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  • 1
    Online Resource
    Online Resource
    Characteristics of the North Pacific Oscillation in CMIP5 Models in Relation to Atmospheric Mean States
    American Meteorological Society ; 2020
    In:  Journal of Climate Vol. 33, No. 9 ( 2020-05-01), p. 3809-3825
    Details
    In: Journal of Climate, American Meteorological Society, Vol. 33, No. 9 ( 2020-05-01), p. 3809-3825
    Abstract: The North Pacific Oscillation (NPO), the second leading atmospheric mode in the North Pacific Ocean, is known to be responsible for climate variability and extremes in adjacent regions. The reproducibility of the NPO in climate models is thus a topic of interest for the more accurate prediction of climate extremes. By investigating the spatial characteristics of the NPO in models from phase 5 of the Coupled Model Intercomparison Project (CMIP5), this study reveals the intimate relationship between the NPO structure and the atmospheric mean states over the North Pacific. The majority of the models reasonably capture the meridional contrast of pressure anomalies, but the detailed horizontal characteristics of the NPO are found to differ among the models. Diagnostic analysis of 30 climate models and long-term observations suggest that systematic bias in the mean atmospheric baroclinicity over the North Pacific crucially affects the horizontal shape and zonal position of the NPO. In the models in which the climatological continental trough over the western North Pacific extends farther to the east, the NPO tends to be simulated farther to the east, strengthening its impact on the downstream climate. In contrast, when the climatological continental trough is reduced in size toward the west, the growth of the NPO is limited to the west, and its influence is weakened downstream. This relationship can be understood via the altered available potential and kinetic energy conversions that feed the total energy of the NPO, primarily stemming from the difference in the mean horizontal temperature gradient and stretching deformation of the mean horizontal wind.
    Type of Medium: Online Resource
    ISSN: 0894-8755 , 1520-0442
    URL: Article
    DOI: 10.1175/JCLI-D-19-0446.1
    RVK:
    UA 4548
    Language: Unknown
    Publisher: American Meteorological Society
    Publication Date: 2020
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    detail.hit.zdb_id: 2021723-7
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  • 2
    Online Resource
    Online Resource
    Seesawing of Winter Temperature Extremes between East Asia and North America
    American Meteorological Society ; 2021
    In:  Journal of Climate Vol. 34, No. 11 ( 2021-06), p. 4423-4434
    Details
    In: Journal of Climate, American Meteorological Society, Vol. 34, No. 11 ( 2021-06), p. 4423-4434
    Abstract: In recent winters, there have been repeated observations of extreme warm and cold spells in the midlatitude countries. This has evoked questions regarding how winter temperature extremes are induced. In this study, we demonstrate that abnormally warm winter weather in East Asia can drive the onset of extremely cold weather in North America approximately one week forward. These seesawing extremes across the basin are mediated by the North Pacific Oscillation (NPO), one of the recurrent atmospheric patterns over the North Pacific. Budget analysis of the quasigeostrophic geopotential tendency equation shows that intense thermal advection over East Asia is able to trigger the growth of the NPO. Vorticity fluxes associated with the upper-level stationary trough then strengthen and maintain the NPO against thermal damping following the onset of the NPO. Differential diabatic heating accompanied by changes in circulation also positively contribute to the growth and maintenance of the NPO. These results imply that recurrent cold extremes, seemingly contrary to global warming, may be an inherent feature resulting from strengthening warm extremes.
    Type of Medium: Online Resource
    ISSN: 0894-8755 , 1520-0442
    URL: Article
    DOI: 10.1175/JCLI-D-20-0789.1
    RVK:
    UA 4548
    Language: Unknown
    Publisher: American Meteorological Society
    Publication Date: 2021
    detail.hit.zdb_id: 246750-1
    detail.hit.zdb_id: 2021723-7
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  • 3
    Online Resource
    Online Resource
    Distinct decadal modulation of Atlantic-Niño influence on ENSO
    Springer Science and Business Media LLC ; 2023
    In:  npj Climate and Atmospheric Science Vol. 6, No. 1 ( 2023-07-29)
    Details
    In: npj Climate and Atmospheric Science, Springer Science and Business Media LLC, Vol. 6, No. 1 ( 2023-07-29)
    Abstract: It is known that winter Atlantic-Niño events can induce the El Niño–Southern oscillation (ENSO) in the following winter with a lag of 1-year during one period. On the other hand, summer Atlantic-Niño events can lead to the ENSO in the subsequent winter with a half-year lag during another period. In this study, we investigate the distinct interdecadal modulation of the effect of the Atlantic-Niños on ENSO by analyzing observational reanalysis datasets. During the mid-twentieth century, the winter Atlantic-Niño exhibited increased intensity and extended westward due to warmer conditions in the tropical western Atlantic. As a result, convection occurred from the Amazon to the Atlantic, triggering an atmospheric teleconnection that led to trade wind discharging and equatorial Kelvin waves, ultimately contributing to the development of ENSO. In contrast, during late twentieth century, summer Atlantic-Niño events were closely linked to the South America low-level jet in boreal spring. This connection led to the formation of widespread and intense convection over the Amazon to the Atlantic region. Then, the Walker circulation was effectively modulated, subsequently triggering ENSO events. Further analysis revealed that the interdecadal modulation of the Atlantic–South America–Pacific mean state plays a crucial role in shaping the impact of Atlantic-Niños on ENSO by modifying not only the characteristics of the Atlantic-Niños but also ocean–atmospheric feedback process. Therefore, improving our understanding of the interdecadal modulation of the climatological mean state over the Pacific to Atlantic regions enables better anticipation of the interaction between the Atlantic and Pacific Oceans.
    Type of Medium: Online Resource
    ISSN: 2397-3722
    URL: Article
    DOI: 10.1038/s41612-023-00429-9
    Language: English
    Publisher: Springer Science and Business Media LLC
    Publication Date: 2023
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  • 4
    Online Resource
    Online Resource
    Altered atmospheric responses to eastern Pacific and central Pacific El Niños over the North Atlantic region due to stratospheric interference
    Springer Science and Business Media LLC ; 2014
    In:  Climate Dynamics Vol. 42, No. 1-2 ( 2014-1), p. 159-170
    Details
    In: Climate Dynamics, Springer Science and Business Media LLC, Vol. 42, No. 1-2 ( 2014-1), p. 159-170
    Type of Medium: Online Resource
    ISSN: 0930-7575 , 1432-0894
    URL: Article
    DOI: 10.1007/s00382-012-1661-0
    Language: English
    Publisher: Springer Science and Business Media LLC
    Publication Date: 2014
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    detail.hit.zdb_id: 1471747-5
    SSG: 16,13
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  • 5
    Online Resource
    Online Resource
    Dynamics of Two Distinct Subseasonal Growth Mechanisms of the North Pacific Oscillation
    American Meteorological Society ; 2022
    In:  Journal of Climate Vol. 35, No. 20 ( 2022-10-15), p. 3141-3156
    Details
    In: Journal of Climate, American Meteorological Society, Vol. 35, No. 20 ( 2022-10-15), p. 3141-3156
    Abstract: This study investigates the growth mechanisms of the North Pacific Oscillation (NPO), one of the primary causes of winter temperature extremes at midlatitudes. We find that the NPO has two distinct origins. One is the Rossby wave propagating across Eurasia that strengthens during cold or warm surges over East Asia. The corresponding vorticity and thermal anomalies grow into the NPO as they move eastward. The other is a local disturbance at the Asian Pacific jet stream exit that amplifies when propagating westward. The dynamical processes behind these two types of NPO growth are investigated by conducting quasigeostrophic geopotential tendency budget analysis, focusing on the relative importance of the vorticity flux and differential heat flux. It is revealed that the contribution of high-frequency eddies is greater in the NPO that grows from a local disturbance. However, NPO growth in both cases is primarily steered by low-frequency vorticity flux, which facilitates eastward or westward propagation through relative or planetary vorticity advections, respectively. Differential heat flux promotes the growth of the NPO before the onset, but dissipates the NPO anomalies afterward. The net effect of the heat flux, however, allows the NPO to amplify and persist through baroclinic instability by constraining the NPO anomalies to have westward vertical tilt. Accordingly, the NPO grows conforming to the dissipative destabilizing mechanism. From the perspective of potential vorticity (PV), the eastward growth of the NPO originates from the downstream advection of PV anomalies accumulated over East Asia, while westward growth is favored by a strong PV gradient near the jet stream. Significance Statement This study examines the origins and growth mechanism of the North Pacific Oscillation (NPO), which causes cold or warm spells in the midlatitudes during winter. Two distinct origins of the NPO are found, which are abnormal temperature events over East Asia and local atmospheric disturbances at the Asian Pacific jet stream exit. Evolutions of the NPO are traced by analyzing the roles of the vorticity and heat fluxes in addition to the contributions of synoptic eddies, which turns out to be more significant for the NPO that grows from a local disturbance. Vorticity flux overall dominates the growth of the NPO, but heat flux also helps the NPO amplify owing to background instability.
    Type of Medium: Online Resource
    ISSN: 0894-8755 , 1520-0442
    URL: Article
    DOI: 10.1175/JCLI-D-21-0837.1
    RVK:
    UA 4548
    Language: Unknown
    Publisher: American Meteorological Society
    Publication Date: 2022
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    detail.hit.zdb_id: 2021723-7
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  • 6
    Online Resource
    Online Resource
    An alterative effect by the tropical North Atlantic SST in intraseasonally varying El Niño teleconnection over the North Atlantic
    Stockholm University Press ; 2013
    In:  Tellus A: Dynamic Meteorology and Oceanography Vol. 65, No. 1 ( 2013-12-01), p. 19863-
    Details
    In: Tellus A: Dynamic Meteorology and Oceanography, Stockholm University Press, Vol. 65, No. 1 ( 2013-12-01), p. 19863-
    Type of Medium: Online Resource
    ISSN: 1600-0870
    URL: Article
    DOI: 10.3402/tellusa.v65i0.19863
    Language: Unknown
    Publisher: Stockholm University Press
    Publication Date: 2013
    detail.hit.zdb_id: 2026987-0
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  • 7
    Online Resource
    Online Resource
    North Atlantic Oscillation impact on the Atlantic Meridional Overturning Circulation shaped by the mean state
    Springer Science and Business Media LLC ; 2023
    In:  npj Climate and Atmospheric Science Vol. 6, No. 1 ( 2023-03-25)
    Details
    In: npj Climate and Atmospheric Science, Springer Science and Business Media LLC, Vol. 6, No. 1 ( 2023-03-25)
    Abstract: Accurate representation of the Atlantic Meridional Overturning Circulation (AMOC) in global climate models is crucial for reliable future climate predictions and projections. In this study, we used 42 coupled atmosphere–ocean global climate models to analyze low-frequency variability of the AMOC driven by the North Atlantic Oscillation (NAO). Our results showed that the influence of the simulated NAO on the AMOC differs significantly between the models. We showed that the large intermodel diversity originates from the diverse oceanic mean state, especially over the subpolar North Atlantic (SPNA), where deep water formation of the AMOC occurs. For some models, the climatological sea ice extent covers a wide area of the SPNA and restrains efficient air–sea interactions, making the AMOC less sensitive to the NAO. In the models without the sea-ice-covered SPNA, the upper-ocean mean stratification critically affects the relationship between the NAO and AMOC by regulating the AMOC sensitivity to surface buoyancy forcing. Our results pinpoint the oceanic mean state as an aspect of climate model simulations that must be improved for an accurate understanding of the AMOC.
    Type of Medium: Online Resource
    ISSN: 2397-3722
    URL: Article
    DOI: 10.1038/s41612-023-00354-x
    Language: English
    Publisher: Springer Science and Business Media LLC
    Publication Date: 2023
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  • 8
    Online Resource
    Online Resource
    Role of tropical atlantic SST variability as a modulator of El Niño teleconnections
    Springer Science and Business Media LLC ; 2014
    In:  Asia-Pacific Journal of Atmospheric Sciences Vol. 50, No. 3 ( 2014-5), p. 247-261
    Details
    In: Asia-Pacific Journal of Atmospheric Sciences, Springer Science and Business Media LLC, Vol. 50, No. 3 ( 2014-5), p. 247-261
    Type of Medium: Online Resource
    ISSN: 1976-7633 , 1976-7951
    URL: Article
    DOI: 10.1007/s13143-014-0013-x
    Language: English
    Publisher: Springer Science and Business Media LLC
    Publication Date: 2014
    detail.hit.zdb_id: 2545937-5
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  • 9
    Online Resource
    Online Resource
    Role of the climatological intertropical convergence zone in the seasonal footprinting mechanism of the El Niño-Southern Oscillation
    American Meteorological Society ; 2021
    In:  Journal of Climate ( 2021-03-30), p. 1-43
    Details
    In: Journal of Climate, American Meteorological Society, ( 2021-03-30), p. 1-43
    Abstract: The North Pacific Oscillation (NPO), a primary atmospheric mode over the North Pacific in boreal winter, is known to trigger the El Niño-Southern Oscillation (ENSO) in the following winter, the process of which is recognized as the seasonal footprinting mechanism (SFM). Based on the analysis of model simulations from the Coupled Model Intercomparison Project Phase 5 (CMIP5), we found that the SFM acts differently among models, and the correlation between the NPO and subsequent ENSO events, called the SFM efficiency, depends on the background mean state of the model. That is, SFM efficiency becomes stronger as the climatological position of the Pacific Intertropical Convergence Zone (ITCZ) moves poleward, representing an intensification of the northern branch of the ITCZ. When the Pacific ITCZ is located poleward, the wind-evaporation-sea surface temperature (SST) feedback becomes stronger as the precipitation response to the SST anomaly is stronger in higher latitudes compared to that of lower latitudes. In addition, such active ocean-atmosphere interactions enhance NPO variability, favoring the SFM to operate efficiently and trigger an ENSO event. Consistent with the model results, the observed SFM efficiency increased during the decades in which the northern branch of the climatological ITCZ was intensified, supporting the importance of the tropical mean state of precipitation around the Pacific ITCZ.
    Type of Medium: Online Resource
    ISSN: 0894-8755 , 1520-0442
    URL: Article
    DOI: 10.1175/JCLI-D-20-0809.1
    RVK:
    UA 4548
    Language: Unknown
    Publisher: American Meteorological Society
    Publication Date: 2021
    detail.hit.zdb_id: 246750-1
    detail.hit.zdb_id: 2021723-7
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  • 10
    Online Resource
    Online Resource
    A linkage between the North Atlantic Oscillation and its downstream development due to the existence of a blocking ridge
    American Geophysical Union (AGU) ; 2011
    In:  Journal of Geophysical Research Vol. 116, No. D11 ( 2011-06-04)
    Details
    In: Journal of Geophysical Research, American Geophysical Union (AGU), Vol. 116, No. D11 ( 2011-06-04)
    Type of Medium: Online Resource
    ISSN: 0148-0227
    URL: Article
    DOI: 10.1029/2010JD015006
    Language: English
    Publisher: American Geophysical Union (AGU)
    Publication Date: 2011
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    SSG: 16,13
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