The Experts below are selected from a list of 327 Experts worldwide ranked by ideXlab platform
R G Roble - One of the best experts on this subject based on the ideXlab platform.
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Modeling diurnal tidal variability with the national center for atmospheric research thermosphere ionosphere mesosphere electrodynamics General Circulation Model
Journal of Geophysical Research, 2001Co-Authors: M E Hagan, R G RobleAbstract:We used the National Center for Atmospheric Research thermosphere-ionosphere-mesosphere-electrodynamics General Circulation Model (TIME-GCM) to calculate the variability of the migrating diurnal tide in a January through December 1993 simulation. While TIME-GCM captures the salient features of the latitudinal, altitudinal, and seasonal variability of the migrating diurnal tide, upper mesospheric meridional wind amplitudes are somewhat smaller than those that have been observed from the ground and space. The discrepancies may be attributable to unresolved uncertainties in tidal forcing and/or dissipation in the TIME-GCM. However, our diagnostic simulation suggests that the nonlinear interactions between the migrating diurnal tide and stationary planetary wave 1 produce measurable nonmigrating diurnal tidal components that modulate migrating diurnal tidal amplitudes and account for significant variability in the upper mesosphere and lower thermosphere.
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a thermosphere ionosphere General Circulation Model with coupled electrodynamics
Geophysical Research Letters, 1992Co-Authors: A D Richmond, E C Ridley, R G RobleAbstract:A new simulation Model of upper atmospheric dynamics is presented that includes self-consistent electrodynamic interactions between the thermosphere and ionosphere. This Model, which we call the National Center for Atmospheric Research thermosphere-ionosphere-electrodynamic General Circulation Model (NCAR/TIE-GCM), calculates the dynamo effects of thermospheric winds, and uses the resultant electric fields and currents in calculating the neutral and plasma dynamics. A realistic geomagnetic field geometry is used. Sample simulations for solar maximum equinox conditions illustrate two previously predicted effects of the feedback. Near the magnetic equator, the afternoon uplift of the ionosphere by an eastward electric field reduces ion drag on the neutral wind, so that relatively strong eastward winds can occur in the evening. In addition, a vertical electric field is generated by the low-latitude wind, which produces east-west plasma drifts in the same direction as the wind, further reducing the ion drag and resulting in stronger zonal winds.
A D Richmond - One of the best experts on this subject based on the ideXlab platform.
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simulation of equatorial electrojet magnetic effects with the thermosphere ionosphere electrodynamics General Circulation Model
Journal of Geophysical Research, 2007Co-Authors: V Doumbia, Astrid Maute, A D RichmondAbstract:[1] In this work, the magnetic variations simulated by the NCAR thermosphere-ionosphere-electrodynamics General Circulation Model (TIE-GCM) in the vicinity of the magnetic equator are examined to evaluate the ability of this Model to reproduce the major features of the equatorial electrojet (EEJ) as observed on the ground as well as on board low-altitude orbiting satellites. The TIE-GCM simulates electric currents of various origins and reproduces their associated magnetic perturbations. We analyze the diurnal and latitudinal variations of the EEJ magnetic effects calculated on the ground in West Africa under approximately the same solar activity condition as in 1993 for the March equinox and June and December solstices. The latitudinal and local time structures of these simulated results correspond well to those that are observed. We also compare longitudinal variations of the midday EEJ magnetic perturbations observed by the CHAMP satellite with the Model predictions. Although the simulations and observations both show multiple maxima and minima in longitude, the locations of these extrema often disagree. In the Model most of the longitudinal variation of the magnetic variations is associated with nondipolar structure of the geomagnetic field. We find that the Modeled contributions of the thermospheric migrating diurnal and semidiurnal tides to the magnetic perturbations have large longitudinal variations, and we suggest that an increase in the amplitude of these tides in the TIE-GCM may cause them to play a major role in explaining the morphology of the EEJ longitudinal variation.
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a thermosphere ionosphere General Circulation Model with coupled electrodynamics
Geophysical Research Letters, 1992Co-Authors: A D Richmond, E C Ridley, R G RobleAbstract:A new simulation Model of upper atmospheric dynamics is presented that includes self-consistent electrodynamic interactions between the thermosphere and ionosphere. This Model, which we call the National Center for Atmospheric Research thermosphere-ionosphere-electrodynamic General Circulation Model (NCAR/TIE-GCM), calculates the dynamo effects of thermospheric winds, and uses the resultant electric fields and currents in calculating the neutral and plasma dynamics. A realistic geomagnetic field geometry is used. Sample simulations for solar maximum equinox conditions illustrate two previously predicted effects of the feedback. Near the magnetic equator, the afternoon uplift of the ionosphere by an eastward electric field reduces ion drag on the neutral wind, so that relatively strong eastward winds can occur in the evening. In addition, a vertical electric field is generated by the low-latitude wind, which produces east-west plasma drifts in the same direction as the wind, further reducing the ion drag and resulting in stronger zonal winds.
Astrid Maute - One of the best experts on this subject based on the ideXlab platform.
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thermosphere ionosphere electrodynamics General Circulation Model for the ionospheric connection explorer tiegcm icon
Space Science Reviews, 2017Co-Authors: Astrid MauteAbstract:The NASA Ionospheric Connection explorer (ICON) will study the coupling between the thermosphere and ionosphere at low- and mid-latitudes by measuring the key parameters. The ICON mission will also employ numerical Modeling to support the interpretation of the observations, and examine the importance of different vertical coupling mechanisms by conducting numerical experiments. One of these Models is the Thermosphere-Ionosphere-Electrodynamics General Circulation Model-ICON (TIEGCM-ICON) which will be driven by tidal perturbations derived from ICON observations using the Hough Mode Extension method (HME) and at high latitude by ion convection and auroral particle precipitation patterns from the Assimilative Mapping of Ionospheric Electrodynamics (AMIE). The TIEGCM-ICON will simulate the thermosphere-ionosphere (TI) system during the period of the ICON mission. In this report the TIEGCM-ICON is introduced, and the focus is on examining the effect of the lower boundary on the TI-system to provide some guidance for interpreting future ICON Model results.
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simulation of equatorial electrojet magnetic effects with the thermosphere ionosphere electrodynamics General Circulation Model
Journal of Geophysical Research, 2007Co-Authors: V Doumbia, Astrid Maute, A D RichmondAbstract:[1] In this work, the magnetic variations simulated by the NCAR thermosphere-ionosphere-electrodynamics General Circulation Model (TIE-GCM) in the vicinity of the magnetic equator are examined to evaluate the ability of this Model to reproduce the major features of the equatorial electrojet (EEJ) as observed on the ground as well as on board low-altitude orbiting satellites. The TIE-GCM simulates electric currents of various origins and reproduces their associated magnetic perturbations. We analyze the diurnal and latitudinal variations of the EEJ magnetic effects calculated on the ground in West Africa under approximately the same solar activity condition as in 1993 for the March equinox and June and December solstices. The latitudinal and local time structures of these simulated results correspond well to those that are observed. We also compare longitudinal variations of the midday EEJ magnetic perturbations observed by the CHAMP satellite with the Model predictions. Although the simulations and observations both show multiple maxima and minima in longitude, the locations of these extrema often disagree. In the Model most of the longitudinal variation of the magnetic variations is associated with nondipolar structure of the geomagnetic field. We find that the Modeled contributions of the thermospheric migrating diurnal and semidiurnal tides to the magnetic perturbations have large longitudinal variations, and we suggest that an increase in the amplitude of these tides in the TIE-GCM may cause them to play a major role in explaining the morphology of the EEJ longitudinal variation.
Toshio Yamagata - One of the best experts on this subject based on the ideXlab platform.
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indian ocean subtropical dipole simulated using a coupled General Circulation Model
Journal of Geophysical Research, 2004Co-Authors: Rieko Suzuki, Satoshi Iizuka, Swadhin K Behera, Toshio YamagataAbstract:[1] The interannual Indian Ocean subtropical dipole (IOSD) event in the southern Indian Ocean is discussed using a coupled General Circulation Model to derive a scenario describing its complete life cycle for the first time. The positive (negative) IOSD is characterized by an anomalous warm (cool) sea surface temperature (SST) in the southwestern region of the Indian Ocean and by an anomalous cool (warm) SST in the southeastern region. The positive event brings about enhanced precipitation in the southeastern Africa during the peak phase. Composite pictures for the positive and negative IOSD clarify that an anomalous latent heat flux is the dominant factor in its formation. This flux anomaly is caused by an anomaly in the climatological wind field, which is associated with a pressure anomaly in the central region of the southern Indian Ocean. Since the flux anomaly starts during austral fall in the year previous to the event peak and develops for the next 9 months, air-sea interaction must play an active role in the formation of the IOSD. The reason the peak of the IOSD is locked to the austral summer is that the latent heat flux influences the sea surface temperature most efficiently in the austral summer when the depth of the surface mixed layer is shallowest. INDEX TERMS: 4215 Oceanography: General: Climate and interannual variability (3309); 4255 Oceanography: General: Numerical Modeling; 4504 Oceanography: Physical: Air/sea interactions (0312); KEYWORDS: Indian Ocean subtropical dipole (IOSD), heat fluxes, air-sea interaction positive feedback
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the indian ocean sst dipole simulated in a coupled General Circulation Model
Geophysical Research Letters, 2000Co-Authors: Satoshi Iizuka, Tomonori Matsuura, Toshio YamagataAbstract:We are successful in simulating the recently discovered ocean-atmosphere coupled phenomenon called the Indian Ocean Dipole for the first time, using a coupled General Circulation Model without flux correction. During the analyzed 50 years of Model integration, the anomalous climate events have appeared 8 times over the Indian Ocean (IO). They are characterized by the cooling of the sea surface temperature (SST) in the southeastern tropical IO and the warming of the SST in the western tropical IO, associated with the anomalous easterly winds along the equator. The spatial pattern of the anomalous SST shows an east-west dipole mode (DM) structure that is similar to the recent reports. The simulated DM events are independent of the El Nino simulated in the same Model. The heat budget analysis shows that the tropical air-sea interaction, which is strongly influenced by ocean dynamics, is crucial in generating the Model DM events.
Tsengdar Lee - One of the best experts on this subject based on the ideXlab platform.
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hurricane forecasting with the high resolution nasa finite volume General Circulation Model
Geophysical Research Letters, 2005Co-Authors: Robert Atlas, Oreste Reale, Bowen Shen, Shianjiann Lin, J D Chern, William M Putman, Tsengdar LeeAbstract:[1] A high-resolution finite volume General Circulation Model (fvGCM), resulting from a development effort of more than ten years, is now being run operationally at the NASA Goddard Space Flight Center and Ames Research Center. The Model is based on a finite volume dynamical core with terrain-following Lagrangian control volume discretization and performs efficiently on massive parallel architectures. The computational efficiency allows simulations at a resolution of a quarter of a degree, which is double the resolution currently adopted by most global Models in operational weather centers. Such fine global resolution brings us closer to overcoming a fundamental barrier in global atmospheric Modeling for both weather and climate, because tropical cyclones can be more realistically represented. In this work, preliminary results are shown. Fifteen simulations of four Atlantic tropical cyclones in 2002 and 2004, chosen because of varied difficulties presented to numerical weather forecasting, are performed. The fvGCM produces very good forecasts of these tropical systems, adequately resolving problems like erratic track, abrupt recurvature, intense extratropical transition, multiple landfall and reintensification, and interaction among vortices.
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hurricane forecasting with the high resolution nasa finite volume General Circulation Model
Geophysical Research Letters, 2005Co-Authors: Robert Atlas, Oreste Reale, Bowen Shen, Shianjiann Lin, J D Chern, William M Putman, Tsengdar LeeAbstract:A high-resolution finite-volume General Circulation Model (fvGCM), resulting from a development effort of more than ten years, is now being run operationally at the NASA Goddard Space Flight Center and Ames Research Center. The Model is based on a finite-volume dynamical core with terrain-following Lagrangian control-volume discretization and performs efficiently on massive parallel architectures. The computational efficiency allows simulations at a resolution of a quarter of a degree, which is double the resolution currently adopted by most global Models in operational weather centers. Such fine global resolution brings us closer to overcoming a fundamental barrier in global atmospheric Modeling for both weather and climate, because tropical cyclones and even tropical convective clusters can be more realistically represented. In this work, preliminary results of the fvGCM are shown. Fifteen simulations of four Atlantic tropical cyclones in 2002 and 2004 are chosen because of strong and varied difficulties presented to numerical weather forecasting. It is shown that the fvGCM, run at the resolution of a quarter of a degree, can produce very good forecasts of these tropical systems, adequately resolving problems like erratic track, abrupt recurvature, intense extratropical transition, multiple landfall and reintensification, and interaction among vortices.
