Response and yield functions of neutron monitor, galactic cosmic-ray spectrum and its solar modulation, derived from all the available world-wide surveys

Nagashima, K.; Sakakibara, S.; Murakami, Kazuaki; Morishita, I.

doi:10.1007/bf02523790

Cited by 65 publications

(56 citation statements)

References 60 publications

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“…We note that the vertical effective cutoff rigidity of Oulu NM is close to the atmospheric cut-off assuming the response function of a neutron monitor near the sea level (e.g. [21,22]). Figure 1 depicts the fine structure of asymptotic directions within the penumbra at the position of Oulu.…”

Section: Asymptotic Directions For a High-latitude Stationmentioning

confidence: 87%

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On Magnetospheric Transmissivity of Cosmic Rays

Kudela

Usoskin

2004

Czechoslovak Journal of Physics

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Results of computations of cosmic-ray trajectories in the model magnetic field obtained for a high-latitude neutron-monitor station (Oulu) and a middle-latitude one (Lomnický Stít) are summarized. The method is slightly different from previous computations by controlling the smoothness of the trajectory. At the lowest rigidity edge of allowed trajectories for Oulu (above the atmospheric cut-off), the external field and the addition of Dst shows variations of the asymptotic directions with the level of geomagnetic activity and with local time of observations. The transmissivity function introduced here, accounting for variability of the magnetic field with changing Kp and with local time, may be used as a reference for description of the average magnetospheric transparency at middle latitudes and it is probably better approximation than IGRF only. There are indications of appearance of windows of allowed trajectories at very low rigidities in the middle latitudes at 500 km (altitude of, e.g., CORONAS satellites or ISS) during the geomagnetic disturbance which is not the case for trajectories computed from the ground. : 96.40.Kk, 95.85.Ry PACS

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Section: Asymptotic Directions For a High-latitude Stationmentioning

confidence: 87%

“…Table 2. In all computations, where the epoch is not explicitly mentioned, the internal field is taken for January 21,1986. An increase of the geomagnetic activity causes a depression of the calculated cut-off.…”

Section: Asymptotic Directions For a High-latitude Stationmentioning

confidence: 99%

On Magnetospheric Transmissivity of Cosmic Rays

Kudela

Usoskin

2004

Czechoslovak Journal of Physics

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“…For a sea-level NM (1030 g/cm 2 ), they give g = 1.57; for a mountain site (680 g/cm 2 ), g = 1.75, etc. Following a similar approach, Webber and Quenby [1959], Bachelet et al [1973], Nagashima et al [1989], and Dorman et al [2000] provide NM response functions for solar minima and maxima. Our definition of R m requires that,…”

Section: Response Functionsmentioning

confidence: 99%

“…Figure 1 illustrates our definition of the median rigidity of a detector response to GCR spectrum. An integral counting rate (%) of a high latitude NM at Deep River (DR) is plotted versus GCR rigidity (R), derived from a differential response curve [Clem and Dorman, 2000, Figure 3] at sea level (1033 g/cm 2 ), given by Nagashima et al [1989], at solar minimum (top curve) and maximum (lower curve). One can easily see that the R m value for DR/NM is low at solar minimum and high at solar maximum.…”

Section: Computed R M Valuesmentioning

confidence: 99%

“…To help clarify the situation, we estimate how much R m value may change from a solar cycle minimum to maximum for a sea-level NM site. For this purpose, we use the differential response function for a sea-level NM (depth = 1033 g/cm 2 ) given by Nagashima et al [1989] and displayed in Figure 3 of Clem and Dorman [2000]. They made a careful analysis of the available latitude surveys, at different depths in the atmosphere, at different phases of solar cycles for 1954 to 1986 (three solar cycles), and used them to derive response functions for NMs at different atmospheric depths during minimum and maximum solar activity epochs.…”

Section: Solar Activity and R M Valuesmentioning

confidence: 99%

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Cosmic ray detector response to transient solar modulation: Forbush decreases

Ahluwalia

Fikani

2007

J. Geophys. Res.

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[1] The observed modulation of galactic cosmic ray (GCR) intensity, on time and spatial scales, contains information regarding their transport in the heliosphere. One way to extract crucial information from the data is to study the rigidity dependence of modulation. A methodology is described to study the rigidity dependence of the short-term variations in galactic cosmic ray intensity Earth, in terms of the median rigidity of detector response (R m ) to cosmic ray spectrum. We define R m as the rigidity below which lies 50% of detector counting rate. For neutron monitors (NMs), it is easily calculated from the latitude survey obtained at sea level and higher elevations. We compute R m values for some NM sites; solar cycle dependence for them is shown to be small. Their practical utility is demonstrated in a study of transient cosmic ray solar modulation (Forbush decreases (FDs)), using data published in the literature. We plot the rigidity dependence of the amplitudes of three large Forbush decreases that occurred during the declining phase of three solar cycles (19, 20, and 21). We show that the Forbush decrease amplitude varies inversely with R m over a large range (1 to 300 GV) of GCR rigidities. Thereby, we rule out the existence of a ''transition rigidity'' suggested by Jokipii even for a short-term modulation (large Forbush decreases). We speculate that the force field model may be applicable to large Forbush decreases.

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Continued decline of South Pole neutron monitor counting rate

et al. 2013

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[1] The counting rate of a neutron monitor at South Pole, Antarctica, displays a long-term decline over the 49 year span from March 1964 to the present. The counting rate follows an 11 year cycle with maxima at times of low solar activity. However, after adjusting for the unusually high overall cosmic ray fluxes in 2009, we find that the 2009 peak rate (based on 27 day averages) was approximately 10% lower than the 1965 peak rate. This change is much larger than that recorded by any other neutron monitor. We suggest that the South Pole monitor, owing to its unique position at both high latitude and high altitude may have a hitherto unsuspected sensitivity to secular changes in the magnetic field of the Earth.

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Response and yield functions of neutron monitor, galactic cosmic-ray spectrum and its solar modulation, derived from all the available world-wide surveys

Cited by 65 publications

References 60 publications

On Magnetospheric Transmissivity of Cosmic Rays

On Magnetospheric Transmissivity of Cosmic Rays

Cosmic ray detector response to transient solar modulation: Forbush decreases

Continued decline of South Pole neutron monitor counting rate

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