Weak Geomagnetic Storms Research Articles

Observed high-latitude GNSS disturbances during a less-than-minor geomagnetic storm

This paper presents the effects of a weak geomagnetic storm event on 17 January 2013. While the Kp index reached a maximum of only 4, this event still caused severe disturbances for Global Navigation Satellite Systems (GNSS)-based positioning services at high latitudes. We present data from the Norwegian Mapping Authority's Real Time Ionospheric Monitor, based on a dense network of geodetic receivers and scintillation indices from scintillation receivers located in Norway. In northern parts of Norway, the centimeter positioning service was severely disturbed for hours. Service-monitoring measurements showed that the effect was significantly worse for a receiver far away from the nearest network reference station.

X-ray spectrophotometer SphinX and particle spectrometer STEP-F of the satellite experiment CORONAS-PHOTON. Preliminary results of the joint data analysis

A joint analysis is carried out of data obtained with the help of the solar X-ray SphinX spectrophotometer and the electron and proton satellite telescope STEP-F in May 2009 in the course of the scientific space experiment CORONAS-PHOTON. In order to determine the energies and particle types, in the analysis of spectrophotometer records data are used on the intensities of electrons, protons, and secondary γ-radiation, obtained by the STEP-F telescope, which was located in close proximity to the SphinX spectrophotometer. The identical reaction of both instruments is noted at the intersection of regions of the Brazilian magnetic anomaly and the Earth’s radiation belts. It is shown that large area photodiodes, serving as sensors of the X-ray spectrometer, reliably record electron fluxes of low and intermediate energies, as well as fluxes of the secondary gamma radiation from construction materials of detector modules, the TESIS instrument complex, and the spacecraft itself. The dynamics of electron fluxes, recorded by the SphinX spectrophotometer in the vicinity of a weak geomagnetic storm, supplements the information about the processes of radial diffusion of electrons, which was studied using the STEP-F telescope.

Specific features of the relativistic electron flux dynamics during the recovery phase of a magnetic storm on April 6, 2000

The energy spectrum of electrons with energies of 0.8–6.0 MeV has been analyzed based on the data of the Express-A2 geostationary satellite and time variations in the fluxes of electrons with energies higher than 0.6 and 2 MeV (according to the GOES-10 satellite data) before and after a weak geomagnetic storm on April 9–10, 2002, which developed during the prolonged (about ten days) recovery phase of a strong magnetic storm on April 6, 2000. The effect of the secondary injection and acceleration caused by an intensification of substorm activity during a weak storm on the electron flux dynamics has been studied for the first time. The energy spectra and time variations in the electron flux dynamics before and after a weak storm have been described based on analytical solutions to the kinetic equation for the electron distribution function with regard to the stochastic acceleration and loss rates. It has been established that there were different acceleration and loss rates before and after the weak storm of April 9–10, 2000.

Multi-instrumental observation of weak magnetic storms occurred during the period, 18–21 March 2002

Multi-instrumental observation of ionospheric responses to two weak magnetic storms occurred during the period, 18–21 March 2002, was conducted using GPS network, MU radar, and ionosondes, over the mid-latitude sector, and compared with the output generated by FLIP model. Latitudinal and temporal variations of GPS–TEC exhibit poleward expansion up to 35°N, during day time hours (around 1000–1300 JST), of 19 and 21 March after the SSCs. It is interesting to note that, although the second storm considered here is very weak, on 20 March after the SSC around mid-night, MU radar observed that neutral wind increases rapidly up to 200 m/s, towards equator and simultaneously, a perturbation component of about 2 TECU is observed by GPS network, around 0100 JST of 21 March, which propagate from north to equator. Ionosondes also revealed that, after the second SSC, around 0200 JST on 21 March, F-layer height increases at Wakkanai, and Kokubunji which propagates to Okinawa, exhibiting a latitudinal dispersion feature, showing the influence of equatorward neutral wind/propagating nature of a powerful wind surge. The equivalent neutral wind derived from FLIP model by including vibrationally excited nitrogen, N 2 ⁎ and without its inclusion are almost identical and in good agreement with the MU radar neutral wind. The interplanetary–magnetosphere scenario of the initial and main phase of the two weak geomagnetic storms considered in the present study are quite different, which is reflected in the ionospheric responses to these events.

Geoeffective Analysis of CMEs Under Current Sheet Magnetic Coordinates

Using 100 CME–ICME events during 1997.01–2002.11, based on the eruptive source locations of CMEs and solar magnetic field observations at the photosphere, a current sheet magnetic coordinate (CMC) system is established in order to statistically study the characteristics of the CME–ICME events and the corresponding geomagnetic storm intensity. The transit times of CMEs from the Sun to the Earth are also investigated, by taking into account of the angle between the CME eruption normal (defined as the vector from the Sun center to the CME eruption source) and the Sun-Earth line. Our preliminary conclusions are: 1. The distribution of the CME sources in our CMC system is obviously different from that in the ordinary heliographic coordinate system. The sources of CMEs are mainly centralized near the heliospheric current sheet (HCS), and the number of events decreases with the increment of the angular distance from the CME source to the HCS on the solar surface; 2. A large portion of the total events belong to the same–side events (referring to the CME source located on the same side of the HCS as the Earth), while only a small portion belong to the opposite–side events (the CME source located on the opposite side of the HCS as the Earth). 3. The intense geomagnetic storms are usually induced by the same–side events, while the opposite side events are commonly associated with relatively weak geomagnetic storms; 4. The angle between the CME normal and the Sun–Earth line is used to estimate the transit time of the CME in order to reflect the influence of propagation characteristic of the CME along the Sun–Earth direction. With our new prediction method in context of the CMC coordinate, the averaged absolute error for these 100 events is 10.33 hours and the resulting relative error is not larger than 30% for 91% of all the events.

CME on March 16, 2001, electron pulsation event and solar-terrestrial phenomena related with CMEs

The electron pulsation event is defined in the paper. Firstly, a slow Halo CME on March 16, 2001 that led to low-energetic solar proton event, electron pulsation event and major geomagnetic storm was analyzed. And then, dozens of events are collected. The interrelations among the solar flare, CME, solar proton event, electron pulsation event and geomagnetic storm are studied. The results show that: (i) Solar proton events can be regarded as the indication that CMEs get to the earth and the electron pulsation events can be regarded as the indication of solar proton flux. (ii) Not only can fast CMEs strongly influence the earth, but also slow CMEs can influence the earth, and its influences are more frequent and cannot be neglected. (iii) Most of high-energetic solar proton events withE≥10 MeV can lead to geomagnetic storms, but most of the medium and weak geomagnetic storms result from low-energetic solar proton events that are caused by CMEs. (iv) Both the electron pulsation events and geomagnetic storms are the link effects of high- and low-energetic solar proton events, but the occurrence of electron pulsation event are generally prior to the geomagnetic storm. So in the circumstance where the near real-time observing data of the low-energetic solar proton event cannot be obtained, we can regard electron pulsation event as the indication of the low-energetic solar proton flux reaching the earth, which can be used as one of the important references of short-term prediction and alert of the geomagnetic storm.

Observations of the Magnetosheath near the Nominal Tail Axis during the Geomagnetic Storm of January 25, 1993

This paper reports plasma and field changes associated with magnetosheath encounters by GEOTAIL near the center of the tail axis at a down tail distance of X = -94 R E during the main phase of a weak geomagnetic storm on January 25, 1993. The magnetosheath entries of the satellite occurred in conjunction with an enhancement in the total pressure, having a temporal scale between 2 and 18 minutes. It is suggested that temporal and/or local structures in the solar wind such as pressure pulses caused these brief encounters. Assuming the flow direction in the magnetosheath to be parallel to the magnetotail boundary, we estimate the tail magnetic flux and the dimension of the tail for the encounter events. It is shown that solar wind variations, which generate geomagnetic storms, alter significantly the orientation as well as the size of the distant tail, such that the magnetosheath can be observed even near the center of the average tail.

Some results of ionospheric slab thickness observations at Lunping

The subject of the present study is to analyze the characteristic variations of the ionospheric slab thickness observed at Lunping Observatory. The slab thickness data obtained from March 1977 to February 1982 were used to analyze the diurnal, seasonal, and solar cycle variations. The diurnal variation showed an unusually large peak that appeared in pre‐sunrise hours, especially during winter time. Lunar variations of slab thickness were obtained by Chapman‐Miller method and discussed. The storm time variation and disturbance daily variation of slab thickness were obtained by selecting 138 strong and weak geomagnetic storms. Superposed epoch method was also used to analyze the geomagnetic activity effect on the variation of slab thickness.