Thesis (M.Sc.)--Chulalongkorn University, 2013

Ionosphere is the upper atmosphere of Earth’s. There are high electron densities or so-called Total Electron Content (TEC), which changes all the time. Especially, low latitudes region often sudden changes both small and large within the ionosphere. Variation of TEC will directly affect to quality the accuracy of the telecommunications system in this region. The main purpose of this research is to study daily, monthly, annual and season variations of the TEC over Thailand by using GPS data between January 2009 and December 2012. The TEC values obtained were calculated in a form of the daily rate of change of total electron content index (ROTI) to demonstrate the ionosphere irregularities. The average daily variations of ROTI show a semiannual trend and an increasing annual of the ionosphere irregularities activity. The occurrence rate of the ionosphere irregularities were found on a large scale during night time. The results also confirmed that the ionosphere irregularities depend on month and season. The ionosphere irregularities reached high occurrence rates during the equinox season (March, April, September and October). In addition, the characteristic of annual variation confirms the spatial distribution of the ionosphere irregularities during nighttime over Thailand. The variations are also severe in the northeastern and central regions. The ionosphere variation results were obtained from the use of GPS data in a central part of Thailand to generate a local VTEC so-called Thai Ionosphere Map (TIM) using a Single Layer Model by Bernese software. The Global Ionosphere Map (GIM) was downloaded and compared with the TIM. The results from April 2010 are selected as an example because this month is the period of high ionosphere variability. A comparison of results between the TIM and GIM shows that a coefficient of correlation value is relatively high (r = 0.87).