Long‐term analysis of ionospheric polar patches based on CHAMP TEC data

Abstract

[1] Total electron content (TEC) from LEO satellites offers great possibility to sound the upper ionosphere and plasmasphere. This paper describes a method to derive absolute TEC observations aboard CHAMP considering multipath effects and receiver differential code bias. The long-term data set of 9 years GPS observations is used to investigate the climatological behavior of high-latitude plasma patches in both hemispheres. The occurrence of polar patches has a clear correlation with the solar cycle, which is less pronounced in the Southern Hemisphere (SH). Summed over all years, we observed a higher number of patches in the SH. The maximum occurrence rate of patches has been found at the dayside polar cusp during 12:00-18:00 MLT (magnetic local time) supporting the mechanisms for patch creation by local particle precipitation and by intrusion of subauroral plasma into the polar cap through tongues of ionization (TOIs). The latter mechanism seems to be even more important in the SH. Investigating the patches in comparison with interplanetary magnetic field (IMF) conditions, we found that decreased IMF Bz and enhanced merging electric field preceded the patch observation; hence, patch creation follows a period of enhanced solar wind input into the magnetosphere/ionosphere. We further found an annual cycle in patch occurrence with maxima at equinox and December solstice and a June solstice minimum which reflects the global ionospheric seasonal asymmetry in electron density. We suggest that enhanced TEC at midlatitudes and low latitudes during December solstice provides a greater possibility to transport high-density plasma to the polar region through the buildup of TOIs.Citation: Noja, M., C. Stolle, J. Park, and H. Lühr (2013), Long-term analysis of ionospheric polar patches based on CHAMP TEC data, Radio Sci., 48,[289][290][291][292][293][294][295][296][297][298][299][300][301]

Climatology of GPS signal loss observed by Swarm satellites

“…Our result shown in Fig. 6 reveals that in both hemispheres the GPS signal losses have a higher occurrence during December solstice, supporting the conclusion of Noja et al (2013) and Chartier et al (2018) that the polar patches have higher occurrence at this season. The possible reason for explaining the different seasonal dependence of polar patches is that Spicher et al (2017) used a method with relative threshold for identifying polar patches (the enhancement must be at least twice that of the background density), while the detection approach used by Noja et al (2013) was based on a mixture of absolute and relative patch magnitudes (besides the relative enhancement, the absolute TEC enhancement must be larger than 4 TECU; 1 TECU = 10 16 electrons m −2 ).…”

“…However, the seasonal dependence of polar patches is still an open issue: some studies reported that the polar patches are mainly a local winter phenomenon in both hemispheres (e.g., Coley and Heelis, 1998;Kivanç and Heelis, 1998;Carlson, 2012;Spicher et al, 2017), while there are also studies found that polar patches have higher occurrence during December solstice months in both hemispheres (e.g., Noja et al, 2013;Chartier et al, 2018). Our result shown in Fig.…”

“…The possible reason for explaining the different seasonal dependence of polar patches is that Spicher et al (2017) used a method with relative threshold for identifying polar patches (the enhancement must be at least twice that of the background density), while the detection approach used by Noja et al (2013) was based on a mixture of absolute and relative patch magnitudes (besides the relative enhancement, the absolute TEC enhancement must be larger than 4 TECU; 1 TECU = 10 16 electrons m −2 ). Noja et al (2013) pointed out that the TEC in the Southern Hemisphere exhibited very small magnitudes rarely exceeding 5 TECU during June solstice, hence their detection algorithm possibly ignore most of the patches, but these small magnitude patches will possibly be detected by Spicher et al (2017) when they only concern the relative enhancements. A detailed discussion about the difference between Noja et al (2013) and Spicher et al (2017) has also been provided in Charter et al (2018).…”

“…Noja et al (2013) pointed out that the TEC in the Southern Hemisphere exhibited very small magnitudes rarely exceeding 5 TECU during June solstice, hence their detection algorithm possibly ignore most of the patches, but these small magnitude patches will possibly be detected by Spicher et al (2017) when they only concern the relative enhancements. A detailed discussion about the difference between Noja et al (2013) and Spicher et al (2017) has also been provided in Charter et al (2018). Our result reveals that for causing the receiver connection loss with GPS satellites, the plasma density gradients along the signal path must exceed a certain threshold.…”

Relation of zonal plasma drift and wind in the equatorial F region as derived from CHAMP observations

“…Chen et al, 2011), affects the phase delay of wave signals (e.g. Jee et al, 2004;Noja et al, 2013), and disturbs communication links (e.g. Basu et al, 1988Basu et al, , 2001Nishioka et al, 2011;Manju et al, 2011).…”