State Key Laboratory of Space Weather

We examine and simulate the electron radiation belt dropout event on 9 October 1990. CRRES observations show that significant depletions of electron fluxes occurred at energies similar to 0.1- 1.0 MeV beyond 6 R-E and at energies >similar to 0.4 MeV within 6 R-E. The three- dimensional kinetic radiation belt model STEERB is used to simulate this dropout event, taking into account the magnetopause shadowing, adiabatic transport, radial diffusion, and plume and chorus wave- particle interactions. Our results show that STEERB code can basically reproduce the observed depletion of similar to 0.1-1.0 MeV electron fluxes throughout the outer radiation belt, suggesting that the competition and combination of all these physical mechanisms can well explain this electron radiation belt dropout event. Citation: Su, Z., F. Xiao, H. Zheng, and S. Wang (2011), CRRES observation and STEERB simulation of the 9 October 1990 electron radiation belt dropout event, Geophys. Res. Lett., 38, L06106, doi: 10.1029/2011GL046873.

Abstract Based on high‐resolution measurements from NASA's Magnetospheric Multiscale mission, we present the dynamics of electrons associated with current systems observed near the diffusion region of magnetic reconnection at Earth's magnetopause. Using pitch angle distributions (PAD) and magnetic curvature analysis, we demonstrate the occurrence of electron scattering in the curved magnetic field of the diffusion region down to energies of 20 eV. We show that scattering occurs closer to the current sheet as the electron energy decreases. The scattering of inflowing electrons, associated with field‐aligned electrostatic potentials and Hall currents, produces a new population of scattered electrons with broader PAD which bounce back and forth in the exhaust. Except at the center of the diffusion region the two populations are collocated and appear to behave adiabatically: the inflowing electron PAD focuses inward (toward lower magnetic field), while the bouncing population PAD gradually peaks at 90° away from the center (where it mirrors owing to higher magnetic field and probable field‐aligned potentials).

A coupled magnetosphere ionosphere thermosphere (CMIT 2.0) model has been developed. It is capable of self‐consistently calculating global ionospheric electric fields that include the imposed magnetospheric convection field, neutral wind dynamo and penetration electric fields. The CMIT 2.0 simulated ionospheric F2 region ion vertical drift velocities at the magnetic equator were compared with those measured by ground‐based instruments during the April 2–5, 2004, storm. CMIT 2.0 captured the temporal variations seen in the measurements during both the quiet and active periods. These temporal variations corresponded mainly to the variations in the high latitude electric fields driven by changes in solar wind conditions. CMIT 2.0, however, overestimated the magnitudes of the variations of the vertical drifts. In addition, CMIT 2.0 simulated the observed pre‐reversal enhancement well. This enhancement was driven mostly by the neutral wind dynamo.

On 14 June 2007, four Time History of Events and Macroscale Interactions during Substorms spacecraft observed a flux transfer event (FTE) on the dayside magnetopause, which has been previously proved to be generated by multiple, sequential X‐line reconnection (MSXR) in a 2‐D context. This paper reports a further study of the MSXR event to show the 3‐D viewpoint based on additional measurements. The 3‐D structure of the FTE flux rope across the magnetospheric boundary is obtained on the basis of multipoint measurements taken on both sides of the magnetopause. The flux rope's azimuthally extended section is found to lie approximately on the magnetopause surface and parallel to the X‐line direction; while the axis of the magnetospheric branch is essentially along the local unperturbed magnetospheric field lines. In the central region of the flux rope, as distinct from the traditional viewpoint, we find from the electron distributions that two types of magnetic field topology coexist: opened magnetic field lines connecting the magnetosphere and the magnetosheath and closed field lines connecting the Southern and Northern hemispheres. We confirm, therefore, for the first time, the characteristic feature of the 3‐D reconnected magnetic flux rope, formed through MSXR, through a determination of the field topology and the plasma distributions within the flux rope. Knowledge of the complex geometry of FTE flux ropes will improve our understanding of solar wind‐magnetosphere interaction.

[1] Cluster CIS ion spectrograms measured during the period of the recent solar minimum between April 2007 and June 2009, when Cluster was deep in the radiation belts with its perigee as close as L = 2, are analyzed. The analysis is complemented by Double Star TC-1 satellite data from HIA ion spectrograms on perigee passes during the period of May 15, 2007 to September 28, 2007. We demonstrate how the background counts produced by energetic particles of the radiation belts in Cluster CIS and Double Star HIA instruments can be interpreted to obtain the locations of the boundaries of the outer and inner belts. The obtained L-MLT distribution of boundaries reflects the general structure of the radiation belts. Closer examination of the time-dependent L locations of the boundaries reveals several dips to lower L-shells (from L = 6 to L = 4) in the outer boundary location. The importance of the solar wind pressure increases for the Earthward shift of the outer boundary of the outer belt is discussed. The location and thickness of the slot region are studied using the determined inner boundaries of the outer belt and the outer boundaries of the inner belt. It was found that during intervals of low activity in the solar wind parameters, the slot region widens, which is consistent with weaker inward radial diffusion, and also with weaker local acceleration that can occur only at higher L-shells outside the plasmasphere. We conclude that boundaries of radiation belts determined from background measurements on the instruments with energy ranges that do not cover the radiation belts' energies provide valuable additional information that is useful for radiation belts' model development and validation.

Abstract. LFEW is a low frequency electromagnetic wave detector mounted on TC-2, which can measure the magnetic fluctuation of low frequency electromagnetic waves. The frequency range is 8 Hz to 10 kHz. LFEW comprises a boom-mounted, three-axis search coil magnetometer, a preamplifier and an electronics box that houses a Digital Spectrum Analyzer. LFEW was calibrated at Chambon-la-Forêt in France. The ground calibration results show that the performance of LFEW is similar to that of STAFF on TC-1. The first results of LFEW show that it works normally on board, and that the AC magnetic interference of the satellite platform is very small. In the plasmasphere, LFEW observed the ion cyclotron waves. During the geomagnetic storm on 8 November 2004, LFEW observed a wave burst associated with the oxygen ion cyclotron waves. This observation shows that during geomagnetic storms, the oxygen ions are very active in the inner magnetosphere. Outside the plasmasphere, LFEW observed the chorus on 3 November 2004. LFEW also observed the plasmaspheric hiss and mid-latitude hiss both in the Southern Hemisphere and Northern Hemisphere on 8 November 2004. The hiss in the Southern Hemisphere may be the reflected waves of the hiss in the Northern Hemisphere.

Abstract Geomagnetic storms affect Earth in various severe ways, including damaging satellites, disrupting power grids, and inducing prompt penetration electric fields (PPEF) through Joule heating in the auroral region. They also cause disturbance dynamo electric fields (DDEF), generate or suppress equatorial plasma bubbles (EPBs), and lead to other significant effects. The extreme geomagnetic storm on 10 May 2024, altered the dynamics of the ionosphere. The ionospheric response was investigated in this study. Our methodology utilized a combined data set, including GNSS receivers in the Latin American sector, and data from ionosondes in São Luis (SALU) and Cachoeira Paulista (CHPI). CHPI also features a Fabry‐Pérot interferometer (FPI) and an All‐Sky Imager (ASI). Super EPB was observed in the American sector. This structure drifted westward at a velocity of ∼140 m/s and had a large latitudinal extension, reaching about 36° geomagnetic latitude, this corresponds to an apex height of around 4,500 km. The depletion lasted for a long duration of 12 hr, from 22:30 to 10:30 UT. The geomagnetic storm caused a super fountain effect, propelling plasma from the equator to a distance of ∼35° latitude, and depositing high‐density plasma on the crest of the equatorial ionization anomaly (EIA).

Since early 2004 the Chinese spacecraft Tan Ce 1 (TC‐1), first component of the Double Star (DSP) mission, has been on an equatorial elliptical orbit (13.4 RE apogee), allowing the study of the dynamics of the Earth's magnetosphere in conjunction with the four European Cluster spacecraft (19.6 RE apogee). The Cluster and Double Star spacecraft orbits are such that the spacecraft are almost in the same meridian, allowing conjugate studies. The four Cluster spacecraft highly eccentric polar orbit at 4 RE perigee permits them to sample the ring current, the radiation belts, and the outer plasmasphere from south to north, almost following the same magnetic flux tube (latitudinal profile), whereas TC‐1, with its very low‐perigee equatorial orbit, gives the plasma profile across L shells. Coordinated ion measurements provided by the Cluster Ion Spectrometry and Hot Ion Analyzer instruments onboard Cluster and TC‐1, respectively, obtained during quiet conditions, disturbed geomagnetic conditions, and an intense storm, are used to analyze crossings of the plasmasphere and the ring current region. Multiple narrow ion energy bands (“nose‐like” structures) are simultaneously observed by both Cluster and TC‐1. These observations reveal the large‐scale character of these structures and pose a challenge for the simulation and modeling of the inner magnetosphere populations.

[1] The long-term temperature profile data sets obtained by Rayleigh lidars at three different northern latitudes within the Network for the Detection of Atmospheric Composition Change were used to derive the middle atmosphere temperature trend and response to the 11 year solar cycle. The lidars were located at the Mauna Loa Observatory, Hawaii (MLO, 19.5°N); the Table Mountain Facility, California (TMF, 34.4°N); and the Observatoire de Haute Provence, France (OHP, 43.9°N). A stratospheric cooling trend of 2–3 K/decade was found for both TMF and OHP, and a trend of ≤0.5 ± 0.5 K/decade was found at MLO. In the mesosphere, the trend at TMF (3–4 K/decade) was much larger than that at both OHP and MLO (<1 K/decade). The lidar trends agree well with earlier satellite and rocketsonde trends in the stratosphere, but a substantial discrepancy was found in the mesosphere. The cooling trend in the upper stratosphere at OHP during 1981–1994 (∼2–3 K/decade) was much larger than that during 1995–2009 (≤0.8 K/decade), coincident with the slightly increasing upper stratospheric ozone density after 1995. Significant temperature response to the 11 year solar cycle was found. The correlation was positive in both the stratosphere and mesosphere at MLO and TMF. At OHP a wintertime negative response in the upper stratosphere and a positive response in the middle mesosphere were observed during 1981–1994, but the opposite behavior was found during 1995–2009. This behavior may not be a direct solar cycle response at all but is likely related to an apparent response to decadal variability (e.g., volcanoes, modulated random occurrence of sudden stratospheric warmings) that is more complex.

Abstract This study analyzes strong sporadic E layer (Es) formation in Boa Vista (BV, 2.8°N, 60.7°W, dip: 18°), a low‐latitude region in the Brazilian sector, which occurred far after the onset of a magnetic storm recovery phase. Such occurrences were observed during seven magnetic storms with available data for BV. Thus, the ionospheric behavior on days around the magnetic storm that occurred on 20 January 2016 was investigated to search for possible explanations. This analysis indicated that the probable mechanism acting during the Es layer strengthening is the zonal westward electric field caused by a disturbance dynamo. The same evidence was also observed in two other magnetic storms at the same location. Hence, a numerical model of the E region dynamics, called MIRE (Portuguese acronym for E Region Ionospheric Model), was used to confirm whether the disturbance dynamo could cause the Es layer intensification. The inputs for the model were the electric field deduced from the vertical drift and the wind components provided by GSWM‐00 model. The simulations indicate that the Es layer density is significantly enhanced when the zonal electric field is present compared to the reference scenario with only the winds. Therefore, it is concluded that the disturbance dynamo electric field is the likely cause of the strong Es layers in the analyzed cases. Finally, the combined results from the model and observational data seem to contribute significantly to advance our understanding of the role of the electric fields in the Es layer formation at low latitudes.

Energetic particles found in planetary magnetospheres and other plasmas often display a power law and an anisotropy (including loss cone and temperature anisotropy). In a recent study, a full relativistic kappa-loss cone (KLC) distribution f κ L is initially introduced to model energetic particles, but f κ L is only associated with loss cone anisotropy. We extend this previous study and develop a generalized relativistic kappa-type (KT) distribution f κ T which incorporates either temperature anisotropy or both loss cone and temperature anisotropy. We carry out numerical calculations for a direct comparison between the new KT distribution, the previous KLC distribution and the kappa distribution f κ , respectively. We find that (a) analogous to f κ L , f κ T satisfies the power law not only at lower energies but also at relativistic energies; (b) analogous to f κ , f κ T contains either temperature anisotropy or both loss cone and temperature anisotropy; (c) the regular kappa distribution is found to decrease faster than the KT distribution with kinetic energy E k especially when θ 2 increases (where θ 2 is the thermal characteristic parameter), e.g. f κ / f κ T ≲ 10 −2 for E k ≳ 2.0 MeV and θ 2 ≳ 0.3; (d) no big difference occurs between both KT and kappa distributions through energies up to ∼500 keV for θ 2 ≲ 0.03 and (e) the three distributions show different anisotropy behaviors even for the same overall anisotropy. The results suggest that the new generalized KT distribution may be applied in space plasmas and other plasmas including laboratory machines where highly energetic particles exist.

Abstract Ionospheric irregularities as plasma bubbles occur in the ionosphere, and generally, they are characterized by the low plasma density regions. The Rate Of TEC Index (ROTI) was defined in terms of the Total Electron Content (TEC) variation and is used to characterize these plasma bubbles. It is essential to evaluate the ROTI behavior since the ionospheric irregularities can cause fluctuations in the radio signal, interfering in the ionospheric data analysis. Therefore, we performed in this work a comparative study of five different methods available to calculate the ROTI to evaluate the most suitable over the Brazilian region. The ROTI was calculated over three GNSS stations at different latitudes: São Luís (SALU, 2°31′S, 44°16′W; dip: −3.8°), Cachoeira Paulista (CHPI, 22°40'S, 44°59'W; dip: −36.4°), and Santa Maria (SMAR, 29°41′S, 53°48′W, dip: −37°). The results show that the most viable method for calculating ROTI in the Brazilian region is based on the Slant TEC equation as defined by Cherniak et al. (2018), https://doi.org/10.1007/s10291‐018‐0730‐1 . Our results are supported by the comparison between the ROTI with TEC maps, ionograms collected at Fortaleza (FZA0M, 3°43'S, 38°32'W, dip: −15.8°), SALU, and CHPI and All‐Sky imagers collected at the São João do Cariri (SJCA, 7°23'S, 36°31'W, dip: −11°) and CHPI. Additionally, we observe Equatorial Plasma Bubbles (EPBs) in the Brazilian region using the ROTI index map.

Abstract During disturbed periods, E region electric fields can cause anomalous Es layer behavior, which is observed in the digital ionosonde data. To investigate the influence of these electric fields in the Es layer development, we analyzed a set of 20 magnetic storms from 2015 to 2018 over Boa Vista (BV, 2.8°N, 60.7°W, dip ∼18°), São Luís (SLZ, 2.3°S, 44.2°W, dip ∼8°), and Cachoeira Paulista (CXP, 22.41°S, 45°W, dip ∼35°). The electric field zonal components during the main and recovery phases of each magnetic storm are computed to study the corresponding characteristics of these Es seen in ionograms. Additionally, a numerical model (MIRE, Portuguese acronym for E Region Ionospheric Model) is used to analyze the Es layer dynamics modification around disturbed times. Using observation data and simulations, we were able to establish a threshold value for the electric field intensity for each region that can affect the Es layer formation. The results sustain that the strong Es layer in BV can be an indicator of the disturbed dynamo event. At SLZ, on the other hand, the Es layers are affected by the competition mechanisms of their formation, as equatorial electrojet irregularities and winds, during the main phase of the magnetic storm. Over CXP, the Es layer dynamics are dominated by the wind shear mechanism. Finally, this study provides new insights into the real impact of the electric field in the Es layer development over the Brazilian sector. Thus, our results lead to a better understanding of the underlying mechanisms related to the Es layer formation and dynamics.

Two case studies are performed to investigate substorm timing and activations based on Double Star TC1, Cluster, Polar, IMAGE, LANL geostationary satellites and ground‐based geomagnetic field measurements. In both events, an earthward flow associated with plasma sheet thinning is measured by Cluster 8–10 min ahead of the auroral breakup. A couple of minutes after the breakup, either TC1 at ∼X‐10 R E first detects plasma sheet expansion and then the LANL satellites near the midnight measure energetic electron injections at geostationary orbit or the LANL satellites first measure the electron injections and then TC1 detects the plasma sheet expansion. More than about 20 min later, Cluster at X∼16 R E and Polar (at higher latitude) successively observe plasma sheet expansion. The open magnetic flux of the polar cap, Ψ, is found to continually increase during the early substorm phase and then to rapidly fall when the IMF turns northward. When Ψ reaches its minimum value, bright and broad auroral activities start to decrease. Tailward progression of the magnetic dipolarization and a poleward expansion of auroral bulges are shown to closely map to one another. These results suggest that substorm activations start in the midtail before ground onset and then move earthward, which leads to an expansion onset in the near‐Earth tail around X∼ ‐(8–9) R E . After onset, the activations progress both earthward and tailward. Substorm onset is possibly related to plasma sheet reconnection of close field lines, while tail lobe reconnection of open field lines release more energy to support the full expansion of the substorm. In a fully developed expansion phase, an initial dipolarization in the near‐Earth may eventually evolve to enable disruption of the cross‐tail current over a wide region of the magnetotail.

Abstract Sporadic‐E (Es) layers are investigated over five Digisonde stations located inside (Santa Maria and Cachoeira Paulista), boundary (São Luís), and outside (Millstone Hill and Port Stanley) the South American Magnetic Anomaly (SAMA) in the course of the 25 August 2018, geomagnetic storm. Data from Digisondes and ground‐based magnetometer and a numerical model of the E‐region (MIRE) are analyzed to search the roles of neutral winds and electric fields as physical processes responsible for the generation of Es layers. Moreover, it is observed for the first time over Santa Maria a type of Es layer that resembles the Esa detected in the auroral region. The characterization of such signatures in ionograms and the investigations of its formation mechanism are the main focus of this study. Hiss waves activities detected by the Van Allen Probe‐B data provide evidence that energetic particle precipitations are the most likely process responsible for this type of Es layer inside the SAMA in the night hours during the geomagnetic storm recovery phase. An attempt is also made to explain the presence of Esq over São Luís in terms of the expansion of the Equatorial Electrojet to higher latitudes. Finally, the results bring a new observational and modeling indication of a concomitant action of multiple formation mechanisms in the Es layers development in the American sector during the 25 August 2018, geomagnetic storm.

Abstract. The spatial distribution and source-region size of chorus waves are important parameters for understanding their generation. In this work, we analyze over 3 years of continuous wave burst-mode data from the Van Allen Probes mission and build a data set of rising-tone and falling-tone chorus waves. For the L shell range covered by Van Allen Probes data (3.5≤L≤7), statistical results demonstrate that the sector where rising tones are most likely to be observed is the dayside during geomagnetically quiet and moderate times and the dawn side during active times. Moreover, rising-tone chorus waves have a higher occurrence rate near the equatorial plane, while the falling-tone chorus waves have a higher possibility to be observed at lower L shell and higher magnetic latitudes. By analyzing the direction of the Poynting wave vector, we statistically investigate the chorus source-region size along a field line, and compare the results with previous theoretical estimates. Our analysis confirms previous conclusions that both rising-tone and falling-tone chorus waves are generated near the equatorial plane, and shows that previous theoretical estimates roughly agree with the observation within a factor of 2. Our results provide important insights into further understanding of chorus generation.

On 10–11 September 2006 the Venus Express magnetometer detected a very strong Interplanetary Coronal Mass Ejection (ICME) event with an average field about 2 times higher than that of a typical ICME at 0.72 AU. While the effective obstacle to the solar wind is compressed to a smaller dimension during this ICME event, the bow shock is located far upstream of its nominal location. The observed shocks are weak and appear very dynamic. The location of the shock crossing can be found all along the Venus Express trajectory, which has an apocenter of 12 RV. We attribute the atypical distant bow shock location as an effect of the extremely low Mach number during the ICME.

Abstract Mesospheric winds have been measured by meteor radar at Cachoeira Paulista (22.7°S; 45°W) since April 1999. The tidal components were analyzed over about 21 years of available data exhibiting an annual and semi‐annual variation. Amplitudes of meridional diurnal (semidiurnal) tide are on averaged 30% (28%) and the zonal ones are 14% (20%) stronger at solar minimum than at solar maximum. The anticorrelation between F10.7 cm solar flux and amplitudes of the semiannual oscillation of diurnal and semidiurnal tides is presented. Additionally, the sporadic E (Es) layers occurrence has an anti‐correlation with solar activity due to the tidal wind variation. A discussion about the physical mechanism is performed in terms of the particle precipitation during High‐Speed Stream (HSS) events according to the solar cycle. Finally, a superposed epoch analysis of the tidal amplitudes during the HSS events in 2018 is presented. And a slight increase in all tidal components is seen when the structure reached the Earth and in the following days showing that indeed the electron precipitation during HSS events affect the tidal amplitudes.

A case study is presented to reveal the detailed process of the ionospheric responses to disturbances in the lower atmosphere when a strong typhoon lands or approaches the mainland. The ionospheric HF Doppler shift data during the periods of two strong typhoons which occurred in 1988 and 1990 respectively are analyzed in detail. The results show that except the appearance of significant wave-like disturbances (in general, medium-scale acoustic-gravity waves AGWs) in the ionosphere there are some new phenomena worth noticing: the temporal evolution of these waves in the two cases show clearly the change of both the main frequency and amplitude, the frequency was getting lower and lower as time elapses, and the amplitude enhanced gradually. After sunset, Spread-F phenomena appeared, showing the role of seeding of the AGWs for exciting of ionospheric irregularities. A comparison is made of the above phenomena with the linear theory of TIDs propagation and also with a nonlinear numerical simulation of the dynamic features of AGWs propagation in the atmosphere. All these results are in good agreement and the main features of ionospheric response to typhoon were thus explained.

Abstract The paper presents the effects of the storm‐time prompt penetration electric fields (PPEF) and traveling atmospheric disturbances (TADs) on the total electron content (TEC), foF2 and hmF2 in the American sector (north and south) during the geomagnetic storm on 23–24 April 2023. The data show a poleward shift of the Equatorial Ionization Anomaly (EIA) crests to 18°N and 20°S in the evening of 23 April (attributed to eastward PPEF) and the EIA crests remaining almost in the same latitudes after the PPEF reversed westward. The thermospheric neutral wind velocity, foF2, hmF2, and TEC variations show that TADs from the northern and southern high latitudes propagating equatorward and crossing the equator after midnight on 23 April. The meridional keograms of ΔTEC show the TAD structures in the north/south propagated with phase velocity 470/485 m/s, wave length 4,095/4,016 km and period 2.42/2.30 hr, respectively. The interactions of the TADs also appear to modify the wind velocities in low latitudes. The eastward PPEF and equatorward TADs also favored the development of a clear/not so clear F3 layer in northern/southern regions of the equator.