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  • Karnauskas, Kristopher B.  (7)
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  • 1
    Online Resource
    Online Resource
    The Effect of the Galápagos Islands on ENSO in Forced Ocean and Hybrid Coupled Models
    American Meteorological Society ; 2008
    In:  Journal of Physical Oceanography Vol. 38, No. 11 ( 2008-11-01), p. 2519-2534
    Details
    In: Journal of Physical Oceanography, American Meteorological Society, Vol. 38, No. 11 ( 2008-11-01), p. 2519-2534
    Abstract: An ocean general circulation model (OGCM) of the tropical Pacific Ocean is used to examine the effects of the Galápagos Islands on the El Niño–Southern Oscillation (ENSO). First, a series of experiments is conducted using the OGCM in a forced context, whereby an idealized El Niño event may be examined in cases with and without the Galápagos Islands. In this setup, the sensitivity of the sea surface temperature (SST) anomaly response to the presence of the Galápagos Islands is examined. Second, with the OGCM coupled to the atmosphere via zonal wind stress, experiments are conducted with and without the Galápagos Islands to determine how the Galápagos Islands influence the time scale of ENSO. In the forced setup, the Galápagos Islands lead to a damped SST anomaly given an identical zonal wind stress perturbation. Mixed layer heat budget calculations implicate the entrainment mixing term, which confirms that the difference is due to the Galápagos Islands changing the background mean state, that is, the equatorial thermocline as diagnosed in a previous paper. In the hybrid coupled experiments, there is a clear shift in the power spectrum of SST anomalies in the eastern equatorial Pacific. Specifically, the Galápagos Islands lead to a shift in the ENSO time scale from a biennial to a quasi-quadrennial period. Mechanisms for the shift in ENSO time scale due to the Galápagos Islands are discussed in the context of well-known paradigms for the oscillatory nature of ENSO.
    Type of Medium: Online Resource
    ISSN: 1520-0485 , 0022-3670
    URL: Article
    DOI: 10.1175/2008JPO3848.1
    Language: English
    Publisher: American Meteorological Society
    Publication Date: 2008
    detail.hit.zdb_id: 2042184-9
    detail.hit.zdb_id: 184162-2
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  • 2
    Online Resource
    Online Resource
    The Role of SST in the East Pacific Warm Pool in the Interannual Variability of Central American Rainfall
    American Meteorological Society ; 2009
    In:  Journal of Climate Vol. 22, No. 10 ( 2009-05-15), p. 2605-2623
    Details
    In: Journal of Climate, American Meteorological Society, Vol. 22, No. 10 ( 2009-05-15), p. 2605-2623
    Abstract: Satellite- and gauge-based precipitation and sea surface temperature (SST) are analyzed to understand the role of SST in the east Pacific warm pool (EPWP) in the interannual variability of Central American rainfall. It is shown that, during the rainy season following the mature phase of an El Niño event, an anomalously warm EPWP can cause a rapid enhancement of the eastern Pacific intertropical convergence zone (EP ITCZ), which directly leads to a positive rainfall anomaly over Central America. Moreover, the timing and amplitude of the SST-enhanced EP ITCZ depends on the persistence of the El Niño event. The longer the equatorial SST anomaly persists, the longer the EPWP is subject to anomalous shortwave heating, and thus the stronger (and later) the subsequent SST enhancement of the EP ITCZ. The implications for regional climate monitoring and predictability are explored; potential predictability of seasonal rainfall is demonstrated 4 months in advance using an SST-based index designed to capture the essence of the above-mentioned mechanism.
    Type of Medium: Online Resource
    ISSN: 1520-0442 , 0894-8755
    URL: Article
    DOI: 10.1175/2008JCLI2468.1
    RVK:
    UA 4548
    Language: English
    Publisher: American Meteorological Society
    Publication Date: 2009
    detail.hit.zdb_id: 246750-1
    detail.hit.zdb_id: 2021723-7
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  • 3
    Online Resource
    Online Resource
    North American Droughts in ERA-40 Global and NCEP North American Regional Reanalyses: A Palmer Drought Severity Index Perspective
    American Meteorological Society ; 2008
    In:  Journal of Climate Vol. 21, No. 10 ( 2008-05-15), p. 2102-2123
    Details
    In: Journal of Climate, American Meteorological Society, Vol. 21, No. 10 ( 2008-05-15), p. 2102-2123
    Abstract: The Palmer drought severity index (PDSI) monitors meteorological and surface hydrological parameters to represent the severity of drought conditions. PDSI datasets are developed for the NCEP North American Regional Reanalysis (NARR) and the 40-yr European Centre for Medium-Range Weather Forecasts (ECMWF) Re-Analysis (ERA-40) to facilitate North American drought research with these datasets. The drought index calculation, in particular, allows diagnostic assessment of the relative contributions of various surface water balance terms in generation of drought conditions by selectively holding these terms to their climatological value in PDSI computations. The length of the diagnosed PDSI permits analysis of subdecadal time-scale variability, such as ENSO, whose influence on North American drought evolution is investigated. ENSO’s considerable drought impact is potentially predictable, especially in the southern half of the United States.
    Type of Medium: Online Resource
    ISSN: 1520-0442 , 0894-8755
    URL: Article
    DOI: 10.1175/2007JCLI1837.1
    RVK:
    UA 4548
    Language: English
    Publisher: American Meteorological Society
    Publication Date: 2008
    detail.hit.zdb_id: 246750-1
    detail.hit.zdb_id: 2021723-7
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  • 4
    Online Resource
    Online Resource
    Observing the Galápagos–EUC Interaction: Insights and Challenges
    American Meteorological Society ; 2010
    In:  Journal of Physical Oceanography Vol. 40, No. 12 ( 2010-12-01), p. 2768-2777
    Details
    In: Journal of Physical Oceanography, American Meteorological Society, Vol. 40, No. 12 ( 2010-12-01), p. 2768-2777
    Abstract: Although sustained observations yield a description of the mean equatorial current system from the western Pacific to the eastern terminus of the Tropical Atmosphere Ocean (TAO) array, a comprehensive observational dataset suitable for describing the structure and pathways of the Equatorial Undercurrent (EUC) east of 95°W does not exist and therefore climate models are unconstrained in a region that plays a critical role in ocean–atmosphere coupling. Furthermore, ocean models suggest that the interaction between the EUC and the Galápagos Islands (∼92°W) has a striking effect on the basic state and coupled variability of the tropical Pacific. To this end, the authors interpret historical measurements beginning with those made in conjunction with the discovery of the Pacific EUC in the 1950s, analyze velocity measurements from an equatorial TAO mooring at 85°W, and analyze a new dataset from archived shipboard ADCP measurements. Together, the observations yield a possible composite description of the EUC structure and pathways in the eastern equatorial Pacific that may be useful for model validation and guiding future observation.
    Type of Medium: Online Resource
    ISSN: 1520-0485 , 0022-3670
    URL: Article
    DOI: 10.1175/2010JPO4461.1
    Language: English
    Publisher: American Meteorological Society
    Publication Date: 2010
    detail.hit.zdb_id: 2042184-9
    detail.hit.zdb_id: 184162-2
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  • 5
    Online Resource
    Online Resource
    The Effect of the Galápagos Islands on the Equatorial Pacific Cold Tongue
    American Meteorological Society ; 2007
    In:  Journal of Physical Oceanography Vol. 37, No. 5 ( 2007-05-01), p. 1266-1281
    Details
    In: Journal of Physical Oceanography, American Meteorological Society, Vol. 37, No. 5 ( 2007-05-01), p. 1266-1281
    Abstract: A reduced-gravity ocean general circulation model of the tropical Pacific Ocean is used to determine potential improvements to the simulated equatorial Pacific cold tongue region through choices in horizontal resolution and coastline geometry—in particular, for the Galápagos Islands. Four simulations are performed, with identical climatological forcing. Results are compared between model grids with and without the Galápagos Islands, with coarse and fine resolutions. It is found that properly including the Galápagos Islands results in the obstruction of the Equatorial Undercurrent (EUC), which leads to improvements in the simulated spatial structure of the cold tongue, including a basinwide warming of up to 2°C in the east-central Pacific. The obstruction of the EUC is directly related to the improvements east of the Galápagos Islands, and for the basinwide reduction of the tropical cold bias through an equatorial dynamical adjustment. The pattern of SST warming resulting from the inclusion of the Galápagos Islands is similar to that of the known cold biases in ocean models and the current National Oceanic and Atmospheric Administration Climate Forecast System. It is thought that such an improvement would have a considerable impact on the ability of coupled ocean–atmosphere and ocean–ecosystem models to produce realistic clouds, precipitation, surface ocean bioproductivity, and carbon cycling in the tropical Pacific Ocean.
    Type of Medium: Online Resource
    ISSN: 1520-0485 , 0022-3670
    URL: Article
    DOI: 10.1175/JPO3048.1
    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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  • 6
    Online Resource
    Online Resource
    Low-Frequency Variability and Remote Forcing of Gap Winds over the East Pacific Warm Pool
    American Meteorological Society ; 2008
    In:  Journal of Climate Vol. 21, No. 19 ( 2008-10-01), p. 4901-4918
    Details
    In: Journal of Climate, American Meteorological Society, Vol. 21, No. 19 ( 2008-10-01), p. 4901-4918
    Abstract: The low-frequency variability of gap winds at the Isthmuses of Tehuantepec and Papagayo is investigated using a 17-yr wind stress dataset merging the remotely sensed observations of Special Sensor Microwave Imager (SSM/I) and Quick Scatterometer (QuikSCAT) satellite sensors. A decadal signal is identified in the Tehuantepec gap winds, which is shown to be related to the Atlantic tripole pattern (ATP). Using linear regression and spectral analysis, it is demonstrated that the low-frequency variability of the Tehuantepec gap winds is remotely forced by the ATP, and the Papagayo gap winds are primarily governed by El Niño–Southern Oscillation (ENSO) with the ATP being of secondary importance. The Tehuantepec (Papagayo) time series of wind stress anomalies can be better reconstructed when the local cross-isthmus pressure difference and large-scale climate information such as the ATP (ENSO) are included, suggesting that there is important information in the large-scale flow that is not transmitted directly through the background sea level pressure gradient. The geostrophic modulation of the easterly trades in the western Caribbean also serve as a remote driver of the Papagayo gap winds, which is itself not fully independent from ENSO. Finally, it is suggested that precipitation variability in the Inter-Americas region is closely related to the same remote forcing as that of the Tehuantepec gap winds, being the ATP and associated large-scale atmospheric circulation.
    Type of Medium: Online Resource
    ISSN: 1520-0442 , 0894-8755
    URL: Article
    DOI: 10.1175/2008JCLI1771.1
    RVK:
    UA 4548
    Language: English
    Publisher: American Meteorological Society
    Publication Date: 2008
    detail.hit.zdb_id: 246750-1
    detail.hit.zdb_id: 2021723-7
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  • 7
    Online Resource
    Online Resource
    Mechanisms for the Interannual Variability of SST in the East Pacific Warm Pool
    American Meteorological Society ; 2009
    In:  Journal of Climate Vol. 22, No. 6 ( 2009-03-15), p. 1375-1392
    Details
    In: Journal of Climate, American Meteorological Society, Vol. 22, No. 6 ( 2009-03-15), p. 1375-1392
    Abstract: In comparison with the western and equatorial Pacific Ocean, relatively little is known about the east Pacific warm pool (EPWP). Observations indicate that the interannual variability of sea surface temperature (SST) in the EPWP is highly correlated (0.95) with the El Niño–Southern Oscillation (ENSO). In this paper, an ocean general circulation model (OGCM) of the tropical Pacific Ocean and various atmospheric and oceanic observations are used to diagnose the physical processes governing the interannual variability of SST in the EPWP. Atmospheric forcings for the OGCM are derived purely from satellite observations between 1988 and 2004. Shortwave heating is identified as playing a dominant role in the interannual SST tendency of the EPWP. The high correlation between SST in the EPWP and eastern equatorial Pacific is therefore explained not by ocean processes, but by an atmospheric link. ENSO-driven equatorial SST anomalies modify the distribution of the overlying atmospheric vertical motions and therefore cloud cover and ultimately shortwave heating. During an El Niño event, for example, the ITCZ is equatorward displaced from its normal position over the EPWP, resulting in anomalously large shortwave heating over the EPWP. Analysis of poleward ocean heat transport and coastal Kelvin waves confirms that oceanic processes are not sufficient to explain the interannual variability of the EPWP.
    Type of Medium: Online Resource
    ISSN: 1520-0442 , 0894-8755
    URL: Article
    DOI: 10.1175/2008JCLI2467.1
    RVK:
    UA 4548
    Language: English
    Publisher: American Meteorological Society
    Publication Date: 2009
    detail.hit.zdb_id: 246750-1
    detail.hit.zdb_id: 2021723-7
    Location Call Number Limitation Availability
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