Siti Aminah Bahari

Ionospheric mapping function for total electron content (TEC) using global positioning system (GPS) data in Malaysia

The ionosphere layer is very important to the communication system. This research involves the determination of total electron content (TEC) in ionosphere based on height in order to determine the appropriate TEC value for Malaysia and for the equitorial region generally. The ionospheric model used is the single layer model based on the Bernese GPS 5.0 Software. The ionosphere TEC map of Malaysia is produced by using the single layer model which can be found in Bernese GPS 5.0 Software. Results show that the ionospheric variation especially the TEC values are different relative to the height studied. The appropriate TEC value for Malaysia is at the height 450 km and the maximun TEC value is at the height of 150 km. These variations play an important role in understanding the TEC nature in ionosphere and thus will simplify the studies about phenomenon happen in ionosphere especially in Malaysia.

Forecasting of ionospheric delay over Parit Raja Station, Johor, using statistical method

GPS is of great importance in precise positioning, however, the accuracy is marked by error sources, i.e. ionospheric effects. The signal information is delayed and the carrier phase experiences an advance due to the dispersive character of the ionosphere. The delay can be more than 100 meters in the worst case scenario and tends to increase with increasing solar activity. This error can be corrected by processing the GPS data if it is known. This paper describes the possibility of using statistical methods to forecast the ionospheric delay which shows repeatable patterns in time series. The statistical method used is the Holt-Winter method due to its ability to forecast time series with repeated trends and seasonal patterns. Based on the TEC data collected during a period of a month, ionospheric delay forecast is generated for the following month, which is then compared with the real data. Results show that there is a 6% error between the forecast and the real ionospheric delay and the error correction for the delay can be more than 90%.

Climatology of successive equatorial plasma bubbles observed by GPS ROTI over Malaysia

The occurrence rate of the equatorial plasma bubble (EPB) with season, solar activity, and geomagnetic conditions are investigated using long-term data sets of Malaysia Real-Time Kinematics Network (MyRTKnet) from 2008 to 2013. The rate of TEC (total electron content) change index (ROTI) in 5 min was derived from MyRTKnet data to detect the EPB with scale sizes around tens of kilometers. Then, the daily east-west cross sections of 2-D ROTI maps were used to examine the EPB features over 100°E–119°E longitudes. The EPBs tend to occur successively in one night along the observational coverage of MyRTKnet during equinoxes in high solar activity years. The perturbations in a form of wavelike structures along the observed longitudes might be responsible for the development of successive EPBs due to high growth rate of the Rayleigh-Taylor instability (RTI) process. On the contrary, the occurrence of successive EPBs is infrequent and the occurrence day of EPB remains active during equinoctial months in low solar activity years. The small growth rate of the RTI process during low solar activity years might require a strong seed perturbation to generate the EPB structure. The occurrence probability of the EPB was found to be similar during quiet and disturbed geomagnetic conditions. The results imply that the strong perturbations play an important role in the development of the EPB in low solar activity years. Nonetheless, the high growth rate of the RTI could cause the successive occurrence of the EPB in high solar activity years.

Development of a VLF receiver system for Sudden Ionospheric Disturbances (SID) detection

Sudden Ionospheric Disturbances (SID) are transient changes in the ionosphere caused by enhancement in X-ray and EUV fluxes during solar flare events. The SuperSID space weather monitor has been developed by Stanford University Solar Center to detect SID via VLF remote sensing. In this paper, a receiver system named as UKM-SuperSID has been developed to detect SID in the equatorial region. The system, which consists of loop antenna, preamplifier and a computer, is able to detect VLF signals with frequency of 19.8 kHz transmitted from North West Cape station (NWC), Australia. The data obtained showed repetitive diurnal variation. During the observation period from 11 December 2011 until 17 January 2012, M and C class solar flares events have been detected, with a class M1.5 flare observed as the largest detected flare. The results showed that the effectiveness of the UKM-SuperSID in detecting SID in the equatorial region thus enables it to be part of the global space weather sensor network.

Regional ionosphere maps over Malaysia during solar minimum

The regional ionosphere maps over Malaysia were studied during the minimum phase of solar cycle 23. Fifty-seven GPS RTK reference stations for the network covering the whole of Malaysia managed by JUPEM were used in this analysis. TEC is the measure of the number of electrons along the path from the satellite and is reported as TEC Units (1 TECU = 1×1016 electrons). The observations of oblique TEC can be obtained from the delays of GPS signals on the carrier frequencies of L1=1575.45 MHz and L2=1227.6 MHz under the assumption of infinitesimal single-layer ionospheric model. For this study, the data on 5th May 2007 and 23rd May 2007 was used. Results show that TEC maps derived from GPS RTK vary with all the geomagnetic activity indices.

Ionospheric TEC Response to the Partial Solar Eclipse Over the Malaysian Region

This paper presents the study of ionospheric behavior during the partial solar eclipse on 9th March 2016 over the Malaysian region. The partial solar eclipse event occurred during quiet solar and magnetic activities with maximum Kp index and geomagnetic Dst indices of 2 and −23 nT respectively. Ionospheric total electron content (TEC) was obtained from three GPS Ionospheric Scintillation and TEC Monitors, installed at the Langkawi National Observatory, Langkawi, LGKW (06°19′N, 99°51′E), Universiti Kebangsaan Malaysia, UKM (02°55′N, 101°46′E) and Universiti Malaysia Sarawak, UNIMAS (01°28′N, 110°25′E) stations. The selected stations have a coverage of between 68 and 87% over Peninsular Malaysia and Sarawak. This study compared the vertical TEC (VTEC) level during the partial solar eclipse period and the VTEC on the day before, the day after and the mean VTEC of quiet days. Results at these three stations show a clear occurrence of VTEC depletion in the range between 6 and 19% during the partial solar eclipse. The findings shows that depletion of VTEC during the partial solar eclipse was due to the reduction of ionization.

A Brief Review: Response of the Ionosphere to Solar Activity Over Malaysia

The variability of solar activity plays an important role in controlling the chemical reactions and physical processes in the ionosphere. To improve our understanding of the characteristics of the ionosphere over Malaysia, a study of the effects of solar activity on the ionosphere is required. This paper focuses on the variations in the ionosphere as a result of solar activity. Variations in the ionosphere are divided into (1) critical frequency profile, (2) maximum usable frequency and minimum frequency, (3) variations of TEC to solar activity, (4) ionospheric delay, (5) scintillation and (6) the equatorial plasma bubble. The paper also provide new information towards a comprehensive explanation of the basis processes involved in improving the prediction capability of the ionospheric model and its related applications.

The observation of equatorial plasma bubble using all sky imager and GPS TEC measurement

In this study, the two-dimensional horizontal structure of EPB was observed using GPS total electron content (TEC) measurement in South East Asia region. Rate of TEC index (ROTI) is calculated from GPS TEC measurement and plotted onto two-dimensional map in geographic coordinate. Depletion of The OI 630.0 nm emission is completely coincided with ROTI enhancement region from GPS TEC measurement. Therefore, the observation using GPS TEC measurement is able to provide spatial and temporal properties of EPB in SEA region.

Diurnal, seasonal and geographic location effects on TEC variation over Malaysia

The ionosphere is a layer in the Earths atmosphere where free electrons exist in sufficient numbers to affect the propagation of electromagnetic waves especially the Global Positioning System (GPS) signals. The study of the Total Electron Content (TEC) variation in the ionosphere and structures is important to ensure the reliability of radio communication systems and accuracy of space weather forecasting. This paper presents the diurnal, seasonal and geographic location effects on TEC variation over Malaysia using Precise Point Positioning (PPP) technique. Since the GPS signals are broadcasted in two widely spread L-band frequency channels namely L1 and L2 consisting of code and phase, it is possible to determine the TEC by employing differencing techniques. This study is conducted using GPS data obtained from 50 stations all over Malaysia. The results of the diurnal analysis show that the mean TEC reaches its maximum during post local noon and its minimum during early morning. The results of the seasonal analysis show that the mean TEC during the equinox months is 35 TECU higher than during the solstice which is only 25 TECU. The seasonal effects on TEC variation is due to the location of the Sun, the movement of plasma around the magnetic equator, and the location of Malaysia. The latitudinal profile of TEC during equinox shows that the location of TEC maximum during the daytime is at southern Malaysia, but changes to the north during nighttime. During solstice, the location of TEC maximum during both day and nighttime is at northern Malaysia, while TEC maximum during early morning is located at southern Malaysia. These results can be used as a reference for ionospheric characterization over Malaysia.

Forecasting of ionospheric delay using the Holt-Winters method

Radio waves such as Global Positioning System (GPS) signals propagate through the ionosphere and experience several effects, one of which is an additional group delay that is approximately proportional to the total number of free electrons encountered by the wave. Accurate correction, prediction and assessment for ionospheric error are needed for accurate measurement. In forecasting ionospheric delay, the statistical method is still considered a new approach. One of the statistical methods is known as the Holt-Winters method, which is based on time series with repeated trends and seasonal patterns. Based on the characteristics of the ionospheric delay that has repeated trends and seasonal patterns, the Holt-Winters method is suited to forecast ionospheric delay. In this research, a forecasting of ionospheric delay was carried out over three chosen stations, namely Parit Raja (1° N, 103° E) in Malaysia, Seattle (47° N, 122° E) and New York (40° N, 73° E) which are both in the United States of America (USA). GPS observation data from August to October in 2005 from the Parit Raja station and from May to July in 2008 from the Seattle and New York stations were used. Results over Parit Raja show that the error between the forecast and the real ionospheric delay value is about 6% for the three months of analysis. In contrast, the results obtained over Seattle and New York show that the percentage of the average error is in the range of 2 % to 6 %. The Holt-Winters method is believed to show a different value of accuracy based on the variation of TEC which is dependent on diurnal and seasonal changes, solar cycle, geographical location, and geomagnetic field. The two stations in the USA were facing seasonal transition at that time; in May and June, it was spring time, while in the middle of July, it was the beginning of summer. Therefore, high variations of TEC value occurred because of the transition of season. The Seattle and New York stations are located at the mid-latitude zone. On the other hand, the Parit Raja station is located in the low latitude zone. The results gave a small error for all three stations; therefore, it can be concluded that the Holt-Winters method is effective and can be used in forecasting ionospheric delay for different regions.