Relationships between patterns of SLP and U.S. drought over the past several centuries

Owing to the limited length of the instrumental climate record, a number of important questions regarding the factors governing changes in continental precipitation and drought variations remain unanswered. In what ways do the temporal and spatial patterns of US drought change over time? To what degree are those patterns linked with larger-scale atmospheric circulation changes? What is the relative importance of climate variability in various regions of the tropics and extratropics in determining patterns of conterminous U.S. drought? It is the goal of this dissertation to address such questions by extending the temporal duration of the relevant climate records through application of a climate field reconstruction ("CFR") approach to longer-term "proxy" climate records. This approach is applied to the reconstruction of seasonal global Sea Level Pressure (SLP) (which is used to infer large-scale atmospheric circulation changes) and conterminous U.S. summer drought over the past three centuries.; A multivariate signal detection approach ("MTM-SVD") is applied, first, to the shorter available instrumental climate record, and then to the longer-term reconstructions, to investigate the evidence and robustness of oscillatory coupled patterns of drought and SLP variability over the past three centuries. These analyses indicate that the El Nino/Southern Oscillation (ENSO) has been a robust interannual climate signal influencing conterminous U.S. summer drought over the past three centuries. A particularly close connection is established between drought variability in the southwestern and south central United States over the past three centuries. The ENSO signal appears to have weakened in amplitude during the early and mid 19th century. A quasidecadal (10-11 year period) oscillatory signal in cold-season SLP that has been detected in other previous studies is found to represent a low-frequency component of ENSO, with similar influences on conterminous U.S. drought. Finally, we find long-term evidence to support the existence of a roughly bidecadal climate signal tied to warm-season SLP anomalies. Consistent with modeling studies of the 20th century variations in U.S. drought, this signal is found to influence drought of the U.S. primarily through a long-term modulation in the strength of the boreal summer Bermuda high pressure system.