Occurrence Of Equatorial Plasma Bubbles Research Articles

Investigation of the latitudinal occurrence rate of ionospheric plasma bubble in case of strong and weak pre–reversal enhancement in Southeast Asia

We used ionosonde and GPS receivers during March–April in 2004–2005 and 2011–2015 to investigate the latitudinal variation of equatorial plasma bubble (EPB) occurrence rate in cases of strong and weak pre-reversal enhancement (PRE). The ionosonde at Chumphon in Thailand was used to estimate the PRE strength. Ten GPS receivers in Southeast Asia, ranging from magnetic latitude (ML) of 4.4°S to 21.6°S, were used to investigate the latitudinal variation of EPB occurrence rate. In the case of strong PRE, the EPB occurrence rates decrease from 38.9% to 34.9% at ML of 4.4°S–7.2°S. Continuously, the occurrence rate increases and reaches the peak (44%) at ML of 9.3°S; afterward, the occurrence rate rapidly decreases and reaches below 5% at ML of 21.6°S. In the case of weak PRE, the occurrence rate decreases from 21.8% at ML of 4.4°S, seems constant (15.3%–16%) at ML of 8.2°S–12.1°S, and reaches less than 5% at ML of 16.1°S. Generally, the EPB occurrence rate and its latitudinal extension in case of strong PRE are higher than that in case of weak PRE. Interestingly, we found that the latitudinal occurrence rate peak of the EPB in case of strong is farther than that in case of weak PRE.

GNSS Ionosphere Sounding of Equatorial Plasma Bubbles

Ground- and space-based Global Navigation Satellite System (GNSS) receivers can provide three-dimensional (3D) information about the occurrence of equatorial plasma bubbles (EPBs). For this study, we selected March 2014 data (during solar maximum of cycle 24) for the analysis. The timing and the latitudinal dependence of the EPBs occurrence rate are derived by means of the rate of the total electron content (TEC) index (ROTI) data from GNSS receivers in China, whereas vertical profiles of the scintillation index S4 are provided by COSMIC (Constellation Observing System for Meteorology, Ionosphere and Climate). The GNSS receivers of the low Earth orbit satellites give information about the occurrence of amplitude scintillations in limb sounding geometry where the focus is on magnetic latitudes from 20° S to 20° N. The occurrence rates of the observed EPB-induced scintillations are generally smaller than those of the EPB-induced ROTI variations. The timing and the latitude dependence of the EPBs occurrence rate agree between the ground-based and spaceborne GNSS data. We find that EPBs occur at 19:00 LT and they are mainly situated above the F2 peak layer which descended from 450 km at 20:00 LT to 300 km at 24:00 LT in the equatorial ionosphere. At the same time, the spaceborne GNSS data also show, for the first time, a high occurrence rate of post-sunset scintillations at 100 km altitude, indicating the coexistence of equatorial sporadic E with EPBs.

Occurrence characteristics of equatorial plasma bubbles and total electron content during solar cycle peak 23rd to peak 24th over Bangalore (13.02∘ N, 77.57∘ E)

We present the monthly, seasonal and annual variation in the ionospheric total electron content (TEC) and % occurrence rate of Equatorial plasma bubble (EPBs) during the lowest to highest solar activity phase for the period of 2002–2013. The Total Electron Content (TEC) is computed using Global Positing System (GPS) from Bangalore (13.02∘ N, 77.57∘ E) IGS station for the period 2002 to 2013. The total 4383 days during the period 2002–2013, out of which 4229 days GPS data were analyzed i.e. 96.48%. Total 1175 days data shows signature of EPBs. The average occurrence rates of EPBs were 5.93% during the disturbed period and 47.07% during quiet period. This shows that the EPBs occurrence rate is higher in quiet period than that of disturbed period. We also found that both the average GPS-TEC and % occurrence rate of plasma bubbles are positively correlated with solar flux for the entire 12 year period. This study investigates the causal linkage between EPBs and TEC using their statistics during the solar minimum and maximum period. The studies on dynamics of EPBs are essential because they affects the satellite communication system, mainly due to depletions in the Total Electron Content (TEC) which encounters most of the effects on GPS signals.

Seasonal variation of plasma bubbles during solar cycle 23–24 over the Brazilian equatorial region

In this study, OI 630.0 nm nightglow image data obtained from an all-sky imaging station located at Sao Joao do Cariri (7.4°S, 36.5°W), have been used to study the occurrence of equatorial plasma bubbles (EPBs) over the Brazilian equatorial region. The observations, which took place from September 2000 to December 2010 (almost eleven years), covered a significant part of solar cycle 23 (descending phase of SC23) and the very beginning of solar cycle 24 (ascending phase of SC24). There were 1337 nights of observations with 666 nights with EPB events, which translates to an occurrence rate of ∼ 49.8%. Of these nights, 1290 were considered quiet (Dst ≥ -50 nT) with ∼ 50% plasma bubbles occurrence rate. The occurrence of EPBs was studied under three solar activity phases – high solar activity phase (HSA, September 2000 – March 2004), moderate solar activity phase (MSA or descending phase, March 2004 – October 2006) and low solar activity phase (LSA, October 2006 – December 2010). The low solar activity phase is part of the peculiar solar cycle 24, considered the weakest in over a century with most sunspotless days (2008–2009). The maximum occurrence of bubbles, equal to 54.2%, was found during the HSA phase, with percentages characterizing MSA and LSA being respectively 52.4% and 45.8%. The analysis also showed clear seasonal variation in the EPB occurrence with maximum rates in summer, spring, autumn, and the minimum rates in winter for all solar activity phases. Overall, there was observed solar cycle variation in each season with maximum occurrence in HSA followed by MSA and then LSA except in autumn where higher occurrence rate was observed in LSA phase than in MSA phase.

Multi-instrument investigation of troposphere-ionosphere coupling and the role of gravity waves in the formation of equatorial plasma bubble

Present study investigates the role of gravity waves in the generation of equatorial plasma bubbles (EPBs) during geomagnetic quiet conditions using co-located observations from Gadanki (13.5oN, 79.2° E) an all sky airglow imager, Gadanki Ionospheric Radar Interferometer (GIRI) and Ionosonde observations from Tirunelveli (8.7° N, 77.8° E). To avoid any changes occurring in the background ionosphere, four consecutive nights of observation during 03–06 February 2014 is used. Out of these four nights, three nights (i.e., 03, 05 and 06 February 2014) exhibit occurrence of EPBs in the OI 630 nm airglow emission and radar plumes and there is no bubble occurrence during one night, though the ionospheric peak altitude (h′F) value is more than 350 km in all these nights. During these four nights the structures observed in the E-region drifts and gravity waves noted in the mesospheric OH emissions are analyzed. It is found that there are common periodic oscillations in the OH peak emission altitude and E-region in three nights (03, 04 and 05 February 2014). The mesospheric gravity wave structures are ray traced to their potential sources in the lower atmosphere and also for the possibility of their propagation to the E-region. Our results suggest that apart from horizontal wavelength and amplitudes, the propagation angle of gravity wave may also be important for seeding of the Rayleigh-Taylor (R-T) instability. Thus, it gives an insight about the role of lower – middle and upper atmospheric coupling on the occurrence of the noted EPBs.

Observation of equatorial plasma bubbles by the airglow imager on ISS-IMAP

Using 630 nm airglow data observed by an airglow imager on the International Space Station (ISS), the occurrence of equatorial plasma bubbles (EPBs) is studied. In order to examine the physical mechanisms in the boundary region between the Earth and the outer space, an ionosphere, mesosphere, upper atmosphere, and plasmasphere mapping (IMAP) mission had been conducted onboard the ISS since October 2012. The visible light and infrared spectrum imager (VISI) is utilized in the ISS-IMAP mission for nadir-looking observation of the earth’s atmospheric airglow. In this study, we automatically select EPBs according to the criterion for extracting the tilted dark lines from VISI data. Using the selected events, the dependence of the occurrence rate of EPBs is examined. There is no other report of the occurrence rate of EPBs using downward-looking visible airglow data (630 nm). In this result, the occurrence rate is high at all longitudes in the equinoctial seasons. In the solstice seasons, in contrast, the occurrence rate is very small especially in the Pacific and American sectors. This result is basically consistent with previous studies, e.g., those determined by plasma density data on DMSP satellites.During the June solstice in 2013, EPBs were observed in association with geomagnetic storms that occurred due to a southward turning of the IMF Bz. Using these events, we examined the storm-time features of the occurrence of EPBs in the Pacific-American sectors during the June solstice. In these sectors, where the occurrence rate of EPBs is very small during solstice seasons, some EPBs were observed in the peak and recovery phases of the storms. This result shows that the prompt penetration of electric fields causes the development of EPBs, in the data we analyzed, the geomagnetic storms did not inhibit the generation of EPB in the Pacific–American sectors.

Statistical Analysis of Separation Distance Between Equatorial Plasma Bubbles Near Suvarnabhumi International Airport, Thailand

AbstractIonospheric disturbances can lead to the major detrimental effects on the availability of ground‐based augmentation system. In low‐latitude regions, equatorial plasma bubbles (EPBs) frequently arise. They originated from the bottom side of the ionosphere with the electron density inside the plasma bubbles lower than the outside area. It is well known that the EPB causes the strong fluctuation on Global Positioning System signals when passing through the ionospheric disturbed regions. Sometimes the EPBs may have more than one front. To better understand the ionospheric anomaly effect on ground‐based augmentation system efficiency, the separation distance between EPBs needs to be studied. In this work, we analyze the slant total electron content from dual‐frequency Global Positioning System receivers near Suvarnabhumi International Airport, Thailand, to ascertain the EPB occurrence. The distance between observed EPBs is computed based on the Haversine formula technique. The results found that the estimated separation distances between depletions on disturbed days in 2015 are in the range of 100 to 1,200 km.

Daily and seasonal variations in the linear growth rate of the Rayleigh-Taylor instability in the ionosphere obtained with GAIA

The linear growth rates of the Rayleigh-Taylor (R-T) instability in the ionosphere from 2011 to 2013 were obtained with a whole atmosphere-ionosphere coupled model GAIA (ground-to-topside model of atmosphere and ionosphere for aeronomy). The effects of thermospheric dynamics driven by atmospheric waves propagating from below on the R-T growth rate are included in the model by incorporating meteorological reanalysis data in the region below 30 km altitude. The daily maximum R-T growth rates for these periods are compared with the observed occurrence days of the equatorial plasma bubble (EPB) determined by the Equatorial Atmosphere Radar (EAR) and Global Positioning System (GPS) in West Sumatra, Indonesia. We found that a high R-T growth rate tends to correspond to the actual EPB occurrence, suggesting the possibility of predicting EPB occurrences with numerical models.

Improved characterization and modeling of equatorial plasma depletions

This manuscript presents a method to identify the occurrence of Equatorial Plasma Bubbles (EPBs) with data gathered from receivers of Global Navigation Satellite System (GNSS). This method adapts a previously existing technique to detect Medium Scale Travelling Ionospheric Disturbances (MSTIDs), which focus on the 2nd time derivatives of total electron content estimated from GNSS signals (2DTEC). Results from this tool made possible to develop a comprehensive analysis of the characteristics of EPBs. Analyses of the probability of occurrence, effective time duration, depth of the depletion and total disturbance of the EPBs show their dependence on local time and season of the year at global scale within the latitude belt from 35°N to 35°S for the descending phase of solar cycle 23 and ascending phase of solar cycle 24, 2002–2014. These results made possible to build an EPBs model, bounded with the Solar Flux index, that simulates the probability of the number of EPBs and their characteristics expected for a representative day at given season and local time (LT). The model results provided insight into different important aspects: the maximum occurrence of bubbles take place near the equatorial anomaly crests, asymmetry between hemispheres and preferred longitudes with enhanced EPBs activity. Model output comparisons with independent observations confirmed its soundness.

Investigation of zonal velocity of equatorial plasma bubbles (EPBs) by using GPS data

The zonal velocity of equatorial plasma bubbles (EPBs) have been studied using various techniques in the past few years. However, the derivation of the zonal drift of EPBs using GPS ROTI have not been studied before. This study aims to investigate the zonal drifts of EPBs using GPS ROTI keogram. The Malaysia Real–Time Kinematic GNSS Network (MyRTKnet) which consists of 78 GPS receivers was used to study the occurrence of EPBs along 96°E - 120°E longitude. The EPBs are detected from daily ROTI keogram that derived from east-west cross section of two dimension of ROTI maps at 5°N for every 5 minutes. On the night of 29 March 2011, 10 consecutive EPBs with periodic spacing between 50 km to 100 km were recorded by MyRTKnet. In this study, we obtained that highest drift velocity is about 277.7 m s-1 at 1400 UT which denoted by EPB 7 whereas the lowest drift velocity is EPB 4 with 27.8 m s-1 at 1600 UT. Besides, the EPBs are propagated towards the east from 200 km to 2800 km with average velocities is about 55.6 m s-1 to 138.9 m s-1.

Equatorial plasma bubbles: Variations of occurrence and spatial scale in local time, longitude, season, and solar activity

AbstractWe examine the location and structure of equatorial topside depletions referred to here as equatorial plasma bubbles (EPBs). The Coupled Ion Neutral Dynamics Investigation Ion Velocity Meter instrument on board the Communication/Navigation Outage Forecasting System is used to measure the ion density from August 2008 to December 2014, a time period in which solar activity transitioned from solar minimum conditions to more moderate solar activity conditions. EPB data are divided into four longitude sectors to determine seasonal and solar cycle variability. In the early phase of the mission, during solar minimum, EPBs occur late in local time, primarily after midnight in all longitude sectors. In the later phase of the mission EPB occurrence after midnight diminishes in all seasons and longitude sectors with the exception of the sector extending from −15° to 60°. An examination of the widths of bubbles indicates that all longitudes show similar distributions between 115 km and 460 km with a prominent peak near 200 km. Among these widths is a distinct width that belongs to discrete individual bubbles with no substructure. We suggest that many bubbles are actually combinations of these individual bubbles; however, in the later phase of the mission there is a population of bubbles that do not conform to this description, perhaps due to the influence of large‐scale plasma motions affecting the background density in which they are embedded.

Solar effect on the Rayleigh-Taylor instability growth rate as simulated by the NCAR TIEGCM

The TIEGCM (Thermosphere Ionosphere Electrodynamics General Circulation Model) is used to investigate the solar effect on the equatorial ionospheric Rayleigh-Taylor (R-T) instability growth rate, which is responsible for the occurrence of the plasma bubbles. The R-T growth rate is calculated for the solar maximum year 2003 and minimum 2009. The growth rate is strongly dependent on the solar activity. During solar maximum, the pre-reversal enhancement is much stronger leading to higher R-T growth rate. The R-T growth rates from the TIEGCM follow the same solar dependence as the observed occurrence of equatorial plasma bubbles by DMSP satellites. The R-T growth rate also enhances when the day/night terminator is parallel to the magnetic field line near the equator. The R-T growth rate does not correlate well with the solar F10.7 index on a short time scale (~10 days) because the field-line integrated electron content gradient cancels out the positive correlation between the vertical ion drift with the F10.7 index. The TIEGCM result shows the importance of the electron content gradient to the R-T growth rate and the plasma bubble occurrence. The bubble occurrence rates were estimated based on the vertical ion drift simulation results.

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

AbstractThe 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.

Periodicity in the occurrence of equatorial plasma bubbles derived from the C/NOFS observations in 2008–2012

AbstractThe quasi‐periodic occurrence of equatorial plasma bubbles is understood in terms of seeding mechanisms in the bottomside F region. However, no quantitative investigation has been conducted to identify how often quasi‐periodic bubbles occur. This study investigates the wave property in the bubble occurrence (or spacing between bubbles) using the measurements of the plasma density in 2008–2012 by the Planar Langmuir Probe on board the Communication/Navigation Outage Forecasting System (C/NOFS) satellite. The wave property is investigated using the Lomb‐Scargle periodograms derived from 664 segments of series of bubbles. In the majority of segments, the spacing between bubbles is represented by the combination of several wave components. Periodic bubbles whose property is represented by a few pronounced wave components are rare events. These results indicate that the spacing between bubbles is generally irregular. The manner of bubble occurrence does not show any notable variation with longitude and season. Because a consistent wave property does not exist in the occurrence of bubbles and the appearance of bubbles in the topside is affected by many factors, the manner of bubble occurrence in satellite observations does not provide a precise diagnostic of seeding mechanisms.

Climatology characterization of equatorial plasma bubbles using GPS data

The climatology of equatorial plasma bubbles (EPBs) for the period 1998–2008 was studied using slant total electron content (sTEC) derived from global positioning system (GPS) data. The sTEC values were calculated from data measured at 67 International GNSS Service (IGS) stations distributed worldwide around the geomagnetic equator and embracing the region of the ionospheric equatorial anomaly (IEA). EPBs and their characteristics were obtained using the Ionospheric Bubble Seeker (IBS) application, which detects and distinguishes sTEC depletions associated with EPBs. This technique bases its analysis on the time variation of the sTEC and on the population variance of this time variation. IBS finds an EPB by default when an sTEC depletion is greater than 5 TEC units (TECu). The analysis of the spatial behavior shows that the largest rate of EPB takes place at the equator and in the South America-Africa sector, while their occurrence decreases as the distance from the magnetic equator increases. The depth and duration of the sTEC depletions also maximize at the equator and in the South America-Africa sector and weaken departing from the equator. The results of the temporal analysis for the data of the IGS stations located in AREQ, NKLG, IISC, and GUAM indicate that the greatest rate of EPB occurrence is observed for high solar activity.

A statistical analysis of equatorial plasma bubble structures based on an all‐sky airglow imager network in China

AbstractThis paper investigates the statistical features of equatorial plasma bubbles (EPBs) using airglow images from 2012 to 2014 from a ground‐based network of four imagers in the equatorial region of China. It is found that (1) EPBs mainly occur during 21:00–00:00 local time (LT) in equinoxes. There is an asymmetry in occurrence rates between March (June) and September equinoxes (December solstices). (2) Most EPBs occur in groups of two to six depletions. The distance between adjacent EPB depletions is ~100–700 km, and the average is 200–300 km. The zonal extension of an EPB group is usually less than 1500 km but can reach 3000 km. (3) EPBs usually have a maximum drift velocity near 100 m/s at 21:00–22:00 LT in 9.5° ± 1.5° geomagnetic latitude and then decrease to 50–70 m/s toward sunrise. (4) The averaged westward tilt angle of most EPBs (with respect to the geographic north‐south) increased from 5°–10° to 23°–30° with LT between 20:00 and 03:00 LT, then decreasing to 10°–20° toward sunrise. (5) When 90 < F10.7 < 140, the maximum magnetic latitudinal extension (PMLE) is usually lower than 15.0° (apex height ~725 km), but it can reach 23.0° (apex height ~1330 km) when F10.7 > 140. The maximum PMLE increases by 3.4°–5.5° when F10.7 changes from 90 to 190. (6) The EPB occurrence patterns and zonal drift velocities are significantly different from those at Kolhapur, India, which locates west to our stations by 20.0°–32.0° in longitude.

Effects of solar and geomagnetic activity on the occurrence of equatorial plasma bubbles over Hong Kong

AbstractIn the present study, the occurrence and characteristics of equatorial plasma bubble (EPB) has been analyzed using the GPS data from continuously operating reference stations network over Hong Kong during 2001–2012. The analysis found maximum EPB occurrences during the equinoctial months and minimum EPB occurrences during the December solstice throughout 2001–2012 except during the solar minimum in 2007–2009. The maximum EPB occurrences were observed in June solstice during 2007–2008, whereas for 2009, EPB occurrences were quite higher for June solstice but slightly smaller than the March equinox. The seasonal maximum in EPB occurrences have been discussed in terms of plasma density seed perturbation caused by gravity waves as well as the post sunset F‐layer rise due to the pre‐reversal enhancement of zonal electric field. Generally, EPB occurrences are found to be more prominent during nighttime hours (19:00–24:00 h) than daytime hours. The day and nighttime EPB occurrences were inferred and found to vary linearly with solar activity and have an annual correlation coefficient (R) of ~ 0.92 with F10.7 cm solar flux and ~0.88 with sunspot number. Moreover, the impact of solar activity on EPB occurrences is found to be dependent on seasons with maximum during the equinox (R = 0.80) and minimum during the summer season (R = 0.68). The detail study of EPB occurrences during two typical cases of geomagnetic storms on 6 November and 24 November 2001 found that the storm on 24 November triggered the EPB occurrence whereas storm on 6 November suppressed the EPB occurrence. The enhancement/suppression of EPB occurrences during storms periods is a consequence of a storm‐induced prompt penetration electric field as well as disturbance dynamo electric field effects associated with the main phase of the geomagnetic storm.

Global equatorial plasma bubble occurrence during the 2015 St. Patrick's Day storm

AbstractAn analysis of the occurrence of equatorial plasma bubbles (EPBs) around the world during the 2015 St. Patrick's Day geomagnetic storm is presented. A network of 12 Global Positioning System receivers spanning from South America to Southeast Asia was used, in addition to colocated VHF receivers at three stations and four nearby ionosondes. The suppression of postsunset EPBs was observed across most longitudes over 2 days. The EPB observations were compared to calculations of the linear Rayleigh‐Taylor growth rate using coupled thermosphere‐ionosphere modeling, which successfully modeled the transition of favorable EPB growth from postsunset to postmidnight hours during the storm. The mechanisms behind the growth of postmidnight EPBs during this storm were investigated. While the latter stages of postmidnight EPB growth were found to be dominated by disturbance dynamo effects, the initial stages of postmidnight EPB growth close to local midnight were found to be controlled by the higher altitudes of the plasma (i.e., the gravity term). Modeling and observations revealed that during the storm the ionospheric plasma was redistributed to higher altitudes in the low‐latitude region, which made the plasma more susceptible to Rayleigh‐Taylor growth prior to the dominance of the disturbance dynamo in the eventual generation of postmidnight EPBs.

Early morning irregularities detected with spaceborne GPS measurements in the topside ionosphere: A multisatellite case study

AbstractWe present observations of the equatorial plasma bubbles (EPB) in the topside ionosphere at early morning hours (05–08 LT) in the recovery phase of the 18–19 February 2014 geomagnetic storm. This rare type of irregularities was detected in the Pacific sector using GPS measurements on board several low‐Earth‐orbit (LEO) satellites. We use a multisatellite constellation consisted of the three Swarm and one TerraSAR‐X satellites, that on 19 February flew in the same region and at similar altitudes ~500 km. The EPB occurrence in the LEO GPS data was observed for several consecutive orbits from ~11 UT to 16–17 UT on 19 February 2014, which suggests the following: (1) rather long duration (hours) of favorable conditions for EPB generation, (2) formation and evolution of EPB over wide longitude range of the Pacific Ocean, and (3) possible movement of the EPB region in the westward direction (with dawn). Registration of the early morning EPB in LEO GPS data was supported by concurrent in situ (Swarm and DMSP (Defense Meteorological Satellite Program)) and ground‐based (ionosonde and GPS) measurements. LEO‐based GPS technique is found to be essential and promising data source to study the topside EPB over regions with lack of the ground‐based facilities. In addition, we use the Prompt Penetration Model and the Thermosphere‐Ionosphere Electrodynamics Global Circulation Model (TIE‐GCM) to identify the possible mechanisms responsible for the observed phenomenon. The model simulation results indicate the occurrence of the zone with the enhanced vertical plasma drift (~40–45 m/s) owing to the disturbance dynamo action in the predawn/dawn sector during 09–17 UT.

An analysis of the quiet time day‐to‐day variability in the formation of postsunset equatorial plasma bubbles in the Southeast Asian region

AbstractPresented is an analysis of the occurrence of postsunset Equatorial Plasma Bubbles (EPBs) detected using a Global Positioning System (GPS) receiver at Vanimo. The three year data set shows that the EPB occurrence maximizes (minimizes) during the equinoxes (solstices), in good agreement with previous findings. The Vanimo ionosonde station is used with the GPS receiver in an analysis of the day‐to‐day EPB occurrence variability during the 2000 equinox period. A superposed epoch analysis (SEA) reveals that the altitude, and the change in altitude, of the F layer height is ∼1 standard deviation (1σ) larger on the days for which EPBs were detected, compared to non‐EPB days. These results are then compared to results from the Thermosphere Ionosphere Electrodynamics General Circulation Model (TIEGCM), which show strong similarities with the observations. The TIEGCM is used to calculate the flux‐tube integrated Rayleigh‐Taylor (R‐T) instability linear growth rate. A SEA reveals that the modeled R‐T growth rate is 1σ higher on average for EPB days compared to non‐EPB days, and that the upward plasma drift is the most dominant contributor. It is further demonstrated that the TIEGCM's success in describing the observed daily EPB variability during the scintillation season resides in the variations caused by geomagnetic activity (as parameterized by Kp) rather than solar EUV flux (as parameterized by F10.7). Geomagnetic activity varies the modeled high‐latitude plasma convection and the associated Joule heating that affects the low‐latitude F region dynamo, and consequently the equatorial upward plasma drift.