Conveners:
Chaosong Huang (cshuang@haystack.mit.edu)
Bela Fejer (bfejer@cc.usu.edu)
2005 Thursday 30 June 0130-0330 PM
The M-I Coupling and Ionospheric Storms workshop was held on Thursday, 30 June 2005 in the Anasazi North Room. About 80 participants attended the workshop. This workshop focused on ionospheric electric fields and global ionospheric disturbances during magnetic storms. Prompt penetration electric fields generally last for less than one hour because of the shielding effects of the ring current. However, a recent study suggest that they can last for several hours. Disturbance winds and neutral composition also play a crucial role in the generation of ionospheric storms. The outstanding problems include what causes the long-duration enhancement of the ionospheric electric field, how significantly the penetration electric field causes ionospheric disturbances, how the penetration electric field effect can be separated from wind dynamo effect, and how the ionospheric electron density disturbances are related to neutral winds and composition changes. The speakers of the workshop presented the latest observational and simulation results related to these problems.
Bela Fejer (USU) began the workshop with a presentation of how prompt penetration electric fields vary with latitude. Temporal variations of penetration electric field patterns at two storm times at different latitudes were derived from simulations using the Rice Convection Model (RCM), and the simulation results were compared with observations. It is concluded that ionospheric conductivity changes strongly affect the local time, latitudinal, and longitudinal variations of the prompt penetration electric fields.
Ray Greenwald (JHU/APL) reported new observations of storm-time ionospheric convective flows obtained with the SuperDARN Wallops radar. The Wallops radar was constructed to provide improved geophysical monitoring instrumentation at GSFC/WFF and to study plasma flows and ionospheric electric fields at mid-latitudes under disturbed geomagnetic conditions. The radar detected very strong plasma convection flows at midlatitudes in two instances of disturbed/storm-time activity within one month. In both cases, the stormtime expansion of the convection cells lasted a number of hours. The observations indicate that there was no temporary undershielding, but rather a long-term reconfiguration of electric fields and plasma convection in the inner magnetosphere.
Chaosong Huang (MIT) presented the observations of penetration electric fields obtained with the Millstone Hill and Jicamarca incoherent scatter radars during magnetic storms. It is shown that the interplanetary electric field can penetrate to the low-latitude ionosphere without obvious attenuation for several hours during the main phase of storms as long as the IMF remains southward. The observations imply that the polarization electric field cannot be built in the ring current when the magnetic activity is strengthening, so the magnetospheric convection electric field can continuously penetrate to the low-latitude ionosphere without shielding.
Joe Huba (NRL) presented the simulation results of storm-time penetration electric fields and ionospheric disturbances with a self-consistent coupling of the RCM and SAMI3 codes. Different variations of the polar cap potential were used in the simulations. It is found that temporal changes in the polar cap potential produce electric fields that modify the F region equatorial drift velocities; the velocities increase in the daytime and decrease in the nighttime by up to a factor of 2. Total electron content (TEC) in the midlatitude ionosphere is increased by up to 35%, and the equatorial fountain effect is enhanced in the post-sunset period.
Naomi Maruyama (HAO/NCAR) also presented simulation results of storm-time ionospheric electric field using the RCM. It is shown that the magnitude of the penetration electric field from simulation depends on the plasma sheet conditions and conductivity as input to the RCM boundary conditions. The simulations reproduced the ionospheric electric fields and density disturbances during the magnetic storms on 31 March 2001 and 17 April 2002 and were in reasonable agreement with observations.
Marlene Colerico (MIT) showed storm-enhanced density (SED) events detected with global GPS network during magnetic storms. Ionospheric SED is characterized by high TEC values (>50 TEC units) and correlated with plasmaspheric drainage plume. SED plumes over Northern Europe and American sectors are compared. This may be the first time that the occurrence of strong SED plumes over European sector was derived. Magnetic conjugacy effects of SED formation were analyzed from GPS and multiple satellite data.
Mariangel Fedrizzi (NOAA/SEC) reported the simulation studies of different mechanisms that are responsible for F-region height changes during geomagnetic storms. Ionosonde observations during the 31 March 2001 storm are compared with the CTIPe model. CTIPe results are in good agreement with the observations. The contributions of mechanisms at middle latitudes include thermospheric wind that is dominant during the night and thermal expansion that is larger in the nightside sector during the first hours after the storm commencement.
Yongliang Zhang (JHU/APL) presented GUVI observations of composition changes and ionospheric behavior during magnetic storms. It is found that energy input (particle and Joule heating) from the magnetosphere causes significant O/N2 depletion down to and beyond the magnetic equator. Time delay between the energy input and O/N2 depletion supports the idea of co-rotation. There is a fairly good positive correlation between O/N2 and TEC. This provides a way to use GUVI O/N2 to estimate TEC over oceans where no land GPS observations are made.
John Emmert (GMU) presented observations of average storm-induced thermospheric disturbance winds. It is shown that the average disturbance winds at equatorial to upper-mid latitudes are mostly westward and equatorward. Daytime disturbance winds extend down to at least 110 km and are generally constant with height above 130 km. Low- and mid-latitude nighttime zonal disturbance winds are westward, with average peak magnitudes of 15 m/s for moderately disturbed conditions to 50 m/s for strongly disturbed conditions.
Hien Vo (NAIC/Arecibo) reported the observations of the low-latitude ionospheric response to the November 2004 magnetic storm obtained with Arecibo all-sky imager and global GPS network. Two sequences of ionospheric density depletion were observed to move northward and westward over Arecibo in response to the large Dst drop. The incoherent scatter radar data from Millstone Hill and Arecibo can be used to address the low latitude formation of SED.