Observations and simulations of the ionospheric and thermospheric response to the December 2006 geomagnetic storm : Initial phase

[1] We have investigated the thermospheric and ionospheric response to the 14–15 December 2006 geomagnetic storm using a Coupled Magnetosphere Ionosphere Thermosphere (CMIT) 2.0 model simulation. In this paper we focus on observations and simulations during the initial phase of the storm (about 8 h), when the shock was driving changes in geospace. The global ionospheric maps of total electron content (TEC), ionosonde data at four stations and Millstone Hill incoherent scatter radar (ISR) observations are compared with the corresponding simulation results from the CMIT model. The observations showed significant positive storm effects occurred in the Atlantic sector after the onset of this storm. The CMIT model is able to capture the temporal and spatial variations of the ionospheric storm effects seen in the GPS TEC observations, although the model slightly underestimates the daytime positive ionospheric storm in the South American sector. The simulations are also in agreement with the ionosonde and ISR ionospheric measurements. Term analysis of the ion continuity equation demonstrates that changes in the electric fields play a dominant role in generating the observed ionospheric positive storm effect in the American sector during the initial phase, although neutral winds and composition changes also contribute. The difference in the strength of the enhancements over North and South America can be explained by the slope of the topside electron density profiles in the two hemispheres. In the southern hemisphere electron densities decrease slowly with altitude, whereas the decrease is much more rapid in the northern (winter) hemisphere. The electric fields, therefore, cannot cause large increases in electron density by uplifting the plasma, so positive storm effects are small in the southern hemisphere compared with the northern hemisphere, even though the increase in hmF2 is greater in the southern hemisphere. Nighttime changes in electron density in other longitude sectors are small, because the topside electron densities also decrease slowly with altitude at night.

[1]  Ying-Hwa Kuo,et al.  Comparison of COSMIC ionospheric measurements with ground-based observations and model predictions : Preliminary results , 2007 .

[2]  A. Coster,et al.  Conjugate localized enhancement of total electron content at low latitudes in the American sector , 2007 .

[3]  Libo Liu,et al.  An analysis of the scale heights in the lower topside ionosphere based on the Arecibo incoherent scatter radar measurements , 2007 .

[4]  S. Solomon,et al.  The ionospheric and thermospheric response to CMEs: Challenges and successes , 2007 .

[5]  S. Solomon,et al.  An analysis of neutral wind generated currents during geomagnetic storms , 2007 .

[6]  R. Schunk,et al.  Duration of an ionospheric data assimilation initialization of a coupled thermosphere‐ionosphere model , 2007 .

[7]  Michael Mendillo,et al.  Storms in the ionosphere: Patterns and processes for total electron content , 2006 .

[8]  Larry J. Paxton,et al.  Global thermosphere‐ionosphere response to onset of 20 November 2003 magnetic storm , 2006 .

[9]  Anthea J. Coster,et al.  Automated GPS processing for global total electron content data , 2006 .

[10]  Timothy Fuller-Rowell,et al.  Interaction between direct penetration and disturbance dynamo electric fields in the storm‐time equatorial ionosphere , 2005 .

[11]  Bodo W. Reinisch,et al.  Recent advances in real-time analysis of ionograms and ionospheric drift measurements with digisondes , 2005 .

[12]  Libo Liu,et al.  Variations of electron density based on long‐term incoherent scatter radar and ionosonde measurements over Millstone Hill , 2005 .

[13]  Timothy L Killeen,et al.  Initial results from the coupled magnetosphere–ionosphere–thermosphere model: thermosphere–ionosphere responses , 2004 .

[14]  Charles C. Goodrich,et al.  Initial results from the coupled magnetosphere ionosphere thermosphere model: magnetospheric and ionospheric responses , 2004 .

[15]  John Lyon,et al.  The Lyon-Fedder-Mobarry (LFM) global MHD magnetospheric simulation code , 2004 .

[16]  Toshitaka Tsuda,et al.  Global dayside ionospheric uplift and enhancement associated with interplanetary electric fields , 2004 .

[17]  R. Roble,et al.  Long-lasting disturbances in the equatorial ionospheric electric field simulated with a coupled magnetosphere-ionosphere-thermosphere model , 2003 .

[18]  O. Witasse,et al.  An updated climatology of thermospheric neutral winds and F region ion drifts above Millstone Hill , 1999 .

[19]  M. Buonsanto.  Ionospheric Storms — A Review , 1999 .

[20]  B. M. Reddy,et al.  A comparative study of global ionospheric responses to intense magnetic storm conditions , 1998 .

[21]  J. Lyon,et al.  Global numerical simulation of the growth phase and the expansion onset for a substorm observed by Viking , 1995 .

[22]  R. Roble,et al.  Magnetosphere‐ionosphere‐thermosphere coupling: Effect of neutral winds on energy transfer and field‐aligned current , 1995 .

[23]  H. W. Kroehl,et al.  What is a geomagnetic storm , 1994 .

[24]  Timothy Fuller-Rowell,et al.  Response of the thermosphere and ionosphere to geomagnetic storms , 1994 .

[25]  G. W. Prölss.  Common origin of positive ionospheric storms at middle latitudes and the geomagnetic activity effect at low latitudes , 1993 .

[26]  Raymond G. Roble,et al.  A thermosphere/ionosphere general circulation model with coupled electrodynamics , 1992 .

[27]  Raymond G. Roble,et al.  A coupled thermosphere/ionosphere general circulation model , 1988 .

[28]  J. Lastovicka,et al.  Eects of geomagnetic storms on the ionosphere and atmosphere , 2001 .

[29]  G. W. Prölss,et al.  Numerical simulation of long-duration positive ionospheric storm effects , 1998 .

[30]  Gerd W. Prölss,et al.  On explaining the local time variation of ionospheric storm effects , 1993 .

[31]  Henry Rishbeth,et al.  Introduction to ionospheric physics , 1969 .