Occurrence Of Equatorial Plasma Bubbles Research Articles

A machine learning approach for estimating the drift velocities of equatorial plasma bubbles based on All-Sky Imager and GNSS observations

Equatorial Plasma Bubbles (EPBs) are zones characterized by fluctuations in plasma densities which form in the low-latitude ionosphere primarily during the post-sunset. They subject radio signals to amplitude and phase variabilities, affecting the functioning of technological systems that utilize the Global Navigation Satellite Systems (GNSS) signals for navigation. Thus, understanding EPB occurrence patterns and morphological features is vital for mitigating their effects. In this work, we employed two GNSS receivers and an All-Sky Imager (ASI) to conduct simultaneous observations on the morphology of EPBs over Brazil. The main objectives of the study were (1) to develop a Random Forest (RF) machine-learning model to estimate and predict the zonal drift velocities of EPBs, and (2) to compare the model predictions with actual EPB drifts inferred from the two instruments, as well as zonal neutral wind speeds obtained from the Horizontal Wind Model (HWM-14). In the model development, we utilized reliable EPB drift measurements made during geomagnetically quiet days between 2013 and 2017 in Brazil. The model predicted the velocities based on parameters including the day of the year, universal time, critical frequency of the F2 layer (foF2), solar and interplanetary indices. The correlation coefficients of 0.98 and 0.96 and RMSE values of 10.61 m/s and 10.06 m/s were obtained upon training and validation correspondingly. We evaluated the accuracy of the model in predicting EPB drifts on two geomagnetically quiet nights where an average correlation coefficient of 0.89 and an RMSE of 15.74 m/s were obtained. The predicted drifts, the zonal neutral wind velocities, and the GNSS and ASI velocity measurements were put into context for validation purposes. Overall, the velocities were comparable and ranged between ∼100 m/s and ∼30 m/s from the hours of 00 UT to 05 UT. The results confirmed the accuracy and applicability of the model, revealing the ionosphere-thermosphere coupling influence on the nocturnal propagation of EPBs under the full activation of the F region dynamo.

Seasonal–Longitudinal Variability of Equatorial Plasma Bubbles Observed by FormoSat-7/Constellation Observing System for Meteorology Ionosphere and Climate II and Relevant to the Rayleigh–Taylor Instability

The FormoSat-7/Constellation Observing System for Meteorology, Ionosphere, and Climate II (FS7/COSMIC2) program has acquired over three hundred thousand equatorial plasma bubble (EPB) observations from 2019 to 2023 in the equatorial and near low-latitude regions. The huge FS7/COSMIC2 database offers an opportunity to perform statistical inspections of the proposed hypothesis on seasonal versus longitudinal variability of EPB occurrence rates relevant to the Rayleigh–Taylor (R-T) instability. The detected EPBs are distributed along the magnetic equator with a half width of ~20° in geomagnetic latitude. The obtained EPB occurrence rates in local time (LT) rose rapidly after sunsets, and could be deconstructed into two overlapped Gaussian distributions resembling a major peak around 23:00 LT and a minor peak around 20:20 LT. The two groups of Gaussian-distributed EPBs in LT were classified as first- and second-type EPBs, which could be caused by different mechanisms such as sporadic E (Es) instabilities and pre-reversal enhancement (PRE) fields. The obtained seasonal–longitudinal distributions of both types of EPBs presented two diffused traces of high occurrence rates, which happened near the days and longitudes when and where the angle between the two lines of magnetic declination and solar terminator at the magnetic equator was equal to zero. Finally, we analyzed the climatological and seasonal–longitudinal variability of EPB occurrences and compared the results with the physical R-T instability model controlled by Es instabilities and/or PRE fields.

Occurrence of Equatorial Plasma Bubbles (EPBs) Over the Indian Region on 15 January 2022 and Their Plausible Connection to the Tonga Volcano Eruption

AbstractThis study focuses on the causes for the generation of equatorial plasma bubbles (EPBs) over the Indian subcontinent and their correlation with atmospheric‐ionospheric disturbances resulting from the eruption of the Tonga volcano on 15 January 2022. Concurrent ionosonde observations obtained from Tirunelveli (8.67°N, 77.81°E) and Prayagraj (25.41°N, 81.93°E) show the presence of spread‐F traces in ionograms. Notably, the EPBs are also accompanied by plasma blobs (PBs), with their pronounced occurrence during midnight at Prayagraj and Tirunelveli. Analysis of in situ electron density observations obtained from the Swarm B and C satellites reveals substantial plasma density depletions associated with EPBs. An intriguing observation is the intensification of Pre‐Reversal Enhancement (PRE) immediately preceding the onset of spread‐F at Tirunelveli due to enhanced eastward F region zonal winds by Tonga Volcano, as seen in the satellite observations. Furthermore, the isofrequency analysis from Tirunelveli shows the presence of gravity wave‐like oscillations in the equatorial F‐region over India. The investigation of Total Electron Content (TEC) obtained from a Pseudo Random Number (PRN)‐14 over Indian longitudes suggests the presence of two dominant modes of Traveling Ionospheric Disturbances (TIDs) with speeds ∼452 m/s and ∼406 m/s having periods in the range of ∼65–75 min. These observations reaffirm that volcano triggered atmospheric/ionospheric disturbances can propagate long distances for several hours and can provide necessary seeding conditions for the generation of EPBs.

Quasi 6‐Day Planetary Wave Oscillations in Equatorial Plasma Irregularities

AbstractThe influence of atmospheric planetary waves on the occurrence of irregularities in the low latitude ionosphere is investigated using Whole Atmosphere Community Climate Model with thermosphere‐ionosphere eXtension (WACCM‐X) simulations and Global Observations of the Limb and Disk (GOLD) observations. GOLD observations of equatorial plasma bubbles (EPBs) exhibit a ∼6–8 day periodicity during January–February 2021. Analysis of WACCM‐X simulations, which are constrained to reproduce realistic weather variability in the lower atmosphere, reveals that this coincides with an amplification of the westward propagating wavenumber‐1 quasi‐six day wave (Q6DW) in the mesosphere and lower thermosphere (MLT). The WACCM‐X simulated Rayleigh‐Taylor (R‐T) instability growth rate, considered as a proxy of EPB occurrence, is found to exhibit a ∼6‐day periodicity that is coincident with the enhanced Q6DW in the MLT. Additional WACCM‐X simulations performed with fixed solar and geomagnetic activity demonstrate that the ∼6‐day periodicity in the R‐T instability growth rate is related to the forcing from the lower atmosphere. The simulations suggest that the Q6DW influences the day‐to‐day formation of EPBs through interaction with the migrating semidiurnal tide. This leads to periodic oscillations in the zonal winds, resulting in periodic variability in the strength of the prereversal enhancement, which influences the R‐T instability growth rate and EPBs. The results demonstrate that atmospheric planetary waves, and their interaction with atmospheric tides, can have a significant impact on the day‐to‐day variability of EPBs.

Identifying the Onset Location of Equatorial Plasma Bubbles (EPBs) and Its Relationship With the Background Ionospheric Conditions

AbstractUsing radars and C/NOFS satellite observations we studied the spatio‐temporal evolution of Equatorial Plasma Bubbles (EPBs) and estimated its onset location across a wide longitudinal sector over Indian and Southeast Asian longitudes. The vertical E × B drift velocity measurements obtained from the Ion Velocity Meter (IVM) on board the C/NOFS satellite and collocated ionosonde observations were used to examine the background ionospheric conditions. Our study shows that the periodic EPBs were present in those longitudes where periodic wave structure in the E × B drift and elevated F layer were observed. In this case study, the comprehensive analysis using the observations from radars and satellite data provides a better understanding on the longitudinal preference of the EPB occurrence and its responsible background mechanisms. This understanding of the onset location and background conditions of EPBs over a large longitudinal area for an extended period can contribute to the development of accurate EPB forecasting models, which are essential to mitigate the detrimental effects of EPBs on communication and navigation systems.

Equatorial Plasma Bubbles Characteristics Studies using IRNSS Data around Bangalore

TEC analysis stands as a cornerstone in navigation, enabling the examination of sudden shifts in Total Electron Content (TEC). Equatorial Plasma Bubbles (EPBs) are discerned through TEC analysis, which proves superior to alternative approaches. This method furnishes insights into EPB occurrences, offering valuable data on their daily and seasonal fluctuations within the ionosphere. Analysis of TEC data from January 2015 to 2022, derived from IRNSS observations in Bangalore, reveals patterns in EPB occurrence correlated with the sunspot cycle and solar flux variations. This alignment, observed during a phase of low solar activity, underscores the reliability of TEC analysis in capturing ionospheric dynamics.

Equatorial Plasma Bubbles: Zonal Thermosphere Wind Influence

There are a number of the theoretical studies pointing to the key role of the zonal thermosphere winds in the equatorial plasma bubble (EPB) generation and evolution. However, there are insufficient observational data to confirm the relationship between these phenomena. To study this relationship, the detailed comparative and correlation analysis of the LT-variations of the EPB occurrence probability and the zonal thermosphere wind velocity was carried out. The data from the EPB observations recorded aboard the ISS-b satellite (~972–1220 km) during the solstice and equinox periods were used. The data from the zonal thermosphere wind velocity observations obtained aboard the CHAMP satellite (~380–450 km) were also used. It was found that these characteristics are similar, when they are compared, and have very strong correlation (R 0.9) in summer, strong correlation (R 0.8) in winter and (R 0.79) at equinox. It was found that in all seasons the delay in the development of the EPB occurrence probability maxima with respect to the maxima of the west wind velocity is 1–3 h. It is in good agreement with the estimation of the time of the seeding perturbation development and the EPB rise to the topside ionosphere altitudes. The results can be considered a new confirmation of the theoretical conclusion (Kudeki model) about the key influence of the zonal west thermosphere winds on the equatorial plasma bubble generation.

Simultaneous observations of equatorial plasma bubbles with an all-sky airglow imager and a HF Doppler sounding system in Taiwan

High-Frequency Doppler (HFD) sounders at low-latitudes often detect characteristic oblique spreading Doppler traces in the spectrogram, known as Oblique Spread Structure (OSS). OSS has been expected to be generated by the dispersion of radio wave reflection due to equatorial plasma bubbles (EPBs). However, it has not yet been confirmed whether OSS is surely a manifestation of EPB by conducting simultaneous observations of EPB and OSS with different observational techniques. Additionally, it remains unclear what kinds of properties of EPB are reflected in the fine structure of OSS. In this study, we investigated three cases of OSSs and EPBs simultaneously observed by a HFD sounding system and an all-sky airglow imager in Taiwan. For the three cases presented here, the timing of OSS occurrence in the HFD data well coincided with that of the EPB appearance in the airglow data. The frequency shift of OSS is quantitatively explained assuming a radio wave reflection at 250–300 km altitudes. These results strongly indicate that OSS is formed by electron density variations at F-region altitudes accompanying EPB; thus, OSS is a manifestation of EPB in the HFD observations. Furthermore, it was suggested that the fine structure of OSS reflected the branching structure of EPB when the multiple branches of EPB reached the intermediate reflection point of the HFD observation. The detection of EPB occurrence and its fine structure using HFD observation enables monitoring of EPB regardless of weather conditions, which will contribute to monitoring the space weather impact of EPBs, for example, on GNSS navigation, in a wide area.Graphical

Investigation of the possible dependence of equatorial plasma bubble with travelling ionospheric disturbances using airglow-imager at Abuja

Airglow images obtained with the aid of a ground-based Airglow Imager (AGI) located at Abuja, Nigeria (Geographic: 7.39°E, 8.99°N; Dip latitude: −1.60°) have been used to study the possible relationship between the occurrence of Atmospheric Gravity Waves (AGWs) and Equatorial Plasma Bubbles (EPBs) to investigate the role AGW plays in the occurrence of EPB. Airglow images covering over two and half years (nighttime only), from June 2015 to August 2018 were used. Three filters of the airglow imager were used in this study, taking observation over 652 days (nights). Results show that AGW occurrence is random with no regular trend and very rare at the station compared with EPB. EPB is found to occur more frequently with local time and seasonal dependence. Peak occurrences of EPB are observed during the equinoctial months. Although concurrent occurrences of the two phenomena are very infrequent, results further show that whenever both phenomena occur simultaneously, the duration of occurrences tends to suggest there exists a relationship between them. The concurrent occurrence of the two phenomena is observed more during post-sunset than post-midnight hours whenever it happens. Although EPB occurs independently of AGW, the results show that on nights where we have concurrent occurrences, EPB occurrence tends to take place earlier than days of EPB occurrence without AGW. We, therefore, conclude from the results obtained in this study that, AGW is not the only factor that contributes to the occurrences of EPB at the station since the AGW observed might not have consistently propagated to the bottomside of the F layer due to its dissipation. However, whenever it occurs, AGW tends to influence the conditions that trigger the occurrence of EPB.

Equatorial plasma bubble intensities across longitudinal sectors of the globe using GNSS observations

We present the first investigation of Equatorial Plasma Bubble (EPB) intensities across longitudinal sectors of the globe using observations from global navigation satellite system (GNSS) receivers. GNSS data from a total of 93 receiver stations located within ±20 degrees of the geomagnetic equator across the globe were used. The data covered periods of years 2014 and 2019 which are respectively years of high and low solar activity in solar cycle 24. We define a parameter known as the Standard deviation of Residual TEC (SRT) to characterize the EPB intensities. The EPB occurrence was defined by day-night differences of the rate of change of TEC index (ROTI). We observed a high correlation (r ∼ 0.80) between the magnitudes of the SRT and ROTI during the EPB occurrence, but the correlation is low (r ∼ 0.37) during non occurrence of EPB. The EPB intensities are greater during seasons with high occurrence rates. The EPB intensities and occurrence rates are also greater during the high solar activity. We found that the post-sunset intensities are greatest in the Atlantic region, followed by the African region, then the American, Australian, Asian, and Pacific regions in that order. The post-midnight intensities are greatest in the African region, followed by the Atlantic, American, Australian, Asian, and Pacific regions in that order.

Global Maps of Equatorial Plasma Bubbles Depletions Based on FORMOSAT‐7/COSMIC‐2 Ion Velocity Meter Plasma Density Observations

AbstractFORMOSAT‐7/COSMIC‐2 is the largest equatorial multi‐satellite constellation of six full‐size satellites to study the equatorial ionosphere. Each satellite is equipped by an ion velocity meter (IVM) instrument to provide high rate in situ plasma density observations along the low‐inclined satellite orbits at ∼530–550 km altitude. Six satellites provide an unprecedented dense coverage of the entire equatorial region around the globe and allow reliable detection of equatorial plasma bubbles (EPBs) and plasma density irregularities at different local times/longitudinal sectors simultaneously. We present a method for detection of EPBs in FORMOSAT‐7/COSMIC‐2 in situ plasma density data and construction of the global maps of EPB geolocations. The results in the form of time series and IVM‐based global Bubble Maps have a great potential for both near real‐time monitoring of space weather conditions and long‐term statistical analysis of EPB occurrence in regional or global scales. We present first FORMOSAT‐7/COSMIC‐2 derived climatological characteristics of the post‐sunset and post‐midnight EPBs occurrence probability and their apex altitudes during a period of low solar activity. Also, we demonstrate the good performance of the FORMOSAT‐7/COSMIC‐2 IVM‐based Bubble Maps when compared to optical images and ground‐based ionosonde observations.

On the Upwelling of the F Layer Base and Prediction of Equatorial Plasma Bubble

AbstractPrediction of equatorial plasma bubbles (EPBs) continues to be a challenge for the scientific community. We present a novel data analysis approach, employed on the collocated radar and ionosonde observations from Gadanki, providing new experimental results for characterizing the overhead upwelling of the bottomside F layer and linking it to EPB formation. Using this new approach we propose a new parameter based on ionosonde observations to predict overhead occurrence of fresh EPB. Employing this new parameter on a fairly large data set of a single ionosonde station we could successfully predict overhead occurrence of all the fresh EPBs about an hour in advance. We also propose how this technique can be used for EPB prediction in a broader longitude zone.

Equatorial Plasma Bubble Occurrence Probability with Respect to Month of Year

Equatorial Plasma Bubble Occurrence Probability with Respect to Month of Year

GOLD Mission's Observation About the Geomagnetic Storm Effects on the Nighttime Equatorial Ionization Anomaly (EIA) and Equatorial Plasma Bubbles (EPB) During a Solar Minimum Equinox

AbstractThe nighttime ionospheric response to a geomagnetic storm that occurred on 23–29 September 2020 is investigated over the South American, Atlantic, and West African longitude sectors using NASA's Global‐scale Observations of the Limb and Disk measurements. On 27 September the solar wind conditions were favorable for prompt penetration electric fields to influence the equatorial ionosphere over extended longitudes. The equatorial ionization anomaly (EIA) crests were shifted 8°–10° poleward compared to the quiet time monthly mean across ∼65°–35°W during the main phase. Ionosonde hmF2 (peak electron density height) measurements from Fortaleza (GG: 3.9°S and 38.4°W) indicated a stronger prereversal enhancement this evening than other nights. As a result, equatorial plasma bubbles (EPB) occurred at these longitudes on this evening. This is the first simultaneous investigation of EIA morphology and EPB occurrence rate over an extended longitude range from geostationary orbit during a geomagnetic storm.

Equatorial Plasma Bubble Occurrence Probability with Respect to Month of Year

In this paper, the variations of the equatorial plasma bubble occurrence probability with respectto month of year are investigated. For this purpose, the data obtained on board the ISS-b satellite (~972–1220 km) in the mid−latitude region ±(25°–55°) DIPLAT of the both hemispheres for a year and a half ofthe observations (August 1978–December 1979) were used. The comparative analysis of the studied characteristicwith the monthly variations of the meridional wind velocity was carried out. For this purpose, thewind velocity data calculated from the Horizontal Wind Model (HWM14) were used. 1. It was revealed thatthe maximal plasma bubble occurrence probability values take place each time during the local winter: December–February in the Northern Hemisphere (~19%) and June–August in the Southern Hemisphere (~29%).The minimal values take place in the local summer: June–August in the Northern Hemisphere (~3%) andDecember–February in the Southern Hemisphere (~4%). As a result, there is asymmetric plasma bubbledevelopment relative to the geomagnetic equator during the solstices. 2. It was revealed that the relativeequality of the plasma bubble occurrence probability values takes place in the histograms of the differenthemispheres during the equinoxes. As a result, there is almost symmetrical plasma bubble spreading relativeto the geomagnetic equator during these periods. 3. It was revealed that the maximal plasma bubbleoccurrence probability values take place in each hemisphere during the local winter, when the meridionalwinds developing there favors the downward bubble plasma and, accordingly, the bubble spreading alongthe flux tube. The minimal plasma bubble occurrence probability values take place in each uplift hemisphereduring the local summer season, when the meridional wind favors the bubble plasma and slows thebubble spreading.

Airglow Observation and Statistical Analysis of Plasma Bubbles over China

Airglow observation is a very effective method to investigate plasma bubbles, and can obtain their horizontal structure. In this study, the image processing method was used to process airglow data, including image enhancement, azimuth correction, and image projection, and the clear image products of equatorial plasma bubbles (EPBs) were obtained. Based on the optical data of the airglow imager in Hainan, we investigated the main optical features of EPBs, and statistically analyzed the occurrence of EPBs from September 2014 to August 2015. The observation results show that EPB exhibits plume-shaped structures, usually tilting westward, and EPB extends to a long distance along the geomagnetic field lines. It is found that the west wall of EPB is relatively stable, while there are some bifurcations on the east wall of EPB, and the bifurcation of EPB becomes more pronounced with time. Moreover, the spatial scale of EPB gradually increases with time, which is about several hundred kilometers, and the drift velocity of EPB is in the range of 40–130 m/s (+/−20 m/s). The statistical results show that EPBs mainly occur in the months of September to November and February to April, with a higher occurrence rate. In terms of seasonal occurrence, EPBs tend to appear more frequently in spring and autumn, and the occurrence rate of EPBs is relatively low in winter and summer.

Equatorial Plasma Bubbles Identification with Single Frequency GNSS Receiver Data

Ionosphere is the highest contributor of positional error in Global Navigation Satellite System (GNSS) owing to the trans-ionospheric signal delay, distortion and possible outage. Equatorial and Low latitudinal ionosphere experiences frequent perturbations in plasma density most of which is due to the presence of Equatorial Plasma Bubbles (EPBs). In order to improve positional and navigational precision of GNSS signals, EPBs must be identified and corrected. EPBs begin to manifest post-sunset and continue to thrive past midnight. This paper proposes a Rate of TEC Index (ROTI) based EPB identifier using single frequency GNSS receiver data. GNSS data has been collected from the archives of Scripps Orbit and Permanent Array Center (SOPAC). The raw data has been downloaded from the global continuous network station, IISC, located at Bangalore (13.0219°N, 77.5671°E) in Receiver Independent Exchange (RINEX) format. Analysis of EPB occurrence has been carried out for six consecutive years in the second half of the 24th solar cycle (2014-2019). The results show a clear surge in the number of EPBs identified in the course of equinoxes.

Field-aligned scale length of depleted structures associated with post-sunset equatorial plasma bubbles

In this study we make use of the Swarm counter-rotation constellation for estimating the typical scale length of the post-sunset equatorial plasma bubbles (EPBs) along fluxtubes. The close approaches between Swarm spacecraft near the equator occurred in September and October 2021, covering the magnetic local time from 19:00 to 23:00, which is favorable for the occurrence of EPBs. It is the first time to show the quasi-simultaneously samplings by Swarm A/C and B of the same fluxtube but at different altitude. The observations frequently reveal plasma density depletions only at one spacecraft altitude, confirming that EPBs extend only over finite parts of the fluxtube. Based on a statistical analysis of double and single EPB detections on the same fluxtube, our results imply the typical field-aligned scale length of the depletion structures associated with EPBs of the order of 550 km. Our detections are from the lower part of the depleted fluxtubes, and they coincide well with the latitudes of the equatorial ionization anomaly. In the upper part of the fluxtube near the magnetic equator, our estimation technique does not work well because of too large field-aligned spacecraft separation of the Swarm satellites.

Equatorial Plasma Bubbles: A Review

The equatorial plasma bubble (EPB) phenomenon is an important component of space weather as the ionospheric irregularities that develop within EPBs can have major detrimental effects on the operation of satellite-based communication and navigation systems. Although the name suggests that EPBs occur in the equatorial ionosphere, the nature of the plasma instability that gives rise to EPBs is such that the bubbles may extend over a large part of the global ionosphere between geomagnetic latitudes of approximately ±15°. The scientific challenge continues to be to understand the day-to-day variability in the occurrence and characteristics of EPBs, such as their latitudinal extent and the development of irregularities within EPBs. In this paper, basic theoretical aspects of the plasma processes involved in the generation of EPBs, associated ionospheric irregularities, and observations of their characteristics using different techniques will be reviewed. Special focus will be given to observations of scintillations produced by the scattering of VHF and higher frequency radio waves while they propagate through ionospheric irregularities associated with EPBs, as these observations have revealed new information about the non-linear development of Rayleigh–Taylor instability in equatorial ionospheric plasma, which is the genesis of EPBs.

Variability of Equatorial Ionospheric Bubbles over Planetary Scale: Assessment of Terrestrial Drivers

Nighttime F-region field-aligned irregularities (FAIs) associated with equatorial plasma bubbles (EPBs) are impacted by terrestrial factors, such as solar irradiance and geomagnetic activity. This paper examines the impact of the planetary-scale periodic variability of terrestrial processes on EPB activity. Continual observations of the Equatorial Atmosphere Radar (EAR) have been utilized to derive the intra-seasonal variability of nighttime F-region FAIs in the context of the terrestrial factors mentioned above. A periodicity analysis using wavelet and Lomb–Scargle (LS) spectral analysis indicated significant amplitudes of the long-period planetary-scale variability in the F-region FAI signal-to-noise ratio (SNR), 10.7 cm flux, and geomagnetic indices, as well as a shorter period of variability. Interestingly, a careful inspection of the time series indicated the planetary-scale variability of F-region FAIs to be reasonably out of phase with the periodic geomagnetic variability. EPB occurrence and the FAI signal-to-noise ratio presented a systematic decrease with an increase in the level of geomagnetic activity. Non-transient quiet-time geomagnetic activity has been found to suppress both the occurrence as well as the strength of F-region FAIs. The impacts of planetary-scale geomagnetic activity appear to be non-identical in the summer and equinoctial EPBs. The results highlight the importance of periodic terrestrial processes in driving the planetary-scale variability of EPBs.