Physical Sciences and Mathematics Commons^™

Examining The Impact Of Synoptic-Scale Waves On Stratospheric Polar Vortex Variability From An Ensemble Forecast Perspective, Michael E. Main

Legacy Theses & Dissertations (2009 - 2024)

Major Sudden Stratospheric Warming (SSW) events are characterized by rapid warming of the polar regions at 10 hPa and are accompanied by a reversal of the 10-hPa zonal-mean zonal wind at 60˚N from westerly to easterly. Following an SSW event, stratospheric thermal and momentum anomalies can progress downward and linger near the tropopause for up to 60 days. These anomalies have major impacts on tropospheric sensible weather including increased likelihood of cold air outbreaks and heavy precipitation events. SSW events are largely forced by upward propagation of planetary-scale Rossby waves from the troposphere to the stratosphere. Synoptic-scale waves can contribute …

Antecedent North Pacific Jet Regimes Conducive To The Development Of Cool Season Continental U.S. Tornado Outbreaks, Jessica Blair

Atmospheric & Environmental Sciences

The occurrence of tornado outbreaks are often associated with considerable societal and economic impacts. The U.S. averages nearly 1000 tornadoes per year that result in 1500 injuries and 80 fatalities, many of which are associated with outbreak days. Additionally, one outbreak alone can cause millions of dollars in property damage. The location of these outbreaks can vary temporally throughout the cool season (September–May) and can vary substantially in terms of their severity.

This study focuses on continental U.S. tornado outbreaks during the cool season and their relation to the state and evolution of the North Pacific jet (NPJ) stream 0–5 …

Predictability Of African Easterly Waves In An Operational Ensemble Prediction System, Travis J. Elless

Legacy Theses & Dissertations (2009 - 2024)

African easterly waves (AEWs) are the primary synoptic-scale weather feature found in sub-Saharan Africa during boreal summer. Many studies have used observations and idealized models to highlight processes associated with the movement and growth of AEWs, yet there have been few studies documenting the performance of operational ensemble prediction systems (EPSs) for these phenomena. Here, the predictability of AEWs in ECMWF EPS forecasts is assessed during two periods of enhanced AEW activity (July--September 2007--2009 and 2011--2013). Specifically, AEW predictability is analyzed through three main areas of focus: 1) verifying AEW position and intensity forecasts, and assessing their relation to convective …

Examining Variability In Model Skill During The 7 January 2013 Sudden Stratospheric Warming Event, Jonathan Lee Blufer

Legacy Theses & Dissertations (2009 - 2024)

Recent analyses of numerical weather prediction models have shown that stratospheric regime changes (e.g. strong and weak vortex events) are not skillfully predicted at medium-range lead times. Motivated by these recent analyses, this thesis investigates the sources of variability in stratospheric forecast skill amongst several operational models initiated at different lead times prior to the 7 January 2013 sudden stratospheric warming (SSW). This study extends upon a previous analysis by the Stratospheric Network for the Assessment of Predictability (SNAP), which concluded that a change in forecast lead-time from 15 to 10 days increased model skill in predicting the 2013 SSW …

Predictability And Dynamics Of Warm-Core Mesoscale Vortex Formation With The 8 May 2009 "Super Derecho" Event, Caleb Todd Grunzke

Theses and Dissertations

The predictability and dynamics of the warm-core mesovortex associated with the northern-flank of the 8 May 2009 “Super Derecho” event are examined by coupling the Advanced Research Weather Forecasting Model with the Data Assimilation Research Testbed facility. A 50-member convection-allowing EnKF ensemble was produced with 6 hourly-cycled analysis and assimilated observations. Cycled analysis started five days prior to 1200 UTC 7 May 2009, at which time the 36 h ensemble forecasts were launched.

The ensemble forecasts all attempted to produce a mesoscale convective system (MCS) but only fourteen percent produced a warm-core mesovortex-like feature similar to the intensity of the …

The Influence Of Assimilated Targeted Observations Upon Ensemble Forecasts Of Convection Initiation, Alexandra Marie Keclik

Theses and Dissertations

The influence of assimilating targeted meso-α- to synoptic-scale observations collected in the upstream, pre-convective environment upon subsequent short-range ensemble forecasts of convection initiation (CI) across the central United States for the fifteen aircraft missions conducted by the Mesoscale Predictability Experiment (MPEX) in May and June 2013 is evaluated in this study. Utilizing the ensemble Kalman filter implementation within the Data Assimilation Research Testbed software package as coupled to version 3.4.1 of the Advanced Research version of the Weather Research and Forecasting model, two nearly-identical thirty- member ensembles of short-range forecasts are conducted for each mission. Initial conditions for one ensemble …

Predictability Of Sea Ice Near Bifurcations, Dawn Marie Kopacz

Theses and Dissertations

There is evidence in Earth’s history of relatively stable climate regimes abruptly transitioning to alternative states. It has been argued that the greatest potential for such abrupt transitions in Earth’s system in the near future is located in the Arctic. Here we analyze the Arctic sea ice evolution of two current generation climate models that exhibit critical transitions. We demonstrate the detectability of two early warning signals: increased variance and increased autocorrelation. We introduce another metric that forewarns of abrupt changes in sea ice; a decrease in predictability before the threshold points. Observations of Arctic sea ice extent are searched …

Associations Between The Madden-Julian Oscillation, Equatorial Rossby Waves, And Extratropical Northern Hemisphere Predictability, Lawrence Gloeckler

Legacy Theses & Dissertations (2009 - 2024)

The Madden-Julian oscillation (MJO), the leading mode of tropical convective and circulation variability on intraseasonal time scales, has become increasingly leveraged to improve empirical prediction of the global atmospheric circulation. Significant progress has been made in recent years to advance subseasonal (10-30-day) prediction of atmospheric circulation anomalies, and much of this progress can be attributed to the inclusion of information about the phase and amplitude of the MJO in various forecast processes. Despite this progress, however, forecasts based only on the state of the MJO omit information about other important tropical convective and circulation anomalies, and coherent MJO signals are …

The Downstream Extratropical Flow Response To Recurving Western North Pacific Tropical Cyclones, Heather M. Archambault

Legacy Theses & Dissertations (2009 - 2024)

The factors that govern the downstream flow response to recurving western North Pacific (WNP) tropical cyclones (TCs) are investigated from climatological, composite analysis, case study, and predictability perspectives. A 1979–2009 climatology of WNP TC recurvature indicates that TC recurvature is followed by a four-day period of above-normal North Pacific meridional flow. The relationship between TC recurvature and above-normal North Pacific meridional flow is found to be stronger in late summer through mid-fall than in early summer and early winter, and stronger for TCs that interact strongly with the jet stream than for TCs that interact weakly with the jet stream. …