Observation and modelling of the upper atmospheric density and winds and their dependence on the geomagnetic conditions

• Antragsteller: Professor Dr. Hermann Lühr
• Fachliche Zuordnung: Physik und Chemie der Atmosphäre
• Förderung: Förderung von 2005 bis 2010
• Projektkennung: Deutsche Forschungsgemeinschaft (DFG) - Projektnummer 15111139

• Erstellungsjahr: 2010

Zusammenfassung der Projektergebnisse

This study contributes to the aim of the CAWSES (Climate and Weather of the Sun-Earth System) project to significantly enhance the understanding of the space environment and its impact on life and society by investigating the local phenomenon of the neutral fountain effect in the dayside thermospheric polar regions. The significant deceleration of the CHAMP satellite at cusp crossings prompted a detailed investigation of the geomagnetically induced cusp region's influence on the neutral upper atmospheric dynamics. Therefore, the total mass density, as derived from CHAMP accelerometer readings, has been studied extensively. It reveals a significant enhancement in the vicinity of the cusp, only visible if displayed in geomagnetic coordinates. Climatological results from a multi-year statistical analysis express a continuous occurence of the phenomenon in both hemispheres (but less pronounced in the South) which is controlled partly by the strength of the solar flux, but more directly by the coupling efficiency of IMF and EMF and the background density. In a 2D-correlation analysis it has been revealed that the merging electric field (in mV/m) has a weight that is by more than 50 times higher than that of P10.7 concerning the dependence of the density anomaly on these both parameters. The ambient air density has been found to be a prime controlling parameter of the amplitude. In a combined CHAMP-EISCAT campaign, a model study on soft particle precipitation and an analysis of periodic density anomaly variations the activating mechanisms of the neutral fountain effect have been studied. As a result, the Pedersen conductivity was found to peak at 140 km altitude, indicating Joule heating even above the E region. Joule heating has been assumed to be one of the main sources of the neutral fountain. We obtained heating rates much larger than derived from an earlier campaign, probably due to the fact that we took into account also small-scale contributions of the effective electric field. The results are consistent with the CHAMP-observed decelerations. Particle precipitation events may enhance the conductivity layer, thus lifting up the altitude of effective Joule heating. This might change the heated population in favour of heavier particles to be transported upward. The following mechanism is suggested to cause the cusp-related density anomaly: The energy input by the solar wind, as characterised by the merging electric field, provides the power for Joule heating of preferably heavy molecules. Soft particle precipitation in the cusp simultaneously enhances the conductivity at higher altitude thus lifting up the heated layer in the cusp. The density anomaly is then caused by local composition changes due to the differential expansion of heavier particles. The density enhancement is more intensive during phases of high solar activity. It affects the upper atmosphere globally. It is important to investigate this phenomenon in detail both, for the modelling community concerning the foreseen input of local features to ionospheric/atmospheric models and for the calculation of spacecraft orbit tracks, fuel budget and space debris monitoring.

Projektbezogene Publikationen (Auswahl)

• Observation and Modelling of the upper atmospheric density and winds and their dependence on geomagnetic activity, DFG SPP meeting, Kühlungsborn, Germany, May 2006
  Rentz, S. and H. Lühr
  
• A statistical analysis of longitudinal dependences of upper thermospheric zonal winds at dipequator latitudes derived from CHAMP, J. Atmo. Sol.-Terr. Phys., 69(12), 1419-1430, 2007
  Häusler, K., H. Lühr, S. Rentz and W. Köhler
  
• Average thermospheric wind patterns over the polar regions, as observed by CHAMP, Ann. Geophys., 25(5), 1093-1101, 2007
  Lühr, H., S. Rentz, P. Ritter, H. Liu and K. Häusler
  
• Combined CHAMP-EISCAT studies on local thermospheric mass density enhancements in the cusp, 13th International EISCAT Workshop 2007, Mariehamn, Finland, August 2007
  Rentz, S., H. Lühr and M. Rietveld
  
• Combined CHAMP-EISCAT studies on local thermospheric mass density enhancements in the cusp, EISCAT-CAWSES Copernicus Newsletter, 1, 2007
  Rentz, S., H. Lühr and M. Rietveld
  
• Density enhancements in the thermospheric cusp region, GFZ PHD Day, Potsdam, Germany, November 2007
  Rentz, S. and H. Lühr
  
• Geomagnetische Signaturen in der aus CHAMP-Beobachtungen abgeleiteten thermosphärischen Dichte und deren besonderes Verhalten in der Cusp, Oberseminar IGEP, Braunschweig, Germany, June 2007
  Rentz, S.
  
• Observations of the low-latitude solar eclipse on 8 April 2005 by CHAMP, J. Geophys. Res., 112, A06303, 2007
  Tomás, A. T., H. Lühr, M. Förster, S. Rentz and M. Rother
  
• Statistical studies on local thermospheric cusp density enhancements, lUGG-IAGA 2007, Perugia, Italy, July 2007
  Rentz, S., H. Lühr, K. Häusler and W. Köhler
  
• THERMOCUSP - Density enhancements in the thermospheric cusp region, CAWSES SPP meeting, Bonn - Bad Godesberg, Germany, January 2007
  Rentz, S. and H. Lühr
  
• Chmatology of the cusp-related thermospheric mass density anomaly, as derived from CHAMP observations, Ann. Geophys., 26, 2807-2823, 2008
  Rentz, S. and H. Lühr
  
• Climatology of the cusp-related thermospheric mass density, as observed by CHAMP, DFG SPP Meeting, Berlin, Germany, September 2008
  Rentz, S. and H. Lühr
  
• Density enhancements in the cusp, EISCAT-CAWSES-Copernicus Statusbericht, 2008
  Rentz, S., H. Lühr and M. Rietveld
  
• Dichteanomalien in der thermosphärischen Cusp-Region, beobachtet mit CHAMP, DPG Frühjahrstagung 2008 - Fachverband Extraterrestrische Physik, Freiburg, Germany, March 2008
  Rentz, S., H. Lühr and M. Rietveld
  
• Die thermospharische Massendichte in der Cusp-Region, beobachtet mit dem Satelliten CHAMP, Theoretisch-Physikalisches Oberseminar, TU Braunschweig, Braunschweig, Germany, July 2008
  Rentz, S.
  
• EISCAT - European Incoherent Scatter Radar, PHD Day 2008, Potsdam, Germany, December 2008
  Rentz, S. and H. Lühr
  
• IMF dependence of high-latitude thermospheric wind pattern derived from CHAMP cross-track measurements, Ann. Geophys., 26, 1581-1595, 2008
  Förster, M., S. Rentz, W. Köhler, H. Liu and S. E. Haaland
  
• Neutral air-upwelling in the cusp region - a response to solar and magnetospheric forcing (solicited), EGU 2009 General Assembly, Vienna, Austria, 2009
  Rentz, S. and H. Lühr
  
• Solar and magnetospheric forcing of the low latitude thermospheric mass density as observed by CHAMP, Ann. Geophys., 27, 2087-2099, 2009
  Müller, S., H. Lühr and S. Rentz
  
• The 27-day modulation of the low latitude ionosphere during a solar maximum, J. Geophys. Res, 114, A04317, 2009
  Kyoung, M., J. Park, H. Kim, V. Kim, H. Kil, J. Lee, S. Rentz, H. Lühr and L. Paxton