Magnetic Storm Effects on the Occurrence and Characteristics of Plasma Bubbles

Abstract

During geomagnetic storms actions of prompt penetration electric fields (PPEF) during the main phase disturbs the equatorial ionosphere. In addition, disturbance dynamo electric fields (DDEF) can follow during the recovery phase to further modify the plasma dynamics of the low-latitude ionosphere. The eastward PPEF and westward DDEF cause sudden or ongoing upward and downward plasma drifts that can cause changes in seasonal-longitudinal occurrence patterns of plasma bubbles. Ionospheric irregularities like plasma bubbles occur all around the year within equatorial latitudes, but their occurrence varies seasonally and with changes in solar activity. The short-term changes in the plasma vertical drift during storms cause enhancement or suppression in the occurrence and intensity of plasma bubbles. Our study investigates the changes in the plasma bubble occurrence pattern and characteristics during different phases of storms. The Communications/Navigation Outages Forecast System (C/NOFS) satellite mission was designed to investigate the ionospheric conditions that lead to the formation of plasma irregularities. We have studied the effects of magnetic storms on the formation and evolution of plasma bubbles during the satellite’s lifetime (2008-2014). During this period encompassing solar minimum and maximum conditions, many magnetic storms of varying intensity developed. Each storm was isolated and divided into initial, main, and recovery phases based on the SYM-H index data observed from geomagnetic observatories. Interplanetary Magnetic Field (IMF) data measured by the Advanced Composition Explorer (ACE) satellite was used to observe fluctuations in magnetic fields during storms. Measurements of plasma density from the Plasma Langmuir Probe (PLP) were used to identify plasma bubble occurrences, and determine their local times, depths, widths, etc. A bubble detection algorithm was developed to detect bubbles from the plasma density data. Measurements of plasma vertical velocities from the Ion Velocity Meter (IVM) were used to determine evening PRE peak velocities and bubble internal vertical velocities. Analysis of 109 storms of varying intensities with available bubble and PRE data between May 2008 and August 2014 has revealed that the most intense plasma bubbles occur during a storm’s main phase when Bz turns southwards as PRE velocities tend to increase during those times. New bubbles develop with large PRE values and the bubble lifetime extends into the recovery phase. Comparisons of bubble depths and internal vertical velocities between the storm’s main phases and quiet periods before have shown significant improvement during storms. The augmentation of the plasma bubbles’ depth and internal velocity become more prominent when the bubble intensities were low during the quiet period before the storms. Furthermore, bubble intensities decrease by the end of the recovery phase along with the decline in the PRE velocities. The growth and decline of the bubble occurrence and characteristics signify the important roles of PPEF and DDEF during storms on the low-latitude ionosphere.