Jong-Kyun Chung

Magnetic signatures of medium-scale traveling ionospheric disturbances as observed by CHAMP

[1] In this work we analyze the global distribution and physical characteristics of nighttime midlatitude magnetic field fluctuations (MMFs) as observed by the CHAMP satellite from 2001 to 2002 (solar maximum) and from 2006 to 2007 (solar minimum). MMFs are defined as medium-scale magnetic fluctuations perpendicular to the mean field, which are not accompanied by plasma density irregularities at the CHAMP altitude (∼400 km). MMFs occur at 15°-40° invariant latitude in the ionospheric F region. The occurrence is rare above the southern Atlantic ocean, and bears little connection to geomagnetic activity. The global MMF occurrence rate depends on season. The occurrence is generally low in equinox, maximizes around east Asia/Oceania and Europe/ northern Atlantic Ocean in June solstice, and peaks above the American continents in December solstice. As the solar cycle declines, the detected MMF occurrence rate also decreases. The MMF occurrence peaks around 2100 LT and slowly decreases toward midnight. In the postmidnight sector, events are practically absent. The MMF occurrence is generally consistent with known features of nighttime medium-scale traveling ionospheric disturbances (MSTIDs), such as the conjugate climatology, and premidnight occurrence peak in the east Asia/Oceania region. But differences in their distributions also exist, implying that factors other than MSTIDs, e.g., ionospheric conductivity, sporadic E layer or plasma instabilities, may play a nonnegligible role in generating MMFs. MMFs have a preferred direction of polarization, which is consistent with that of MSTIDs and again corroborates the close connection between these two phenomena. We interpret the observed magnetic deflections in terms of field-aligned currents (FACs). The estimated wavelength range (∼200-500 km) of associated FAC pairs also agrees well with the size of MSTID density structures.

Seasonal Variations of Mesospheric Gravity Waves Observed with an Airglow All-sky Camera at Mt. Bohyun, Korea (36° N)

We have carried out all-sky imaging of OH Meinel, O 2 atmospheric and OI 557.7 nm airglow layers in the period from July of 2001 through September of 2005 at Mt. Bohyun, Korea (36.2° N, 128.9° E, Alt = 1,124 m). We analyzed the images observed during a total of 153 clear moonless nights and found 97 events of band-type waves. The characteristics of the observed waves (wavelengths, periods, and phase speeds) are consistent with internal gravity waves. The wave occur- rence shows an approximately semi-annual variation, with maxima near solstices and minima near equinoxes, which is consistent with other studies of airglow wave observations, but not with those of mesospheric radar/lidar observations. The observed waves tended to propagate westward during fall and winter, and eastward during spring and summer. Our ray tracing study of the observed waves shows that majority of the observed waves seemed to originate from meso- spheric altitudes. The preferential directions and the apparent source altitudes can be explained if the observed waves are secondary waves generated from primary waves that have been selected by the filtering process and break up at the mesospheric altitudes.

Receiver DCB Estimation and Analysis by Types of GPS Receiver

This paper analyzes that the global positioning system (GPS) receiver differential code bias (DCB) has effect on the estimation the ionosphere total electron content (TEC). The data from nine permanent GPS sites of the Korea Astronomy and Space Science Institute (KASI) were used for the estimation of the receiver DCB before (Trimble 4000 SSi) and after (Trimble NetRS) the receiver replacement, using the singular value decomposition method. The results showed that the estimated mean value of the receiver DCB varied from 0.11 ns (nanosecond) to 7.54 ns before the receiver replacement, but the receiver DCBs shoed large values than 20 ns except some stations after the replacement. The receiver DCB showed a relatively large difference by types of the receivers, and, as a result, it had a great effect on the estimation the ionosphere TEC using GPS.

Quality Assessment of Tropospheric Delay Estimated by Precise Point Positioning in the Korean Peninsula

Over the last decade, the Global Navigation Satellite System (GNSS) has been increasingly utilized as a meteorological research tool. The Korea Astronomy and Space Science Institute (KASI) has also been developing a near real-time GNSS precipitable water vapor (PWV) information management system that can produce a precise PWV for the Korean Peninsula region using GNSS data processing and meteorological measurements. The goal of this paper is to evaluate whether the precise point positioning (PPP) strategy will be used as the new data processing strategy of the GNSS-PWV information management system. For this purpose, quality assessment has been performed by means of a comparative analysis of the troposphere zenith total delay (ZTD) estimates from KASI PPP solutions (KPS), KASI network solutions (KNS), and International GNSS Service (IGS) final troposphere products (IFTP) for ten permanent GNSS stations in the Korean Peninsula. The assessment consists largely of two steps: First, the troposphere ZTD of the KNS are compared to those of the IFTP for only DAEJ and SUWN, in which the IFTP are used as the reference. Second, the KPS are compared to the KNS for all ten GNSS stations. In this step, the KNS are used as a new reference rather than the IFTP, because it was proved in the previous step that the KNS can be a suitable reference. As a result, it was found that the ZTD values from both the KPS and the KNS followed the same overall pattern, with an RMS of 5.36 mm. When the average RMS was converted into an error of GNSS-PWV by considering the typical ratio of zenith wet delay and PWV, the GNSS-PWV error met the requirement for PWV accuracy in this application. Therefore, the PPP strategy can be used as a new data processing strategy in the near real-time GNSS-PWV information management system.

Global Positioning System Total Electron Content Variation over King Sejong Station in Antarctic under the Solar Minimum Condition Between 2005 and 2009

The total electron content (TEC) using global positioning system (GPS) is analyzed to see the characteristics of ionosphere over King Sejong station (KSJ, geographic latitude , longitude , corrected geomagnetic latitude ) in Antarctic. The GPS operational ratio during the observational period between 2005 and 2009 is 90.1%. The annual variation of the daily mean TEC decreases from January 2005 to February 2009, but increase from the June 2009. In summer (December-February), the seasonal mean TEC values have the maximum of 26.2 2.4 TEC unit (TECU) in 2005 and the minimum of 16.5 2.8 TECU in 2009, and the annual differences decrease from 3.0 TECU (2005-2006) to 1.4 TECU (2008-2009). However, on November 2010, it significantly increases to 22.3 2.8 TECU which is up to 5.8 TECU compared with 2009 in summer. In winter (June-August), the seasonal mean TEC slightly decreases from 13.7 4.5 TECU in 2005 to 8.9 0.6 TECU in 2008, and the annual difference is constantly about 1.6 TECU, and increases to 10.3 1.8 TECU in 2009. The annual variations of diurnal amplitude show the seasonal features that are scattered in summer and the enhancements near equinoxes are apparent in the whole years. In contrast, the semidiurnal amplitudes show the disturbed annual peaks in winter and its enhancements near equinoxes are unapparent. The diurnal phases are not constant in winter and show near 12 local time (LT). The semidiurnal phases have a seasonal pattern between 00 LT and 06 LT. Consequently, the KSJ GPS TEC variations show the significant semidiurnal variation in summer from December to February under the solar minimum between 2005 and 2009. The feature is considered as the Weddell Sea anomaly of larger nighttime electron density than a daytime electron density that has been observed around the Antarctica peninsula.

Statistics of Ionospheric Storms Using GPS TEC Measurements Between 2002 and 2014 in Jeju, Korea

Using the Total Electron Content (TEC) data from the Global Navigation Service System (GNSS) site in Jeju, operated by the Korea Astronomy and Space Science Institute (geographic location: , ; geomagnetic location: ) for 2002-2014 in Korea, the results of the statistical analysis of positive and negative ionospheric storms are presented for the first time. In this paper, ionospheric storms are defined as turbulences that exceed 50% of the percentage differential Global Positioning System (GPS) TEC ratio () with monthly median GPS TEC. During the period of observations, the total number of positive ionospheric storms ( > 50%) was 170, which is greater than five times the number of negative ionospheric storms (

Ionospheric Behaviors Over Korea Peninsula During the Super Geomagnetic Storm Using GPS Measurements

The super-geomagnetic storms called 2003 Halloween event globally occurred during the period of 29 through 31 which are the following days when the solar flares of X18 class exploded on 28 October 2003. The S4 index from GPS signal strength and the peak electron density (NmF2) from GPS tomography method are analyzed according to the date. The occurrences of the cycle slip and scintillation in the GPS signals are

ESTIMATION OF INTRINSIC WAVE PARAMETERS AND MOMENTUM FLUXES OF MESOSPHERIC GRAVITY WAVES OVER KOREA PENINSULA USING ALL-SKY CAMERA AND FABRY-PEROT INTERFEROMETER

We estimate the momentum fluxes of short-period gravity waves which are observed in the OI 557.7 nm nightglow emission with all-sky camera at Mt. Bohyun () in Korea. The intrinsic phase speed (), the intrinsic period (), and vertical wavelength () are also deduced from the horizontal wavelength (), observed period (), propagation direction (), observe phase speed () of the gravity wave on the all-sky images. The neutral winds to deduce intrinsic wave parameters are measured with Fabry-Perot interferometer on Shigaraki () in Japan. We selected 5-nights of observations during the period between July 2002 and December 2006 considering of the weather and instrument conditions in two observation sites. The mean values of intrinsic parameter of gravity waves are

The First Measurement of Seasonal Trends in the Equatorial Ionospheric Anomaly Trough at the CHUK GNSS Site During the Solar Maximum in 2014

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Radio Occultation Mission in Korea Multi-Purpose Satellite KOMPSAT-5

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