Reversal of Long-Term Trend in Baseline Ozone Concentrations at the North American West Coast

Abstract. A rigorous method is presented for determining the ozone concentration in the onshore flow of marine air at the North American west coast. By combining the data available from all marine boundary layer sites with simultaneous wind data, decadal temporal trends of MBL ozone concentrations in all seasons are established with high precision. The average springtime temporal trend over the past two decades is 0.46 ppbv/yr with a 95% confidence limit of 0.13 ppbv/yr, and statistically significant trends are found for all seasons except autumn, which does have a significantly smaller trend than other seasons. The average trend in mean annual ozone concentration is 0.34±0.09 ppbv/yr. These decadal trends at the North American west coast present a striking comparison and contrast with the trends reported for the European west coast at Mace Head, Ireland. The trends in the winter, spring and summer seasons compare well at the two locations, while the Mace Head trend is significantly greater in autumn. Even though the trends are similar, the absolute ozone concentrations differ markedly, with the marine air arriving at Europe in all seasons containing 7±2 ppbv higher ozone concentrations than marine air arriving at North America. Further, the ozone concentrations at the North American west coast show no indication for stabilizing as has been reported for Mace Head. In a larger historical context the background boundary layer ozone concentrations over the 130 years covered by available data have increased substantially (by a factor of two to three), and this increase continues at present, at least in the marine boundary layer (MBL) of the Pacific coast region of North America. The reproduction of the increasing trends in MBL ozone concentrations over the past two decades as well as the difference in the ozone concentrations between the two coastal regions will present a significant challenge for global chemical transport models. Further, the ability of the models to at least semi-quantitatively reproduce the longer-term, historical trends may an even greater challenge.

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Large-Scale Cross-Shelf Variability in Pigment Concentrations Along the North American West Coast

Primary Productivity and Biogeochemical Cycles in the Sea ◽

10.1007/978-1-4899-0762-2_68 ◽

1992 ◽

pp. 529-529

Author(s):

A. Thomas ◽

P. T. Strub

Keyword(s):

North American ◽

West Coast ◽

American West ◽

Large Scale ◽

North American West ◽

The North ◽

Pigment Concentrations

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Changes in Winter Atmospheric Rivers along the North American West Coast in CMIP5 Climate Models

Journal of Hydrometeorology ◽

10.1175/jhm-d-14-0080.1 ◽

2015 ◽

Vol 16 (1) ◽

pp. 118-128 ◽

Cited By ~ 105

Author(s):

Michael D. Warner ◽

Clifford F. Mass ◽

Eric P. Salathé

Keyword(s):

Water Vapor ◽

North American ◽

West Coast ◽

American West ◽

Climate Models ◽

Water Vapor Transport ◽

The West ◽

North American West ◽

The North ◽

Extreme Precipitation Events

Abstract Most extreme precipitation events that occur along the North American west coast are associated with winter atmospheric river (AR) events. Global climate models have sufficient resolution to simulate synoptic features associated with AR events, such as high values of vertically integrated water vapor transport (IVT) approaching the coast. From phase 5 of the Coupled Model Intercomparison Project (CMIP5), 10 simulations are used to identify changes in ARs impacting the west coast of North America between historical (1970–99) and end-of-century (2070–99) runs, using representative concentration pathway (RCP) 8.5. The most extreme ARs are identified in both time periods by the 99th percentile of IVT days along a north–south transect offshore of the coast. Integrated water vapor (IWV) and IVT are predicted to increase, while lower-tropospheric winds change little. Winter mean precipitation along the west coast increases by 11%–18% [from 4% to 6% (°C)−1], while precipitation on extreme IVT days increases by 15%–39% [from 5% to 19% (°C)−1]. The frequency of IVT days above the historical 99th percentile threshold increases as much as 290% by the end of this century.

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