Some purposes and methods of the satellite measurements of the ignorospheric response on the solar flares

Phys. Chem. Earth (C), Vol. 26, No. 4, pp. 259-263,200l

Pergamon

0 2001Elsevier Science Ltd. All rights reserved 1464-1917/00/$ - see front matter

PII: S1464-1917(00)00118-5

Some Purposes and Methods of the Satellite Measurements of the Ignorospheric Response on the Solar Flares S. V. Avakyan

Aerospace Physical Optics Laboratory of S. I. Vavilov State Optical Institute, Tuchkov Lane 1, St. Petersburg, 199034, Russia Received 24 April 1998; revised II November 1998; accepted 4 January I999

Abstract. The paper describes methods for measuring of the response of the ignorosphere to solar flares including small tethered systems. The small tethered satellites are very suitable for the following experiments: 1. Measurements of the high ionospheric photoelectron and Auger electron spectra because there is no large shadow effect from the satellite body at large pitch-angles and also parasitic photoelectron fluxes from the satellite body are small. 2. Measurements of the increase in emissions of the upper atmosphere and the investigation of the relationship between satellite glow and its altitude and dimensions. 3. Measurements of the increase in the electron and ion densities including optical and mass-spectrometric recording of the double charged positive ions which are formed due to Auger effect at the altitudes of ignorosphere. Q 2001 Elsevier Science Ltd. Ail rights reserved

1 Introduction

The most intensive response to solar flares takes place at altitudes a little higher than 100 km, namely - in the ignorosphere. This is connected with the fact that the relative magnification of solar fluxes has a maximum in the shortwavelength spectral range below 2-3 nm, and with the main role of X-ray radiation in the formation of ionospheric photoelectron and Auger electron spectra, which is the principal factor of additional ionization and UV-excitation (Avakyan et al., 1998a). However, in the existing reference models of ionizing solar radiations, the spectral range shorter than 5 nm is commonly not presented (Richards et al., 1994, Hinteregger et al., 1981). The best model is the reference model (Schmidtke, 1984) based on data of satellite AE-E, but even this model does not provide values of ionizing solar flux for wavelengths shorter than 1.8 nm.

Correspondence

to: S. Y. Avakyan

2 On the experimental basis for the problem of modeling of the upper atmospheric response to the solar flares

At present there is no monitoring in the spectral range from 0.8 nm to 120 nm which is of the most important influence on the upper and middle atmosphere including ignorosphere. There are only single measurements by means rockets and satellites. The monitoring in long-wavelength spectral range (above 120 nm) already exists, but in longterm monitoring of the solar X-ray radiation on the series of satellites SOLRAD, SMS and, most recent, GOES, only the spectral range shorter than 0.8 nm is presented. For the region of 0.8-100 nm the measurements of the absolute solar fluxes were carried out only one third of the time during all the cosmic era (Schmidtke, 1992). The main reason for the absence of the permanent solar radiation patrol is exclusively connected with technical and methodological difficulties of space measurements in this spectral range (Avakyan, Yefremov, 1995, Avakyan, 1998a). The second gap lies in our knowledge about the response of the ionospheric and upper atmospheric UVemission parameters to the solar flares of different classes. The main growth of the solar ionizing flux during flares takes place in the soft X-ray region, where the main part of quantum energy is transferred to photoelectrons and the Auger electrons during photoionization. To verify the calculation models, it is necessary to be able to compare calculation results with experimental photoelectron spectra measured at ionospheric altitudes. However, these measurements have not been carried out, and at present we have published the data pertaining only to high altitudes, which were obtained by spacecraft ISIS (Wrenn, 1974) for an altitude of about 3000 km (including the period of solar flares, for electron energy as high as 400 eV). These data confirm considerable decrease (by several times even for the quiet Sun) in the intensities of photoelectron fluxes in all models which do not take into account the Auger electrons (Avakyan et al., 1994). At present there are still no meas-

S. V Avakyan: Satellite Measurements

260

of the lgnorospheric

urements of photoelectron spectra during solar flares at any altitudes of the ignorosphere. But at these ignorospheric altitudes below 200 km the largest increase in the photoelectron spectrum intensity takes place especially as regards the Auger electron intensity. However, the principal gap in the experimental determination of the ionospheric and upper atmospheric response to the solar flares is the absence of the quantitative measurements of this additional effect. Indeed, in the ground radio-sounding of the ionosphere during solar flares, usually there were the conditions of full radiowave absorption and, therefore, the experimental data on the flare ionization growth for different ionospheric regions are scarce. The emissions of the dayglow in the upper atmosphere in the W-spectral range (for example, within 135-160 nm, that is, within the Lyman-Birge-Hoptield system of the N, bands) are determined only by the direct process of electron excitation there by showing the direct response to the growth of solar ionizing flux during flare. These measurements are very scarce (Opal, 1973). At the same time, only a combined experiment, providing simultaneous measurements of the solar ionizing flux, UV-dayglow emissions, and of the ionospheric photoelectron spectrum, allows verification of the calculating and predicting models (Avakyan, Kudrjashev, 1996).

3 On the possibilities investigation

of small tethered of the ignorosphere

satellites

in the

The most considerable response to solar flares in the nearEarth space is the growth of ionization and W-excitation rates in the upper atmosphere. During the thermal phase of

Response on the Solar Flares

the flare, the main increase in these parameters arises from X-ray solar radiation. In (Avakyan, Kudrjashev. 1984a, 1984b), we have shown for the first time that modeling of the upper atmosphere and ionosphere response to the solar flares would be correct only if both photoelectrons and Auger electrons are taken into account. In Figures 1 a, b the steps near 370 and 510 eV are connected with the contribution of Auger electrons emitted from nitrogen and oxygen without (a) and during (b) solar flares. Verification of this conclusion needs measurements of the photoelectron spectra by small tethered satellites at ignotospheric altitudes. For some reason these small satellites are better than large ones. The question is that in the teal space experiments the electron energy analyzer is usually placed directly on the surface of the satellite body. In this case there are two effects which make the measurements of ionospheric photoelectron fluxes by large satellites difficult, if at all possible. First the satellite body may present an obstacle preventing ionospheric photoelectrons of some values of pitch-angles from entering the analyzer. Secondly the parasitic photoelectrons emitted from the satellite body can be detected as well. The maximum contribution of the photoelectrons emitted from the satellite body is determined in paper (Avakyan, 1979). It is shown that this contribution is especially great for photoelectrons of high energy (2100 eV). It is also shown that these parasitic photoelectrons would be detected by the satellite analyzer only when the satellite size exceeds 2 Larmor radii. Therefore, in case of high energy electrons at small altitudes of the ignorosphere the dimension of the satellite body must be more than 1.5 m. Then for an energy analyzer with ordinary parameters, i. e. resolution (AE/E) of about 20% and the exit angle Clof k3.5”, the maximum signal from the parasitic photoelectrons can be one order of magnitude greater than

photoelectron flux, el~cm-2.s-‘.sr-‘.eV-’

Fig. la. The photoelectron spectra with the contribution zenith angle of Sun equal to 90” during quiet Sun

of Auger processes (solid curve) and without that (dashed curve) at the altitude equal 160 km, at

261

S. V Avakyan: Satellite Measurementsof the IgnorosphericResponseon the Solar Flares

photoelectron flux, el.cm-*.s-‘.sr-‘.eV-’

loo 10

30

50

70

90

200

300

400

500

Ee,eV

Fig. lb. The photoelectronspectra with the contribution of Auger processes(solid curve) and without that (dashed curve) at the altitude equal 125 km, at zenith angle of Sun equal to 63” during the solar flare 2B X1 2.5 February 1969

the signal from the ionospheric photoelectrons. The collection area of photoelectrons (S)‘with the energy E,, at the satellite surface is a part of a ring with radii: p=5.9.10’ c m, (E,fAE/2)“‘sina/eH,

(1)

where m, and e are the mass and charge of the electron, respectively, a is the photoelectron pitch-angle which is varying in the limits 90”-fY
AE=20 eV, the area of entrance window (s) is 1 cm-‘) when measuring the ionospheric photoelectrons then the intensity of the ionospheric photoelectrons would be equal to F=N/s.R.AE=5.2- IO5 electronscm-2&-‘sr-‘-eV-‘. For E,=lOO eV this value exceeds essentially the values measured at satellites, which are about 5.104 electroncm-*s-‘sr-‘.eV-’ and also exceed the theoretical value of ionospheric photoelectrons intensity. To eliminate the influence of photoelectrons emitted from the satellite surface one has either to use a satellite of small size or to place the analyzer on the special holder as far from the satellite surface as 2 Larmor radii (or even further). The small tethered satellites are also very suitable for measurements of variations in UV-airglow emissions during solar flares because maximum excitation rates for optical emissions (for instance, system of bands Lyman-BirgeHopfield) are observed just in the ignorosphere. The reason is that, first, the tethered satellites allow the emission to be observed along optical layers (at the tangential direction). secondly, there is no influence of the absorption of LBHemission by Schumann-Runge continuum of O2 at heights of 140-160 km while at the observations from the regular satellites in nadir are substantially influenced. Finally, by means of variation of the tethered satellite altitude it becomes possible to study the height profiles of the excitation rate of the upper level a$ of the LBH system of bands including the largest increase in its intensity due to X-ray radiation of solar flares.

S. V Avakyan: Satellite Measurements of the Ignorospheric Response on the Solar Flares

262 H, km ,

400

2oc

I

I

III

I

I

II

I IO3

IO? rate of production, ions/cm’s

Fig. 2. The rates of direct photoionization photoelectron curve)

(I)

and additional ionization by

and Auger electron (2) during solar nare 28

and for quiet

Sun (dashed

curve)

at the zenith

angle

XI

(solid

of Sun equal

to 70”

By changing the tethered satellite altitude the contribution of the satellite glow can be determined. According to the data obtained at the satellite S 3-4 (Conway et af., 1987) this contribution at the LBH system bands depends on the altitude as [NZ]’ or [N?]‘.[O] do. For other spectral ranges of the satellite glow ‘the dependence on the altitude is much weaker and it approximately repeats the dependence of the atmospheric density. However the intensity of the satellite glow depends strongly on the satellite size in the direction of the flight and therefore for small tethered satellites it may be low. . At the altitudes of 100 km and a little higher there is a maximum of the ionization rate during solar flares, Fig. 2. In this case the greatest contribution results from the addi-

H, km 300

I

200

4 Conclusion

100

rate of production. ions/cm’.s

Fig. 3. The production rates for ionospheric ions NZfC, 02++ and O+’ due to Auger processes at the solar photoionization (zenith angle of Sun equal 0”) during

ionization by photoelectrons and Auger electrons (Avakyan, Kudrjashev, 1984a, b). However, so far the contribution of the X-ray spectral region shorter than 3. I nm was underestimated. The point is that in this region each absorption of an X-ray quantum is followed by the Auger effect which produces a positive doubly charged ion and two electrons: a photoelectron and Auger electron. Thus two ion-electron pairs are generated in the ionosphere by the absorption of one X-ray quantum with the wavelength shorter than 3.1 nm. Therefore, the contribution of the direct photoionization in the E-region during the flares of 2B ball increases by 25-35%. These results on the rates of the additional ion formation were obtained by an accurate calculation of the entire photoelectron spectrum for energies lower than 600 eV (Avakyan, Kudrjashev, 1984a, b). At ignorospheric altitudes the maxima of the double charged producing rate due to Auger effect are located, Fig. 3. The ionospheric ions Nr++and 02++were not detected by the mass spectrometric experiments because their peaks coincide with mass spectrometric peaks of the ordinary atomic ions N’ and 0’. It was shown in (Prasad, Furman, 1975) that the presence of O2++ions could explain the large density of the aurora1 0’ ions obtained in the in situ measurements at heights of 116-120 km. In (Avakyan, 1978) it was shown that taking into account the Auger effect contribution to the formation of the OZf+ions the density of these ions exceeded that of 0’ ionospheric ions at the heights from 100 to 130 km. It is very important to note that the main part of double charged atomic and molecular ions produced by Auger effect turn up in excited states that lie higher than the ground state by several eV. This phenomenon is displayed in the spectra of Auger electron (Moddeman ef al., 1971). The production rate of excited ions NZ++and O?++obtained in (Avakyan, 1978) by using typical night spectrum of aurora1 precipitating electrons and the model of spectral degradation with altitude, correspond to aurora IBC 11, that was given in (Banks et al., 1974). These data enable to estimate that the emission rate of the ions NZ+’ in aurora IBC II in vertical direction is equal to 70 R (Avakyan, 1978). Lately some of these emissions (see for example (Mathur, 1993, Avakyan, 1998b)) have been observed in laboratory experiments. There are emission from OZfC ions (the blue bands 417,443, and 470 nm), NO” ion (3 17,496, and 885 nm), and perhaps the bands of N2f+ (I59 nm, near: 515, 6 15, 650, and 760 nm). These airglow emissions can be observed along optical layers (at the tangential direction) from tethered satellites at the altitudes near 120 km.

tional

solar tlare

The most intensive response to the solar flares takes place at altitudes near 100 km. The response consists in the increase of the degree of ionization and in the intensification of the photoelectron spectrum and of the optical emission

S. V Avakyan: Satellite Measurements of the Ignorospherlc Response on the Solar Flares

of the upper atmosphere. However the complex measurements of the response to the solar flare still have not been carried out because in situ measurements at given altitudes are very difficult. Very suitable for these experiments could be the small tethered satellites: for investigations of ionospheric photoelectrons of high energy and UV-airglow, for massspectrometric detection of 0”, N” and NO” ions and detection of optical emissions N,* and 02++ionospheric ions.

References Avakyan, S.V., Doubly charged molecular ions in the aurora1 ionosphere, Geomagn. Aeronomy, 18.4,652-656, 1978. Avakyan, S.V., About the method of the investigation of ionospheric photoelectrons from satellites, Researches on geomagnerism. aeronomy and solar physics (Issledovanya pa geomagneti:m. aeronomy i phisike Solntza). 17, 153-156, 1979. Avakyan, S.V., Outlook for the creation of permanent solar EUV and soft X-ray radiation patrol, Adv. Space Res.. 21. l/2, 325-328. 1998a. Avakyan. S.V., Auger effect in the optics of the upper atmosphere, J. oj Optical Technology, 65. 1 I. 4-l 0, 1998b. Avakyan, S.V. and Kudrjashev, C.S., The excitation and ionization at the upper atmosphere during solar flares with consideration of the photoelectrons. Geomogn. Aeronomy. 24, 4,693-695, 1984a. Avakyan, S.V. and Kudrjashev, C.S., The spectrum of photoelectrons in the upper atmosphere of Earth during the solar Bares, Cosmic Research, 22, 6,889-894, 1984b. Avakyan, S.V. and Kudrjashev, G.S., About the predicting and modeling of the solar flare upper atmospheric and ionospheric response. 3/sr Scientific Assembly of COSPAR. Abstracts, Univ. of Birmingham. p, 241. 1996. Avakyan, S.V. and Vefrcmov. A.I., Strategy for the patrol of the solar soft x-ray and extrcmc ultraviolet flux. in ,Y-ray and extreme uhrovioler optics. cds. R. B. Hoover. A. B. C. Walker, Proc. SPIE. 2515, 301309. 1995.

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Avakyan, S.V., Vdovin, A.I., and Pustarnakov, V.F., Near-Earth space ionization and penetration radiations. Handbook, St. Petersburg, Gidrometeoizdat, 501 p., 1994. Avakyan, S.V., Bin, R.N., Lavrov, V.M., and Ogurtsov, G.S., Co/iision processes and excitation of ultraviolet emission from planetaty atmospheric gases: A Hondbook of cross sections, ed. S. V. Avakyan, Gordon and Breach Publishing Group, London, 356 p., 1998. Banks, P.M., Chappell, C.R., and Nagy, A.F., A new model for the interaction of aurora1 electrons with the atmosphere: spectral degradation, backscatter, optical emission and ionization, J. Geophys. Res.. 79, AIO, 1459-1470,1974. Conway, R.R., Meier, R.R., Strobel, D.F., and Huffman, R.E., The far ultraviolet vehicle glow of the S 3-4 satellite, Geophys. Res. Len., II. 6.628-63 I, 1987. Eastman, D.E., A survey of photoemission measurements using synchrotron radiation in the 5