This study presents initial results of the ionospheric scintillation in the F layer using the S4 index derived from the radio occultation experiment (RO‐S4) on FORMOSAT‐7/COSMIC‐2 (F7/C2). With the ...sufficiently dense RO‐S4 observations at low latitudes, it is possible to construct hourly, global scintillation maps to monitor equatorial plasma bubbles (EPBs). The preliminary F7/C2 RO‐S4 during August 2019 to April 2020 show clear scintillation distributions around American and the Atlantic Ocean longitudes. The RO‐S4 near Jicamarca are compared with range‐time‐intensity (RTI) maps of the 50 MHz radar, and the results show that the occurrence of intense RO‐S4 in the range 0.125–0.5 are co‐located with the bottomside of the spread‐F patterns. Increases in RO‐S4 at the upward phase of bottom‐side oscillations is theoretically consistent with large‐scale wave seeding of the EPBs. The locations and occurrences of the RO‐S4 greater than 0.5 are consistent with airglows depletions from the NASA GOLD mission. Climatology analyses show that monthly occurrences of RO‐S4 > 0.5 agree well with the monthly EPB occurrences in GOLD 135.6 nm image, and show a similar longitudinal distribution to that of DMSP and C/NOFS in‐situ measurements. The results suggest that the RO‐S4 intensities can be utilized to identify EPBs of specific scales.
Plain Language Summary
The equatorial plasma bubbles (EPBs), a tropical convective space weather phenomenon, in the low‐latitude ionosphere could affect satellite communications, positioning and navigation by disrupting the radio signals transmitted from satellite to the Earth surface across them. The radio signals scintillate when transmitting through sufficiently developed EPBs; thus, the level of scintillation is related to the EPB strength. Real‐time observation is important for monitoring and forecast of the EPBs for mitigation of the radio signal scintillation. This study presents the preliminary results of the global distributions of signal scintillation for observing EPBs on an hourly basis using the low‐latitude satellite constellation equipped with Global Navigation Satellite System radio occultation receivers onboard F7/C2. The rapid observations of the EPBs provide real‐time monitoring and modeling opportunity and potential to better understanding their appearance and formation mechanism.
Key Points
This study presents early results of the FORMOSAT‐7/COSMIC‐2 RO‐S4‐index caused by equatorial plasma bubbles
There are good correlations with ground‐based ROTI, the bottomside oscillations, satellite airglow, and in‐situ observations
The RO‐S4s within 0.125–0.5 represent onset of bubbles while those above 0.5 represent mature bubbles
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
We report preliminary results of a global 3-D ionospheric electron density reanalysis demonstration study during 2002-2011 based on multisource data assimilation. The monthly global ionospheric ...electron density reanalysis has been done by assimilating the quiet days ionospheric data into a data assimilation model constructed using the International Reference Ionosphere (IRI) 2007 model and a Kalman filter technique. These data include global navigation satellite system (GNSS) observations of ionospheric total electron content (TEC) from ground-based stations, ionospheric radio occultations by CHAMP, GRACE, COSMIC, SAC-C, Metop-A, and the TerraSAR-X satellites, and Jason-1 and 2 altimeter TEC measurements. The output of the reanalysis are 3-D gridded ionospheric electron densities with temporal and spatial resolutions of 1 h in universal time, 5deg in latitude, 10deg in longitude, and approx.30 km in altitude. The climatological features of the reanalysis results, such as solar activity dependence, seasonal variations, and the global morphology of the ionosphere, agree well with those in the empirical models and observations. The global electron content derived from the international GNSS service global ionospheric maps, the observed electron density profiles from the Poker Flat Incoherent Scatter Radar during 2007-2010, and foF2 observed by the global ionosonde network during 2002-2011 are used to validate the reanalysis method. All comparisons show that the reanalysis have smaller deviations and biases than the IRI-2007 predictions. Especially after April 2006 when the six COSMIC satellites were launched, the reanalysis shows significant improvement over the IRI predictions. The obvious overestimation of the low-latitude ionospheric F region densities by the IRI model during the 23/24 solar minimum is corrected well by the reanalysis. The potential application and improvements of the reanalysis are also discussed.
Abstract
Acoustic-gravity waves are generally considered to be one of the major factors that drive changes of the total electron content in the ionosphere. However, causal mechanisms of couplings ...between sources in the lithosphere and responses in the atmosphere and the ionosphere are not fully understood, yet. A barometer in the cave of the SBCB station records an unusual phenomenon of larger amplitudes in air pressure changes inside than those at the Xinwu station (outside). Accordingly, the comparison between the recorded data at the SBCB and Xinwu station can drive investigations of potential sources of the unusual phenomenon. Analytical results of phase angle differences reveal that the air pressure outside the cave at the Xinwu station often leads air pressure changes inside at the SBCB station at relatively low frequency bands. In contrast, the larger pressure changes at frequencies > ~ 5 × 10
–4
Hz inside the cave at the SBCB station lead smaller changes outside at the Xinwu station. To expose causal mechanisms of the unusual phenomenon, continuous seismic waveforms are further conducted for examination. When the horizontal and vertical ground velocities of ground vibrations yield a difference in the phase angle close to 90°, coherence values between the air pressure changes and ground vibrations become large. This suggests that the pressure-shear vertical ground vibrations can drive air pressure changes. Meanwhile, the results shed light on investigating the existence of acoustic waves near the Earth’s surface using a partially confined space underground due to that the assumptions of the waves can propagate upward into the atmosphere driving changes in the ionosphere.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
This study examines the seasonal and interannual variation of the major migrating tidal components in midlatitude to low‐latitude total electron content (TEC) observations from the FORMOSAT‐3/COSMIC ...(Constellation Observing System for Meteorology, Ionosphere, and Climate) satellite constellation from 2007 to 2011. Although the absolute amplitudes of the TEC zonal mean and migrating tidal components show a strong positive relation to the increasing and decreasing phases of the solar cycle, the relative tidal amplitudes following normalization by maximum background values show a more varied response to solar activity levels. Features of ionospheric local time variation produced by individual migrating tidal components are consistent from year to year, with DW1 forming the equatorial daytime peak in TEC, SW2 corresponding to the generation of the equatorial ionization anomaly (EIA) crests, and TW3 contributing to the TEC trough between the EIA crests. Numerical experiments using Thermosphere‐Ionosphere‐Electrodynamics General Circulation Model (TIE‐GCM) are also performed to determine the sensitivity of the ionospheric migrating tides to upward propagating migrating tidal components from the neutral mesosphere and lower thermosphere (MLT). Zonal mean TECs decrease when MLT tidal forcing is applied and are particularly sensitive to the MLT DW1. Most of the ionospheric SW2 response is attributable to MLT SW2 forcing, enhancing the EIA crests by amplifying the equatorial fountain. TW3 in the model is generated through both in situ photoionization and nonlinear interaction between DW1 and SW2.
Key PointsIonosphere migrating tidal structure consistent in 2007‐2011 COSMIC TECs.Relation between migrating tides in MLT and ionosphere explored using TIEGCM.SW2 sensitive to MLT forcing. MLT DW1 alters zonal mean TEC seasonal variation.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
The formation of the sporadic E (Es) layer can be interpreted in several different ways, with wind shear theory and the meteor ionization mechanism being the most commonly used explanations. ...Nevertheless, neither the wind shear theory nor the meteor ionization mechanism alone can completely explain the formation of the Es layer. The meteor ionization mechanism cannot interpret the different activity in this layer between the Northern and Southern Hemispheres, while the wind shear theory cannot explain the source of the large amount of ionized particles in the Es layer. In this study, the activity in the Es layer is compared with information about meteors and the global vertical speed of ionized particles. The information about meteors is obtained from International Meteor Organization and Radio Meteor Observing Bulletin. The global vertical speed information for ionized particles is calculated using the International Geomagnetic Reference Field model, Horizontal Wind Model (HWM07), and Mass Spectrometer‐Incoherent Scatter model. The activity in the Es layer is based on the value of the irregular degree index, which is derived from the signal‐to‐noise ratio obtained from Formosa Satellite Mission‐3/Constellation Observing System for Meteorology, Ionosphere, and Climate (FORMOSAT‐3/COSMIC) Global Positioning System radio occultation mission. Taking both wind shear theory and the meteor ionization mechanism together, the source of the ionized particles in the Es layer and the difference in the activity in the Es layer between Northern and Southern Hemispheres can thus be explained more completely.
Key Points
Use two mechanisms to explain the activity of Es layer
The ID index is used for the comparison
The formation of Es layer is explained more completely
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
We examine ionospheric electron temperatures (Te) observed by HINOTORI satellite during three earthquakes; M6.6 occurred in November 1981, M7.4 and M6.6 in January 1982 over Philippine, respectively. ...It is found that Te around the epicenters significantly decreases in the afternoon periods within 5 days before and after the three earthquakes. The region of ionosphere disturbance extends to 80–120 degrees in longitude. A tendency exists that duration of the disturbance becomes longer as the increase of earthquake magnitude. F2 peak frequency, foF2 and virtual height, h'F from a chain of 4 ionosonde stations located in the longitude zone of 120°E–130°E are used together with electron density(Ne), that is observed simultaneously onboard HINOTORI satellite to find possible cause mechanisms of the abnormal reduction of electron temperatures. Behavior of HINOTORI Te/Ne and ionosonde foF2/h'F implies the existence of westward electric field over epicentre. Our finding suggests that simple two plasma instruments might be able to play a fundamental role to study ionosphere disturbance associated with earthquake, if the constellation of small/mini satellites is organized and the orbits are properly chosen.
The Weddell Sea Anomaly (WSA) is a recurrent feature of the austral summer midlatitude ionosphere where electron densities are observed to maximize during the local nighttime. In this study, tidal ...decomposition is applied to FORMOSAT‐3 (Formosa Satellite)/Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) total electron content (TEC) and electron density observations between 2007 and 2012 to quantify the components dominating local time and spatial variation in the WSA region. Our results present some of the first three‐dimensional spaceborne analyses of the WSA from a tidal perspective over multiple years. We find that the features of the WSA can be reconstructed as the result of superposition between the dominant diurnal standing (D0), eastward wave number 1 (DE1), westward wave number 2 (DW2), and stationary planetary wave 1 (SPW1) components in TECs, producing the characteristic midnight WSA peak. The D0, DE1, DW2, and SPW1 components are found to be an interannually recurring feature of the southern midlatitude to high‐latitude ionosphere during the summer, manifesting as enhancements in electron density around 300 km altitude of the summer middle to high magnetic latitudes. The phases of the aforementioned nonmigrating diurnal signatures in electron density in this region are near evanescent, suggesting in situ generation, rather than upward propagation from below. However, the SPW1 signature shows some signs of an eastward tilt with altitude, suggesting possible downward propagation. The relation of these components to possible generation via in situ photoionization or plasma transport along magnetic field lines is also discussed using results from the Ground‐to‐topside model of Atmosphere and Ionosphere for Aeronomy (GAIA) general circulation model (GCM), connecting the tidal interpretation of the WSA to previously examined generation mechanisms.
Key Points
WSA is composed of D0, DE1, DW2, and SPW1 tidal/SPW signatures
The 2007–2012 COSMIC observations show that WSA tidal/SPW components repeat annually
Examined potential WSA generation mechanisms from tidal/SPW interpretation
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
It has long been suggested that the existence of ionospheric oscillations at multiday periodicities can be explained in part, by the penetration of propagating planetary waves into the E region ...ionospheric dynamo. In this study, global‐scale observations of mesosphere and lower thermosphere (MLT) temperatures from TIMED/SABER and total electron content (TEC) results from GPS derived global ionosphere maps are examined for signs of potential upward planetary wave coupling, around the time of an intense quasi 2 day wave (QTDW) event in the MLT region during 1 December 2005 to 28 February 2006. The periodicity and zonal wave number of westward 3 (W3) and westward 2 (W2) QTDWs are resolved continuously in equatorial ionization anomaly (EIA) latitude TEC values at the same times as corresponding QTDW events in SABER temperatures. Additionally, signatures of an E1 ultrafast Kelvin (UFK) or inertia‐gravity wave with period around 60 h (2.5 d) are also resolved. While the TECs also show signs of geomagnetic activity, the coherence and consistency of the aforementioned disturbances between the MLT and the ionosphere suggest that they cannot be attributed to geomagnetic forcing. We find that such propagating planetary waves can produce transient variability of the EIAs, though the effectiveness and hemispheric symmetry of such coupling also depends on factors other than the maximum planetary wave amplitude in the MLT.
Key Points
Multiday periodicities in ionosphere that can be caused by planetary waves (PWs)
Observed PW upward coupling events using SABER MLT temperatures and GPS TECs
Period and zonal wavenumber of quasi two‐day and ultra fast Kelvin wave seen in EIAs
Historical records truthfully document human life and activities associated with climate and environmental changes. Based on the official historical records for the years 1–1911 Common Era (i.e., a ...period of 1911 years), we examine how the 408 epidemic events, occurring in 282 years, are related to solar activity, geographical locations, seasons, and natural disasters of anomalous temperature and irregular precipitation, in China. The epidemics occur more frequently during the low solar activity period. The inland area and area north to the climate boundary of Qinling–Huaihe Line along 35° geographic latitude, in particular, suffer epidemics more often during low solar activity periods. In fact, 45% or more epidemics occurred in summer, while less than 9% occurred in winter. The infection is highly related to social distancing, and therefore the epidemics also occur likely in areas with high-density population or heavy traffic. Statistical tests further demonstrate that natural disasters owing to anomalous temperature and irregular precipitation act as mediators which significantly cause the epidemics in ancient China.
Tsunami ionospheric disturbances (TIDs) of the 26 December 2004 Mw 9.3 Sumatra earthquake are detected by the total electron content (TEC) of ground‐based receivers of the global positioning system ...(GPS) in the Indian Ocean area. It is found that the tsunami waves triggered atmospheric disturbances near the sea surface, which then traveled upward with an average velocity of about 730 m/s (2700 km/hr) into the ionosphere and significantly disturbed the electron density within it. Results further show that the TIDs, which have maximum height of about 8.6–17.2 km, periods of 10–20 min, and horizontal wavelengths of 120–240 km, travel away from the epicenter with an average horizontal speed of about 700 km/hr (190 m/s) in the ionosphere.
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