pudovkin@snoopy.phys.spbu.ru

tel.: 7 (812) 428 46 34

 Research Topics: solar physics, physics of solar wind, physics of magnetosphere, ionosphere and aurorae events, physics of lower atmosphere.

A method of separating the magnetospheric electric field onto the potential and vortex components is proposed. It is shown that the motion of auroral arcs located at closed magnetic field lines is determined by the potential component of the magnetospheric electric field and does not depend on the field-aligned potential drop. At the same time, the ionospheric plasma motion is driven by the ionospheric electric field and depends on the field-aligned voltage. Auroral arc and ionospheric plasma velocities coincide during periods of relatively low auroral activity, and significantly differ when that activity is high.

Magnetic field reconnection at the magnetopause proceeds as superposition of quasi-stationary reconnection and burst-like pulses of spontaneous reconnection. There is shown that in the cusp region the poleward motion of auroral arcs correlates with the Y-component of the magnetopause electric field. This relationship drastically violates during periods of a rapid increase of the southward component of the IMF when all the arcs rapidly move to the equator. This disturbance is characterized by a sunward convection of the ionospheric plasma in the polar cap.

i) The effective polytropic index g _eff in a magnetized anisotropic plasma is obtained in the frame of one-fluid, double-adiabiatic magnetohydrodynamics. The value of g _eff is found to depend on the characteristics of the plasma flow, and on the temperature anisotropy. It is shown that the most probable value of g _eff is 1.4 - 1.9 at the bow shock, and it may be less than unity in the magnetopause region.

ii) The influence of the energy transfer between the perpendicular and parallel (with respect to the magnetic field) proton temperatures on adiabatic index profiles across the magnetosheath is discussed, and a method of estimating the characteristic relaxation time of the proton temperature anisotropy is proposed. It is shown that in spite of the rather complicated behaviour of the g ^ and g _|| indices across the sheath, the effective polytropic index g _eff calculated for the entire magnetosheath equals 1.6-1.7.

i) A model of the magnetosheath structure is extended to estimate the magnetopause standoff distance from solar wind data. It is shown that the magnetopause erosion may be explained in terms of the magnetosheath magnetic field penetration into the magnetosphere. Having combined the magnetosheath model by Pudovkin et al. and the magnetosheath field penetration model, it is possible to predict the magnetopause standoff distance from solar wind parameters.

ii) Parameters of the solar wind plasma and magnetic field in the magnetosheath are calculated for an anisotropic plasma model in the Chew-Goldberger-Low approximation. To bring agreement between the model values of the temperature anisotropy with experimental data, the existence of an intensive proton pitch-angle diffusion is assumed. In the case when the relaxation time is of order of the plasma transport time, the value of T^ /T_|| may amount the values observed in the magnetosheath.

4. Global MHD Modeling of the Solar Wind

A self-consistent two-dimensional simulation of the plasma flow in a dipole-like magnetic field configuration has been performed. The features of the present formulation are: (i) incorporation of the heat and momentum addition due to WKB Alfven waves propagating outward from the Sun and providing additional acceleration to the coronal plasma flow; (ii) extension of the computational domain out to 1~AU. The governing dissipationless single-fluid MHD equations written in the equatorial plane of the spherical coordinate system are solved by employing a time-relaxation technique to obtain a steady-state solution in the near-sun (1-20 Rs) region. Then the steady solution is extended to 1 AU by means of a marching-along-radius numerical scheme. We assumed the polytropic index to be 1.12 and the driven velocity amplitude of Alfven waves at the coronal base (1 Rs) to vary from 0 to 45 km/s when the radial magnetic field increases from 0 to 4 G. Solutions with and without Alfven waves are compared and it is shown that only those with waves are appropriate for reproducing the parameters observed in high-velocity solar wind streams. In agreement with Ulysses observations, the results of simulation demonstrate (i) absence of a marked gradient in the radial magnetic field distribution across the polar high-velocity stream, (ii) the velocity does not change considerably in this stream, but slightly increases toward its center, (iii) the momentum flux density is higher over the pole than near the equator, while the mass flux density shows a slight increase toward the equator.

New solutions of unsteady reconnection problem in compressible plasma are obtained using modified seismic Gagniard-Hoop method. The decay of a current sheet into large-amplitude moving MHD waves is considered self-consistently with MHD disturbances in the surrounding media. A 3-D unsteady Petschek-type reconnection model is applied to the data analysis on so-called flux transfer events (FTEs) at the dayside magnetopause, and it is shown that bursty reconnection may rather good fit experimental data.

Magnetic reconnection in inhomogeneous current sheets is studied. The structure of reconnection layer has been investigated, and it was shown that Petschek shocks have some kind of memory. The fact is that shocks have remembered the velocity of accelerated plasma in diffusion region and when moving along inhomogeneous field they still accelerate plasma to the same velocity.

The problem of reconnection of magnetic field lines was solved in time-dependent case for finit length reconnection line with presence of velocity and magnetic field shears in compressible plasma. Investigation of this solution shows velocity shear to increase amplitude of surface waves on current sheet significantly up to the height of field reversal (FR) region. The results of theoretical investigations were compared to satellite magnetopause crossing data and shows satisfactory similarity. A special attention was paid to processes of plasma acceleration at different sets of magnetohydrodynamical discontinuities.

A problem of time-dependent reconnection of inhomogeneous magnetic fields was solved in the vicinity of magnetosphere nose. A case of special interest is two consequent pulses of reconnection of inhomogeneous magnetic fields. Two FR-regions are moving along current sheet one behind other and after finite time leader FR-region are caught and joined by the following FR-region. The results obtained were used in solar flare model constructing.

A special program for investigation several reconnection pulses were constructed and results obtained were applied to the event 29 October 1979 (ISEE mission) and it has been shown that this event consists of two reconnection pulses. A new model of auroral arcs motion in the night side ionosphere was worked out based on the suggestion that reconnection process in the magnetotail generates Alfven wave and field-aligned current which propagates in the inhomogeneous plasma to the acceleration region 1-2 Re above the ionosphere. It turns out that auroral arcs dynamics depends on plasma gradient in the magnetotail, position of the reconnection line and the reconnection rate behaviour.

Following a pulse of reconnection, propagating field reversal regions (FRRs) bounded with slow shocks form. Inside these FRRs, the magnetic energy is decreased, leading to accelerated plasma jets. As a result of fast motion of FRRs, there is accumulation of magnetic energy external to their leading fronts (analogous to the snow plow accumulation in front of a moving snow plow), and a corresponding energy rarefaction in their wake regions. During reconnection pulse the currents are deflected from the wake to the FRR, but the total current in the current sheet turns out to be unchanged. Topology of magnetic field can change only during switch-on phase, but when electric field in the diffusion region switches-off reconnected magnetic flux does not change any more.

Spatial distribution and temporal variation of the electric field intensity in the diffusion region are considered for a model of a thick current sheet. There is shown that at the reconnection line and in the vicinity of the latter, the induced electric field may be homogeneous and hence curl-free; the sources of that field are concentrated mainly in the Field Reversal Regions where . The rate of electric field decay at the reconnection line is shown to be mainly determined by the rate of the diffusion of the magnetic field across the region of the anomalous resistivity.

 6. Magnetic Reconnection in the Solar Atmosphere and in the Solar Wind

A method of separating electric field in the flare region onto the potential and vortex (induced) parts is used. According to the proposed model, the motion of flare ribbons from the central line of the flare region is caused by the vortex component of the coronal electric field, while the motion of bright spots within the flare region in direction to the central line is driven by the potential component of that field. Intensity of the both components of the flare region electric field is estimated to equal approximately 1-3 V cm^-1 which provides the input of the electromagnetic energy into the active region at a rate about 10¹⁰ erg cm^-2 sec^-1.

Numerical simulation of the magnetic field reconnection across the IMF sector boundary shows that the reconnection line may be carried by the solar wind out of the region of the anomalous resistivity. This makes it possible to observe at the Earth orbit magnetic loops open to the Sun as well as from it. Besides, it is shown that the current sheet in the vicinity of the reconnection line has to split into two currents. Experimental data on the structure of the sector boundaries are analyzed, and it is shown that the currents at them really are often splitted.

The model of tail-like current sheet dynamics based on a numerical solution of nonideal one-fluid compressive MHD equation system was developed. Simulation technique is build up on a base of two-step Lax-Wendroff and Dufort-Frankel explicit schemes. The process of magnetic reconnection initiated by local increase of plasma resistivity was studied via model simulation. A feedback between macroscale MHD process and microscale processes of plasma instability and anomalous resistivity development is taken into account. It is shown, that inducted electric field penetrates from the local resistivity region across magnetic field as fast magnetosonic wave of rarefaction, and as fast magnetosonic wave of compression along of the magnetic field. Regions of accelerated plasma and reconnected loops of magnetic field (outflow regions) are separated from inflow regions by high-amplitude slow waves. The low-hybrid drift plasma instability localises on regions of high gradient of total pressure, which drift into the sheet and toward dipole-like boundary. The computations show that plasma convection in the vicinity of the resistivity region is more complex that it was predicted by linear theory and includes the vortex-type flow.

New method of remote sensing of plasma pressure and current density in the current sheet was developed based on low altitude spacecraft measurements of particle precipitation; its testing on real data from NOAA spacecraft showed a reasonable agreement of computed parameters with the values known from direct measurements in the magnetospheric current sheet.

Characteristics of ion isotropic boundaries in the dayside oval were studied based on NOAA particle data; a comparizon with model computation based on the magnetospheric model confirmed that, like on the nightside, the ion isotropic precipitation is formed by the nonadiabatic scattering in the regions of strong curvature of the magnetic field lines and, therefore, they can also be used for remote sounding of magnetospheric configuration.

Based on direct multipoint observations it was shown that on long scale the plasma sheet convection may concentrate in the narrow sector of the tail, and that during substorm expansion the plasma sheet is heated very inhomogeneously. The narrow (~1 h MLT wide) plasma injections to geostationary orbit has been shown to occur during long convection bays, they optical (UV) fingerprints (auroral streamers) were found to develop equatorward starting from the oval polar boundary. A possibility was tested to estimate the plasma pressure and current density based on low altitude spacecraft data, and possibility of regular monitoring the tail configuration in the near tail based on the DMSP data was shown. New method was used for estimation of tail current density from observations of flapping current sheet at one spacecraft. The orientations of interplanetary discontinuities have been studied statistically as well as their magnetospheric effects.

Variations of the direct solar radiation (S) during a few intensive solar proton events were considered. It was shown that the S value decreased during the solar proton events. The minimum of S-value observed on the day before solar proton event produced apparently by the X-ray emissions of solar flares.

Variations of the air temperature altitudinal profile during Forbush decreases of the Galactic Cosmic Ray flux intensity are considered with the use of data of aerological balloon soundings carried out at local noon in Sodankyla (Finland). There was shown that on «windless» days Forbush decreases are followed by the warming of the troposphere and cooling of the stratosphere.

Changes of the yearly solar radiation input associated with Galactic cosmic ray (GCR) variations have been investigated for the high-latitudinal belt, as well as the influence of these changes on the lower atmosphere circulation. It has been found that the radiation input reveals a negative correlation with GCR intensity at high latitudes. The increase of the solar radiation is shown to be associated with the decrease of the intensity of the zonal circulation in cold season, especially in the West phase of the quasibiennual oscillations of the atmosphere. Thus, the solar energy input at high latitudes modulated by GCR variations is shown to be a possible energy source of the long-term solar activity effects in the lower atmosphere dynamics.

1. Heyn M.F., Semenov V.S. Rapid reconnection in compressible plasma. Phys. Plasmas, 3, 2725-2741, 1996.
2. Pudovkin, M.I., Brekke, A., Zaitseva, S.A., Nozawa, S. Magnetospheric and ionospheric electric fields and dynamics of aurorae. Proc. Third International Conference on Substorms (ICS-3), Versailles, France, 12-17 May 1996, ESA SP-389, 141-145, 1996.
3. Pudovkin, M.I., Zaitseva, S.A., Sandholt, P.E., Egeland, A. Relationship between the cusp aurora poleward motion velocity and solar wind. Proc. Third International Conference on Substorms (ICS-3), Versailles, France, 12-17 May 1996, ESA SP-389, 737-742, 1996.
4. Runov, A.V., Pudovkin, M.I. Two-dimensional MHD model of magnetic reconnection in the current sheet of finite thickness. Geomagnetism and Aeronomy, v.35, N 3, p.13-20, 1996 (in Russian).
5. Runov, A.V., Pudovkin, M.I. Two-dimensional MHD model of magnetic reconnection in the heliospheric current sheet. Geomagn. and Aeron., v.36, N 4, 1-7, 1996 (in Russian).
6. Semenov V.S. Nonstationary Petschek's reconnection. Geomagn.Aeron., 36, 1-17, 1996.
7. Semenov V.S., G.R.Lawrence, R.P.Rijnbeek, and H.K.Biernat. The analogy between magnetic flux tubes and strings applied to interaction and reconnection. "The Solar Wind - Magnetosphere Interaction 2'', Eds. H.K.Biernat, H.P.Ladreiter, S.J.Bauer and C.J.Farrugia, Osterreichische Akademie der Wissenschaften, Wien, 1996.
8. Semenov V.S., M.F.Heyn. Compressible reconnection. "Magnetopause Reconnection and Aurora Dynamics'', Eds. V.S.Semenov, H.K.Biernat, R.P.Rijnbeek, and H.O.Rucker, Osterreichische Akademie der Wissenschaften, Wien, p.51-69, 1996.
9. Semenov V.S., M.F.Heyn. Magnetic reconnection and compressible MHD waves. "The Solar Wind - Magnetosphere Interaction 2'', Eds. H.K.Biernat, H.P.Ladreiter, S.J.Bauer and C.J.Farrugia, Oster- reichische Akademie der Wissenschaften, Wien, 1996.
10. Sergeev V.A., M.V. Kubyshkina, Low altitude image of particle acceleration and magnetospheric reconfiguration at substorm onset, J.Geomagn.Geoelectr., 48, 877-885, 1996.
11. Sergeev, V.A., T.I. Pulkkinen, and R.J. Pellinen, Coupled- mode scenario for the magnetospheric dynamics, J.Geophys. Res., 101, 13047-13065, 1996.
12. Usmanov A.V., 3-D MHD simulation of the solar wind between 1 solar radius and 1 Rs, Proceedings of The Third SOLTIP Symposium, Beijing, China, October 14-18, 1996.
13. Usmanov A.V., A global 3-D MHD solar wind model with Alfven waves, In Proceedings of the Solar Wind 8 Conference, 26-30 June 1995, Dana Point, U.S.A., p.141-144, 1996.
14. Veretenenko, S.V., Pudovkin, M.I. Variations of total cloudiness during the splashs of solar cosmic rays. Geomagnetism and Aeronomy, v.36, N 1, 153-156, 1996 (inRussian).
15. Pudovkin, M.I., Steen, A., and Brandstrom, U. Vorticity in the magnetospheric plasma and its signatures in the aurora dynamics. Space Sci. Revs., v.80, 411-444, 1997.
16. Runov A.V., Pudovkin M.I., 2D MHD modelling of the early phase of magnetic field reconnection. In: Problems of Geospace. Ed. M.I. Pudovkin, B.P. Besser, W. Riedler, A.M. Lyatskaya. Austrian Academy of Sci., Wien, p.157-162, 1997.
17. Pudovkin, M.I., Zaitseva S.A., Besser B.P. The magnetopause erosion and the magnetosheath magnetic field penetration into the dayside magnetosphere. Adv. Space Res., 19, N 12, pp.1909-1912, 1997.
18. Runov A.V., Pudovkin M.I. Magnetic reconnection in a thick current layer. In: The Solar Wind - Magnetosphere System 2, Proc. Intern. Workshop (Graz, September 27- 29, 1995). Ed. H.K. Biernat, H.P. Ladreiter, S.J. Bauer, C.J. Farrugia. Verlag der Ostrreichischen Akademie der Wissenschaften, Wien, Austria, 177-186, 1997.
19. Pudovkin M.I., Veretenenko S.V., Pellinen R. and Kyro E. Meteorological characteristic changes in the high-latitudinal atmosphere associated with Forbush-decreases of the galactic cosmic rays. Advances in Space Research, 1997, 20, N 6, p.1169-1172.
20. Veretenenko S.V. and Pudovkin M.I. Cosmic ray variation influence on the total radiation fluxes in the lower atmosphere. Advances in Space Research, 1997, 20, N 6, pp.1173-1176.
21. Pudovkin M.I., Meister C.-V., Besser B.P., Biernat H.K. The effective polytropic index in a magnetized plasma. J.Geophys.Res., 102, N A12, pp.27145-27149, 1997.
22. Veretenenko S.V., Pudovkin M.I. Variations of solar radiation and galactic cosmic rays in 11-year cycle of solar activity. Proc. conf. in memoriam of M.V. Gnevyshev and A.I. Ohl, Pulkovo, GAO, St.Petersburg, May, pp.28-32, 1997 (in Russian).
23. Pudovkin M.I., Morozova A.L. Time evolution of the temperature altitudinal profile in the lower atmosphere during solar proton events. JASTPh, 59, N 17, 2159-2166, 1997.
24. Semenov V.S., Drobysh O.A. and Heyn M.F., Nonlinear MHD-waves originated by the process of magnetic reconnection, Geomag.Aeronom., 37, N 3, pp.12-20, 1997
25. Semenov V.S., Drobysh O.A. and Heyn M.F., MHD model of FTE in compressible plasma, Geomag.Aeronom., 37, N 3, pp.21-31, 1997
26. M.T.Kiendl, H.K.Biernat, V.S.Semenov, Topological aspects of inhomogeneous reconnection, in: `The Solar Wind -- Magnetosphere Interaction 2'', Eds. H.K.Biernat, H.P.Ladreiter, S.J.Bauer and C.J.Farrugia, Osterreichische Akademie der Wissenschaften, Wien, pp. 143-150, 1997
27. Sergeev V.A., G.R.Bikkuzina, P.T.Newell, Dayside isotropic precipitation of energetic protons, Ann.Geophys.,15, 1233- 1245, 1997.
28. Pudovkin M.I., Zaitseva S.A., Shumilov N.O., Meister C.-V. Large scale electric fields in solar flare regions. Solar Phys., v.178, N 1, p.563-574, 1998.
29. Pudovkin M.I., Egeland A. Large-scale electric fields in the dayside magnetosphere. In: Polar Cap Boundary Phenomena, NATO ASI book, Kluwer Acad. Pub. Ed. by J. Moen and A. Egeland, p.141-156, 1998.
30. Runov A.V., Pudovkin M.I., Meister K.-V. Dynamics of the current sheet with the non-zero normal magnetic field component at the development of local anomalous resistivity. Geomagnetsm and aeronomy, v.38, N 2, 51-59, 1998.
31. Veretenenko S.V., Pudovkin M.I. Variations of solar radiation input for the 11-year solar activity cycle. Geomagnetism and aeronomy, v.38, N 5, p.33-42, 1998.
32. Pudovkin M.I., B.P.Besser, S.A.Zaitseva. Magnetopause stand-off distance in dependence on the magnetosheath and solar wind parameters. Ann.Geophys., v.16, 388-396, 1998.
33. Biernat H.K., V.S.Semenov, O.A.Drobysh, C.J.Farrugia, N.V.Erkaev, Time-varying reconnection: Quantitative analytical results, in: `Polar Cap Boundary Phemomena'', Eds. J.Moen et al.,Kluver Academic Publ.,Netherlands, pp. 41-50, 1998.
34. Semenov V.S., Acceleration processes in the course of dayside solar wind-magnetopause interaction, Adv. Space Sci., vol. 21, No.4, pp.583-590, 1998.
35. Newell, P.T., V.A.Sergeev, G.R.Bikkuzina, S.Wing, Characterizing the state of the magnetosphere: testing the ion precipitation maxima latitude (b2i) and the ion isotropy boundary, J.Geophys.Res., 103, 4739-4745, 1998.
36. Pudovkin, M.I., A.V.Runov, S.A.Zaitseva, B.P.Besser, and C.-V.Meister, Electric currents at the IMF sector boundaries, Solar Physics, vol.184, N1, pp 173-186, 1999.