Deep River Neutron Monitor Research Articles

Upper limit for fourth harmonic of cosmic ray solar daily variation: 1963–2015

In 1970s we analyzed the neutron monitor (NM) and muon telescope (MT) data from the global network for 1966–1970 to determine the amplitude and phase of the significant harmonics constituting the galactic cosmic ray (GCR) daily anisotropy in solar time. The median rigidity of response (Rm) of detectors to GCR spectrum covered a wide range (16–134GV). The results were reported at the international cosmic ray conferences (ICRCs) held at Denver [1973], Munich [1975] and Paris [1981]. It was inferred that GCR solar daily anisotropy consists of only three harmonics, namely the diurnal (1cpd, first harmonic), the semidiurnal (2cpd, second harmonic) and the tridiurnal (3cpd, third harmonic), with power spectral densities in the ratio 800:20:1 for the Deep River NM data (Rm=16GV) for 1962–1971. The fourth harmonic (4cpd) was absent in these analyses. Since then the volume of data from the global network of NMs and MTs has increased significantly; particularly the multidirectional MT network, with larger Rm values. This motivates us to ascertain whether 4cpd peak is absent in the cosmic ray solar daily variation data at the global sites, over a longer time period (1963–2015). Our informed conjecture is that 4cpd peak is insignificant at 2σ-level of experimental error for a range of Rm values (11–60GV). The discovery of a physically significant fourth harmonic would challenge the theorists to come up with a model for GCR transport in the heliosphere revealing hitherto unknown feature(s) of solar modulation.

Study of Higher Harmonics of Cosmic Ray Intensity on Quiet Days at Deep River Neutron Monitoring Station

The cosmic ray (CR) intensity data recorded with Deep River Neutron Monitoring Station have been investigated on quietest days (QD) for higher harmonics of daily variation during solar cycle 21 and 22. It has been observed that inspite of the abrupt change in the amplitude and phase of tri-diurnal and quart diurnal anisotropy in CR intensity, the amplitude of third harmonic is quite significant throughout the period of investigation with larger amplitude during the year 1980 and 1985. Thus, tri-diurnal anisotropy clearly shows 11 year variation at mid latitude neutron monitoring station.

An analytical model for the prediction of a micro-dosimeter response function

A rapid analytical procedure for the prediction of a micro-dosimeter response function in low Earth orbit (LEO), correlated with the Space Transportation System (STS, shuttle) Tissue Equivalent Proportional Counter (TEPC) measurements is presented. The analytical model takes into consideration the energy loss straggling and chord length distribution of the detector, and is capable of predicting energy deposition fluctuations in a cylindrical micro-volume of arbitrary aspect ratio (height/diameter) by incoming ions through both direct and indirect (δ ray) events. At any designated (ray traced) target point within the vehicle, the model accepts the differential flux spectrum of Galactic Cosmic Rays (GCRs) and/or trapped protons at LEO as input. On a desktop PC, the response function of TEPC for each ion in the GCR/trapped field is computed at the average rate of 30 s/ion. The ionizing radiation environment at LEO is represented by O’Neill’s GCR model (2004), covering charged particles in the 1 ⩽ Z ⩽ 28 range. O’Neill’s free space GCR model is coupled with the Langley Research Center (LaRC) angular dependent geomagnetic cutoff model to compute the transmission coefficient in LEO. The trapped proton environment is represented by a LaRC developed time dependent procedure which couples the AP8MIN/AP8MAX, Deep River Neutron Monitor (DRNM) and F10.7 solar radio frequency measurements. The albedo neutron environment is represented by the extrapolation of the Atmospheric Ionizing Radiation (AIR) measurements. The charged particle transport calculations correlated with STS 51 and 114 flights are accomplished by using the most recent version (2005) of the LaRC deterministic High charge ( Z) and Energy TRaNsport (HZETRN) code. We present the correlations between the TEPC model predictions (response function) and TEPC measured differential/integral spectra in the lineal energy ( y) domain for both GCR and trapped protons, with the conclusion that the model correctly accounts for the increase in flux at low y values where energetic ions are the primary contributor. We further discuss that, even with the incorporation of angular dependency in the cutoffs, comparison of the GCR differential/integral flux between STS 51 and 114 TEPC measured data and current calculations indicates that there still exists an underestimation by the simulations at low to mid range y values. This underestimation is partly related the exclusion of the secondary pion particle production from the current version of HZETRN.

High amplitude anisotropic wave trains in cosmic rays

In the present study the occurrence of an unusual class of high amplitude anisotropic wave trains in the cosmic ray neutron intensity, which is distinctly different from the average diurnal variation as well as from other recognized types of high amplitude anisotropic wave trains are noted and the directional distribution in the interplanetary space determined. The major objective of this paper is to study the first three harmonics of high amplitude anisotropic wave trains of cosmic ray intensity over the period 1981–1994 for Deep River Neutron Monitoring station. The significant characteristics of these events are that the high amplitude wave trains show a maximum intensity of diurnal component in a direction earlier than 1800 h/co-rotational direction. It is noticed that these events are weakly dependent on high-speed solar wind streams or by the sources on the Sun responsible for producing these streams such as polar coronal holes. However, the possibility of occurrence of these events during high-speed solar wind streams cannot be denied. The occurrence of high amplitude events is dominant for positive polarity of B z . Majority of the HAEs have occurred when D st-index remains negative and A p-index remains ⩽ 18 nT . All the three harmonics of HAEs except the amplitude of second harmonic do not show any significant correlation associated with D st and A p-index. The corotating streams produce significant deviations in cosmic ray intensity as well as in solar wind speed during high amplitude anisotropic wave train events.

Harmonics of Low Amplitude Anisotropic Wave Train Events in Cosmic Ray Intensity

The unusually low amplitude anisotropic wave train events (LAWEs) in cosmic ray intensity using the ground based Deep River neutron monitor data has been studied during the period 1991–1994. It has been observed that the amplitude of the diurnal anisotropy for LAWE events significantly remains quite low and statistically constant as compared to the quiet day annual average amplitude for majority of the events. The time of maximum of the diurnal anisotropy of LAWE significantly shifts towards earlier hours as compared to the co-rotational direction and remains in the direction of quiet day annual average anisotropy for majority of the events. On the other hand, the amplitude of the semi/tri-diurnal anisotropy remains statistically the same and high whereas, phase shift towards later hours as compared to the quiet day annual average values for majority of the LAWEs. The diurnal anisotropy vectors are found to shifts towards earlier hours for 50% of the events; whereas they are found to shifts towards later hours for rest of the events (50%) relative to the average vector for the entire period. It is also noted that the amplitude of these vectors are found to increase significantly with the shift of the diurnal anisotropy vectors towards later hours. The high-speed solar wind streams do not play a significant role in causing the LAWE events on short-term basis, however it may be responsible in causing these events on long-term basis (Mishra and Mishra 2007). Occurrence of LAWE is dominant, when the polarity of Bx and Bz remains positive and polarity of By remains negative, which is never been reported earlier. The amplitude of first harmonic shows good anti-correlation and direction of first and third harmonic shows nearly good anti-correlation with solar wind velocity, whereas the direction of second harmonic shows nearly good anti-correlation with interplanetary magnetic field strength.

Low amplitude anisotropic wave trains in cosmic rays

In the present study the occurrence of an unusual class of low amplitude anisotropic wave trains in the cosmic ray neutron intensity, which is distinctly different from the average diurnal variation as well as from other recognized types of low amplitude anisotropic wave trains are noted and the directional distribution in the interplanetary space determined. The major objective of this paper is to study the first three harmonics of low amplitude anisotropic wave trains of cosmic ray intensity over the period 1981–1994 for Deep River neutron monitoring station. The significant characteristic of these events is that the low amplitude wave trains shows a maximum intensity of diurnal component in a direction earlier than 18:00 h/co-rotational direction. It is noticed that these events are not caused either by the high-speed solar wind streams or by the sources on the Sun responsible for producing these streams such as polar coronal holes. However the possibility of occurrence of these events during high-speed solar wind streams cannot be denied. The occurrence of low amplitude events is dominant for positive polarity of B z . The disturbance storm time index i.e. D st, remains consistently negative only for majority of the low amplitude wave train events, which is never been reported earlier. The amplitude as well as direction of first two harmonics seems to remain unaffected with the variation in the D st and A p-index. However, the amplitude as well as direction of third harmonic found to deviates with the increase of D st and A p-index. The corotating streams produce significant deviations in cosmic ray intensity as well as in solar wind speed during low amplitude anisotropic wave train events.

Interplanetary magnetic clouds and cosmic ray modulation

We studied the cosmic ray intensity variation due to interplanetary magnetic clouds during an unusual class of low amplitude anisotropic wave train events. The low amplitude anisotropic wave train events in cosmic ray intensity have been identified using the data of ground based Deep River neutron monitor and studied during the period 1981–1994. Even though the occurrence of low amplitude anisotropic wave trains does not depend on the onset of interplanetary magnetic clouds, but the possibility of occurrence of these events cannot be overlooked during the periods of the interplanetary magnetic cloud events. It is observed that the solar wind velocity remains higher (> 300) than normal and the interplanetary magnetic field B remains lower than normal on the onset of the interplanetary magnetic cloud during the passage of low amplitude wave trains. It is also noted that the proton density remains significantly low during high solar wind velocity, which is expected. The north south component of interplanetary magnetic field Bz turns southward to one day before the arrival of cloud and remains in the southward direction after the arrival of a cloud. During these events the cosmic ray intensity is found to increase with increase of solar wind velocity. The superposed epoch analysis of cosmic ray intensity for these events during the onset of interplanetary magnetic clouds reveals that the decrease in cosmic ray intensity starts not at the onset of the cloud but after a few days. The cosmic ray intensity increases on arrival of the magnetic cloud and decreases gradually after the passage of the magnetic cloud.

Unusual anisotropic wave trains in cosmic rays

Several workers have attempted to find out the possible origin of the “high amplitude wave trains” of enhanced diurnal variation of cosmic rays and to develop a suitable realistic theoretical model that can explain the different harmonics in individual days. The various observed harmonics of the cosmic-ray variation may be understood on a unified basis if the free-space cosmic-ray anisotropy is non-sinusoidal in form. The major objective of this paper is to study the first three harmonics of high-amplitude wave trains of cosmic-ray intensity over the period 1981–1994 for Deep River neutron monitoring station. The main characteristic of these events is that the high-amplitude wave trains show a maximum intensity of diurnal component in a direction earlier than 18:00 h/co-rotational direction. It is noteworthy that the amplitude significantly enhanced and the phase remains in the co-rotational direction during the years close to solar-activity maximum for first harmonic. Significant deviations have been observed in the semi-diurnal amplitude after the onset of solar-activity maximum. This leads us to conclude that the amplitude as well as direction of the first harmonic and the amplitude of second harmonic are correlated with solar-activity cycle during these HAEs. The amplitude and phase of all the three harmonics (diurnal/semi-diurnal/tri-diurnal) are not found to depend on the polarity of Bz component of interplanetary magnetic field for long-term variation. The occurrence of high-amplitude events is dominant for the positive polarity of Bz component of IMF. The occurrence of HAEs is dominant during the period of average solar-wind velocity, but their occurrence during HSSWSs cannot be denied. The possibility of occurrence of these events is more during the periods of co-rotating streams. The occurrence of HAE is dominant when Dst-index remains negative and this point is not reported earlier in the litterature. All the high amplitude events occurred, when geomagnetic activity index, Ap, remains ⩽20.

Third harmonics of cosmic ray intensity on quiet days at Deep River Neutron Monitoring Station

The cosmic ray (CR) intensity data recorded in Deep River Neutron Monitoring Station have been investigated on quietest days (QD) for third harmonics of daily variation during solar cycles 21 and 22. It has been observed that in spite of abrupt change in the amplitude and phase of tri-diurnal anisotropy in CR intensity, the amplitude is quite significant throughout the period of investigation with larger amplitude during the years 1980 and 1985. Thus, tri-diurnal anisotropy clearly shows 11-year variation at the mid latitude neutron monitoring station.

Harmonics of exceptionaly low amplitude anisotropic wave train events in cosmic ray intensity

The unusually low amplitude anisotropic wave train events (LAEs) in cosmic ray intensity using the ground based Deep River neutron monitor data has been studied during the period 1991–94. It has been observed that the phase of the diurnal anisotropy for the majority of the LAE events remains in the co-rotational direction. However, for some of the LAE events the phase of the diurnal anisotropy shifts towards earlier hours as compared to the annual average values. On the other hand, the amplitude of the semi-diurnal anisotropy remains statistically the same, whereas phase shift-towards later hours; a similar trend has also been found in case of tri-diurnal anisotropy. The high-speed solar wind streams do not play a significant role in causing the LAE events. The occurrence of LAE is independent of the nature of the Bz component of IMF polarity.

A study of daily variation in cosmic ray intensity during high/low amplitude days

A detailed study has been conducted on the long-term changes in the diurnal, semi-diurnal and tri-diurnal anisotropies of cosmic rays in terms of the high/low amplitude anisotropic wave train events (HAE/LAE) during the period 1981–94 using the neutron monitor data from Deep River Neutron Monitoring Station. In all, 38 HAE and 28 LAE cases have been studied. An inter-comparison of the first three harmonics during these events has been made so as to understand the basic reason for the occurrence of these types of events. It has been observed that the phase of diurnal anisotropy shifts towards earlier hours for HAEs and it shifts towards earlier hour as compared to 18-h direction for LAEs. For semi-diurnal anisotropy, phase remains statistically the same for both HAE and LAE. In the case of tri-diurnal anisotropy, phase is evenly distributed for both types of events. The interplanetary magnetic field (IMF) and solar wind plasma (SWP) parameters during these events are also investigated. It has also been observed that HAE/LAEs are weakly dependent on high-speed solar wind velocity. The two types of solar wind streams (corotating streams and flare-generated streams) produce significant deviations in cosmic ray intensity during HAE/LAE.

Effect of interplanetary transients on low amplitude anisotropic wave trains in cosmic rays

The occurrence of an unusual class of low amplitude anisotropic wave trains in the cosmic ray neutron intensity, which is distinctly different from the average diurnal variation as well as from other recognized types of low amplitude anisotropic wave trains are noted and the directional distribution in the interplanetary space determined. The major objective of this paper is to study the first three harmonics of low amplitude anisotropic wave trains of cosmic ray intensity over the period 1991–1994 for Deep River neutron monitoring station. The significant characteristic of these events is that the low amplitude wave trains shows a maximum intensity of diurnal component in a direction earlier than 1800 h/co-rotational direction. It is noticed that these events are not caused either by the high-speed solar wind streams or by the sources on the Sun responsible for producing these streams such as polar coronal holes. The direction of the tri-diurnal anisotropy shows a good negative correlation with Bz component of interplanetary magnetic field. The occurrence of low amplitude events is dominant for positive polarity of Bz. The Disturbance Storm Time index i.e., D st, remains consistently negative only throughout all the low amplitude wave train events, which is never been reported earlier.

Interplanetary turbulences causing unusual anisotropic wave trains in cosmic rays

The various observed harmonics of the cosmic ray variation may be understood on a unified basis if the free space cosmic ray anisotropy is non-sinusoidal in form. The major objective of this paper is to study the first three harmonics of high amplitude wave trains of cosmic ray intensity over the period 1991–1994 for Deep River Neutron Monitoring Station. The main characteristic of these events is that the high amplitude wave trains shows a maximum intensity of diurnal component in a direction earlier than 1800 Hr/co-rotational direction. It is noticed that these events are not caused either by the high-speed solar wind streams or by the sources on the Sun responsible for producing these streams such as polar coronal holes. The direction of semi-diurnal anisotropy shows negative correlation with Bz. The occurrence of high amplitude events is dominant for the positive polarity of Bz component of IMF. The diurnal amplitude of these events shows a negative and the time of maximum shows a weak correlation with disturbance storm time index Dst. The direction of tri-diurnal anisotropy of these events is found to significantly correlate with geomagnetic activity index Ap.

Unusually low-amplitude anisotropic wave-train events of cosmic ray intensity during 1981–1994

Investigation has been made for unusually low-amplitude anisotropic wave train events (LAE) for cosmic ray intensity data of Deep River neutron monitoring station during the period 1981–94. It has been observed that the phase of diurnal anisotropy remains in the same co-rotational direction for most of the LAEs while the phase shifts to early hours for some of the LAEs in diurnal anisotropy. During minimum solar activity, LAEs have been observed to be dominant. Solar wind plasma (SWP) parameters, inter-planetary magnetic field and various features at solar disk have also been studied. The amplitude remains low continuously for most of the days while the phase shifts to earlier hours. Occurrence of LAE is independent of the nature of interplanetary magnetic field (IMF).

PERIODICITY IN DAILY VARIATION OF COSMIC RAY INTENSITY AS AN EFFECT OF SOLAR POLOIDAL MAGNETIC FIELD ORIENTATION

A detailed analysis of the Deep River neutron monitor (NM) data for four different phases of solar activity cycle and for four groups of days chosen according to their different geomagnetic conditions is being carried out. It is found that the 60 quiet day (QD) in a year serve a better purpose for investigating the short/long term variation in cosmic ray (CR) intensity. Furthermore, data has been harmonically analysed for the period 1964–95 to investigate the effect of solar poloidal magnetic field (SPMF) orientation in daily variation (diurnal/semi-diurnal) of CR on geomagnetically QD. The phase of the diurnal and semi-diurnal anisotropy vectors on QD has shown a significant shift to early hours when the SPMF in the northern hemisphere (NH) is positive during the periods 1971–79 and 1992–95 as compared to that during the periods 1964–70 and 1981–90 when the SPMF in NH is negative, showing a periodic nature of daily variation in CR intensity with SPMF.

Energy Spectrum of Galactic 10–100 MeV Protons in Quiet Sun Periods

The dynamics of the proton energy spectrum during the solar cycle is studied. The spectra were determined by 1–100 MeV particle fluxes measured by different instruments mounted aboard the Earth's IMP-8 satellite for more than one hundred quiet-time intervals in the period between 1974 and 1991. The galactic branch of the spectra (Ep > 10 MeV) constructed for every quiet interval was fitted by a power law function, J =CEν. The theory predicts that in the 1–100 MeV energy range, where the adiabatic cooling of particles is dominant, ν = 1, while we have derived a ν double-peak distribution. The main maximum has the mean value 〈ν〉 = 1.35. The mean value of the second, much weaker maximum, is 〈ν〉 = 0.95. Within the main maximum, ν values are distributed in accordance with the Gaussian law with a standard deviation 〈D/ν〉 = 0.12. The substantial difference of ν from unity requires the elaboration of a new model of modulation processes in the inner heliosphere. The ν values corresponding to the second maximum show that modulation processes correspond sometimes to theoretical conceptions. It is shown that ν correlates weakly with parameters A and γ describing the solar branch of the spectrum (J(E) = AE–γ). At the same time, a more significant correlation is observed between ν and the solar activity index, Rz , the counting rate of the Deep River neutron monitor, and the energy value in the minimum of the energy spectrum flux, Emin .

DAILY VARIATION IN COSMIC RAY INTENSITY ON DIFFERENT GEOMAGNETIC CONDITIONS

A new concept of data analysis has been attempted for studying the long/short term daily variations in cosmic ray (CR) intensity recorded with neutron monitors/meson telescopes. Fourier Technique has been applied on four different types of groups of days chosen according to their different geomagnetic conditions. The selected groups are 60 quietest days (60 QD), 120 quiet days (120 QD), continuous quiet days (CQD) and All Days (AD) in a year. CQD is a new set of days selected on the basis of Ap and Kp values. These are the days when transient magnetic variations are supposed to be regular and smooth continuously for a span of at least three days. The criteria of selection of CQD is based upon the mathematical manipulation with Ap index. The data of Deep River neutron monitoring station is used for the period 1985–1995, to investigate for a com-parative study of diurnal anisotropy in CR intensity on 60 QD, 120 QD, CQD and AD. It is observed that 60 QD are most suitable for the anisotropic studies on short/long term basis. The time/spatial variations in the amplitude and phase of the diurnal anisotropy become more pronounced for 60 QD for the period under investigation.

Correlation of the heliospheric current sheet tilts to galactic cosmic ray modulations and solar wind speed

The comparison of the heliospheric current sheet tilts from 1971 to 1992 with cosmic ray intensities recorded at Deep River neutron monitor, solar wind speeds and sunspot numbers, has been investigated. Our results have indicated that the inclination of heliospheric neutral sheet is a suitable parameter for studying disturbances in the interplanetary medium. The observed differences in the sensitivity of cosmic ray intensity to changes in the neutral sheet tilt angles before and after the reversal of interplanetary magnetic field polarity have been studied. A much stronger intensity-tilt angle correlation was found when the solar magnetic field in the north polar region was directed inward than it was outward. The slope of the regression line for the 1981–1989 epoch (qA < 0) was a factor five larger than for the 1971–1978 epoch (qA > 0). A strong correlation was found between the inclination of neutral sheet and solar wind speeds in the ecliptic plane. Furthermore, an excellent correlation was obtained between sunspot numbers and tilt angles of neutral sheet and it was dependent on the reversal of the Sun's magnetic field. The physical significance of our results is discussed.

Transverse cosmic ray gradients in the heliosphere and the solar diurnal anisotropy

We describe a new scheme for computing the asymmetric part of the cosmic ray particle density gradient. The method makes use of the ecliptic components (Ar, Aϕ) of the cosmic ray solar diurnal anisotropy observed with a detector on spinning Earth and the interplanetary magnetic field sector structure in the heliosphere. We apply this methodology, to compute the magnitudes and directions of the asymmetric (Gθa) particle density gradient in the heliosphere for selected intervals of time during the 1965 to 1993 period. Data from six detectors of the global network are used for this purpose. Their median rigidity of response (Rm) covers the following range: 10 GV ≤ Rm ≤ 300 GV of the galactic cosmic ray (GCR) spectrum. We find that Gθa is well behaved over an intermediate rigidity range (10 GV ≤ Rm ≤, 67 GV) where it is inversely proportional to the rigidity (R) of the GCR protons. At higher rigidities (R ≳ 100 GV), it may fall off more steeply and even reverse sign at large (≳ 1 AU) off‐ecliptic distances. The direction of Gθa changes consistently immediately after each observed solar polar field reversal. Sudden, conspicuous, short‐lived (∼ 1 year) reversals of Gθa are observed during the declining phases of solar activity cycles 20(1974) and 21(1984). They may be caused by a sudden burst of solar activity late in the cycle. We have determined Gθa values from Deep River neutron monitor data (Rm = 16 GV) for the 1965 to 1993 period. Extreme computed values range from (3.0 ± 0.8)%/AU in 1968 to (−2.4 ± 0.8)%/AU in 1987.

Is there a twenty year wave in the dirunal anisotropy of cosmic rays?

We have analyzed data obtained with the Deep River neutron monitor and the underground vertical muon telescope at Embudo for the period 1965–79. Our data in conjunction with other published data show that for 1957–70 the diurnal anisotropy is unidirectional; with direction along 18 hour LT (east‐west). During 1971–79, the diurnal anisotropy consists of two components. One is in east‐west direction and the other is the radial component, with direction along 12 hour LT. The latter attains a maximum amplitude in 1976. We find no evidence for the existence of the twenty year wave in the diurnal anisotropy of cosmic rays.