Effect Of Ulf Wave Index In Magnetospheric Plasma Dynamics

EFFECT OF ULF WAVE INDEX IN MAGNETOSPHERIC PLASMA DYNAMICS A. K. Singh and S. K. Dohare Department of Physics, University of Lucknow,Lucknow-226007 Email: [email protected] INTRODUCTION 8000 2500 (eV-s/m)

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In the magnetosphere the solar wind causes the possible occurrence of geomagnetic disturbances . In the recent years the new conceptions of magnetospheric plasma dynamics are being developed in which turbulence play Vitol role (Antonova,2000, Borovsky and Funsten, 2003). The turbulence of solar wind drives and existence of natural MHD waveguide and resonator in ULF range (1mHz to 1 Hz) ensures magnetospheric response. So much of the turbulent nature of sun earth interaction can be monitored with ground based ULF observatories. Various geomagnetic indices are (Kp, Dst AE etc.) are used to monitored electrodynamics of sun-earth environment .Since the ground based observations at one selected observatories or at any one meridian does not give any information about the level of activity on the global scale, so a new ULF wave index was developed in order to estimate the global wave activity of magnetosphere (Kozyreva et al. 2007). Romonave et al. (2007) used the ULF index to study the acceleration of energetic electron in the earth’s magnetosphere. In this paper we have shown the variation of ULF index introduced by Kozyreva et al. and the relativistic electron energy and momentum and its impact on space weather studies .The aim of present work to validate the significance of ULF indices with relativistic electron dynamics and demonstrate the space weather related problems and its applications.

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WAVE INDEX & RELATIVISTIC ELECTRON DYNAMICS Ultra Low Frequency (ULF) waves, naturally occurring plasma waves in the 1mHz to 1 Hz band, are seen in all region of the magnetosphere form high to equatorial latitude. ULF waves are also transmitted from the magnetosphere through the ionosphere to the ground . Since the ionosphere act as a sink form the magnetosphere phenomena , ground based and ionosphere signatures play an important role in understanding the interaction with the solar energy source. ULF waves are proxy of global ULF activity and these waves are generated via various kinds of drift instabilities (Pilipenko, 1990). The energy of electron depends on the excited solar wind enhancement with fast mode and the ULF wave power grows with increase with solar wind velocity .Fig 1 and 2 showing the variation of ULF index with energy and momentum of relativistic electron . The physical interpretation of fig is related with different latitude and longitude the calculated value of ULF index at that point find the exact measurement of excitation of relativistic electron. At a fixed latitude the value of ULF index is calculated and corresponding which the energy of relativistic electron is also calculated. On that place the excitation is more than coupling tendency is more and weather is sporadic .On the other hand the if excitation is less , than the coupling is less and weather is calm. This will give the exact situation of space weather and in the forthcoming event and can play an important role in weather forecasting. The ULF index has developed to characterizing the turbulent level of geomagnetic field and analysis of relativistic electron enhancements during the space weather event.

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Different types of indices are used as important tool to measure the energy flow in definite regions of solar wind magnetosphere-ionosphere system and these indices characterize the steady state level of electrodynamics in earth upper atmosphere . The sporadic movement of solar wind drivers and resonators in the magnetospheric plasma in ULF frequency range ensures a periodic magnetic field forcing the boundary layers . Hence much sporadic nature of plasma processes of solar wind magnetosphere ionosphere interaction can be monitored with ground based receiver and space satellite in the ULF frequency range. The construction of ULF waves index is used to characterize the short scale variability of near earth electromagnetic processes. ULF index have derived from spectral features of ULF power from a global array of stations in northern hemisphere. The data have used from the different observatory (Weimer et al. 2003). According to Kozyreva at different stations the data have been inspected and select a cutoff frequency that is converted in to X-Y coordinate system .For any universal time hour , the magnetometer station in chosen MLT sector and CGM latitude range. After this for selected stations , the power spectral density id calculated with DFT in 1 hour band . At each station the noise and spectral power makes total power that introduced as global ULF wave index.

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Fig 1 & 2: Variation of energy and momentum with ULF wave index

RESULT AND DISCUSSION The continuous emitting of radiation from the sun provides the huge amount of energy in the earth’s magnetosphere and this is responsible for the ring current formation .This newly developed ULF index provides the facility to characterization and monitoring of turbulent level of solar wind magnetosphere interaction . This index is basically driven from ground based or satellite observations. The energy of relativistic electron depend on the solar wind condition . The turbulence of solar wind passing the magnetosphere is controlled by the level of upstream turbulence . The presence of turbulence inside and outside of the magnetosphere should have a profound effects on the large scale dynamics. The observed decrease of ULF excitation efficiency with the solar wind velocity increase contradicts the notion on the over reflection of magnetosphere ULF modes at the magnetopause under high velocity (Mann et al. 1999).The energy and momentum of relativistic electron are related with the excitation of solar wind . Any steady state assumption are in fact invalid because the solar wind represents a rapidly time varying environment to which the magnetosphere is continuously exposed.

CONCLUSION The new ULF wave index is simple and convenient tool for the description of the wave activity in an important and powerful frequency range of the magnetosphere system and it can be applied to various space physics and space weather problems like solar wind and the IMF interaction with the magnetosphere, substorm physics , high speed streams , ring current dynamic structure , study of storm and substorm related with ULF waves, role of electron acceleration belt formation . This ULF index is analogous to geomagnetic indices that have been derived form the ground and the satellite magnetometer observational data and useful for the study and relativistic electron energization

Acknowledgment:

AKS is thankful to Department of Science and Technology (DST), government of India providing the financial support as a research project (file no. SR/S4/AS: 261/06). Authors are also thankful to Prof. Kozyreva et al. for helping in study of ULF wave index and providing the data.

REFERENCES Antonova, E.E. (2000), Large scale magnetospheric turbulence and topology of magnetospheric currents, Adv. Space. Res.25, 7-8, 1567-1570, DOI:10.1016/S0273-1177(99)00669-9. Borovsky, J.E. and H.O. Funsten (2003), Role of solar wind turbulence in the coupling of the solar wind to the Earth’s magnetosphere, J. Geophysics. Res 108, A6, 1246, DOI:10.1029/2002JA009601. Kozyreva, O.V., V. A. Pilipenko, M.J. Engebretson, K. Yumoto, J.Watermann, and N. Romanova (2007), In search of a new ULF wave index: Comparison of Pc5 power with the dynamics of geostationary relativistic electrons, Planet. Space. Sci.55, 755-769, DOI: 10.1016/j.pss.2006.03.013. Pilipenko, V. A. (1990), ULF waves on the ground and in the space, J.Atmos. Terr. Phys. 52, N12, 1193-1209, DOI: 10.1016/0021-9169(90)90087-4. Singh, A. K. (2003), Ultra Low Frequency (ULF) waves , In: R. P. Singh, R Singh, A. K. Singh( Ed.) Solar Terrestrial Environment : Space weather, Allied Publisher, new Delhi, 429-440, 2003. Weimer, D. R., Ober, D. M., Maynard, N.C., Collier, M.R. McComos, D. J. Ness, N. F., Smith, C. W., Watermann, J., 2003, Predicting IMF propagation delay times using the minimum variance technique, J. Geophys. Res., 108, 1026.