Phase Of Storm Research Articles

Properties of the Geomagnetic Storm Main Phase and the Corresponding Solar Wind Parameters on 21–22 October 1999

We use the SYM-H index to indicate the ring current index. We find that there were two periods during which the SYM-H index decreased quickly during the main phase of the geomagnetic storm on 21–22 October 1999. The first period from 11:44 p.m. UT on 21 October 1999 to 1:35 a.m. UT on 22 October 1999 is defined as step 1. Another period from 3:36 a.m. UT to 5:49 a.m. UT on 22 October 1999 is defined as step 3. The durations of step 1 and step 3 are defined as Δt1 and Δt3, respectively. The variation of the pressure-corrected SYM-H index during step 1 and step 3 are defined as ΔSYMHob1∗ and ΔSYMHob3∗, respectively. The interplanetary (IP) sources responsible for ΔSYMHob1∗ and ΔSYMHob3∗ are determined as the solar wind during period 1 and period 3, respectively. We find that the largest southward component of the interplanetary magnetic field (Bsmax) during period 3 was larger than that during period 1, and the largest solar wind dawn-to-dusk electric field (Eymax) during period 3 was also larger than that during period 1. We also find that the time integral of Ey during period 3 was much larger than that during period 1. However, we find that |ΔSYMHob1∗| was larger than |ΔSYMHob3∗|, and |ΔSYMHob1∗/Δt1| was larger than |ΔSYMHob3∗/Δt3|, indicating that the geomagnetic activity intensity during a period does not depend on Bsmax or Eymax, nor does it depend on the time integral of Ey. What is the reason for this? We find that the solar wind dynamic pressure during period 1 was larger than that during period 3, indicating that the geomagnetic storm intensity during a period not only depends on the solar wind speed and Bs, but it also depends on the solar wind dynamic pressure. The magnetosphere took 4 min to respond to the IP shock. When the z-component of the interplanetary magnetic field (IMF) turned from northward to southward, the response time of the SYM-H index to the southward component of the IMF was 21 min.

Intense Equatorial Electrojet and Counter Electrojet Caused by the 15 January 2022 Tonga Volcanic Eruption: Space‐ and Ground‐Based Observations

AbstractWe present space‐ and ground‐based multi‐instrument observations demonstrating the impact of the 2022 Tonga volcanic eruption on dayside equatorial electrodynamics. A strong counter electrojet (CEJ) was observed by Swarm and ground‐based magnetometers on 15 January after the Tonga eruption and during the recovery phase of a moderate geomagnetic storm. Swarm also observed an enhanced equatorial electrojet (EEJ) preceding the CEJ in the previous orbit. The observed EEJ and CEJ exhibited complex spatiotemporal variations. We combine them with the Ionospheric Connection Explorer neutral wind measurements to disentangle the potential mechanisms. Our analysis indicates that the geomagnetic storm had minimal impact; instead, a large‐scale atmospheric disturbance propagating eastward from the Tonga eruption site was the most likely driver for the observed intensification and directional reversal of the equatorial electrojet. The CEJ was associated with strong eastward zonal winds in the E‐region ionosphere, as a direct response to the lower atmosphere forcing.

On the Magnetosphere‐Ionosphere Coupling During the May 2021 Geomagnetic Storm

AbstractOn 12 May 2021 the interplanetary doppelgänger of the 9 May 2021 coronal mass ejection impacted the Earth's magnetosphere, giving rise to a strong geomagnetic storm. This paper discusses the evolution of the various events linking the solar activity to the Earth's ionosphere with special focus on the effects observed in the circumterrestrial environment. We investigate the propagation of the interplanetary coronal mass ejection and its interaction with the magnetosphere—ionosphere system in terms of both magnetospheric current systems and particle redistribution, by jointly analyzing data from interplanetary, magnetospheric, and low Earth orbiting satellites. The principal magnetospheric current system activated during the different phases of the geomagnetic storm was correctly identified through the direct comparison between geosynchronous orbit observations and model predictions. From the particle point of view, we have found that the primary impact of the storm development is a net and rapid loss of relativistic electrons from the entire outer radiation belt. Our analysis shows no evidence for any short‐term recovery to pre‐storm levels during the days following the main phase. Storm effects also included a small Forbush decrease driven by the interplay between the interplanetary shock and subsequent magnetic cloud arrival.

Low- and Mid-Latitude Ionospheric Response to the 2013 St. Patrick’s Day Geomagnetic Storm in the American Sector: Global Ionosphere Thermosphere Model Simulation

In this study, the low-and mid-latitude ionospheric response to the main phase of the 2013 St. Patrick’s Day geomagnetic storm in the American sector on the dayside has been investigated using the ground-based measurements and the Global Ionosphere Thermosphere Model (GITM). First, it is found that the observed ionospheric response can be well reproduced by GITM when it is driven by the electric potential and electron precipitation patterns derived from the Assimilative Mapping of Ionospheric Electrodynamics (AMIE) technique. The AMIE-driven GITM simulation also significantly improves the data-model comparison as compared with the simulation driven by the high-latitude empirical models. Second, it is found that the transport process associated with the neutral wind is largely responsible for the observed ionospheric response. Specifically, the traveling atmospheric disturbances (TADs) propagating from the opposite hemisphere play an important role in the formation of the negative storm phase at low and middle latitudes. Third, it is found that the asymmetric negative storm phases occurred at the nominal equatorial ionization anomaly (EIA) peak region in the afternoon sector are mainly attributed to the interaction of the TADs launched in different hemispheres with different phase speeds. Specifically, stronger Joule heating deposited in the northern hemisphere (NH) generates TADs with faster phase speeds than those launched in the southern hemisphere (SH). Consequently, the locations where the TADs originated from the different hemispheres interact are asymmetric about the geomagnetic equator, leading to the formation of asymmetric ionospheric negative storm phases. This study highlights the importance of accurately specifying high-latitude electrodynamic forcings in global I-T simulations and provides a new insight into the cause of the interhemispheric asymmetry phenomena during geomagnetic storms.

Findings of the unusual plasma bubble occurrences at dawn during the recovery phase of a moderate geomagnetic storm over the Brazilian sector

In this work, we observe for the first time the unusual pre-sunrise Equatorial Plasma Bubbles (EPBs) during a moderate geomagnetic storm recovery phase caused by the High-Speed Solar Wind Stream (HSS) on February 17, 2015, over the Brazilian sector. Therefore, this study aims to explain the generation mechanism of this uncommon event, which started at 08:00 UT on February 18, 2015. We used Multiple Global Navigation Satellite Systems (Multi-GNSS, GPS, and GLONASS) data to produce two-dimensional maps of the Rate Of TEC index (ROTI) that show EPB features elongated in magnetic meridians. Also, Digisonde data from São Luís (2.53° S, 44.30° W, dip angle: 8.57°), Boa Vista (12.81° N, 60.67° W, dip angle: 33.71°), and Campo Grande (20.44° S, 54.64° W, dip angle: 25.98°), and magnetometer data at São Luís and Eusébio (3.89° S, 38.45° W, dip angle: 17.96°). Our analysis shows that the unusual pre-sunrise plasma bubbles lasted longer after sunrise, around 1 h. Finally, we showed that these EPBs are likely driven by a disturbance wind dynamo effect, which helps to understand the role of the external factors in EPBs development.

Arctic–Antarctic asymmetry of the ionospheric weather

The state of the ionosphere is investigated on a global scale, in the Arctic and Antarctic regions poleward of 60° magnetic latitudes. The Total Electron Content, TEC, enhancement (as represented by the global WU, polar WUN and WUS indices) and depletion (WL, WLN and WLS), and the respective ranges (WE, WEN and WES) are evaluated from global GIM-W index maps. GIM-W maps are derived from JPL GIM-TECs converted to geomagnetic coordinate frame for Solar Cycles 23–24. Using a superimposed epoch analysis, we examined 380 geo-storms caused by high speed solar wind stream, Vsw, with time t0 set at onset of the Dst storm and Dstmin ≤ −50 nT. Single-sign positive and negative storm effects are detected in both Arctic and Antarctic, when the polar WUN, WLN, WUS or WLS index is equal to zero for 10–20% of the pre-storm period, 5–25% for the main storm phase, and 7–25% during recovery. These asymmetric single-sign conditions violate the correlation between WUS (WUN) and WLN (WLS) data and global Dst, WU, WL and WE indices, demonstrated for the extreme storm on 15–17 July 2000 (Dst = −301 nT). The persistent single-sign conditions are observed in the polar segments for the both disturbed and quiet times from 1994 to 2021. The peak of the monthly single-sign conditions up to 50% of time occurs during the polar summer when the solar wind – polar ionosphere interaction at the open field lines facing the Sun is strengthened due to reduced magnetosphere shielding the solar wind. A long-term Arctic–Antarctic asymmetry is observed from 1994 to 2021, with larger values of daily polar indices WUN, WUS, WUN and WLS found for the winter hemisphere (the ‘winter anomaly’) while contribution of the multiple single-sign zeros yields the reduced monthly values at summer. The asymmetry is likely caused by the difference in the solar irradiance that is minimized at the dominant high-latitude winter night-time, compared to the sunlit summer conditions in the opposite hemisphere. Higher values of asymmetry index AIWU and AIWL shows dominant North Hemisphere variance over South Hemisphere during December solstice reversed towards the June solstice presumably related with dynamical influences of the lower atmosphere.

Local Persistent Ionospheric Positive Responses to the Geomagnetic Storm in August 2018 Using BDS-GEO Satellites over Low-Latitude Regions in Eastern Hemisphere

We present the ionospheric disturbance responses over low-latitude regions by using total electron content from Geostationary Earth Orbit (GEO) satellites of the BeiDou Navigation Satellite System (BDS), ionosonde data and Swarm satellite data, during the geomagnetic storm in August 2018. The results show that a prominent total electron content (TEC) enhancement over low-latitude regions is observed during the main phase of the storm. There is a persistent TEC increase lasting for about 1–2 days and a moderately positive disturbance response during the recovery phase on 27–28 August, which distinguishes from the general performance of ionospheric TEC in the previous storms. We also find that this phenomenon is a unique local-area disturbance of the ionosphere during the recovery phase of the storm. The enhanced foF2 and hmF2 of the ionospheric F2 layer is observed by SANYA and LEARMONTH ionosonde stations during the recovery phase. The electron density from Swarm satellites shows a strong equatorial ionization anomaly (EIA) crest over the low-latitude area during the main phase of storm, which is simultaneous with the uplift of the ionospheric F2 layer from the SANYA ionosonde. Meanwhile, the thermosphere O/N2 ratio shows a local increase on 27–28 August over low-latitude regions. From the above results, this study suggests that the uplift of F layer height and the enhanced O/N2 ratio are possibly main factors causing the local-area positive disturbance responses during the recovery phase of the storm in August 2018.

Mapping a Magnetic Superstorm: March 1989 Geoelectric Hazards and Impacts on United States Power Systems

AbstractA study is made of the relations between geomagnetic and geoelectric field variation, Earth‐surface impedance, and operational interference (“anomalies”) experienced on electric‐power systems across the contiguous United States during the 13–14 March, 1989, magnetic storm. For this, a 1‐min‐resolution sequence of geomagnetic field maps is constructed from magnetometer time series acquired at ground‐based observatories. Induced geoelectric field maps are calculated by convolving the geomagnetic maps with magnetotelluric impedance tensors. During the storm, anomalies were concentrated where the lithosphere is electrically resistive, and when and where geoelectric field amplitudes were high. This was particularly true in the Mid‐Atlantic, Northeast, and the upper Midwest. Few anomalies were experienced in other parts of the Midwest and across much of the West, where the lithosphere is more conductive, and when and where geoelectric field amplitudes were low. Peak 1‐min‐resolution geoelectric field amplitude ranged from 21.66 V/km in Maine and 19.02 V/km in Virginia to <0.02 V/km in Idaho. Latitude‐dependent organization of geoelectric hazards by auroral‐zone electrojet currents is detectable, but it is much weaker than geographic organization due to surface impedance. Hazardous geoelectric fields were induced during different storm phases, at different local times, and, by inference, by a variety of ionospheric currents. Compared to geoelectric field amplitudes realized across the United States during March 1989, hazard maps used by utility companies to estimate systems exposure have much less geographic detail and a much smaller maximum‐to‐minimum range in geoelectric field amplitude. Future research would benefit from denser geomagnetic monitoring, additional magnetotelluric surveying, and access to power‐system impact data.

Ionospheric Signatures During G2, G3 and G4 Storms in Mid‐Latitude

AbstractThis paper presents a wavelet‐based analysis of ionospheric irregularities induced by three different geomagnetic storms of varying strength and interplanetary origin over three mid‐latitudes stations, viz. Moscow, Fairford, and Rome. We observed the highest decrease in ionospheric variables (foF2, total electron content (TEC), and NmF2) during the negative phase of the G4 storm. Interestingly, hmF2 exhibits the opposite trend in terms of variation. The maximum ionization height (hmF2) for the G4 event is 500 km (during the main phase) and 150 km (during the recovery phase). Within 2–3 hr of the G4 event, the value of hmF2 is found to decline by 70%. The largest reduction (80%) in critical frequency (foF2) is observed during the negative phase of this event, which is also confirmed by the continuous wavelet transform results. During the negative phase, we observed noticeable power shifts in the signal of the ionospheric parameters toward the lower Fourier period band. During the G4 storm—Particularly during the negative phase—The lowest power linked with the ionospheric parameter's signal was discovered. Additionally, we used detrended cross‐correlation analysis to investigate the correlation and time lag between geomagnetic indices (Symmetric H‐component (SYM‐H) & auroral electrojet) and ionospheric parameters (foF2, NmF2, hmF2 & TEC). The significant association between SYM‐H and ionospheric parameters suggests that the magnetosphere‐ionosphere interaction produces intense electric field disturbances and winds in the mid‐latitudes, resulting in the perturbation of hmF2, foF2, TEC, and NmF2.

Superposed Epoch Analyses of Geoelectric Field Disturbances in Japan in Response to Different Geomagnetic Activities

AbstractAn increase in geomagnetically induced currents (GICs) is an inevitable result of geomagnetic field disturbances, and is harmful to the power grid, in particular, at high latitudes. At mid and low latitudes, the amplitude of the GICs is, in general, small, but large‐amplitude GICs are often observed during magnetic storms. It is of importance to understand major characteristics and extreme values of GICs at mid and low latitudes. For the geoelectric field disturbances ΔE observed at Kakioka (27.8° geomagnetic latitude) in Japan in 1996–2004, we performed superposed epoch analyses with respect to three types of geomagnetic disturbances: (a) storm sudden commencements (SSCs)/sudden impulses (SIs), (b) main phase of magnetic storms, and (c) bay disturbances. It is shown that the SSCs/SIs and the main phase of the magnetic storms are equally important for causing large‐amplitude disturbances of ΔE at Kakioka. GICs are thought to be amplified when the SIs and/or the bay disturbances occur during the magnetic storms. The maximum value of ΔE tends to be correlated with the maximum value of ΔH during the three types of events, where ΔH is the horizontal component of the geomagnetic field. Assuming that a quasi‐linear relationship between the maximum ΔE and the maximum ΔH is valid, we estimated GICs at three substations in Japan for an extreme SSCs/SIs, and the extreme magnetic storms. This scheme could be applicable to estimate roughly the GICs against extreme events, and to forecast the maximum GICs in a real‐time manner.

A Rapid Localized Deceleration of Earth's Radiation Belt Relativistic Electrons Driven by Storm Proton Injection

AbstractEarth's radiation belt relativistic electron dropouts frequently occur during the main phase of geomagnetic storms, which have been partially attributed to the ring current ion enhancements causing geomagnetic field reconfigurations. In contrast to early studies on the global radiation belt response to the ring current buildup on a timescale of several hours, we here describe a rapid, localized, significant decay of relativistic electrons driven by freshly injected energetic protons during the 27 May 2017 geomagnetic storm. Near the proton injection front, the magnetic field lines were stretched outward, with an inferred migration of their equatorial crossings by ∼0.5 RE during several minutes. Because of the betatron and Fermi decelerations, the relativistic electron fluxes decreased by 2–3 orders of magnitude with pitch‐angle distributions evolving from pancake/flat‐top type to cigar type. This rapid localized response pattern of relativistic electrons could be general over strong particle injections during both geomagnetic storms and substorms.

Trifurcate structure of oxygen band EMIC waves excited in a warm magnetospheric plasma

Applying linear dispersion theory to a warm collisionless plasma, we investigate the effect of hot ion composition on electromagnetic ion cyclotron (EMIC) wave generation. The growth rate of oxygen band waves can divide into three components if hot anisotropic heavy ions are included. Their wave frequencies (0.05 ΩH+, 0.03 ΩH+, and 0.01 ΩH+) are sorted in relation to the cyclotron frequencies of H+, He+, and O+ ions (ΩH+, ΩH+/4, and ΩH+/16). The three sub-bands within the oxygen band form an unusual trifurcate structure of growth rate. A link between the three sub-bands and three hot species has been definitively established. That is to say, hot H+, He+, and O+ ions are responsible for the generation of sub-bands. The unstable frequencies of oxygen band waves are directly modulated by the actual composition of magnetospheric ions. The largest growth can arise between the extremely low frequency and the gyrofrequency of O+ (ΩO+). When O+ ions become the dominant hot component during the storm phase, oxygen waves can be generated at much lower frequencies than ΩO+. We perform a parametric study of oxygen sub-band generation in the magnetosphere by using a statistical survey of the plasma composition measured by the Van Allen Probes. The trifurcate structure of growth rate appears at wide L shells from the outer plasmasphere to the geostationary orbit. The new findings demonstrate that wave structures in the oxygen band are more complex than the hydrogen and helium bands. This may provide insight into the nature of the EMIC instability.

Ionospheric Reconstruction Using GNSS Signals Around an Anomaly Crest Location in Indian Longitude Sector

AbstractThe present study aims to reconstruct the vertical ionospheric electron density (IED) profile using computerized ionospheric tomography (CIT) techniques, over the northern crest of the equatorial ionization anomaly (EIA) which is one of the most geo‐physically sensitive regions of Indian longitude sector. Total electron content (TEC) measurements obtained from GNSS signals from receivers located at Kolkata (22.57°N, 88.36°E), Purulia (23.33°N, 86.36°E), and Siliguri (26.73°N, 88.39°E) and International GNSS Service (IGS) stations of Port Blair (11.64°N, 92.71°E), Bangalore (13.02°N, 77.57°E), Hyderabad (17.42°N, 78.55°E), Lucknow (26.91°N, 80.96°E) and Lhasa (29.66°N, 91.10°E) have been incorporated into the tomography algorithm for ionospheric reconstructions. Among the different iterative techniques used for retrieving IED profiles on a 2‐dimensional altitude versus latitude plane fixed at a certain longitude, simultaneous iterative reconstruction technique (SIRT) was shown to be the optimum choice based on the representation of the EIA phenomenon and reconstruction accuracy. A comparative assessment between two ionospheric models IRI2016 and PIM1.4 was performed, with PIM based initial guess for inversions resulting in lower reconstruction errors. The 2D CIT algorithm was then used to reconstruct the hourly vertical IED profiles to study the impact of the severe G4‐class St. Patrick's Day storm on 17 March 2015 and reconstructed electron densities showed a large increase over the values obtained from the geomagnetically quiet day of 10 March 2015, indicating a positive ionospheric storm phase. Ionospheric response to the G1‐class geomagnetic disturbance on 5 December 2017 and the average F‐region IED values have also been compared with a geomagnetically quiet day of 3 December 2017.

A Statistical Study of Poleward Traveling Ionospheric Disturbances Over the African and American Sectors During Geomagnetic Storms

AbstractWe present statistical results of traveling ionospheric disturbances (TIDs) with origin near the geomagnetic equator during geomagnetic storms that occurred within the period of 2010–2018. Based on storm criteria of Kp > 4 and Dst ≤ −50 nT, we have analyzed total electron content perturbations derived from Global Navigational Satellite Systems observations within a latitude range of 40°S–60°N and longitude ranges of 20°–40°E and 50°–70°W representing the African and American sectors. Although the northern hemispheric part of the African sector has limited data coverage, results show that the launched TIDs do not exceed the latitudinal distance of 20°–25° from their origin during the analyzed period. A statistically similar result is observed over the American sector with launched poleward TIDs constrained largely within ±20°–30° around the geomagnetic equator. Where data are available, majority of these cases are linked to changes in ionospheric electrodynamics, especially the enhancement of equatorial electrojet (EEJ), although there are other observations that are not explained by EEJ variability. This indicates that there may be other physical mechanisms that play a role in launching TIDs at the geomagnetic equator during disturbed conditions. An important result is that large‐scale and medium‐scale TIDs have been found to occur predominantly during the main and recovery phases of geomagnetic storms, respectively, at least over the African sector.

Statistical study and corresponding evolution of plasmaspheric plumes under different levels of geomagnetic storms

Abstract. Using observations of Van Allen Probes, we present a statistical study of plasmaspheric plumes in the inner magnetosphere. Plasmaspheric plumes tend to occur during the recovery phase of geomagnetic storms. Furthermore, the results imply that the occurrence rate of observed plasmaspheric plume in the inner magnetosphere is larger during stronger geomagnetic activity. This statistical result is different from the observations of the Cluster satellite with much higher L shells in most orbital periods, which suggests that the plasmaspheric plume near the magnetopause tends to be observed during moderate geomagnetic activity (Lee et al., 2016). In the following, the dynamic evolutions of plasmaspheric plumes during a moderate geomagnetic storm in February 2013 and a strong geomagnetic storm in May 2013 are simulated through group test particle simulation. It is obvious that the plasmaspheric particles drift out on open convection paths due to sunward convection during both geomagnetic storms. It seems that the outer plasmaspheric particles exhaust the energy available to them sooner, and the plasmasphere shrinks faster during strong geomagnetic storms. As a result, the longitudinal width of the plume is narrower, and the plume is limited to lower L shells during the recovery phase of strong geomagnetic storm. The simulated evolutions may provide a possible interpretation for the occurrence rates: Van Allen Probes tend to observe plumes during stronger geomagnetic storms, and the Cluster satellite with higher L shells tends to observe plumes during moderate geomagnetic storms.

Geomagnetic Storm Effect on F2-Region Ionosphere during 2012 at Low- and Mid-Latitude-Latitude Stations in the Southern Hemisphere

The ionospheric effects of six intense geomagnetic storms with Dst index ≤ −100 nT that occurred in 2012 were studied at a low-latitude station, Darwin (Geomagnetic coordinates, 21.96° S, 202.84° E), a low-mid-latitude station, Townsville (28.95° S, 220.72° E), and a mid-latitude station, Canberra (45.65° S, 226.30° E), in the Australian Region, by analyzing the storm–time variations in the critical frequency of the F2-region (foF2). Out of six storms, a storm of 23–24 April did not produce any ionospheric effect. The storms of 30 September–3 October (minimum Dst = −122 nT) and 7–10 October (minimum Dst = −109 nT) are presented as case studies and the same analysis was done for the other four storms. The storm of 30 September–3 October, during its main phase, produced a positive ionospheric storm at all three stations with a maximum percentage increase in foF2 (∆foF2%) of 45.3% at Canberra whereas during the recovery phase it produced a negative ionospheric storm at all three stations with a maximum ∆foF2% of −63.5% at Canberra associated with a decrease in virtual height of the F-layer (h’F). The storm of 7–10 October produced a strong long-duration negative ionospheric storm associated with an increase in h’F during its recovery phase at all three stations with a maximum ∆foF2% of −65.1% at Townsville. The negative ionospheric storms with comparatively longer duration were more pronounced in comparison to positive storms and occurred only during the recovery phase of storms. The storm main phase showed positive ionospheric storms for two storms (14–15 July and 30 September–3 October) and other three storms did not produce any ionospheric storm at the low-latitude station indicating prompt penetrating electric fields (PPEFs) associated with these storms did not propagate to the low latitude. The positive ionospheric storms during the main phase are accounted to PPEFs affecting ionospheric equatorial E × B drifts and traveling ionospheric disturbances due to joule heating at the high latitudes. The ionospheric effects during the recovery phase are accounted to the disturbance dynamo electric fields and overshielding electric field affecting E × B drifts and the storm-induced circulation from high latitudes toward low latitudes leading to changes in the natural gas composition [O/N2] ratio.

Spatial Features of a Super Substorm in the Main Phase of the Magnetic Storm of April 5, 2010

Spatial Features of a Super Substorm in the Main Phase of the Magnetic Storm of April 5, 2010

The Seed Populations in the Earth's Outer Radiation Belt During the Main Phase of Magnetic Storms: A Statistical Study

AbstractUsing the data from Van Allen Probes, we investigate in detail the seed populations in the outer radiation belt during the storm main phase. Based on the different flux variations of the seed electrons before the storm and around the storm peak, these storm events are divided into “flux decay events,” “flux enhancement events” and “strong flux enhancement events.” For flux decay events, a shorter storm main phase (≤12 hr) and smaller southward interplanetary magnetic field (IMF) and solar wind electric field (−15 nT < Bzmin < −5 nT, 2 mV/m < Eymax < 7 mV/m) are found. For flux enhancement events, large southward Bzmin and Eymax (−29 nT < Bzmin < −10 nT, 5 mV/m < Eymax < 11 mV/m) for the shorter main phase or smaller southward Bzmin and Eymax (−23 nT < Bzmin < −5 nT, 3 mV/m < Eymax < 11 mV/m) for the longer main phase (>12 hr) are observed. For strong flux enhancement events, larger southward Bzmin and Eymax (−32 nT < Bzmin < −13 nT, 5 mV/m < Eymax < 22 mV/m) for the shorter main phase or smaller southward Bzmin and Eymax (−26 nT < Bzmin < −9 nT, 3 mV/m < Eymax < 16 mV/m) for the longer main phase are observed. These suggest that the flux variations of the seed electrons during the storm main phase are highly influenced by the duration of the storm main phase, southward IMF, and solar wind electric field.

Bioaerosols as Evidence of Atmospheric Circulation Anomalies over the Okhotsk Sea and Shantar Islands in the Late Glacial–Holocene

Allochthonous biofossil distribution in the blanket peat bog of Bolshoy Shantar Island was used to analyze atmospheric circulation anomalies in the north-western Okhotsk Sea over the last 12.6 ka. The main aim of this study was to determine periods of intensification of deep cyclones and extreme storms. The composition of bioaerosols is significantly influenced by atmospheric zonal and meridional transport anomalies associated with anomalies of the monsoon system of Northeast Asia, atmospheric fronts and cyclone trajectories. Marine diatoms enter the peatland from the sea during extreme storms and record the passage of sea cyclones in the autumn-winter, whereas the distribution of allochthonous pollen indicates the intensity of continental cyclones. We used Pinus pumila pollen as an indicator of heavy snowfalls and winter cyclone activity. Fifteen phases of extreme storms were identified. Changes in ice coverage also played an important role in bioaerosol emission. During cold periods, emissions of bioaerosols mainly occurred in the open sea, whereas during warm periods, emissions occurred near the coast. The recurrence and intensity of cyclones during the cold seasons depends on displacement of the Siberian High and Aleutian Low. Periods of continental cyclones intensified in spring-summer and coincided with periods of active winter cyclogenesis.

Swarm satellite observations of the effect of prompt penetration electric fields (PPEFs) on plasma density around noon and midnight side of low latitudes during the 07–08 september 2017 geomagnetic storm

In this paper, using plasma density data (Ne) obtained from the Swarm satellite, the effect of prompt penetration electric fields (PPEFs) on the distribution of plasma density at low latitudes during the 07–08 September 2017 geomagnetic storm is discussed. The observations of enhancements and reductions in ionospheric plasma around noon and midnight in association with the orientation of the north–south component of the interplanetary magnetic field (IMF Bz) are presented during the main phase and the recovery phase of geomagnetic storm. The days of 05–06 September 2017 were selected as geomagnetically quiet days, and the plasma density data on these days were plotted as a quiet-time reference. The plasma enhancements and reductions in the low latitudes are found closely related to the magnetic local time (MLT), the orientation of IMF Bz, the main phase and the recovery phase of geomagnetic storm. During the main phase of geomagnetic storm with southward IMF Bz, plasma density increased around noon (10:00–11:00 MLT), while plasma density decreased around midnight (22:00–23:00 MLT). During the recovery phase of geomagnetic storm with northward IMF Bz, plasma density decreased around noon (10:00–11:00 MLT), while plasma density increased around midnight (22:00–23:00 MLT). The plasma density around both noon and midnight after the geomagnetic storm shows a distribution very similar to the distribution of plasma density during the geomagnetically quiet period. It is assumed that PPEFs are responsible for these results. During the main phase of the geomagnetic storm, the eastward PPEFs cause an increase in plasma density around the noon side while the westward PPEFs cause a decrease in plasma density around midnight side.