Jens Mielich

Validation of GPS Ionospheric Radio Occultation results onboard CHAMP by Vertical Sounding Observations in Europe

Ionospheric radio occultation (IRO) measurements have a big potential for monitoring the ionospheric behavior on global scale for now- and forecasting the ionospheric impact on radio systems. In this article we validate the retrieved vertical electron density profiles (EDPs) derived from IRO measurements onboard CHAMP by using vertical sounding measurements at five European vertical sounding stations — Athens, Dourbes, Juliusruh, Rome and Tortosa. Since first IRO measurement onboard CHAMP in April 2001, more than 70000 electron density profiles have been retrieved by a model assisted technique so far. The comparison of IRO retrieved EDPs with ionosonde profiles obtained from the above mentioned stations will be discussed.

Pilot Ionosonde Network for Identification of Traveling Ionospheric Disturbances

Travelling Ionospheric Disturbances (TIDs) are the ionospheric signatures of atmospheric gravity waves (AGWs). Their identification and tracking is important because the TIDs affect all services that rely on predictable ionospheric radio wave propagation. Although various techniques have been proposed to measure TID characteristics, their real-time implementation still has several difficulties. In this contribution, we present a new technique, based on the analysis of oblique Digisonde-to-Digisonde (D2D) “skymap” observations, to directly identify TIDs and specify the TID wave parameters based on the measurement of angle-of-arrival, Doppler frequency, and time-of-flight of ionospherically reflected high-frequency (HF) radio pulses. The technique has been implemented for the first time for the Net-TIDE project with data streaming from the network of European Digisonde DPS4D observatories. The performance is demonstrated during a period of moderate auroral activity, assessing its consistency with independent measurements such as data from auroral magnetometers and electron density perturbations from Digisondes and GNSS stations. Given that the different types of measurements used for this assessment were not made at exactly the same time and location, and that there was insufficient coverage in the area between the AGW sources and the measurement locations, we can only consider our interpretation as plausible and indicative for the reliability of the extracted TID characteristics. In the framework of the new TechTIDE project (European Commission H2020), a retrospective analysis of the Net-TIDE results in comparison with those extracted from GNSS TEC-based methodologies is currently being attempted, and the results will be the objective of a follow up paper.

On the dynamics of large‐scale traveling ionospheric disturbances over Europe on 20 November 2003

Ionospheric disturbances, often associated with geomagnetic storms, may cause threats to radio systems used for communication and navigation. One example is the super storm on 20th November 2003, when plenty of strong and unusual perturbations were reported. This paper reveals additional information on the dynamics in the high latitude ionosphere over Europe during this storm. Here, analyses of wavelike Travelling Ionospheric Distrubances (TIDs) over Europe are presented, based on estimates of the Total Electron Content (TEC) derived from ground-based Global Navigation Satellite System (GNSS) measurements. These TIDs are ionospheric signatures of thermospheric surges initiated by space weather events. The source region of these TIDs is characterized by enhanced spatial gradients, TEC depression, strong uplift of the F2-layer, the vicinity of the eastward auroral electrojet and strong aurora E-layers. Joule heating is identified as the most probable driver for the TIDs observed over Europe during 20th November 2003. The sudden heating of the thermosphere leads to strong changes in the pressure and thermospheric wind circulation system, which in turn generates thermospheric wind surges observed as TID signatures in the TEC. Either the dissipation of the eastward auroral electrojet or particle precipitation are considered as the source mechanism for the Joule heating.In the course of the storm, the TEC observations show a southward shift of the source region of the TIDs. These meridional dislocation effects are obviously related to a strong compression of the plasmasphere. The presented results demonstrate the complex interaction processes in the thermosphere-ionosphere-magnetosphere system during this extreme storm.