Intense Geomagnetic Activity Research Articles

Solar and interplanetary sources of major geomagnetic storms during 1996–2002

During the 7‐year period of the current solar cycle, 64 geoeffective coronal mass ejections (CMEs) were found to produce major geomagnetic storms (DST < −100 nT) at the Earth. In this paper we examine solar and interplanetary properties of these geoeffective coronal mass ejections (CMEs). The observations reveal that full‐halo CMEs are potential sources of intense geomagnetic activity at the Earth. However, not all full‐halo CMEs give rise to major geomagnetic storms, which complicates the task of space weather forecasting. We examine solar origins of the geoeffective CMEs and their interplanetary effects, namely, solar wind speed, interplanetary shocks, and the southward component of the interplanetary magnetic field, in order to investigate the relationship between the solar and interplanetary parameters. In particular, the present study aims at ascertaining solar parameters that govern important interplanetary parameters responsible for producing major geomagnetic storms. Our investigation shows that fast full‐halo CMEs associated with strong flares and originating from a favorable location, i.e., close to the central meridian and low and middle latitudes, are the most potential candidates for producing strong ram pressure at the Earth's magnetosphere and hence intense geomagnetic storms. The results also show that the intensity of geomagnetic storms depends most strongly on the southward component of the interplanetary magnetic field, followed by the initial speed of the CME and the ram pressure.

Geoeffectiveness of interplanetary shocks during solar minimum (1995–1996) and solar maximum (2000)

Plasma and magnetic field parameter variations across fast forward interplanetary shocks are analyzed during the last solar cycle minimum (1995–1996, 15 shocks), and maximum year 2000 (50 shocks). It was observed that the solar wind velocity and magnetic field strength variation across the shocks were the parameters better correlated with Dst. Superposed epoch analysis centered on the shock showed that, during solar minimum, B z profiles had a southward, long-duration variation superposed with fluctuations, whereas in solar maximum the B z profile presented 2 peaks. The first peak occurred 4 hr after the shock, and seems to be associated with the magnetic field disturbed by the shock in the sheath region. The second peak occurred 19 hr after the shock, and seems to be associated with the ejecta fields. The difference in shape and peak in solar maximum (Dst peak =−50 nT, moderate activity) and minimum (Dst peak =−30 nT, weak activity) in average Dst profiles after shocks are, probably, a consequence of the energy injection in the magnetosphere being driven by different interplanetary southward magnetic structures. A statistical distribution of geomagnetic activity levels following interplanetary shocks was also obtained. It was observed that during solar maximum, 36% of interplanetary shocks were followed by intense (Dst≤−100 nT) and 28% by moderate (−50≤Dst <−100 nT) geomagnetic activity. During solar minimum, 13% and 33% of the shocks were followed by intense and moderate geomagnetic activity, respectively. Thus, during solar maximum a higher relative number of interplanetary shocks might be followed by intense geomagnetic activity than during solar minimum. One can extrapolate, for forecasting goals, that during a whole solar cycle a shock has a probability of around 50–60% to be followed by intense/moderate geomagnetic activity.

Ring current dynamics during the 13-18 July 2000 storm period

We study the development of the terrestrial ring current during the time interval of 13–18 July, 2000, which consisted of two small to moderate geomagnetic storms followed by a great storm with indices Dst=−300 nT and Kp=9. This period of intense geomagnetic activity was caused by three interplanetary coronal mass ejecta (ICME) each driving interplanetary shocks, the last shock being very strong and reaching Earth at ∼ 14 UT on 15 July. We note that (a) the sheath region behind the third shock was characterized by B z fluctuations of ∼35 nT peak-to-peak amplitude, and (b) the ICME contained a negative to positive B z variation extending for about 1 day, with a ∼ 6-hour long negative phase and a minimum B z of about −55 nT. Both of these interplanetary sources caused considerable geomagnetic activity (Kp=8 to 9) despite their disparity as interplanetary triggers. We used our global ring current-atmosphere interaction model with initial and boundary conditions inferred from measurements from the hot plasma instruments on the Polar spacecraft and the geosynchronous Los Alamos satellites, and simulated the time evolution of H+, O+, and He+ ring current ion distributions. We found that the O+ content of the ring current increased after each shock and reached maximum values of ∼ 60% near minimum Dst of the great storm. We calculated the growth rate of electromagnetic ion cyclotron waves considering for the first time wave excitation at frequencies below O+ gyrofrequency. We found that the wave gain of O+ band waves is greater and is located at larger L shells than that of the He+ band waves during this storm interval. Isotropic pitch angle distributions indicating strong plasma wave scattering were observed by the imaging proton sensor (IPS) on Polar at the locations of maximum predicted wave gain, in good agreement with model simulations.

A linear relationship between postnatal geomagnetic activity and self-reports of epileptic seizures in young adults.

To test the hypothesis of a linear relationship between the intensity of geomagnetic activity during the first two days after birth and the development of epilepsy, the responses of the item "I have had an epileptic seizure" was obtained from the Personal Philosophy Inventories of 1,453 students who had been enrolled in first-year psychology courses over a 13-yr. period. The only statistically significant effect was linear and was between the successive 10 nT (nanoTesla) increments of the intensity of geomagnetic activity during the two days after birth and the percentage of students who reported epileptic seizures. The percentage of subjects reporting a history of seizures ranged from 1% for those born when the activity was less than 10 nT to 4% for those born when this activity exceeded 40 nT.

Geomagnetic field variations at low and high latitude during the January 10–11, 1997 magnetic cloud

On Jan. 10–11, 1997 a wide magnetic cloud reached the Earth triggering intense geomagnetic activity. Observations performed at low and very high latitude show that the same features appear simultaneously in correspondence to different changes in the solar wind conditions. In particular, highly polarized modes are simultaneously observed at the same discrete frequencies after the passage of the high density solar wind region following the cloud. SI's and ULF waves polarization are also examined in a wide latitudinal and longitudinal extent.

Characteristics of upstream energetic (E≥50 keV) ion events during intense geomagnetic activity

In this work we examine the statistical presence of some important features of upstream energetic (≥50 keV) ion events under some special conditions in the upstream region and the magnetosphere. The 125 ion events considered in the statistic were observed by the IMP 7 and IMP 8 spacecraft, at ∼35 RE from the Earth, during nine long time intervals of a total of 153 hours. The time intervals analyzed were selected under the following restrictions: existence of high proton flux (i.e., ≥900 p cm−2 s−1 sr−1) and of a great number of events (an occurrence frequency of ∼10 events per 12 hours in the whole statistics) in the energy range 50–220 keV. The most striking findings are the following: (1) The upstream events were observed during times with high values of the geomagnetic activity index Kp (≥3‐); (2) all of the upstream events (100%) have energy spectra extending up to energies E≥290keV; (3) 86% of these events are accompanied by relativistic (E ≥ 220 keV) electrons; and (4) the majority of the upstream ion events (82%) showed noninverse velocity dispersion during their onset phase (22% of the events showed forward velocity dispersion, and 60% showed no velocity dispersion at all when 5.5‐min averaged observations were analyzed). Further statistical analysis of this sample of upstream particle events shows that the 50‐ to 220‐keV proton flux shows a positive correlation with the following parameters: the Kp index of geomagnetic activity and the flux of the high‐energy (290–500 keV) protons and (≥220 keV) electrons. More specific findings are the following: (1) The spectral index γ for a power law distribution of ions detected by the National Oceanic and Atmospheric Administration Energetic Particle Experiment (EPE) instrument (50 ≤ E ≤ 220 keV) and The Johns Hopkins University Applied Physics Laboratory Charged Particle Measurement Experiment (CPME) instrument (290 ≤ E ≤ 500 keV) ranges between 2 and 6, with maximum probability between 4 and 5 and (2) the peak‐to‐background flux ratio of the 290‐ to 500‐keV protons and ≥220‐keV electrons increases with the time duration of upstream events. We infer that the vast majority of the upstream ion events considered in this study (under conditions of intense particle activity in the upstream region and enhanced geomagnetic activity within the magnetosphere) can be consistently explained in terms of particle leakage from the magnetosphere.

Coronal hole‐active region‐Current sheet (CHARCS) Association with intense interplanetary and geomagnetic activity

Intense geomagnetic storms (Dst ≤ −100 nT) have been associated with interplanetary structures involving large‐intensity (Bs ≥ 10 nT) and long‐duration (T ≥ 3 hours) values of the southward component of the IMF. We show that near solar maximum, the solar origin of such structures seems to be associated with active regions* (involving flares and/ or filament eruptions) occurring close to the streamer belt and to growing low‐latitude coronal holes. It is also shown that low‐latitude coronal holes had a dual‐peak solar cycle distribution during solar cycle 21, similar to that previously reported for the above mentioned interplanetary and geomagnetic phenomena.

The use of various interplanetary scintillation indices within geomagnetic forecasts

Abstract. Interplanetary scintillation (IPS), the twinkling of small angular diameter radio sources, is caused by the interaction of the signal with small-scale plasma irregularities in the solar wind. The technique may be used to sense remotely the near-Earth heliosphere and observations of a sufficiently large number of sources may be used to track large-scale disturbances as they propagate from close to the Sun to the Earth. Therefore, such observations have potential for use within geomagnetic forecasts. We use daily data from the Mullard Radio Astronomy Observatory, made available through the World Data Centre, to test the success of geomagnetic forecasts based on IPS observations. The approach discussed here was based on the reduction of the information in a map to a single number or series of numbers. The advantages of an index of this nature are that it may be produced routinely and that it could ideally forecast both the occurrence and intensity of geomagnetic activity. We start from an index that has already been described in the literature, INDEX35. On the basis of visual examination of the data in a full skymap format modifications were made to the way in which the index was calculated. It was hoped that these would lead to an improvement in its forecasting ability. Here we assess the forecasting potential of the index using the value of the correlation coefficient between daily Ap and the IPS index, with IPS leading by 1 day. We also compare the forecast based on the IPS index with forecasts of Ap currently released by the Space Environment Services Center (SESC). Although we find that the maximum improvement achieved is small, and does not represent a significant advance in forecasting ability, the IPS forecasts at this phase of the solar cycle are of a similar quality to those made by SESC.

The use of various interplanetary scintillation indices within geomagnetic forecasts

Interplanetary scintillation (IPS), the twinkling of small angular diameter radio sources, is caused by the interaction of the signal with small-scale plasma irregularities in the solar wind. The technique may be used to sense remotely the near-Earth heliosphere and observations of a sufficiently large number of sources may be used to track large-scale disturbances as they propagate from close to the Sun to the Earth. Therefore, such observations have potential for use within geomagnetic forecasts. We use daily data from the Mullard Radio Astronomy Observatory, made available through the World Data Centre, to test the success of geomagnetic forecasts based on IPS observations. The approach discussed here was based on the reduction of the information in a map to a single number or series of numbers. The advantages of an index of this nature are that it may be produced routinely and that it could ideally forecast both the occurrence and intensity of geomagnetic activity. We start from an index that has already been described in the literature, INDEX35. On the basis of visual examination of the data in a full skymap format modifications were made to the way in which the index was calculated. It was hoped that these would lead to an improvement in its forecasting ability. Here we assess the forecasting potential of the index using the value of the correlation coefficient between daily Ap and the IPS index, with IPS leading by 1 day. We also compare the forecast based on the IPS index with forecasts of Ap currently released by the Space Environment Services Center (SESC). Although we find that the maximum improvement achieved is small, and does not represent a significant advance in forecasting ability, the IPS forecasts at this phase of the solar cycle are of a similar quality to those made by SESC.

The effect of the mid-latitude ionospheric trough on whistler mode ducting during magnetic storms

Whistler-mode signals observed at Faraday, Antarctica (65° S, 64° W, Λ=50.8°) show anomalous changes in group delay and Doppler shift with time during the main phase of intense geomagnetic activity. These changes are interpreted as the effect of refracting signals into and out of ducts near L=2.5 by electron concentration gradients associated with edges of the mid-latitude ionospheric trough. The refraction region is observed to propagate equatorwards at velocities in the range 20–85 ms −1 during periods of high geomagnetic activity ( K p ≥ 5), which is in good agreement with typical trough velocities. Model estimates of the time that the trough edges come into view from Faraday show a good correlation with the observed start times of the anomalous features. Whistler-mode signals observed at Dunedin, New Zealand (46° S, 171° E, Λ=52.5°) that have propagated at an average L-shell of 2.2 (Λ=47.6°) do not show such trough-related changes in group delay. These observations are consistent with a lower occurrence of the trough at lower invariant latitudes.

Variations in the FUV dayglow after intense auroral activity

A localized ∼55% decrease is observed in the brightness of Earth's FUV dayglow in the morning sector at 130.4 nm after an interval of intense geomagnetic activity. This large decrease is interpreted as being the consequence of auroral‐associated heating which reduces the thermospheric column density of O relative to that of N2. Spatial extent of the observed decrease exceeds 107 km² at the −25% level, and the depth of the decrease lessens during more than two hours of observations. These remote observations provide the first instantaneous, two‐dimensional measurement of the large‐scale spatial extent of such a change in thermospheric composition.

Observations of V = 1–0 emission from thermospheric nitric oxide by ISAMS

The Improved Stratospheric and Mesospheric Sounder (ISAMS) on the Upper Atmosphere Research Satellite (UARS) has made global measurements of emission from the 1→0 band of nitric oxide (NO), using a limb viewing geometry in which the tangent point is scanned from 0 km to &gt;150 km. Vertical profiles of atmospheric radiance often show a peak around 120 km altitude, due to the relatively high temperatures and densities of NO(v=1) found in the lower thermosphere. In this letter we report on some aspects of the radiance from NO(v=1), in particular observations of the lower thermosphere during periods of quiet and intense geomagnetic activity.

Ultralow frequency waves in the magnetotails of the Earth and the outer planets

Ultralow frequency waves with periods greater than 2 minutes are characteristic features of planetary magnetotails. At Jupiter, changes in the wave characteristics across the boundary between the plasma sheet and the lobe have been used to identify this important plasma boundary. In the terrestrial lobes the wave amplitude can be relatively large, especially during intervals of intense geomagnetic activity. We have now evaluated the wave power seen in the lobes of the magnetotails of the Earth, Jupiter, Saturn and Uranus to evaluate a proposal by Smith et al. that the propagating waves generated by the Kelvin-Helmholtz instability on the magnetopause can heat the plasma through a resonant absorption of these waves. Our results indicate that the wave power in the lobes is generally small and can be easily understood in the framework of coupled MHD waves generated in the plasma sheet.

On the equivalence of the solar wind coupling parameter ε and the magnetospheric energy output parameter UT during intense geomagnetic storms

For intervals with intense geomagnetic activity it is shown that the solar wind coupling parameter ε and the magnetospheric output parameter U T are equivalent and that ranges of values of ε can be set up in terms of values of the ring current-time constant τ. These conclusions were originally suggested by Akasofu (1981, Space Sci. Rev. 28, 111).

The determination of relative effective atmospheric densities at 800 km using SEASAT laser range data

A method to determine relative effective atmospheric densities from variations within the recovered drag coefficients of long-arc orbits is presented. Application to SEASAT laser range data yields relative densities at heights near 800 km over daily intervals. For moderate levels of the base density (solar flux ∼ 150 × 10 −22 W m −2 Hz −1), along-track gravity field and solar radiation pressure errors are shown to have little effect on the derived values. A constant scale error in the solar radiation pressure model has little effect for any level of the base density. Observed densities during a period of intense geomagnetic activity establish that, in general, thermospheric models underestimate the atmospheric response at heights near 800 km. By deriving observed and modelled density profiles, it is possible to predict where a good orbital fit with a single drag scale factor can occur.

July 29, 1977, magnetospheric studies: Impulsive waves, global dynamics and geomagnetic indices

This paper concludes the initial series of reports on the CDAW (Coordinated Data Analysis Workshop) study of the events of July 29, 1977. The primary purpose of this presentation is to point out interrelations among other papers in the series and to show how they increase our knowledge of how the magnetosphere operates. The day in question included intervals of intense geomagnetic activity, with an initial impulsive response to an interplanetary shock followed by numerous substorms. The latter half of the day was of special interest because the activity was limited to high latitudes in the northern polar cap, where it was substantial. Problems of magnetospheric physics addressed with the CDAW study are herein grouped into several general areas. The immediate response of the magnetosphere to changes in the solar wind (shock or other) was considered in studies of impulsive waves, which were traced through the magnetosphere to the ground and interpreted in terms of fast‐mode wave propagation. The geometry and microstructure of the magnetopause, following the arrival of an interplanetary shock, were analyzed with data from near‐geostationary satellites. The global magnetic geometry was modeled for the entire day. Plasma sheet convection was monitored at low and high altitudes. A model of particle convection during the first quarter of the day gave important evidence that the convection electric field penetrated to small radial distances for extended intervals. A large substorm at midday was unusually well documented with data from geostationary spacecraft and ground observatories. In reviewing those data this paper addresses the question of control of the local time of substorm onset. A model is presented that relates the local time of substorm onset to the sector of the tail earliest stressed following the onset of dayside reconnection. The late‐day data provided evidence of lobe magnetic field reconnection when the solar wind magnetic field was pointing north. This paper marshals the evidence for different reconnection patterns and introduces an alternative pattern not previously considered. Remarks on the way in which the day's observations bear on several indices of geomagnetic activity end the summary.

Mechanism of the relations between the changes of the geomagnetic field, solar corpuscular radiation, atmospheric circulation, and climate.

The correlations between geomagnetic, climatic, and meteorological phenomena were investigated with the object of demonstrating the function of the geomagnetic pole and changes of its position in controlling the climate and weather. A tentative model has been proposed to enable one to understand the causes of the generation of glacial and interglacial periods, as well as the causes which effect changes of climate (BUCHA, 1976a).The analyses of various types of geomagnetic and atmospheric manifestations have disclosed certain associations. The coincidence in the occurrence of increased spectral densities with regard to geomagnetic activity and the variations of atmospheric pressure over the geomagnetic pole shows the relation between their periodicities. The results imply that the changes in the intensity of corpuscular radiation, indicated by geomagnetic activity, affect the temperature and pressure patterns over the geomagnetic pole and polar region significantly, so that a pronounced modification of the general circulation may take place, as shown schematically (BUCHA, 1976b).As a result of investigating the relations between the variations of geomagnetic activity and meteorological factors a mechanism of solar-terrestrial relationships and a model of the changes of atmospheric circulation in the Northern Hemisphere are proposed; this provides a probable explanation of the causes of the fluctuation of the climate, of dry and cold periods and of differing vegetation conditions in various years in dependence on the intensity of geomagnetic activity (BUCHA, 1976b, 1977a).

Mechanism of solar-terrestrial relations and changes of atmospheric circulation

As a result of investigating the relations between the variations of geomagnetic activity and meteorological factors [1, 2] a mechanism of solar-terrestrial relationships and a model of the changes of atmospheric circulation in the Northern Hemisphere are proposed; this provides an explanation of the causes of the fluctuation of the climate, of dry and cold periods and differing vegetation conditions in various years in dependence on the intensity of geomagnetic activity.

Direct measurements of nighttime thermospheric winds and temperatures, 2. Geomagnetic storms

A high-resolution Fabry-Perot spectrometer has been used at Fritz Peak Observatory, Colorado (39.9°N, 105.5°W), to determine the nighttime thermospheric temperatures and winds during geomagnetic storm periods from the line profiles and Doppler shifts of the (O I) 15867-K (6300 A) line emission. Data obtained during four geomagnetic storm periods in 1974 are presented: March 20–22, October 15–20, June 29 to July 8, and April 16–27. The data are compared to temperatures determined from the Ogo 6 global empirical model of neutral composition and temperature and to winds calculated from a semiempirical dynamic model of the neutral thermosphere. The results show considerable variations in the dynamic character of the thermosphere which are also related to the intensity of geomagnetic activity. During geomagnetic storms the nighttime equatorward winds are greatly enhanced from their quiet time values with a maximum measured velocity of 640 m s−1 during a Kp = 9 storm. The zonal winds generally develop a westward component relative to the geomagnetic quiet zonal winds. During intense geomagnetic activity the zonal winds are westward at 100–200 m s−1 in the early evening hours, flowing in the direction of magnetospheric convection and opposite of model predictions. The meridional winds measured south of the site are generally smaller than those measured to the north. Sometimes the meridional winds measured north and south of the station flow in opposite directions. The nighttime neutral gas temperatures are observed to increase from their geomagnetic quiet values during the storm and are in general concurrence with the Ogo 6 model predictions.

Upper Atmosphere Heating near the Auroral Zones

IT has long been supposed1–5 that there is a significant heat input into the upper atmosphere at high latitudes—either by Joule heating2,3 or by absorption of charged particles5. The density of the upper atmosphere certainly increases at times of geomagnetic disturbance6,7 and the effects seem to be enhanced8,9 at higher latitudes with a shorter time delay between the peak geomagnetic disturbance and the maximum density9. Recently DeVries10 has analysed air densities measured by the LOGACS accelerometer during the period of intense geomagnetic activity (aP∼400) on May 25–26, 1967. The increase in density on the nightside auroral zone (crossed at ∼2230 h LT at a height of 190 km) coincided with the onset of activity and the increase propagated to mid-latitudes after a delay of a few hours.