Browsing by Author "Heelis, R. A."
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- Forecasting Equatorial Ionospheric Convective Instability With ICON Satellite MeasurementsHysell, D. L.; Kirchman, A.; Harding, B. J.; Heelis, R. A.; England, Scott L. (American Geophysical Union, 2023-05)Measurements from the Ionospheric Connections Explorer satellite (ICON) form the basis of direct numerical forecast simulations of plasma convective instability in the postsunset equatorial F region ionosphere. ICON data are selected and used to initialize and force the simulations and then to test the results one orbit later when the satellite revisits the same longitude. Data from the IVM plasma density and drifts instrument and the MIGHTI red-line thermospheric winds instrument are used to force the simulation. Data from IVM are also used to test for irregularities (electrically polarized plasma depletions). Fourteen datasets from late March 2022, were examined. The simulations correctly predicted the occurrence or non-occurrence of irregularities 12 times while producing one false positive and one false negative. This demonstrates that the important telltales of instability are present in the ICON state variables and that the important mechanisms for irregularity formation are captured by the simulation code. Possible refinements to the forecast strategy are discussed.
- Low latitude thermospheric responses to magnetic stormsEarle, Gregory D.; Davidson, R. L.; Heelis, R. A.; Coley, W. R.; Weimer, Daniel R.; Makela, J. J.; Fisher, D. J.; Gerrard, Andrew J.; Meriwether, J. (American Geophysical Union, 2013-06-01)Thermospheric density and neutral velocity perturbations associated with three magnetic storms in the autumn season of 2011 are examined using data from the neutral wind meter (NWM) on the Communication/Navigation Outage Forecast System (C/NOFS) satellite. The data from perigee passes near 400km altitude show marked increases in neutral density during the storms and associated increases in horizontal neutral flow speeds. These thermospheric responses are characterized by enhanced meridional neutral flows with peak perturbation amplitudes near 100m/s and relative neutral density enhancements ranging from 50-100%. The increases in the neutral density and meridional flow velocity at equatorial latitudes occur about 5-7h after the initial perturbations are observed in the z component of the interplanetary magnetic field (IMF), and they persist for 20-30h. The perturbations in the neutral density are in good agreement with temperature increases predicted by an empirical model that has been validated using data from the CHAMP and Gravity Recovery and Climate Experiment missions, with a maximum lag time of similar to 1-1.5h between the model temperature increases and the observed density perturbations. The model temperatures are in excellent agreement with ground-based low-latitude temperature measurements during the storms. Ground-based wind measurements during one of the storms provide additional data for comparison with the perturbation wind amplitudes measured aboard the satellite.
- Storm time meridional wind perturbations in the equatorial upper thermosphereHaaser, R. A.; Davidson, R.; Heelis, R. A.; Earle, Gregory D.; Venkatraman, S.; Klenzing, J. (American Geophysical Union, 2013-05-01)We present observations from the Coupled Ion Neutral Dynamics Investigation (CINDI) of storm time meridional winds in the neutral atmosphere near the magnetic equator at 400km altitude. Observations near the magnetic equator in the southern geographic hemisphere are dominated by energy inputs from the southern Polar Regions that produce south to north (equatorward) wind perturbations to accompany perturbations in the neutral density and temperature. In one exceptional case, when observations are made near midnight and the north magnetic pole rotates through the midnight sector, north to south (poleward) meridional wind perturbations are observed just south of the magnetic equator. Accompanying perturbations in the neutral density on the dayside and the nightside are consistent with observed increases in the ion temperature and inferred increases in the neutral temperature in accord with hydrostatic equilibrium.