Equatorial and low latitude spread-F irregularity characteristics over the Indian region and their prediction possibilities |
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| Institution: | 1. Radio and Atmospheric Sciences Division, National Physical Laboratory, New Delhi 110012, India;2. Space Physics Laboratory, Vikram Sarabhai Space Centre, Trivandrum 695022, India;3. Department of Physics, Andhra University, Visakhapatnam 530003, India;1. NASRDA Center for Atmospheric Research, Kogi State University, Anyigba Campus, Nigeria;2. Ionospheric & Space Physics Laboratory, Department of Physics, University of Lagos, Nigeria;3. Department of Physics, University of Calabar, Nigeria;4. Department of Physics, Federal University of Agriculture, Makurdi, Nigeria;5. Department of Surveying & Geo-informatics, Nnamdi Azikiwe University, Awka, Nigeria;1. Centre of Studies in Resources Engineering, Indian Institute of Technology Bombay, Mumbai 400076, India;2. Indian Institute of Geomagnetism, Mumbai 400005, India;1. Department of Geophysics, Peking University, Beijing 100871, China;2. National Space Science Center, Chinese Academy of Sciences, Beijing 100190, China;3. State Key Laboratory of Space Weather, National Space Science Center, Chinese Academy of Sciences, Beijing 100190, China;4. Science China Press, Beijing 100717, China;1. Addis Ababa University, Institute of Geophysics Space Science and Astronomy, CNCS, Department of Physics, P. O. Box 1176, Addis Ababa, Ethiopia;2. Washera Geospace and Radar science Research Laboratory, Department of Physics, Bahir Dar University, P.O. Box 79, Bahir Dar, Ethiopia |
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| Abstract: | To study the occurrence characteristics of equatorial spread-F irregularities and their latitudinal extent, simultaneous digital ionosonde data (January–December 2001) from Trivandrum (8.2°N), Waltair (17.7°N) and Delhi (28.6°N) and 4 GHz scintillation data from Sikandarabad (26.8°N) and Chenglepet (10.4°N), and 250 MHz scintillation data from Bhopal (23.2°N) for equinoxes period are analysed. It is noted that except summer months, occurrence of spread F is always maximum at Trivandrum, minimum at Delhi and moderate at Waltair. During equinoxes and winter months. Their occurrences at higher latitude station are always conditional to their prior occurrences at lower latitudes indicating their association with the generation of equatorial plasma bubble and associated irregularities. Scintillation occurrences also follow the similar pattern. During the summer months, the spread-F occurrences are highest at equatorial location Trivandrum, moderate at Delhi and minimum at Waltair and seem to be caused by irregularities generated locally especially over Delhi.To gain forecasting capability, night-to-night occurrences of spread-F/scintillation at these locations are examined in relation to post sunset rise of h’F and upward ExB drift velocity over the magnetic equator using Trivandrum ionosonde data. It is noted that except the summer months, the spread-F at Trivandrum, Waltair and Delhi are observed only when equatorial ExB (h’F) is more than about 15 m/s (325 km), 20 m/s (350 km) and 25 m/s (375 km), respectively. With these threshold values their corresponding success rate of predictions are more than 90%, 50% and 15% at the respective locations. Whereas in the case of GHz scintillations near equator are observed only when ExB (h’F) is more than 15 m/s (325 km), whereas for low latitude, the same should be 30 m/s (400 km) and their success rate of prediction is about 90% and 30%, respectively. The intensity of 4 GHz scintillation at low latitude is also found to be positively correlated with equatorial upward ExB drift velocity values, whereas correlation is poor with that of equatorial scintillations. In conclusions, near magnetic equator threshold values of ExB or h’F can be successfully used for the night-to-night prediction of spread-F/scintillations occurrences, whereas these are necessary but not sufficient for their prediction at higher latitudes. For that some other controlling parameters like background electron density, neutral winds, gravity waves, etc. should also be examined. |
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