TY - JOUR
T1 - Equatorial GPS ionospheric scintillations over Kototabang, Indonesia and their relation to atmospheric waves from below
AU - Ogawa, Tadahiko
AU - Miyoshi, Yasunobu
AU - Otsuka, Yuichi
AU - Nakamura, Takuji
AU - Shiokawa, Kazuo
N1 - Funding Information:
Acknowledgments. GPS observations at the EAR site have been conducted in collaboration with RISH of Kyoto University and LAPAN of Indonesia since September 2002. We are deeply grateful to the staff of LAPAN for their extensive collaborations to the observations. We thank S. Sridharan and T. Yokoyama for their help in the data analysis. Tbb data were supplied through Kochi University, Japan. This work is supported by Grant-in-Aid for Scientific Research on Priority Area-764 (13136201) of the Ministry of Education, Culture, Sports, Science and Technology of Japan, and partly by the 21st Century COE Program “Dynamics of the Sun-Earth-Life Interactive System (SELIS)” of Nagoya University.
PY - 2009
Y1 - 2009
N2 - Using Global Positioning System (GPS) satellites, we have been conducting equatorial ionospheric scintillation observations at Kototabang, Indonesia since January 2003. Scintillations caused by equatorial plasma bubbles appear between 2000 and 0100 LT in equinoctial months with a seasonal asymmetry, and their activity decreases with decreasing solar activity. A comparison between scintillation index (S4) and Earth's brightness temperature (Tbb) variations suggests that the scintillation activity can be related to tropospheric disturbances over the Indian Ocean to the west of Kototabang. To understand better the reasons of day-to-day variability of S4, we analyze S4, rbb and lower thermospheric neutral wind (u′2̄) data. The results show that 54 fluctuates with periods of about 2.5, 5, 8, 14 and 25 days, possibly due to atmospheric waves from below and that similar periods are also found in the Tbb and u′2̄ variations. Using a general circulation model, we made numerical simulations to determine the behavior of neutral wind in the equatorial thermosphere. The results indicate the following: (1) 2- to 20-day waves dissipate rapidly above about an altitude of 125 km, and 0.5- to 3-hour waves become predominant above 100 km, (2) zonal winds above 200 km altitude are, on the whole, eastward during sunset-sunrise, (3) zonal wind patterns due to short-period (1-4 h) atmospheric gravity waves (AGWs) above 120 km altitude change day by day, exhibit wavy structures with scale lengths of about 30-1000 km and, as a whole, move eastward at about 100-1 while changing patterns over time. These simulations suggest that the Rayleigh-Taylor instability responsible for plasma bubble generation can be seeded by AGWs with short periods of about 0.5-3 h, and that background conditions necessary for this instability are modulated by planetary-scale atmospheric waves propagating up to an altitude of about 120 km from below.
AB - Using Global Positioning System (GPS) satellites, we have been conducting equatorial ionospheric scintillation observations at Kototabang, Indonesia since January 2003. Scintillations caused by equatorial plasma bubbles appear between 2000 and 0100 LT in equinoctial months with a seasonal asymmetry, and their activity decreases with decreasing solar activity. A comparison between scintillation index (S4) and Earth's brightness temperature (Tbb) variations suggests that the scintillation activity can be related to tropospheric disturbances over the Indian Ocean to the west of Kototabang. To understand better the reasons of day-to-day variability of S4, we analyze S4, rbb and lower thermospheric neutral wind (u′2̄) data. The results show that 54 fluctuates with periods of about 2.5, 5, 8, 14 and 25 days, possibly due to atmospheric waves from below and that similar periods are also found in the Tbb and u′2̄ variations. Using a general circulation model, we made numerical simulations to determine the behavior of neutral wind in the equatorial thermosphere. The results indicate the following: (1) 2- to 20-day waves dissipate rapidly above about an altitude of 125 km, and 0.5- to 3-hour waves become predominant above 100 km, (2) zonal winds above 200 km altitude are, on the whole, eastward during sunset-sunrise, (3) zonal wind patterns due to short-period (1-4 h) atmospheric gravity waves (AGWs) above 120 km altitude change day by day, exhibit wavy structures with scale lengths of about 30-1000 km and, as a whole, move eastward at about 100-1 while changing patterns over time. These simulations suggest that the Rayleigh-Taylor instability responsible for plasma bubble generation can be seeded by AGWs with short periods of about 0.5-3 h, and that background conditions necessary for this instability are modulated by planetary-scale atmospheric waves propagating up to an altitude of about 120 km from below.
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U2 - 10.1186/BF03353157
DO - 10.1186/BF03353157
M3 - Article
AN - SCOPUS:68949126995
VL - 61
SP - 397
EP - 410
JO - Earth, Planets and Space
JF - Earth, Planets and Space
SN - 1343-8832
IS - 4
ER -