Great fep events and space weather radiation hazard levels, alert for event start, probabilities of false and missed alerts

L.I. Dorman ^1,2, L.A. Pustil’nik ¹, A. Sternlieb ¹, and I.G. Zukerman ¹

NOAA Space Weather Scale establishes 5 gradations of FEP events, what are called Solar Radiation Storms: from S5 (the highest level of radiation, corresponded to the flux of solar protons with energy >10 MeV about ) up to S1 (the lowest level, the flux about for protons with energy >10 MeV). From our opinion, by ground level CR neutron monitors and muon telescopes it is possible monitoring and forecast (by using much higher energy particles than smaller energy particles caused the main radiation hazard) FEP events of levels S5, S4 and S3. With increasing of FEP event level of radiation will increase the accuracy of forecasting. According to Dorman (2002a,b), in the first, for satellite damage and influence on people health and technology, on communications by HF radio-waves more important is the total fluency of FEP during the event than the protons flux what is used now in NOAA Space Weather Scale; in the second, the level S5 (corresponds to the flux , or fluency for protons with ) is not maximal, but can be much higher and with much smaller probability than S5 (Dorman and Venkatesan, 1993; Dorman and Pustil’nik, 1995, 1999). As it was shown recently by McCracken et al. (2001), the dependence of event probability from fluency can be prolonged at least up to for protons with , what was observed in FEP of September 1869 according to data of nitrate contents in polar ice (see Fig. 1).

Fig. 1. The dependence of FEP events probability (number of events per year) from the value of fluence according to direct satellite and NM data, nitrate in polar ice data and cosmogenic nuclide data on the moon (McCracken et al., 2001).

This type of great dangerous events is very rarely (about one in few hundred years). According to Fig 1 it is not excluded that in principle can occurred very great FEP events with fluency in 10 and even in 100 times bigger (correspondingly one in few thousand and one in several ten thousand years). So, we suppose to correct the very important classification, developed by NOAA, in two directions: to use fluency F of FEP during all event (in units ) instead of flux I, and to extend levels of radiation hazard. As result, the modernized classification of FEP events is shown in Table 1.

Table 1. Extended NOAA Space Weather Scale for Solar Radiation Storms

FEP events radiation hazard			Fluence 30MeV protons	Frequ-ency
S7	Ultra extreme	Biological: Lethal doze for astronauts, for passengers and crew on commercial jets; great influence on people health and gene mutations on the ground Satellite operations: very big damages of satellites electronics and computers memory, damage to solar panels, loosing of many satellites Other systems: complete blackout of HF (high frequency) communications through polar and middle-latitude regions, big position errors make navigation operations extremely difficult.	1011	One in few thousand years
S6	Very extreme	Biological: About lethal doze for astronauts, serious influence on passengers and crew health on commercial jets; possible influence on people health and genes mutations on the ground Satellite operations: a big damages of satellites electronics and computers memory, damage to solar panels, loosing of several satellites Other systems: complete blackout of HF communications through polar regions, some position errors make navigation operations very difficult.	1010	One in few hundred years
S5	Extreme	Biological: unavoidable high radiation hazard to astronauts on EVA (extra-vehicular activity); high radiation exposure to passengers and crew in commercial jets at high latitudes (approximately 100 chest X-rays) is possible. Satellite operations: satellites may be rendered useless, memory impacts can cause loss of control, may cause serious noise in image data, star-trackers may be unable to locate sources; permanent damage to solar panels possible. Other systems: complete blackout of HF (high frequency) communications possible through the polar regions, and position errors make navigation operations extremely difficult.	109	One in 20-50 years
S4	Severe	Biological: unavoidable radiation hazard to astronauts on EVA; elevated radiation exposure to passengers and crew in commercial jets at high latitudes (approximately 10 chest X-rays) is possible. Satellite operations: may experience memory device problems and noise on imaging systems; star-tracker problems may cause orientation problems, and solar panel efficiency can be degraded. Other systems: blackout of HF radio communications through the polar regions and increased navigation errors over several days are likely.	108	One in 3-4 years
S3	Strong	Biological: radiation hazard avoidance recommended for astronauts on EVA; passengers and crew in commercial jets at high latitudes may receive low-level radiation exposure (approximately 1 chest X-ray). Satellite operations: single-event upsets, noise in imaging systems, and slight reduction of efficiency in solar panel are likely. Other systems: degraded HF radio propagation through the polar regions and navigation position errors likely.	107	One per year

Let us note, that the expected frequency of FEP events in the last column of Table 1 is averaged over solar cycle. Really, this frequency is much higher in periods of high solar activity than in periods of low solar activity (Dorman et al., 1993; Dorman and Pustil’nik, 1995, 1999).

SHORT DESCRIPTION OF THE METHOD OF AUTOMATICALLY SEARCH OF THE START OF GROUND FEP EVENTS
Let us consider the problem of automatically searching for the start of ground FEP events. Of course, the patrol of the Sun and forecast of great solar flares are very important, but not enough: only very small part of great solar flares produce dangerous FEP events. In principal this exact forecast can be made by using high-energy particles (few GeV/nucleon and higher) whose transportation from the Sun is characterized by much bigger diffusion coefficient than for small and middle energy particles. Therefore high-energy particles arrive from the Sun much earlier (8-20 minutes after acceleration and escaping into solar wind) than the lower energy particles that cause a main dangerous situation in space and in atmosphere (see Table 1). The flux of high-energy particles is very small and cannot be dangerous for people and electronics. The problem is that this very small flux is very difficult to measure with enough accuracy on satellites to use for forecast (it needs very large effective surfaces of detectors and very large weight). From other side, high-energy particles of galactic or solar origin are measured continuously by ground-based neutron monitors, ionization chambers and muon telescopes with very large effective surface areas (many square meters) that provide very small statistical errors. It was shown on the basis of data in periods of great historical FEP events (as the greatest of February 23, 1956 and many tens of others), that one-minute on-line data of high energy particles could be used for forecasting of incoming dangerous fluxes of particles with much smaller energy. The method of coupling (response) functions (Dorman, 1957; Dorman et al., 2000; Clem and Dorman, 2000) allows us to calculate the expected flux above the atmosphere, and out of the Earth's magnetosphere from ground based data. Let us describe the principles and on-line operation of programs "FEP-Search-1 min", "FEP-Search-2 min", and so on, developed and checked in the Emilio Segre' Observatory of ICRC. The determination of increasing flux is made by comparison with intensity averaged from 120 to 61 minutes before the present Z-th one-minute data. For each Z minute data, starts the program "FEP-Search-1 min". The program for each Z-th minute determines the values
, (1)
, (2)
where and are one-minute total intensities in the sections of neutron super- monitor A and B.

If simultaneously

2.5, 2.5, (3)
the program "FEP-Search-1 min" repeat the calculation for the next Z+1-th minute and if Eq. 3 is satisfied again, the onset of great FEP is determined and programs "FEP-Collect" and "FEP-Research" described in the next section, are started.

If Eq. 3 is not satisfied, the program "FEP-Search-2 min" searches for the start of an increase by using two-min data characterized by . In this case, the program "FEP-Search-2 min" will calculate values

, (4)
, (5)
If the result is negative (no simultaneous increase in both channels of total intensity ≥ 2.5, i.e. the condition ≥ 2.5, ≥ 2.5 fails), then "FEP-Search-3 min" uses the average of three minutes Z-2, Z-1 and Z with . If this program also gives a negative result, then the program "FEP-Search-5 min" uses the average of five minutes Z-4, Z-3, Z-2, Z-1 and Z with . If this program also gives negative result, i.e. all programs "FEP-Search-K min"(where K=1,2,3,5) give negative result for the Z-th minute, it means that in the next 30-60 minutes there will be no radiation hazard (this information can be also very useful). After obtaining this negative result, the procedure repeats for the next, Z+1-th minute, and so on. If any positive result is obtained for some Z-minute, the "FEP-Search" programs checked the next Z+1- minute data. If the obtained result is again positive, then the program "FEP-Spectrum" determined the FEP spectrum (see Paper 2, Dorman et al., 2003a).

Let us note that the similar program will be work in the case of three sections A, B and C: instead of Eq. 3 the necessary condition for determining of great FEP starting will be

, , (6)
THE PROBABILITY OF FALSE ALARMS
The Case of Two Independent Channels

Because the probability function , that the probability of an accidental increase with amplitude more than 2.5 in one channel will be

= , (7)
that means one in 161.3 minutes (in one day we expect 8.93 accidental increases in one channel). The probability of accidental increases simultaneously in both channels will be

= (8)
that means one in 26007 minutes  18 days. The probability that the increases of 2.5 will be accidental in both channels in two successive minutes is equal to
= (9)
that means one in 6.76minutes 1286 years. If this false alarm (one in about 1300 years) is sent, it is not dangerous, because the first alarm is preliminary and can be cancelled if in the third successive minute is no increase in both channels bigger than 2.5 (it is not excluded that in the third minute there will be also an accidental increase, but the probability of this false alarm is negligible:
(10)
that means one in years. Let us note that the false alarm can be sent also in the case of solar neutron event (which really is not dangerous for electronics in spacecrafts or for astronauts health), but this event usually is very short (only few minutes) and this alarm will be automatically canceled in the successive minute after the end of solar neutron event.
The Case of Three Independent Channels

In this case the probability of accidental increases simultaneously in three channels will be

= (11)
that means one in about 8 years. The probability that the increases of 2.5 will be accidental in three channels in two successive minutes is equal to
= (12)
that means one in years. Therefore in the case of three independent channels we don’t need to wait of the result fore the third minute. For the not dangerous very short (only few minutes) solar neutron event, the alarm will be automatically canceled in the successive minute after the end of solar neutron event (the same situation as in the case of two independent channels).
THE PROBABILITY OF MISSED TRIGGERS
The Case of Two Independent Channels

The probability of missed triggers depends very strong from the amplitude of increase. Let us suppose for example that we have a real increase with amplitude A = k. The trigger will be missed if in any of both channels and in any of both successive minutes the increase of intensity will be less than 2.5 (as a result of negative statistical fluctuations). For realization of this case, the statistical fluctuation in one of channels must be negative with amplitude more than (k-2.5). The probability of this negative fluctuation in one channel in one minute is equal

= , (13)
and the probability of missed trigger for two successive minutes of observation simultaneously in two channels is 4 times larger:

= . (14)
For example, if k = 7 (that for ESO corresponds to an increase of about 9.8 %), the probability of missed trigger will be

= . (15)
It means that missed trigger is expected only one per about 70000 events. In Table 2 are listed probabilities of missed triggers as a function of the amplitude of increase A (in ).
Table 2. Probabilities and of missed triggers as a function of amplitude of increase A (in )

Channels	A, 	4.5	5.0	5.5	6.0	6.5	7.0	7.5
Two
Three		0.136

The Case of Three Independent Channels

In this case instead of Eq. 14 will be (see the last row in the Table 2):

= . (16)

DISCUSSION AND CONCLUSION

1. We assumed extended NOAA Space Weather Scale for Solar Radiation Storms (see Table 1).

2. Considered method of automatically searching for the onset of great, dangerous FEP on the basis of one-minute NM data practically does not give false alarms (even for two channels the false preliminary alarm is expected only one in about 1300 years, and for false final alarm one in years).

3. None dangerous solar neutron events also can be separated automatically.

4. We estimated the probability of missed triggers; it was shown that for events with amplitude of increase the probability of a missed trigger for two and three independent channels is smaller than and , correspondingly (this probability decreases sufficiently with increasing of amplitude A, see Table 2).

5. Historical ground FEP events show very fast increase of amplitude at the start of event (for example, in great FEP event of February 23, 1956 amplitudes of increase in the Chicago NM were at 3.51 UT – 1%, at 3.52 UT – 35%, at 3.53 UT – 180%; in this case, the missed trigger can be only for the first minute at 3.51 UT).

6. The described method can be used in many Cosmic Ray Observatories where one-minute data are detected.
ACKNOWLEDGEMENTS
Our great thanks to Prof. Yuval Ne’eman for constant interest and support of the work of Israel Cosmic Ray Center and Emilio Segre’ Observatory, and J. Allen, A.V. Belov, E.A. Eroshenko, N. Iucci, K.G. McCracken, M. Murat, M. Parisi, M.A. Shea, D.F. Smart, M. Storini, G. Villoresi, and V.G. Yanke for useful discussions.

The work of NM on Mt. Hermon is supported by Tel Aviv University, UNIRoma-Tre, and IFSI-CNR Collaboration. This research is partly supported by EU INTAS Grant 00810.

REFERENCES

Carmichael, H., Space Sci. Rev., 1, 28, 1962.

Clem J.M. and L.I. Dorman “Neutron monitor response functions”, Space Science Rev., 93, 335-360, 2000.

Dorman L.I., Cosmic Ray Variations. Gostekhteorizdat, Moscow, 1957.

Dorman I.V., L.I. Dorman, and D. Venkatesan, Proc. 23-th ICRC, Calgary, 4, 79-82, 1993.

Dorman L.I. and L.I. Miroshnichenko, Solar Cosmic Rays. FIZMATGIZ, Moscow, 1968.

Dorman L.I. and L.A. Pustil'nik, Proc. 24-th ICRC, Rome, 4, 86-89, 1995.

Dorman L.I. and L.A. Pustil’nik, Proc. 26-th ICRC, Salt Lake City, 6, 407-410, 1999.

Dorman L.I. and D. Venkatesan “Solar cosmic rays”, Space Sci. Rev., 64, 183-362, 1993.

Dorman, L.I., G. Villoresi, N. Iucci, M. Parisi, and N.G. Ptitsyna, J. Geophys. Res., 105, 21047, 2000.

Duggal, S.P., Rev. Geophys. Space Phys., 17, 1021, 1979.

McCracken K.G., D.F. Smart, M.A. Shea, and G.A.M. Dreschhoff, Proc. 27-th ICRC, Hamburg, 8, 3209, 2001.

Stoker P.H. “Relativistic solar cosmic rays”, Space Sci. Rev., 73, 327, 1995.
E-mail address of Lev I. Dorman: lid@physics.technion.ac.il, lid1@ccsg.tau.ac.il

Manuscript received ; revised ; accepted

Directory: institutes -> advanced -> cosmic
cosmic -> Pundak D. 1, Pustil’nik L. 1,2

Download 66.05 Kb.

Share with your friends: