Modelling and Observation of Sporadic E Layers and their dependence on upper atmospheric dynamics
Zusammenfassung der Projektergebnisse
The project was based on GPS radio occultation (RO) measurements performed by the low-Earth orbiting satellites CHAMP, GRACE and FORMOSAT-3/COSMIC between 2001 and 2009. The large number of daily GPS RO measurements, their global distribution and the high vertical resolution of the profiles are excellent preconditions for investigations of the lower ionosphere on a global scale. The GPS RO data were used to receive a global and comprehensive picture of sporadic E layer occurrence and the associated coupling process between neutral atmosphere and ionosphere. Sporadic E layer occurrence underlies variations on several time scales. The observed diurnal fluctuations with higher rates during daytime and lower rates at night are interfered by an annual cycle where the largest values are measured in summer. The variations are caused by geophysical parameters controlling the sporadic E formation. The interaction of these parameters, namely the deposition of metallic ions in the lower ionosphere, the horizontal intensity of Earth's magnetic field and vertical wind shear, is summarized in the wind shear theory that describes the sporadic E formation process at mid-latitudes. The results of our project support the theoretically expected relationship between the sporadic E formation process and the discussed parameters. Investigations of coupling processes between sporadic E occurrence and winds in the lower thermosphere were performed at northern mid-latitudes. The meteor radar provides wind and meteor rate measurements which were compared with seasonal sporadic E rates. It was found that the vertical zonal wind shear produced by the semidiurnal tide has the strongest influence on sporadic E behavior in northern mid-latitudes. On seasonal average, sporadic E rates show a clear semidiurnal structure in altitude/local time cross–sections throughout the year following the downward moving phase of the tidal wind shear. The ion concentration in the ionosphere depends on the meteor influx reaching its maximum in early summer. In the first half of the year, daily sporadic E rates follow very closely the course of the daily meteor number. But the differences observed in the second half of the year can only be explained when taking into account additionally the wind conditions.
Projektbezogene Publikationen (Auswahl)
- A climatology of multiple tropopauses derived from GPS radio occultations with CHAMP and SAC-C. Geophys. Res. Lett., 33, 2006
T. Schmidt, G. Beyerle, S. Heise, J. Wickert, and M. Rothacher
- A global analysis of wave potential energy in the lower stratosphere derived from 5 years of GPS radio occultation data with CHAMP. Geophys. Res. Lett., 33, 2006
A. de la Torre, T. Schmidt, and J. Wickert
- Gravity waves above the Andes detected from GPS radio occultation temperature profiles: Jet mechanism? Geophys. Res. Lett., 33, 2006
A. de la Torre, P. Alexander, P. Llamedo, C. Menéndez, T. Schmidt, and J. Wickert
- A global climatology of ionospheric irregularities derived from GPS radio occultation. Geophys. Res. Lett., 35, 2008
C. Arras, J. Wickert, G. Beyerle, S. Heise, and T. Schmidt, C. Jacobi
- Comparison of mesopause region meteor radar winds, medium frequency radar winds and low frequency drifts over Germany. Adv. Space Res., 43:247–252, 2009
C. Jacobi, C. Arras, D. Kürschner, W. Singer, P. Hoffmann, and D. Keuer
- GPS radio occulation: Results from CHAMP, GRACE and FORMOSAT-3/COSMIC. TAO, 1:35–50, 2009
J. Wickert, G. Michalak, T. Schmidt, G. Beyerle, C. Z. Cheng, S. B. Healy, S. Heise, C. Y. Huang, N. Jakowski, W. Köhler, C. Mayer, D. Offiler, E. Ozawa, A. G. Pavelyev, M. Rothacher, B. Tapley, and C. Arras
- Semidiurnal tidal signature in sporadic E occurrence rates derived from GPS radio occultation measurements at higher midlatitudes. Ann. Geophys., 27:2555–2563, 2009
C. Arras, C. Jacobi, and J. Wickert
- Estimated errors in a global gravity wave climatology from GPS radio occultation temperature profiles. Adv. Space Res., 46:174–179, 2010
A. de la Torre, P. Llamedo, P. Alexander, T. Schmidt, and J. Wickert
- Sporadic E signatures revealed from multi-satellite radio occultation measurements. Adv. Radio Sci., 8:225–230, 2010
C. Arras, C. Jacobi, J. Wickert, S. Heise, and T. Schmidt
- Global sporadic E layer characteristics obtained from GPS radio occultation measurements. In F.-J. Lübken, editor, Climate And Weather of the Sun-Earth System (CAWSES): Highlights from a priority program. Springer, Dordrecht, The Netherlands, 2012
C. Arras, J. Wickert, C. Jacobi, G. Beyerle, S. Heise, and T. Schmidt
