Equatorial plasma bubbles (EPBs) can cause rapid fluctuations in amplitude and phase of radio signals traversing the ionosphere and in turn produce serious ionospheric scintillations and disrupt ...satellite-based communication links. Whereas numerous studies on the generation and evolution of EPBs have been performed, the prediction of EPB and ionospheric scintillation occurrences still remains unresolved. The generalized Rayleigh–Taylor (R–T) instability has been widely accepted as the physical mechanism responsible for the generation of EPBs. But how the factors, which seed the development of R–T instability and control the dynamics of EPBs and resultant ionospheric scintillations, change on a short-term basis are not clear. In the East and Southeast Asia, there exist significant differences in the generation rates of EPBs at closely located stations, for example, Kototabang (0.2°S, 100.3°E) and Sanya (18.3°N, 109.6°E), indicating that the decorrelation distance of EPB generation is small (hundreds of kilometers) in longitude. In contrast, after the initial generation of EPBs at one longitude, they can drift zonally more than 2000 km and extend from the magnetic equator to middle latitudes of 40° or higher under some conditions. These features make it difficult to identify the possible seeding sources for the EPBs and to accurately predict their occurrence, especially when the onset locations of EPBs are far outside the observation sector. This paper presents a review on the current knowledge of EPBs and ionospheric scintillations in the East and Southeast Asia, including their generation mechanism and occurrence morphology, and discusses some unresolved issues related to their short-term forecasting, including (1) what factors control the generation of EPBs, its day-to-day variability and storm-time behavior, (2) what factors control the evolution and lifetime of EPBs, and (3) how to accurately determine ionospheric scintillation from EPB measurements. Special focus is given to the whole process of the EPB generation, development and disruption. The current observing capabilities, future new facilities and campaign observations in the East and Southeast Asia in helping to better understand the short-term variability of EPBs and ionospheric scintillations are outlined.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Global Navigation Satellite System (GNSS) radio occultation (RO) has been an active method to explore the earth’s atmosphere since 1995. RO-inverted bending angles have significantly contributed to ...atmospheric weather and climate research via data assimilation. However, the used bending angles still contain residual ionospheric error (RIE) after the well-known linear combination correction and should be removed. In this study, we propose to calibrate the RIE using ray-tracing RO bending angle profiles for the first time. The ionospheric background used for ray-tracing was obtained by a Kalman filter data assimilation algorithm through ingesting multisource ionospheric data. More than 380,000 COSMIC RO events during 2008–2013 were simulated via the EGOPS software for statistical calibration. To evaluate the improving performance, we focus on analyzing the deviation of the bending angle from that of National Center for Atmospheric Research climatology results between 60 and 80 km before and after the calibration. It is found that the amplitude of RIE during daytime is significantly reduced. The ‘three troughs’ feature of RIE due to the ionosphere is almost eliminated. The solar activity dependence of RIE can also be calibrated to some extent. We further define a parameter named calibration efficiency to evaluate the calibration performance of the method is > 40% at low latitudes and > 80% at the ‘three troughs’ regions. The results demonstrate that our calibration method works well. It could be potentially used to reduce the RIE in GNSS RO bending angles.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
It is commonly believed that solar eclipses have a great impact on the ionosphere‐thermosphere (I‐T) system within the eclipse shadow, but little attention has been paid to the global response to ...these events. In this study, we investigate the global upper atmospheric responses to the recent Great American Solar Eclipse that occurred on 21 August 2017 using a high‐resolution coupled ionosphere‐thermosphere‐electrodynamics model. The simulation results show that the ionosphere and thermosphere response to the eclipse is not just local but global. Large‐scale traveling atmospheric disturbances (TADs), seen in the thermospheric temperature and winds, were triggered from the eclipse region and propagated in a southeast direction when the eclipse ended. A large total electron content (TEC) enhancement occurred over South America after the eclipse was over. The TEC enhancement was primarily the result of transport by the thermospheric wind perturbations associated with the eclipse‐induced TADs. The perturbations of TEC, neutral temperature, and winds exhibited asymmetric distributions with respect to the totality path during the solar eclipse. Furthermore, ionospheric electrodynamic processes also play an important role in the global responses of the I‐T system to the solar eclipse. Unlike the case of large‐scale TADs propagating from the eclipse region to other locations in the globe, the ionospheric electric fields and plasma drifts began to show significant perturbations even during the local pre‐eclipse period when local wind and temperature had not been perturbed. This is related to the instantaneous global response of the ionospheric current system to changes in the ionospheric conductivity and winds in the eclipse region.
Plain Language Summary
The ionosphere is a region at about 60–1,000 km, where the upper atmosphere includes the layers of the mesosphere and thermosphere and the neutral gas is partially ionized by the solar irradiation. During the solar eclipse, the ionosphere‐thermosphere (I‐T) system within the Moon's shadow can be greatly changed by the reduction of solar flux and energy input. However, little attention has been paid to the global I‐T responses. High‐resolution simulations of the 21 August 2017 solar eclipse provide us new insight that the I‐T response to the eclipse is not just local but global. Eclipse passage generated global perturbations of the ionosphere and thermosphere through dynamic and electrodynamic processes.
Key Points
The solar eclipse caused thermospheric and ionospheric changes over the entire globe
Large‐scale TADs were triggered by the eclipse and caused TEC enhancements over South America after the eclipse
Ionospheric plasma drifts strongly responded to the solar eclipse due to global wind and electrodynamics coupling
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
On 12 May 2008 at 0628 UT a major earthquake Ms = 8.0 struck Wenchuan County (31.0°N, 103.4°E) in southwest China. The maximum ionospheric electron density at F2 peak (NmF2) recorded an unusual large ...enhancement during the afternoon‐sunset sector by the Chinese ionosondes over Wuhan (30.5°N, 114.4°E) and Xiamen (24.4°N, 123.9°E), which are close to the earthquake epicenter. An averaged increase at these two stations is about 2 times on a geomagnetic quiet day, 9 May (Kp ≤ 2), 3 days prior to the earthquake, relative to the median value of 1–12 May, whereas the increase was much less significant over Yamagawa (31.2°N, 130.6°E) and Okinawa (26.7°N, 128.2°E) in Japan. Combining the data from the network of 58 global positioning system receivers around China and the global ionospheric map, the variations of the total electron content reveal the region where enhancement persisted for a long period to be within longitudes 90°–130°E. Our results suggest that this abnormal enhancement is most possibly a seismo‐ionospheric signature.
Since Roble and Dickinson (1989), who drew the community's attention about the greenhouse gas effect on the ionosphere, huge efforts have been implemented on ionospheric climate study. However, ...direct comparison between observations and simulations is still rare. Recently, the Wuhan ionosonde observations were digitized and standardized through unified method back to 1947. In this study, the NCAR‐TIEGCM was driven by Mauna Loa Observatory observed CO2 level and International Geomagnetic Reference Field (IGRF) geomagnetic field to simulate their effects on ionospheric long‐term trend over Wuhan. Only March equinox was considered in both data analysis and simulation. Simulation results show that the CO2 and geomagnetic field have comparable effect on hmF2 trend, while geomagnetic field effect is stronger than CO2 on foF2 trend over Wuhan. Both factors result in obvious but different diurnal variations of foF2/hmF2 long‐term trends. The geomagnetic field effect is nonlinear versus years since the long‐term variation of geomagnetic field intensity and orientation is complex. Mean value of foF2 and hmF2 trend is (−0.0021 MHz/yr, −0.106 km/yr) and (−0.0022 MHz/yr, −0.0763 km/yr) for observation and simulation, respectively. Regarding the diurnal variation of the trend, the simulation accords well with that of observation except hmF2 results around 12 UT. Overall, good agreement between observation and simulation illustrates the good quality of Wuhan ionosonde long‐term data and the validity of ancient ionosphere reconstruction based on realistic indices driving simulation.
Key Points
Ionospheric foF2/hmF2 over Wuhan show negative long‐term trend with diurnal variation using ANN method based on 70 years' observations
NCAR‐TIEGCM simulations driven by realistic CO2 level and geomagnetic field show generally good agreement with observations over Wuhan
CO2 and geomagnetic field have comparable effect on hmF2 trend, while geomagnetic field effect is stronger than CO2 on foF2 trend over Wuhan
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
The Earth’s magnetosphere is the outermost layer of the geospace system deflecting energetic charged particles from the Sun and solar wind. The solar wind has major impacts on the Earth’s ...magnetosphere, but it is unclear whether the same holds for solar flares—a sudden eruption of electromagnetic radiation on the Sun. Here we use a recently developed whole geospace model combined with observational data from the 6 September 2017 X9.3 solar flare event to reveal solar flare effects on magnetospheric dynamics and on the electrodynamic coupling between the magnetosphere and its adjacent ionosphere, the ionized part of Earth’s upper atmosphere. We observe a rapid and large increase in flare-induced photoionization of the polar ionospheric E-region at altitudes between 90 km and 150 km. This reduces the efficiency of mechanical energy conversion in the dayside solar wind–magnetosphere interaction, resulting in less Joule heating of the Earth’s upper atmosphere, a reconfiguration of magnetosphere convection, as well as changes in dayside and nightside auroral precipitation. This work thus demonstrates that solar flare effects extend throughout the geospace via electrodynamic coupling, and are not limited—as previously believed—to the atmospheric region where radiation energy is absorbed1.The solar wind affects the magnetosphere, but whether this holds true for solar flares was unclear. By combining geospace modelling with observations, solar flares are shown to influence the dynamics of the magnetosphere and its ionosphere coupling.
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GEOZS, IJS, IMTLJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBMB, UL, UM, UPUK, ZAGLJ
In this study, we studied the ionospheric responses to solar flares during 1999–2006 by using GOES 0.1–0.8 nm X‐ray, 26–34 nm EUV, and GPS/total electron content (TEC). The solar zenith angle (SZA) ...dependence was quantitatively investigated by analyzing global TEC enhancements during about 100 X‐class flares. The mean ratio of ΔTEC at SZA = 90° to ΔTEC at SZA = 0° is about 0.39. The statistical results show that a limb flare has less effect on the ionosphere than a central flare does because the main ionization source of the ionosphere, solar EUV radiation, can be absorbed by thick solar gas due to large central meridian distance (CMD), which is called the CMD effect. Furthermore, the CMD effect decreases with decreasing flare X‐ray class. The results show that TEC responses are not highly related to solar X‐ray flux enhancement with correlation coefficient of 0.6, but more closely related to solar EUV flux enhancement with correlation coefficient of 0.91 for 26–34 nm EUV. The combination of X‐ray flux and flare location is also a good indicator for TEC response: The correlation coefficient of ∆X‐ray*cos(CMD) and ∆TEC is as high as 0.95. The seasonal dependence in TEC response is also investigated. There are larger responses in equinoxes than in solstices. The seasonal variation of neutral density is considered to be a main cause of the season dependence of TEC response.
Key Points
The solar zenith angle dependence was quantitatively investigated
Flare location effect decreases with decreasing solar flare class
Statistically analyzed the seasonal dependence of TEC responses
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) electron density profiles are used to investigate the nighttime midlatitude ionospheric trough (MIT). We find that at ...midnight the longitudinally deepest MIT occurs to the west of the geomagnetic pole in both the Northern and Southern Hemispheres during the equinox seasons and local summer. The deepest MIT could be ascribable to the enhanced depletion caused by horizontal neutral wind. In the early evening, the eastward neutral wind prevails in the midlatitude F region, which blows the plasma downward where the declination is eastward in the Northern Hemisphere but westward in the Southern Hemisphere, both lying to the west of the geomagnetic pole. The downward drift would enhance the plasma depletion for more molecular composition at lower altitude. In addition, we find for the first time that the location of nighttime MIT minimum oscillated with a periodicity of 9 days and an amplitude of about 1°–1.5° geomagnetic latitude during 2007–2008, associated with the recurrent high‐speed solar wind. Our results shed new light on the empirical description and numerical simulation of MIT.
Key Points
Deepest MIT occurs to the west of the geomagnetic pole in the N and S Hemispheres
The deepest MIT could be ascribed to the enhanced depletion by horizontal wind
MIT is found to oscillate periodically at 9 days about 2 to 3 deg from peak to peak
Scientific attention has recently been focused on the coupling of the earth＇s upper atmosphere and ionosphere. In the present work, we review the advances in this field, emphasizing the studies and ...contributions of Chinese scholars. This work first in- troduces new developments in the observation instruments of the upper atmosphere. Two kinds of instruments are involved： optical instruments （lidars, FP interferometers and all-sky airglow imagers） and radio instruments （MST radars and all-sky meteor radars）, Based on the data from these instruments and satellites, the researches on climatology and wave disturbances in the upper atmosphere are then introduced. The studies on both the sporadic sodium layer and sporadic E-layer are presented as the main works concerning the coupling of the upper atmosphere and the low ionosphere. We then review the investigations on the ionospheric longitudinal structure and the causative atmospheric non-migrating tide as the main progress of the coupling between the atmosphere and the ionospheric F2-region. Regarding the ionosphere-thermosphere coupling, we introduce studies on the equatorial thermospheric anomaly, as well as the influence of the thermospheric winds and gravity waves to the iono- spheric F2-region. Chinese scholars have made much advancement on the coupling of the ionosphere and upper atmosphere, including the observation instruments, data precession, and modeling, as well as the mechanism analysis.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OBVAL, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
In this letter, we present multisatellite observations of the evolution of subauroral polarization streams (SAPS) during intense storms (ISs) and quiet time substorms (QSs). SAPS occurred during 37 ...ISs and 30 QSs were analyzed. Generally, SAPS occur after the southward turning of the interplanetary magnetic field (IMF) with time lags of 0–1.5 h for ISs and 0–2.5 h for QSs. SAPS usually occurred 0–3 h after the beginning of storm main phases and 0–2 h after the substorm expansion onsets. The lifetimes of SAPS are generally longer than the durations of southward IMF and storm main phases. During QSs, the lifetimes of SAPS are shorter than the duration of the ISs. Superposed epoch analysis shows different evolution patterns of SAPS during ISs and QSs. The results of this study provide both physical insight and constrains to modeling the magnetosphere‐ionosphere‐thermosphere coupling.
Key Points
The generation and evolution of the SAPS are closely related to southward IMF
The lifetime of the SAPS is linearly correlated with the duration of southward IMF
The SAPS exhibit different evolution pattern during intense storms and quiet time substorms
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
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