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  • 1
    Online Resource
    Online Resource
    Relationships between Tracer Ages and Potential Vorticity in Unsteady Wind-Driven Circulations
    American Meteorological Society ; 2005
    In:  Journal of Physical Oceanography Vol. 35, No. 11 ( 2005-11-01), p. 2250-2267
    Details
    In: Journal of Physical Oceanography, American Meteorological Society, Vol. 35, No. 11 ( 2005-11-01), p. 2250-2267
    Abstract: The relationships between different tracer ages and between tracer age and potential vorticity are examined by simulating barotropic double-gyre circulations. The unsteady model flow crudely represents aspects of the midlatitude, middepth ocean circulation including inhomogeneous and anisotropic variability. Temporal variations range in scale from weeks to years, although the statistics are stationary. These variations have a large impact on the time-averaged tracer age fields. Transport properties of the tracer age fields that have been proved for steady flow are shown to also apply to unsteady flow and are illustrated in this circulation. Variability of tracer ages from ideal age tracer, linear, and exponential transient tracers is highly coordinated in phase and amplitude and is explained using simple theory. These relationships between different tracer ages are of practical benefit to the problem of interpreting tracer ages from the real ocean or from general circulation models. There is also a close link between temporal anomalies of tracer age and potential vorticity throughout a significant fraction of the domain. There are highly significant anticorrelations between ideal age and potential vorticity in the subtropical gyre and midbasin jet region, but correlation in the central subpolar gyre and eastern part of the domain is not significant. The existence of the relationship is insensitive to the character of the flow, the tracer sources, and the potential vorticity dynamics. Its structure may be understood by considering the different time-mean states of the tracer age and potential vorticity, the different tracer sources and sinks, and the effect of variability in the flow. Prediction of the correlation without knowledge of the time-mean fields is a harder problem, however. Detecting the correlation between potential vorticity and tracer age in the real ocean will be difficult with typical synoptic oceanographic transect data that are well-sampled in space, but sparse in time. Nevertheless, it is reasonable to suppose the correlation exists in some places.
    Type of Medium: Online Resource
    ISSN: 1520-0485 , 0022-3670
    URL: Article
    DOI: 10.1175/JPO2812.1
    Language: English
    Publisher: American Meteorological Society
    Publication Date: 2005
    detail.hit.zdb_id: 2042184-9
    detail.hit.zdb_id: 184162-2
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  • 2
    Online Resource
    Online Resource
    Evaluating Simulations of Interhemispheric Transport: Interhemispheric Exchange Time Versus SF 6 Age
    American Geophysical Union (AGU) ; 2019
    In:  Geophysical Research Letters Vol. 46, No. 2 ( 2019-01-28), p. 1113-1120
    Details
    In: Geophysical Research Letters, American Geophysical Union (AGU), Vol. 46, No. 2 ( 2019-01-28), p. 1113-1120
    Abstract: Different conclusions from previous studies evaluating model simulations of interhemispheric transport are reconciled The simulated interhemispheric exchange time τ ex agrees well with observations, but the simulated SF 6 age in the SH is older than observed Transport from the northern extratropics into the tropics is too slow in most models, which has a larger effect on SF 6 age in the SH than τ ex
    Type of Medium: Online Resource
    ISSN: 0094-8276 , 1944-8007
    URL: Article
    DOI: 10.1029/2018GL080960
    Language: English
    Publisher: American Geophysical Union (AGU)
    Publication Date: 2019
    detail.hit.zdb_id: 2021599-X
    detail.hit.zdb_id: 7403-2
    SSG: 16,13
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  • 3
    Online Resource
    Online Resource
    Tropical Widening: From Global Variations to Regional Impacts
    American Meteorological Society ; 2020
    In:  Bulletin of the American Meteorological Society Vol. 101, No. 6 ( 2020-06), p. E897-E904
    Details
    In: Bulletin of the American Meteorological Society, American Meteorological Society, Vol. 101, No. 6 ( 2020-06), p. E897-E904
    Abstract: Over the past 15 years, numerous studies have suggested that the sinking branches of Earth’s Hadley circulation and the associated subtropical dry zones have shifted poleward over the late twentieth century and early twenty-first century. Early estimates of this tropical widening from satellite observations and reanalyses varied from 0.25° to 3° latitude per decade, while estimates from global climate models show widening at the lower end of the observed range. In 2016, two working groups, the U.S. Climate Variability and Predictability (CLIVAR) working group on the Changing Width of the Tropical Belt and the International Space Science Institute (ISSI) Tropical Width Diagnostics Intercomparison Project, were formed to synthesize current understanding of the magnitude, causes, and impacts of the recent tropical widening evident in observations. These working groups concluded that the large rates of observed tropical widening noted by earlier studies resulted from their use of metrics that poorly capture changes in the Hadley circulation, or from the use of reanalyses that contained spurious trends. Accounting for these issues reduces the range of observed expansion rates to 0.25°–0.5° latitude decade ‒1 —within the range from model simulations. Models indicate that most of the recent Northern Hemisphere tropical widening is consistent with natural variability, whereas increasing greenhouse gases and decreasing stratospheric ozone likely played an important role in Southern Hemisphere widening. Whatever the cause or rate of expansion, understanding the regional impacts of tropical widening requires additional work, as different forcings can produce different regional patterns of widening.
    Type of Medium: Online Resource
    ISSN: 0003-0007 , 1520-0477
    URL: Article
    DOI: 10.1175/BAMS-D-19-0047.1
    Language: Unknown
    Publisher: American Meteorological Society
    Publication Date: 2020
    detail.hit.zdb_id: 2029396-3
    detail.hit.zdb_id: 419957-1
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  • 4
    Online Resource
    Online Resource
    Transit time distributions in Lake Issyk-Kul : LAKE ISSYK-KUL TRANSIT TIMES
    American Geophysical Union (AGU) ; 2002
    In:  Geophysical Research Letters Vol. 29, No. 24 ( 2002-12), p. 84-1-84-4
    Details
    In: Geophysical Research Letters, American Geophysical Union (AGU), Vol. 29, No. 24 ( 2002-12), p. 84-1-84-4
    Type of Medium: Online Resource
    ISSN: 0094-8276
    URL: Article
    DOI: 10.1029/2002GL016201
    Language: English
    Publisher: American Geophysical Union (AGU)
    Publication Date: 2002
    detail.hit.zdb_id: 2021599-X
    detail.hit.zdb_id: 7403-2
    SSG: 16,13
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  • 5
    Online Resource
    Online Resource
    Tropospheric Age‐of‐Air: Influence of SF 6 Emissions on Recent Surface Trends and Model Biases
    American Geophysical Union (AGU) ; 2021
    In:  Journal of Geophysical Research: Atmospheres Vol. 126, No. 19 ( 2021-10-16)
    Details
    In: Journal of Geophysical Research: Atmospheres, American Geophysical Union (AGU), Vol. 126, No. 19 ( 2021-10-16)
    Abstract: The mean age since air was last at the Northern Hemisphere (NH) midlatitude surface features large (small) meridional gradients in the tropics (extratropics) Recent mean age trends in the Southern Hemisphere (SH), estimated from measurements of SF 6 , likely reflect shifts in SF 6 emissions, not transport changes Modeled SF 6 ages in the SH are older than observed, partly due to overestimation in simulated SF 6 mixing ratios near NH emissions regions
    Type of Medium: Online Resource
    ISSN: 2169-897X , 2169-8996
    URL: Article
    DOI: 10.1029/2021JD035451
    Language: English
    Publisher: American Geophysical Union (AGU)
    Publication Date: 2021
    detail.hit.zdb_id: 710256-2
    detail.hit.zdb_id: 2016800-7
    detail.hit.zdb_id: 2969341-X
    SSG: 16,13
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  • 6
    Online Resource
    Online Resource
    Ventilation Rates Estimated from Tracers in the Presence of Mixing
    American Meteorological Society ; 2007
    In:  Journal of Physical Oceanography Vol. 37, No. 11 ( 2007-11-01), p. 2599-2611
    Details
    In: Journal of Physical Oceanography, American Meteorological Society, Vol. 37, No. 11 ( 2007-11-01), p. 2599-2611
    Abstract: The intimate relationship among ventilation, transit-time distributions, and transient tracer budgets is analyzed. To characterize the advective–diffusive transport from the mixed layer to the interior ocean in terms of flux we employ a cumulative ventilation-rate distribution, Φ(τ), defined as the one-way mass flux of water that resides at least time τ in the interior before returning. A one-way (or gross) flux contrasts with the net advective flux, often called the subduction rate, which does not accommodate the effects of mixing, and it contrasts with the formation rate, which depends only on the net effects of advection and diffusive mixing. As τ decreases Φ(τ) increases, encompassing progressively more one-way flux. In general, Φ is a rapidly varying function of τ (it diverges at small τ), and there is no single residence time at which Φ can be evaluated to fully summarize the advective–diffusive flux. To reconcile discrepancies between estimates of formation rates in a recent GCM study, Φ(τ) is used. Then chlorofluorocarbon data are used to bound Φ(τ) for Subtropical Mode Water and Labrador Sea Water in the North Atlantic Ocean. The authors show that the neglect of diffusive mixing leads to spurious behavior, such as apparent time dependence in the formation, even when transport is steady.
    Type of Medium: Online Resource
    ISSN: 1520-0485 , 0022-3670
    URL: Article
    DOI: 10.1175/2006JPO3471.1
    Language: English
    Publisher: American Meteorological Society
    Publication Date: 2007
    detail.hit.zdb_id: 2042184-9
    detail.hit.zdb_id: 184162-2
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  • 7
    Online Resource
    Online Resource
    Causes and Impacts of Tropical Widening
    American Meteorological Society ; 2020
    In:  Bulletin of the American Meteorological Society Vol. 101, No. 7 ( 2020-07), p. 602-606
    Details
    In: Bulletin of the American Meteorological Society, American Meteorological Society, Vol. 101, No. 7 ( 2020-07), p. 602-606
    Type of Medium: Online Resource
    ISSN: 0003-0007 , 1520-0477
    URL: Article
    DOI: 10.1175/BAMS-D-19-0047.A
    Language: Unknown
    Publisher: American Meteorological Society
    Publication Date: 2020
    detail.hit.zdb_id: 2029396-3
    detail.hit.zdb_id: 419957-1
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  • 8
    Online Resource
    Online Resource
    How Rapidly Do the Southern Subtropical Oceans Respond to Wind Stress Changes?
    American Geophysical Union (AGU) ; 2020
    In:  Journal of Geophysical Research: Oceans Vol. 125, No. 7 ( 2020-07)
    Details
    In: Journal of Geophysical Research: Oceans, American Geophysical Union (AGU), Vol. 125, No. 7 ( 2020-07)
    Abstract: There is a decadal to centennial response time for temperature, salinity, and ideal age in mode waters to an increase in the wind stress Wind‐driven trends in temperature, salinity, and ideal age may continue for several decades even if there is a pause in wind stress trends The response time of the ideal age to an increase in wind stress is much younger than the ideal age itself
    Type of Medium: Online Resource
    ISSN: 2169-9275 , 2169-9291
    URL: Article
    DOI: 10.1029/2020JC016236
    Language: English
    Publisher: American Geophysical Union (AGU)
    Publication Date: 2020
    detail.hit.zdb_id: 2016804-4
    detail.hit.zdb_id: 161667-5
    detail.hit.zdb_id: 3094219-6
    SSG: 16,13
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  • 9
    Online Resource
    Online Resource
    Response of Southern Ocean Ventilation to Changes in Midlatitude Westerly Winds
    American Meteorological Society ; 2019
    In:  Journal of Climate Vol. 32, No. 17 ( 2019-09-01), p. 5345-5361
    Details
    In: Journal of Climate, American Meteorological Society, Vol. 32, No. 17 ( 2019-09-01), p. 5345-5361
    Abstract: Changes in ventilation of the Southern Hemisphere oceans in response to changes in midlatitude westerly winds are examined by analyzing the ideal age tracer from global eddy-permitting ocean–ice model simulations in which there is an abrupt increase and/or a meridional shift in the winds. The age response in mode and intermediate waters is found to be close to linear; the response of a combined increase and shift of peak winds is similar to the sum of the individual responses to an increase and a shift. Further, a barotropic response, following Sverdrup balance, can explain much of the age response to the changes in wind stress. There are similar peak decreases (of around 50 years) in the ideal age for a 40% increase or 2.5° poleward shift in the wind stress. However, while the age decreases throughout the thermocline for an increase in the winds, for a poleward shift in the winds the age increases in the north part of the thermocline and there are decreases in age only south of 35°S. As a consequence, the change in the volume of young water differs, with a 15% increase in the volume of water with ages younger than 50 years for a 40% increase in the winds but essentially no change in this volume for a 2.5° shift. As ventilation plays a critical role in the uptake of carbon and heat, these results suggest that the storage of anthropogenic carbon and heat in mode and intermediate waters will likely increase with a strengthening of the winds, but will be much less sensitive to a meridional shift in the peak wind stress.
    Type of Medium: Online Resource
    ISSN: 0894-8755 , 1520-0442
    URL: Article
    DOI: 10.1175/JCLI-D-19-0039.1
    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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  • 10
    Online Resource
    Online Resource
    Recent Tropical Expansion: Natural Variability or Forced Response?
    American Meteorological Society ; 2019
    In:  Journal of Climate Vol. 32, No. 5 ( 2019-03-01), p. 1551-1571
    Details
    In: Journal of Climate, American Meteorological Society, Vol. 32, No. 5 ( 2019-03-01), p. 1551-1571
    Abstract: Previous studies have documented a poleward shift in the subsiding branches of Earth’s Hadley circulation since 1979 but have disagreed on the causes of these observed changes and the ability of global climate models to capture them. This synthesis paper reexamines a number of contradictory claims in the past literature and finds that the tropical expansion indicated by modern reanalyses is within the bounds of models’ historical simulations for the period 1979–2005. Earlier conclusions that models were underestimating the observed trends relied on defining the Hadley circulation using the mass streamfunction from older reanalyses. The recent observed tropical expansion has similar magnitudes in the annual mean in the Northern Hemisphere (NH) and Southern Hemisphere (SH), but models suggest that the factors driving the expansion differ between the hemispheres. In the SH, increasing greenhouse gases (GHGs) and stratospheric ozone depletion contributed to tropical expansion over the late twentieth century, and if GHGs continue increasing, the SH tropical edge is projected to shift further poleward over the twenty-first century, even as stratospheric ozone concentrations recover. In the NH, the contribution of GHGs to tropical expansion is much smaller and will remain difficult to detect in a background of large natural variability, even by the end of the twenty-first century. To explain similar recent tropical expansion rates in the two hemispheres, natural variability must be taken into account. Recent coupled atmosphere–ocean variability, including the Pacific decadal oscillation, has contributed to tropical expansion. However, in models forced with observed sea surface temperatures, tropical expansion rates still vary widely because of internal atmospheric variability.
    Type of Medium: Online Resource
    ISSN: 0894-8755 , 1520-0442
    URL: Article
    URL: Article
    DOI: 10.1175/JCLI-D-18-0444.1
    DOI: 10.1175/jcli-d-18-0444.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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