Commencement Of Geomagnetic Storm Research Articles

A Method for Recognition of Sudden Commencements of Geomagnetic Storms Using Digital Differentiating Filters

This article describes a method for recognizing sudden commencement events using digital differentiating filters. This method is applied to INTERMAGNET observatory data. Maximum amplitude derivatives for the magnetic components (X, Y, Z) and the total intensity (F) of the geomagnetic field are introduced, and the decision-making rule is formulated. The authors developed a procedure for selecting optimal digital differentiating filters. Estimates of probabilities of correct and false recognition of sudden commencements were obtained. The calculations of the probabilistic characteristics have confirmed the effectiveness of the method.

Statistical Analysis of Solar Radio Burst Type III and Type IV with Relation to Solar Activities

Solar activities are natural phenomena that occur at the solar surface by ejecting energy into interplanetary space and consequently hitting Earth’s atmosphere where the commencement of geomagnetic storms. Generally, solar radio bursts originated at the same level as the solar flares, Coronal Mass Ejections (CMEs) and shock at solar atmosphere which the Sun project the radio energy into the interstellar medium. This is a novel study to investigate the correlation between solar burst type IV and type III based on their properties. The analysis is based on the statistical data of type IV and type III solar bursts from 2006 – 2011. The statistics of solar burst type IV associated with type III were obtained through e-Callisto (Compact Astronomical Low-frequency Low-cost Instrument for Spectroscopy Transportable Observatory) Spectrometer in the years 2006 until 2011. The aim of this study is to find out whether type III bursts preserved energy to solar bursts type IV thus led to the formation of geomagnetic storm. Statistical data from this study showed that most of the burst type IV were preceded and followed by type III burst. The total number of type IV events studied was 37, with 20 preceded by type III and the remainder with other types. Predominantly, solar bursts events are accompanied with great solar flares (class X and M) producing major storms. Although the study did not show much correlation between bursts type IV and type III in producing these storms, there are several possible explanations for this result. It may be the case that solar events such as solar flare, CMEs and active region ejected from the solar disc is not heading towards Earth and the energy has eventually dispersed into the interplanetary medium.

Ground‐based observations of nitric oxide in the mesosphere and lower thermosphere over Antarctica in 2012–2013

AbstractWe report temporal variations of the partial column density of nitric oxide (NO) in an altitude range 75–105 km at Syowa Station, Antarctica, from January 2012 to September 2013. We found two patterns of NO temporal variation: (1) a seasonal cycle with a maximum in winter and a minimum in summer, and (2) short‐term enhancements on a time frame of 5–10 days associated with solar activities. In the seasonal cycle, the variation pattern of NO showed good agreement with scotoperiod of solar radiation rather than the downwelling atmospheric transport, suggesting that photodissociation is the main driver of the seasonal variation. To study the short‐term enhancements, we compared the NO column density with the proton and electron fluxes obtained by the POES/METOP (Polar Orbiting Environmental Satellite/Meteorological Operational) satellites. There is a weak but significant correlation between the NO and the electron flux, but no correlation between the NO and the proton flux. We also made a detailed comparison of the time series of NO and proton/electron fluxes for 12 selected 25‐day time frames, and found that at least two remarkable NO enhancements occurred without any solar proton events (SPEs). During electron precipitation, the NO column density peaked 1–5 days after the commencement of geomagnetic storms, whereas the relationship between NO and the solar proton is not clear because the electron flux also increased at the same time. These results suggest that energetic electron precipitation may be a major cause of NO enhancements above Syowa Station in the auroral region, even during SPEs.

Low latitude ionospheric effects near longitude 120°E during the great geomagnetic storm of july 2000

A great geomagnetic storm occurred on July 15/16, 2000 with a minimum value of about −300 nT in Dst index. Collecting digisonde data from ionospheric stations at Chungli, Wuhan, Kokubunji and Anyang, the ionospheric responses at the low latitudes near longitude 120°E during this storm are analyzed in this paper. There was a strong negative phase storm at low latitudes on July 16. The G-condition in the ionograms was clearly seen on the early first day after the commencement of geomagnetic storm. Those were considered to be caused by the storm-induced increase in the concentration ratios of neutral molecular O2 or N2 to atom O. On July 17 and some days thereafter, a positive phase storm appeared. In addition, anomalous equatorial ionization anomaly (EIA) inhibitions and developments were observed on July 16 and 17. There were also prominent nighttime enhancements in f0F2 during these days, and the diurnal variation of f0F2 was less clear than before.

Geomagnetic storm effects on zonal and meridional equatorial electrojet currents

The sudden commencements of geomagnetic storms at the equatorial electrojet station Kondaikanal are characterized by simultaneous increases of both the horizontal field H and the westerly declination D(W) or the decrease of eastward field, Y. The amplitudes of the SSC in H or Y fields (ΔH and ΔY) show a maximum deviation around midday hours. The ratio of ΔY to ΔH is about 0.23 for any hour of the day or night. During the main phase of the storm, the fluctuations in the H and Y components at Kodaikanal vary in unison with each other. Occasional large decreases of the H field at Kodaikanal at daytime hours during the main phase of the storm do not have corresponding decrease of H at Alibag or in the equatorial Dst index. These events are shown to be associated with the sudden disappearance of the equatorial type of sporadic E(Esq) at Kodaikanal indicating a temporary reversal of the ionospheric electric field over the magnetic equator to westward direction. The observed storm time variations of the magnetic fields at an equatorial electrojet station are suggested to be due to the combined effects of the equatorial ring current and of the electric field changes at the ionospheric region transmitted from high latitudes.

Correction [to “On the poleward expansion of ionospheric absorption regions triggered by sudden commencements of geomagnetic storms”

Correction [to “On the poleward expansion of ionospheric absorption regions triggered by sudden commencements of geomagnetic storms”

EquatorialEregion electric field changes associated with a geomagnetic storm sudden commencement

The sudden commencement of geomagnetic storms occurring during daytime hours is shown to amplify or even to initiate equatorial ionospheric instabilities associated with the q type of sporadic E layer and the scatter propagation of VHF radio waves. The negative impulse of a ssc- + type of event is seen to be reproduced faithfully in the transequatorial VHF radio wave propagation, first as a sudden decrease of the signal strength and then as an increase. It is suggested that the enhancement of the H field over the magnetic equator during ssc events is due to the imposition of an additional electric field over the equatorial region, causing additional ssc-associated electrojet currents.

Interplanetary shock waves and comet brightness fluctuations during June-August 1972

A series of anomalous events associated with solar activity occurred in interplanetary space in June and August 1972. These events include non-Io-associated decametric emission from Jupiter; brightness variations of the periodic comets Schwassmann-Wachmann 1 and Giacobini-Zinner; interplanetary shock waves detected by Pioneer 9 and 10, Heos 2, and Prognoz and Prognoz 2; interplanetary scintillations; and sudden commencements of geomagnetic storms. Trajectories and deceleration characteristics for the shock waves are estimated primarily from observations using solar radio, in situ, and geomagnetic data. Generally, the trajectories indicate a piston-driven character to about 0.3–0.4 AU, after which the shocks decay to a blastlike motion with a shock velocity variation approximately inversely proportional to the heliocentric radius. Most of the shock waves apparently decayed into magnetoacoustic waves between 2 and 4 AU. In our opinion this decay explains the fact that no anomalous events occurred at either Jupiter or P/Schwassmann-Wachmann I at 5.2 and 5.6 AU, respectively, during August 1972.

A study of Sudden Commencements of Geomagnetic Storms at Trivandrum

The occurrence frequency distribution of SC (+) is not showing any siginifiacnt variation with local time, while the SC(-+) cases occur, in the equatorial station Trivandurm, during the day-time electrojet. There is a direct relationship between the severity of the SC storm and the rate of filed change of the SC amplitude and rise time. At this station, the polarization of the SC field vector in the horizontal plane is linear.

Discussion of paper by E. J. Stegelmann and C. H. von Kenschitzki, ‘On the interpretation of the sudden commencement of geomagnetic storms’

It was pointed out some years ago [Dessler et al. 1960] that a major part of the rise time of a sudden commencement can be accounted for as the period of time in which the enhanced solar wind sweeps over the outer boundary of the geomagnetic field, plus the difference in propagation time from different points on the boundary. The dimensions of the outer boundary of the geomagnetic field are of the order of 105 km, so that an enhanced wind of 103 km/sec characteristically takes about 102 seconds to engulf the field and enhance the compression of the field. Typical propagation times within the field differ by 102 seconds. The basic idea was simply that the compression of the geomagnetic field at the surface of the earth results from the algebraic sum of all the compressive forces exerted by the wind on the outer boundary of the field [Parker, 1958]. Any changes in the compressive forces on the outer boundary are communicated inward at about the Alfven velocity [Francis et al., 1959]. Enhanced compression of the boundary starts somewhere on the solar side, at which time a slight increase in compression begins to propagate through the geomagnetic field as a hydromagnetic wave. With the passage of time more and more of the boundary is compressed as the enhanced wind sweeps by in space. The rising compression communicates throughout the field with the Alfven speed, and levels off only after the enhanced wind fully encloses the geomagnetic field.

On the interpretation of the sudden commencement of geomagnetic storms

The propagation and geometric attenuation of hydromagnetic waves in the earth's magnetic field are calculated by the methods of geometrical optics. The waves are assumed to be generated by point sources located at a distance of 6 earth radii from the center of the earth. It is shown that the ray tracing method cannot be used to explain the rise time of sudden commencements of geomagnetic storms. However, the calculated propagation times of hydromagnetic disturbances can give an understanding of delay times and latitude dependence of arrival times. If extended sources are considered, the following conclusion results from our analysis: According to geometric optics, hydromagnetic disturbances of the fast mode produced at 6 earth radii by the interaction of a solar plasma front with the earth's magnetosphere will reach the earth only if they are produced in a region within a radius of a few thousand kilometers of the subsolar point.

Cosmic noise absorption accompanying geomagnetic storm sudden commencements

Cosmic noise absorption coinciding with the sudden commencement of geomagnetic storms has been studied for 71 SC events from the data recorded at 25 riometer stations at or near the auroral zone during the period July 1958-- December 1960. The greatest absorption was registered at stations near the central line of the auroral zone. The effect was observed simultaneously on the day and on the night side of the earth. This type of absorption was earlier found to be associated with bremsstrahlung X rays created by electrons entering the lower ionosphere. The source of these electrons has not been definitely established by the present study. Although the data tends to favor a source outside the earth's magnetosphere, no definite conclusion is possible because of the present uncertainties concerning the trapped radiation belts. (auth)

Rise times versus magnitudes of sudden commencements of geomagnetic storms

A study of the rise times versus the magnitudes of the positive sudden commencements of 41 randomly selected geomagnetic storms recorded at Alibag (ф = 9.5°, Λ = 143.6°, geomagnetic coordinates) for the period 1949–1960 is presented. The study shows rise times of 1 to 6 minutes and shows that the rise times have an inverse relationship with the magnitudes of the SC's—the rise time being smaller as the magnitude is larger, and vice versa. The Chapman and Ferraro theory of the SC predicts rise times of less than about two minutes with an inverse relationship between rise time and amplitude. On the other hand, numerical computations by Dessler and co-workers from a hydromagnetic model have shown this inverse relationship and have shown rise times of the order of 1 to 6 minutes, which appear to fit better with the data of Alibag presented in this paper.

Studies on sudden commencements of geomagnetic storms using IGY data from United States stations

This report contains studies of geomagnetic storm variations recorded at a network of seven IGY stations in the United States together with records for other observatories operated by the United States. The distance between adjacent stations of the network ranges from 360 to 510 km. Geomagnetic variations at these stations were usually quite similar, as would be expected. During magnetic storms, however, remarkable differences occurred even between adjacent stations. About half of the sudden commencements of the horizontal component showed different shapes at adjacent stations for the same magnetic storm. From the data obtained from these results, and from observations at more distant stations, the behavior of sudden commencements is examined. The data also show that the variations of the vertical component of the sudden commencement differ in ways suggesting notable irregularities of the earth's conductivity in the central part of the United States. In addition, occasional examples of bay-shaped variations during magnetic storms, which are quite nonuniform over the closely spaced net, are illustrated and analyzed.