Plasma Bubble Occurrence Research Articles

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.

Investigation of the Physical Mechanisms of the Formation and Evolution of Equatorial Plasma Bubbles During a Moderate Storm on 17 September 2021

AbstractWe investigate in detail the occurrence and evolution of ionospheric equatorial plasma bubbles (EPBs) during a moderate storm on 17 September 2021, using Global‐scale Observations of the Limb and Disk (GOLD) observations and Whole Atmosphere Community Climate Model‐eXtended (WACCM‐X) simulations. GOLD observations show that there were no EPBs on 16 September before the storm but EPBs occurred after the storm commencement on 17 September. The EPBs extended to ∼30° magnetic latitude. A diagnostic analysis of WACCM‐X simulations reveals that the rapid enhancement of prompt penetration electric fields (PPEFs) after the sudden storm commencement is the main reason that triggered the occurrence of the EPBs. Further quantitative analysis shows that vertical plasma drifts, which are enhanced by the PPEF, played a dominant role in strengthening the Rayleigh‐Taylor instability, leading to the occurrence of the EPBs and the large latitudinal extension of the EPBs to ∼30° magnetic latitude during the night of 17 September.

Magnetic Storm Effects on the Occurrence and Characteristics of Plasma Bubbles

AbstractThe Communications/Navigation Outages Forecast System satellite mission was designed to investigate the ionospheric conditions that lead to the formation of irregularities. Here, we have studied the effect of magnetic storms on the formation and evolution of plasma bubbles during the satellite's lifetime (2008–2015). During this period encompassing solar minimum and maximum conditions, many magnetic storms of varying intensity developed, producing a unique and rich data set of 248 storms (14 intense, 69 moderate, and 165 weak) that occurred during the same timeframe to examine the role of external magnetospheric drivers in the production and dynamics of equatorial plasma bubbles. We have used the Planar Langmuir Probe and Ion Velocity Meter instruments to elucidate the role of magnetic storm intensity on the bubble's depth, internal speed, width, occurrence, and lifetime. The pre‐reversal enhancement (PRE) tends to increase during the main phase and when BZ is southward. New bubbles occur during large excursions of the PRE value. The bubble lifetime extends and remains active during the main and part of the recovery phase. The plasma velocity within the bubbles increases and typically becomes over 100 m/s during significant PRE and BZ negative times. The depth of bubbles reaches values close to 100% during intense storms. In general, the intensity of the storms seems to control and augment the plasma bubbles' depth, width, and internal velocity.

Equinoctial asymmetry of plasma bubble occurrence and electric field at evening: GPS and ionosonde measurements in Southeast Asia

We have investigated equinoctial asymmetry of scintillation occurrence and zonal irregularity drift velocity observed with closely-spaced GPS receivers at Kototabang (0.20°S, 100.32°E; geomagnetic latitude 10.6°S), Indonesia during a period from 2003 to 2016, and found that the scintillation occurrence rate is higher in Mar. equinox than in Sep. equinox, and that the eastward drift velocity at post-sunset is higher in Mar. equinox than in Sep. equinox. This result is consistent with previous work done by Otsuka et al. (2006), who have analyzed scintillation and zonal drift velocity data obtained at Kototabang in 2003–2004, and suggests that the eastward drift velocity corresponding to the downward electric field at post-sunset may be related to the pre-reversal enhancement of eastward electric field, which could play an important role in generating plasma bubble. In this study, we have investigated vertical drift velocity by analyzing the ionosonde data obtained near magnetic equator (Chumphon, Bac Lieu, and Cebu) during a period from 2003 to 2016, and found that the upward drift velocity at post-sunset is larger in Mar. equinox than Sep. equinox. We also find that solar activity dependence of the zonal and vertical drift velocities is more clearly seen in Mar. equinox than in Sep. equinox. In order to consider the mechanism causing the equinoctial asymmetry of the drift velocities, foF2 obtained by the ionosondes is also analyzed. We find that foF2 also depends on solar activity more clearly in Mar. equinox than in Sep. equinox, and that foF2 during high solar activity conditions is higher in Mar. equinox than in Sep. equinox. These results suggest that in Mar. equinox, due to high electron density, intense electric field could be generated through the F-region dynamo so that plasma bubble likely occurs.

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.

First Detection of Midlatitude Plasma Bubble by SuperDARN During a Geomagnetic Storm on May 27 and 28, 2017

AbstractWe used the global navigation satellite system‐total electron content (TEC) and Super Dual Auroral Radar Network (SuperDARN) radar to elucidate the characteristics of the plasma bubble extending to midlatitudes over North America during a geomagnetic storm on 27 and 28 May 2017. To identify plasma bubbles, we analyzed the rate of the TEC index (ROTI), which is a good indicator of the occurrence of plasma bubbles. The enhanced ROTI region expanded up to 50°N (geomagnetic latitude), and the upper limit of this region coincided with the equatorward wall of the midlatitude trough. Two‐dimensional ROTI maps show that the enhanced midlatitude ROTI region moved westward at a bulk speed of approximately 310 m/s. The Fort Hays East SuperDARN radar also detected the radar echo, showing the existence of plasma density irregularities at ∼10‐m scales within the midlatitude plasma bubble. The radar echo had a westward velocity of ∼300 m/s, which is almost consistent with the westward motion of the enhanced midlatitude ROTI region. We deduced that the westward propagation of the plasma bubble could be caused by a poleward sub‐auroral polarization stream electric field. The observed radar echo overlapping with the enhanced ROTI region had a narrower spectral width (<50 m/s) than that of the auroral activity. This feature resembled that of the type 1 echo, although the Doppler velocity was smaller than the ion acoustic speed at the F‐region height. This is the first case in which plasma density irregularities within plasma bubbles were captured by the SuperDARN radar.

Equatorial Plasma Bubble Occurrence Probability with Respect to Month of Year

Equatorial Plasma Bubble Occurrence Probability with Respect to Month of Year

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.

Dependence of Ionospheric Responses on Solar Wind Dynamic Pressure During Geomagnetic Storms Using Global Long‐Term GNSS‐TEC Data

AbstractTo elucidate the effect of solar wind dynamic pressure on the activities of ionospheric plasma irregularities in both high‐latitude and equatorial regions, we analyzed the long‐term global navigation satellite system (GNSS) total electron content (TEC) data from 2000 to 2018 and performed a superposed epoch analysis of the GNSS rate of the TEC index (ROTI), solar wind, interplanetary magnetic field (IMF), and geomagnetic index. We found that during the main phase of geomagnetic storms, the activities of ionospheric plasma irregularities were considerably enhanced in both high‐latitude and equatorial regions under high‐pressure conditions, and the equatorward edge of the auroral oval moved to lower latitudes. The poleward edge of the enhanced low‐latitude ROTI region (occurrence region of the plasma bubbles) in the evening sector extended to higher latitudes under high‐pressure conditions. During the recovery phase of geomagnetic storms, the plasma bubble occurrence in the dusk sector was suppressed under high‐pressure conditions. Our results suggest that the high‐latitude convection electric field and the penetration and disturbance dynamo electric fields at low latitudes become stronger during geomagnetic storms when the solar wind dynamic pressure is enhanced. This is because the conversion from solar wind energy to electromagnetic energy in the magnetosphere is enhanced by the formation of a high plasma pressure area in the high‐latitude cusp and mantle region. Therefore, not only the southward IMF but also solar wind dynamic pressure are important factors for varying global ionospheric responses during geomagnetic storms.

Ionospheric Turbulence: A Challenge for GPS Loss of Lock Understanding

AbstractIonospheric irregularities may affect electromagnetic signals propagating through the ionosphere and consequently contribute to the malfunctioning of the Global Navigation Satellite Systems hindering their accuracy and reliability. In this study, we use data recorded on board two of the three satellites of the Swarm constellation (namely, Swarm A and Swarm B) from 15 July 2014 to 31 December 2021 to assess the possible dependence of the Global Positioning System (GPS) signals loss of lock on the presence of a specific kind of ionospheric irregularities. To accomplish this task we study the scaling features of the electron density fluctuations through the structure function analysis simultaneously to the occurrence of loss of lock events through measurements recorded by the Langmuir probes and the precise orbit determination antennas on board Swarm A and Swarm B satellites. We find that the plasma density irregularities in a turbulent state characterized by intermittent structures and extremely high values of the Rate Of change of electron Density Index can lead to GPS loss of lock events. This is always true at mid and high latitudes, especially inside the auroral oval. In the equatorial belt, this happens in at least 75% of identified GPS loss of lock events that basically coincide with the occurrence of plasma bubbles.

Spread-F characteristics over Tucumán near the southern anomaly crest in South America during the descending phase of solar cycle 24

Ionospheric F-region irregularities can acutely affect navigation and communication systems. To develop predictive capabilities on their occurrence, it is key to understand their variabilities in a wide range of time scales. Previous studies at low latitudes in South America have been performed mostly in the eastern region. However, there are still few reports on the spread-F over Argentina owing to a lack of ionosonde data. This work presents the analysis of the spread-F (range spread-F and frequency spread-F) and plasma bubble occurrence characteristics near the southern crest of the Equatorial Ionization Anomaly in Argentina (Tucumán, 26.8°S, 65.2°W; magnetic latitude 15.5°S). We used ionosonde and Global Positioning System (GPS) data from November 2014 to December 2019 for different solar and geomagnetic conditions. The data show that spread-F and plasma bubble occurrence rates peak in local summer and are minimum in equinox and winter, respectively. There is a negative correlation between each type of spread-F and solar activity, whereas the opposite happens for plasma bubbles. Geomagnetic activity suppresses the generation of spread-F in equinox and summer and enhances it in winter. Plasma bubble occurrence is higher during disturbed days than during quiet days, but under medium solar activity, summer months register more plasma bubbles in quiet conditions. Range spread-F observed in winter under low solar activity is not associated with plasma bubbles originated at the magnetic equator. These results contribute to the knowledge necessary to improve the prediction of the spatial and temporal distribution of the night-time ionospheric irregularities.

Impact of Anthropogenic Emission Changes on the Occurrence of Equatorial Plasma Bubbles

AbstractIn this work, we examine the impact of increased anthropogenic emissions on equatorial plasma bubble (EPB) occurrence by modeling the growth rate of Rayleigh‐Taylor (R‐T) instability (), which is closely related to EPB generation. Using the global coupled ionosphere‐thermosphere‐electrodynamics model‐institute of geology and geophysics, Chinese Academy of Sciences model, is calculated under three different CO2 emission levels. As CO2 increases, significantly increases at low altitudes (<∼260 km) and decreases at high altitudes (>∼320 km). In the altitudes in between, increases (decreases) before (after) midnight. Longitudinal variability of the change is manifested apparently above ∼280 km, while it is insignificant for low altitudes. Term analysis revealed that changes in the gravity term and the electric‐field term are the main causes and that the neutral‐wind term is insignificant. The investigation indicates that increased anthropogenic emissions can change EPB occurrence and, in turn, the radio‐communication system and therefore influence modern technological systems, which is expected to be more serious in the future.

Impact of Anthropologic Emission Changes on the Occurrence of Equatorial Plasma Bubbles

Impact of Anthropologic Emission Changes on the Occurrence of Equatorial Plasma Bubbles

The Importance of Counting: A New Index to Correctly Quantify Equatorial Plasma Bubble Occurrence in COSMIC Radio Occultation Data

AbstractThe Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) Radio Occultation data has been previously used as a way of investigating the climatology of Equatorial Plasma Bubbles (EPB). These low‐density regions can cause random phase and amplitude scintillation of satellite signals and forecasting these is an important priority in the space physics community. The ability to build useful forecasting models depends on the underlying data sets used in testing and validating these models. Correctly identifying days of EPB activity is important, but statistical studies using large data sets require the use of automated detection methods. Many of these detection methods heavily reduce data sets by removing unfavorable data, such as COSMIC profiles where the maximum scintillation occurs in the E region. This study presents a new F region s4max9sec index that can be used to study the presence of F region scintillation without excluding profiles that exhibit E region scintillation. The new index is shown to decrease EPB occurrence through the increase in available data, and is also shown to detect EPB events previously excluded from climatological studies. Calculation of the climatology using the new index is shown to resolve some differences that exist in the EPB climatology literature, particularly the location of the maximum scintillation occurrence during the equinox seasons. The use of this index is highlighted as a potential for studying F region scintillation in the presence of E region scintillation; an area of research that needs to be expanded for a complete understanding of EPBs.

Ground and satellite-based observations of ionospheric plasma bubbles and blobs at 5.65° latitude in the Brazilian sector

This investigation uses simultaneous observations from all-sky imager system and an ionosonde collocated at Araguatins (5.65° S, 48.07° W and dip-latitude of 4.17° S), a near-equatorial region in Brazil. These simultaneous observations were used to investigate the occurrence of plasma bubbles and blobs in the field of the imaging system and their association with atypical range Spread-F signature in ionograms. Also, in-situ observation of plasma density from Swarm satellites were used to support the ground-based observations. Using a few cases, a methodology will be established to identify in the plasma blobs (atypical ESF) in the ionograms when there is the simultaneous observation of plasma bubbles and blobs in the field of view of the ionosonde. For this purpose, simultaneous sequence of OI 630.0 nm nightglow images and ionograms are presented for different case studies; 1. when there is the absence of a plasma bubble or blob, 2. when there is only the occurrence of plasma bubbles and 3. when there is the occurrence of plasma bubbles and blobs, in order to compare traces in the ionogram in all these case studies. With these we can cover all kinds of signatures in the ionograms corresponding to no irregularities, plasma bubbles only and plasma bubbles-blobs. These OI 630.0 nm nightglow and ionograms recorded simultaneously make it possible to establish a novel methodology to recognize in ionograms cases when there is the occurrence of Spread-F signature associated with bubble-blob in the FOV of the ionosonde.

On the solar activity dependence of midnight equatorial plasma bubbles during June solstice periods

The occurrence of midnight Equatorial Plasma Bubbles (EPBs) during the June solstice period of the ascending phase of solar cycle 24, from 2010 to 2014, was studied using data from the 47 MHz Equatorial Atmosphere Radar (EAR) at Kototabang, Indonesia. The analysis shows that the occurrence of midnight hour EPBs was at its maximum during the low solar activity year 2010 and monotonically decreased thereafter with increasing solar activity. Details of the dependence of midnight hour EPB occurrence on solar activity were investigated using SAMI2 model simulation with a realistic input of <i><b>E</b></i> × <i><b>B</b></i> drift velocity data obtained from the CINDI-IVM onboard the C/NOFS satellite. Results obtained from term-by-term analysis of the flux tube integrated linear growth rate of RT instability indicate that the formation of a high flux tube electron content height gradient (steep vertical gradient) region at higher altitudes, due to the elevated F layer, is the key factor enhancing the growth rate of RT instability during low solar activity June solstices. Other factors are discussed in light of the relatively weak westward zonal electric field in the presence of the equatorward neutral wind and north-to-south transequatorial wind around the midnight hours of low solar activity June solstices. Also discussed are the initial seeding of RT instability by MSTIDs and how the threshold height required for EPB development varies with solar activity.

Equatorial Plasma Bubbles: Occurrence Probability versus Local Time

The character of the variability of the LT distributions of the equatorial plasma bubble occurrence probability with an increase of the recording altitude is under consideration. The conditions of the high and maximal solar activity, when the generation of the plasma bubbles is the most active, are examined. For this purpose the detailed comparative analysis of the LT distributions of the equatorial plasma bubble occurrence probability derived from the ISS-b (~972–1220 km), Hinotori (~650 km), ROCSAT-1 (~600 km), AE-E (~300–475 km), and CHAMP (~380–450 km) satellite data was done. The pronounced trend of the local time shift of the bubble occurrence probability maximum with an increase of the altitude is revealed. Thus, if the maximum occurs after sunset (~2030–2200 LT) at the bottom-side of the F-layer, it shifts toward the premidnight (~2100–2400 LT, ~600 km), then to the postmidnight (~0100–0300 LT, ~650 km), and, finally, to the predawn hours (~0300–0400 LT, ~972–1220 km) as the observation altitude increases. The most typical velocities of the equatorial plasma bubble rise are found to be ~150–300 m/s, which correspond to the numerous observational data.

On the Assessment of Daily Equatorial Plasma Bubble Occurrence Modeling and Forecasting

AbstractPredicting the daily variability of Equatorial Plasma Bubbles (EPBs) is an ongoing scientific challenge. Various methods for predicting EPBs have been developed, however, the research community is yet to scrutinize the methods for evaluating and comparing these prediction models/techniques. In this study, 12 months of co‐located GPS and UHF scintillation observations spanning South America, Atlantic/Western Africa, Southeast Asia, and Pacific sectors are used to evaluate the Generalized Rayleigh‐Taylor (R‐T) growth rates calculated from the Thermosphere Ionosphere Electrodynamics General Circulation Model (TIEGCM). Various assessment metrics are explored, including the use of significance testing on skill scores for threshold selection. The sensitivity of these skill scores to data set type (i.e., GPS versus UHF) and data set size (30, 50, 60, and 90 days/events) is also investigated. It is shown that between 50 and 90 days is required to achieve a statistically significant skill score. Methods for conducting model‐model comparisons are also explored, including the use of model “sufficiency.” However, it is shown that the results of model‐model comparisons must be carefully interpreted and can be heavily dependent on the data set used. It is also demonstrated that the observation data set must exhibit an appropriate level of daily EPB variability in order to assess the true strength of a given model/technique. Other limitations and considerations on assessment metrics and future challenges for EPB prediction studies are also discussed.

Equatorial Plasma Bubble Occurrence Under Propagation of MSTID and MLT Gravity Waves

AbstractWe observed a signature of equatorial plasma bubbles (EPBs) followed by a medium‐scale traveling ionospheric disturbance (MSTID) crossing the solar terminator over the geomagnetic equator during the period of post‐sunset rise (PSSR) of the F layer. Simultaneous observations of the EPBs and the MSTIDs by ground‐based Global Navigation Satellite System receivers and OI 630‐nm imagers, ionospheric parameters by ionosondes, and mesosphere–lower thermosphere (MLT) gravity waves (MLT‐GWs) by OH airglow imagers have been carried out in the equatorial and low‐latitude region of Brazil. On 16–17 September 2015, MSTIDs with very fast horizontal phase speeds, propagating toward northeast (NE), were observed over the latitude region of 0–30°S in the afternoon to evening time zone. It was geomagnetically quiet time (Kp: 2–3). An EPB development was observed after one of the MSTIDs crossed the solar terminator at 22:00 UT. Large‐scale MLT‐GWs with slower phase speeds were also observed both at São João do Cariri (7.5°S, 35.0°W) propagating from southwest (SW) to NE and Cachoeira Paulista (22.7°S, 45.0°W) propagating northward. This is to report on what we consider as a signature of direct seeding of EPBs by an MSTID that was likely induced by a secondary GW from tropospheric deep cloud convections to the south. This study highlights a possible dynamical process from the troposphere to ionosphere via this vertical coupling process over the 2,500 km of horizontal distance.

Study on Seasonal Variations of Plasma Bubble Occurrence over Hong Kong Area Using GNSS Observations

In this study, the characteristics and causes of the seasonal variations in plasma bubble occurrence over the Hong Kong area were investigated using the local Global Navigation Satellite System (GNSS) network. Generally, the occurrences of plasma bubbles were larger in the two equinoxes than in the two solstices. Furthermore, two seasonal asymmetries in plasma bubble occurrence were observed: plasma bubble activity was more frequent in the spring equinox than in the autumn equinox (equinoctial asymmetry), and more frequent in the summer solstice than in the winter solstice (solstitial asymmetry). The equinoctial asymmetry could be explained using the Rayleigh–Taylor (R–T) instability mechanism, due to larger R–T growth rates in the spring equinox than in the autumn equinox. However, the R–T growth rate was smaller in the summer solstice than in the winter solstice, suggesting the R–T instability mechanism was inapplicable to the solstitial asymmetry. Our results showed there were more zonally propagating atmospheric gravity waves (GWs) induced by thunderstorm events over the Hong Kong area in the summer solstice than the winter solstice. So, the solstitial asymmetry could be attributed to the seeding mechanism of thunderstorm-driven atmospheric GWs.