciding about tornadogenesis success. To test this conclusion, the relative importance of vertical vorticity generation in the cold pool to the intensification by the low-level updraft is systematically evaluated in CM1. It is found that small changes in both of these parameters can cause a bifurcation between the tornadic and nontornadic cases, demonstrating the nonlinearity of tornadogenesis. The relative importance of the updraft and cold pool intensities depends on the position within the 2D spectrum spanned by the two parameters, with e.g., intensification of the updraft being most important in the moderate cold pool strength range. In the second article, the vorticity dynamics during tornadogenesis is more formally investigated to answer the question of what mechanism is responsible for large near-ground vertical vorticity in parcels during and after tornadogenesis. The simulations suggest that pre-tornadic vortex patches are predominantly generated by downdrafts (downdraft mechanism) but that once a corner flow has formed in a tornado, abrupt tilting of near-ground horizontal vorticity into the vertical begins to dominate (in-and-up mechanism). This result unifies the extant literature, in which both mechanisms have been shown to be important, depending on when the vorticity maximum was analyzed. The third study seeks to better understand why supercell-external factors such as other storms or airmass boundaries frequently seem to instigate tornadogenesis, a notion which is shown to be consistent with a statistical analysis of radar data of 136 supercell tornadoes. In the CM1 simulations, a longer residence time of vorticity maxima in the updraft region is favorable for tornado formation. The residence time is largely controlled by the near-ground flow speed of the supercell outflow relative to the updraft. In cases in which external outflow impacts but not undercuts the supercell from the southwest, the high pressure perturbation within and ahead of the external outflow can decelerate the updraft-relative flow, and hence serve as a catalyst for tornadogenesis. The results of the three studies are combined to form an updated conceptual model of tornadogenesis, which takes both the tornado-scale and storm-scale processes into account."]},{"key":"dc:format.mimetype","label":"Dc Format Mimetype","values":["application/pdf"]},{"key":"dc:title","label":"Title","values":["Insights into tornadogenesis and tornado dynamics from idealized simulations"]}]}],"canonical_facts":{"dc:contributor.committeechair":["Dahl, Johannes"],"dc:contributor.committeemember":["Bruning, Eric","Parker, Matthew","Weiss, Christopher"],"dc:creator":["Fischer, Jannick"],"dc:date.accessioned":["2022-08-25T20:02:51Z"],"dc:date.available":["2022-08-25T20:02:51Z"],"dc:date.issued":["2022-08"],"dc:description.abstract":["Research over the last decades has resulted in a robust understanding of many aspects of tornadoes, such as the environmental conditions necessary for storms with tornado potential and the complex dynamics of mature tornadoes. However, the detailed processes during tornadogenesis are still less understood. One reason for this might be the difficulty to investigate the complex interactions of the tornado-scale and the storm-scale processes. A deeper understanding of these dynamics during tornadogenesis seems necessary to better predict which storm in an environment with tornado potential will produce a tornado, which is arguably one of the largest challenges for operational tornado warnings. This dissertation presents a collection of three journal articles with different research questions related to tornadogenesis on the interface between tornado-scale and storm-scale dynamics. The main tool is numerical simulation with the Bryan Cloud Model (CM1), configured in highly-idealized setups to focus on the specific research question. The first article is motivated by recent studies which suggest that all supercells have vertical vorticity maxima which could be intensified to tornado strength, but that the presence of a robust and strong low-level mesocyclone is the critical factor deciding about tornadogenesis success. To test this conclusion, the relative importance of vertical vorticity generation in the cold pool to the intensification by the low-level updraft is systematically evaluated in CM1. It is found that small changes in both of these parameters can cause a bifurcation between the tornadic and nontornadic cases, demonstrating the nonlinearity of tornadogenesis. The relative importance of the updraft and cold pool intensities depends on the position within the 2D spectrum spanned by the two parameters, with e.g., intensification of the updraft being most important in the moderate cold pool strength range. In the second article, the vorticity dynamics during tornadogenesis is more formally investigated to answer the question of what mechanism is responsible for large near-ground vertical vorticity in parcels during and after tornadogenesis. The simulations suggest that pre-tornadic vortex patches are predominantly generated by downdrafts (downdraft mechanism) but that once a corner flow has formed in a tornado, abrupt tilting of near-ground horizontal vorticity into the vertical begins to dominate (in-and-up mechanism). This result unifies the extant literature, in which both mechanisms have been shown to be important, depending on when the vorticity maximum was analyzed. The third study seeks to better understand why supercell-external factors such as other storms or airmass boundaries frequently seem to instigate tornadogenesis, a notion which is shown to be consistent with a statistical analysis of radar data of 136 supercell tornadoes. In the CM1 simulations, a longer residence time of vorticity maxima in the updraft region is favorable for tornado formation. The residence time is largely controlled by the near-ground flow speed of the supercell outflow relative to the updraft. In cases in which external outflow impacts but not undercuts the supercell from the southwest, the high pressure perturbation within and ahead of the external outflow can decelerate the updraft-relative flow, and hence serve as a catalyst for tornadogenesis. The results of the three studies are combined to form an updated conceptual model of tornadogenesis, which takes both the tornado-scale and storm-scale processes into account."],"dc:format.mimetype":["application/pdf"],"dc:identifier.uri":["https://hdl.handle.net/2346/90007"],"dc:language.iso":["eng"],"dc:subject":["Tornado","Supercell","Tornadogenesis","Thunderstorm","Parcels","Trajectories","Simulation","Radar","Fluid Dynamics"],"dc:title":["Insights into tornadogenesis and tornado dynamics from idealized simulations"],"dc:type":["Dissertation"],"thesis:degree_discipline":["Atmospheric Science"],"thesis:degree_level":["Doctoral"],"thesis:degree_name":["Doctor of Philosophy"],"thesis:institution_name":["Texas Tech University"]},"updated_at":"2026-07-24T05:04:51Z"}