DSpace Collection:

Mid-latitude ionosphere observed by ground-based GPS during intense geomagnetic storms in October 2003 and November 2004

2022-03-24T07:13:53Z

Title: Mid-latitude ionosphere observed by ground-based GPS during intense geomagnetic storms in October 2003 and November 2004 Authors: Chung, Jong-Kyun; Jee, Geonhwa Abstract: Ionospheric variabilities can be very important to the qualities and propagation of the radio signals of the global navigation satellite system, which is mostly used in the mid-latitudes. The mid-latitude ionosphere is often considered to be a well-understood and uninteresting stable region of the ionosphere during past few decades. However, it was reported from the large ground-based GPS TEC networks that dramatic changes can occur in the mid-latitude ionosphere especially during geomagnetic storm (Foster, 1993; Tsurutani et al., 2005). During geomagnetic storms, positive and negative phases of ionospheric disturbances are used to describe the increase and decrease of ionospheric electron densities, respectively. We analyze the negative and positive phases of ionospheric storms by using the ground-based GPS TEC data measured in the northeast Asian sector during the intense geomagnetic storms on 29-31 October 2003 and 8-11 November 2004. The positive phase on 8 November 2004 persisted except for dawn, and its maximum value is about 65 TECU, which is almost 3 times greater than the monthly mean TEC values. The positive phase on 10 November 2004 began to occur during the day and lasted for more than 6 hours, and its peak value was about 30 TECU at 23 LT. The other positive storms on 29-31 October 2003 were observed only during daytime and the nighttime TEC was similar or slightly lower than the monthly value. The positive phase on 29-31 October 2003 was significantly weaker than the storms on 8 and 10 November 2004 in which the asymmetric feature of O/N2 ratio from the GUVI/TIMED observation was more distinct. We will also discuss the ionospheric effects on the GPS L1 qualities during intense geomagnetic storms.

Assessment of GPS global ionosphere maps (GIM) by comparison between CODE GIM and TOPEX/Jason TEC data: Ionospheric perspective

2022-03-24T07:12:25Z

Title: Assessment of GPS global ionosphere maps (GIM) by comparison between CODE GIM and TOPEX/Jason TEC data: Ionospheric perspective Authors: Chung, Jong-Kyun; Lee, Han-Byul; Kim, Yong Ha; Jee, Geonhwa; Cho, J. Abstract: We performed a comprehensive comparison between GPS global ionosphere map (GIM) and TOPEX/Jason (T?\\\\J) total electron content (TEC) data for the periods of 1998？2009 in order to assess the performance of GIM over the global ocean where the GPS ground stations are very sparse. Using the GIM model constructed by the Center for Orbit Determination in Europe at the University of Bern, the GIM TEC values were obtained along the T?\\\\J satellite orbit at specific locations and times of measurements and then binned into various geophysical conditions for direct comparison with the T?\\\\J TEC. On the whole, the GIM model was able to reproduce the spatial and temporal variations of the global ionosphere as well as the seasonal variations. However, the GIM model was not accurate enough to represent the well?\\\\known ionospheric structures such as the equatorial anomaly, the Weddell Sea Anomaly, and the longitudinal wave structure. Furthermore, a fundamental limitation of the model seems to be evident in the unexpected negative differences (i.e., GPS < T?\\\\J) in the northern high?\\\\latitude and the southern middle?\\\\ and high?\\\\latitude regions in comparison with the T?\\\\J TECS. The positive relative differences (i.e., GIM > T?\\\\J) at night represent the plasmaspheric contribution to GPS TEC, which is maximized, reaching up to 100% of the corresponding T?\\\\J TEC values in the early morning sector. In particular, the relative differences decreased with increasing solar activity, and this may indicate that the plasmaspheric contribution to the maintenance of the nighttime ionosphere does not increase with solar activity, which is different from what we normally anticipate.

Plasmaspheric contribution to the ionospheric GPS TEC

2022-03-24T07:12:03Z

Title: Plasmaspheric contribution to the ionospheric GPS TEC Authors: Kim, Yong Ha; Jee, Geonhwa; Lee, Han Byul; Cho, Jung Ho; Chung, Jong-Kyun Abstract: We performed a comprehensive comparison between GPS Global Ionosphere Map (GIM) and TOPEX/Jason (T-J) TEC data for the periods of 1998~2009 in order to assess the performance of GIM over the global ocean where the GPS ground stations are very sparse. Using the GIM model constructed by CODE at University of Bern, the GIM TEC values were obtained along the T-J satellite orbit at the locations and times of the measurements and then binned into various geophysical conditions for direct comparison with the T-J TECs. On the whole, the GIM model was able to reproduce the spatial and temporal variations of the global ionosphere as well as the seasonal variations. However, the GIM model was not accurate enough to represent the well-known ionospheric structures such as the equatorial anomaly, the Weddell Sea Anomaly, and the longitudinal wave structure. Furthermore, there seems to be a fundamental limitation of the model showing the unexpected negative differences (i.e., GPS < T-J) in the northern high latitude and the southern middle and high latitude regions. The positive relative differences (i.e., GIM > T-J) at night represent the plasmaspheric contribution to GPS TEC, which is maximized, reaching up to 100% of the corresponding T-J TEC values in the early morning sector. In particular, the relative differences decreased with increasing solar activity and this may indicate that the plasmaspheric contribution to the maintenance of the nighttime ionosphere does not increase with solar activity, which is different from what we normally anticipate. Among these results, the plasmaspheric contribution to the ionospheric GPS TEC will be presented in this talk and the rest of it will presented in the companion paper (poster presentation).

The plasmaspheric effects on the maintenance of the nighttime ionosphere

2022-03-24T07:13:48Z

Title: The plasmaspheric effects on the maintenance of the nighttime ionosphere Authors: Jee, Geonhwa; Lee, Han Byul; Chung, Jong-Kyun; Kim, Yong Ha Abstract: The plasmasphere, or the inner magnetosphere is a region of the Earth's magnetosphere consisting of low energy plasma. It is located above the ionosphere and dynamically interact with it along the magnetic field lines. During the daytime, the ions in the ionosphere, produced by solar EUV radiation, are diffused upward along the magnetic field lines at mid-latitudes and become the main source of the plasmaspheric plasma density. During the nighttime, however, the ions in the plasmasphere can diffuse downward to the ionosphere where the significant parts of the ionospheric density are depleted by the recombination with neutrals. In order to study the effects of this downward plasma transport on the nighttime ionosphere, we utilized the total electron content (TEC) data measured from the JASON satellite from 2002 to the current. This satellite measures not only the ionospheric TEC from the ground to the satellite orbit altitude (1336 km) but also the plasmaspheric TEC by the dual-frequency GPS receiver aboard the satellite. We analyzed these ionospheric and plasmaspheric TEC measurements for different seasons and solar activities to study the contribution of the plasmaspheric TEC to the maintenance of the nighttime ionospheric TEC.