Abstract
Understanding the role of climate variability in modulating the behavior of land-falling atmospheric rivers (ARs) is important for seasonal and subseasonal predictability for water resource management and flood control. We examine daily activity of ARs targeting the Northern California coast over six decades using observations of synoptic-scale circulation, high-resolution precipitation, and a long-term AR detection catalog to quantify distinct types of land-falling ARs categorized by their circulation features. We demonstrate how dramatically different atmospheric states evolve into landfalling ARs along distinct pathways that are modulated by interannual (El Niño/Southern Oscillation (ENSO) and the Pacific Decadal Oscillation) and subseasonal (Arctic Oscillation, Pacific North American Pattern, Western Pacific Oscillation, and the Eastern Pacific Oscillation) modes of large-scale climate variability. Different configurations of climate variability modes are shown to favor ARs having different characteristics in terms of synoptic evolution, integrated vapor transport and landfall orientation resulting in different patterns of precipitation over the landscape. In particular, our results show that while ENSO plays an important role in modulating the synoptic evolution of ARs and their orientation at landfall, subseasonal regional climate modes, which also influence landfall orientation as well as the position of the storm track, appear to be more influential than ENSO in modulating precipitation variability in California. This could have implications for seasonal to subseasonal (S2S) forecasting. Finally, we examine AR activity over the most recent and highly anomalous winter 2016–2017 and show how the unprecedented wet conditions in Northern California were at least partly due to the persistence of ARs characterized by a southward storm track and southerly orientation, which represent the type of ARs associated with heavy rainfall in California, and which are associated with the negative phase of subseasonal regional teleconnection patterns.
Highlights
California is home to over 38 million people and counting, an extensive agriculture industry and a large diverse economy, all relying on volatile water resources derived during the cool season and stored in mountain snowpack and engineered reservoirs
To identify links between atmospheric rivers (ARs) and large-scale climate variability modes, we used the monthly indices for El Niño/Southern Oscillation (ENSO) and the Pacific Decadal Oscillation (PDO) and daily indices for the Arctic Oscillation (AO), Pacific/ North American (PNA), Western Pacific Oscillation (WPO), and Eastern Pacific Oscillation (EPO)
ENSO does not significantly affect the frequency of AR landfalls in Northern California, it does affect landfall characteristics and so, we investigate the role of ENSO in modulating the synoptic evolution of ARs, which can result in different orientations at landfall (Fig. 4), and different precipitation patterns (Figs. 7, 8)
Summary
California is home to over 38 million people and counting, an extensive agriculture industry and a large diverse economy, all relying on volatile water resources derived during the cool season and stored in mountain snowpack and engineered reservoirs. GSR’17 examined seven decades of landfalling AR activity along the west coast of North America and described relationships between seasonal AR-related vertically integrated vapor transport (IVT) and large-scale modes of climate variability. They found strong relationships between AR activity and the Pacific Decadal Oscillation (PDO) as well as with coastal sea surface temperature (SST) anomalies representing the northeastern Pacific “blob” described by Bond et al (2015), which clearly contributed to an AR deficit in California and Oregon in winters 2013–2014 and 2014–2015 (GSR’17).
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
