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  • 1
    Online Resource
    Online Resource
    Analysis links Pacific decadal variability to drought and streamflow in United States
    American Geophysical Union (AGU) ; 1999
    In:  Eos, Transactions American Geophysical Union Vol. 80, No. 51 ( 1999-12-21), p. 621-625
    Details
    In: Eos, Transactions American Geophysical Union, American Geophysical Union (AGU), Vol. 80, No. 51 ( 1999-12-21), p. 621-625
    Abstract: The two leading patterns of Pacific decadal sea surface temperature (SST) variability are strongly linked to large‐scale patterns of warm‐season drought and streamflow in the United States, recent analysis shows. The predictive potential of this link may contribute to the development of warm‐season hydroclimate forecasts in the United States. Understanding of low‐frequency variations in drought and streamflow would be important for both agriculture and water resources management. The two leading patterns are what we call the Pacific Decadal Oscillation (PDO) and the North Pacific mode. Their link with drought and streamflow patterns was notably expressed in the 1960s when severe drought in the northeast (the 1962–66 “Northeastern” drought) and exceptional positive SST anomalies in the North Pacific Ocean (Figures 1a, 1b) both occurred. Analysis of upper tropospheric circulation anomalies showed the North Pacific to be a source region of wave activity affecting the drought area in these summers. The anomalous circulation was vertically coherent and opposed the climatological low‐level moisture inflow over the eastern United States associated with the western extension of the Bermuda High.
    Type of Medium: Online Resource
    ISSN: 0096-3941 , 2324-9250
    URL: Article
    DOI: 10.1029/99EO00412
    Language: English
    Publisher: American Geophysical Union (AGU)
    Publication Date: 1999
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  • 2
    Online Resource
    Online Resource
    Evolution of the North American Monsoon System
    American Meteorological Society ; 1998
    In:  Journal of Climate Vol. 11, No. 9 ( 1998-09), p. 2238-2257
    Details
    In: Journal of Climate, American Meteorological Society, Vol. 11, No. 9 ( 1998-09), p. 2238-2257
    Type of Medium: Online Resource
    ISSN: 0894-8755 , 1520-0442
    URL: Article
    DOI: 10.1175/1520-0442(1998)011〈2238:EOTNAM〉2.0.CO;2
    RVK:
    UA 4548
    Language: English
    Publisher: American Meteorological Society
    Publication Date: 1998
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  • 3
    Online Resource
    Online Resource
    Evaluation of CMIP5 retrospective simulations of temperature and precipitation in northeastern Argentina
    Wiley ; 2018
    In:  International Journal of Climatology Vol. 38, No. S1 ( 2018-04)
    Details
    In: International Journal of Climatology, Wiley, Vol. 38, No. S1 ( 2018-04)
    Abstract: It is generally agreed that models that better simulate historical and current features of climate should also be the ones that more reliably simulate future climate. This article describes the ability of a selection of global climate models (GCMs) of the Coupled Model Intercomparison Project Phase 5 (CMIP5) to represent the historical and current mean climate and its variability over northeastern Argentina, a region that exhibits frequent extreme events. Two types of simulations are considered: Long‐term simulations for 1901–2005 in which the models respond to climate forcing (e.g. changes in atmospheric composition and land use) and decadal simulations for 1961–2010 that are initialized from observed climate states. Monthly simulations of precipitation and temperature are statistically evaluated for individual models and their ensembles. Subsets of models that best represent the region's climate are further examined. First, models that have a Nash–Sutcliffe efficiency of at least 0.8 are taken as a subset that best represents the observed temperature fields and the mean annual cycle. Their temperature time series are in phase with observations ( r 〉 0.92), despite systematic errors that if desired can be corrected by statistical methods. Likewise, models that have a precipitation Pearson correlation coefficient of at least 0.6 are considered that best represent regional precipitation features. GCMs are able to reproduce the annual precipitation cycle, although they underestimate precipitation amounts during the austral warm season (September through April) and slightly overestimate the cold season rainfall amounts. The ensembles for the subsets of models achieve the best evaluation metrics, exceeding the performance of the overall ensembles as well as those of the individual models.
    Type of Medium: Online Resource
    ISSN: 0899-8418 , 1097-0088
    URL: Issue
    URL: Article
    DOI: 10.1002/joc.2018.38.issue-S1
    DOI: 10.1002/joc.5441
    RVK:
    RA 1000
    Language: English
    Publisher: Wiley
    Publication Date: 2018
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    SSG: 14
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  • 4
    Online Resource
    Online Resource
    Wavelike Southern Hemisphere Extratropical Teleconnections
    American Meteorological Society ; 1992
    In:  Journal of the Atmospheric Sciences Vol. 49, No. 2 ( 1992-01), p. 155-177
    Details
    In: Journal of the Atmospheric Sciences, American Meteorological Society, Vol. 49, No. 2 ( 1992-01), p. 155-177
    Type of Medium: Online Resource
    ISSN: 0022-4928 , 1520-0469
    URL: Article
    DOI: 10.1175/1520-0469(1992)049〈0155:WSHET〉2.0.CO;2
    RVK:
    UA 4800
    Language: English
    Publisher: American Meteorological Society
    Publication Date: 1992
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    SSG: 16,13
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  • 5
    Online Resource
    Online Resource
    Intense Rainfall Events Affecting the La Plata Basin
    American Meteorological Society ; 2006
    In:  Journal of Hydrometeorology Vol. 7, No. 4 ( 2006-08-01), p. 769-787
    Details
    In: Journal of Hydrometeorology, American Meteorological Society, Vol. 7, No. 4 ( 2006-08-01), p. 769-787
    Abstract: The circulation features associated with intense precipitation events over the La Plata Basin (LPB) during the austral summers of 2001/02 and 2002/03 are investigated using the Eta Model runs generated at the University of Maryland. Based on the main mode of variability over LPB, two regions were selected: (i) the region of Brazil that is at the core of the South American summer monsoon system (SAMS) and (ii) the central region of LPB in southeastern South America (SESA). First, a comparison between the 24-h total precipitation in the Eta Model and the 24-h observed precipitation was made. Results show that the Eta Model captures well the temporal variability of precipitation events in both regions, although a positive bias is noticed over SAMS. Likewise, the model reproduces the distribution of precipitation rate over SESA, but not over SAMS. Nevertheless, the distribution of the moisture flux convergence intensity, which represents the dynamical forcing, is closer in shape to the observed precipitation distribution, suggesting that the model can be a useful tool in identifying the forcing for heavy precipitation events over both regions. Composites of atmospheric and surface variables were constructed for intense precipitation events during austral summer over both regions. Intense rainfall over the central La Plata Basin (SESA) is linked to an amplified upper-tropospheric midlatitude wave pattern in which rainfall occurs just east of an enhanced cyclonic circulation. Accompanying this circulation pattern, an enhanced low-level jet (LLJ) transports warm, moist air from the Amazon toward the region, contributing to an increase in the thermal contrast over SESA. The combined patterns of thermal and dynamical variables suggest that large-scale systems, like frontal systems, are important in producing intense rainfall events. The SAMS region events have a similar upper-level structure as in SESA, but they are longer lived. In this case, the moisture fluxes are determined by an eastward shift of the LLJ, but also directly from the Amazon Basin to the north. As expected, precipitation events produce large increases of simulated runoff. The largest impact is on the SESA region, affecting the streamflow of the Paraná, Paraguay, and Uruguay, the three main rivers of the LPB.
    Type of Medium: Online Resource
    ISSN: 1525-7541 , 1525-755X
    URL: Article
    DOI: 10.1175/JHM520.1
    Language: English
    Publisher: American Meteorological Society
    Publication Date: 2006
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  • 6
    Online Resource
    Online Resource
    Evaluation of WRF Model Forecasts and Their Use for Hydroclimate Monitoring over Southern South America
    American Meteorological Society ; 2016
    In:  Weather and Forecasting Vol. 31, No. 3 ( 2016-06), p. 1001-1017
    Details
    In: Weather and Forecasting, American Meteorological Society, Vol. 31, No. 3 ( 2016-06), p. 1001-1017
    Abstract: Weather forecasting and monitoring systems based on regional models are becoming increasingly relevant for decision support in agriculture and water management. This work evaluates the predictive and monitoring capabilities of a system based on WRF Model simulations at 15-km grid spacing over the La Plata basin (LPB) in southern South America, where agriculture and water resources are essential. The model’s skill up to a lead time of 7 days is evaluated with daily precipitation and 2-m temperature in situ observations for the 2-yr period from 1 August 2012 to 31 July 2014. Results show high prediction performance with 7-day lead time throughout the domain and particularly over LPB, where about 70% of rain and no-rain days are correctly predicted. Also, the probability of detection of rain days is above 80% in humid regions. Temperature observations and forecasts are highly correlated ( r 〉 0.80) while mean absolute errors, even at the maximum lead time, remain below 2.7°C for minimum and mean temperatures and below 3.7°C for maximum temperatures. The usefulness of WRF products for hydroclimate monitoring was tested for an unprecedented drought in southern Brazil and for a slightly above normal precipitation season in northeastern Argentina. In both cases the model products reproduce the observed precipitation conditions with consistent impacts on soil moisture, evapotranspiration, and runoff. This evaluation validates the model’s usefulness for forecasting weather up to 1 week in advance and for monitoring climate conditions in real time. The scores suggest that the forecast lead time can be extended into a second week, while bias correction methods can reduce some of the systematic errors.
    Type of Medium: Online Resource
    ISSN: 0882-8156 , 1520-0434
    URL: Article
    DOI: 10.1175/WAF-D-15-0130.1
    Language: Unknown
    Publisher: American Meteorological Society
    Publication Date: 2016
    detail.hit.zdb_id: 2025194-4
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  • 7
    Online Resource
    Online Resource
    North American Regional Reanalysis
    American Meteorological Society ; 2006
    In:  Bulletin of the American Meteorological Society Vol. 87, No. 3 ( 2006-03), p. 343-360
    Details
    In: Bulletin of the American Meteorological Society, American Meteorological Society, Vol. 87, No. 3 ( 2006-03), p. 343-360
    Type of Medium: Online Resource
    ISSN: 0003-0007 , 1520-0477
    URL: Article
    DOI: 10.1175/BAMS-87-3-343
    Language: English
    Publisher: American Meteorological Society
    Publication Date: 2006
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    detail.hit.zdb_id: 419957-1
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  • 8
    Online Resource
    Online Resource
    Characteristics of the Southern Hemisphere Winter Storm Track with Filtered and Unfiltered Data
    American Meteorological Society ; 1996
    In:  Journal of the Atmospheric Sciences Vol. 53, No. 3 ( 1996-02), p. 468-481
    Details
    In: Journal of the Atmospheric Sciences, American Meteorological Society, Vol. 53, No. 3 ( 1996-02), p. 468-481
    Type of Medium: Online Resource
    ISSN: 0022-4928 , 1520-0469
    URL: Article
    DOI: 10.1175/1520-0469(1996)053〈0468:COTSHW〉2.0.CO;2
    RVK:
    UA 4800
    Language: English
    Publisher: American Meteorological Society
    Publication Date: 1996
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    SSG: 16,13
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  • 9
    Online Resource
    Online Resource
    How Does Soil Moisture Influence the Early Stages of the South American Monsoon?
    American Meteorological Society ; 2008
    In:  Journal of Climate Vol. 21, No. 2 ( 2008-01-15), p. 195-213
    Details
    In: Journal of Climate, American Meteorological Society, Vol. 21, No. 2 ( 2008-01-15), p. 195-213
    Abstract: This article discusses the feedbacks between soil moisture and precipitation during the early stages of the South American monsoon. The system achieves maximum precipitation over the southern Amazon basin and the Brazilian highlands during the austral summer. Monsoon changes are associated with the large-scale dynamics, but during its early stages, when the surface is not sufficiently wet, soil moisture anomalies may also modulate the development of precipitation. To investigate this, sensitivity experiments to initial soil moisture conditions were performed using month-long simulations with the regional mesoscale Eta model. Examination of the control simulations shows that they reproduce all major features and magnitudes of the South American circulation and precipitation patterns, particularly those of the monsoon. The surface sensible and latent heat fluxes, as well as precipitation, have a diurnal cycle whose phase is consistent with previous observational studies. The convective inhibition is smallest at the time of the precipitation maximum, but the convective available potential energy exhibits an unrealistic morning maximum that may result from an early boundary layer mixing. The sensitivity experiments show that precipitation is more responsive to reductions of soil moisture than to increases, suggesting that although the soil is not too wet, it is sufficiently humid to easily reach levels where soil moisture anomalies stop being effective in altering the evapotranspiration and other surface and boundary layer variables. Two mechanisms by which soil moisture has a positive feedback with precipitation are discussed. First, the reduction of initial soil moisture leads to a smaller latent heat flux and a larger sensible heat flux, and both contribute to a larger Bowen ratio. The smaller evapotranspiration and increased sensible heat flux lead to a drier and warmer boundary layer, which in turn reduces the atmospheric instability. Second, the deeper (and drier) boundary layer is related to a stronger and higher South American low-level jet (SALLJ). However, because of the lesser moisture content, the SALLJ carries less moisture to the monsoon region, as evidenced by the reduced moisture fluxes and their convergence. The two mechanisms—reduced convective instability and reduced moisture flux convergence—act concurrently to diminish the core monsoon precipitation.
    Type of Medium: Online Resource
    ISSN: 1520-0442 , 0894-8755
    URL: Article
    DOI: 10.1175/2007JCLI1846.1
    RVK:
    UA 4548
    Language: English
    Publisher: American Meteorological Society
    Publication Date: 2008
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  • 10
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    Online Resource
    Studies of North American continental‐scale hydrology using Eta model forecast products
    American Geophysical Union (AGU) ; 1996
    In:  Journal of Geophysical Research: Atmospheres Vol. 101, No. D3 ( 1996-03-20), p. 7305-7319
    Details
    In: Journal of Geophysical Research: Atmospheres, American Geophysical Union (AGU), Vol. 101, No. D3 ( 1996-03-20), p. 7305-7319
    Abstract: In this study, the forecast products of the National Meteorological Center's Eta model during the period August 1993 to March 1994 are critically examined to gain insight into the quality of the first guess fields used in the model's four‐dimensional data assimilation and the usefulness of the forecast products in diagnostic studies involving unmeasured hydrological variables. We find that the Eta model 12–36 hour forecasts produce patterns of monthly precipitation that are a reasonably good approximation of the monthly observed precipitation fields for the period under consideration. The diurnal cycle of the water vapor fluxes and their seasonal changes obtained from the model forecasts are also in good agreement with observations. During the warm months the stationary component of the forecast fluxes includes a good representation of the low‐level jet (LLJ) that is an important means for the transport of moisture from the Gulf of Mexico into the Great Plains. The LLJ decays during autumn, when it is replaced by the transient component of the fluxes as the means of transport of water vapor from the Gulf of Mexico region into the United States. Finally, evaporation estimates were derived from the convergence of the fluxes of the forecast fields and model and observed values of precipitation. All estimates agree within 0.5 mm d −1 and showed a reasonable seasonal cycle, with maximum evaporation during the warm season and a minimum evaporation during February.
    Type of Medium: Online Resource
    ISSN: 0148-0227
    URL: Article
    DOI: 10.1029/95JD02373
    Language: English
    Publisher: American Geophysical Union (AGU)
    Publication Date: 1996
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