skip to main content
US FlagAn official website of the United States government
dot gov icon
Official websites use .gov
A .gov website belongs to an official government organization in the United States.
https lock icon
Secure .gov websites use HTTPS
A lock ( lock ) or https:// means you've safely connected to the .gov website. Share sensitive information only on official, secure websites.

Explore Research Products in the PAR
It may take a few hours for recently added research products to appear in PAR search results.


  • NSF Public Access
  • Search Results
  • The spring transition of the North Pacific jet and its relation to deep stratosphere-to-troposphere mass transport over western North America
Title: The spring transition of the North Pacific jet and its relation to deep stratosphere-to-troposphere mass transport over western North America
Abstract. Stratosphere-to-troposphere mass transport to the planetaryboundary layer (STT-PBL) peaks over the western United States during borealspring, when deep stratospheric intrusions are most frequent. Thetropopause-level jet structure modulates the frequency and character ofintrusions, although the precise relationship between STT-PBL and jetvariability has not been extensively investigated. In this study, wedemonstrate how the North Pacific jet transition from winter to summer leadsto the observed peak in STT-PBL. We show that the transition enhancesSTT-PBL through an increase in storm track activity which produceshighly amplified Rossby waves and more frequent deep stratosphericintrusions over western North America. This dynamic transition coincideswith the gradually deepening PBL, further facilitating STT-PBL in spring. Wefind that La Niña conditions in late winter are associated with anearlier jet transition and enhanced STT-PBL due to deeper and more frequenttropopause folds. An opposite response is found during El Niñoconditions. El Niño–SouthernOscillation (ENSO) conditions also influence STT-PBL in late spring or earlysummer, during which time La Niña conditions are associated with largerand more frequent tropopause folds than both El Niño and ENSO-neutralconditions. These results suggest that knowledge of ENSO state and the North Pacific jet structure in late winter could be leveraged for predicting thestrength of STT-PBL in the following months.  more » « less
Award ID(s):
1756958
PAR ID:
10308573
Author(s) / Creator(s):
; ; ; ;
Date Published:
Journal Name:
Atmospheric Chemistry and Physics
Volume:
21
Issue:
4
ISSN:
1680-7324
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. ; ; ; ; (, Atmospheric Chemistry and Physics)
    Abstract. The El Niño–Southern Oscillation (ENSO) is known to modulate the strength and frequency of stratosphere-to-troposphere transport (STT) of ozone over the Pacific–North American region during late winter to early summer. Dynamical processes that have been proposed to account for this variability include variations in the amount of ozone in the lowermoststratosphere that is available for STT and tropospheric circulation-relatedvariations in the frequency and geographic distribution of individual STTevents. Here we use a large ensemble of Whole Atmosphere Community Climate Model(WACCM) simulations (forced by sea-surface temperature (SST) boundaryconditions consistent with each phase of ENSO) to show that variability inlower-stratospheric ozone and shifts in the Pacific tropospheric jetconstructively contribute to the amount of STT of ozone in the NorthAmerican region during both ENSO phases. In terms of stratosphericvariability, ENSO drives ozone anomalies resembling the Pacific–NorthAmerican teleconnection pattern that span much of the lower stratospherebelow 50 hPa. These ozone anomalies, which dominate over other ENSO-drivenchanges in the Brewer–Dobson circulation (including changes due to both thestratospheric residual circulation and quasi-isentropic mixing), stronglymodulate the amount of ozone available for STT transport. As a result,during late winter (February–March), the stratospheric ozone response to theteleconnections constructively reinforces anomalous ENSO-jet-driven STT ofozone. However, as ENSO forcing weakens as spring progresses into summer(April–June), the direct effects of the ENSO-jet-driven STT transportweaken. Nevertheless, the residual impacts of the teleconnections on theamount of ozone in the lower stratosphere persist, and these anomalies inturn continue to cause anomalous STT of ozone. These results should provehelpful for interpreting the utility of ENSO as a subseasonal predictor ofboth free-tropospheric ozone and the probability of stratospheric ozoneintrusion events that may cause exceedances in surface air qualitystandards. 
    more » « less
  2. ; ; ; (, Journal of Climate)
    Abstract Current climate models have relatively high skills in predicting El Niño–Southern Oscillation (ENSO) phase (i.e., El Niño, neutral, and La Niña), once leaping over the spring predictability barrier. However, it is still a big challenge to realistically forecast the ENSO amplitude, for instance, whether a predicted event will be strong, moderate, or weak. Here we demonstrate that the accumulated westerly wind events (WWEs)/easterly wind surges (EWSs) and oceanic recharged/discharged states are both of importance in accurate ENSO amplitude forecasts. El Niño and La Niña events exhibit asymmetric temporal and spatial features in the atmospheric and oceanic preconditions. El Niño amplitude at the peak season is closely associated with the accumulated WWEs over the eastern equatorial Pacific from the previous December to May and the recharged state in the western equatorial Pacific during February. In contrast, the amplitude of La Niña events is sensitive to the accumulated EWSs over the equatorial western Pacific from the previous November to April and the discharged state extending from the equatorial western to central Pacific during February. Considering these asymmetric atmospheric and oceanic preconditions of El Niño and La Niña cases, a statistical model is established to accurately forecast the ENSO amplitude at its mature phase during 1982–2018, which is validated to be robust based on a 1-yr cross-validation and independent sample tests. The feasibility and the limitation of the established statistical model are also discussed by examining its practical utility. 
    more » « less
  3. ; ; (, Geophysical Research Letters)
    Abstract In around 1990, significant shifts occurred in the spatial pattern and temporal evolution of the El Niño‐Southern Oscillation (ENSO), with these shifts showing asymmetry between El Niño and La Niña phases. El Niño transitioned from the Eastern Pacific (EP) to the Central Pacific (CP) type, while La Niña's multi‐year (MY) events increased. These changes correlated with shifts in ENSO dynamics. Before 1990, El Niño was influenced by the Tropical Pacific (TP) ENSO dynamic, shifting to the Subtropical Pacific (SP) ENSO dynamic afterward, altering its spatial pattern. La Niña was influenced by the SP ENSO dynamic both before and after 1990 and has maintained the CP type. The strengthened SP ENSO dynamic since 1990, accompanied by enhanced precipitation efficiency during La Niña, make it easier for La Niña to transition into MY events. In contrast, there is no observed increase in precipitation efficiency during El Niño. 
    more » « less
  4. ; ; ; ; (, Journal of Climate)
    null (Ed.)
    Abstract Winter surface air temperature (SAT) over North America exhibits pronounced variability on subseasonal, interannual, decadal, and interdecadal time scales. Here, reanalysis data from 1950–2017 are analyzed to investigate the atmospheric and surface ocean conditions associated with its subseasonal to interannual variability. Detrended daily SAT data reveal a known warm west/cold east (WWCE) dipole over midlatitude North America and a cold north/warm south (CNWS) dipole over eastern North America. It is found that while the North Pacific blocking (PB) is important for the WWCE and CNWS dipoles, they also depend on the phase of the North Atlantic Oscillation (NAO). When a negative-phase NAO (NAO − ) coincides with PB, the WWCE dipole is enhanced (compared with the PB alone case) and it also leads to a warm north/cold south dipole anomaly in eastern North America; but when PB occurs with a positive-phase NAO (NAO + ), the WWCE dipole weakens and the CNWS dipole is enhanced. The PB events concurrent with the NAO − (NAO + ) and SAT WWCE (CNWS) dipole are favored by the Pacific El Niño–like (La Niña–like) sea surface temperature mode and the positive (negative) North Pacific mode. The PB-NAO + has a larger component projecting onto the SAT WWCE dipole during the La Niña winter than during the El Niño winter because a more zonal wave train is formed. Strong North American SAT WWCE dipoles and enhanced projections of PB-NAO + events onto the SAT WWCE dipole component are also readily seen for the positive North Pacific mode. The North Pacific mode seems to play a bigger role in the North American SAT variability than ENSO. 
    more » « less
  5. ; ; ; ; ; ; ; ; ; (, Hydrological Processes)
    Abstract This Scientific Briefing presents results from a nearly 10‐year hydrometric and isotope monitoring network across north‐central Costa Rica, a region known as a headwater‐dependent system. This monitoring system has recorded different El Niño and La Niña events and the direct/indirect effects of several hurricane and tropical storm passages. Our results show that El Niño‐Southern Oscillation (ENSO) exerts a significant but predictable impact on rainfall amount anomalies, groundwater level and spring discharge, as evidenced by second‐order water isotope parameters (e.g., line conditioned‐excess or line‐conditioned (LC)‐excess). Sea surface temperature anomaly (El Niño Region 3) is correlated with a reduction in mean annual and cold front rainfall across the headwaters of north‐central Costa Rica. During El Niño conditions, rainfall is substantially reduced (up to 69.2%) during the critical cold fronts period, limiting groundwater recharge and promoting an early onset of minimum baseflow conditions (up to 5 months). In contrast, La Niña is associated with increased rainfall and groundwater recharge (up to 94.7% during active cold front periods). During La Niña, the long‐term mean spring discharge (39 Ls−1) is exceeded 63–80% of the time, whereas, during El Niño, the exceedance time ranges between 26% and 44%. The regional hydroclimatic variability is also imprinted on the hydrogen and oxygen isotopic compositions of meteoric waters. Drier conditions favoured lower LC‐excess in rainfall (−17.3‰) and spring water (−6.5‰), whereas wetter conditions resulted in greater values (rainfall = +17.5‰; spring water = +10.7‰). The lower and higher LC‐excess values in rainfall corresponded to the very strong 2014–2016 El Niño and 2018 La Niña, respectively. During the recent triple‐dip 2021–23 La Niña, LC‐excess exhibited a significant and consistently increasing trend. These findings highlight the importance of combining hydrometric, synoptic and isotopic monitoring as ENSO sentinels to advance our current understanding of ENSO impacts on hydrological systems across the humid Tropics. Such information is critical to constraining the 21st century projections of future water stress across this fragile region. 
    more » « less
  • Citation Formats
  • MLA
  • APA
  • Chicago
  • BibTeX
  • Save / Share this Record
  • Send to Email