Deep convection is an important component of atmospheric circulations that affects many aspects of weather and climate. Therefore, improved understanding and realistic simulations of
deep convection are critical to both operational and climate forecasts. Large-eddy simulations (LESs) often are used with observations to enhance understanding of convective processes.
This study develops and evaluates a nested-LES method using the Weather Research and Forecasting (WRF) model. Our goal is to evaluate the extent to which the WRF nested-LES approach is
useful for studying deep convection during a real-world case. The method was applied on 2 September 2013, a day of continental convection having a robust set of ground and airborne data
available for evaluation. A three domain mesoscale WRF simulation is run first. Then, the finest mesoscale output (1.35 km grid length) is used to separately drive nested-LES domains with
grid lengths of 450 and 150 m. Results reveal that the nested-LES approach reasonably simulates a broad spectrum of observations, from reflectivity distributions to vertical velocity
profiles, during the study period. However, reducing the grid spacing does not necessarily improve results for our case, with the 450 m simulation outperforming the 150 m version. We find
that simulated updrafts in the 150 m simulation are too narrow to overcome the negative effects of entrainment, thereby generating convection that is weaker than observed. Increasing the
sub-grid mixing length in the 150 m simulation leads to deeper, more realistic convection, but comes at the expense of delaying the onset of the convection. Overall, results show that both
the 450 m and 150 m simulations are influenced considerably by the choice of sub-grid mixing length used in the LES turbulence closure. Finally, the simulations and observations are used
to study the processes forcing strong midlevel cloud-edge downdrafts that were observed on 2 September. Results suggest that these downdrafts are forced by evaporative cooling due to
mixing near cloud edge and by vertical perturbation pressure gradient forces acting to restore mass continuity around neighboring updrafts. We conclude that the WRF nested-LES approach
provides an effective method for studying deep convection for our real-world case. The method can be used to provide insight into physical processes that are important to understanding
observations. The WRF nested-LES approach could be adapted for other case studies in which high-resolution observations are available for validation. / A Dissertation submitted to the Department of Earth, Ocean and Atmospheric Science in partial fulfillment of the requirements for the degree of Doctor of
Philosophy. / Fall Semester 2015. / November 10, 2015. / convective dynamics, deep convection, large-eddy simulation, WRF / Includes bibliographical references. / Henry E. Fuelberg, Professor Directing Dissertation; Ingo Wiedenhoever, University Representative; Robert E. Hart, Committee Member; Mark A. Bourassa,
Committee Member; Vasu Misra, Committee Member; Francis J. Turk, Committee Member.
| Identifer | oai:union.ndltd.org:fsu.edu/oai:fsu.digital.flvc.org:fsu_291298 |
| Contributors | Heath, Nicholas Kyle (authoraut), Fuelberg, Henry E. (professor directing dissertation), Wiedenhöver, Ingo, 1966- (university representative), Hart, Robert E. (Robert Edward), 1972- (committee member), Bourassa, Mark Allan, 1962- (committee member), Misra, Vasubandhu, 1970- (committee member), Turk, Francis J. (committee member), Florida State University (degree granting institution), College of Arts and Sciences (degree granting college), Department of Earth, Ocean, and Atmospheric Science (degree granting department) |
| Publisher | Florida State University |
| Source Sets | Florida State University |
| Language | English, English |
| Detected Language | English |
| Type | Text, text |
| Format | 1 online resource (109 pages), computer, application/pdf |
Page generated in 0.0023 seconds