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[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]

In the post-sunset tropical ionospheric F-region plasma density often exhibits depletions, which are usually called equatorial plasma bubbles (EPBs). In this paper we give an overview of the Swarm Level 2 Ionospheric Bubble Index (IBI), which is a standard scientific data of the Swarm mission. This product called L2-IBI is generated from magnetic field and plasma observations onboard Swarm, and gives information as to whether a Swarm magnetic field observation is affected by EPBs. We validate the performance of the L2-IBI product by using magnetic field and plasma measurements from the CHAMP satellite, which provided observations similar to those of the Swarm. The L2-IBI product is of interest not only for ionospheric studies, but also for geomagnetic field modeling; modelers can de-select magnetic data which are affected by EPBs or other unphysical artifacts.

In this work we analyze the global distribution and physical characteristics of nighttime midlatitude magnetic field fluctuations (MMFs) as observed by the CHAMP satellite from 2001 to 2002 (solar maximum) and from 2006 to 2007 (solar minimum). MMFs are defined as medium‐scale magnetic fluctuations perpendicular to the mean field, which are not accompanied by plasma density irregularities at the CHAMP altitude (∼400 km). MMFs occur at 15°–40° invariant latitude in the ionospheric F region. The occurrence is rare above the southern Atlantic ocean, and bears little connection to geomagnetic activity. The global MMF occurrence rate depends on season. The occurrence is generally low in equinox, maximizes around east Asia/Oceania and Europe/northern Atlantic Ocean in June solstice, and peaks above the American continents in December solstice. As the solar cycle declines, the detected MMF occurrence rate also decreases. The MMF occurrence peaks around 2100 LT and slowly decreases toward midnight. In the postmidnight sector, events are practically absent. The MMF occurrence is generally consistent with known features of nighttime medium‐scale traveling ionospheric disturbances (MSTIDs), such as the conjugate climatology, and premidnight occurrence peak in the east Asia/Oceania region. But differences in their distributions also exist, implying that factors other than MSTIDs, e.g., ionospheric conductivity, sporadic E layer or plasma instabilities, may play a nonnegligible role in generating MMFs. MMFs have a preferred direction of polarization, which is consistent with that of MSTIDs and again corroborates the close connection between these two phenomena. We interpret the observed magnetic deflections in terms of field‐aligned currents (FACs). The estimated wavelength range (∼200–500 km) of associated FAC pairs also agrees well with the size of MSTID density structures.

Abstract. Total electron content (TEC) between Low-EarthOrbit (LEO) satellites and the Global Navigation Satellite System (GNSS) satellites can be used to constrain the three-dimensional morphology of equatorial plasma bubbles (EPBs). In this study we investigate TEC measured onboard the Challenging Minisatellite Payload (CHAMP) from 2001 to 2005. We only use TEC data obtained when CHAMP passed through EPBs: that is, when in situ plasma density measurements at CHAMP altitude also show EPB signatures. The observed TEC gradient along the CHAMP track is strongest when the corresponding GNSS satellite is located equatorward and westward of CHAMP with elevation angles of about 40-60 • . These elevation and azimuth angles are in agreement with the angles expected from the morphology of the plasma depletion shell proposed by Kil et al. (2009).