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Articles by A.F.M. Zain
Total Records ( 2 ) for A.F.M. Zain
  M. Abdullah , A.F.M. Zain , M.H. Jusoh , N. Misran and W.A. Mubarak
  Problem statement: Ionospheric precursors of earthquake have been studied by scientists and seismologists. This study aims at examining the relationship between the ionosphere and earthquake precursors. The effects of the anomalous electric field that penetrates the ionosphere on the electron concentration can be measured experimentally. This study reports on the variability of the Total Electron Content (TEC) during the December 26, 2004 earthquake in North Sumatra (epicentre: 3.295°N, 95.982°E) which measured 9.3 on the Richter scale. Approach: The ionospheric TEC near North Sumatra between December 19 to 31 was calculated between 22:00 and 24:00 and between 02:00 and 06:00 local time (LT) using a dual frequency Global Positioning System (GPS) receiver. It was recorded for a period of 13 days, which is seven days before and five days after the earthquake. The GPS data was taken from the Department of Survey and Mapping Malaysia in the north of Malaysia (4.1°N, 99.8°E), which is near North Sumatra. Four sets of data were selected from different GPS satellites that passed near the epicentre. Results: Results show good agreement with the existence of earthquake precursors. TEC variability was detected at night and in the early morning of 21 December 2004 (five days before the earthquake) and 25 December 2004 (a day before). Findings show an increase in the electron concentration level at the station closest to the epicentre and the TEC varies from 2-10 TEC unit. Conclusion/Recommendations: The findings correspond with previous research and literature in this field. Further studies on the parameters that cause the change in the ionospheric TEC due to earthquakes are needed if this is to be used as part of an earthquake early warning prediction system.
  M. Abdullah , A.F.M. Zain , Y.H. Ho and S. Abdullah
  Problem Statement: Ionospheric scintillations, which cause significant effects on satellite signals for communication and navigation, often takes place in equatorial region such as Malaysia. However, this disturbance is not fully understood due to few studies performed. This research reports the study and monitoring activity on Total Electron Content (TEC) and ionospheric scintillation in Malaysia using GPS measurements. Approach: One dual-frequency GPS receiver was positioned at the main station in Parit Raja, West Malaysia (1.86° N, 103.8° E) and Sipitang, East Malaysia (5.10° N, 115.56° E) respectively. Dual-frequency GPS data collected during the one-month ionospheric experimental campaign was used for TEC and scintillation computation and analysis. The TEC with 15 sec interval were computed from combined L1 and L2 code-pseudorange and carrier phase measurements. Whereas, the scintillation parameter S4 index was computed as a standard deviation of the received signal power normalized to average signal power every 60 sec on L1. A corrected S4 (without noise effects) was also computed and used in the analysis. Results: It was found that the daily maxima vTEC for Parit Raja (PR) ranged from 38-100 TECU, which is generally higher than those of Sipitang, which ranged from 30-42 TECU. However, a general consistency for both stations can be seen during the 1 month campaign period. Conclusions/Recommendations: In conclusion, these results show good agreement in the existence of the equatorial anomaly observed during moderate solar flux conditions and undisturbed geomagnetic condition. This will contributes to the knowledge of equatorial ionosphere and help in space weather condition. However, to better understand and characterize the ionosphere over Malaysia, more campaigns should be encouraged.
 
 
 
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