[1] Ground-level enhancements (GLEs) are sudden, sharp, and short-lived increases in cosmic ray intensities registered by neutron monitors. These enhancements are known to take place during powerful solar eruptions. In the present investigation, the cosmic ray intensities registered by the Oulu neutron monitor have been studied for the period between January 1979 and July 2009. Over this span of time, increase rates of 32 GLEs have been deduced. In addition, we have studied characteristics of the 32 event-associated solar flares, coronal mass ejections (CMEs), and solar energetic particle (SEP) fluxes. We found that all of the 32 GLEs were associated with solar flares, CMEs, and SEP fluxes. Approximately 82% of the events were associated with X-class flares. Most of the flares that were associated with GLEs of increase rates >10% originated from the active regions located on the southwest hemisphere of the Sun. The average speed (1726.17 km/s) of GLE-associated CMEs was much faster than the average speed (423.39 km/s) of non-GLE-associated CMEs. It also became evident that ∼67% GLEs were associated with very fast (>1500 km/s) CMEs. Although a GLE event is often associated with a fast CME, this alone does not necessarily cause the enhancement. Solar flares with strong optical signatures may sometimes cause GLE. High SEP fluxes often seem to be responsible for causing GLEs as the correlation with SEP fluxes implies.

Cosmic rays registered by Neutron Monitor on the surface of the Earth are believed to originate from outer space, and sometimes also from the exotic objects of the Sun. Whilst the intensities of the cosmic rays are observed to be enhanced with sudden, sharp and short-lived increases, they are termed as ground level enhancements (GLEs). They are the occurrences in solar cosmic ray intensity variations on short-term basis, so different solar factors erupted from the Sun can be responsible for causing them. In this context, an attempt has been made to determine quantitative relationships of the GLEs having peak increase > 5% with simultaneous solar, interplanetary and geophysical factors from 1997 through 2006, thereby searching the responsible factors which seem to cause the enhancements. Results suggest that GLE peaks might be caused by solar energetic particle fluxes and solar flares. The proton fluxes which seemed to cause GLE peaks were also supported by their corresponding fluences. For most of the flares, the time integrated rising portion of the flare emission refers to the strong portion of X-ray fluxes which might be the concern to GLE peak. On an average, GLE peak associated X-ray flux (0.71 × 10 −4 w/m 2 ) is much stronger than GLE background associated X-ray flux (0.11 × 10 −6 w/m 2 ). It gives a general consent that the GLE peak is presumably caused by the solar flare. Coronal mass ejection alone does not seem to cause GLE. Coronal mass ejection presumably causes geomagnetic disturbances characterized by geomagnetic indices and polarities of interplanetary magnetic fields.

Abstract-A geomagnetic storm is a global disturbance in Earth's magnetic field usually occurred due to abnormal conditions in the interplanetary magnetic field (IMF) and solar wind plasma emissions caused by various solar phenomenon. Furthermore the magnitude of these geomagnetic effects largely depend upon the configuration and strength of potentially geo-effective solar/interplanetary features. In the present study the identification of 220 geomagnetic storms associated with disturbance storm time (Dst) decrease of more than -50 nT to -300 nT, have been made, which are observed during 1996-2007, the time period spanning over solar cycle 23. The study is made statistically between the Dst strength (used as an indicator of the geomagnetic activity) and the peak value obtained by solar wind plasma parameters and IMF B as well as its components. We have used the hourly values of Dst index and the wind measurements taken by various satellites. Our results inferred that yearly occurrences of geomagnetic storms are strongly correlated with 11-year sunspot cycle. We observed that IMF B is highly geo-effective during the main phase of magnetic storms, while it more significant at the time of storm peak, which is further contributed by southward component of IMF Bz, substantiating earlier findings. The correlation between Dst and wind velocity is higher, as compared with IMF Bz and ion density. It has been verified that geomagnetic storm intensity is correlated well with the total magnetic field strength of IMF better than with its southward component.

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Today's challenge for space weather research is to quantitatively predict the dynamics of the magnetosphere from measured solar wind and interplanetary magnetic field (IMF) conditions. ::: Do ::: you ::::: mean : A cCorrelative studies between the Ggeomagnetic Sstorms (GMSs) and the various interplanetary (IP) field/plasma parameters have been performed to search for the causes of geomagnetic activity and developing models for predictioning of the occurrence of GMSs, which are important for space weather predictions. In the present paper weWe foundfind a possible co-relation ofbetween geomagnetic stormGMSs withand solar wind and IMF parameters in three different situations and also derived the linear relation equation for all parameters in three situations. : ? On the basis of the present statistical study, we developed an empirical model. With the help of this model, we can predict all categories of geomagnetic stormGMSs. ::: Do ::: you ::::: mean This model is based on the following fact. T: the total interplanetary magnetic fieldIMF B total can be used asto trigger an alarm offor geomagnetic stormGMSs, when sudden changes in total magnetic field B total occur., itThis is athe first alarm on condition for a storm's arrival. It is observed in the present study that the southward B z-component of the IMF is an important factor for describing geomagnetic stormGMSs. And it is theA result of the paper is that the magnitude of B z is maximum neither during the initial phase (at the instant of the IP shock) nor during the main phase (at the instant of Disturbance storm time (Dst) minimum). : ? So iIt is seen in this study that there is a time delay between the maximum value of southward B z and the Dst minimum, and this time delay can be used in the prediction of the intensity of a magnetic storm two-three hours before ofthe main phase of a geomagnetic stormGMS. :: Do :::: you ::::: mean : A linear relation havehas been derived between the maximum value of the southward component of B z and the Dst, which for prediction is Dst = (−0.06) + (7.65)B z + t. Some auxiliary conditions should be fulfilled with this, for example the speed of the solar wind should, on average, be on average 350 km s −1 to 750 km s −1 , plasma betaβ should be low and, most importantly, plasma temperature should be low for intense storms.