Benjamin J. Hatchett

Placing the 2012–2015 California-Nevada drought into a paleoclimatic context: Insights from Walker Lake, California-Nevada, USA

Assessing regional hydrologic responses to past climate changes can offer a guide for how water resources might respond to ongoing and future climate change. Here we employed a coupled water balance and lake evaporation model to examine Walker Lake behaviors during the Medieval Climate Anomaly (MCA), a time of documented hydroclimatic extremes. Together, a 14C-based shoreline elevation chronology, submerged subfossil tree stumps in the West Walker River, and regional paleoproxy evidence indicate a ~50 year pluvial episode that bridged two 140+ year droughts. We developed estimates of MCA climates to examine the transient lake behavior and evaluate watershed responses to climate change. Our findings suggest the importance of decadal climate persistence to elicit large lake-level fluctuations. We also simulated the current 2012–2015 California-Nevada drought and found that the current drought exceeds MCA droughts in mean severity but not duration.

Avalanche Fatalities during Atmospheric River Events in the Western United States

AbstractThe occurrence of atmospheric rivers (ARs) in association with avalanche fatalities is evaluated in the conterminous western United States between 1998 and 2014 using archived avalanche reports, atmospheric reanalysis products, an existing AR catalog, and weather station observations. AR conditions were present during or preceding 105 unique avalanche incidents resulting in 123 fatalities, thus comprising 31% of western U.S. avalanche fatalities. Coastal snow avalanche climates had the highest percentage of avalanche fatalities coinciding with AR conditions (31%–65%), followed by intermountain (25%–46%) and continental snow avalanche climates (<25%). Ratios of avalanche deaths during AR conditions to total AR days increased with distance from the coast. Frequent heavy to extreme precipitation (85th–99th percentile) during ARs favored critical snowpack loading rates with mean snow water equivalent increases of 46 mm. Results demonstrate that there exists regional consistency between snow avalanche ...

Characteristics of Sundowner winds near Santa Barbara, CA from a dynamically downscaled climatology. Part I: Environment and effects near the surface

Abstract Sundowners are downslope windstorms that occur over the southern slopes of the east–west-trending Santa Ynez range in Santa Barbara County, California. In the past, many extreme fires in the area, including the Painted Cave, Montecito Tea, Jesusita, and Sherpa fires, have occurred during sundowner events. A high-resolution 11-yr dynamically downscaled climatology was produced using a numerical weather prediction model in order to elucidate the general dynamical characteristics of sundowners. The downscaled climatology is validated with observations during the 2016 Sherpa fire. A sundowner index (SI) is computed from the climatology that quantifies the magnitude of adiabatic warming and northerly (downslope) wind component during sundowner events. The SI allows for the classification of historical events into categories of various strengths. The primary characteristics of strong sundowners from this classification include 1) internal gravity wave breaking over the Santa Ynez range, 2) initiation i...

Exploring the Origins of Snow Drought in the Northern Sierra Nevada, California

AbstractThe concept of snow drought is gaining widespread interest as the climate of snow-dominated mountain watersheds continues to change. Warm snow drought is defined as above- or near-average a...

Fingerprints of the thermal equator

© 2018 Macmillan Publishers Limited, part of Springer Nature. All rights reserved. unique in its spatial collocation with a massive pile of subducted lithosphere. Ying Zhou’s3 observations are thus intriguing because they suggest the existence of a semi-deep upwelling within a deep subduction setting. Her proposed explanation, of passive, wet mantle upwelling in reaction to sudden slab foundering, opens a window to explain surficial plume indicators and will hopefully motivate the broader geoscience disciplines to reconsider the physical source mechanism of Yellowstone volcanism. ❐ Karin Sigloch Department of Earth Sciences, University of Oxford, Oxford, UK. e-mail: karin.sigloch@earth.ox.ac.uk

A 22-Year Climatology of Cool Season Hourly Precipitation Thresholds Conducive to Shallow Landslides in California

AbstractCalifornia’s winter storms produce intense rainfall capable of triggering shallow landslides, threatening lives and infrastructure. This study explores where hourly rainfall in the state me...

The Record Los Angeles Heat Event of September 2010: 1. Synoptic‐Scale‐Meso‐β‐Scale Analyses of Interactive Planetary Wave Breaking, Terrain‐ and Coastal‐Induced Circulations

On 27 September 2010 the Los Angeles Civic Center reached its all-time record maximum temperature of 45 °C before 1330 LDT with several other regional stations observing all-time record breaking heat early in that afternoon. This record event is associated with a general circulation pattern predisposed to hemispheric wave breaking. Three days before the event, wave breaking organizes complex terrain and coastal-induced processes that lead to isentropic surface folding into the Los Angeles Basin. The first wave break occurs over the western two-thirds of North America leading to trough elongation across the southwestern U.S. Collocated with this trough is an isentropic potential vorticity filament that is the locus of a thermally indirect circulation central to warming and associated thickness increases and ridging westward across the Great Basin. In response to this circulation, two subsynoptic wave breaks are triggered along the Pacific Coast and the IPV filament is coupled to the breaking waves and the interaction produces a subsynoptic low pressure center and a deep vortex aloft over the southeastern California desert. This coupling leads to advection of an elevated mixed layer over Point Conception the night before the record-breaking heat that creates a coastally trapped low pressure area southwest of Los Angeles. The two low pressure centers create a low-level pressure gradient and east-southeasterly jet directed offshore over the Los Angeles Basin by sunrise on the 27th. This allows the advection of low-level warm air from the inland terrain towards the coastally-trapped disturbance and descending circulation resulting in record heating.

North Pacific Mesoscale Coupled Air-Ocean Simulations Compared with Observations

The overall objective of this study was to improve the representation of regional ocean circulation in the North Pacific by using high resolution atmospheric forcing that accurately represents mesoscale processes in ocean-atmosphere regional (North Pacific) model configuration. The goal was to assess the importance of accurate representation of mesoscale processes in the atmosphere and the ocean on large scale circulation. This is an important question, as mesoscale processes in the atmosphere which are resolved by the high resolution mesoscale atmospheric models such as Weather Research and Forecasting (WRF), are absent in commonly used atmospheric forcing such as CORE forcing, employed in e.g. the Community Climate System Model (CCSM).