Geomagnetic Storm Period Research Articles

Investigation into the linear relationship between the AE, Dst and ap indices during different magnetic and solar activity conditions

There are numerous geomagnetic indices used in monitoring various magnetospheric and ionospheric phenomena. Some of the most widely used indices are the ap, AE and Dst. In this work, the relationship between these three geomagnetic indices is investigated at different levels of solar and magnetic activity. 3-h average data spanning 8-years were used—high (HSA), moderate (MSA) and low solar activity (LSA) periods cover the years 1999–2001, 2004–2005, and 2006, 2009–2010 respectively. All the investigated correlation pairs recorded the highest/lowest during the LSA/HSA periods. The ap/AE correlation was found to be highest ranging within 70–78 % at any solar activity. The ap versus AE and Dst multiple correlation reached 94.0, 92.1, and 89.2 % for HSA, MSA, and LSA conditions, respectively, and 72.1, 83.3, and 80.0 % for the main phase, recovery phase and quiet conditions respectively. Moreover, higher percentage correlations were observed for the ap/AE pair at any geomagnetic conditions than for the ap/Dst and AE/Dst pairs. The ring current index Dst is observed to have a greater influence on ap during geomagnetic storm periods.

Fresh and evolutionary‐type field‐aligned irregularities generated near sunrise terminator due to overshielding electric fields

AbstractThe unusual evolution of fresh and intense field‐aligned irregularities (FAI) near sunrise terminator which further sustained for more than 90 min of postsunrise period was observed by Equatorial Atmosphere Radar at Kototabang during a minor geomagnetic storm period. These FAI echoes were initially observed around 250–350 km altitudes, growing upward under eastward polarization electric fields indicating the plasma bubbles that are fully depleted along the flux tube. The background low‐latitude F layer dynamics that lead to the development of these dawn time FAI have been investigated from two ionosondes at near magnetic conjugate low‐latitude locations. A minor geomagnetic storm was in progress which did not appear to cause any large electric field perturbations at preceding postsunset to midnight period over Indonesian sector. However, the prompt penetration of overshielding electric fields associated with sudden northward turning of interplanetary magnetic field Bz caused spectacular ascent of F layer and development of fresh, intense, and upward evolutionary plasma bubbles near sunrise terminator.

Determining the spectra of radiation belt electron losses: Fitting DEMETER electron flux observations for typical and storm times

The energy spectra of energetic electron precipitation from the radiation belts are studied in order to improve our understanding of the influence of radiation belt processes. The Detection of Electromagnetic Emissions Transmitted from Earthquake Regions (DEMETER) microsatellite electron flux instrument is comparatively unusual in that it has very high energy resolution (128 channels with 17.9 keV widths in normal survey mode), which lends itself to this type of spectral analysis. Here electron spectra from DEMETER have been analyzed from all six years of its operation, and three fit types (power law, exponential, and kappa‐type) have been applied to the precipitating flux observations. We show that the power law fit consistently provides the best representation of the flux and that the kappa‐type is rarely valid. We also provide estimated uncertainties in the flux for this instrument as a function of energy. Average power law gradients for nontrapped particles have been determined for geomagnetically nondisturbed periods to get a typical global behavior of the spectra in the inner radiation belt, slot region, and outer radiation belt. Power law spectral gradients in the outer belt are typically −2.5 during quiet periods, changing to a softer spectrum of ∼−3.5 during geomagnetic storms. The inner belt does the opposite, hardening from −4 during quiet times to ∼−3 during storms. Typical outer belt e‐folding values are ∼200 keV, dropping to ∼150 keV during geomagnetic storms, while the inner belt e‐folding values change from ∼120 keV to >200 keV. Analysis of geomagnetic storm periods show that the precipitating flux enhancements evident from such storms take approximately 13 days to return to normal values for the outer belt and slot region and approximately 10 days for the inner belt.

Observations of nitric oxide in the Antarctic middle atmosphere during recurrent geomagnetic storms

AbstractWe report ground‐based measurements of the polar middle atmosphere made using a 230–250 GHz passive microwave radiometer deployed at Troll station (72°01′S 02°32′E, L shell of L = 4.8), Antarctica. Our observations show enhanced mesospheric nitric oxide (NO) volume mixing ratio (VMR) during a series of small recurrent geomagnetic storms in the 2008 austral winter, reaching 1.2 ppmv on day 200 (18 July). The Lomb normalized periodogram of the NO VMR time series averaged over 65‐80 km for days 130 to 220 of 2008 (9 May to 7 August) shows a peak exceeding the 95% confidence limit at 25.8 days, close to the synodic rotation period for low‐latitude solar coronal holes. The highest correlations between the radiometer NO VMR data and trapped and quasi‐trapped electron count rates for L = 3.5‐5.5 from the Polar Orbiting Environment Satellites 90° telescope are for the >30 keV (90e1) channel (rmax = 0.56, lag time of 5.1 days) and >100 keV (90e2) channel (rmax = 0.57, lag time of 4.4 days). Maximum correlation between NO VMR and the >700 keV (90P6) channel data is lower but lag times are close to zero. Superposed epoch analyses for the eight most significant geomagnetic storm periods and three Carrington rotations (2070‐2072) within the 90 day observation period indicate that significant NO abundance observed at 65‐80 km in the Antarctic mesosphere may be produced directly by >200 keV electron precipitation or originate from a source at higher altitudes, e.g., production by >30 keV electrons followed by downward transport.

Estimating the propagation characteristics of large‐scale traveling ionospheric disturbances using ground‐based and satellite data

In this article, the propagation characteristics of large‐scale traveling ionospheric disturbances (LS TIDs) are estimated during the geomagnetic storm periods of 14–16 May 2005 and 25–27 September 2011 over South Africa. One and two GPS arrays have been independently considered for the storms of 15 May 2005 and 26 September 2011, respectively. The average periods of dominant modes (≈ 2.5–3.5h) in the time series data were determined by applying wavelet analysis on both ionosonde and GPS data. The consideration of diurnal GPS total electron content (TEC) variability from receivers along three different longitude sectors showed a time shift in TEC enhancement with increasing latitude, the first indication of equatorward motion of the traveling ionospheric disturbances (TIDs). The statistical method (based on GPS radio interferometry) employed shows that these TIDs were mostly propagating nearly equatorward (for both storm periods), which is consistent with the existing literature about storm‐induced TIDs. On storm days, TID horizontal velocities have been determined in the range of ≈200–500m/s. The analysis of diurnal TEC response from different stations confirmed that the positive storm effect observed on 15 May 2005 was a result of the large‐scale TIDs of wavelength ≈4000 km. On the other hand, the estimated wavelengths of LS TIDs on 26 September 2011 were ≈2400–3400km between 10 and 17 UT. A time lag is observed between the times at which enhancements in TEC, ionosonde foF2, and hmF2 data are revealed, and this has been attributed to the passage of the TID.

An evaluation of the IRI-2007 storm time model at low latitude stations

This paper discusses the ability of the International Reference Ionosphere IRI-2007 storm time model to predict foF2 ionospheric parameter during geomagnetic storm periods. Experimental data (based on availability) from two low latitude stations: Vanimo (geographic coordinates, 2.7 °S, 141.3 °E, magnetic coordinates, 12.3 °S, 212.50 °E) and Darwin (geographic coordinates, 12.45 °S, 130.95 °E, magnetic coordinates, 22.9 °S, 202.7 °E) during nine storms that occurred in 2000 (Rz12=119), 2001(Rz12=111) and 2003 (Rz12=64) are compared with those obtained by the IRI-2007 storm model. The results obtained show that the percentage deviation between the experimental and IRI predicted foF2 values during these storm periods is as high as 100% during the main and recovery phases. Based on the values of “relative deviation module mean” (RDMM) obtained (i.e. between 0.08 and 0.60), it is observed that there is a reasonable to poor agreement between measured foF2 values and the IRI-storm model prediction values during main and recovery phases of the storms under investigation. As a result, in addition to other studies that have been carried out from different sectors, more studies are required to be carried out. This will enable IRI community to improve on the present performance of the model. In general the IRI-storm model predictions follow normal trend of the foF2 measured values but does not reproduce well the measured values.

Empirical STORM-E model: II. Geomagnetic corrections to nighttime ionospheric E-region electron densities

Auroral nighttime infrared emission observed by the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument onboard the Thermosphere–Ionosphere–Mesosphere Energetics and Dynamics (TIMED) satellite is used to develop an empirical model of geomagnetic storm enhancements to E-region electron densities. The empirical model is called STORM-E and will be incorporated into the 2012 release of the International Reference Ionosphere (IRI). The proxy for characterizing the E-region response to geomagnetic forcing is NO+(v) Volume Emission Rates (VER) derived from the TIMED/SABER 4.3μm channel limb radiance measurements. The storm-time response of the NO+(v) 4.3μm VER is most sensitive to auroral particle precipitation. A statistical database of storm-time to climatological quiet-time ratios of SABER-observed NO+(v) 4.3μm VER are fit to widely available geomagnetic indices using the theoretical framework of linear impulse-response theory. The STORM-E model provides a dynamic storm-time correction factor to adjust a known nighttime quiescent E-region electron density peak concentration for geomagnetic enhancements due to auroral particle precipitation. Part I of this series gives a detailed description of the algorithms and methodologies used to derive NO+(v) VER from SABER 4.3μm limb emission measurements. In this paper, Part II of the series, the development of the E-region electron density storm-time correction factor is described. The STORM-E storm-time correction factor is fit to a single geomagnetic index. There are four versions of the STORM-E model, which are currently independent of magnetic local time. Each version is fit to one of the following indices: HP, AE, Ap, or Dst. High-latitude Incoherent Scatter Radar (ISR) E-region electron density measurements are compared to STORM-E predictions for various geomagnetic storm periods during solar cycle 23. These comparisons show that STORM-E significantly improves the prediction of E-region electron density enhancements due to auroral particle precipitation, in comparison to the nominal IRI model or to the quiet-time baseline electron density concentrations measured by ISR. The STORM-E/ISR comparisons indicate that the STORM-E fits to the Ap-, AE-, and HP-indices are comparable in both absolute accuracy and relative dynamical response. Contrarily, the Dst-index does not appear to be a suitable input driver to parameterize the E-region electron density response to geomagnetic activity.

First observational evidence for opposite zonal electric fields in equatorial E and F region altitudes during a geomagnetic storm period

The strong westward electrojet and simultaneous upward drift of the equatorial ionospheric peak observed over South‐East Asia and Indian equatorial regions during the prolonged Dst minimum phase of an intense geomagnetic storm during 14–15 December 2006 are investigated for the altitudinal variation of zonal electric field polarity using ground based and space‐borne observations. The results show first observational evidence for simultaneous existence of daytime westward and eastward zonal electric fields at equatorial E and F region altitudes, respectively, in a wide longitude sector. While the westward electric fields at E region altitudes cause westward electrojet, at the same time, the eastward zonal electric fields atFregion altitudes cause the upward drift of the equatorial ionospheric peak and reinforcement of the equatorial ionization anomaly (EIA) even in the topside ionosphere (∼660 km). The reversal of the electric fields is found to occur at ∼280 km height. A clear bifurcation of F region plasma at ∼280 km is evident in the iso‐electron density contours due to these oppositely polarized zonal electric fields, which manifests as an unusually deep cusp between F1 and F2 layers on equatorial ionograms.

Comparison of Dst forecast models for intense geomagnetic storms

We have compared six Dst forecast models using 63 intense geomagnetic storms (Dst ≤ −100 nT) that occurred from 1998 to 2006. For comparison, we estimated linear correlation coefficients and RMS errors between the observed Dst data and the predicted Dst during the geomagnetic storm period as well as the difference of the value of minimum Dst (ΔDstmin) and the difference in the absolute value of Dst minimum time (ΔtDst) between the observed and the predicted. As a result, we found that the model by Temerin and Li (2002, 2006) gives the best prediction for all parameters when all 63 events are considered. The model gives the average values: the linear correlation coefficient of 0.94, the RMS error of 14.8 nT, the ΔDstmin of 7.7 nT, and the absolute value of ΔtDst of 1.5 hour. For further comparison, we classified the storm events into two groups according to the magnitude of Dst. We found that the model of Temerin and Lee (2002, 2006) is better than the other models for the events having −100 ≤ Dst < −200 nT, and three recent models (the model of Wang et al. (2003), the model of Temerin and Li (2002, 2006), and the model of Boynton et al. (2011b)) are better than the other three models for the events having Dst ≤ −200 nT.

Responses of equatorialFregion to different geomagnetic storms observed by GPS in the African sector

[1] This article presents the first results regarding the investigation of the response of the equatorial ionospheric F region in the African sector during geomagnetic storm periods between April 2000 and November 2007 using GPS-derived vertical total electron content observed at Libreville, Gabon (0.35°N, 9.67°E, dip latitude −8.05°S). We performed a superposed epoch analysis of the storms by defining the start time of the epoch as the storm onset time. During geomagnetic storms, the altered electric fields contribute significantly to the occurrence of negative and positive ionospheric storm effects. Our results showed that the positive storm effects are more prevalent than the negative storm effects and generally last longer irrespective of storm onset times. Also, the positive storm effects are most pronounced in the daytime than in the premidnight and postmidnight periods.

The effects of earthward directed interplanetary coronal mass ejections on near-Earth S band signal links

[1] Human space exploration is expected to enter its next phase in the coming decades as the United States prepares to return to the Moon or perhaps venture even further with a crewed mission to a near-Earth asteroid. Both mission classes are viewed by NASA as precursors of eventual crewed missions to Mars. In anticipation of extensive robotic and human presence in the space environment beyond the protection of the Earth's magnetosphere, it is important to better quantify and bound effects of earthward directed solar storms not just on the human body but also on engineering signals. In this paper, we study the effects of solar storms on S band (∼2.3 GHz) radio links in the near-Earth environment, primarily for application to navigation. In particular, we are concerned with induced long-period signatures on Doppler tracking data that could be confused with the Earth's gravity signature, resulting in perturbed trajectory solutions of returning spacecraft during Earth entry targeting. We have quantified “worst-case” levels of such induced signatures on S band signal phase using model predictions based on measured in situ charged particle content from satellites and have compared these results with signatures seen in actual tracking data during periods of interplanetary coronal mass ejections (ICME) and related geomagnetic storms. We show that induced Doppler can mask Earth gravity field effects in navigation trajectory solutions at S band, a commonly used frequency for near-Earth communications and navigation. Finally, we suggest a few ways that such effects can be identified, alleviated or eliminated in near real-time.

Comparison of modeled electron densities and electron and ion temperatures with Arecibo observations during undisturbed and geomagnetic storm periods of 7-11 September 2005

[1] The electron density and the electron and ion temperatures measured by the Arecibo radar at 496 km altitude and NmF2 observed by the Puerto Rico ionosonde are compared with those produced by the model of the ionosphere and plasmasphere to study the time-dependent response of the ionosphere to geomagnetic forcing during the undisturbed and geomagnetic storm periods of 7–11 September 2005. The reasonable agreement between the model results and data requires the modified HWM90 wind and the modified NRLMSISE-00 neutral temperature. The pronounced positive daytime storm changes in NmF2 are created by increases in the upward wind-induced plasma drift due to the neutral wind, while the geomagnetic storm decreases in [N2] and [O2] and the enhanced disturbed upward wind-induced plasma drift cause the pronounced positive nighttime disturbances in NmF2. The storm neutral wind-induced plasma drift and neutral composition changes are responsible for the pronounced negative daytime NmF2 disturbances. The F2 layer transport from lower to higher altitudes by the upward wind-induced plasma drift decreases the distance between the hmF2 and our chosen altitude for study of the topside ionosphere. This results in the increase of the electron density at this chosen altitude due to a more weakly reduction in the electron density with altitude. The pronounced postmidnight peaks observed in the topside electron density over Arecibo are provided by these increases in the electron density.

The relation between geomagnetic pulsations and an increase in the fluxes of geosynchronous relativistic electrons during geomagnetic storms

The dynamics of the Pc5 and Pi1 pulsation characteristics and relativistic electron fluxes at geostationary orbit were comparatively analyzed for three nine-day intervals, including quiet periods and periods of geomagnetic storms. It was shown that relativistic electron fluxes increase considerably when the power of global Pc5 pulsations and the index of midlatitude irregular Pi1 pulsations increase simultaneously. The correlation between the characteristics of Pi1 and Pc5 geomagnetic pulsations and the level of the relativistic electron flux at geostationary orbit during the magnetic storm recovery phase were studied. It was shown that the correlation coefficient of the relativistic electron maximal fluxes during the magnetic storm recovery phase with the parameter of midlatitude Pi1 pulsations is slightly higher than such a correlation coefficient with the solar wind velocity.

EMIC wave activity during geomagnetic storm and nonstorm periods: CRRES results

Electromagnetic ion cyclotron (EMIC) waves have been observed during geomagnetic storms and are thought to contribute to ring current and radiation belt particle loss during the main phase. Ground‐based storm time studies alternatively observe the majority of storm time Pc1‐2 pulsations during the recovery phase. In this study we look at the occurrences of EMIC waves during 119 storms occurring throughout the CRRES mission. The storms were defined using the Sym‐H index. The storm was divided into three phases: pre‐onset, main, and recovery (80% of minimum Sym‐H value). The majority, 56.25%, of storm time EMIC waves were found to occur during the main phase, while 35.57% were observed in the recovery phase. The recovery phase definition was then extended to 6 days after the minimum in order to compare with past ground studies. Although more EMIC waves were observed during this extended recovery phase, the maximum occurrence rate of EMIC waves remains in the main phase. A slight increase does appear in the 4–6 days after the minimum Sym‐H value. The mean occurrence location of EMIC waves was at L = 6.07, MLT = 15.12. This suggests that EMIC waves may have been generated when the ring current and plasmasphere or plasma plume particle populations overlap, often observed during the main phase due to storm dynamics. The rise in the occurrence rate in the extended recovery phase potentially is dominated by the process of plasmaspheric expansion after the end of the storm.

Spectral characteristics of protons in the Earth's plasmasheet: statistical results from Cluster CIS and RAPID

Abstract. We present a study of the spectral characteristics of protons in the Earth's plasma sheet for various geomagnetic disturbance levels. The study is based on about 5400 h of data combined from the Cluster RAPID and CIS instruments obtained during the tail season (July–October). The overall proton spectral shape is generally that of a κ distribution, that is, resembling a Maxwellian at lower energies which smoothly merges into a power-law tail at higher energies. The actual spectral long-term slope depends on various magnetospheric driver parameters, but is on average around 3.5–4. During disturbed conditions, such as geomagnetic storm or substorm periods, a shift in the characteristic energy is observed. For two individual storms, we also found a hardening of the spectra. Unlike the electron spectra, we do not see any significant local time dependence in the spectral slope, but we find higher average ion fluxes in the dusk side. We also do not find any direct response in the energy spectra to changes in the interplanetary magnetic field or solar wind dynamic pressure. This suggests that energization of the ions are mainly due to internal processes in the plasma sheet.

Drifting ELF/VLF Emissions Observed at Low Latitude Ground Station During Geomagnetic Storm

We have reported for the first time total seven strong events of drifting ELF/VLF discrete emissions observed on 28th–29th April, 1990 in the pre-midnight sector at Varanasi (Geomag. lat. 14°55′N, long. 154°E, L = 1.07). The events exhibit a regular increasing as well as decreasing frequency drifts and are mainly discrete periodic emissions of riser, faller and hook types observed during a geomagnetic storm period, with minimum Dst-index −98 nT and Kp-index ≥ 5. The frequency drift in ELF/VLF emissions at low latitudes seems to be a rare phenomenon. The repetition period and the frequency drift rate have been evaluated for all the recorded events. The frequency drifts have been interpreted in terms of a combined effect of L-shell drift of interacting energetic electrons and the change in convection electric fields during the storm developments. The computed maximum spectral power density \( \left\langle {B_{f}^{2} } \right\rangle_{\max } \)of the wave varies between 1.8 × 10−21 and 4.08 × 10−22 Gauss2/Hz, whereas frequency drift rates are in agreement with the observed values.

Characteristics of ELF/VLF drifting emissions observed at low latitude station Varanasi during geomagnetic substorms

If the frequency within a set of periodic emissions changes significantly, the set is called drifting emissions. In this paper, characteristics of drifting ELF/VLF emissions are examined based on the ELF/VLF data recorded at low latitudes ground station Varanasi (geom. lat. 14° 55/ N, long. 154° E, L=1.07) during the period Jan., 1990 to Dec., 1990. Total seven strong events of drifting ELF/VLF emissions have been observed on 28-29 April, 1990 at pre-midnight sector out of which 3 events were analyzed in detail. The observed ELF/VLF emissions exhibit a regular frequency drifts, increasing as well as decreasing drift. The ELF/VLF emissions observed are mainly periodic emissions of rising and falling tone chorus. These emissions were observed during a geomagnetic storm period, when minimum Dst-index was −98 nT and KP-index ≥ 5. The repetition period, sweep rate and the frequency drift rate have been evaluated for all events. We have also computed the spectral power density, location of plasmapause, maximum intensity and maximum frequency attained. The generation mechanism of these drifting ELF/VLF emissions is explained in terms of a quasi-linear electron synchrotron instability model for wave excitation. The frequency drift in these emissions have been interpreted in terms of a combined effect of L-shell drift of energetic electrons and the change in convections electric field during the substorm developments. The computed maximum spectral power density of the wave varies between 1.8 × 10-21 to 4.08 × 10-22 Gauss2/Hz. The computed frequency drift rates of these drifting emissions are found in good agreement with that of experimentally observed values.

A generation mechanism of chorus emissions using BWO theory

In this paper, discrete VLF chorus emissions recorded at low latitude ground station Jammu (geomag. Lat. = 22° 26/ N, L = 1.17) are reported and their characteristics based on complete spectral analysis have been carried out. These discrete chorus emissions are generated during a strong geomagnetic storm period of 2-7 May, 1998. We have computed the sweep rate, repetition period, source region, and drift rate of the individual chorus elements. It is observed that the sweep rate increases with time. To explain the various temporal and spectral features of these emissions, a possible generation mechanism has been presented based on the backward wave oscillator (BWO) regime in the magnetospheric cyclotron maser. On the basis of this model, we have computed some discrete chorus emission parameters as well as magnetospheric parameters relevant to the generation process. A comparison of the computed and observed magnetospheric parameters has been presented. These results show a good agreement with the BWO model.

Characteristics of discrete VLF falling-tone chorus emissions observed at low latitude ground station Jammu

Abstract The discrete VLF chorus emissions recorded at low latitude ground station Jammu (geomag. lat. = 22°26′N, L = 1.17) are reported and their characteristics based on spectral analysis have been carried out. These discrete chorus emissions are falling tone emissions which are rarely observed at low latitude ground stations. These discrete chorus emissions are generated during a strong geomagnetic storm period of 2–7 May, 1998. We have computed the frequency sweep rate, repetition period and source region of the individual chorus elements. It is observed that the sweep rate increases with time.

Non-radial solar wind flows and IMF B z during 1973–2003

The characteristics of latitudinal angles of solar wind flow ( θ v) observed near earth have been studied during the period 1973–2003. The average magnitude of θ v shows distinct enhancements during the declining and maximum phases of the sunspot cycles. A close association of B z component of IMF in the GSE system and the orientation of meridional flows in the solar wind is found which depends on the IMF sector polarity. This effect has been studied in typical geomagnetic storm periods. The occurrence of non-radial flows is also found to exhibit heliolatitudinal dependence during the years 1975 and 1985 as a characteristic feature of non-radial solar wind expansion from polar coronal holes.