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  • Jucker, Martin  (7)
  • 1
    Online Resource
    Online Resource
    The Generic Nature of the Tropospheric Response to Sudden Stratospheric Warmings
    American Meteorological Society ; 2020
    In:  Journal of Climate Vol. 33, No. 13 ( 2020-07-01), p. 5589-5610
    Details
    In: Journal of Climate, American Meteorological Society, Vol. 33, No. 13 ( 2020-07-01), p. 5589-5610
    Abstract: The tropospheric response to midwinter sudden stratospheric warmings (SSWs) is examined using an idealized model. SSW events are triggered by imposing high-latitude stratospheric heating perturbations of varying magnitude for only a few days, spun off from a free-running control integration (CTRL). The evolution of the thermally triggered SSWs is then compared with naturally occurring SSWs identified in CTRL. By applying a heating perturbation, with no modification to the momentum budget, it is possible to isolate the tropospheric response directly attributable to a change in the stratospheric polar vortex, independent of any planetary wave momentum torques involved in the initiation of an SSW. Zonal-wind anomalies associated with the thermally triggered SSWs first propagate downward to the high-latitude troposphere after ~2 weeks, before migrating equatorward and stalling at midlatitudes, where they straddle the near-surface jet. After ~3 weeks, the circulation and eddy fluxes associated with thermally triggered SSWs evolve very similarly to SSWs in CTRL, despite the lack of initial planetary wave driving. This suggests that at longer lags, the tropospheric response to SSWs is generic and it is found to be linearly governed by the strength of the lower-stratospheric warming, whereas at shorter lags, the initial formation of the SSW potentially plays a large role in the downward coupling. In agreement with previous studies, synoptic waves are found to play a key role in the persistent tropospheric jet shift at long lags. Synoptic waves appear to respond to the enhanced midlatitude baroclinicity associated with the tropospheric jet shift, and preferentially propagate poleward in an apparent positive feedback with changes in the high-latitude refractive index.
    Type of Medium: Online Resource
    ISSN: 0894-8755 , 1520-0442
    URL: Article
    URL: Article
    DOI: 10.1175/JCLI-D-19-0697.1
    DOI: 10.1175/jcli-d-19-0697.s1
    RVK:
    UA 4548
    Language: Unknown
    Publisher: American Meteorological Society
    Publication Date: 2020
    detail.hit.zdb_id: 246750-1
    detail.hit.zdb_id: 2021723-7
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  • 2
    Online Resource
    Online Resource
    Nonlinear Interaction Between the Drivers of the Monsoon and Summertime Stationary Waves
    American Geophysical Union (AGU) ; 2021
    In:  Geophysical Research Letters Vol. 48, No. 14 ( 2021-07-28)
    Details
    In: Geophysical Research Letters, American Geophysical Union (AGU), Vol. 48, No. 14 ( 2021-07-28)
    Abstract: Monsoons are due to a non‐additive response to three forcings: land‐sea contrast, orography, and ocean heat transport The non‐additivity in precipitation leads to a non‐additive response of the upper level stationary waves and Asian monsoon anticyclone Gross moist stability can account for this effect, but not the land‐sea breeze paradigm
    Type of Medium: Online Resource
    ISSN: 0094-8276 , 1944-8007
    URL: Article
    DOI: 10.1029/2020GL092321
    Language: English
    Publisher: American Geophysical Union (AGU)
    Publication Date: 2021
    detail.hit.zdb_id: 2021599-X
    detail.hit.zdb_id: 7403-2
    SSG: 16,13
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  • 3
    Online Resource
    Online Resource
    Stationary Waves Weaken and Delay the Near-Surface Response to Stratospheric Ozone Depletion
    American Meteorological Society ; 2023
    In:  Journal of Climate Vol. 36, No. 2 ( 2023-01-15), p. 565-583
    Details
    In: Journal of Climate, American Meteorological Society, Vol. 36, No. 2 ( 2023-01-15), p. 565-583
    Abstract: An intermediate-complexity moist general circulation model is used to investigate the factors controlling the magnitude of the surface impact from Southern Hemisphere springtime ozone depletion. In contrast to previous idealized studies, a model with full radiation is used; furthermore, the model can be run with a varied representation of the surface, from a zonally uniform aquaplanet to a configuration with realistic stationary waves. The model captures the observed summertime positive Southern Annular Mode response to stratospheric ozone depletion. While synoptic waves dominate the long-term poleward jet shift, the initial response includes changes in planetary waves that simultaneously moderate the polar cap cooling (i.e., a negative feedback) and also constitute nearly one-half of the initial momentum flux response that shifts the jet poleward. The net effect is that stationary waves weaken the circulation response to ozone depletion in both the stratosphere and troposphere and also delay the response until summer rather than spring when ozone depletion peaks. It is also found that Antarctic surface cooling in response to ozone depletion helps to strengthen the poleward shift; however, shortwave surface effects of ozone are not critical. These surface temperature and stationary wave feedbacks are strong enough to overwhelm the previously recognized jet latitude/persistence feedback, potentially explaining why some recent comprehensive models do not exhibit a clear relationship between jet latitude/persistence and the magnitude of the response to ozone. The jet response is shown to be linear with respect to the magnitude of the imposed stratospheric perturbation, demonstrating the usefulness of interannual variability in ozone depletion for subseasonal forecasting.
    Type of Medium: Online Resource
    ISSN: 0894-8755 , 1520-0442
    URL: Article
    URL: Article
    DOI: 10.1175/JCLI-D-21-0874.1
    DOI: 10.1175/JCLI-D-21-0874.s1
    RVK:
    UA 4548
    Language: Unknown
    Publisher: American Meteorological Society
    Publication Date: 2023
    detail.hit.zdb_id: 246750-1
    detail.hit.zdb_id: 2021723-7
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  • 4
    Online Resource
    Online Resource
    The Downward Influence of Sudden Stratospheric Warmings: Association with Tropospheric Precursors
    American Meteorological Society ; 2019
    In:  Journal of Climate Vol. 32, No. 1 ( 2019-01-01), p. 85-108
    Details
    In: Journal of Climate, American Meteorological Society, Vol. 32, No. 1 ( 2019-01-01), p. 85-108
    Abstract: Tropospheric features preceding sudden stratospheric warming events (SSWs) are identified using a large compendium of events obtained from a chemistry–climate model. In agreement with recent observational studies, it is found that approximately one-third of SSWs are preceded by extreme episodes of wave activity in the lower troposphere. The relationship becomes stronger in the lower stratosphere, where ~60% of SSWs are preceded by extreme wave activity at 100 hPa. Additional analysis characterizes events that do or do not appear to subsequently impact the troposphere, referred to as downward and non-downward propagating SSWs, respectively. On average, tropospheric wave activity is larger preceding downward-propagating SSWs compared to non-downward propagating events, and associated in particular with a doubly strengthened Siberian high. Of the SSWs that were preceded by extreme lower-tropospheric wave activity, ~2/3 propagated down to the troposphere, and hence the presence of extreme lower-tropospheric wave activity can only be used probabilistically to predict a slight increase or decrease at the onset, of the likelihood of tropospheric impacts to follow. However, a large number of downward and non-downward propagating SSWs must be considered ( & gt;35), before the difference becomes statistically significant. The precursors are also robust upon comparison with composites consisting of randomly selected tropospheric northern annular mode (NAM) events. The downward influence and precursors to split and displacement events are also examined. It is found that anomalous upward wave-1 fluxes precede both cases. Splits exhibit a near instantaneous, barotropic response in the stratosphere and troposphere, while displacements have a stronger long-term influence.
    Type of Medium: Online Resource
    ISSN: 0894-8755 , 1520-0442
    URL: Article
    URL: Article
    DOI: 10.1175/JCLI-D-18-0053.1
    DOI: 10.1175/jcli-d-18-0053.s1
    RVK:
    UA 4548
    Language: English
    Publisher: American Meteorological Society
    Publication Date: 2019
    detail.hit.zdb_id: 246750-1
    detail.hit.zdb_id: 2021723-7
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  • 5
    Online Resource
    Online Resource
    The Building Blocks of Northern Hemisphere Wintertime Stationary Waves
    American Meteorological Society ; 2020
    In:  Journal of Climate Vol. 33, No. 13 ( 2020-07-01), p. 5611-5633
    Details
    In: Journal of Climate, American Meteorological Society, Vol. 33, No. 13 ( 2020-07-01), p. 5611-5633
    Abstract: An intermediate-complexity moist general circulation model is used to investigate the forcing of stationary waves in the Northern Hemisphere boreal winter by land–sea contrast, horizontal heat fluxes in the ocean, and topography. The additivity of the response to these building blocks is investigated. In the Pacific sector, the stationary wave pattern is not simply the linear additive sum of the response to each forcing. In fact, over the northeast Pacific and western North America, the sum of the responses to each forcing is actually opposite to that when all three are imposed simultaneously due to nonlinear interactions among the forcings. The source of the nonlinearity is diagnosed using the zonally anomalous steady-state thermodynamic balance, and it is shown that the background-state temperature field set up by each forcing dictates the stationary wave response to the other forcings. As all three forcings considered here strongly impact the temperature field and its zonal gradients, the nonlinearity and nonadditivity in our experiments can be explained, but only in a diagnostic sense. This nonadditivity extends up to the stratosphere, and also to surface temperature, where the sum of the responses to each forcing differs from the response if all forcings are included simultaneously. Only over western Eurasia is additivity a reasonable (though not perfect) assumption; in this sector land–sea contrast is most important over Europe, while topography is most important over western Asia. In other regions, where nonadditivity is pronounced, the question of which forcing is most important is ill-posed.
    Type of Medium: Online Resource
    ISSN: 0894-8755 , 1520-0442
    URL: Article
    URL: Article
    DOI: 10.1175/JCLI-D-19-0181.1
    DOI: 10.1175/jcli-d-19-0181.s1
    RVK:
    UA 4548
    Language: Unknown
    Publisher: American Meteorological Society
    Publication Date: 2020
    detail.hit.zdb_id: 246750-1
    detail.hit.zdb_id: 2021723-7
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  • 6
    Online Resource
    Online Resource
    The Impact of SST Biases in the Tropical East Pacific and Agulhas Current Region on Atmospheric Stationary Waves in the Southern Hemisphere
    American Meteorological Society ; 2020
    In:  Journal of Climate Vol. 33, No. 21 ( 2020-11-01), p. 9351-9374
    Details
    In: Journal of Climate, American Meteorological Society, Vol. 33, No. 21 ( 2020-11-01), p. 9351-9374
    Abstract: Climate models in phase 5 of the Coupled Model Intercomparison Project (CMIP5) vary significantly in their ability to simulate the phase and amplitude of atmospheric stationary waves in the midlatitude Southern Hemisphere. These models also suffer from a double intertropical convergence zone (ITCZ), with excessive precipitation in the tropical eastern South Pacific, and many also suffer from a biased simulation of the dynamics of the Agulhas Current around the tip of South Africa. The intermodel spread in the strength and phasing of SH midlatitude stationary waves in the CMIP archive is shown to be significantly correlated with the double-ITCZ bias and biases in the Agulhas Return Current. An idealized general circulation model (GCM) is used to demonstrate the causality of these links by prescribing an oceanic heat flux out of the tropical east Pacific and near the Agulhas Current. A warm bias in tropical east Pacific SSTs associated with an erroneous double ITCZ leads to a biased representation of midlatitude stationary waves in the austral hemisphere, capturing the response evident in CMIP models. Similarly, an overly diffuse sea surface temperature gradient associated with a weak Agulhas Return Current leads to an equatorward shift of the Southern Hemisphere jet by more than 3° and weak stationary wave activity in the austral hemisphere. Hence, rectification of the double-ITCZ bias and a better representation of the Agulhas Current should be expected to lead to an improved model representation of the austral hemisphere.
    Type of Medium: Online Resource
    ISSN: 0894-8755 , 1520-0442
    URL: Article
    URL: Article
    DOI: 10.1175/JCLI-D-20-0195.1
    DOI: 10.1175/JCLI-D-20-0195.s1
    RVK:
    UA 4548
    Language: Unknown
    Publisher: American Meteorological Society
    Publication Date: 2020
    detail.hit.zdb_id: 246750-1
    detail.hit.zdb_id: 2021723-7
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  • 7
    Online Resource
    Online Resource
    A QBO Cookbook: Sensitivity of the Quasi‐Biennial Oscillation to Resolution, Resolved Waves, and Parameterized Gravity Waves
    American Geophysical Union (AGU) ; 2022
    In:  Journal of Advances in Modeling Earth Systems Vol. 14, No. 3 ( 2022-03)
    Details
    In: Journal of Advances in Modeling Earth Systems, American Geophysical Union (AGU), Vol. 14, No. 3 ( 2022-03)
    Abstract: Sensitivity of the quasi‐biennial oscillation (QBO) to resolution, dissipation, wave forcing, and parameterized gravity waves is explored in a single framework The influence of these factors on the QBO can be related to their impact on wave‐induced momentum fluxes in the deep tropics The QBO period can be tuned independently of its amplitude, but the vertical structure (particularly at lower levels) is harder to capture
    Type of Medium: Online Resource
    ISSN: 1942-2466 , 1942-2466
    URL: Article
    DOI: 10.1029/2021MS002568
    Language: English
    Publisher: American Geophysical Union (AGU)
    Publication Date: 2022
    detail.hit.zdb_id: 2462132-8
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