Karakteristik Equatorial Plasma Bubbles (EPB) dari Pengamatan Radar Atmosfer Equator (EAR)

Fenomena-fenomena seperti Equatorial Plasma Bubbles/ Equatorial Spread F (EPB/ESF) dan Equatorial Ionization Anomaly (EIA) sangat berpotensi terjadi di wilayah atmosfer atas Indonesia (ionosfer) yang terletak dalam zona aktif gangguan lapisan ionosfer, yaitu dalam rentang + 15 lintang geomagnet. Fenomena-fenomena tersebut akan mengganggu beroperasinya sistem komunikasi radio maupun satelit berupa adanya gangguan dalam amplitudo maupun fase dari gelombang radio yang diterima penerima di bumi, dikenal dengan istilah sintilasi.Dalam penelitian ini dibahas beberapa karakteristik penting yang teramati oleh sistem Equatorial Atmosphere Radar yang telah dioperasikan di Kototabang (0,20S, 100,32E; 10,36S dip lat). Sistem antenna Radar disusun sedemikian sehingga mampu mengamati gangguan lapisan ionosfer yang terjadi tegak lurus terhadap garis-garis medan magnet, teramati sebagai Field Aligned Irregularities (FAI). Berdasarkan hasil pengolahan data diperoleh dua macam gelembung plasma yaitu post-sunset dan post-midnight yang keduanya dikendalikanoleh mekanisme fisis yang berbeda. Variasi musiman kejadian kedua jenis ketidakteraturan plasma tersebut juga ditampilkan dalam makalah ini. Bulan-bulan equinox (Maret-April atau September-Oktober) adalah bulan-bulan dimana post-sunset FAI terjadi lebih sering dibanding post-midnight. Sementara bulan-bulan solstice (Desember-Januari atau Juni-Juli) adalah bulan-bulan dimana post-midnight FAI lebih sering terjadi. Gambaran tentang arah penjalaran memberikan pemahaman baru tentang bagaimana perkembangan ketidakteraturan yangterjadi waktu ke waktu, baik secara horizontal maupun vertikal. Hasilnya memberi gambaran lebih baik tentang mekanisme kejadian EPB/ESF yang sangat bermanfaat dalam pengembangan model ketidakstabilan plasma, serta untuk melengkapi hasil pengamatan peralatan lain yang sudah ada.AbstractPhenomena such as Equatorial Plasma Bubbles/Equatorial Spread F (EPB/ ESF) and the Equatorial Ionization Anomaly (EIA) was potentially occured in the Indonesian region of the upper atmosphere (ionosphere) located in the active zone ionosphere disturbances, that is in the range of + 15 latitude geomagnetic. These phenomena would disrupt the operation of radio and satellite communications systems in the form of a disturbance in the amplitude and phase of the received radio wave receivers on Earth, known as scintillation. In this study addressed several important characteristics observed by the Equatorial Atmosphere Radar system that has operated in Kototabang (0.20S, 100.32E; 10.36S dip lat). Radar antenna system is arranged so that is able to observe the ionosphere interference that occurs perpendicular to the magnetic field lines, is observed as a Field Aligned irregularities (FAI). From EAR data analysis obtained two types of plasma bubbles post-sunset and post-midnightwhich is driven by two kinds of different physical mechanisms. Seasonal variation of both plasma irregularities are discussed in this paper. In equinox months (March-April or September-October), post-sunset are frequently occurred rather than post-midnight. While in solstice months (December-January or June-July) post-midnight are frequently occurred. The propagation direction provide more detail explanation related to development of irregularities time by time horizontally and vertically. The results not only suggested the better understandings of mechanism of EPB/ESF occurrence, but also contributed on development of plasma instability model andsupported observations by other instrument which have already operated

First detection of the plasma bubbles over Europe

18th EISCAT symposiumSession E6: The ERG mission and magnetosphere-ionosphere couplingMay 27 (Sat), Poster Sessio

Comparison of equatorial plasma bubble zonal drifts and neutral winds velocity over Southeast Asia

The purpose of the presented study is to investigate the zonal drifts of Equatorial Plasma Bubbles (EPB) which applied two different ground-based instruments. Malaysia Real-Time Kinematics GNSS Network (MyRTKnet), consists more than 78 GPS receivers was used to observe EPB along 96° East to 120° East longitudes. Subsequently, zonal drift of EPBs derived from GPS-ROTI is compared with neutral winds velocity from Fabry-Perot interferometer (FPI). On 10 April 2013, we founded the maximum drift is about 194.4 m/s at 1430 UT to 1500 UT whereas the minimum drift is 111.1 m/s at 1330 UT to 1400 UT. The results illustrate that temporal variations of EPB zonal drift velocities are consistent with the neutral winds

AATR an ionospheric activity indicator specifically based on GNSS measurements

This work reviews an ionospheric activity indicator useful for identifying disturbed periods affecting the performance of Global Navigation Satellite System (GNSS). This index is based in the Along Arc TEC Rate (AATR) and can be easily computed from dual-frequency GNSS measurements. The AATR indicator has been assessed over more than one Solar Cycle (2002–2017) involving about 140 receivers distributed world-wide. Results show that it is well correlated with the ionospheric activity and, unlike other global indicators linked to the geomagnetic activity (i.e. DST or Ap), it is sensitive to the regional behaviour of the ionosphere and identifies specific effects on GNSS users. Moreover, from a devoted analysis of different Satellite Based Augmentation System (SBAS) performances in different ionospheric conditions, it follows that the AATR indicator is a very suitable mean to reveal whether SBAS service availability anomalies are linked to the ionosphere. On this account, the AATR indicator has been selected as the metric to characterise the ionosphere operational conditions in the frame of the European Space Agency activities on the European Geostationary Navigation Overlay System (EGNOS). The AATR index has been adopted as a standard tool by the International Civil Aviation Organization (ICAO) for joint ionospheric studies in SBAS. In this work we explain how the AATR is computed, paying special attention to the cycle-slip detection, which is one of the key issues in the AATR computation, not fully addressed in other indicators such as the Rate Of change of the TEC Index (ROTI). After this explanation we present some of the main conclusions about the ionospheric activity that can extracted from the AATR values during the above mentioned long-term study. These conclusions are: (a) the different spatial correlation related with the MOdified DIP (MODIP) which allows to clearly separate high, mid and low latitude regions, (b) the large spatial correlation in mid latitude regions which allows to define a planetary index, similar to the geomagnetic ones, (c) the seasonal dependency which is related with the longitude and (d) the variation of the AATR value at different time scales (hourly, daily, seasonal, among others) which confirms most of the well-known time dependences of the ionospheric events, and finally, (e) the relationship with the space weather events.Postprint (published version

EVALUATION OF THE GNSS POSITIONING PERFORMANCE UNDER INFLUENCE OF THE IONOSPHERIC SCINTILLATION

The ionosphere may not only degrade the accuracy of the GNSS positioning but also reduce its availability because there is a high dependence between signal losses and ionospheric irregularities. Irregularities in the Earth’s ionosphere may produce rapid fluctuations in phase and amplitude. These rapid fluctuations are called ionospheric scintillation. Thus, loss of signal can occur due to the effects of diffraction and refraction, which cause a weakening in the signal received by the GNSS receivers. In this way, this paper aims to evaluate the magnitude of ionospheric scintillation in Brazil and the performance of the positioning under its influence in the period of high solar activity in the current cycle (24), through the Spearman correlation analysis and the Wavelet periodogram. For that, three-year time series (2012 to 2014) of the S4 index and 3D MSE (Mean Squared Error) of three Brazilian stations with different ionospheric conditions were considered, PALM (near the Geomagnetic Equator) PRU2 (Equatorial region and Anomalies) and POAL (Mid-latitude region). Thus, it was possible to evaluate the correlation between the accuracy of the precise point positioning using only the C/A code of the GPS satellite and the S4 index. As a result, there was a correlation of 53% and 51%, using the Spearman method, for the PALM and PRU2 series, respectively. In addition, considering the analysis of space-frequency in relation to time by the Wavelet coherence method, a correlation of more than 70% is noted in the period of greatest 3D MSE concerning the spring and autumn equinox months

Mapping equatorial ionospheric profiles over peninsular Malaysia using gps tomography

The ionospheric conditions over Malaysia are profoundly critical not only duea to its location that is near to the equator but also due to the high solar activity that occurred during the 11-years solar cycle. The two-dimensional (2D) single thin layer model (SLM) has been widely used to monitor and model the ionosphere. However, this model only focuses on the height of the maximum densities of the electron, which lies within 300 kilometre (km) to 450 km above the Earth and therefore neglects the information of bottom and topside of the ionosphere. Hence, a three-dimensional (3D) ionospheric structure is proposed to address these limitations. The aim of this study is to model the electron density profile over Peninsular Malaysia using Global Positioning System (GPS) ionospheric tomography method. In doing so, the Malaysian Real-time Kinematic Network (MyRTKnet) over Malaysia was utilized to derive the total electron content (TEC) maps. It was found that the variations of the TEC increase with decreasing of latitude and longitude, and gradually change from East to West direction. The GPS-derived TEC from the years 2009 to 2014 shows that the maximum yearly mean TEC over Malaysia is up to 58 TEC unit (TECU), recorded during the year 2014 which was associated with high sunspot numbers. The maximum yearly mean and the minimum peak of diurnal variations occur at 08 universal time (UT) and 21UT respectively. Next, the receiver code bias (DCBr) was estimated for MyRTKnet stations using the adopted algorithm from IONOLAB-BIAS. For assessment purpose, this method shows a good estimation of DCBr with the International Global Navigation Satellite System (GNSS) Service (IGS) analysis centre compared to with Bernese software. Then, the GPS ionospheric tomography module was developed to reconstruct the electron density profile over Peninsular Malaysia. The results were validated with the nearest ionosonde station and the ionospheric global models such as the International Reference Ionosphere (IRI) model and NeQuick model. It was found that the differences between GPS ionospheric tomography with the models are small during the daytime but large at night-time. It was also found that, the GPS ionospheric tomography appears to be more agreeable with the IRI model than with NeQuick model. For the validation of the NmF2 parameters with the IRI model and ionosonde measurements, the GPS ionospheric tomography is more agreeable with the ionosonde than with the IRI model. The results also show that the GPS ionospheric tomography is capable to show the vertical ionospheric profile over the study area during quiet ionospheric conditions and its irregularities during disturbed conditions of the ionosphere. Overall, it was found that the GPS ionospheric tomography method is suitable for examining and monitoring the ionospheric variations and irregularities in support of the space weather studies in Peninsular Malaysia

Initial morphological results of the GPS L - band amplitude scintillation from Tarawa equatorial station

We present initial morphological features of the Global Positioning Systems (GPS) L1 and L2 band amplitude scintillations at Tarawa equatorial station (geog: 1.33°N, 173.01°E, geomag: 2.68°S, 114.26°W), Kiribati, for the period September 2017 to November 2018 which falls in the low solar activity period of solar cycle 24 (average sunspot number, 11.6). The scintillation data were analyzed for the diurnal and seasonal variations, geomagnetic activity, and solar flare dependences of the S4 index. No daytime scintillations were observed during the entire study period on either of the bands. Nighttime scintillations had maximum occurrence during equinox months followed by summer and winter. L2 band showed an increased level of scintillation activity compared to the L1 band. The scintillation activity was enhanced during the magnetically disturbed days compared to quiet days. Scintillations during geomagnetic storms were dominantly confined in the pre-midnight hours and scintillations were completely absent during solar flare events

Simultaneous observations of equatorial F-region plasma depletions over Brazil during the Spread-F Experiment (SpreadFEx)

From September to November 2005, the NASA Living with a Star program supported the Spread-F Experiment campaign (SpreadFEx) in Brazil to study the effects of convectively generated gravity waves on the ionosphere and their role in seeding Rayleigh-Taylor instabilities, and associated equatorial plasma bubbles. Several US and Brazilian institutes deployed a broad range of instruments (all-sky imagers, digisondes, photometers, meteor/VHF radars, GPS receivers) covering a large area of Brazil. The campaign was divided in two observational phases centered on the September and October new moon periods. During these periods, an Utah State University (USU) all-sky CCD imager operated at São João d'Aliança (14.8° S, 47.6° W), near Brasilia, and a Brazilian all-sky CCD imager located at Cariri (7.4° S, 36° W), observed simultaneously the evolution of the ionospheric bubbles in the OI (630 nm) emission and the mesospheric gravity wave field. The two sites had approximately the same magnetic latitude (9–10° S) but were separated in longitude by ~1500 km. <br><br> Plasma bubbles were observed on every clear night (17 from Brasilia and 19 from Cariri, with 8 coincident nights). These joint datasets provided important information for characterizing the ionospheric depletions during the campaign and to perform a novel longitudinal investigation of their variability. Measurements of the drift velocities at both sites are in good agreement with previous studies, however, the overlapping fields of view revealed significant differences in the occurrence and structure of the plasma bubbles, providing new evidence for localized generation. This paper summarizes the observed bubble characteristics important for related investigations of their seeding mechanisms associated with gravity wave activity

The Effect of F‐Layer Zonal Neutral Wind on the Monthly and Longitudinal Variability of Equatorial Ionosphere Irregularity and Drift Velocity

The effect of eastward zonal wind speed (EZWS) on vertical drift velocity (E × Bdrift) that mainly controls the equatorial ionospheric irregularities has been explained theoretically and through numerical models. However, its effect on the seasonal and longitudinal variations of E × B and the accompanying irregularities has not yet been investigated experimentally due to lack of F‐layer wind speed measurements. Observations of EZWS from GOCE and ion density and E × B from C/NOFS satellites for years 2011 and 2012 during quite times are used in this study. Monthly and longitudinal variations of the irregularity occurrence, E × B, and EZWS show similar patterns. We find that at most 50.85% of longitudinal variations of E × B can be explained by the longitudinal variability of EZWS only. When the EZWS exceeds 150 m/s, the longitudinal variation of EZWS, geomagnetic field strength, and Pedersen conductivity explain 56.40–69.20% of the longitudinal variation of E × B. In Atlantic, Africa, and Indian sectors, from 42.63% to 79.80% of the monthly variations of the E × B can be explained by the monthly variations of EZWS only. It is found also that EZWS and E × B may be linearly correlated during fall equinox and December solstice. The peak occurrence of irregularity in the Atlantic sector during November and December is due to the combined effect of large wind speed, solar terminator‐geomagnetic field alignment, and small geomagnetic field strength and Pedersen conductivity. Moreover, during June solstices, small EZWS corresponds to vertically downward E × B, which suggests that other factors dominate the E × B drift rather than the EZWS during these periods.Key PointsZonal neutral wind controls more the seasonal variations of E × B drift than the longitudinal variations of E × B driftAt most 50.85% of the longitudinal variations of E × B drift are accounted for by the eastward zonal neutral wind speed onlyZonal neutral wind speed and E × B drift may be linearly correlated during fall equinox and December solsticePeer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/155994/1/jgra55709.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/155994/2/jgra55709_am.pd

Evidence for the In‐Situ Generation of Plasma Depletion Structures Over the Transition Region of Geomagnetic Low‐Mid Latitude

On a geomagnetic quiet night of October 29, 2018, we captured an observational evidence of the onset of dark band structures within the field-of-view of an all-sky airglow imager operating at 630.0 nm over a geomagnetic low-mid latitude transition region, Hanle, Leh Ladakh. Simultaneous ionosonde observations over New Delhi shows the occurrence of spread-F in the ionograms. Additionally, virtual and peak height indicate vertical upliftment in the F layer altitude and reduction in the ionospheric peak frequency were also observed when the dark band pass through the ionosonde location. All these results confirmed that the observed depletions are indeed associated with ionospheric F region plasma irregularities. The rate of total electron content index (ROTI) indicates the absence of plasma bubble activities over the equatorial/low latitude region which confirms that the observed event is a mid-latitude plasma depletion. Our calculations reveal that the growth time of the plasma depletion is ∼2 h if one considers only the Perkins instability mechanism. This is not consistent with the present observations as the plasma depletion developed within ∼25 min. By invoking possible Es layer instabilities and associated E-F region coupling, we show that the growth rate increases roughly by an order of magnitude. This strongly suggests that the Cosgrove and Tsunoda mechanism may be simultaneously operational in this case. Furthermore, it is also suggested that reduced F region flux-tube integrated conductivity in the southern part of onset region created conducive background conditions for the growth of the plasma depletion on this night