New Methods In Wavelet Analysis And Their Application To The Understanding Of Hydroclimate Variability In The Mid-atlantic Region Of The United States
Open Access
- Author:
- Schulte, Justin A
- Graduate Program:
- Meteorology
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- August 19, 2015
- Committee Members:
- Raymond Gabriel Najjar Jr., Dissertation Advisor/Co-Advisor
Raymond Gabriel Najjar Jr., Committee Chair/Co-Chair
Sukyoung Lee, Committee Member
Chris Eliot Forest, Committee Member
Christopher J Duffy, Committee Member
M Ing Li, Special Member - Keywords:
- Climate
Wavelet Analysis
Hydrology
Statistics
Time Series Analysis
Estuary
Drought
Pluvial - Abstract:
- New statistical and topological methods in wavelet analysis are developed to help fully understand historical hydroclimate variability. The methods improve upon existing methods and enhance confidence in results. In particular, a geometric significance test was found to produce results similar to an existing areawise significance test while being more computationally flexible and efficient. The geometric test determined that features in wavelet power of the North Atlantic Oscillation (NAO) are indistinguishable from a red-noise background, suggesting that the NAO is a stochastic, unpredictable process, which could render difficult the future projections of the NAO under a changing global system. The geometric test did, however, identify features in the wavelet power spectrum of an El Niño index (Niño 3.4) as distinguishable from a red-noise background. A topological analysis of pointwise significance patches determined that holes, deficits in pointwise significance embedded in significance patches, are capable of identifying important structures, some of which are undetected by the geometric and areawise tests. Niño 3.4 time series contains numerous phase-coherent oscillations that could be interacting nonlinearly. Another statistical test, the cumulative areawise test, was also developed and was found to have greater statistical power than the geometric test in most cases, especially when the signal-to-noise ratio is high. The new testing procedure was applied to the time series of the Atlantic Multi-decadal Oscillation (AMO), the NAO, Pacific Decadal Oscillation (PDO), and the Niño 3.4 index and determined that the NAO, PDO, and AMO are consistent with red-noise processes, whereas significant power was found in the 2-7 year period band for the Niño 3.4 index. High-order wavelet methods were developed to understand nonlinear climate phenomenon. A local autobicoherence spectrum of the QBO time series showed that the QBO time series contained a mode with a period of 28 months that was phase-coupled to a harmonic with a period of 14 months. An additional nonlinearly interacting triad was found among modes with periods of 10, 16, and 26 months. The oscillations were found to be skewed so that negative QBO regimes were preferred, and also asymmetric in the sense that phase transitions between the easterly and westerly phases occurred more rapidly than those from westerly to easterly regimes. The developed methods were applied to Mid-Atlantic region hydroclimatic time series. The results from the wavelet analysis showed that 18- and 26-year periodicities were embedded in the streamflow time series of the Delaware, Hudson, and Susquehanna Rivers. Decadal variability of streamflow was coherent with the El-Niño/Southern Oscillation and the PDO. The Southern Oscillation explained 37-54% of the 1960s drought, 33-49% of the 1970s pluvial, and 19-50% of the 2000s pluvial in the three river basins. A composite analysis with meteorological data determined that the anomalously high daily streamflow events during the recent pluvial were associated with Rossby waves emanating from the tropics and sea-level pressure (SLP) dipole pattern over eastern North America (ENA). A new ENA SLP dipole index was constructed, which could explain more daily streamflow variance than the existing climate indices. iv The ENA dipole index was also found to be phase-locked to the Gulf Stream Index at a period of 74 months so that salinity variability at that timescale may have resulted from ENA dipole-related changes in precipitation.