95

ENERGETICS OF ULF/ELF PLASMA WAVES IN THE SOLAR WIND AND OUTER EARTH'S MAGHETOSPHERE

S.I.Klimov

Space Research Institute, Russian Academy of Sciences, Moscow

deployed at special booms which excludes the possible shadowing and reduces the influence of the spacecraft body on sensors. All these factors ABSTRACT provide the low level of the backround High apogee orbits of Prognoz-8 (1980) and electromagnetic noise of electric and magnetic field Prognoz-10 (1985) satellites and low noise level of experiments. electric field, magnetic field and plasma flux The wave experiment flown on the Prognoz-8,-10 satellites were able to measure fluctuations of the fluctuations instruments have provided an plasma flow (P), current density (J), eleotric(E) opportunity of ULF/ELF waves (0.1-100 Hz) study in and magnetic(B) fields (Refs. 1, 3). In particular, both quiet and disturbed magnetospheric conditions. these instruments were designed to perform detailed Conducted for the first time direct measurements in measurements in the low frequency range. the Solar Wind in the ULF/ELF range of fluctuation Figure 1 demonstrates the sequence of data from one spectra of electric field E and ion component of orbit (96 hours) gathered with the wave instrument plasma flow P have shown that hourly averaged E and .. on Prognoz-8. The data presented in this Figure are F apectra are in quiet conditiqns for E (10 averaged over 5 rain. It is seen that the low -lOlV/mHz (2-105 Hz) and for F UO^lOjcounts percm frequency oscillations of the electric field and s Hz (2-70 Hz). In the disturbed conditions (on plasma flow are prominent features of the shock the sector boundaries and discontinuities) hourly transition region and various boundaries encountered averaged values of power spectral density are 2:3 in the Earth's magnetosphere. The low frequency times higher than in quiet regions. It was shown, measurements, in particular those of the plasma flow that most of solar wind energy dissipation in the (P), can be use to detect the shock encounters. Bow Shock front is provided by the oscillations in The project "INTERSHOCK" was primarily dedicated to the doppler shifted lower hybrid frequency range studies of the fine structure of the Earth's bow (5-30 Hz) - 10" erg/cm' rather than by iono-sound shock. However, the Prognoz-8 and Prognoz-10 oscillations - 10"'" erg/cm"*. spacecraft also provided the wave measurements in the different regions of the Earth's magnetosphere.

The project "INTERSHOCK" (Réf. 1) was dedicated to l.BOW SHOCK the investigation of the interaction between the solar wind (SW) and the Earth's magnetosphere. Whistlers and ion acoustic waves were first wave Particular attention was draw to plasma and wave modes identified at the Earth's bow shock measurements in the magnetosheath,at the Earth's bow (Refs. 4, 5). However, these discoveries did not shock and magnetopause. This project was carried out clarify all problems related to the energy with two spacecraft: Prognoz-8 launched on 25 dissipation on the collisionless bow shock. In December 1980 and Prognoz-10 launched on 26 April particular, the mechanisms of ion and electron 1985. The scientific instruments flown onboard heatings remained unknown (Refs. 6, 7). spacecraft were built in the cooperation between Wave measurement:; performed by the Prognoz-8 and -10 research groups from USSR, Poland ( Prognoz-8 ) and spacecraft showed that all these problems cannot be Chechoslovakia. solved by use of data gathered by prior expérimenta. The Prognoz-type spacecraft was enjected onto the It was mainly due to the lack of detailed orbit with apogee of about 200000 km. The outbound measurements in the range of low hybrid frequency and inbound raagnetosphere encounters were expected which was not sufficiently covered with the wave at high and low !attitudes respectively. The instruments flown onboard satellites launched before Prognoz-type satellite (Réf. 2) waa rotating around Prognoz-8 and -10. Two peaks at frequencies of the axis pointed to the Sun with accuracy of a few 2-8 Hz and 20-40 Hz, are the permanent features of degrees. The spin period was typically of about 2 wave observations near the shock front (Réf. 8). min. The solar panels were located in the rotation Figure 2 showa the integral level of power of plane. Their relatively constant orientation with magnetic (Da) and electric (De ) field fluctuations respect to the Sun light and slow rotation of the in the frequency range from 0.1 to 25 Hz. This spacecraft injure the low level of the frequency range covers the range of low hybrid electromagnetic background noiae caused by the frequency which is estimated to be of about ficw Hz. rebuilding of the photoelecton sheet of the The rump of the bow shock is crossed between spacecraft and the extracurrent structures of the 07:09:10 and 07:09:30 UT. It is seen that both solar panels. The electric and magnetic sensors were paraneters De and 0% reach their naxiaa just

Proceedmgs of the 26th ESLAB Symposium - Study of the Solar-Terrestrial System, held in Killarney. Ireland. 16-19 June 7992 (ESA SP-346 September 1992) Ut- Ut" 96

PROGNOZ-8.1981

?igure 1. The Prognoz-B monitoring data from one orbit.

mV2 m"2 100 Bf.nT/Hz'71 10 1 ,

10'1 -

706 710 05 I 2 5 10 20Hz 05 1 5 IO 20 Hz Figure 2. The Prognoz-10 bow shock crossing on 8.10. Figure 3. E and B plasma wave spectra measured on 85. Bx magnetic field, mean squares of fluctuation Prognoz-10 in: 1- the foot, 1- near the ramp. 3- amplitudes of the magnetic field Db and electric behind the ramp. field De in the frequency region from 0.1 Hz to 25 Hz. before the shock ramp. Figure 3 demonstrates the incoming ions leads to the excitation of whistler dynamics of electric and magnetic fields wavo,3 at shocks with Mach numbers greater then 10 fluctuations through the shock transition region. (Réf. 12). Three succesive spectra of both electic and magnetic The instabilities related with the ion beam generate signals are shown being measured in the shock foot the magnetosonic waves in the range of the low (1), ramp (2) and downstream region (3). Maximum hybrid frequency. Another wave mode identified as a level of fluctuations is observed at frequencies whistler, is driven by the nonlinear evolution of between 4-6 Hz in the shock foot and at frequency of the shock front (Refs. 13, 14). about 0.7 Hz in tha shock ramp and downstream The problem which embrasses the interpretation of region. wave data is that of the distinction between spatial It is well established (Refs. 9-11) that the and temporal variations. The wave properties in the significant portion of the kinetic energy of the plasma rest frame (i.e. polarization, frequency and incoming solar wind flow is transfered to the that phase velocity) remain ambiguious whilst this of the reflected ions at the quaaiperpendicular problem is unsolved. A method based on simultaneous I; shock. The opposite flows of the reflecting and observations of magnetic field and current 97

100

«0

so-

40: \

20-

20.00 40.00 «0.00 MOO 7.09.28 Time(sec) 7.10.48

Figure 4. Waveforms of the Bx and By magnetic field. Figure 5. Wavelength on the bow shock front crossing Jy electric current, density and Ez electric field by Prognoz-10 at 8.10.85. 1- frequency <1 Hz; 2- recorded during the Prognoz-10 bow shock crossing on frequency range 2-5 Hz; 07.16:40 is beginning of the 8.18.85. foot; 07.17:20 is magnetosheath. fluctuations can help to overcome this difficulty The maximum value of the wavelength is comparable (Refs. 3, 15). Indeed, the Maxwellian equations with the gyroradius of solar wind protons. Indeed, 7"B=J and 7-8=0 (1) the ion gyroradius (jv) is estimated to be of 130 allow to derive the folowing expresion and 80 km for two crossings presented in Figure 5. K(«,)=J(w)/BM (2) The solar wind velocity Vsw equals 480 km/a, where K(U,) is the wave vector, JM and B(CU) are the magnetic field strength B0 is of 20 nT at the ramp Fourier components of the current density and for both encounters. The angle between Bc and Ve is magnetic field respectively. Thus, simultaneous 57 deg. and 71 deg. respectevely. Thus, the maximum measurements of both current and magnetic field wavelength of emissions observed upstream of the fluctuations performed by a single spacecraft make ramp does not exceed the gyroradius of protons it possible to find out the dispersion relations of reflected from the bow shock. waves. The following figures illustrates an Figure 6 shows a typical dispersion curve in the application of this method. spacecraft reference system. Wave data gathered near Figure 4 presents, from top to bottom, two magnetic the upstream edge of the shock foot have been used field components B» and Ey, current density Jx and in its derivation. The circular polarization of the one electric field component Ez. All parameters are waves which has been established in this section sampled with a rate of 50 Hz. Distinct Have packages allows to substitute the absolute values of J(w) and are observed in the foot region. Levels and shapes B(IJ) with their projections on coordinate axis. The of signals sharply change at the ramp. A high levels projection of the solar wind velocity Vo on the of correlation are evident between various average wave vector (i.e. drift velocity V«») is parameters. shown with the straight line in Figure 6. Its value Two magnetic field componenets Bx and B» are used to is about 200 kmXs. It is clearly seen in this figure find the wave vector and polarization in the that wave phase velocities are approximately equal following frequency intervals: 0.4-1.5 Hz, 2-5 Hz, to the drift velocity. This fact leads to the reveal the existence of different wave modes in the conclusion that ELF waves with large phase shock foot. The minimum variance analysis applied to velocities are propagating in the upstream the magnetic field data is carried out to find the direction; waves with low phase velocities are angle between the background magnetic field and the convected to the downstream region. wave vector (Réf. 16). This angle is found to be of Wave frequencies in the plasma rest frame can be 46130 deg. for three selected frequency intervals. calculated with following equation It should be mentioned that there is an uncertainty f"(k)=IkxVo/2<«T-f(k) (4) in the sigh of wave vector. Figures 6b,c,d present typical dispersion curves Wave packages observed in the foot region have a derived with this formula in the shock foot. It is circular polarization (Réf. 15). The waves in the seen that wave frequencies are strongly affected by frequency range from 0.4 Hz to 10 Hz are left-hand the Doppler shift caused by the solar wind velocity. polarized; the right-hand polarization predominates The dispertion curves displayed in Figure 6 at frequencies above 11-13 Hz. describe: the fast hydromagnetic whistlers with the The cospectral characteristics, coherency and phase right-hand circular polarization in the frequency shift in the frequency range 0-24 Hz was calculated ranges 0.4-1.5 Hz and 2-4 Hz; the left-hand for the data set depicted in Figure 4 (Réf. 17). It intermediate ion-cyclotron waves in the frequency is seen that the linear polarized waves are observed range 4-5.5 Hz and the right-hand polarized at frequencies above 15 Hz and below 1.5 Hz. whistlers in the frequency range 6.5-9 Hz. The equation (2) can be rewritten as Thus, the results obtained in thia section lead to >(o)-(c/2) BMXJ(W) (3) the following hypothesis about the energy where A(W) is the wavelength, B(w» and J(i~) are transformation at the bow shock. The solar wind flow Fourrier components of the magnetic field and deccelarating in the shock foot provides a source of current oscillations. It can be seen in Figure 5 free energy for a wave generation in region close to that the wavelengths of emissions which have maximum the ramp. Fast oblique hydromagnetic whisters are amplitudes lay in the interval from 5 km to 120 km; excited in the low hybrid frequency range. Both typical wavelengths in the region upstream of the positive dispersion and group velocity exceeding shock ramp are of 100 - 120 km. that of the solar wind permit whiatlera to propagate into the solar wind region forming the r 98

2.SOLAR WIND The Prognoz-8,-10 spacecraft mostly operated in the ï OfM solar wind. In the calm solar wind, typical spectral densities of electric oscillations averaged over one hour are of 10~*V/m Hz at 2 Hz and 10"6VXm Hz at 105 Hz; ion flow fluctuations are of 10 r v counts/cm a Hz at 2Hz and 10 counts/cm s Hz at 70 Hz. The amplitudes of fluctuations increase in 2 02 » s a 10 12 /,Hz OtS or 3 times when the spacecraft crosses sector boundaries and discontinuities. Electric field fluctuations in the frequency ranges below 20 Hz and above 18 Hz recorded by Prognoz-8 m- and ISBE-3 respectively have been studied in (Réf. 19). It has been established that spectra recorded at interplanetary shocks can be fitted with the power law in the frequency range 2-20 Hz. The law index is typically of -2.25 and -1.3 for quasiparallel and quasiperpendicular shocks 2. respectively. The law index slightly depends on the amplitude of electric field fluctuation in the range

13H9T5M 13WJ" 250 13HIT.OM 13H»3"750 LOCAL TIME Figure 7. 4-min averaged spectra of electricfield fluctuations as observed on Prognoz-6 from 02:00 OT Figure 9. Waveforms of the electric field intensity to 10:00 UT on 27.08.1981. (a) and plasma flux fluctuation (b) measured every 6.7 ms. At that time the sahtellite was in the magnetosphere, at local time 17 and latitude 40.

"V"yvy , :

E

Figure 10. Example of the high amplitude electric field burst, registreted in the cuap aboard Prognoz-8 at 05.54:50 UT 07.04.1981, sampling rate is 150 Hz. Figure 8. The same as Figure 7 for the case of penetrated into the magnetosphere. Unfortunately, on 19/20.09.1981 from 17:00 UT to 01:00 UT. Prognoz-8 we do not have full magnetic field measurements and threfore it is impossible to identify the nature of the phenomenon observed. The Electric noise associated with plaama clouds are analysis of high amplitude fluctuations measured by observed in the frequency range < < . Spectra of GEOS-2 (Réf. 23) appearing as intensive short fluctuations typically fall with the increasing of duration bursts, has indicated that the best frequency; a distinct maximum presents at possible explanation is a nonlinear Alfvenic frequencies around alM, typically between 12 and 25 structure traversed by the satellite. The high Hz. Waves are observed in form of separated bursts. amplitude fluctuations are connected with the The integral level of fluctuations reachs values of convection of plasmas in transverse electro-magnetic a few mV/m. fields. In this sense it is natural to suppose that Hear the magnetopause at Prognoz-8 was detected one sees high amplitude nonlinear waves noving over plasma waves with extremely high amplitude. During satellite. This is supported by the observed the period of about 10 minutes several waves bursts correlation or anticorrelation of the electric field with characteristic time 2-20 sec and amplitude from and ion flux fluctuations (Figure 9). 10 up to several tens mV/m were found accompanied by In certain cases . iore intense impulses with K>50 more hidh frequency waves with time scale 0,2 sec. mV/m are much more rarely observed. The event in This waves ( Figure 9) were found both in the Figure 10 was registrated 10 minutes before electric field and in the plasma flux fluctuations Prognoz-8 finally cross magnetopauae and was channels (it is important to notice that we have accompanied by accelerated electrons with the energy measured only fluctuations, not DC components). The above 100 eV (Réf. 24). Very probable explanation comparison of the plasma waves with the energetic for this spike is the burst reconnection with spectra of ions from the MOSITOR device (Refs. 1, appropriate inductive electric field like FTB 22) has shown that the high amplitude structure is events. On the contrary, solar wind plasaoida with located at the boundary of a plasma clouds, a plasma an excess momentum density with respect to the structure consisting of magnetosheath plasma wich background can penetrate inpulaive inseide the

Uf- r 100

geomagnetic field through the cusp. The measurement 11. Scudder J D, Mangeney A, Lacombe C, Harvey C C, on Prognoz-8 of only one electric, two magnetic Wu C S & Anderson R R 1986, The resolved layer of a field components and ZD plasma ones did not allow us collisionless, highô, supercritical to constract a representative model of this event. quasiperpendicular shock J wave, 3, Vlasov electrodynamics, J. Geophys. Res., 91, 11075-11097. 4.CONCLUSION 12. Galeev A A, Klimov S I, Nozdrachev M N, Sagdeev R Z & Sokolov A Yu 1986, Dynamics of spectra of Collisionless space plasma is proved to be a medium magnetosonic oscillations in front of Earth Bow where dynamics is determined not only by particles Shock and mechanism of their generation. Sov. Phys. but by a wide spectrum of plasma wave motions. These jJETP, 90,5. effects are of particular importance especially at the thin boundaries in the magnetosphere such as bow 13. Galeev A A, Fisher S, Klimov S I, Krasnoselskikh shock, magnetopause, neutral sheet and plasma sheet V V, Nozdrachev M N, Vaisberg O L,Voita J & boundary layer. Wave-particle interaction in the G.N.Zastenker 1991, INTERSHOCK-project:results and plasma results in such processes as: (1) anomalous problems, Proceedings of European workshop on transport processes (pitch-angle diffusion, Collisionless shocks.March 11-13, CNET/CNES, 11-13. anomalous conductivity, turbulent mass diffusion); (2) energy redistribution and plasma heating; (3) 14. Krasnosel'skikh V V ial.1985, Fast electron generation of anisotropic distribution functions and acceleration in quasiperpendicular shocks and type their relaxation; (4) generation of la^-ge scale II solar radio bursts, Astron. and Astrophys., 149, instabilities. Experience of previous missions have 323-329. shown that for comprehensive study of these process multisatellite measurements are necessary. One of 15.Romanov S A, Klimov S I & Mironenko P A 1991, such experiments is INTERBALL Project, in which Experimental derivation of ELF waves dispersion plasma wave investigations play one of the major relations and evidence of wave coupling in the roles (Réf.25). Earth's Bow Shock foot region from the results of the Prognoz-lO. Adv. Space Res., 11, 9, 19-24. 5.REFERENCES 16. Sonnerup B U O & Cahill L J,Jr, 1967, 1. FischerS (Ed.) 1985.INTERSHOCK project. Magnetopause: structure and altitude from Publications of the Astronomical Institute of Explorer-12 observations, J. Geophys. Res., 72, 171. Chechoslovak Academy of Science, Prague, N60. 17. Krasnosel'skikh VV & al 1991, On the nature of 2. SOLAR ACTIVITY INVESTIGATION and SPASE SYSTEMS. low frequency turbulence in the foot of strong 1984, (in Russian), Nauka, Moscow, quasi-perpendicular shocks, Adv. Space Res., 11, 9, 15-18. 3. Klimov S I, Nozdrachev M N & al 1986, Plasma wave investigation on the Prognoz-10 satellite. Kosmich. 18. Nozdrachev M N, Petrukovich A A 1992, Issl. (in russian), 24, 2, 177-184. ULF/ELFelektromagnetic waves associated with the quasiperpendicular Earth's bow shock crossings, 4. Scarf F L , Moses S L, Kennel C F, Greenstadt E This issue. W& Coroniti F U 1987, Plasma waves near collisionless shocks, Proceedings of the 19. Vaisberg O L, Scarf F, Borodkova N&Nozdrachev M International conference on Collisionless shocks, 1987, ELF-emissions from interplanetary shocks Balatonfured, Hungary, 1-7 June, Budapest, MTI, observed on Prognoz-8 and ISEE-3, in Solar maximum 19-41. analysis, ed. by Stepanov V. and V.Obridko, VNU Science Press, Holland. 5. Gurnett D A 1985, Waves and instabilities in collisionless shocks. Colliaionless shocks in the 20. AndersonR R, Harvey C C, Hoppe M M, Tsurutani B Heliosphere: Reviews of current research, Geophys. T, Eastman I E, & Etcheto J 1982, Plasma waves near Monogr. 35, 207-224. the magnetopause.J.Geophys. Res., 87, A4, 2087-2107. 6. Sagdeev R Z 1964, Collective processes and shocks 21. Blecki J, Kossacki K & al 1988, ELF plasma in a rarefied plasma, Questions of plasma theory, waves associated with plasma jets near the Earth Leontovich M (Ed), Moscow, 20. magnetopause aa observed by Prognoz-8, Physica Scripta, 37, 623-631. 7. Galeev A A 1976, Collisionless shocks, Physics of Solar-Planetary environments,Williams D J (Ed), AGU 22. Jimenez R 1984, Ph.D. thesis, Space Research publication, Boulder, 464. Institute, USSR Academy of Science, Moscow. 8. Vaisberg O L, Galeev A A, Zastenker G N, Klimov S 23. Rezeau L, Morane A, Perraut S, Roux A, & Schmidt I, Nozdrachev M N, Sagdeev R Z, Sokolov A Yu, & R 1989,J. Geophys. Res., 94, 101. Shapiro V D 1983, Electron acceleration in the front of strong collisionless shock wave, Sov Phys JETP, 24. Savin S P, Zelenyi L M, & Prokhorenko V I 1990, Engl. Transi., 58, 4, 716-721. Specific tasks of multiple scale plasma measurements in REGATTA-CLUSTER sistem, Proc. Int. Workshop on 9. Formizano V 1985, Collisionless shock waves in Space Plasma Physics Investigations by Cluster and space and in Astrophysics. Proc. ESA workshop on Regatta, Graz, Austria, ESA SP-306, 7-16. future missions in solar, heliospheric and space plasma physics, ESA SP-235, 83-100. 25. Klimov S & al 1992, Role of the Interball small scale investigations in the GGS program, This issue. 10. Scopke N 4 al 1983, Evolution of ion distribution across the nearly perpendicular bow shock: specularly and non-specularly reflected gyration ions, J. Oeophys.Res., 88,A8,6121. I

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