Comparison of Boundary Layer and Upstream Trough Uncertainty on Atmospheric River and Waveguide Perturbation Forecasts
Abstract
Atmospheric Rivers (ARs) are responsible for the majority of poleward water vapor transport into the midlatitudes as well as a substantial fraction of heavy precipitation events in many parts of the world. These features are typically located ahead of a cold front of an extratropical cyclone, and often in conjunction with warm conveyor belt in the cyclone#s warm sector, which are associated with substantial latent heat release and perturbations to the upper-tropospheric waveguide due to large upper-tropospheric divergence. Previous studies have suggested that downstream waveguide forecasts are sensitive to both the properties of the AR and to the structure of the upstream waveguide, but it is not clear which aspect is more important for accurately predicting downstream forecasts. The goal of this proposal is to evaluate the extent to which downstream waveguide forecasts are sensitive to the lower tropospheric AR properties vs. the upstream waveguide using a combination of ensemble Model for Prediction Across Scales (MPAS) forecasts and advanced diagnostics. During the first phase of this work, we will build upon lessons learned during the Atmospheric River Reconnaissance program by utilizing the ensemble-based sensitivity technique with these ensemble forecasts to evaluate hypotheses on the relative sensitivity of downstream forecasts to both upper and lower tropospheric features. In addition, we will evaluate the extent to which the upstream upper tropospheric uncertainty influences the AR and subsequently creates variability in the waveguide. Once the sensitive regions are identified, we will carry out a series of perturbed initial conditions experiments whereby the lower tropospheric or upper-tropospheric sensitive regions are independently perturbed and the forecasts from this forecast will be compared against the control. The differences between these forecasts will be evaluated using a process-based perspective, including heat, moisture, and potential vorticity budgets in an Eulerian and Lagrangian framework, which will elucidate how the forecast differences grow during the forecast. If years 4-5 are funded, the final aspect of this work will be to investigate how SST uncertainty influencessurface fluxes upstream and within the AR and in turn the downstream waveguide forecast. Here, we will compare our control ensemble forecasts whereby each ensemble member has the same SST with a second set of ensemble forecasts where each member has variability in the SST that is consistent with the uncertainty in SST. We hypothesize that the forecasts with SST uncertainty will have greatervariability in surface fluxes, AR properties and hence downstream waveguide variability. The outcome of this project is a better understanding of what processes govern the evolution of Atmospheric Rivers, which are associated with extreme precipitation and winds, and can be a source of large variability into the midlatitude waveguide, resulting in uncertain high impact weather forecasts downstream, which will benefit global U. S. Navy operations. Approved for public release.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Apr 10, 2025
- Source ID
- N000142512209
Entities
People
- Ryan Torn
Organizations
- Office of Naval Research
- Research Foundation for the State University of New York
- United States Navy