A study of the relationship between geo-magnetic storms and ionospheric disturbances at mid-latitudes

The problem of the ionospheric disturbances associated with geomagnetic storms is examined with the goal of searching for a relationship between the time-developments of the two phenomena. Faraday rotation measurements of total electron content (N_T) are used to monitor the ionospheric F-region at a mid-latitude site, while a variety of geomagnetic parameters are examined as possible ways of following the geomagnetic variations. The ionospheric and geomagnetic data taken during 28 individual storms from 1967 to 1969 are used to search for a predictive scheme which can be tested using data from 17 storms in 1970. The specific aim is to find the geomagnetic parameter whose time-development can best forecast whether or not the ionospheric response will include an initial positive phase prior to the normally extended period of F-region depletions. Correlations between N_T and the geomagnetic indices K_p, and equatorial Dst(H) prove to be wholly inadequate. The local times of main-phase-onset (MPO) determined from the equatorial Dst(H) indices as well as from local horizontal component data, also prove to be unsatisfactory. The best correlations are obtained using local measurements of the total geomagnetic field (F). These results show that a storm commencement (SC) will produce an enhancement in n_t during the afternoon period following the SC unless there is an intervening post-midnight period with a strong depression of the geomagnetic field. Operationally this is taken to be a depression in F of at least 100γ near 03:00 LT     

Analysis of plasma and field conditions during some intensely geo-effective transient solar/interplanetary disturbances of solar cycle 23

The problem of solar wind-magnetosphere coupling is investigated for intense geomagnetic storms (Dst < -100nT) that occurred during solar cycle 23. For this purpose interplanetary plasma and field data during some intensely geo-effective transient solar/interplanetary disturbances have been analysed. A geomagnetic index that represents the intensity of planetary magnetic activity at subauroral latitude and the other that measures the ring current magnetic field, together with solar plasma and field parameters (V, B, Bz, σB, N, and T) and their various derivatives (BV,-BVz, BV², -BzV², B²V, Bz²V, NV²) have been analysed in an attempt to study mechanism and the cause of geo-effectiveness of interplanetary manifestations of transient solar events. Several functions of solar wind plasma and field parameters are tested for their ability to predict the magnitude of geomagnetic storm.     

Longitude dependent response of the GPS derived ionospheric ROTI to geomagnetic storms

The local time dependent effects of geomagnetic storm on the ionospheric TEC and Rate of change of TEC Index (ROTI) are studied here using the GPS data for four different low latitude stations: Ogaswara, Japan (24.29?°N, 153.91?°E; Geomagnetic: 17.21?°N, 136.16?°W); Surat, India (21.16?°N, 72.78?°E; Geomagnetic: 12.88?°N, 146.91?°E); Bogota, Colombia (4.64?°N, ?74.09?°E; Geomagnetic: 14.42?°N, 1.67?°W); and Kokee park Waimea, Hawaii, US (22.12?°N, ?159.67?°E; Geomagnetic: 22.13?°N, 91.19?°W). The solar wind velocity and geomagnetic indices: Dst, Kp and IMF Bz are utilized to validate the geomagnetic storms registered during the years 2011 and 2012. Using the GPS based TEC data and computed values of ROTI, the storm induced ionospheric irregularities generation and inhibition has been studied for all stations. The present study suggests that, the F-region irregularities of a scale length of few kilometers over the magnetic equator are locally affected by geomagnetic storms. This study also shows a good agreement (70–84 %) with the Aaron’s criteria (Aarons, Radio Sci., 26:1131–1149, 1991; Biktash, Ann. Geophys., 19:731–739, 2004) as significant absence and enhancement of ROTI was found to be influenced by the local time of the negative peak of Dst index association.     

Response of low latitude ionosphere to the geomagnetic storm of May 30

Response of low latitude ionosphere to the geomagnetic storm of May 30, 2005 in the Indian longitude sector has been investigated by using the GPS data recorded at three stations namely, Udaipur, Hyderabad and Bengaluru. The event is noteworthy due to the fact that the Z component of interplanetary magnetic field (IMF Bz) remained southward for about 10 hours, coincident with the local day time for the Indian longitude sector, along with significantly higher values of AE and ASY-H indices. However, we neither found any evidence for the presence of long lasting storm time electric fields nor could we infer episodes of eastward-westward penetration of electric fields under steady southward IMF Bz and unsteady ring current conditions. On the storm day, the maximum enhancement in the total electron content has been found to be about 60%. The ionosonde observations also showed increased critical frequency (foF₂) and the height (h_PF₂) of the F layer. The foF₂ was enhanced by ∼60% which is consistent with the enhancement in total electron content. The slow rise and long duration enhancement of h_PF₂ and foF₂ have been attributed to the upwelling by the meridional neutral winds, caused by continuous energy inputs at higher latitudes. The poleward expansion of the equatorial ionization anomaly has also been observed on May 30. On May 31, the following day of the storm, significantly suppressed anomaly with near absence of its northern crest in the Indian longitude sector, revealed the effect of storm induced disturbance dynamo electric fields.     

Latitudinal characteristics of the geomagnetic field during the storm of 15–16 July 2000

In this paper geomagnetic disturbances at middle and low latitudes are discussed by using geomagnetic data of the magnetic storm of 15–16 July 2000. This storm is a response to the solar Bastille Day flare on 14 July. Generally, the geomagnetic disturbances at middle and low latitudes during a storm are mainly caused by three magnetospheric–ionospheric current systems, such as the ring current system (RC), the partial ring current and its associated region II field-aligned currents (PR), and the region I field-aligned currents (FA). Our results show that: (1) The northward turning of IMF-Bz started the sudden commencement of the storm, and its southward turning caused the main phase of the storm. (2) The PR- and FA-currents varied violently in the main phase. In general, the field of the FA-current was stronger than that of the PR-current. (3) In the first stage of the recovery phase, the RC-field gradually turned anti-parallel to the geomagnetic axis from a 15° deviation, and the local time (Λ) pointed by the RC-field stayed at 16:00. After that, Λ rotated with the stations, and the RC-field was not anti-parallel to the geomagnetic axis, but 5°–10° deviated. These facts suggest that the warped tailward part of the ring current decays faster than the symmetric ring current.     

Solar and interplanetary disturbances causing moderate geomagnetic storms

The effect of solar and interplanetary disturbances on geomagnetospheric conditions leading to 121 moderate geomagnetic storms (MGS) have been investigated using the neutron monitor, solar geophysical and interplanetary data during the period 1978–99. Further, the duration of recovery phase has been observed to be greater than the duration of main phase in most of the cases of MGS. It has further been noted that Ap-index increases on sudden storm commencement (SSC) day than its previous day value and acquires maximum value on the day of maximum solar activity. Generally, the decrease in cosmic ray (CR) intensity and Dst begins few hours earlier than the occurrence of MGS at Earth. Furthermore, negative Bz pointing southward plays a key causal role in the occurrence of MGS and the magnitude and the duration of Bz and Bav also play a significant role in the development of MGS. The solar features Hα, X-ray solar flares and active prominences and disappearing filaments (APDFs) which have occurred within lower helio-latitudinal/helio-longitudinal zones produce larger number of MGS. Solar flares seem to be the major cause for producing MGS.     

Detemination of the ring current radii from cosmic ray neutron monitor data for the 17 December 1971 magnetic storm

Variations of the cosmic ray cut-off rigidities have been observed at mid latitudes during the magnetic storm period 16–18 December 1971. In the present paper the cut-off changes over Europe are determined on an hourly basis from the registrations of 10 European neutron monitor stations. As a first order approximation it is assumed that the observed cut-off variations originate from a spherical current sheet concentric with the Earth and with a current density proportional to the cosine of the geomagnetic latitude. Applying results obtained by Treiman (1953), the radii of the current sphere can then be deduced from the dependences of the relative cut-off rigidity variations on geomagnetic latitude. The sphere is found to be located between 4 and 6 Earth radii during the main phase of the magnetic storm on 17 December 1971. A comparison of these results with in situ measurements carried out in the equatorial plane by Explorer 45 shows good agreement.     

Plasmaspheric hiss observed in the topside ionosphere at mid- and low-latitudes

Latitudinal characteristics of ELF hiss in mid- and low-latitudes have been statistically studied by using ELF/VLF electric field spectra (50 Hz-30 kHz) from ISIS-1 and -2 received at Kashima station, Japan from 1973 to 1977. Most ISIS ELF/VLF data observed in mid- and low-latitude include ELF hiss at frequencies below a few kHz. The ELF hiss has the strongest intensity among VLF phenomena observed by the ISIS electric dipole antenna in mid- and low-latitudes, but the ELF hiss has no rising structure like the chorus in the detailed frequency-time spectrum. The ELF hiss is classified into the steady ELF hiss whose upper frequency limit is approximately constant with latitude and the ELF hiss whose upper frequency limit increases with latitude. These two types of ELF hiss occur often in medium or quiet geomagnetic activities. Sometimes there occurs a partial or complete lack of ELF hiss along an ISIS pass.Spectral shape and bandwidth of ELF hiss in the topside ionosphere are very similar to those of plasmaspheric hiss and of inner zone hiss. The occurrence rate of steady ELF hiss is about 0.3 near the geomagnetic equator and decreases rapidly with latitude around L = 3. Hence it seems likely that ELF hiss is generated by cyclotron resonant instability with electrons of several tens of keV in the equatorial outer plasmasphere beyond L = 3.Thirty-seven per cent of ELF hiss events received at Kashima station occurred during storm times and 63% of them occurred in non-storm or quiet periods. Sixty-seven per cent of 82 ELF hiss events during storm times were observed in the recovery phase of geomagnetic storms. This agrees with the previous satellite observations of ELF hiss by search coil magnetometers. The electric field of ELF hiss becomes very weak every 10 s, which is the satellite spin period, in mid- and low-latitudes, but not near the geomagnetic equator. Ray tracing results suggest that waves of ELF hiss generated in the equatorial outer plasmasphere propagate down in the electrostatic whistler mode towards the equatorial ionosphere, bouncing between the LHR reflection points in both the plasmaspheric hemispheres.     

On relation between mid-latitude ionospheric ionization and quasi-trapped energetic electrons during 15 December 2006 magnetic storm

We report simultaneous observations of intense fluxes of quasi-trapped energetic electrons and substantial enhancements of ionospheric electron concentration (EC) at low and middle latitudes over the Pacific region during the geomagnetic storm on 15 December 2006. Electrons with energy of tens of keV were measured at altitude of ～800–900 km by POES and DMSP satellites. Experimental data from COSMIC/FS3 satellites and global network of ground-based GPS receivers were used to determine height profiles of EC and vertical total EC, respectively. A good spatial and temporal correlation between the electron fluxes and EC enhancements was found. This fact allows us to suggest that the quasi-trapped energetic electrons can be an important source of ionospheric ionization at middle latitudes during magnetic storms.     

Effect of magnetic activity on ionospheric time delay at low latitude

The purpose of this work is to investigate the effect of magnetic activity on ionospheric time delay at low latitude Station Bhopal (geom. lat. 23.2°N, geom. long. 77.6°E) using dual frequency (1575.42 and 1227.60 MHz) GPS measurements. Data from GSV4004A GPS Ionospheric Scintillation and TEC monitor (GISTM) have been chosen to study these effects. This paper presents the results of ionospheric time delay during quiet and disturbed days for the year 2005. Results show that maximum delay is observed during quiet days in equinoxial month while the delays of disturbed period are observed during the months of winter. We also study the ionospheric time delay during magnetic storm conditions for the same period. Results do not show any clear relationship either with the magnitude of the geomagnetic storm or with the main phase onset (MPO) of the storm. But most of the maximum ionospheric time delay variations are observed before the main phase onset (MPO) or sudden storm commencement (SSC) as compared to storm days.     

Storm time response of GPS-derived total electron content (TEC) during low solar active period at Indian low latitude station Varanasi

The present paper analyzes the dual frequency signals from GPS satellites recorded at Varanasi (Geographic latitude 25°, 16′ N, longitude 82°, 59′ E) near the equatorial ionization anomaly (EIA) crest in India, to study the effect of geomagnetic storm on the variation of TEC, during the low solar active period of May 2007 to April 2008. Three most intense—but still moderate class—storms having a rapid decrease of Dst-index observed during the GPS recorded data have been analyzed, which occurred on 20 November 2007, 9 March 2008 and 11 October 2008 were selected and storm induced features in the vertical TEC (VTEC) have been studied considering the mean VTEC value of quiet days as reference level. The possible reasons for storm time effects on VTEC have been discussed in terms of local time dependence, storm wind effect as well as dawn-dusk component of interplanetary electric field (IEF) Ey intensity dependence.     

A model of ionospheric F-2 region storms in middle latitudes

The proposed ionospheric storm model is based on a heat source located at magnetic noon on Feldstein's auroral oval. The rotation of the Earth produces an apparent motion of the source which is greater than the speed of the disturbance. This gives rise to a wake or front which sweeps over the globe and determines the onset time of the negative phase which results from a change in chemical composition. At the front, focussing will occur which accounts for the sudden drop in electron density (or contents) sometimes observed. The calculated onset times of the negative phase are compared with observations for a number of storms. The local onset times vary from 12 at the latitude of the source to around 24 at 10° geomagnetic latitude. This model predicts that the onset of the negative phase at a given location, for storm which commence between about 2000 LT to about 1000 LT, is independent of the time of storm commencement.     

An Approach to the Relationship Between Magnetic Clouds and the Recovery Phase of Geomagnetic Storms

Using an elliptical cross-section model for the study of the magnetic topology of magnetic clouds (MCs) in the interplanetary medium, we develop an analytical approach to their relationship with geomagnetic storms. Assuming an axially symmetric ring current and once we have obtained the disturbances produced in its current density due to the passage of a MC through it (whose axis has a latitude θ, a longitude φ, and its cross-section has an orientation ζ), then we determine the decrease in the value of the geomagnetic field at the Earth's equator, i.e., the D _st index. The D _st model presented allows us to estimate the physical parameters which characterize the symmetric ring current during the recovery phase of the storm time. The theoretical and experimental D _st indexes are compared for four intense geomagnetic storms (D _st<−100 nT), all of them associated with MCs. As seen in the figures presented, the fits are good for every storm. In view of these results we conclude that the effects of a MC over the symmetric ring current can explain the main profile of the recovery phase of a geomagnetic storm.     

Geomagnetic field variation during winter storm at localized southern and northern high latitude

This paper presents the effect of geomagnetic storm on geomagnetic field components at Southern (Maitri) and Northern (Kiruna) Hemispheres. The Indian Antarctic Station Maitri is located at geom. long. 66.03° S; 53.21° E whereas Kiruna is located at geom. long. 67.52° N; 23.38° E. We have studied all the geomagnetic storms that occurred during winter season of the year 2004–2005. We observed that at Southern Hemisphere the variation is large as compared to the Northern Hemisphere. Geomagnetic field components vary when the interplanetary magnetic field is oriented in southward direction. Geomagnetic field components vary in the main phase of the ring current. Due to southward orientation of vertical component of IMF reconnection takes place all across the dayside that transports plasma and magnetic flux which create the geomagnetic field variation.     

Ionospheric foF2 storm forecasting using neural networks

The ionosphere shows a large degree of variability on time scales from hours to the solar cycle length. This variation is associated with magnetospheric storms, the Earth's rotation, the season, and the level of solar activity. To make accurate predictions of key ionospheric parameters all these variations must be considered. Neural networks, which are data driven non-linear models, are very useful for such tasks. In this work we examine if the F2 layer plasma frequency, foF2, at a single ionospheric station can be predicted 1 to 24 hours in advance by using information of past foF2 observations, magnetospheric activity, and time as inputs to neural networks. Particular attention has been paid to periods when great geomagnetic storms were in progress with the aim to develop a successful ionospheric storm forecasting tool.     

Geoeffectiveness of magnetic clouds occurred during solar cycle 23

Highly variable conditions prevail in the geospace environment due to the variations in Solar activity. The characteristics of the magnetic clouds (MCs) and their effects on geosphere, which have occurred during the period January 1996 to December 2006; have been investigated. No systematic trend has been observed between MCs and Solar activity cycle which is analyzed on the basis of maximum Sunspot number in that particular year. 85% MCs are found to be geoeffective. MCs are divided into two major classes: unipolar and bipolar. Unipolar MCs are of south (S) or north (N) type while bipolar MCs are of south-north (SN) or north-south (NS) type. During Solar cycle 23, SN-type MCs dominated over NS-type MCs. Highly intense geomagnetic storms (GMSs) of Dst <−300 nT follow from SN or S-type MCs. No preference is observed for right handed (RH) or left handed (LH) clouds for being geoeffective. MCs of very high speed lead to intense GMSs. The correlation coefficient (r) of southward component of magnetic field (Bz), total magnetic field (B) and their products with plasma flow speed (VB and VBz) with Dst are observed to be r=0.78, −0.81, −0.79 and 0.82, respectively, which suggests that these parameters are reliable indicators of the strength of GMS. SN clouds do not always lead to more fall in Dst value (or lead to high strength of GMS) than NS clouds for similar value of Bz minimum associated with both type of MCs.     

Magnetic Clouds: Solar Cycle Dependence,Sources, and Geomagnetic Impacts

Magnetic clouds (MCs) are transient magnetic structures giving the strongest southward magnetic field (Bz south) in the solar wind. The sheath regions of MCs may also carry a southward magnetic field. The southward magnetic field is responsible for space-weather disturbances. We report a comprehensive analysis of MCs and Bz components in their sheath regions for 1995 to 2017. 85% of 303 MCs contain a south Bz up to 50 nT. Sheath Bz during the 23 years may reach as high as 40 nT. MCs of the strongest magnetic magnitude and Bz south occur in the declining phase of the solar cycle. Bipolar MCs depend on the solar cycle in their polarity, but not in the occurrence frequency. Unipolar MCs show solar-cycle dependence in their occurrence frequency, but not in their polarity. MCs with the highest speeds, the largest total-\(B\) magnitudes, and sheath Bz south originate from source regions closer to the solar disk center. About 80% of large Dst storms are caused by MC events. Combinations of a south Bz in the sheath and south-first MCs in close succession have caused the largest storms. The solar-cycle dependence of bipolar MCs is extended to 2017 and now spans 42 years. We find that the bipolar MC Bz polarity solar-cycle dependence is given by MCs that originated from quiescent filaments in decayed active regions and a group of weak MCs of unclear sources, while the polarity of bipolar MCs with active-region flares always has a mixed Bz polarity without solar-cycle dependence and is therefore the least predictable for Bz forecasting.     

Solar Wind Streams And Intense Geomagnetic Storms Observed During 1986–1991

We have analyze the set of 70 intense geomagnetic storms associatedwith D_st decrease of more than 100 nT, observed duringthe period (1986–1991). We have compile these selected intensegeomagnetic storm events and find out their association with twotypes of solar wind streams and different interplanetary parameters.We concluded that the maximum numbers of intense geomagneticstorms are associated with transient disturbances in solar wind streams,which causes strong interplanetary shocks in interplanetary medium.The association of supersonic shocks and magnetic clouds with intensegeomagnetic storms have also been discussed.     

Auroral Evidence for Early High Solar Activities

This paper describes four aurora displays in south Arabia (Yemen), around latitude 16N, during the 9th, 13th, 14th, and 15th centuries. The first event is considered to be the earliest Arabian recorded event of aurora. The second and third events confirmed the case of strong solar activity during the end of the 12th century and mid 15th century, respectively. The fourth event was around solar maximum activity in 1449 ad. So, these records could be considered as proxies for intense geomagnetic solar storms, during early solar activities.     

The solar particle events of May 23 and May 28, 1967

McMath plage region 8818 passed over the visible solar disk on May 17–31, 1967. It was very active from its first appearance on the Eastern limb, several times producing bright optical flares and hard X-ray emission, accompanied by intense type II, type IV and centimeter radio bursts. Nevertheless, no solar particles could be detected near the earth until the evening of May 23, when three bright flares were observed in close succession at 25°–28° E. During the following build-up of the solar particle flux over 36 hours, the galactic cosmic ray flux > 1 GeV decreased gradually by about 5%. The flux of solar particles decreased in two steps on May 25, both accompanied by decreases in the equatorial geomagnetic field. These field depressions are attributed to storm plasma ejected from the parent flare of the May 23 particle event. The propagation of solar particles from May 23 on thus appears to be strongly affected by storm plasma from the parent flare of the May 23 event, without any indications of solar particles being trapped in that plasma.A later particle event early on May 28 was also associated with a bright flare in McMath region 8818, at 33° W. This event displayed a rapid build-up, with electrons arriving first, and an exponential decay. A smooth proton peak, 20 min wide, was detected on May 30 closely associated with an SSC attributed to plasma ejection from the parent flare of the May 28 event.Between the geomagnetic storms beginning on May 25 and May 30 an anomalous daily variation was observed in the cosmic ray flux >1 GeV, the time of maximum falling 7–10 hours earlier than normal. Storm time increases in the flux of galactic cosmic rays were seen on May 26 when the equatorial geomagnetic field was depressed by more than 400 . Low latitude auroras were also observed during that time.On leave from the University of Uppsala, Sweden.