Relationship of ground level enhancements with solar, interplanetary and geophysical parameters

Abstract

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.

On the relationship between ground level enhancement and solar flare

“…We know that the intensities of solar flares (which propagate through interplanetary space) are registered by satellites at the geostationary orbit in the near‐Earth space, whereas the intensities of cosmic rays (which propagate through interplanetary space and are slowly caused by interactions with magnetic fields) are registered by neutron monitors on the surface of the Earth. Consequently, there are time lags between the registration of cosmic ray intensities and the registration of solar flare intensities [ Firoz et al , 2010b]. To find out such time lags, we considered cross‐correlation analysis as it provides correlations between courses of two time series in which the observations of one data series are correlated with the observations of another data series at various lags and leads.…”

“…We analyzed the data of cosmic ray intensities registered by the Oulu neutron monitor (ONM) (http://oldcr.oulu.fi) for the period of 1986–2006 consisting of GLE events from GLE41 event through GLE70 event. To deduce the increase rate of the cosmic ray intensity of each GLE event, the equation proposed by Firoz et al [2010a] was modified later by Firoz et al [2010b]. The modified form of the equation exploited to study the increase rate of each GLE event is given as where I r (%) is the increase rate, I j is the CRI of the time series for the whole time window of the GLE event, and j is defined as j = 1, 2, 3 … n for the whole time window.…”

“…The series of the precursor CRI is defined as k = 1, 2, 3 … m . More details about the theorem have been illustrated by Firoz et al [2010a, 2010b]. One example of the increase rate deduced by using this expression is demonstrated in Figure 1 (top).…”

“…In this context, Firoz et al [2010a] noted that coincidence of CME‐driven shocks with the solar flare might intensify the cosmic ray intensity (CRI). In another development, Firoz et al [2010b] proposed that, since solar flares are able to release relativistic high‐energy particles, GLEs can be studied as the consequence of solar flares. Several researchers [e.g., Cliver , 1982; Cane et al , 2002] also agreed that the particle acceleration in solar flares might play an important role in GLE production.…”

A Correlative Study of Geomagnetic Storms Associated with Solar Wind and IMF Features During Solar Cycle 23

“…These kind of long-duration events were termed as High-Intensity Long-Duration Continuous AE Activity events (HILDCAA events). In a study of such events made by Tsurutani and Gonzalez (1987), it was suggested that continuous injections to the ring current take place during these events in such manner that the ring current does A Correlative Study of Geomagnetic Storms Associated with Solar Wind and IMF Features During Solar Cycle 23 not, or cannot, decay rapidly [15][16][17][18]. Various studies have reported that these geo-effective events are further associated with CME's, solar flares, SEPs and also with other solar wind transients [19][20][21][22].…”