Analysis of Mid-to-High Latitude GNSS Total Electron Content and its Variability during Solar Cycle 24 Minimum

Abstract:

During the past decade, GNSS total electron content (TEC) observations have been extended beyond the mid-latitudes to provide continuous and expanded coverage of the Arctic and Antarctic regions. Taking advantage of this, GNSS TEC observations, hosted in the CEDAR Madrigal database, will be used to provide a summary of measured and differential TEC during the current solar cycle 24. This study illustrates the strength of this database, especially when merged with additional observations, e.g. all-sky camera images. We will briefly summarize median TEC conditions over solar cycle 24 and then separately examine the variability of TEC through the measurement of an activity index for traveling ionospheric disturbances (TIDs). The TEC summary will include medians and standard deviations, for both hemispheres, and for a variety of latitudes, longitudes, magnetic local times, and seasons. Our emphasis will be on high latitudes which in the past have only been sparsely sampled. Comparisons will be made with predictions from the International Reference Ionosphere model and the E-CHAIM model. In addition, examples of TEC enhancements due to high-latitude precipitation events will be shown with supporting images of auroral activity from all-sky cameras images.

The variability of the background TEC during solar minimum conditions (from 2017-on) will be studied utilizing a separate traveling ionospheric disturbance (TID) database. This data base has been established using the computed difference between each line of sight (LOS) TEC and its smoothed estimate, where the smoothing was based on a Savitzky-Golay low-pass filter with a 30-min window fitted to the LOS TEC. From the TID database, a TID activity index, which allows the variability of the TEC to be quantified, has been defined as the median of the absolute value of observed TIDs over a 1-minute interval. For our analysis, this TID index is calculated for separate 5 x 5 degrees areas, including high and mid -latitude regions, for all longitudes with sufficient data coverage. Analysis of this TID activity index enables the examination of TEC variability over different regions and the investigation of plausible causes for observed increases (geomagnetic storms, tropospheric weather, polar vortex strength, etc.).