Atmospheric Blocking and Other Large‐Scale Precursor Patterns of Landfalling Atmospheric Rivers in the North Pacific: A CESM2 Study

Benedict, James J.; Clement, A. C.; Medeiros, Brian

doi:10.1029/2019jd030790

Cited by 32 publications

(31 citation statements)

References 71 publications

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“…The life cycles of WLAR events are associated with a tripole pattern of geopotential height anomalies over the North Pacific that persists for 1 week (from Days −2 to +5) with an anomalous low over the central North Pacific and anomalous highs over northeastern Asia and the subtropical Northeast Pacific (Figure ). A similar tripole pattern associated with landfalling ARs over Oregon is shown in Benedict et al (). On Day −5, an anomalous high appears over northeastern Asia and an anomalous low emerges over the North Pacific (Figure a).…”

Section: Distinct Evolutions Of Landfalling Ar Eventssupporting

confidence: 79%

“…Meanwhile, reduced precipitation over the northern West Coast is attributed to the moisture flux divergence anomaly. While previous work has shown the large‐scale patterns associated with precipitation over the west coast of North America (Benedict et al, ; Carrera et al, ; Higgins et al, ; Jiang & Deng, ; Lackmann & Gyakum, ), our study further demonstrates that the life cycle of AR events can serve as an indicator to show how the large‐scale patterns modulate the pathway of moisture transport prior to the precipitation over land.…”

Section: Summary and Discussionsupporting

confidence: 48%

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Impact of Distinct Origin Locations on the Life Cycles of Landfalling Atmospheric Rivers Over the U.S. West Coast

Yang

Kim

2019

JGR Atmospheres

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An atmospheric river (AR) event represents strong poleward moisture transport and is defined as a series of spatiotemporally connected instantaneous AR objects. Utilizing an AR tracking algorithm with a depth-first search (a widely used algorithm in computer science), we examine the life cycle characteristics of AR events that make landfall over the U.S. West Coast by their distinct origin locations. Landfalling AR events from the Northwest Pacific (120°E-170°W, WLAR events) temporally last longer (5.3 versus 3.6 days on average) and have stronger intensity of integrated vapor transport (508 versus 388 kg m −1 s −1 on average) than those originating from the Northeast Pacific (125°W-170°W, ELAR events). A persistent tripole geopotential height anomaly pattern over the North Pacific modulates the origin locations and propagation of landfalling AR events. WLAR events are associated with anomalous highs over northeastern Asia and the Northeast Pacific and an anomalous low over the central North Pacific. This pattern provides favorable conditions for WLAR events to start, propagate northeastward, and make landfall in the northwestern West Coast. WLAR events contribute approximately 25% of the total winter precipitation over Washington and British Columbia. ELAR events are associated with a similar tripole pattern to the WLAR events with an eastward shift. The anomalous low over the Northeast Pacific helps ELAR events to start, propagate northeastward, and make landfall in the southwestern West Coast. Precipitation induced by ELAR events contributes up to 30% of total winter precipitation over California.Plain Language Summary Atmospheric rivers (ARs) are strong poleward water vapor transport events in the lower troposphere. AR events are important to water resources over the U.S. West Coast. We compared the characteristics, circulation patterns, and precipitation of landfalling AR events over the U.S. West Coast based on their origin locations. In general, landfalling AR events originating from the Northwest Pacific (120°E-170°W) last longer temporally and have stronger intensities than those from the Northeast Pacific (125°W-170°W). The life cycles (origin, propagation, and termination) of landfalling AR events and AR-related precipitation are strongly modulated by large-scale tripole geopotential height anomaly pattern over the North Pacific basin.

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Section: Distinct Evolutions Of Landfalling Ar Eventssupporting

confidence: 79%

Section: Summary and Discussionsupporting

confidence: 48%

Impact of Distinct Origin Locations on the Life Cycles of Landfalling Atmospheric Rivers Over the U.S. West Coast

Yang

Kim

2019

JGR Atmospheres

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“…For the SH, we consider blocking events that last 4 days or more, to account for the greater transience of the SH (Berrisford et al, 2007). An assessment of NH blocking using slightly different metrics can also found in Gettelman et al (2019), their Figure 15, and Benedict et al (2019).…”

Section: Blockingmentioning

confidence: 99%

An Evaluation of the Large‐Scale Atmospheric Circulation and Its Variability in CESM2 and Other CMIP Models

et al. 2020

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The Community Earth System Model 2 (CESM2) is the latest Earth System Model developed by the National Center for Atmospheric Research in collaboration with the university community and is significantly advanced in most components compared to its predecessor (CESM1). Here, CESM2's representation of the large‐scale atmospheric circulation and its variability is assessed. Further context is providedthrough comparison to the CESM1 large ensemble and other models from the Coupled Model Intercomparison Project (CMIP5 and CMIP6). This includes an assessment of the representation of jet streams and storm tracks, stationary waves, the global divergent circulation, the annular modes, the North Atlantic Oscillation, and blocking. Compared to CESM1, CESM2 is substantially improved in the representation of the storm tracks, Northern Hemisphere (NH) stationary waves, NH winter blocking and the global divergent circulation. It ranks within the top 10% of CMIP class models in many of these features. Some features of the Southern Hemisphere (SH) circulation have degraded, such as the SH jet strength, stationary waves, and blocking, although the SH jet stream is placed at approximately the correct location. This analysis also highlights systematic deficiencies in these features across the new CMIP6 archive, such as the continued tendency for the SH jet stream to be placed too far equatorward, the North Atlantic westerlies to be too strong over Europe, the storm tracks as measured by low‐level meridional wind variance to be too weak and a lack of blocking in the North Atlantic sector.

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“…where g is the gravitational acceleration, q is the specific humidity, v is the horizontal wind, and p is pressure. The zonal and meridional components of this vector are readily available in the ERA-Interim dataset (Berrisford et al, 2011), and the IVT magnitude follows from…”

Section: Reanalysis Data and Key Diagnosticsmentioning

confidence: 99%

A global climatological perspective on the importance of Rossby wave breaking and intense moisture transport for extreme precipitation events

Vries

Jan²

2021

Weather Clim. Dynam.

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Abstract. Extreme precipitation events (EPEs) frequently cause flooding with dramatic socioeconomic impacts in many parts of the world. Previous studies considered two synoptic-scale processes, Rossby wave breaking and intense moisture transport, typically in isolation, and their linkage to such EPEs in several regions. This study presents for the first time a global and systematic climatological analysis of these two synoptic-scale processes, in tandem and in isolation, for the occurrence of EPEs. To this end, we use 40-year ERA-Interim reanalysis data (1979–2018) and apply object-based identification methods for (i) daily EPEs, (ii) stratospheric potential vorticity (PV) streamers as indicators of Rossby wave breaking, and (iii) structures of high vertically integrated horizontal water vapour transport (IVT). First, the importance of these two synoptic-scale processes is demonstrated by case studies of previously documented flood events that inflicted catastrophic impacts in different parts of the world. Next, a climatological quantification shows that Rossby wave breaking is associated with >90 % of EPEs over central North America and the Mediterranean, whereas intense moisture transport is linked to >95 % of EPEs over many coastal zones, consistent with findings of atmospheric river-related studies. Combined Rossby wave breaking and intense moisture transport contributes up to 70 % of EPEs in several subtropical and extratropical regions, including (semi)arid desert regions where tropical–extratropical interactions are of key importance for (heavy) rainfall. Odds ratios of EPEs linked to the two synoptic-scale processes suggest that intense moisture transport has a stronger association with the occurrence of EPEs than Rossby wave breaking. Furthermore, the relationship between the PV and IVT characteristics and the precipitation volumes shows that the depth of the wave breaking and moisture transport intensity are intimately connected with the extreme precipitation severity. Finally, composites reveal that subtropical and extratropical EPEs, linked to Rossby wave breaking, go along with the formation of upper-level troughs and cyclogenetic processes near the surface downstream, reduced static stability beneath the upper-level forcing (only over water), and dynamical lifting ahead (over water and land). This study concludes with a concept that reconciles well-established meteorological principles with the importance of Rossby wave breaking and intense moisture transport for the formation of EPEs. Another conclusion with major implications is that different combinations of Rossby wave breaking and intense moisture transport can reflect a large range of EPE-related weather systems across climate zones and can thus form the basis for a new classification of EPE regimes. The findings of this study may contribute to an improved understanding of the atmospheric processes that lead to EPEs and may find application in climatic studies on extreme precipitation changes in a warming climate.

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Atmospheric Blocking and Other Large‐Scale Precursor Patterns of Landfalling Atmospheric Rivers in the North Pacific: A CESM2 Study

Cited by 32 publications

References 71 publications

Impact of Distinct Origin Locations on the Life Cycles of Landfalling Atmospheric Rivers Over the U.S. West Coast

Impact of Distinct Origin Locations on the Life Cycles of Landfalling Atmospheric Rivers Over the U.S. West Coast

An Evaluation of the Large‐Scale Atmospheric Circulation and Its Variability in CESM2 and Other CMIP Models

A global climatological perspective on the importance of Rossby wave breaking and intense moisture transport for extreme precipitation events

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