1) Sensitivity to hydrologic whiplash in the tree-ring record of the high Sierra Nevada
Year-to-year variability of precipitation and temperature has significant consequences for water management decision making. “Whiplash” is a term which describes this variability at its most severe, referring to events at various timescales in which the hydroclimate switches between extremes. Tree-rings in semi-arid environments like the Northern Sierra Nevada, including Truckee-Carson River Basins in California/Nevada) can provide proxy records of hydroclimate as their annual growth is tied directly to limitations in water-year rainfall and temperature. In this study, a pool of total ring width indices from five snow-adapted conifer species (Abies magnifica, Juniperus occidentalis, Pinus ponderosa, Pinus jeffreyi, Tsuga mertensiana) were used to develop a series of standardized reconstructions of annualized hydroclimate phenomena using stepwise forward linear regression. A nonparametric analysis approach was then used to determine positive and negative whiplash events in reconstructed and instrumental precipitation records. Multivariate analysis of the resulting timeseries datasets illustrates relationships between reconstructions and
recorded whiplash events and allows for determination of patterns in tree-ring growth response. Individualized species response provides analytical and methodological insight for past and potential climate reconstruction using similar approaches.
2) The Cycloscope of Andrew Ellicott Douglass: Analog computing from early 20th century climate science resurrected
Over 100 years ago, Andrew Ellicott Douglass, the father of dendrochronology, sought a device for determining theperiodicity of time series data. Of particular interest to Douglass was the 11.5-year period in sunspot records, which he believed would leave its characteristic cycle in tree rings. Studying climate records from the SW United States, Douglass hypothesized that sunspot minima (when there were fewer cool spots on the surface of the sun) would increase global temperatures and intensify oceanic evaporation. This would then result in more rainfall to trees in the SW. If he could trace evidence of this solar cycle in tree-rings, they could then be used as a proxy record for solar activity beyond the period during which records were kept. He dedicated his life's work to pursuing this possibility and, in the process, created the scientific discipline of dendrochronology. Before the advent of digital computing, frequency analysis through Fourier transforms and other mathematical methods was impractically time consuming, especially for the hundreds of tree ring series Douglass had amassed. In order to quickly identify specific periodicities in a time series, Douglass (with the assistance of Stanford University) designed and built several machines which he called “Cycloscopes”. The latter version, the “Merriam Cycloscope”, a brilliant and elegant opto-mechanical analog computer, still survives to this day. Although largely untouched for almost 70 years, the details of its operation and whether or not it still functioned at all, seemed lost to time. With generous permission from the Laboratory of Tree Ring Research and assistance from Dr. Charlotte Pearson, Dr. Peter Brewer, and Dr. Meg Jackson Fox from the Center for Creative Photography, we not only demonstrated its enduring functionality, but we also replicated the methodology used by Douglass over a century ago and analyzed modern tree ring chronologies for the elusive sunspot periodicity.