Browsing by Author "Stolle, C."
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Item Open Access Equatorial ionospheric electrodynamic perturbations during Southern Hemisphere stratospheric warming events(American Geophysical Union, 2013-03) Olson, M. E.; Fejer, B. G.; Stolle, C.; Lühr, H.; Chau Chong Shing, Jorge LuisWe use ground-based and satellite measurements to examine, for the first time, the characteristics of equatorial electrodynamic perturbations measured during the 2002 major and 2010 minor Southern Hemisphere sudden stratospheric warming (SSW) events. Our data suggest the occurrence of enhanced quasi-two fluctuations during the 2002 early autumnal equinoctial warming. They also show a moderately large multi-day perturbation pattern, resembling those during arctic SSW events, during 2002 late equinox, as the major SSW was weakening. We also compare these data with extensive recent results that showed the fundamentally important role of lunar semidiurnal tidal effects on low latitude electrodynamic perturbations during of arctic SSW events.Item Open Access Equatorial zonal electric fields during the 2002-2003 sudden stratospheric warming event(Instituto Geofísico del Perú, 2009) Olson, Michael E.; Fejer, B. G.; Stolle, C.; Chau Chong Shing, Jorge Luis; Goncharenko, L. P.For nearly fifty years, the Jicamarca Radio Observatory (11.95°S, 76.87°W, 2°N dip latitude) near Lima, Peru, has measured ionospheric plasma drifts. Over the last ten years, measurements of plasma drift velocities have also been measured using radar observations of the equatorial 150 km altitude región (Kudeki and Fawcett, 1993; Chau and Woodman, 2004).Item Open Access Estimating the daytime Equatorial Ionization Anomaly strength from electric field proxies(American Geophysical Union, 2008-09-10) Stolle, C.; Manoj, C.; Lühr, H.; Maus, S.; Alken, P.The Equatorial Ionization Anomaly (EIA) is a significant feature of the low‐latitude ionosphere. During daytime, the eastward electric field drives a vertical plasma fountain at the magnetic equator creating the EIA. Since the eastward electric field is also the driving force for the Equatorial Electrojet (EEJ), the latter is positively correlated with the EIA strength. We investigate the correlation between the zonal electric field and the EIA in the Peruvian sector and compare the results with correlations of the EEJ versus EIA strength. Analyzing 5 years of Challenging Minisatellite Payload (CHAMP) electron density measurements, plasma drift readings from the Jicamarca Unattended Long‐term Investigations of the Ionosphere and Atmosphere (JULIA) radar, and magnetic field observations at Huancayo and Piura, we find the EEJ strength and the zonal electric field to be suitable proxies for the EIA intensity. Both analyses reveal high correlation coefficients of cc > 0.8. A typical response time of the EIA to variations in the zonal electric field is ∼1–2 h, and it is ∼2–4 h after EEJ strength variations. Quantitative expressions are provided, which directly relate the EIA parameters to both proxies. From these relations, we infer that an EIA develops also during weak Counter Electrojets (CEJs), but no EIA forms when the vertical plasma drift is zero. For positive EEJ magnetic signatures to form, a minimum eastward electric field of 0.2 mV/m is required on average. The above‐mentioned delay between EIA and EEJ variations of ∼3 h is further confirmed by the investigation of the EIA response to transitions from CEJ to EEJ, e.g., during late morning hours.Item Restricted Lunar-dependent equatorial ionospheric electrodynamic effects during sudden stratospheric warmings(American Geophysical Union, 2010) Fejer, B. G.; Olson, M. E.; Chau Chong Shing, Jorge Luis; Stolle, C.; Lühr, H.; Goncharenko, L. P.; Yumoto, K.; Nagatsuma, T.We have used plasma drift and magnetic field measurements during the 2001–2009 December solstices to study, for the first time, the longitudinal dependence of equatorial ionospheric electrodynamic perturbations during sudden stratospheric warmings. Jicamarca radar measurements during these events show large dayside downward drift (westward electric field) perturbations followed by large morning upward and afternoon downward drifts that systematically shift to later local times. Ground-based magnetometer measurements in the American, Indian, and Pacific equatorial regions show strongly enhanced electrojet currents in the morning sector and large reversed currents (i.e., counterelectrojets) in the afternoon sector with onsets near new and full moons during northern winter warming periods. CHAMP satellite and ground-based magnetic field observations indicate that the onset of these equatorial afternoon counterelectrojets is longitude dependent. Our results indicate that these large electrodynamic perturbations during stratospheric warming periods are due to strongly enhanced semidiurnal lunar wave effects. The results of our study can be used for forecasting the occurrence and evolution of these electrodynamic perturbations during arctic winter warmings.