ENERGY ESTIMATION OF THE INTERPLANETARY PLASMA DURING STRONGEST GEOMAGNETIC STORMS OF THE CURRENT 24 SOLAR CYCLE ON MARCH 2015 The geomagnetic storms on March 2015 are the most powerful storms during the current solar cycle. They develop in time period of three days. In the first day, 17-th March, the geomagnetic index Kp reaches the value Kp = 8, in the second day Kp = 6 and in the third day Kp = 5, respectively. The considered geomagnetic storms occur in the decreasing part of the 24-th solar cycle. Yordan Tassev [1], Lachezar Mateev [1], Peter Velinov [1], Alexander Mishev [3], Dimitrinka Tomova [2] [1] Institute for Space Research and Technology, Bulgarian Academy of Sciences, Sofia; [2] "St. Kliment Ohridski", University of Sofia, Bulgaria; [3] ReSolve CoE, University of Oulu, Finland They result from the interaction between the solar plasma shock wave, which is created by the Coronal Mass Ejection on 15 March 2015 and the terrestrial magnetosphere. Before reaching the magnetosphere, the shock wave passes through the equilibrium point of Lagrange L1. It occurs 1 hour before the interaction of the shock wave with the magnetosphere.

In this point are situated some space probes as ACE, SOHO and WIND which measure the interplanetary medium parameters: such parameters as solar wind velocity and density, magnetic field intensity and interplanetary plasma temperature, respectively. Using the on this way measured parameters, it is possible to calculate the kinetic energy density: E K = (1/2) n |V| 2 ; n=m p N; the magnetic energy density: E M = |B| 2 / (2  0 ); and the thermal energy density: E T = (3/2) N k Tp; of the solar plasma flux. Here N is the plasma density of solar wind, k is Boltzman constant, Tp is solar protons temperature, B is the interplanetary magnetic field intensity,  0 is magnetic permeability of vacuum, V is solar wind velocity [1]. In the investigated period a powerful Forbush decrease of the galactic cosmic rays intensity occurs. It reaches -4.5%, which is seen in the data of the neutron monitor in Oulu, Finland. A quantitative analysis of the ionization effects in the ionosphere and the atmosphere in the time period March 2015 is made. During the storm, which lasted for more than two days, cosmic radiation levels in the stratosphere jumped by more than 6%. Radiation levels did not return to normal until a week after the CME strike. Spaceweather.com and the students of Earth to Sky Calculus launched a series of weather balloons--before, during and after the storm--to measure the storm's effect on Earth's upper atmosphere.Earth to Sky Calculus [1]. Heliophysics, Plasma Physics of the Local Cosmos. Edited by Carolus J. Schrijver and George L. Siscoe. Cambridge University Press 2009.

We consider consequently as an example the magnetic, kinetic and thermal energies density which are drawn on the three Figures from March On the Figures it is clearly seen that the total magnetic energy has a significant increase one day before the storm on 16 th March with values exceeding 5х J/m 3 towards the median value which is 2х J/m 3. The same is valid also for the kinetic energy where once more on 16 th March the deviation values reach 4х10 -9 J/m 3 towards the median values which are 1х10 -9 J/m 3. The difference is 3х10 -9 J/m 3.

If we consider separately В z and v z then we could not make such comparison because we have different physical magnitudes in spite of the visual similarity of the time course of the В z and v z data. But when we transform them in energy they are already commensurable in relation of dimensions. Then we can say surely that there is a change in the magnetic energy as also in the kinetic energy of the solar wind flow one day before the geomagnetic storm. It doesn’t mean at all that we have found a predictor of the geomagnetic storm, but only that we have a physical process which probably relates the velocity of the solar wind flow with the magnetic flux. There is a physical sense in this assumption, because the magnetic field propagates fully refrigerated in the solar plasma and depends on its velocity. This is only one example for the fact of different energies comparison which can describe and even can serve as predictor for physical processes which participate in the geomagnetic storm. If we look at the last Figure which draws the parameter of Akasofu, we will see clearly the absolutely steady and non changeable in time parameter course until the moment of the storm itself, when it increases drastically. After that it returns rapidly its the primary state and doesn’t show any previous changes before the geomagnetic storm.

Conclusions: Why we use the energetic assessments and not the well known parameters which describe the solar plasma flow? The different parameters as velocity, temperature, magnetic flux have different dimensions (magnitudes) and their comparison is impossible. When obtaining the different energies as kinetic, thermal and magnetic, it is possible to appreciate the contribution of each of them for the geomagnetic storm appearance. The time development of each energy can be considered as time series which describe the interplanetary medium behavior and the propagating there solar plasma. Also these time series can be investigated for forecasting properties which are available there. Each one from the three energies density: kinetic, thermal and magnetic, is more informative than the Akasofu parameter epsilon from the point of view of the geomagnetic storms. END