Geology topics

Courtenay Strong

Publications and source records attributed to Courtenay Strong.

4 recordsLinked to original sources

USGS2023

Atlantic-Pacific influence on western U.S. hydroclimate and water resources

The El Niño Southern Oscillation (ENSO) in the tropical Pacific Ocean is an important driver of winter precipitation variability over western North America as a whole, but ENSO exhibits a weak and inconsistent relationship with precipitation in several critically important headwaters including the upper Colorado River Basin. We present interactions between North Atlantic sea surface temperatures (SSTs) and ENSO that influence western U.S. precipitation, accounting for substantial variability in areas where ENSO alone yields limited guidance. Specifically, we performed a statistical analysis on hemispheric SSTs and western U.S. winter precipitation in a century of observations and a 10,000-year perpetual current-climate simulation. In both frameworks, the leading coupled pattern is ENSO, and the second pattern links an Atlantic Quadpole Mode (AQM) of SST variability to precipitation anomalies over most of the western U.S., including the transition zone where ENSO provides little predictability. The AQM SST anomalies are expansive in latitude, but its primary mechanism appears to involve a strengthening/shifting of the intertropical convergence zone (ITCZ) over northern South America and the tropical Atlantic. The ENSO pattern accounts for a larger fraction of the total covariance between SSTs and precipitation (65% versus 12% for the AQM pattern), but the percent anomalies of precipitation associated with ENSO and the AQM are comparable in magnitude, meaning 20% or larger over much of the western U.S. The interaction between ENSO and AQM influences precipitation across the western U.S., with cold AQM generally reducing precipitation irrespective of ENSO whereas warm AQM increases the amount of precipitation and the area of influence of ENSO; knowledge of these interactions can increase predictability of western U.S. precipitation.

western United States↗

USGS2020

Step increase in eastern U.S. precipitation linked to Indian Ocean warming

A step increase in annual precipitation over the eastern U.S. in the early 1970’s commenced five decades of invigorated hydroclimate, with ongoing impacts on streamflow and water resources. Despite its far-reaching impacts, the dynamical origin of this change is unknown. Here, analyses of a century of atmospheric and oceanic data trace the dynamics to changes in the Indian Ocean. Spring and fall precipitation explain more than half the annual eastern-U.S. precipitation variance over the century, and changes in fall are predominantly responsible for the step increase. The driving mechanism is emergence of a pan-Pacific atmospheric wave emanating from deep convection over the warming Indian Ocean. Documentation of this fall teleconnection draws attention to projected anthropogenic increases in tropical oceanic heat content, and their potential impacts on hydroclimate of the midlatitudes.

Geophysical Research Letters↗

USGS2020

Climate dipoles as continental drivers of plant and animal populations

Ecological processes, such as migration and phenology, are strongly influenced by climate variability. Studying these processes often relies on associating observations of animals and plants with climate variability indices, such as the El Niño–Southern Oscillation. A characteristic of climate indices is the simultaneous emergence of opposite extremes of temperature and precipitation across continental scales, known as climate dipoles. The role of climate dipoles in shaping ecological and evolutionary processes has been largely overlooked. We review emerging evidence that climate dipoles can entrain species dynamics, and offer a framework for identifying ecological dipoles using broad-scale biological data. Given future changes in climatic and atmospheric processes, climate and ecological dipoles will likely shift in their intensity, distribution, and timing.

Trends in Ecology and Evolution↗

USGS2017

Observed variations in U.S. frost timing linked to atmospheric circulation patterns

Several studies document lengthening of the frost-free season within the conterminous United States (U.S.) over the past century, and report trends in spring and fall frost timing that could stem from hemispheric warming. In the absence of warming, theory and case studies link anomalous frost timing to atmospheric circulation anomalies. However, recent efforts to relate a century of observed changes in U.S. frost timing to various atmospheric circulations yielded only modest correlations, leaving the relative importance of circulation and warming unclear. Here, we objectively partition the U.S. into four regions and uncover atmospheric circulations that account for 25–48% of spring and fall-frost timing. These circulations appear responsive to historical warming, and they consistently account for more frost timing variability than hemispheric or regional temperature indices. Reliable projections of future variations in growing season length depend on the fidelity of these circulation patterns in global climate models.

Nature Communications↗