Climate Variability of Atmospheric Rivers and Droughts over the West Coast of the United States from 2006 to 2019

Paul R Zechiel,Sen Chiao

doi:10.3390/atmos12020201

Paul R Zechiel, Sen Chiao

Open Access

https://doi.org/10.3390/atmos12020201

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Journal: Atmosphere	Publication Date: Feb 3, 2021
Citations: 6	License type: CC BY 4.0

Affiliation: San Jose State University

Abstract

Water resources are crucial to the livelihood and sustainability of the general public across the western United States. This study covers the timespan of both the third driest drought in Californian history between 2012 and 2015 as well as the extreme atmospheric river year in 2016–2017. The evaluation of vertical moisture profiles using Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) Radio Occultation (RO) data, National Centers for Environmental Prediction (NCEP)/National Center for Atmospheric Research (NCAR) Reanalysis of 500 hPa geopotential heights, 1000–500 hPa thickness, Optimum Interpolation (OI) Sea Surface Temperature (SST), NOAA/NDBC buoy data, and NASA, MEaSUREs, Gridded Sea Surface Height Anomalies (SSHA) were performed. The daily COSMIC time evolution from 2006 through 2015 showed a flat to slightly upward trend of both temperature and water vapor profiles through the entirety of the western US drought. Subsequently, a significant increase of temperatures and water vapor were recorded in early 2016 before the extreme Atmospheric River (AR) season of 2016–2017. The quantitative analyses suggest that warmer SST and higher SSHA lead to an increase of heat fluxes from the ocean into the troposphere, which forces thickness changes and thus the position of troughs in the geopotential height field changes afterwards, consequently pushing the trough eastward over the Pacific Northwest and potentially leading to an active AR year in the western US. It appears that regional COSMIC RO moisture profiles, seasonal SST, and SLH anomalies may serve as a precursor for seasonal or sub-seasonal precipitation outlook along the western US.

Highlights

Atmospheric Rivers (ARs) are responsible for over 90% of the poleward water vapor transport, while only covering about 10% of the global longitudinal area (Neiman et al.2008b; Rutz et al 2014) [1,2]
Regional reanalysis of geopotential height, 1000–500 hPa thickness, sea surface height anomalies, sea surface temperature, and COSMIC moisture and temperature profiles were evaluated in this study from 2006 to 2019
This study was designed to evaluate the COSMIC data and how it can be used to improve our current understanding of AR occurrence along the west coast

Summary

Introduction

Atmospheric Rivers (ARs) are responsible for over 90% of the poleward water vapor transport, while only covering about 10% of the global longitudinal area (Neiman et al.2008b; Rutz et al 2014) [1,2]. Atmospheric River events are an essential source of moisture and precipitation that are observed along the west coast and are a key factor in the prevalence of droughts and floods. Water resources are critical issues that California is facing today and will continue to face amidst the threat of global climate change. Global environmental changes have potentially increased flooding threats along the western United States after multi-year droughts (Dettinger 2011) [4]. Considering the ability to end droughts and the geographic disparity of California’s resources, understanding the strength and climatology of ARs and their impact on the west coast is essential for water management, reservoir operations, and the mitigation of flood risks

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