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VII 7-11 2003 75- ...

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Cosmic Ray Group of Lebedev Physical Institute RAS carries out longterm cosmic ray measurements in the atmosphere by radiosounding since up to present. During quiet periods, the radiation in the atmosphere is due to Galactic Cosmic Rays. The enhanced radiation level is observed at altitudes above 20 km during Solar Proton Events and Electron Precipitation Events (EPEs). Protons penetrate rather deep in the atmosphere while electrons are absorbed at altitudes of ~70100 km. However, the bremsstrahlung X-rays generated by precipitating electrons may be detected by the radiosounds at altitudes of ~2035 km. The subject of this paper is related to the EPEs recorded in the atmosphere. The long-term cosmic ray balloon experiment, as well as the method of electron precipitation events evaluation is described in details in [1It is necessary to note, that comparative analysis of experimental data obtained at northern polar latitudes (Olenya, Norilsk and Tixie) lead to conclusion that the energetic electron precipitation is widely extended over a longitude (~80), i.e. in ~50 % of cases precipitation recorded at Tixie (geomagnetic latitude and longitude are 6548', 21522') was also observed at Olenya (6507', 13221'). In ~20 % of cases the EPEs observed at Olenya were seen at Tixie. Furthermore, the EPEs recorded at Norilsk (6405', 17955') also were observed at Olenya in ~30 % of cases, and contrary, the events observed at Olenya also were observed at Norilsk in ~23 % cases. Observations at these stations during the events were not absolutely simultaneous, but the significant fluxes of very energetic photons were recorded at both sites.

Numerous EPEs were observed at Olenya (Murmansk region; geomagnetic cutoff rigidity Rc=0.6 GV, invariant latitude =65, McIlwain parameter L=5.6) in 1958-2002. Below, we present some of the results of analysis of the experimental data obtained at Olenya.

Solar cycle phase dependence of the electron precipitation events rates Figure 1 shows the yearly number of electron precipitation events (EPEs) and evolution of solar activity cycle in terms of yearly sunspot number (Rz).

Apparently, the electron precipitation occurs more frequently during the decay EPEs per year Figure 1. Yearly means of electron precipitation event (EPEs) number, recorded in stratosphere at Murmansk region with patrol correction and sunspot number Rz.

Data on EPEs before 1965 are not complete. There is an 11-year cycle with maximum around solar minimum.

of a solar activity cycle. This result is in agreement with findings by Gonzales, et al. on the dual-peak solar cycle distribution of intense geomagnetic storms and low-latitude geo-effective coronal holes appearance [10]. These coronal holes are the main sources of corotating high-speed solar wind streams during the solar cycle descending phases. The yearly occurrence rate of EPEs correlates with yearly number of geomagnetic storms produced by corotating high-sped solar wind streams [11]. They are numerous during 1973-1974, 1983-1984, and 1993-1994. Also, we note that a maximum number of satellite anomalies, was recorded onboard Meteostat, Tele-X satellites during 1994 [12]. These satellite anomalies were produced by relativistic electron flux at geostathionary orbit.

During this year a numerous EPEs were recorded in the atmosphere.

We choose the observations at Olenya during the period from 1970 up to 1987. During this time the ballooning was rather often (practically everyday and often two or more flights per day) and 240 electron precipitation events were recorded. We evaluated a distribution of EPEs over a year as the monthly occurrence rates of EPEs relative to the total number of EPEs recorded in the atmosphere (240). This distribution is shown in Figure 2. There are two peaks in the EPEs occurrence rate: the first is very distinct in April and the second one is rather extended covering August-October period.

EPE OCCURRENCE RATE (%)

J F M A M J J A S O N D

Figure 2. The monthly occurrence rate (in % per month) of the Electron Precipitation Events observed in the atmosphere at Olenya during 1970-1987. (Total number of EPEs is The existence of semiannual variation in the various manifestations of geomagnetic activity and geomagnetic indices is well-known during more than 150 years. To explain this variation, the various physical effects, including the Russel-McPherron, equinoctial, axial effects were proposed in the past [e.g., 13The changes of solar wind parameters, interplanetary magnetic field (IMF), inclination of the Earth's magnetic dipole relative to IMF are the main factors of the seasonal variation origin. In Table the dates of maximum of geomagnetic activity related to the above effects are listed.

Table. Dates corresponding to maximum of geomagnetic activity in relation to the known effects and the maximum EPE occurrence during a year.

Also, the periods of maximum occurrence rate of EPEs in the atmosphere are presented. We note, that the first maximum of EPE occurrence (see Figure 2) is in accordance with the period of maximum geomagnetic activity expected from the Russel-McPherron effect. The second peak of EPEs occurrence is extended and, probably, due to superposition of the listed above effects.

Geomagnetic disturbances and EPEs observations in the atmosphere We analyzed the available geomagnetic databases on Sudden Storm Commencements (SSC), daily fluences of relativistic electrons observed by GOES satellite at geostationary orbit, equatorial Dst- index and auroral electrojet AE index [16]. We found that only ~ 13 % of EPEs occurred on a day when the SSC was recorded. Then we applied superposed epoch analysis to the SSC and EPEs databases. A day of EPEs registration at Olenya was chosen as a zero - day and the daily SSC occurrence rate for 10 days before and 10 days after the zero day were examined. The result obtained is presented in Figure 3.



It is clearly seen that the EPEs occurrences are most probable ~2 days after the geomagnetic Sudden Storm Commencements (panel A). Figure 3 (panel B) shows that EPEs mainly happen at a level of electron fluxes at geostationary orbit of > 2108 cm-2 sr -1day-1.

The results related to Dst and AE indices show that electron precipitation events often occurred during the main phase of geomagnetic disturbances when the -Dst and AE indices were increased (panel C and D). It is in accordance with the model suggesting the strong electron acceleration in the magnetosphere onetwo days after the SSC [17, 18]. At this time there is a main process of electron acceleration of low energy electron population (previously injected during the substorm) up to high energy (several MeV).

Figure 3. From top to bottom: the results of superimposed epochs analysis of the Sudden Storm Commencements (SSC) daily occurrence rate, daily electron fluences (E> MeV) recorded at geostationary orbit onboard GOES, daily Dst- and AE indices.

The 0-day corresponds to the day of electron precipitation event as observed at Olenya. The rms of the data are shown by vertical bars.

- The energetic electron precipitation events in the atmosphere at northern polar latitude (Olenya station) occurred 1-2 days after the SSC. During this time increased relativistic electron flux was observed onboard GOES at geostationary orbit.

- There is a quasi-11-year cycle in precipitation event occurrence rate shifted with respect to solar activity cycle. The electron precipitation events occur more frequently at descending phase of a solar cycle. Our result is in agreement with findings by Gonzales, et al. (1996) on the dual-peak solar cycle distribution of intense geomagnetic storms.

- The EPE occurrence demonstrates a semiannual variation with two maxima.

The first is in April and the second one is rather extended covering AugustOctober period. We believe, that the first peak is in accordance with the expectation of Russel-McPherron effect. A second peak is complex and, probably, due to the superposition of axial, equinoctial and Russel-McPherron effects.

This work is partly supported by Russian Foundation for Basic Research grants no. 02-02-16262, 01-02-16131, 03-02-31002, and grant INTAS 2000References 1. Charakhchyan A. N. 1967, Uspekhi Fizicheskix Nauk, 287, 2. Stozhkov, Y. I., 1985, Doctor Tezis, Lebedev Physical Institute, 244 p.

3. Bazilevskaya G. A., Krainev M. B., Stozhkov Yu. I., et al., 1991, J. Geomag. and Geoelectr. 43. Suppl., 4. Makhmutov V. S., Bazilevskaya G. A., Podgorny A. I., et al., 1995, Proc. 24th ICRC. Italy, Rome 4, 1114.

5. Bazilevskaya G. A., Makhmutov V. S., 1999, Izvestiya RAN, ser. fiz., 63, 1670 (in russian) 6. Makhmutov V. S., Bazilevskaya G. A., Krainev M. B., et al., 2001, Izvestiya RAN, ser. fiz., 65, 403 (in russian) 7. Makhmutov V. S., Bazilevskaya G. A., Krainev M. B., et al., 2001, Proc. 27th ICRC, Hamburg, 8. Makhmutov V. S., Bazilevskaya G. A., Krainev M. B., 2003, Adv. Space Res., 2003, v.31, no.4, 9. Bazilevskaya G. A., Makhmutov V. S., Svirzhevskaya A. K., et al., 2002, Proc.

XXV Annual Seminar. Apatity, 10. Gonzales, W.D., Tsurutani, B.T., McIntosh, P.S., et al., Geophys. Res. Lett., 1996, 23, no.19, 11. Richardson et al., Geophys. Res. Lett., 2001, v.28, no.13, 12. Wu et al., Adv. Space Res., 2000, v.26, no.1, 13. Kamide Y., Baumjohann W., Daglis I. A., et al.,1998, J. Geophys. Res. 103, 17, 14. Cliver E.W., Kamide Y., Ling A.G., 2000, J. Geophys, Res. 105, 15. Orlando M., Moreno G., Parisi M., Storini M., 1993, Geophys. Res. Lett. 20, 16. http://nssdc.gsfc.nasa.gov/omniweb/ow.html 17. Hruska A. and Hruska J., 1989, J. Geophys, Res. 94, 18. Blake D.N., Pulkinen T.I., Li X. et al., 1998, J. Geophys. Res. 103, 17, , , , 7-11

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INDUCTIVE DYNAMIC MODELS OF LONG-TERM

SOLAR ACTIVITY VARIATIONS

Central astronomical observatory of RAS, Saint-Petersburg, Russia, solar1@gao.spb.ru

Abstract

The inductive self-organizing methods have been used for building dynamic autoregressive models of long-term solar activity variations. Two sets of Wolf numbers (cycles (-5 - 22) and (-59 22)) have been processed. Linear and nonlinear models connecting maximal amplitudes and time durations of successive 11-year cycles were synthesized. Models which use parameters of odd and even cycles separately are more adequate for first set. As to second set the nonlinearity of models turns out more valuable. The most accuracy of models has been achieved when the solar cycle duration as parameter is included.





On the base of these models some forecast values have been calculated. All of them show tendency of solar activity decreasing in some next cycles. The lowest cycles in century probably will be in 30-40-th, with Wolf numbers being approximately equal those of Dalton minimum in 19-th century. But in second part of 21century the solar activity apparently will be increase.

This work was supported by INTAS (grant 01-0550) and RFBR (grant 01-07-90289 ) , 11- , . , 11- 11- .

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