Spatial and Temporal Distributions of Ionospheric Irregularities Derived from Regional and Global ROTI Maps

Abstract

Major advancements in the monitoring of both the occurrence and impacts of space weather can be made by evaluating the occurrence and distribution of ionospheric disturbances. Previous studies have shown that the fluctuations in total electron content (TEC) values estimated from Global Navigation Satellite System (GNSS) observations clearly exhibit the intensity levels of ionospheric irregularities, which vary continuously in both time and space. The duration and intensity of perturbations depend on the geographic location. They are also dependent on the physical activities of the Sun, the Earth’s magnetic activities, as well as the process of transferring energy from the Sun to the Earth. The aim of this study is to establish ionospheric irregularity maps using ROTI (rate of TEC index) values derived from conventional dual-frequency GNSS measurements (30-s interval). The research areas are located in Southeast Asia (15°S–25°N latitude and 95°E–115°E longitude), which is heavily affected by ionospheric scintillations, as well as in other regions around the globe. The regional ROTI map of Southeast Asia clearly indicates that ionospheric disturbances in this region are dominantly concentrated around the two equatorial ionization anomaly (EIA) crests, occurring mainly during the evening hours. Meanwhile, the global ROTI maps reveal the spatial and temporal distributions of ionospheric scintillations. Within the equatorial region, South America is the most vulnerable area (22.6% of total irregularities), followed by West Africa (8.2%), Southeast Asia (4.7%), East Africa (4.1%), the Pacific (3.8%), and South Asia (2.3%). The generated maps show that the scintillation occurrence is low in the mid-latitude areas during the last solar cycle. In the polar regions, ionospheric irregularities occur at any time of the day. To compare ionospheric disturbances between regions, the Earth is divided into ten sectors and their irregularity coefficients are calculated accordingly. The quantification of the degrees of disturbance reveals that about 58 times more ionospheric irregularities are observed in South America than in the southern mid-latitudes (least affected region). The irregularity coefficients in order from largest to smallest are as follows: South America, 3.49; the Arctic, 1.94; West Africa, 1.77; Southeast Asia, 1.27; South Asia, 1.24; the Antarctic, 1.10; East Africa, 0.89; the Pacific, 0.32; northern mid-latitudes, 0.15; southern mid-latitudes, 0.06.

Signatures of Equatorial Plasma Bubbles and Ionospheric Scintillations from Magnetometer and GNSS Observations in the Indian Longitudes during the Space Weather Events of Early September 2017

“…The analysis of the correlations between ROTI and S4/σ Φ using GPS data in low latitude Hong Kong, demonstrates the consistent relationships among the indices for the geomagnetically disturbed days, emphasizing the feasibility of ROTI observations to characterize the ionospheric scintillations [39]. Moreover, the advantage of ROTI over the standard S4 is that it is calculated based on recordings from the regular dual-frequency GNSS receivers, which are relatively more abundant than the specialized scintillation monitoring (S4 and σ Φ ) GNSS receivers across any region [92]. Moreover, in the African longitude sector, Okoh et al [20] showed that there was ~67% agreement in the occurrence of plasma bubbles (detected by an airglow imager) and significant ROTI fluctuations (captured by GNSS receivers within the field of view of the airglow imager).…”

Correlation of Rate of TEC Index and Spread F over European Ionosondes

“…Although many researchers have used GPS-based ROTI as a monitoring index for ionospheric irregularities over the equatorial and the polar ionosphere [6,41,42], over the mid-latitude ionosphere it has been less exploited. Several global-based ROTI mapping studies discussed ROTI features over the mid-latitudes [39,43]. Liu et al (2020) [44] demonstrated the statistics of the interhemispheric (E-F layer) coupling of ionospheric irregularities in terms of ROTI over mid-latitude ionosphere by using COSMIC radio occultation data and reported a maximum (~70%) occurrence of E and F region irregularities during June in the Northern Hemisphere.…”

A Retrospective of Global Navigation Satellite System Ionospheric Irregularities Monitoring Networks in Brazil

“…These scintillations monitors, as they provide the carrier pseudorange and phase besides the signal intensity, the TEC and the parameters rate of TEC (ROT) and ROT index (ROTI) (Pi et al 1997) can also be determined. Jesus et al (2020) and Nguyen et al (2022), among other authors, pointed out that ROTI and S 4 are well correlated. The main aim of this work is to provide the description of the GNSS-based scintillation monitoring networks at the Brazilian territory.…”