Browsing by Author "Retterer, J. M."
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Item Restricted Global equatorial plasma bubble occurrence during the 2015 St. Patrick's Day storm(American Geophysical Union, 2016-01-18) Carter, B. A.; Yizengaw, E.; Pradipta, R.; Retterer, J. M.; Groves, K.; Valladares, C.; Caton, R.; Bridgwood, C.; Norman, R.; Zhang, K.An analysis of the occurrence of equatorial plasma bubbles (EPBs) around the world during the 2015 St. Patrick's Day geomagnetic storm is presented. A network of 12 Global Positioning System receivers spanning from South America to Southeast Asia was used, in addition to colocated VHF receivers at three stations and four nearby ionosondes. The suppression of postsunset EPBs was observed across most longitudes over 2 days. The EPB observations were compared to calculations of the linear Rayleigh‐Taylor growth rate using coupled thermosphere‐ionosphere modeling, which successfully modeled the transition of favorable EPB growth from postsunset to postmidnight hours during the storm. The mechanisms behind the growth of postmidnight EPBs during this storm were investigated. While the latter stages of postmidnight EPB growth were found to be dominated by disturbance dynamo effects, the initial stages of postmidnight EPB growth close to local midnight were found to be controlled by the higher altitudes of the plasma (i.e., the gravity term). Modeling and observations revealed that during the storm the ionospheric plasma was redistributed to higher altitudes in the low‐latitude region, which made the plasma more susceptible to Rayleigh‐Taylor growth prior to the dominance of the disturbance dynamo in the eventual generation of postmidnight EPBs.Item Restricted Modeling the low-latitude ionospheric electron density and plasma turbulence in the November 2004 storm period(Elsevier, 2010-03) Retterer, J. M.; Ilma, Ronald; Kelley, M. C.; Chau Chong Shing, Jorge Luis; Valladares, C. E.; Gentile, L. C.; Groves, K.The storm period of 8–12 November 2004 offers an opportunity for insight into the phenomena of low-latitude ionospheric structure during geomagnetically disturbed times because of the strength of the disturbances, the timing of the storms, and the instrumentation that was operating during the interval. We will take advantage of these factors to model the ambient ionosphere and the plasma turbulence responsible for radio scintillation within it, using the AFRL low-latitude ambient/turbulent ionospheric model and the storm-time model features described in the companion paper [Retterer, J.M., Kelley, M.C., 2009. Solar-wind drivers for low-latitude ionospheric models during geomagnetic storms. J. Atmos. Solar-Terr. Phys., this issue]. The model plasma densities show very good agreement with the densities measured by the Jicamarca ISR as well as with the total electron content (TEC) measured by the Boston College South American chain of GPS receivers. The detection by the radar of coherent returns from plasma turbulence match well the times of predicted ionospheric instability. The predicted geographic extent of the occurrence of equatorial plasma bubbles was matched by DMSP satellite observations and our forecasts of scintillation strength were validated with measurements of S4 at Ancon and Antofagasta by stations of the AFRL SCINDA network.Item Open Access Theoretical relationship between maximum value of the post-sunset drift velocity and peak-to-valley ratio of anomaly TEC(American Geophysical Union, 2004-02-11) Basu, B.; Retterer, J. M.; De La Beaujardiére, O.; Valladares, C. E.; Kudeki, E.Theoretical study of electron density distribution in the nighttime equatorial ionosphere shows that linear relationships with statistically significant correlation coefficients exist between the maximum value of the post‐sunset plasma drift velocity and the peak‐to‐valley ratio of anomaly TEC. The study is based on the low‐latitude density model of Air Force Research Laboratory (AFRL) and the obtained relationships are valid for the longitudinal sector of Jicamarca incoherent scatter radar whose drift velocity measurements are used. The significance of this finding lies in the fact that the maximum value of the post‐sunset vertical plasma drift velocity is an important parameter for determining both the intensity and the latitudinal distribution of equatorial scintillation. When the parameter is not available from any direct measurement, the linear relationships may be used to estimate it from the measured peak‐to‐valley ratio of anomaly TEC.