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  • 1
    Online Resource
    Online Resource
    The pattern across the continental United States of evapotranspiration variability associated with water availability
    Frontiers Media SA ; 2015
    In:  Frontiers in Earth Science Vol. 3 ( 2015-07-15)
    Details
    In: Frontiers in Earth Science, Frontiers Media SA, Vol. 3 ( 2015-07-15)
    Type of Medium: Online Resource
    ISSN: 2296-6463
    URL: Article
    DOI: 10.3389/feart.2015.00035
    Language: Unknown
    Publisher: Frontiers Media SA
    Publication Date: 2015
    detail.hit.zdb_id: 2741235-0
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  • 2
    Online Resource
    Online Resource
    African Easterly Jet: Structure and Maintenance
    American Meteorological Society ; 2009
    In:  Journal of Climate Vol. 22, No. 17 ( 2009-09-01), p. 4459-4480
    Details
    In: Journal of Climate, American Meteorological Society, Vol. 22, No. 17 ( 2009-09-01), p. 4459-4480
    Abstract: This article investigates the African easterly jet (AEJ), its structure, and the forcings contributing to its maintenance, critically revisiting previous work that attributed the maintenance of the jet to soil moisture gradients over tropical Africa. A state-of-the-art global model in a high-end computer framework is used to produce a three-member 73-yr ensemble run forced by observed SST to represent the control run. The AEJ as produced by the control is compared with the representation of the AEJ in the 40-yr ECMWF Re-Analysis (ERA-40) and other observational datasets and found to be very realistic. Five experiments are then performed, each represented by sets of three-member 22-yr-long (1980–2001) ensemble runs. The goal of the experiments is to investigate the role of meridional soil moisture gradients, different land surface properties, and orography. Unlike previous studies, which have suppressed soil moisture gradients within a highly idealized framework (i.e., the so-called bucket model), terrestrial evaporation control is here achieved with a highly sophisticated land surface treatment and with an extensively tested and complex methodology. The results show that the AEJ is suppressed by a combination of absence of meridional evaporation gradients over Africa and constant vegetation, even if the individual forcings taken separately do not lead to the AEJ disappearance, but only its modification. Moreover, the suppression of orography also leads to a different circulation in which there is no AEJ. This work suggests that it is not just soil moisture gradients but a unique combination of geographical features present only in northern tropical Africa that causes and maintains the jet.
    Type of Medium: Online Resource
    ISSN: 1520-0442 , 0894-8755
    URL: Article
    DOI: 10.1175/2009JCLI2584.1
    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
    Impacts of Local Soil Moisture Anomalies on the Atmospheric Circulation and on Remote Surface Meteorological Fields during Boreal Summer: A Comprehensive Analysis over North America
    American Meteorological Society ; 2016
    In:  Journal of Climate Vol. 29, No. 20 ( 2016-10-15), p. 7345-7364
    Details
    In: Journal of Climate, American Meteorological Society, Vol. 29, No. 20 ( 2016-10-15), p. 7345-7364
    Abstract: A series of stationary wave model (SWM) experiments are performed in which the boreal summer atmosphere is forced, over a number of locations in the continental United States, with an idealized diabatic heating anomaly that mimics the atmospheric heating associated with a dry land surface. For localized heating within a large portion of the continental interior, regardless of the specific location of this heating, the spatial pattern of the forced atmospheric circulation anomaly (in terms of 250-hPa eddy streamfunction) is largely the same: a high anomaly forms over west-central North America and a low anomaly forms to the east. In supplemental atmospheric general circulation model (AGCM) experiments, similar results are found; imposing soil moisture dryness in the AGCM in different locations within the U.S. interior tends to produce the aforementioned pattern, along with an associated near-surface warming and precipitation deficit in the center of the continent. The SWM-based and AGCM-based patterns generally agree with composites generated using reanalysis and precipitation gauge data. The AGCM experiments also suggest that dry anomalies imposed in the lower Mississippi River valley have remote surface impacts of particularly large spatial extent, and a region along the eastern half of the U.S.–Canadian border is particularly sensitive to dry anomalies in a number of remote areas. Overall, the SWM and AGCM experiments support the idea of a positive feedback loop operating over the continent: dry surface conditions in many interior locations lead to changes in atmospheric circulation that act to enhance further the overall dryness of the continental interior.
    Type of Medium: Online Resource
    ISSN: 0894-8755 , 1520-0442
    URL: Article
    DOI: 10.1175/JCLI-D-16-0192.1
    RVK:
    UA 4548
    Language: English
    Publisher: American Meteorological Society
    Publication Date: 2016
    detail.hit.zdb_id: 246750-1
    detail.hit.zdb_id: 2021723-7
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  • 4
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    Online Resource
    Prospects for Advancing Drought Understanding, Monitoring, and Prediction
    American Meteorological Society ; 2015
    In:  Journal of Hydrometeorology Vol. 16, No. 4 ( 2015-08-01), p. 1636-1657
    Details
    In: Journal of Hydrometeorology, American Meteorological Society, Vol. 16, No. 4 ( 2015-08-01), p. 1636-1657
    Abstract: This paper summarizes and synthesizes the research carried out under the NOAA Drought Task Force (DTF) and submitted in this special collection. The DTF is organized and supported by NOAA’s Climate Program Office with the National Integrated Drought Information System (NIDIS) and involves scientists from across NOAA, academia, and other agencies. The synthesis includes an assessment of successes and remaining challenges in monitoring and prediction capabilities, as well as a perspective of the current understanding of North American drought and key research gaps. Results from the DTF papers indicate that key successes for drought monitoring include the application of modern land surface hydrological models that can be used for objective drought analysis, including extended retrospective forcing datasets to support hydrologic reanalyses, and the expansion of near-real-time satellite-based monitoring and analyses, particularly those describing vegetation and evapotranspiration. In the area of drought prediction, successes highlighted in the papers include the development of the North American Multimodel Ensemble (NMME) suite of seasonal model forecasts, an established basis for the importance of La Niña in drought events over the southern Great Plains, and an appreciation of the role of internal atmospheric variability related to drought events. Despite such progress, there are still important limitations in our ability to predict various aspects of drought, including onset, duration, severity, and recovery. Critical challenges include (i) the development of objective, science-based integration approaches for merging multiple information sources; (ii) long, consistent hydrometeorological records to better characterize drought; and (iii) extending skillful precipitation forecasts beyond a 1-month lead time.
    Type of Medium: Online Resource
    ISSN: 1525-755X , 1525-7541
    URL: Article
    DOI: 10.1175/JHM-D-14-0164.1
    Language: English
    Publisher: American Meteorological Society
    Publication Date: 2015
    detail.hit.zdb_id: 2042176-X
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  • 5
    Online Resource
    Online Resource
    Seasonal Variability in the Mechanisms behind the 2020 Siberian Heatwaves
    American Meteorological Society ; 2022
    In:  Journal of Climate Vol. 35, No. 10 ( 2022-05-15), p. 3075-3090
    Details
    In: Journal of Climate, American Meteorological Society, Vol. 35, No. 10 ( 2022-05-15), p. 3075-3090
    Abstract: Record-breaking heatwaves and wildfires immersed Siberia during the boreal spring of 2020 following an anomalously warm winter. Springtime heatwaves are becoming more common in the region, with statistically significant trends in the frequency, magnitude, and duration of heatwave events over the past four decades. Mechanisms by which the heatwaves occur and contributing factors differ by season. Winter heatwave frequency is correlated with the atmospheric circulation, particularly the Arctic Oscillation, while the frequency of heatwaves during the spring months is highly correlated with aspects of the land surface including snow cover, albedo, and latent heat flux. Idealized AMIP-style experiments are used to quantify the contribution of suppressed Arctic sea ice and snow cover over Siberia on the atmospheric circulation, surface energy budget, and surface air temperature in Siberia during the winter and spring of 2020. Sea ice concentration contributed to the strength of the stratospheric polar vortex and Arctic Oscillation during the winter months, thereby influencing the tropospheric circulation and surface air temperature over Siberia. Warm temperatures across the region resulted in an earlier-than-usual recession of the winter snowpack. The exposed land surface contributed to up to 20% of the temperature anomaly during the spring through the albedo feedback and changes in the ratio of the latent and sensible heat fluxes. This, in combination with favorable atmospheric circulation patterns, resulted in record-breaking heatwaves in Siberia in the spring of 2020.
    Type of Medium: Online Resource
    ISSN: 0894-8755 , 1520-0442
    URL: Article
    DOI: 10.1175/JCLI-D-21-0432.1
    RVK:
    UA 4548
    Language: Unknown
    Publisher: American Meteorological Society
    Publication Date: 2022
    detail.hit.zdb_id: 246750-1
    detail.hit.zdb_id: 2021723-7
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  • 6
    Online Resource
    Online Resource
    Northern Eurasian Heat Waves and Droughts
    American Meteorological Society ; 2014
    In:  Journal of Climate Vol. 27, No. 9 ( 2014-05-01), p. 3169-3207
    Details
    In: Journal of Climate, American Meteorological Society, Vol. 27, No. 9 ( 2014-05-01), p. 3169-3207
    Abstract: This article reviews the understanding of the characteristics and causes of northern Eurasian summertime heat waves and droughts. Additional insights into the nature of temperature and precipitation variability in Eurasia on monthly to decadal time scales and into the causes and predictability of the most extreme events are gained from the latest generation of reanalyses and from supplemental simulations with the NASA Goddard Earth Observing System model, version 5 (GEOS-5). Key new results are 1) the identification of the important role of summertime stationary Rossby waves in the development of the leading patterns of monthly Eurasian surface temperature and precipitation variability (including the development of extreme events such as the 2010 Russian heat wave); 2) an assessment of the mean temperature and precipitation changes that have occurred over northern Eurasia in the last three decades and their connections to decadal variability and global trends in SST; and 3) the quantification (via a case study) of the predictability of the most extreme simulated heat wave/drought events, with some focus on the role of soil moisture in the development and maintenance of such events. A literature survey indicates a general consensus that the future holds an enhanced probability of heat waves across northern Eurasia, while there is less agreement regarding future drought, reflecting a greater uncertainty in soil moisture and precipitation projections. Substantial uncertainties remain in the understanding of heat waves and drought, including the nature of the interactions between the short-term atmospheric variability associated with such extremes and the longer-term variability and trends associated with soil moisture feedbacks, SST anomalies, and an overall warming world.
    Type of Medium: Online Resource
    ISSN: 0894-8755 , 1520-0442
    URL: Article
    DOI: 10.1175/JCLI-D-13-00360.1
    RVK:
    UA 4548
    Language: English
    Publisher: American Meteorological Society
    Publication Date: 2014
    detail.hit.zdb_id: 246750-1
    detail.hit.zdb_id: 2021723-7
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  • 7
    Online Resource
    Online Resource
    On the Development and Demise of the Fall 2019 Southeast U.S. Flash Drought: Links to an Extreme Positive IOD
    American Meteorological Society ; 2021
    In:  Journal of Climate Vol. 34, No. 5 ( 2021-03), p. 1701-1723
    Details
    In: Journal of Climate, American Meteorological Society, Vol. 34, No. 5 ( 2021-03), p. 1701-1723
    Abstract: Much of the southeast United States experienced record dry conditions during September of 2019, with the area in abnormally dry to exceptional drought conditions growing from 25% at the beginning of the month to 80% by the end of the month. The drought ended just as abruptly due to above-normal rain that fell during the second half of October. In this study we employed MERRA-2 and the GEOS-5 AGCM to diagnose the underlying causes of the drought’s onset, maintenance, and demise. The basic approach involves performing a series of AGCM simulations in which the model is constrained to remain close to MERRA-2 over prespecified areas that are external to the drought region. The start of the drought appears to have been forced by anomalous heating in the central/western tropical Pacific that resulted in low-level anticyclonic flow and a tendency for descending motion over much of the Southeast. An anomalous ridge associated with a Rossby wave train (emanating from the Indian Ocean region) is found to be the main source of the most intense temperature and precipitation anomalies that develop over the Southeast during the last week of September. A second Rossby wave train (emanating from the same region) is responsible for the substantial rain that fell during the second half of October to end the drought. The links to the Indian Ocean dipole (with record positive values) as well as a waning El Niño allow some speculation as to the likelihood of similar events occurring in the future.
    Type of Medium: Online Resource
    ISSN: 0894-8755 , 1520-0442
    URL: Article
    DOI: 10.1175/JCLI-D-20-0428.1
    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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  • 8
    Online Resource
    Online Resource
    The Simulation and Subseasonal Forecasting of Hydrological Variables: Insights from a Simple Water Balance Model
    American Meteorological Society ; 2022
    In:  Journal of Hydrometeorology Vol. 23, No. 11 ( 2022-11), p. 1719-1736
    Details
    In: Journal of Hydrometeorology, American Meteorological Society, Vol. 23, No. 11 ( 2022-11), p. 1719-1736
    Abstract: Past work has shown that a land surface model’s (LSM) implicit (not explicitly coded) relationships between soil moisture and both evapotranspiration (ET) and runoff largely determine the LSM’s hydrological behavior. Here we estimate the relationships that appear to be operating in the real world and compare them to those of the LSM component of a state-of-the-art Earth system model (ESM). The two sets of relationships are determined by calibrating them within a simple water balance model (WBM): once using stream gauge observations from small, unregulated rivers over the eastern half of the United States, and once using the runoffs generated by the LSM as part of a state-of-the-art atmospheric reanalysis. Hydrological simulations and subseasonal hydrological forecasts performed with the two calibrated versions of the WBM provide two key results. First, the version calibrated to the LSM-generated runoffs does successfully reproduce, to first order, the hydrological behavior of the full LSM within its ESM environment. Second, of the two WBM versions, the one calibrated to the observations reproduces more accurately a broad collection of fully independent streamflow observations as well as a similarly broad collection of in situ soil moisture measurements. Taken together, the two results suggest that the observations-calibrated ET and runoff efficiency functions do successfully represent, at least to some degree, soil moisture controls over hydrological variability in nature and can serve as potentially useful targets for further LSM development. Significance Statement For all their complexity, and for all the work that underlies their development, the land surface model components of Earth system models may be suboptimal in fundamental yet unstudied ways. Here we estimate how the joint control of soil moisture over evapotranspiration and runoff processes in nature differs from that built implicitly into a state-of-the-art land model. Validation exercises demonstrate how this difference appears to lead to reduced accuracy in the land model’s simulation and forecasting of such hydrological variables as streamflow and soil moisture. Our results indicate that the relationships estimated for nature could serve as a potentially valuable target for further land model development.
    Type of Medium: Online Resource
    ISSN: 1525-755X , 1525-7541
    URL: Article
    DOI: 10.1175/JHM-D-22-0050.1
    Language: Unknown
    Publisher: American Meteorological Society
    Publication Date: 2022
    detail.hit.zdb_id: 2042176-X
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  • 9
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    Online Resource
    Attribution of the 2017 Northern High Plains Drought
    American Meteorological Society ; 2019
    In:  Bulletin of the American Meteorological Society Vol. 100, No. 1 ( 2019-01), p. S25-S29
    Details
    In: Bulletin of the American Meteorological Society, American Meteorological Society, Vol. 100, No. 1 ( 2019-01), p. S25-S29
    Type of Medium: Online Resource
    ISSN: 0003-0007 , 1520-0477
    URL: Article
    URL: Article
    DOI: 10.1175/BAMS-D-18-0115.1
    DOI: 10.1175/bams-d-18-0115.2
    Language: Unknown
    Publisher: American Meteorological Society
    Publication Date: 2019
    detail.hit.zdb_id: 2029396-3
    detail.hit.zdb_id: 419957-1
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  • 10
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    Online Resource
    Investigation of the 2016 Eurasia heat wave as an event of the recent warming
    IOP Publishing ; 2020
    In:  Environmental Research Letters Vol. 15, No. 11 ( 2020-11-01), p. 114018-
    Details
    In: Environmental Research Letters, IOP Publishing, Vol. 15, No. 11 ( 2020-11-01), p. 114018-
    Abstract: This study investigates the physical mechanisms that contributed to the 2016 Eurasian heat wave during boreal summer season (July–August, JA), characterized by much higher than normal temperatures over eastern Europe, East Asia, and the Kamchatka Peninsula. It is found that the 2016 JA mean surface air temperature, upper-tropospheric height, and soil moisture anomalies are characterized by a tri-pole pattern over the Eurasia continent and a wave train-like structure not dissimilar to recent (1980–2016) trends in those quantities. A series of forecast experiments designed to isolate the impacts of the land, ocean, and sea ice conditions on the development of the heat wave is carried out with the Global Seasonal Forecast System version 5. The results suggest that the tri-pole blocking pattern over Eurasia, which appears to be instrumental in the development of the 2016 summer heat wave, can be viewed as an expression of the recent trends, amplified by record-breaking oceanic warming and internal land-atmosphere interactions.
    Type of Medium: Online Resource
    ISSN: 1748-9326
    URL: Article
    DOI: 10.1088/1748-9326/abbbae
    Language: Unknown
    Publisher: IOP Publishing
    Publication Date: 2020
    detail.hit.zdb_id: 2255379-4
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