Regional ionospheric disturbance index over Malaysia using GPS data

Abstract

Ionospheric disturbances have significant impacts on a wide range of technological systems and services that rely on radio wave propagation through the ionosphere. These disturbances, caused by space weather events and natural phenomena, lead to disruptions in communication, navigation, and satellite-based operations. The determination of the ionospheric disturbance index is necessary for several important reasons, primarily related to mitigating the effects of ionospheric disruptions on communication, navigation, and other technological systems. The global ionospheric disturbance index provides a broad overview of space weather impacts, whereas the regional ionospheric disturbance index provides a more localized and context-specific assessment of ionospheric disturbances within a specific geographical area. Thus, it is necessary for Malaysia to investigate a regional ionospheric disturbance index that can detect ionospheric disturbances and classify their characteristics. The characteristics of the ionosphere can be monitored using Total Electron Content (TEC), a parameter that can be derived from Global Positioning System (GPS) data. The purpose of this research is to develop a regional ionospheric disturbance index over Malaysia using TEC data from GPS. Five GPS location over Malaysia were assessed, commencing with Selangor (3.06 ̊N, 101.54 ̊E), Pahang (4.18 ̊N, 102.04 ̊E), Sarawak (3.16 ̊N, 113.03 ̊E), Sabah (5.04 ̊N, 118.33 ̊E), and Langkawi (6.35 ̊N, 99.8 ̊E). To determine the level of disturbance, the log of TEC was calculated in relation to the running median of 15 quiet days to the observed days. The thresholds of the index were established to indicate the level of disturbance, with positive and negative signatures of ±1 representing a quiet state and ±2 indicating moderate disturbance. A moderate ionospheric storm is indicated by ±3, whereas ±4 represents a severe ionospheric storm. In addition, yearly solar activity analyses were performed for this study. To validate the regional disturbance index, two case studies were presented: a severe storm that occurred on April 23, 2012, and July 15, 2012, with minimum Dst of-120 nT and -139 nT, respectively. The threshold of the disturbance index indicates a severe storm on April 23, 2012, at 1900 UT, which was early morning of April 24, in the Malaysian region, while in another case, the result indicates no severe storm where the index ranges from ±1 to ±3. To determine the rate of occurrence of ionospheric disturbance, 12 years of data from 2003 to 2014 were analyzed, and the occurrence varied with solar activity. The percentage of positive severe storms (+4) from 2003 to 2014 was 2.49%, whereas the percentage of negative severe storms (-4) was 6.75%. In conclusion, this disturbance index will aid in quantifying geomagnetic storms and determining their impacts in Malaysia. The index will give valuable local insight into the time-varying properties of the regional ionosphere.