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  • 1
    Electronic Resource
    Electronic Resource
    Anisotropic spectra in two-dimensional turbulence on the surface of a rotating sphere (2001)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 13 (2001), S. 225-240 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The anisotropic characteristics of small-scale forced 2D turbulence on the surface of a rotating sphere are investigated. In the absence of rotation, the Kolmogorov k−5/3 spectrum is recovered with the Kolmogorov constant CK(approximate)6, close to previous estimates in plane geometry. Under strong rotation, in long-term simulations without a large-scale drag, a −5 slope emerges in the vicinity of the zonal axis (kx→0), while a −5/3 slope prevails in other sectors far away from the zonal axis in the wave number plane. This picture is consistent with the new flow regime recently simulated by Chekhlov et al. [Physica D 98, 321–334 (1995)] and Smith and Waleffe [Phys. Fluids 11, 1608–1622 (1999)] on the beta plane. The concentration of energy in the zonal components and breaking of isotropy are caused by the strongly anisotropic spectral energy transfer and the stabilization of zonal mean flow by the meridional gradient of the planetary vorticity. The sharp tilt-up of the spectrum along the zonal axis was qualitatively understood through the scale-dependent stability property of the zonal flow. Under planetary rotation, the capacity for the zonal jets to hold energy and remain stable sharply increases with an increase of the meridional scale of the jets. In our simulations that were virtually inviscid at the large scales, the energy spectrum along the zonal axis tilts up all the way to the largest possible scale, indicating an apparent up-scale energy "cascade" along the zonal axis. This apparent up-scale cascade corresponds to a process of continuous mergers of zonal jets that does not cease until reaching the largest scale. This picture is consistent with the inviscid scenario for jet merging discussed by Manfroi and Young [J. Atmos. Sci. 56, 784–800 (1999)]. It contrasts the viscous scenario (for flows under the influence of a constant bottom drag) simulated in several previous studies, in which a distinct and finite jet scale emerges asymptotically. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1327594
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  • 2
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    Anisotropic spectra in two-dimensional turbulence on the surface of a rotating sphere (2001)
    American Institute of Physics
    Details
    Publication Date: 2001-01-01
    Print ISSN: 1070-6631
    Electronic ISSN: 1089-7666
    Topics: Physics
    Published by American Institute of Physics
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  • 3
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    Universal n−5 spectrum of zonal flows on giant planets (2001)
    American Institute of Physics
    Details
    Publication Date: 2001-06-01
    Print ISSN: 1070-6631
    Electronic ISSN: 1089-7666
    Topics: Physics
    Published by American Institute of Physics
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  • 4
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    Modeling the Effect of Desert Urbanization on Local Climate and Natural Dust Generation: A Case Study for Erbil, Iraq (2020)
    Molecular Diversity Preservation International
    Details
    Publication Date: 2020-09-28
    Description: This study uses a suite of meteorological and land-surface models to quantify the changes in local climate and surface dust fluxes associated with desert urbanization. Formulas connecting friction velocity and soil moisture to dust generation are used to quantify surface fluxes for natural wind-blown dust. The models are used to conduct a series of simulations for the desert city of Erbil across a period of rapid urbanization. The results show significant nighttime warming and weak but robust daytime cooling associated with desert urbanization. A slight reduction in near-surface wind speed is also found in the areas undergoing urbanization. These findings are consistent with previous empirical and modeling studies on other desert cities. Numerical models and empirical formulas are used to produce climatological maps of surface dust fluxes as a function of season, and for the pre- and post-urbanization eras. This framework can potentially be used to bridge the gap in observation on the trends in local dust generation associated with land-use changes and urban expansions.
    Electronic ISSN: 2413-8851
    Topics: Architecture, Civil Engineering, Surveying
    Published by Molecular Diversity Preservation International
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  • 5
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    An Updated Analysis of Northern Hemisphere Submonthly Retrograde Waves (2019)
    American Meteorological Society
    Details
    Publication Date: 2019-12-01
    Description: This study performs an updated analysis of Northern Hemisphere retrograde disturbances that were first identified by classical observational studies as one of the dominating coherent structures in the higher latitudes on the submonthly time scale. Analyzing 8–30-day bandpass-filtered data based on reanalysis, a set of criteria on the phase and amplitude of zonal wave-1 Fourier coefficients of geopotential height anomalies at 250 mb (1 mb = 1 hPa) and 60°N are used to identify strong retrograde-wave events in the spirit of Madden and Speth. The new catalog of retrograde-wave events from 1979 to 2017 is used to extract basic statistics and structures of retrograde waves across all major events. The results broadly agree with those reported in the classical observational studies, reaffirming the robustness of the phenomenon. The new catalog can be used to aid further studies on the mechanisms and predictability of retrograde waves. As an example, an analysis of isentropic potential vorticity over the Pacific sector for selected retrograde-wave events reveals the common occurrence of an extrusion of low-PV air into the higher latitudes, followed by a westward shift of the low-PV patch and vortex shedding. Future directions of research surrounding the retrograde-wave phenomenon are discussed.
    Print ISSN: 0022-4928
    Electronic ISSN: 1520-0469
    Topics: Geography , Geosciences , Physics
    Published by American Meteorological Society
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  • 6
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    A Comparative Study of Precipitation and Evaporation between CMIP3 and CMIP5 Climate Model Ensembles in Semiarid Regions (2014)
    American Meteorological Society
    Details
    Publication Date: 2014-05-09
    Description: The twentieth-century climatology and twenty-first-century trend in precipitation P, evaporation E, and P − E for selected semiarid U.S. Southwest and Mediterranean regions are compared between ensembles from phases 3 and 5 of the Coupled Model Intercomparison Project (CMIP3 and CMIP5). The twentieth-century simulations are validated with precipitation from observation and evaporation from reanalysis. It is found that the Special Report on Emissions Scenarios (SRES) A1B simulations in CMIP3 and the simulations with representative concentration pathways (RCPs) 4.5 and 8.5 in CMIP5 produce qualitatively similar seasonal cycles of the twenty-first-century trend in P − E for both semiarid regions. For the southwestern United States, it is characterized by a strong drying trend in spring, a weak moistening trend in summer, a weak drying trend in winter, and an overall drying trend for the annual mean. For the Mediterranean region, a drying trend is simulated for all seasons with an October maximum and July minimum. The consistency between CMIP3 and CMIP5 scenarios indicates that the simulated trend is robust; however, while the trend in P − E is negative in spring for the southwestern United States for all CMIP ensembles, CMIP3 predicts a strongly negative trend in P and minor negative trend in E whereas both CMIP5 scenarios predict a nearly zero trend in P and positive trend in E. For the twentieth-century simulations, the P, E, and P − E of the two model ensembles are statistically indistinguishable for most seasons. This “stagnation” of the simulated climatology from CMIP3 to CMIP5 implies that the hydroclimatic variable biases have not decreased in the newer generation of models. Notably, over the southwestern United States the CMIP3 models produce too much precipitation in the cold season. This bias remains almost unchanged in CMIP5.
    Print ISSN: 0894-8755
    Electronic ISSN: 1520-0442
    Topics: Geography , Geosciences , Physics
    Published by American Meteorological Society
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  • 7
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    Unusual Behavior in Atmospheric Angular Momentum during the 1965 and 1972 El Niños (2003)
    American Meteorological Society
    Details
    Publication Date: 2003-08-01
    Print ISSN: 0894-8755
    Electronic ISSN: 1520-0442
    Topics: Geography , Geosciences , Physics
    Published by American Meteorological Society
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  • 8
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    A Comparison of Decadal-to-Interdecadal Variability and Trend in Reanalysis Datasets Using Atmospheric Angular Momentum (2012)
    American Meteorological Society
    Details
    Publication Date: 2012-07-01
    Description: An intercomparison of the global relative angular momentum MR in five reanalysis datasets, including the Twentieth Century Reanalysis (20CR), is performed for the second half of the twentieth century. The intercomparison forms a stringent test for 20CR because the variability of MR is known to be strongly influenced by the variability of upper-tropospheric zonal wind whereas 20CR assimilated only surface observations. The analysis reveals good agreement for decadal-to-multidecadal variability among all of the datasets, including 20CR, for the second half of the twentieth century. The discrepancies among different datasets are mainly in the slowest component, the long-term trend, of MR. Once the data are detrended, the resulting decadal-to-multidecadal variability shows even better agreement among all of the datasets. This result indicates that 20CR can be reliably used for the analysis of decadal-to-interdecadal variability in the pre-1950 era, provided that the data are properly detrended. As a quick application, it is found that the increase in MR during the 1976/77 climate-shift event remains the sharpest over the entire period from 1871 to 2008 covered by 20CR. The nontrivial difference in the long-term trend between 20CR and the other reanalysis datasets found in this study provides a caution against using 20CR to determine the trend on the centennial time scale that is relevant to climate change. These conclusions are restricted to the quantities that depend strongly on the upper-tropospheric zonal wind, but the approach adopted in this work will be useful for future intercomparisons of the low-frequency behavior of other climate indices in the reanalysis datasets.
    Print ISSN: 0894-8755
    Electronic ISSN: 1520-0442
    Topics: Geography , Geosciences , Physics
    Published by American Meteorological Society
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  • 9
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    Hindcasts of Tropical Atlantic SST Gradient and South American Precipitation: The Influences of the ENSO Forcing and the Atlantic Preconditioning (2009)
    American Meteorological Society
    Details
    Publication Date: 2009-05-01
    Description: Hindcast experiments for the tropical Atlantic sea surface temperature (SST) gradient G1, defined as tropical North Atlantic SST anomaly minus tropical South Atlantic SST anomaly, are performed using an atmospheric general circulation model coupled to a mixed layer ocean over the Atlantic to quantify the contributions of the El Niño–Southern Oscillation (ENSO) forcing and the preconditioning in the Atlantic to G1 in boreal spring. The results confirm previous observational analyses that, in the years with a persistent ENSO SST anomaly from boreal winter to spring, the ENSO forcing plays a primary role in determining the tendency of G1 from winter to spring and the sign of G1 in late spring. In the hindcasts, the initial perturbations in Atlantic SST in boreal winter are found to generally persist beyond a season, leaving a secondary but nonnegligible contribution to the predicted Atlantic SST gradient in spring. For 1993/94, a neutral year with a large preexisting G1 in winter, the hindcast using the information of Atlantic preconditioning alone is found to reproduce the observed G1 in spring. The seasonal predictability in precipitation over South America is examined in the hindcast experiments. For the recent events that can be validated with high-quality observations, the hindcasts produced dryness in boreal spring 1983, wetness in spring 1996, and wetness in spring 1994 over northern Brazil that are qualitatively consistent with observations. An inclusion of the Atlantic preconditioning is found to help the prediction of South American rainfall in boreal spring. For the ENSO years, discrepancies remain between the hindcast and observed precipitation anomalies over northern and equatorial South America, an error that is partially attributed to the biased atmospheric response to ENSO forcing in the model. The hindcast of the 1993/94 neutral year does not suffer this error. It constitutes an intriguing example of useful seasonal forecast of G1 and South American rainfall anomalies without ENSO.
    Print ISSN: 0894-8755
    Electronic ISSN: 1520-0442
    Topics: Geography , Geosciences , Physics
    Published by American Meteorological Society
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  • 10
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    Centennial Trend and Decadal-to-Interdecadal Variability of Atmospheric Angular Momentum in CMIP3 and CMIP5 Simulations (2013)
    American Meteorological Society
    Details
    Publication Date: 2013-05-31
    Description: The climatology and trend of atmospheric angular momentum from the phase 3 and the phase 5 Climate Model Intercomparison Project (CMIP3 and CMIP5, respectively) simulations are diagnosed and validated with the Twentieth Century Reanalysis (20CR). It is found that CMIP5 models produced a significantly smaller bias in the twentieth-century climatology of the relative MR and omega MΩ angular momentum compared to CMIP3. The CMIP5 models also produced a narrower ensemble spread of the climatology and trend of MR and MΩ. Both CMIP3 and CMIP5 simulations consistently produced a positive trend in MR and MΩ for the twentieth and twenty-first centuries. The trend for the twenty-first century is much greater, reflecting the role of greenhouse gas (GHG) forcing in inducing the trend. The simulated increase in MR for the twentieth century is consistent with reanalysis. Both CMIP3 and CMIP5 models produced a wide range of magnitudes of decadal and interdecadal variability of MR compared to 20CR. The ratio of the simulated standard deviation of decadal or interdecadal variability to its observed counterpart ranges from 0.5 to over 2.0 for individual models. Nevertheless, the bias is largely random and ensemble averaging brings the ratio to within 18% of the reanalysis for decadal and interdecadal variability for both CMIP3 and CMIP5. The twenty-first-century simulations from both CMIP3 and CMIP5 produced only a small trend in the amplitude of decadal or interdecadal variability, which is not statistically significant. Thus, while GHG forcing induces a significant increase in the climatological mean of angular momentum, it does not significantly affect its decadal-to-interdecadal variability in the twenty-first century.
    Print ISSN: 0894-8755
    Electronic ISSN: 1520-0442
    Topics: Geography , Geosciences , Physics
    Published by American Meteorological Society
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