Rajesh Kumar Mishra – författare

Document from the year 2023 in the subject Physics - Astronomy, , language: English, abstract: Coronal Mass Ejections are vast structures of plasma and magnetic fields that are expelled from the sun into the heliosphere. This material is detected by remote sensing and in-situ spacecraft observations. The present study deals with the influence of four types of CMEs namely Asymmetric 'Full' Halo CMEs, Partial Halo CMEs, Asymmetric and Complex 'Full' Halo CMEs and 'Full' Halo CMEs on cosmic ray neutron monitor intensity. The data of ground based neutron monitor of Moscow and CME events observed with instruments onboard and Wind spacecraft have been used in the present analysis. The method of superposed epoch (Chree) analysis has been used to the arrival times of these CMEs. It is noteworthy that the frequency of occurrence of Asymmetric 'Full' Halo CMEs is significantly high, whereas frequency of occurrence of Asymmetric and Complex 'Full' Halo CMEs is low compared to other CMEs. Significant enhancement in cosmic ray intensity is observed after 4 days of the onset of asymmetric full halo and 6 days after the onset of full halo CMEs. The fluctuations in cosmic ray intensity are more prior to the onset of both types of the CMEs. However, during Partial Halo CMEs the cosmic ray intensity peaks, 8- 9 days prior to the onset of CMEs and depressed 3 days prior to the onset of CMEs, whereas in case of asymmetric and complex full CMEs, the intensity depressed 2 days prior to the onset of CMEs and enhanced 2 days after the onset of CMEs. The deviations in cosmic ray intensity are more pronounced in case for asymmetric and complex full halo CMEs compared to other CMEs. The cosmic ray intensity shows nearly good anti-correlation with IMF strength (B) during asymmetric full halo CMEs and partial halo CMEs, whereas it shows poor correlation with B during other CMEs. The IMF, B significantly decreased five days prior to the onset of asymmetric and full halo CMEs and four days after the onset of partial halo CMEs, whereas IMF strength (B) significantly enhanced 5-6 days prior and after the onset of asymmetric and complex full halo CMEs. IMF strength (B) significantly depressed 2 days prior and 4 days after the onset of full halo CMEs. However, IMF, B significantly enhanced from its minimum to maximum values in 2 days interval prior to the onset of CMEs and in 3 days interval after the onset of CMEs.

Document from the year 2023 in the subject Physics - Other, , language: English, abstract: A lot of efforts have been made to find out the possible origin of the 'high amplitude anisotropic wave trains' of enhanced diurnal variation of cosmic rays and to develop a suitable realistic theoretical model, which can explain the different harmonics in individual days. The main objective of this work 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 and their association with different solar and interplanetary transients. The amplitude of all the three harmonics (diurnal/semi-diurnal/tri-diurnal) of HAE events significantly remains quite high and statistically constant as compared to the annual average amplitude for majority of the events, whereas the time of maximum significantly shifts towards earlier hours for first harmonic and towards later hours for second and third harmonic as compared to the co-rotational direction for majority of the events. The occurrence of HAE events is dominant, when the value of interplanetary magnetic field (B) remains in the range (4 -10 nT); the product Ap x Dst remains negative only the ion density remains ? 20. It is noteworthy that the occurrence of high amplitude day is dominant during solar activity minimum years (1986-87) and solar activity maximum years (1991-92). The amplitude as well as time of maximum of the cosmic ray diurnal anisotropy is positively correlated to the sunspot numbers during HAEs.

Scientific Essay from the year 2023 in the subject Physics - Astronomy, , language: English, abstract: This work aims to investigate the phenomenon of unusual variations in cosmic ray intensity in the period 1981-1994, particularly in the context of interplanetary magnetic clouds and low-amplitude anisotropic wave trains. The text provides a detailed analysis of the relationship between low-amplitude anisotropic wave trains and interplanetary perturbations, particularly with respect to changes in cosmic ray intensity. By analysing data from the Deep River Neutron Monitor, the interaction between high solar wind velocities, the orientation of the interplanetary magnetic field and the proton density is highlighted.

Scientific Study from the year 2024 in the subject Physics - Astronomy, , language: English, abstract: This study investigates the phenomenon of Low Amplitude Anisotropic Wave Train Events (LAWEs) in cosmic ray intensity using data from the ground-based Deep River neutron monitor for the period 1991-94. The analysis reveals that the amplitude of diurnal anisotropy during LAWE events consistently remains low and statistically constant compared to the quiet day annual average amplitude for the majority of events. Furthermore, the timing of the maximum diurnal anisotropy for LAWE events shifts significantly towards earlier hours, aligning with the co-rotational direction and remaining consistent with the direction of quiet day annual average anisotropy for most events. Conversely, the amplitude of semi/tri-diurnal anisotropy remains statistically high and unchanged. However, the phase shift occurs towards later hours compared to the quiet day annual average values for the majority of LAWEs. Analysis of diurnal anisotropy vectors reveals a shift towards earlier hours in 50% of events and a shift towards later hours in the remaining 50%, relative to the average vector for the entire period. Additionally, it is observed that the amplitude of these vectors significantly increases with the shift towards later hours. The study suggests that high-speed solar wind streams do not play a significant role in causing LAWE events on a short-term basis, but they may contribute to these events on a long-term basis. The occurrence of LAWE is found to be dominant when the polarity of Bx and Bz remains positive, and the polarity of By remains negative a phenomenon not reported previously. Furthermore, the amplitude of the first harmonic exhibits a good anti-correlation with solar wind velocity, while the direction of the first and third harmonics shows nearly good anti-correlation. The direction of the second harmonic shows nearly good anti-correlation with interplanetary magnetic field strength.

Scientific Study from the year 2024 in the subject Physics - Astronomy, , language: English, abstract: The most energetic phenomena in the heliosphere are known to be coronal mass ejections (CMEs), which acquire their energy from the Sun's strained magnetic fields. Coronal Mass Ejections disrupt the flow of the solar wind and produce disturbances that strike the Earth with sometimes catastrophic results. Coronal mass ejections are often associated with solar flares and prominence eruptions but they can also occur in the absence of either of these processes. The frequency of CMEs varies with the sunspot cycle. At solar minimum we observe about one CME a week. Near solar maximum we observe an average of 2 to 3 CMEs per day. We have studied different characteristics of coronal mass ejection based on the observation form Large Angel and Spectrometric Coronagraph (LASCO) on board of the Solar and Heliospheric Observatory (SOHO) space craft during the period 1996 -2006. It is noteworthy that the rate of occurrence of Class B CMEs is more than class A CME's. The occurrence spectrum of both classes of CMEs follows the trend of the phase of solar cycle and maximum number both types CME's seems to be occurred during maximum solar activity. It is also observed that the maximum number of class A, Class B CMEs have speed range 0-500 km/sec. We have observed that maximum number of Class A, Class B CME's occurred in apparent angular width range 00-900. It is also found that the maximum number of class A and class B CME's have occurred when the position angle ranges in 50-1000 and 2500-3000 respectively.

Scientific Study from the year 2024 in the subject Physics - Astronomy, , language: English, abstract: An investigation has been made to study the cosmic-ray decreases occurring during 2006 with respect to the arrival times of interplanetary shocks and magnetic clouds. We have identified three interplanetary magnetic cloud events during 5 February 2006, 13 April 2006 and 14 April 2006. The interplanetary magnetic field (B), north-south component of interplanetary magnetic field (Bz), solar wind velocity, sunspot number (R) and disturbance storm time index (Dst) associated with these events has been studied in the present work. Data (neutron monitor count rate) from Newark Neutron Monitor 9NM64 has been used. The north-south component of IMF (Bz) produce large geomagnetic disturbance on the onset of interplanetary magnetic clouds. The deviations in the interplanetary and solar wind plasma parameters are significantly correlated to the magnetic cloud events. The increase in Dst index, sunspot number (R) and Bz after the magnetic cloud event produces increase in cosmic ray intensity.

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