Synoptic Features Associated with Temporally Coherent Modes of Variability of the North Pacific Jet Stream

2017 ◽  
Vol 30 (1) ◽  
pp. 39-54 ◽  
Author(s):  
Kyle S. Griffin ◽  
Jonathan E. Martin
Keyword(s):  
North America ◽  
North Pacific ◽  
Jet Stream ◽  
Eof Analysis ◽  
Western North America ◽  
Synoptic Scale ◽  
Exit Region ◽  
Low Level ◽  
The North ◽  
The North Pacific

Time-extended EOF (TE-EOF) analysis is employed to examine the synoptic-scale evolution of the two leading modes of the North Pacific jet stream variability, namely, its zonal extension–retraction (TE-EOF 1) and the north–south shift of its exit region (TE-EOF 2). Use of the TE-EOF analysis enables a temporally coherent examination of the synoptic-scale evolution preceding and following peaks in each of the two leading modes that provides insight into the preferred evolutions of the North Pacific jet. Composite analyses are constructed based upon selecting peaks in the principal component time series of both phases of each TE-EOF whose magnitude exceeded 1.5 standard deviations. Jet extension events are associated with an anomalous cyclonic circulation over the Gulf of Alaska that induces a low-level warm anomaly over western North America. Jet retractions are associated with a nearly opposite configuration characterized by an anomalous anticyclonic circulation over the Aleutians and anomalous low-level cold anomaly over western North America. Similar but lower-amplitude upper-level patterns are noted in the composites of the corresponding poleward-/equatorward-shifted jet phases, with the poleward shift of the jet exit region tied to anomalously low geopotential heights over Alaska and anomalous low-level warmth over north-central North America. An equatorward shift of the exit region is tied to positive height anomalies over Alaska with downstream cold anomalies occurring in western North America. The more extreme downstream impacts that characterize TE-EOF 2 are also longer lasting (>5 days), suggesting potential utility in medium-range forecasts.

The Development of the North Pacific Jet Phase Diagram as an Objective Tool to Monitor the State and Forecast Skill of the Upper-Tropospheric Flow Pattern

2019 ◽  
Vol 34 (1) ◽  
pp. 199-219 ◽  
Author(s):  
Andrew C. Winters ◽  
Daniel Keyser ◽  
Lance F. Bosart
Keyword(s):  
Phase Diagram ◽  
North America ◽  
Flow Pattern ◽  
Zonal Wind ◽  
North Pacific ◽  
The State ◽  
Forecast Skill ◽  
Exit Region ◽  
The North ◽  
The North Pacific

Abstract Previous studies employing empirical orthogonal function (EOF) analyses of upper-tropospheric zonal wind anomalies have identified the leading modes of North Pacific jet (NPJ) variability that prevail on synoptic time scales. The first mode corresponds to a zonal extension or retraction of the exit region of the climatological NPJ, while the second mode corresponds to a poleward or equatorward shift of the exit region of the climatological NPJ. These NPJ regimes can strongly influence the character of the large-scale flow pattern over North America. Consequently, knowledge of the prevailing NPJ regime and the forecast skill associated with each NPJ regime can add considerable value to operational medium-range (6–10-day) forecasts over North America. This study documents the development of an NPJ phase diagram, which is constructed from the two leading EOFs of 250-hPa zonal wind anomalies during 1979–2014 excluding the summer months (June–August). The projection of 250-hPa zonal wind anomalies at one or multiple times onto the NPJ phase diagram provides an objective characterization of the state or evolution of the upper-tropospheric flow pattern over the North Pacific with respect to the two leading EOFs. A 30-yr analysis of GEFS reforecasts with respect to the NPJ phase diagram demonstrates that forecasts verified during jet retraction and equatorward shift regimes are associated with significantly larger average errors than jet extension and poleward shift regimes. An examination of the best and worst forecasts further suggests that periods characterized by rapid NPJ regime transition and the development and maintenance of North Pacific blocking events exhibit reduced forecast skill.

scholarly journals Asian dust storm influence on North American ambient PM levels: observational evidence and controlling factors

2008 ◽  
Vol 8 (10) ◽  
pp. 2717-2728 ◽  
Author(s):  
T. L. Zhao ◽  
S. L. Gong ◽  
X. Y. Zhang ◽  
D. A. Jaffe
Keyword(s):  
North America ◽  
North Pacific ◽  
Asian Dust ◽  
Observational Evidence ◽  
Dust Storms ◽  
Western North America ◽  
Transport Pathway ◽  
The North ◽  
Asian Dust Storms ◽  
The North Pacific

Abstract. New observational evidence of the trans-Pacific transport of Asian dust and its contribution to the ambient particulate matter (PM) levels in North America was revealed, based on the interannual variations between Asian dust storms and the ambient PM levels in western North America from year 2000 to 2006. A high correlation was found between them with an R2 value of 0.83. From analysis of the differences in the correlation between 2005 and 2006, three factors explain the variation of trans-Pacific transport and influences of Asian dust storms on PM levels in western North America. These were identified by modeling results and the re-analysis data. They were 1) Strength of frontal cyclones from Mongolia to north eastern China: The frontal cyclones in East Asia not only bring strong cold air outbreaks, generating dust storms in East Asia, but also lift Asian dust into westerly winds of the free troposphere for trans-Pacific transport; 2) Pattern of transport pathway over the North Pacific: The circulation patterns of westerlies over the North Pacific govern the trans-Pacific transport pattern. Strong zonal airflow of the westerly jet in the free troposphere over the North Pacific favor significant trans-Pacific transport of Asian dust; 3) Variation of precipitation in the North Pacific: The scavenging of Asian dust particles by precipitation is a major process of dust removal on the trans-Pacific transport pathway. Therefore, variation of precipitation in the North Pacific could affect trans-Pacific transport of Asian dust.

scholarly journals Asian dust storm influence on North American ambient PM levels: observational evidence and controlling factors

2007 ◽  
Vol 7 (4) ◽  
pp. 9663-9686 ◽  
Author(s):  
T. L. Zhao ◽  
S. L. Gong ◽  
X. Y. Zhang ◽  
D. A. Jaffe
Keyword(s):  
North America ◽  
North Pacific ◽  
Asian Dust ◽  
Observational Evidence ◽  
Dust Storms ◽  
Western North America ◽  
Transport Pathway ◽  
The North ◽  
Asian Dust Storms ◽  
The North Pacific

Abstract. New observational evidence of the trans-Pacific transport of Asian dust and its contribution to the ambient particulate matter (PM) levels in North America was revealed, based on the interannual variations between Asian dust storms and the ambient PM levels in western North America from year 2000 to 2006. A high correlation was found between them with an R2 value of 0.83. From analysis of the differences in the correlation between 2005 and 2006, three factors explain the variation of trans-Pacific transport and influences of Asian dust storms on PM levels in western North America. These were identified by modeling results and the re-analysis data. They were 1) Strength of frontal cyclones from Mongolia to north eastern China: The frontal cyclones in East Asia not only bring strong cold air outbreaks, generating dust storms in East Asia, but also lift Asian dust into westerly winds of the free troposphere for trans-Pacific transport; 2) Pattern of transport pathway over the North Pacific: The circulation patterns of westerlies over the North Pacific govern the trans-Pacific transport pattern. Strong zonal airflow of the westerly jet in the free troposphere over the North Pacific favor significant trans-Pacific transport of Asian dust; 3) Variation of precipitation in the North Pacific: The scavenging of Asian dust particles by precipitation is a major process of dust removal on the trans-Pacific transport pathway; therefore, variation of precipitation in the North Pacific could affect trans-Pacific transport of Asian dust.

scholarly journals Can ENSO-Like Convection Force an ENSO-Like Extratropical Response on Subseasonal Time Scales?

2018 ◽  
Vol 31 (20) ◽  
pp. 8339-8349 ◽  
Author(s):  
Michael Goss ◽  
Sukyoung Lee ◽  
Steven B. Feldstein ◽  
Noah S. Diffenbaugh
Keyword(s):  
North America ◽  
El Niño ◽  
North Pacific ◽  
El Nino ◽  
La Niña ◽  
Convective Heating ◽  
Western North America ◽  
The North ◽  
La Nina ◽  
The North Pacific

A daily El Niño–Southern Oscillation (ENSO) index is developed based on precipitation rate and is used to investigate subseasonal time-scale extratropical circulation anomalies associated with ENSO-like convective heating. The index, referred to as the El Niño precipitation index (ENPI), is anomalously positive when there is El Niño–like convection. Conversely, the ENPI is anomalously negative when there is La Niña–like convection. It is found that when precipitation becomes El Niño–like (La Niña–like) on subseasonal time scales, the 300-hPa geopotential height field over the North Pacific and western North America becomes El Niño–like (La Niña–like) within 5–10 days. The composites show a small association with the MJO. These results are supported by previous modeling studies, which show that the response over the North Pacific and western North America to an equatorial Pacific heating anomaly occurs within about one week. This suggests that the mean seasonal extratropical response to El Niño (La Niña) may in effect simply be the average of the subseasonal response to subseasonally varying El Niño–like (La Niña–like) convective heating. Implications for subseasonal to seasonal forecasting are discussed.

scholarly journals The spring transition of the North Pacific jet and its relation to deep stratosphere-to-troposphere mass transport over western North America

2021 ◽  
Vol 21 (4) ◽  
pp. 2781-2794
Author(s):  
Melissa L. Breeden ◽  
Amy H. Butler ◽  
John R. Albers ◽  
Michael Sprenger ◽  
Andrew O'Neil Langford
Keyword(s):  
North America ◽  
El Niño ◽  
North Pacific ◽  
El Nino ◽  
Late Winter ◽  
Western North America ◽  
The North ◽  
Jet Structure ◽  
Stratospheric Intrusions ◽  
The North Pacific

Abstract. Stratosphere-to-troposphere mass transport to the planetary boundary layer (STT-PBL) peaks over the western United States during boreal spring, when deep stratospheric intrusions are most frequent. The tropopause-level jet structure modulates the frequency and character of intrusions, although the precise relationship between STT-PBL and jet variability has not been extensively investigated. In this study, we demonstrate how the North Pacific jet transition from winter to summer leads to the observed peak in STT-PBL. We show that the transition enhances STT-PBL through an increase in storm track activity which produces highly amplified Rossby waves and more frequent deep stratospheric intrusions over western North America. This dynamic transition coincides with the gradually deepening PBL, further facilitating STT-PBL in spring. We find that La Niña conditions in late winter are associated with an earlier jet transition and enhanced STT-PBL due to deeper and more frequent tropopause folds. An opposite response is found during El Niño conditions. El Niño–Southern Oscillation (ENSO) conditions also influence STT-PBL in late spring or early summer, during which time La Niña conditions are associated with larger and more frequent tropopause folds than both El Niño and ENSO-neutral conditions. These results suggest that knowledge of ENSO state and the North Pacific jet structure in late winter could be leveraged for predicting the strength of STT-PBL in the following months.

scholarly journals The Spring Transition of the North Pacific Jet and its Relation to Deep Stratosphere-to-Troposphere Mass Transport over Western North America

2020 ◽  
Author(s):  
Melissa Leah Breeden ◽  
Amy Hawes Butler ◽  
John Robert Albers ◽  
Michael Sprenger ◽  
Andrew O’Neil Langford
Keyword(s):  
Boundary Layer ◽  
North America ◽  
Mass Transport ◽  
North Pacific ◽  
Late Winter ◽  
Western North America ◽  
The North ◽  
Jet Structure ◽  
Stratospheric Intrusions ◽  
The North Pacific

Abstract. Stratosphere-to-troposphere mass transport to the planetary boundary layer (STT-PBL) peaks over the western United States during boreal spring, when deep stratospheric intrusions are most frequent. The tropopause-level jet structure modulates the frequency and character of intrusions, although the precise relationship between STT-PBL and jet variability has not been extensively investigated. In this study, we demonstrate how the north Pacific jet transition from winter to summer leads to the observed peak in STT-PBL. We show that the transition enhances STT-PBL through an increase in storm track activity which produces highly-amplified Rossby waves and more frequent deep stratospheric intrusions over western North America. This dynamic transition coincides with the gradually deepening planetary boundary layer, further facilitating STT-PBL in spring. We find that La Niña conditions in late winter are associated with an earlier jet transition and enhanced STT-PBL due to deeper and more frequent tropopause folds. An opposite response is found during El Niño conditions. ENSO conditions also influence STT-PBL in late spring/early summer, during which time La Niña conditions are associated with larger and more frequent tropopause folds than both El Niño and ENSO neutral conditions. These results suggest that knowledge of ENSO state and the north Pacific jet structure in late winter could be leveraged for predicting the strength of STT-PBL in the following months.

scholarly journals The Role of Upstream Midtropospheric Circulations in the Sierra Nevada Enabling Leeside (Spillover) Precipitation. Part II: A Secondary Atmospheric River Accompanying a Midlevel Jet

2009 ◽  
Vol 10 (6) ◽  
pp. 1327-1354 ◽  
Author(s):  
Michael L. Kaplan ◽  
Christopher S. Adaniya ◽  
Phillip J. Marzette ◽  
K. C. King ◽  
S. Jeffrey Underwood ◽  
...  
Keyword(s):  
Sierra Nevada ◽  
North Pacific ◽  
Stage Iv ◽  
Convective Heating ◽  
Exit Region ◽  
Low Level ◽  
Convective Systems ◽  
Atmospheric River ◽  
The North ◽  
The North Pacific

Abstract The synoptic structure of two case studies of heavy “spillover” or leeside precipitation—1–2 January 1997 and 30–31 December 2005—that resulted in Truckee River flooding are analyzed over the North Pacific beginning approximately 7 days prior to the events. Several sequential cyclone-scale systems are tracked across the North Pacific, culminating in the strengthening and elongation of a polar jet stream’s deep exit region over northern California and Nevada. These extratropical cyclones separate extremely cold air from Siberia from an active intertropical convergence zone with broad mesoscale convective systems and tropical cyclones. The development of moisture surges resulting in leeside flooding precipitation over the Sierra Nevada is coupled to adjustments within the last wave in the sequence of cyclone waves. Stage I of the process occurs as the final wave moves across the Pacific and its polar jet streak becomes very long, thus traversing much of the eastern Pacific. Stage II involves the development of a low-level return branch circulation [low-level jet (LLJ)] within the exit region of the final cyclone scale wave. Stage III is associated with the low-level jet’s convergence under the upper-level divergence within the left exit region, which results in upward vertical motions, dynamic destabilization, and the development of mesoscale convective systems (MCSs). Stage IV is forced by the latent heating and subsynoptic-scale ridging caused by each MCS, which results in a region of diabatic isallobaric accelerations downstream from the MCS-induced mesoridge. During stage IV the convectively induced accelerating flow, well to the southeast of the upper-level jet core, organizes a midlevel jet and plume of moisture or midlevel atmospheric river, which is above and frequently out of phase with (e.g., southeast of) the low-level atmospheric river described in Ralph et al. ahead of the surface cold front. Stage V occurs as the final sequential midlevel river arrives over the Sierra Nevada. It phases with the low-level river, allowing upslope and midlevel moisture advection, thus creating a highly concentrated moist plume extending from near 700 to nearly 500 hPa, which subsequently advects moisture over the terrain. When simulations are performed without upstream convective heating, the horizontal moisture fluxes over the Sierra Nevada are reduced by ∼30%, indicating the importance of convection in organizing the midlevel atmospheric rivers. The convective heating acts to accelerate the midlevel jet flow and create the secondary atmospheric river between ∼500 and 700 hPa near the 305-K isentropic surface. This midlevel moisture surge slopes forward with height and transports warm moist air over the Sierra Nevada to typically rain shadowed regions on the lee side of the range. Both observationally generated and model-generated back trajectories confirm the importance of this convectively forced rapid lifting process over the North Pacific west of the California coast ∼12 h and ∼1200 km upstream prior to heavy leeside spillover precipitation over the Sierra Nevada.

Carex lyngbyei excluded from the flora of eastern North America, and taxonomic notes on related species and hybrids

1987 ◽  
Vol 65 (6) ◽  
pp. 1187-1198 ◽  
Author(s):  
Jacques Cayouette
Keyword(s):  
North America ◽  
North Pacific ◽  
Related Species ◽  
Hybrid Origin ◽  
Eastern North America ◽  
Herbarium Specimens ◽  
Western North America ◽  
Pollen Stainability ◽  
The North ◽  
The North Pacific

Carex lyngbyei has been reported from a few stations in eastern North America over the last century. Herbarium specimens so identified from that area are morphologically very diverse and are quite different from the typical C. lyngbyei along the North Pacific coastline and Iceland. This eastern material was found to belong to four species (C. aquatilis, C. crinita var. gynandra, C. paleacea, and C. recta) and six different hybrids (C. ×saxenii, C. ×gardneri, C. ×exsalina, C. ×subnigra, C. ×super-goodenoughii, and C. ×grantii). Pollen stainability of typical C. lyngbyei and of putative C. lyngbyei from eastern North America supported these revisions: it was high in species and low in hybrids or in species of hybrid origin such as C. recta. In western North America, C. lyngbyei has either 2n = 68, 70, or 72 chromosomes and meiosis appears to be regular. In contrast, some putative C. lyngbyei from eastern Quebec showed a highly disturbed meiosis. Consequently C. lyngbyei is excluded from eastern North America.

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