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  • 1
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    The ENSO Effects on Tropical Clouds and Top-of-Atmosphere Cloud Radiative Effects in CMIP5 Models (2015)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The El Nino-Southern Oscillation (ENSO) effects on tropical clouds and top-of-atmosphere (TOA) cloud radiative effects (CREs) in Coupled Model Intercomparison Project Phase5 (CMIP5) models are evaluated using satellite-based observations and International Satellite Cloud Climatology Project satellite simulator output. Climatologically, most CMIP5 models produce considerably less total cloud amount with higher cloud top and notably larger reflectivity than observations in tropical Indo-Pacific (60 degrees East - 200 degrees East; 10 degrees South - 10 degrees North). During ENSO, most CMIP5 models considerably underestimate TOA CRE and cloud changes over western tropical Pacific. Over central tropical Pacific, while the multi-model mean resembles observations in TOA CRE and cloud amount anomalies, it notably overestimates cloud top pressure (CTP) decreases; there are also substantial inter-model variations. The relative effects of changes in cloud properties, temperature and humidity on TOA CRE anomalies during ENSO in the CMIP5 models are assessed using cloud radiative kernels. The CMIP5 models agree with observations in that their TOA shortwave CRE anomalies are primarily contributed by total cloud amount changes, and their TOA longwave CRE anomalies are mostly contributed by changes in both total cloud amount and CTP. The model biases in TOA CRE anomalies particularly the strong underestimations over western tropical Pacific are, however, mainly explained by model biases in CTP and cloud optical thickness (tau) changes. Despite the distinct model cloud biases particularly in tau regime, the TOA CRE anomalies from cloud amount changes are comparable between the CMIP5 models and observations, because of the strong compensations between model underestimation of TOA CRE anomalies from thin clouds and overestimation from medium and thick clouds.
    Keywords: Meteorology and Climatology
    Type: Paper IUGG-1890 , NF1676L-21378 , General Assembly of the International Union of Geodesy and Geophysics (IUGG); Jun 22, 2015 - Jul 02, 2015; Prague; Czechoslovakia
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  • 2
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    Interannual to Decadal Variability of Ocean Evaporation as Viewed from Climate Reanalyses (2015)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Questions we'll address: Given the uncoupled framework of "AMIP" (Atmosphere Model Inter-comparison Project) experiments, what can they tell us regarding evaporation variability? Do Reduced Observations Reanalyses (RedObs) using Surface Fluxes and Clouds (SFC) pressure (and wind) provide a more realistic picture of evaporation variability? What signals of interannual variability (e.g. El Nino/Southern Oscillation (ENSO)) and decadal variability (Interdecadal Pacific Oscillation (IPO)) are detectable with this hierarchy of evaporation estimates?
    Keywords: Meteorology and Climatology; Oceanography
    Type: MSFC-E-DAA-TN29056 , MSFC-E-DAA-TN28011 , American Meteorology Society Meeting; Jan 10, 2016 - Jan 14, 2016; New Orleans, LA; United States
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  • 3
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    North American Drought and Links to Northern Eurasia: The Role of Stationary Rossby Waves (2017)
    In:  CASI
    Details
    Publication Date: 2019-07-12
    Description: This chapter provides an overview of the role of stationary Rossby waves in the sub-seasonal development of warm season drought over North America and subsequent downstream development of climate anomalies over northern Eurasia. The results are based on a case study of a stationary Rossby wave event that developed during 20 May 15 June 1988. Simulations with the NASA Goddard Earth Observing System (GEOS-5) atmospheric general circulation model highlight the importance of the mean jet streams in guiding and constraining the path and speed of wave energy propagation. In particular, convective anomalies that developed over the western Pacific in late May (in the presence of the strong North Pacific jet) produce a predilection for persistent upper-level high anomalies over central North America about ten days later, leading to the rapid development of severe dry conditions there. There are indications of continued downstream wave energy propagation that reaches northern Eurasia about two weeks later, leading to the development of dry conditions over eastern Europe and western Russia, and cool and wet conditions over western Europe and central northern Eurasia. The results suggest that stationary Rossby waves can serve as a source of predictability for sub-seasonal development of droughts over North America and northern Eurasia.
    Keywords: Meteorology and Climatology
    Type: GSFC-E-DAA-TN44773
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  • 4
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    Prediction Skill of U.S. Flash Droughts in Subseasonal Experiment (SubX) Model Hindcasts (2018)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Droughts that establish themselves over a short period of time (weeks to a few months), referred to as flash droughts, can have devastating impacts on agriculture, water resources, and ecosystems. The ability to predict such droughts in advance would greatly enhance our preparation for them and potentially reduce their impacts. The sub-seasonal time scale at which flash droughts occur emphasizes the importance of producing forecasts at weekly or finer intervals that extend beyond the numerical weather prediction time frame. Here we assess the ability of eight global forecast systems, each participating in the Sub-seasonal Experiment project (SubX), to predict key features associated with rapidly developing droughts over the United States during the last two decades. MERRA2 reanalysis is used as observations. Prediction skill for temperature and precipitation anomalies during these events is limited to the first 1-2 weeks after initialization for most hindcasts. However, there are some hindcasts in which large anomalies are well predicted 3-4 weeks or more in advance. The physical mechanisms that are key to the development of surface anomalies, including quasi-stationary atmospheric waves, were also evaluated. Most hindcasts were unable to capture the development or progression of such drought-inducing circulation features more than 1-2 weeks in advance.
    Keywords: Geosciences (General)
    Type: GSFC-E-DAA-TN63852 , American Geophysical Union (AGU) Fall Meeting; Dec 10, 2018 - Dec 14, 2018; Washington, D.C.; United States
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  • 5
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    Flash Drought as Captured by MERRA-2: Disentangling the Contributions of Precipitation Deficit and Excess Energy (2018)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Flash droughts uncharacteristically rapid dryings of the land system are naturally associated with extreme precipitation deficits. Such precipitation deficits, however, do not tell the whole story. Land surface drying can be exacerbated by anomalously high evapotranspiration (ET) rates driven, for example, by anomalously high temperatures (e.g., during heatwaves) and/or anomalously high incoming radiation (e.g., from reduced cloudiness). In this study the relative contributions of precipitation and ET anomalies to flash drought generation are quantified through the analysis of diagnostic fields contained within the MERRA-2 reanalysis product. Unique to the overall approach is the explicit treatment of soil moisture impacts on ET an ET anomaly that is negative relative to the local long-term climatological mean is still considered positive in terms of its contribution to a flash drought, if it is high for the concurrent value of soil moisture. Maps produced in the analysis show the fraction of flash drought production stemming specifically from ET anomalies and the degree to which these ET anomalies are related to temperature and radiation anomalies. ET is found to have a large impact, for example, on flash drought production in the east-central US and in parts of Russia known from past studies to be prone to heatwave-related drought.
    Keywords: Earth Resources and Remote Sensing
    Type: GSFC-E-DAA-TN63590 , American Geophysical Union (AGU) Fall Meeting; Dec 10, 2018 - Dec 14, 2018; Washington, DC; United States
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  • 6
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    A Realization of Bias Correction Method in the GMAO Coupled System (2018)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Over the past several decades, a tremendous effort has been made to improve model performance in the simulation of the climate system. The cold or warm sea surface temperature (SST) bias in the tropics is still a problem common to most coupled ocean atmosphere general circulation models (CGCMs). The precipitation biases in CGCMs are also accompanied by SST and surface wind biases. The deficiencies and biases over the equatorial oceans through their influence on the Walker circulation likely contribute the precipitation biases over land surfaces. In this study, we introduce an approach in the CGCM modeling to correct model biases. This approach utilizes the history of the model's short-term forecasting errors and their seasonal dependence to modify model's tendency term and to minimize its climate drift. The study shows that such an approach removes most of model climate biases. A number of other aspects of the model simulation (e.g. extratropical transient activities) are also improved considerably due to the imposed pre-processed initial 3-hour model drift corrections. Because many regional biases in the GEOS-5 CGCM are common amongst other current models, our approaches and findings are applicable to these other models as well.
    Keywords: Geosciences (General)
    Type: GSFC-E-DAA-TN51194 , AMS Annual Meeting; Jan 07, 2018 - Jan 11, 2018; Austin, TX; United States
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  • 7
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    The Role of DYNAMO In-Situ Observations in Improving NASA CERESlike Daily Surface and Atmospheric Radiative Flux Estimates (2017)
    In:  CASI
    Details
    Publication Date: 2019-06-14
    Description: The daily surface and atmospheric radiative fluxes from NASA Clouds and the Earth's Radiant Energy System (CERES) Synoptic 1 degree (SYN1deg) Ed3A are among the most widely used data to study cloudradiative feedback. The CERES SYN1deg data are based on FuLiou radiative transfer computations that use specific humidity (Q) and air temperature (T) from NASA Global Modeling and Assimilation Office (GMAO) reanalyses as inputs and are therefore subject to the quality of those fields. This study uses in situ Q and T observations collected during the Dynamics of the MaddenJulian Oscillation (DYNAMO) field campaign to augment the input stream used in the NASA GMAO reanalysis and assess the impact on the CERES daily surface and atmospheric longwave estimates. The results show that the assimilation of DYNAMO observations considerably improves the vertical profiles of analyzed Q and T over and near DYNAMO stations by moistening and warming the lower troposphere and upper troposphere and drying and cooling the midupper troposphere. As a result of these changes in Q and T, the computed CERES daily surface downward longwave flux increases by about 5 W m(exp 2), due mainly to the warming and moistening in the lower troposphere; the computed daily topofatmosphere (TOA) outgoing longwave radiation increases by 23 W m(exp 2) during dry periods only. Correspondingly, the estimated local atmospheric longwave radiative cooling enhances by about 5 W m(exp 2) (78 W m(exp 2)) during wet (dry) periods. These changes reduce the bias in the CERES SYN1deglike daily longwave estimates at both the TOA and surface and represent an improvement over the DYNAMO region.
    Keywords: Meteorology and Climatology; Earth Resources and Remote Sensing
    Type: NF1676L-26741 , Earth and Space Science (e-ISSN 2333-5084); 4; 4; 164-183
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  • 8
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    Northeast Colorado Extreme Rains Interpreted in a Climate Change Context (2015)
    In:  CASI
    Details
    Publication Date: 2019-07-12
    Description: The probability for an extreme five-day September rainfall event over northeast Colorado, as was observed in early September 2013, has likely decreased due to climate change.
    Keywords: Meteorology and Climatology
    Type: GSFC-E-DAA-TN17634
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  • 9
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    An Enhanced Seasonal Transition that Intensified Summer Drought in the Central U.S. (2015)
    In:  CASI
    Details
    Publication Date: 2019-07-12
    Description: Precipitation in the central U.S. decreases by about 25% during the seasonal transition from June to July, and this precipitation decrease has been observed to have intensified since 1979. Such an intensification could enhance future spring drought occurrences such as was the case in the 2012 "flash drought" in the Midwestern U.S., where conditions evolved quickly from being abnormally dry to exceptionally dry within a mere month from June to July. In this study, various atmospheric and land reanalysis datasets were analyzed to examine the trend calculated from 1979 to 2012 in the June-to-July seasonal transition. It was found that the change in precipitation deficit was accompanied by increased downward shortwave radiation flux and tropospheric subsidence, enhanced evaporative fraction, as well as an elevated planetary boundary layer height. The change in the tropospheric circulation encompassed an anomalous ridge over the western U.S. and a trough on either side; this wave-form circulation pattern is known to induce dry conditions in the central U.S. Possibly, the trends in the June-to-July seasonal shifts in precipitation, drought severity and tropospheric circulation intensified the 2012 "flash drought" in timing and extent. The knowledge of the trends allows one to anticipate the evolution of spring onset of drought into the summer.
    Keywords: Meteorology and Climatology
    Type: GSFC-E-DAA-TN17680
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  • 10
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    Could the 2012 Drought in Central U.S. Have Been Anticipated? A Review of NASA Working Group Research (2015)
    In:  CASI
    Details
    Publication Date: 2019-07-12
    Description: This paper summarizes research related to the 2012 record drought in the central United States conducted by members of the NASA Energy and Water cycle Study (NEWS) Working Group. Past drought patterns were analyzed for signal coherency with latest drought and the contribution of long-term trends in the Great Plains low-level jet, an important regional circulation feature of the spring rainy season in the Great Palins. Long-term changes in the seasonal transition from rainy spring into dry summer were also examined. Potential external forcing from radiative processes, soil-air interactions, and ocean teleconnections were assessed as contributors to the intensity of the drought. The atmospheric Rossby wave activity was found to be a potential source of predictability for the onset of drought. A probabilistic model was introduced and evaluated for its performance in predicting drought recovery in the Great Plains.
    Keywords: Meteorology and Climatology
    Type: GSFC-E-DAA-TN17681
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