Global/Seasonal/Local-time Distributions of Low Latitude Ionospheric Plasma Blobs Observed by ROCSAT-1 in 1999 to 2004

• Main Authors: Yu-Jhong Shih, 施禹仲
• Other Authors: Shin-yi Su
• Format: Others
• Language: en_US
• Published: 2009
• Online Access: http://ndltd.ncl.edu.tw/handle/35gm8h

碩士 === 國立中央大學 === 太空科學研究所 === 97 === A plasma blob is an irregularity structure with density enhancement above the background in the nighttime ionosphere. The first report of the plasma blob observation was made with Hinotori in 1981, but the occurrence mechanism of the plasma blob is still unknown. An auto-search program is designed to find the plasma blob occurrence distribution in the ROCSAT-1 data taken during the high to moderate solar activity years of 1999 to 2004. The result of the plasma blob occurrence probability is presented in the distributions in longitude/dip-latitude/local-time/season/magnetic activity/solar activity. In the longitude distribution, although the plasma blob occurrence probability has a longitudinal variation, there is no apparent variation between ±15° dip-latitude, which is very different from the plasma bubble occurrences, and this is evident that the plasma bubble and plasma blob have different occurrence mechanisms. For the dip-latitude distribution, we find that the plasma blob has a minimum occurrence probability from -15° to 15° in dip-latitude and increases toward the higher latitudes. For the local-time variation, the plasma blob occurrence probability has a maximum around midnight, and it decreases slowly after midnight and decreases rapidly after 04 LT in most seasons. For the seasonal variation, the occurrence probability of the plasma blob is larger at solstice than at equinox. Furthermore, it has the maximum occurrence probability in both northern and southern hemispheres during the June solstice. During magnetic disturbed periods (Kp≧3), the plasma blob occurrence probability only indicates a small variation after midnight. That is, the magnetic disturbance seems to have little effect on the plasma blob occurrences. This is different to the equatorial bubbles in which the occurrence probability will increase after midnight during the magnetic disturbed time [e.g. Watanabe and Oya, 1986]. For the solar activity effect, the plasma blob seems to have more occurrences during low solar activity years which is opposite to the occurrences of the equatorial bubble [e.g. Su et al., 2006; Watanabe and Oya, 1986].