The Dynamics And Predictability Of Major Hurricanes: Influences Of Initial Condition Uncertainty And Model Error Explored Using Ensemble Data Assimilation
Open Access
- Author:
- Nystrom, Robert Glenn
- Graduate Program:
- Meteorology and Atmospheric Science
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- June 05, 2020
- Committee Members:
- Steven J Greybush, Dissertation Advisor/Co-Advisor
Steven J Greybush, Committee Chair/Co-Chair
Eugene Edmund Clothiaux, Committee Member
Anthony Carl Didlake, Jr., Committee Member
Richard B Alley, Outside Member
Scott A Braun, Special Member
Paul Markowski, Program Head/Chair - Keywords:
- Tropical Cyclones
Ensemble Data Assimilation
Atmospheric Predictability
Air-Sea Interactions - Abstract:
- The dynamics and predictability of tropical cyclones (TCs) are systematically examined through a series of real and idealized model simulations. In particular, the relative influences of environmental and inner-core initial condition (IC) and model errors–related to horizontal resolution, coupled ocean-atmosphere interactions, and the surface-exchange coefficients of momentum and enthalpy–are examined. In addition, pathways for improved TC prediction through improved ensemble data assimilation (DA) methodologies are demonstrated. Using real-time convection-permitting ensemble simulations of Hurricane Joaquin (2015), the large real-time track and intensity forecast uncertainties are systematically dissected. It is shown that the unusually large track uncertainty was primarily the result of IC uncertainty in the near-TC steering flow and the large intensity forecast uncertainty is primarily the result of inner-core IC uncertainty. Next, the intensity prediction of the record-breaking intensification of hurricane Patricia (2015) is shown to be improved through a combination of effective ensemble DA, with assimilation of airborne radial velocity observation, increased model horizontal resolution and by the choice of the model representation of the surface-exchange coefficients. The influence of uncertainties in the model representation of the surface-exchange coefficients on simulated TC intensity are further examined through coupled ocean-atmosphere and uncoupled (atmosphere only) simulations of hurricane Patricia and it is found that the intensity forecast uncertainty is not significantly reduced through negative ocean feedbacks when uncertainty to the surface drag coefficient is considered. The influences of the surface-exchange coefficients on TC intensity are then demonstrated to be consistent with those predicted by an analytical model through a series of idealized axisymmetric TC simulations. Lastly, the opportunity to successfully estimate the model representation of the surface exchange coefficients using ensemble DA is demonstrated through a series of observing system simulation experiments (OSSEs).