North Pacific atmospheric rivers and their influence on western North America at the Last Glacial Maximum

Lora, Juan M.; Mitchell, Jonathan L.; Risi, Camille; Tripati, Aradhna

doi:10.1002/2016gl071541

Cited by 131 publications

(138 citation statements)

References 54 publications

(80 reference statements)

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“…AR tracks generally follow a southwest‐to‐northeast trajectory over the Pacific (Figure a), consistent with the IVT object tracks of Sellars et al () and the path of the Pacific storm track (e.g., Lora et al, ). However, some ARs take a more meridional path, particularly those originating over the eastern tropical Pacific (example track highlighted in Figure a).…”

Section: Resultssupporting

confidence: 83%

Recent Warming of Landfalling Atmospheric Rivers Along the West Coast of the United States

et al. 2019

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Atmospheric rivers (ARs) often generate extreme precipitation, with AR temperature strongly influencing hydrologic impacts by altering the timing and magnitude of runoff. Long‐term changes in AR temperatures therefore have important implications for regional hydroclimate—especially in locations where a shift to more rain‐dominated AR precipitation could affect flood risk and/or water storage in snowpack. In this study, we provide the first climatology of AR temperature across five U.S. West Coast subregions. We then assess trends in landfalling AR temperatures for each subregion from 1980 to 2016 using three reanalysis products. We find AR warming at seasonal and monthly scales. Cool‐season warming ranges from 0.69 to 1.65 °C over the study period. We detect monthly scale warming of >2 °C, with the most widespread warming occurring in November and March. To understand the causes of AR warming, we quantify the density of AR tracks from genesis to landfall and analyze along‐track AR temperature for each month and landfall region. We investigate three possible influences on AR temperature trends at landfall: along‐track temperatures prior to landfall, background temperatures over the landfall region, and AR temperature over the coastal ocean adjacent to the region of landfall. Generally, AR temperatures at landfall more closely match coastal and background temperature trends than along‐track AR temperature trends. The seasonal asymmetry of the AR warming and the heterogeneity of influences have important implications for regional water storage and flood risk—demonstrating that changes in AR characteristics are complex and may not be directly inferred from changes in the background climate.

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Section: Resultssupporting

confidence: 83%

Recent Warming of Landfalling Atmospheric Rivers Along the West Coast of the United States

et al. 2019

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“…Strong midlatitude jets are associated with an increase in eddy kinetic energy (storminess) (Penny et al, ), which should increase mixing depths and nutrient delivery to surface waters (O'Gorman, ). However, the presence of the Laurentide Ice Sheet likely deflected (or possibly bifurcated) the westerly storm track (Bromwich et al, ; COHMAP, ; Kirby et al, ; Oba et al, ; Oster et al, ), shifting it as much as 10° latitude to the south in the middle of the North Pacific (Lora et al, ; Figure ). The more southerly storm track likely pushed this zone of storminess into the subtropical gyre, and models corroborate a net decrease in eddy kinetic energy over much of the Subarctic Pacific (Li & Battisti, ; Lora et al, ).…”

Section: Discussionmentioning

confidence: 99%

Paleoproductivity and Stratification Across the Subarctic Pacific Over Glacial‐Interglacial Cycles

Costa

McManus

Anderson

2018

Paleoceanog and Paleoclimatol

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In the Subarctic Pacific, variability in productivity on glacial‐interglacial timescales is often attributed to changes in stratification and nutrient delivery to the surface, but the mechanisms driving this relationship are poorly constrained. Records extending beyond the last glacial maximum from both the open ocean and the marginal seas are required to investigate the timing and magnitude of different influential processes through the full glacial cycle. In this study we generated 231Pa/230Th over 210,000 years in order to capture two full glacial cycles of paleoproductivity on the Juan de Fuca Ridge in the East Subarctic Pacific. The sedimentary 231Pa/230Th ratios are always equal to or greater than the seawater production ratio (0.093), consistent with enhanced biological scavenging in this region. The temporal pattern of 231Pa/230Th burial is remarkably coherent with changes in climate, with high values (0.20) during peak interglacial periods descending to low values (0.10) during peak glacial conditions, consistent with other long productivity records from this region. We investigate the possible contributions of temperature, sea ice formation, Bering Strait closure, wind strength, upwelling, and subsurface nutrient concentrations as possible mechanisms by which physical and/or chemical stratification emerged during glacial periods. Due to the low sea surface salinity in the North Pacific, cooling actually weakens the density gradient in surface (0–200 m) waters. To create the steep density profiles that characterize physical stratification, additional processes to reduce the salinity of surface waters must occur during glacial periods. We suggest that regional sea ice formation and Bering Strait closure may have contributed to freshening surface waters and enhancing physical stratification during glacial periods. Additionally, simulated weak winds in this region due to the southward shift of the glacial westerlies may have further reduced surface mixing depths in the Subarctic Pacific. Finally, previous model simulations suggest strong glacial wind stress curl in the Subarctic Pacific, but enhanced Ekman divergence of nutrient‐poor subsurface waters would have little impact on stimulating productivity in surface waters of the Subarctic Pacific. We therefore suggest that the combined effects of surface freshening, weak winds, and lower subsurface nutrient concentrations may all have contributed to lower productivity during glacial periods in the Subarctic Pacific.

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“…This gives rise to a meridionally split jet [e.g., Kutzbach and Wright, 1985;Manabe and Broccoli, 1985;Bartlein et al, 1998;Bromwich et al, 2004;Löverström et al, 2014;Lora et al, 2016] with a comparatively weak northern flow branch and a considerably stronger branch to the south of the LIS margin [Lora et al, 2016, Figure 3a]. The preference for the southern flow branch is also indicated by proxy records as an equatorward displacement of the large-scale precipitation patterns in western North America [e.g., Whitlock and Bartlein, 1997;Asmerom et al, 2010;Wagner et al, 2010;Ibarra et al, 2014;Oster et al, 2015;Lora et al, 2017]. Why the southern flow branch is preferred remains largely unexplored but has been proposed to be related to changes in the North Pacific sea surface temperature field and the strong meridional temperature gradients at the southern margin of the ice sheet Löfverström and Liakka, 2016].…”

Section: Large-scale Circulation Changesmentioning

confidence: 99%

Abrupt regime shifts in the North Atlantic atmospheric circulation over the last deglaciation

Löfverström

Lora

2017

Geophysical Research Letters

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We analyze modeling results of the North Atlantic atmospheric winter circulation from a transient climate simulation over the last 21,000 years. In agreement with previous studies, we find that the midlatitude jet stream assumes a strong, stable, and zonal disposition so long as the North American ice sheets remain in their continent‐wide Last Glacial Maximum (LGM) configuration. However, when the Laurentide ice sheet (LIS) and Cordilleran ice sheet separate (∼14,000 years ago), the jet stream abruptly changes to a tilted circulation regime, similar to modern. The proposed explanation is that the dominant stationary wave source in the North Atlantic sector changes from the LIS to the Cordilleran mountain range during the saddle collapse. As long as the LIS dominates, the circulation retains the zonal LGM state characterized by prevalent stationary wave reflection in the subtropical North Atlantic. When the Cordillera takes over, the circulation acquires its modern disposition with a weak and meridionally tilted jet stream and storm track.

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North Pacific atmospheric rivers and their influence on western North America at the Last Glacial Maximum

Cited by 131 publications

References 54 publications

Recent Warming of Landfalling Atmospheric Rivers Along the West Coast of the United States

Recent Warming of Landfalling Atmospheric Rivers Along the West Coast of the United States

Paleoproductivity and Stratification Across the Subarctic Pacific Over Glacial‐Interglacial Cycles

Abrupt regime shifts in the North Atlantic atmospheric circulation over the last deglaciation

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