https://repository.kopri.re.kr/handle/201206/5464 2026-04-07T05:39:41Z 2026-04-07T05:39:41Z Jee, Geonhwa https://repository.kopri.re.kr/handle/201206/8828 2022-03-24T07:13:12Z 2015-03-27T00:00:00Z

Title: Magnetospheric effects on the upper atmosphere in the polar region Authors: Jee, Geonhwa

2015-03-27T00:00:00Z Lee, Han-Byul Stanley C. Solomon Jee, Geonhwa https://repository.kopri.re.kr/handle/201206/6093 2022-03-24T07:11:30Z 2014-01-01T00:00:00Z

Title: Global ionospheric total electron contents (TECs) during the last two solar minimum periods Authors: Lee, Han-Byul; Stanley C. Solomon; Jee, Geonhwa Abstract: The last solar minimum period was anomalously extended and low in EUV irradiance compared with previous solar minima. It can readily be expected that the thermosphere and the ionosphere must be correspondingly affected by this low solar activity. While there have been unanimous reports on the thermospheric changes, being cooler and lower in its density as expected, the ionospheric responses to low solar activity in previous studies were not consistent with each other, probably due to the limited ionospheric observations used for them. In this study, we utilized the measurements of total electron content (TEC) from TOPEX and JASON-1 satellites during the periods of 1992 to 2010, which includes both the last two solar minimum periods, in order to investigate how the ionosphere responded to the extremely low solar activity during the last solar minimum compared with previous solar minimum. Although the global daily mean TECs show negligible differences between the two solar minimum periods, the global TEC maps reveal that there are significant systematic differences ranging from about 30% to +50% depending on local time, latitude, and season. The systematic variations of the ionospheric responses seem to mainly result from the relative effects of reduced solar EUV production and reduced recombination rate due to thermospheric changes during the last solar minimum period.

2014-01-01T00:00:00Z Lee, Han-Byul Ja-Soon Shim Kim, Yong Ha Jee, Geonhwa https://repository.kopri.re.kr/handle/201206/6113 2022-03-24T07:11:30Z 2013-01-01T00:00:00Z

Title: Characteristics of global plasmaspheric TEC in comparison with the ionosphere simultaneously observed by Jason-1 satellite Authors: Lee, Han-Byul; Ja-Soon Shim; Kim, Yong Ha; Jee, Geonhwa Abstract: We compared the global plasmaspheric total electron content (pTEC) with the ionospheric TEC (iTEC) simultaneously measured by Jason-1 satellite during the declining phase of solar cycle 23 (2002？ 2009) to investigate the global morphology of the plasmaspheric density in relation to the ionosphere. Our study showed that the plasmaspheric density structures fundamentally follow the ionosphere, but there are also significant differences between them. Although the diurnal variations are very similar to each region, the plasmasphere shows much weaker variations, only approximately 1 TECU day-night difference. By analyzing the day-night differences in the plasmasphere, we found that the plasmaspheric contribution to the nighttime ionosphere does not increase with solar activity and the largest contribution occurs during June solstice. The plasmasphere shows similar seasonal variations to the ionosphere, except for the semiannual variation, which is essentially absent in the plasmasphere. There is also an important difference in the annual variation: although the annual variation in the ionosphere exists regardless of longitude, it occurs only at American sector in the plasmasphere. As solar activity increases to moderate level, the pTEC substantially enhances from approximately 2 to 4 TECU at the initial increase of solar activity below F10.7p = 100 and then quickly slows down while the iTEC almost linearly enhances. Although it is well known that magnetic storms are the major source of plasmaspheric density depletion, pTEC does not show this aspect of the plasmasphere probably due to the relatively small Kp values for high magnetic activity (Kp > 2.5) in the current study.

2013-01-01T00:00:00Z Kim, Yong Ha Kim, Jeong-Han Jee, Geonhwa Lee, Changsup https://repository.kopri.re.kr/handle/201206/6523 2022-03-24T07:13:11Z 2013-01-01T00:00:00Z

Title: VHF meteor radar at King Sejong Station, Antarctica Authors: Kim, Yong Ha; Kim, Jeong-Han; Jee, Geonhwa; Lee, Changsup Abstract: Since 2002, we have been observing the mesosphere and lower thermosphere (MLT) region over King Sejong Station (KSS;62.22°S, 58.78°W), Antarctica, using various instruments such as the Spectral Airglow Temperature Imager (SATI), All Sky Camera (ASC) and VHF meteor radar. The meteor radar, installed in March 2007, continuously measures neutral winds in the altitude region 70？110 km and neutral temperature near the mesopause 24 h？d-1, regardless of weather conditions. In this study, we present results of an analysis of the neutral wind data for gravity wave activity over the tip of the Antarctic Peninsula, where such activity is known to be very high. Also presented is temperature estimation from measurement of the decay times of meteor trails, which is compared with other temperature measurements from SATI and the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument onboard the Thermosphere Ionosphere Mesosphere Energy and Dynamics (TIMED) satellite.

2013-01-01T00:00:00Z