Four Atmospheric Circulation Regimes Over the North Pacific and Their Relationship to California Precipitation on Daily to Seasonal Timescales

Guirguis, Kristen; Gershunov, Alexander; DeFlorio, Michael J.; Shulgina, Tamara; Monache, Luca Delle; Subramanian, Aneesh; Corringham, Thomas W.; Ralph, F. Martin

doi:10.1029/2020gl087609

Cited by 14 publications

(16 citation statements)

References 40 publications

(62 reference statements)

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“…Higher pressure (lower pressure) in north‐central (node 11) and subtropical eastern pacific (node 18) was associated with higher (lower) SLP in node 22 (Figures 5c and 5d), while the signs of the relationship between SLP in the west Indian ocean (node 1) and node 22 were opposite (Figure 5e). Higher pressure in node 11 was suggested to be a factor for steering the wet winter air masses away from CA (Cvijanovic et al., 2017; Guirguis et al., 2020).…”

Section: Resultsmentioning

confidence: 99%

“…The majority of CMIP6 model causal networks also confirmed the strong teleconnection between node 22 SLP and CA precipitation (passing a binomial test at a 95% confidence level). Over node 22, the west coast higher pressure pushes storm tracks away from CA, resulting in anomalously drier winters (Choi et al., 2016; Cvijanovic et al., 2017; Seager et al., 2015, 2017), while lower pressure is robustly associated with wetter winters (Guirguis et al., 2020; Seager et al., 2015). Over the central‐southern CA, both observation and the majority of CMIP6 models (13 out of 18) agreed on the secondary control of northeastern pacific region (node 18) SLP on CA precipitation.…”

Section: Resultsmentioning

confidence: 99%

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Wetter California Projected by CMIP6 Models With Observational Constraints Under a High GHG Emission Scenario

Zhu

Riley

et al. 2022

Earth's Future

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As the world's fifth‐largest economy entity, California (CA) is vulnerable to climate changes especially the magnitude of winter (wet season) precipitation that is closely linked to regional drought severity, vegetation growth, and wildfire activities. However, the fate of CA precipitation in the future remains highly uncertain, for example, the state‐of‐the‐art Earth system models (ESMs) from the Coupled Model Intercomparison Project Phase 6 (CMIP6) projected −3% to +42% and −27% to +63% precipitation changes in northern and central‐southern CA, respectively, under the high greenhouse gas (GHG) emission scenario (SSP585). In this work, we applied the Pareto optimality concept and used observed teleconnection patterns (causal relationships between ocean regions and CA precipitation) to mechanistically constrain CMIP6 projected CA precipitations. We estimated that precipitation will robustly increase by 0.4–1.3 mm d−1 (10–34%) over northern CA and increase by 0.1–0.5 mm d−1 (7–32%) over central‐southern CA by the end of the 21st century compared with present‐day. Up to 71% of ESM projection uncertainties were reduced mainly due to the strong and consistent causal relationship between North American west coast sea level pressure and CA precipitation in both observations and CMIP6 models. Our results suggest that teleconnection patterns are powerful mechanistic constraints that can help explain and reduce uncertainties in ESM projections.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Wetter California Projected by CMIP6 Models With Observational Constraints Under a High GHG Emission Scenario

Zhu

Riley

et al. 2022

Earth's Future

View full text Add to dashboard Cite

show abstract

“…Guirguis et al. (2018, 2020) identified similar circulation modes that have >70% of concurrence with ARs that make landfall over Northern California/Pacific Northwest, and they also highlighted the importance of these modes in driving hydrologic extremes across time scales. In light of this information, we name EOF3 the “CPM.” The power spectrum density of PC3 (Figure 2c) suggests that in general the mode is indistinguishable from red noise, though it exceeds the 95% confidence line at around 70–80 days and at ∼120 days.…”

Section: Resultsmentioning

confidence: 96%

“…Therefore, while being much less prominent for total variation of Z500, PC3 is more important for California precipitation than other leading modes of variability. Guirguis et al (2018Guirguis et al ( , 2020 identified similar circulation modes that have >70% of concurrence with ARs that make landfall over Northern California/Pacific Northwest, and they also highlighted the importance of these modes in driving hydrologic extremes across time scales. In light of this information, we name EOF3 the "CPM."…”

Section: The Cpm and Its Connection To California Mean Precipitationmentioning

confidence: 87%

A Distinct Atmospheric Mode for California Precipitation

et al. 2021

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The hydrologic cycle in California is strongly influenced by wet‐season (November–April) precipitation. Here, we demonstrate the existence of an influential mode of North Pacific atmospheric pressure variability that regulates wet‐season precipitation variability over both northern and southern California. This mode, named as the “California precipitation mode” (CPM), is statistically distinct from other well‐known modes of pressure variability such as the Pacific‐North American pattern. In addition to controlling wet‐season mean precipitation, positive days of the CPM coincide with up to 90% of the extreme (>99th percentile) precipitation days and 76% of detected atmospheric rivers (ARs) days, while the negative days correspond with 60% of the dry days. CMIP6 models capture the CPM remarkably well, including its statistical separation from the other well‐known modes of pressure variability. The models also reproduce the CPM's strong association with California wet‐season precipitation, giving confidence in the models’ dynamics relating to regional hydrologic extremes. However, the models also exhibit biases in regional hydrologic extremes. The CPM is a useful way to understand the origins of those biases and select the more credible models for further analysis: Models with unrealistically strong gradients in the CPM pressure pattern generally oversimulate larger wet extremes and produce excessively long dry intervals in the historical period. Thus the hydrologic biases can be traced to the particular aspects of North Pacific atmospheric dynamics.

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“…Figure 1c shows the collective in uence of the four modes, where we see that together these modes explain 25-90% variance in the portion of the domain most relevant for west coast weather. The NP4 dataset used in this study is described in Guirguis et al (2020b) and is available at https://doi.org/10.6075/J0154FJJ.…”

Section: North Paci C Atmospheric Circulation Regimesmentioning

confidence: 99%

Weather Patterns Driving Atmospheric Rivers, Santa Ana Winds, Floods, and Wildfires During California Winters Provide Evidence for Increasing Fire Risk

Guirguis

Gershunov

Hatchett

et al. 2021

Preprint

Self Cite

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Floods caused by atmospheric rivers and wildfires fanned by Santa Ana winds are common occurrences in California with devastating societal impacts. Planning for these types of events is critical to protect life and property, and extending the lead-times of predictability for these types of events improves emergency response. A better understanding of linkages between large-scale atmospheric circulation patterns and extreme weather represents an important step towards improving predictability and preparedness on subseasonal-to-seasonal (S2S) timescales and for climate change adaptation. In this work, we show that winter weather variability in California, including the occurrence of extreme and impactful events, is linked to four atmospheric circulation regimes over the North Pacific Ocean previously named and identified as the “NP4 modes”. These modes interact on daily timescales to produce recurring winter weather patterns that are major drivers of atmospheric river landfalls, Santa Ana winds, floods, and wildfires. Many recent California natural hazard events resulted from compounding and cascading extremes including frequent atmospheric river landfalls (wet, fuel-producing years) or lack thereof (drought) and followed by Sana Ana-driven wildfires that render the landscape susceptible to hydrologic hazards posed by short-duration high-intensity precipitation events. This historical perspective of atmospheric circulation and impacts over 70 years reveals that weather patterns are changing in a way that enhances wildfire risk in California, while the frequency of weather patterns linked to historical floods is not diminishing. These changes highlight the rising hazards of compounding weather extremes in California’s present and future.

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Four Atmospheric Circulation Regimes Over the North Pacific and Their Relationship to California Precipitation on Daily to Seasonal Timescales

Cited by 14 publications

References 40 publications

Wetter California Projected by CMIP6 Models With Observational Constraints Under a High GHG Emission Scenario

Wetter California Projected by CMIP6 Models With Observational Constraints Under a High GHG Emission Scenario

A Distinct Atmospheric Mode for California Precipitation

Weather Patterns Driving Atmospheric Rivers, Santa Ana Winds, Floods, and Wildfires During California Winters Provide Evidence for Increasing Fire Risk

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