I hypothesize that the correlation coefficients between IPW and Td will be greatest when using seasonal mean averages of IPW and Td, and they will decrease with shortened mean timescales (from seasonal to three-days). Second, I hypothesize that there is a unique relationship between IPW/Td that may signal monsoon onset. To conduct this study, I used the North American Regional Reanalysis (NARR) dataset (1979-2015). For ten locations in the Southwest, I conducted a series of statistical analyses between IPW, Td, and accumulated precipitation. I determined that there is a correlation between the two as set forth by Reitan (1963) as well as (Benwell 1965; Smith 1966; Ojo 1970). However, from the results I concluded this relationship is highly variable, spatially and temporally. Additionally, when comparing the three-hour, three-day, and the weekly mean measurements, I can conclude that, for my study, timescale averaging did enhance the IPW/Td relationship from three-hour to weekly as expected. The temporal and spatial evolution of the IPW/Td correlation as presented in this thesis may provide a framework for future research that reevaluates the NAM’s domain and the associated methods for determining its onset.
This study explores long-term deviations from wind averages, specifically near the surface across central North America and adjoining oceans (25°–50°N, 60°–130°W) for 1979–2012 (408 months) by utilizing the North American Regional Reanalysis 10-m wind climate datasets. Regions where periods of anomalous wind speeds were observed (i.e., 1 standard deviation below/above both the long-term mean annual and mean monthly wind speeds at each grid point) were identified. These two climatic extremes were classified as wind lulls (WLs; below) or wind blows (WBs; above). Major findings for the North American study domain indicate that 1) mean annual wind speeds range from 1–3 m s-1 (Intermountain West) to over 7 m s-1 (offshore the East and West Coasts), 2) mean durations for WLs and WBs are high for much of the southeastern United States and for the open waters of the North Atlantic Ocean, respectively, 3) the longest WL/WB episodes for the majority of locations have historically not exceeded 5 months, 4) WLs and WBs are most common during June and October, respectively, for the upper Midwest, 5) WLs are least frequent over the southwestern United States during the North American monsoon, and 6) no significant anomalous wind trends exist over land or sea.
The influence of the Atlantic Multidecadal Oscillation (AMO) produces pronounced regional variability in drought over the Caribbean, Central America and equatorial South America area. Through spatial statistical analyses, we identified a marked dichotomy between drought values of the Standardized Precipitation Evapotranspiration Index (SPEI) in northern Mexico and equatorial South America as a function of the AMO. The relationship is such that significant negative correlations between the drought index and phase of the AMO are identified for northern Mexico and on the Atlantic side of Central America. This indicates that drought (negative values of the SPEI) episodes are linked to the positive phase of the AMO. Alternately, there are high positive correlations between the AMO and on the Pacific side of Central America, the Caribbean and mainly in the northern South American area closest to the equator. Although many potential causes have been proposed in explanation of precipitation variability over the region, this geographic dichotomy suggests that movement of the Intertropical Convergence Zone (ITCZ) may play a significance role. The heightened vulnerability of the developing nations in this region to drought episodes makes forecasting droughts of great importance. These nations are greatly dependent on water intensive industries to maintain economic development. Thus, the findings of this research can assist in informing drought preparedness strategies to mitigate significant losses due to drought.