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  • 1
    Online Resource
    Online Resource
    The Equatorial Thermocline Outcropping—A Seasonal Control on the Tropical Pacific Ocean–Atmosphere Instability Strength
    American Meteorological Society ; 2002
    In:  Journal of Climate Vol. 15, No. 19 ( 2002-10), p. 2721-2739
    Details
    In: Journal of Climate, American Meteorological Society, Vol. 15, No. 19 ( 2002-10), p. 2721-2739
    Type of Medium: Online Resource
    ISSN: 0894-8755 , 1520-0442
    URL: Article
    DOI: 10.1175/1520-0442(2002)015〈2721:TETOAS〉2.0.CO;2
    RVK:
    UA 4548
    Language: English
    Publisher: American Meteorological Society
    Publication Date: 2002
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    detail.hit.zdb_id: 2021723-7
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  • 2
    Online Resource
    Online Resource
    ENSO’s Phase Locking to the Seasonal Cycle in the Fast-SST, Fast-Wave, and Mixed-Mode Regimes
    American Meteorological Society ; 2000
    In:  Journal of the Atmospheric Sciences Vol. 57, No. 17 ( 2000-09), p. 2936-2950
    Details
    In: Journal of the Atmospheric Sciences, American Meteorological Society, Vol. 57, No. 17 ( 2000-09), p. 2936-2950
    Type of Medium: Online Resource
    ISSN: 0022-4928 , 1520-0469
    URL: Article
    DOI: 10.1175/1520-0469(2000)057〈2936:ESPLTT〉2.0.CO;2
    RVK:
    UA 4800
    Language: English
    Publisher: American Meteorological Society
    Publication Date: 2000
    detail.hit.zdb_id: 218351-1
    detail.hit.zdb_id: 2025890-2
    SSG: 16,13
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  • 3
    Online Resource
    Online Resource
    Non‐normal growth of Kelvin–Helmholtz eddies in a sea breeze
    Wiley ; 2014
    In:  Quarterly Journal of the Royal Meteorological Society Vol. 140, No. 684 ( 2014-10), p. 2147-2157
    Details
    In: Quarterly Journal of the Royal Meteorological Society, Wiley, Vol. 140, No. 684 ( 2014-10), p. 2147-2157
    Abstract: The generalized stability of a sea‐breeze front is analyzed using a two‐dimensional model. The objective is to understand the mechanisms leading to the shedding of eddies behind the sea‐breeze front, as seen in observations, laboratory experiments and numerical models. Regions with Ri 〈 1/4 are not always associated with instability in this spatially inhomogeneous flow and significant transient growth is found in the absence of normal‐mode instability, for both Ri ≤ 1/4 and Ri 〉 1/4. The energy source for optimal growth is the vertical shear of the mean horizontal wind, the vertical shear in the upper part of the front and the horizontal shear in the lower part. The growth begins with vertical advection by the perturbation velocity of the mean flow momentum located in the upper part of the front. Perturbations eventually propagate away from the localized shear area and a feedback mechanism is needed for this growth to be sustained. This feedback occurs through temperature anomalies in the upper part of the front inducing pressure‐gradient anomalies in the lower part. These gradients lead to a growing vertical wind component and this vertical wind component then enters the upper part of the front, which reinforces the extraction of energy, thereby closing the feedback loop and leading to both normal‐mode instability and, in the stable regime, large non‐normal growth. We find that both the instability and the non‐normal growth are vulnerable to parameter changes that weaken this feedback loop.
    Type of Medium: Online Resource
    ISSN: 0035-9009 , 1477-870X
    URL: Issue
    URL: Article
    DOI: 10.1002/qj.2014.140.issue-684
    DOI: 10.1002/qj.2285
    RVK:
    UA 1000
    RVK:
    UA 7650
    Language: English
    Publisher: Wiley
    Publication Date: 2014
    detail.hit.zdb_id: 3142-2
    detail.hit.zdb_id: 2089168-4
    SSG: 14
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  • 4
    Online Resource
    Online Resource
    Frequency Domain Multimodel Analysis of the Response of Atlantic Meridional Overturning Circulation to Surface Forcing
    American Meteorological Society ; 2013
    In:  Journal of Climate Vol. 26, No. 21 ( 2013-11-01), p. 8323-8340
    Details
    In: Journal of Climate, American Meteorological Society, Vol. 26, No. 21 ( 2013-11-01), p. 8323-8340
    Abstract: The dynamics of the Atlantic meridional overturning circulation (AMOC) vary considerably among different climate models; for example, some models show clear peaks in their power spectra while others do not. To elucidate these model differences, transfer functions are used to estimate the frequency domain relationship between surface forcing fields, including sea surface temperature, salinity, and wind stress, and the resulting AMOC response. These are estimated from the outputs of the Coupled Model Intercomparison Project phase 5 (CMIP5) and phase 3 (CMIP3) control runs for eight different models, with a specific focus on Geophysical Fluid Dynamics Laboratory Climate Model, version 2.1 (GFDL CM2.1), and the Community Climate System Model, version 4 (CCSM4), which exhibit rather different spectral behavior. The transfer functions show very little agreement among models for any of the pairs of variables considered, suggesting the existence of systematic model errors and that considerable uncertainty in the simulation of AMOC in current climate models remains. However, a robust feature of the frequency domain analysis is that models with spectral peaks in their AMOC correspond to those in which AMOC variability is more strongly excited by high-latitude surface perturbations that have periods corresponding to the frequency of the spectral peaks. This explains why different models exhibit such different AMOC variability. These differences would not be evident without using a method that explicitly computes the frequency dependence rather than a priori assuming a particular functional form. Finally, transfer functions are used to evaluate two proposed physical mechanisms for model differences in AMOC variability: differences in Labrador Sea stratification and excitation by westward-propagating subsurface Rossby waves.
    Type of Medium: Online Resource
    ISSN: 0894-8755 , 1520-0442
    URL: Article
    DOI: 10.1175/JCLI-D-12-00717.1
    RVK:
    UA 4548
    Language: English
    Publisher: American Meteorological Society
    Publication Date: 2013
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  • 5
    Online Resource
    Online Resource
    Essential Ingredients to the Dynamics of Westerly Wind Bursts
    American Meteorological Society ; 2019
    In:  Journal of Climate Vol. 32, No. 17 ( 2019-09-01), p. 5549-5565
    Details
    In: Journal of Climate, American Meteorological Society, Vol. 32, No. 17 ( 2019-09-01), p. 5549-5565
    Abstract: Westerly wind bursts (WWBs) are brief, anomalously westerly winds in the tropical Pacific that play a role in the dynamics of ENSO through their forcing of ocean Kelvin waves. They have been associated with atmospheric phenomena such as tropical cyclones, the MJO, and convectively coupled Rossby waves, yet their basic mechanism is not yet well understood. We study WWBs using an aquaplanet general circulation model, and find that eastward-propagating convective heating plays a key role in the generation of model WWBs, consistent with previous studies. Furthermore, wind-induced surface heat exchange (WISHE) acts on a short time scale of about two days to dramatically amplify the model WWB winds near the peak of the event. On the other hand, it is found that radiation feedbacks (i.e., changes in the net radiative anomalies accompanying westerly wind bursts) are not essential for the development of WWBs, and act as a weak negative feedback on WWBs and their associated convection. Similarly, sensible surface heat flux anomalies are not found to have an effect on the development of model WWBs.
    Type of Medium: Online Resource
    ISSN: 0894-8755 , 1520-0442
    URL: Article
    DOI: 10.1175/JCLI-D-18-0584.1
    RVK:
    UA 4548
    Language: Unknown
    Publisher: American Meteorological Society
    Publication Date: 2019
    detail.hit.zdb_id: 246750-1
    detail.hit.zdb_id: 2021723-7
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  • 6
    Online Resource
    Online Resource
    Processes Contributing to North American Cold Air Outbreaks Based on Air Parcel Trajectory Analysis
    American Meteorological Society ; 2023
    In:  Journal of Climate Vol. 36, No. 3 ( 2023-02-01), p. 931-943
    Details
    In: Journal of Climate, American Meteorological Society, Vol. 36, No. 3 ( 2023-02-01), p. 931-943
    Abstract: Wintertime cold air outbreaks are periods of extreme cold, often persisting for several days and spanning hundreds of kilometers or more. They are commonly associated with intrusions of cold polar air into the midlatitudes, but it is unclear whether the air mass’s initial temperature in the Arctic or its cooling as it travels is the determining factor in producing a cold air outbreak. By calculating air parcel trajectories for a preindustrial climate model scenario, we study the role of the origin and evolution of air masses traveling over sea ice and land and resulting in wintertime cold air outbreaks over central North America. We find that not all Arctic air masses result in a cold air outbreak when advected into the midlatitudes. We compare trajectories that originate in the Arctic and result in cold air outbreaks to those that also originate in the Arctic but lead to median temperatures when advected into the midlatitudes. While about one-third of the midlatitude temperature difference can be accounted for by the initial height and temperature in the Arctic, the other two-thirds are a result of differences in diabatic heating and cooling as the air masses travel. Vertical mixing of cold surface air into the air mass while it travels dominates the diabatic cooling and contributes to the cold events. Air masses leading to cold air outbreaks experience more negative sensible heat flux from the underlying surface, suggesting that preconditioning to establish a cold surface is key to producing cold air outbreaks. Significance Statement Wintertime cold air outbreaks can cause temperatures to plummet tens of degrees below freezing over the northern United States, with the potential to damage agriculture, infrastructure, and human health. Accurate predictions under climate change could help mitigate these effects, but there is disagreement over whether cold air outbreaks have declined in line with the already-observed global warming trend or persisted in spite of it. Focusing on cold air outbreaks that originate from the Arctic, we find that there must be additional cooling of the traveling air mass by mixing with very cold surface air as it moves south over North America in order to result in a cold outbreak.
    Type of Medium: Online Resource
    ISSN: 0894-8755 , 1520-0442
    URL: Article
    DOI: 10.1175/JCLI-D-22-0204.1
    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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  • 7
    Online Resource
    Online Resource
    Factors Affecting ENSO’s Period
    American Meteorological Society ; 2008
    In:  Journal of the Atmospheric Sciences Vol. 65, No. 5 ( 2008-05-01), p. 1570-1586
    Details
    In: Journal of the Atmospheric Sciences, American Meteorological Society, Vol. 65, No. 5 ( 2008-05-01), p. 1570-1586
    Abstract: Accurately capturing the observed mean period of ENSO in general circulation models (GCMs) is often challenging, and it is therefore useful to understand which parameters and processes affect this period. A computationally efficient simulation-based approach is used to extract both the dominant eigenvalues and corresponding eigenvectors of the linearized model from the Zebiak–Cane intermediate-complexity model of ENSO without having to directly construct the linearization. The sensitivity of the period to a variety of parameters is examined, including atmosphere–ocean coupling, atmospheric heating parameterization, thermocline depth zonal profile, western boundary reflection coefficient, atmospheric and ocean wave speeds or Rossby radii of deformation, ocean decay time, and the strength of the annual cycle. In addition to the sensitivity information, the spatial structures of the main fields (SST, thermocline thickness, and more) that are involved in period changes are obtained to aid in the physical interpretation of the sensitivities. There are three main time lags that together compose one-half of a model ENSO period: the Rossby-plus-Kelvin wave propagation time for a wind-caused central Pacific disturbance to propagate to the western ocean and back, SST dynamics that determine the lag between eastern ocean thermocline anomalies and eastern ocean SST anomalies, and the “accumulation” lag of integrating a sufficient delayed wave signal arriving from the western ocean to cancel the eastern ocean anomalies. For any of the parameter changes considered, the eigenvector changes show that the largest contributor to the period change is from changes to the last of these three mechanisms. Physical mechanisms that affect this accumulation delay are discussed, and the case is made that any significant change to ENSO’s period is in turn likely to involve changes to this delay.
    Type of Medium: Online Resource
    ISSN: 1520-0469 , 0022-4928
    URL: Article
    DOI: 10.1175/2007JAS2520.1
    RVK:
    UA 4800
    Language: English
    Publisher: American Meteorological Society
    Publication Date: 2008
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    detail.hit.zdb_id: 2025890-2
    SSG: 16,13
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  • 8
    Online Resource
    Online Resource
    The Role of Atmospheric Feedbacks in Abrupt Winter Arctic Sea Ice Loss in Future Warming Scenarios
    American Meteorological Society ; 2021
    In:  Journal of Climate Vol. 34, No. 11 ( 2021-06), p. 4435-4447
    Details
    In: Journal of Climate, American Meteorological Society, Vol. 34, No. 11 ( 2021-06), p. 4435-4447
    Abstract: Winter Arctic sea ice loss has been simulated with varying degrees of abruptness across global climate models (GCMs) run in phase 5 of the Coupled Model Intercomparison Project (CMIP5) under the high-emissions extended RCP8.5 scenario. Previous studies have proposed various mechanisms to explain modeled abrupt winter sea ice loss, such as the existence of a wintertime convective cloud feedback or the role of the freezing point as a natural threshold, but none have sought to explain the variability of the abruptness of winter sea ice loss across GCMs. Here we propose a year-to-year local positive feedback cycle in which warm, open oceans at the start of winter allow for the moistening and warming of the lower atmosphere, which in turn increases the downward clear-sky longwave radiation at the surface and suppresses ocean freezing. This situation leads to delayed and diminished winter sea ice growth and allows for increased shortwave absorption from lowered surface albedo during springtime. Last, the ocean stores this additional heat throughout the summer and autumn seasons, setting up even warmer ocean conditions that lead to further sea ice reduction. We show that the strength of this feedback, as measured by the partial temperature contributions of the different surface heat fluxes, correlates strongly with the abruptness of winter sea ice loss across models. Thus, we suggest that this feedback mechanism may explain intermodel spread in the abruptness of winter sea ice loss. In models in which the feedback mechanism is strong, this may indicate the possibility of hysteresis and thus irreversibility of sea ice loss.
    Type of Medium: Online Resource
    ISSN: 0894-8755 , 1520-0442
    URL: Article
    URL: Article
    DOI: 10.1175/JCLI-D-20-0558.1
    DOI: 10.1175/JCLI-D-20-0558.s1
    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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  • 9
    Online Resource
    Online Resource
    Modulation of Westerly Wind Bursts by Sea Surface Temperature: A Semistochastic Feedback for ENSO
    American Meteorological Society ; 2007
    In:  Journal of the Atmospheric Sciences Vol. 64, No. 9 ( 2007-09-01), p. 3281-3295
    Details
    In: Journal of the Atmospheric Sciences, American Meteorological Society, Vol. 64, No. 9 ( 2007-09-01), p. 3281-3295
    Abstract: Westerly wind bursts (WWBs) in the equatorial Pacific are known to play a significant role in the development of El Niño events. They have typically been treated as a purely stochastic external forcing of ENSO. Recent observations, however, show that WWB characteristics depend upon the large-scale SST field. The consequences of such a WWB modulation by SST are examined using an ocean general circulation model coupled to a statistical atmosphere model (i.e., a hybrid coupled model). An explicit WWB component is added to the model with guidance from a 23-yr observational record. The WWB parameterization scheme is constructed such that the likelihood of WWB occurrence increases as the western Pacific warm pool extends: a “semistochastic” formulation, which has both deterministic and stochastic elements. The location of the WWBs is parameterized to migrate with the edge of the warm pool. It is found that modulation of WWBs by SST strongly affects the characteristics of ENSO. In particular, coupled feedbacks between SST and WWBs may be sufficient to transfer the system from a damped regime to one with self-sustained oscillations. Modulated WWBs also play a role in the irregular timing of warm episodes and the asymmetry in the size of warm and cold events in this ENSO model. Parameterizing the modulation of WWBs by an increase of the linear air–sea coupling coefficient seems to miss important dynamical processes, and a purely stochastic representation of WWBs elicits only a weak ocean response. Based upon this evidence, it is proposed that WWBs may need to be treated as an internal part of the coupled ENSO system, and that the detailed knowledge of wind burst dynamics may be necessary to explain the characteristics of ENSO.
    Type of Medium: Online Resource
    ISSN: 1520-0469 , 0022-4928
    URL: Article
    DOI: 10.1175/JAS4029.1
    RVK:
    UA 4800
    Language: English
    Publisher: American Meteorological Society
    Publication Date: 2007
    detail.hit.zdb_id: 218351-1
    detail.hit.zdb_id: 2025890-2
    SSG: 16,13
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  • 10
    Online Resource
    Online Resource
    Quantifying the Dependence of Westerly Wind Bursts on the Large-Scale Tropical Pacific SST
    American Meteorological Society ; 2007
    In:  Journal of Climate Vol. 20, No. 12 ( 2007-06-15), p. 2760-2768
    Details
    In: Journal of Climate, American Meteorological Society, Vol. 20, No. 12 ( 2007-06-15), p. 2760-2768
    Abstract: The correlation between parameters characterizing observed westerly wind bursts (WWBs) in the equatorial Pacific and the large-scale SST is analyzed using singular value decomposition. The WWB parameters include the amplitude, location, scale, and probability of occurrence for a given SST distribution rather than the wind stress itself. This approach therefore allows for a nonlinear relationship between the SST and the wind signal of the WWBs. It is found that about half of the variance of the WWB parameters is explained by only two large-scale SST modes. The first mode represents a developed El Niño event, while the second mode represents the seasonal cycle. More specifically, the central longitude of WWBs, their longitudinal extent, and their probability seem to be determined to a significant degree by the ENSO-driven signal. The amplitude of the WWBs is found to be strongly influenced by the phase of the seasonal cycle. It is concluded that the WWBs, while partially stochastic, seem an inherent part of the large-scale deterministic ENSO dynamics. Implications for ENSO predictability and prediction are discussed.
    Type of Medium: Online Resource
    ISSN: 1520-0442 , 0894-8755
    URL: Article
    DOI: 10.1175/JCLI4138a.1
    RVK:
    UA 4548
    Language: English
    Publisher: American Meteorological Society
    Publication Date: 2007
    detail.hit.zdb_id: 246750-1
    detail.hit.zdb_id: 2021723-7
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