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Energetics of Ulf/Elf Plasma Waves in the Solar Wind and Outer Earth's Maghetosphere

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Energetics of Ulf/Elf Plasma Waves in the Solar Wind and Outer Earth's Maghetosphere 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.
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