Atmospheric response to electric field pulse

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Pergamon

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Adv. Space Res. Vol. 30, No. 11, pp. 2597-2600, 2002 © 2002 COSPAR. Published by Elsevier Science Ltd. All fights reserved Printed in Great Britain 0273-1177/02 $22.00 + 0.00 PII: S0273-1177(02)00226-0

A T M O S P H E R I C R E S P O N S E TO E L E C T R I C FIELD PULSE N.V. Smirnova, A.N.Lyakhov, S.I.Kozlov 1

l Instit-.ute of Geospheres Dynamics, 38/6 Leninskij pr-kt, Moscow, 117J3~, Russia ABSTRACT

The complete plasmochemical model was developed for the study of electric field perturbations impact on aeronomy of middle atmosphere and lower ionosphere. The model includes the following set of processes: dissociation, dissociative recombination and dissociative ionization, ionization, excitation, electron attachement and detachement, various ion-molecule reactions of positive and negative ions. It allows to calculate a lot of excited components and density variations of long-lived minor neutral components, which are especially important for the consideration of the sequence of perturbations. The simulation results on elves dynamics are presented. The comparison of calculated spectra and intensities with experiment is encouraging. The significant role of electron attachement processes at the heights of blue jet origin is shown. The scenario for the relationship between anomalous ground conductivity and blue jet (red sprite) is proposed. © 2002 COSPAR. Published by Elsevier Science Ltd. All rights reserved. INTRODUCTION Thunderstorm specific optical events referred to as blue jets, red sprites and elves are intensively studied during last decade. From our point of view these events do play the role of natural markers of' the electrical and chemical processes in the middle atmosphere, namely the transition of electric field in the atmosphere from the ground level of thunderstorm activity up to the ionosphere. Then if one has the correct model, then one can describe the whole set of plasmochemical processes in atmosphere and explain the plenty of experimental evidence on the aforementioned optical events. Otherwise, our understanding and, thus the models, of the middle atmosphere requires significant improvement. Initial efforts, to understand these optical events focused mainly with the processes in thunderstorms (Sentman et al., 1995a, 1995b, Sukhorukov and Stubbe, 1998: Rowland, 1998, Pasko et al., 1996, 1997, 1999, Taranenko et al., 1993). Therefore these models do not include a complex set of photochemical and ionization/recombination processes in lower atmosphere, though the last determines the overall response of the medium to any kind of perturbation. By our opinion the ca:[culations of optical emissions is to be preceded by the precise simulation of excited, charged and minor neutra]L components (which are important for the altitudes of blue jets and blue starters), under the pulse of electric field. The last allows to determine the relative role of various radiative components. Such a model is of great importance for the global simulation of thunderstorm activity, because any of the realistic thunderstorm scenario involves the modification of the medium by the sequence of lightning discharges. PLASMOCHEMICAL MODEL Our plasmoehemical model, includes the following 36 components : O(3p), O(1D), 0(1S), O2(A3E+), O2(1Ag), 03, H, OH, H20, H02, H2, H202, N(4S), NO, N20, NO2, O2(blE+), N(2D), N2(C3IIu), N2(B3Hg), N2(a'] E~), N2(A3E+), O +, N +, NO +, 0 +, 0 +. H20, NO +. N2, NO +. C02, H30 +, H30 +. OH, 02, C03, 0 - , NO 3 and electrons. The following processes are included: dissociation, dissociative recombination and dissociative ionization , ionization, excitation, electron attachment and detachement, various ion-molecule reactions of positive and negative ions and a lot of photochemical processes. It allows to calculate optical emissions in the wide range (from ultraviolet to infrared) namely: N2 (1P) system (575.5 n m - 1050.8 nm), N2(2P) system '328.5 am - 545.2 nm), N+(1N) system (391.4 nan- 522.8 nm), and 2597

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N.V. Smirnova et al.

the following emissions: 280.0-360.0 nm, 320.0 am, 337.1 nm, 346.6 nm, 373.0 nm, 520.0 nm, 557.7 nm, 630.0 nm, 761.9 nm and in IR range - 1.04 #m, 1.27 #m. The specific feature of the model is that it is self-consistent on initial conditions, so in the absence of perturbation all densities remain constant. The detailed discussion of the model and the constant rates of the processes can be found in (Borisov et al., 1993, Smirnova et al., 2000). The necessity of electron attachment including together with the self-consistent determination of critical electric field is of especially importance for the blue jets consideration (Smirnova et al., 2000). ELECTROMAGNETIC

PULSE AND ELVES The aforementioned model was applied for the simulation of the optical events at the altitudes of ~ 8 5 - 90 km, caused by electromagnetic pulse (EMP) of lightning. For the EMP description we have used the model of Uman (1985), that includes electrostatic, induction and electromagnetic pulse field components. If the current is considered as a vertical straight channel, then the electric field at a location (r, ~o,z) in a cylindrical coordinate system resulting from a small part dz at the height 2 will be (with reduction of a small typesetting error from (Uman, 1985))

dEr(r,~,z,t)

d2 [3r(_z_-2) ~0t = 47r¢0 L R5 j(2, 7 - R / c ) d T + + 3r(z

-

cR 4

2) . j ( 2 , t

r(z- 2) _~ c2 R ~

/~z(r, ~a,z, t) = d__~2, gz[2(z - 2) 2 - r 2 • L t j ( 2 , 7 47rc0 R5 2(z - 2) 2 - r 2 -~

cR 4

(1)

R/c)+

-

•

]

R/c)dT +

- -

r2 Oj • j ( 2 , t - R / c ) - c 2 R 3 . -~]

(2)

Here R is the distance from the point (0, 0, 2) to (r, ~, z). The fine structure of N2(1P), N2(2P) systems for the elves at 90 km is presented on Figure 1. 30 N2(1P

~

25

"% 20 ;0

600

700

800 X, nm

900"

1000

1100

m =15

" "50.5

nm

~.<--470.9nm

0.05. 10

0.03

//I/ 300

350

400

k, nm

450

500

550

Fig.1 Elves spectra at 90 km in N2 (1P) (top), N2 (2P) (bottom) systems

00

0.5

Time sec

1.5

L___ x 10~

Fig.2 Elves spectra at 90 km during the sequence of

perturbations

These emissions were calculated with fluorescence efficiencies from (Davidson and O'Neil, 1964), for the case of the positive cloud-to-ground discharge I = 270 kA, pulse duration 300 #s, distance from discharge

AtmosphericResponseto ElectricFieldPulse

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L =43 km. The spectra presented are in good agreement with the measured one (Hampton et al., 1996). The ratio of integral intensities in "red" and "blue" bands is ,,~ 5.7 with the absorption in the atmosphere column taken into account. In Figure 2 the, case of the sequence of three lightning EMPs is presented. It is clear that under the pulse the event is "red colored" (~=750.0 nm corresponds to solid line), while during the relaxation phase it would be "blue colored", due to longer life-time of N +. It's worthwhile to note that the specific ratios depend on the certain thunderstorm scenario: frequencies, currents and positions of lightning. Meanwhile, the simulation shows that during the thunderstorm the action of EMP may lead to the appearance of a blue background with red "flashes" of microsecond duration. TRANSITION OF ELECTRIC FIELD PULSE THROUGH THE LOWER STRATOSPHERE AND THE PROBLEM OF BLUE JET The existing models of blue jet require either the presence of background electric field of significant magnitude (E ~,, {).3 - 0.5Ecr) (Sukhorukov and Stubbe, 1998) or the absence of electron attachment (Pasko et al., 1996). The recent results on our model (Smirnova et al., 2000) show that: (1) at lower altitudes attachment is the main sink for electrons; (2) if an electric field is less than the critical one, then attachment rate increase with E faster than ionization frequency, thus leading to the disappearance of electrons in the predischaxge phase (Figure 3). Strictly speaking this means that the requirement of large background E is not necessary. (3) The critical electric field is to be determined selflOe r lO 3 consistently within the framework of assumed plasmo[e]~s / '" ......................................... chemical processes. The simulation has shown, that 1°6 I [el°"t in the framework of negative streamer model (Sukhorukov and Stubbe, 1998) the electron density [el -~ 106 104 [ cm -3 (at 30 km) can be reached only if E -~ 1.45Ecr. In such a large field not only the electron conductiv102 I ity increases significantly, but the ion conductivity too. 100 [ ~ E=I.5E The later changes due to a) increasing of ion density in discharge; (b) changing of positive and negative ion ! composition - the transition from heavy ions to lighter 10 2I ions with higher mobility. The increasing of ion con10-4| ~ h 3-4 ductivity stays significant time after the pulse tran10-e 10-6 10-4 10-2 Time, s e c sition. This fact is to be taken into account in the simulation of blue jets and low-altitude red sprites. Fig.3 Electron density at 30 krn under the electric The simulation results show that for the aforemen- pulse propagation tioned case of negative streamer propagation the intensities of red and blue bands will be: J r e d / J b l u e "~ 0.11 at 30 km and ~- 13.28 at 40 km, that coincides well with the model (Sukhorukov and Stubbe, 1998). DISCUSSION The aforementioned models still remain the open question about the scarcity of the blue jets. The red sprites (which we did not discuss here) axe well explained by the quasielectrostatic model (Pasko et al., 1997, 1999) at high alti.tudes, but the "low" sprites and their small-scale structure axe still unexplained. A number of hypothesizes have been proposed up to date. Meanwhile, they can be summarized as an introduction of atmosphere fluctuations into the model (Pasko et al., 1997). Therefore we propose to consider another facts that can play a role in optical events appeaxance. The Sprite'94 and Sprite'98 campaigns (Sentman et al., 1995a,1995b, Baxrington-Leigh et al., 1999) evidence present the maps of lightning strokes by National Lightning Detection Network with observed sprites and jets being mapped. If one will place these maps onto the geological maps of Texas, Oklahoma and South California then, it i s easy to see, that the powerful positive cloud-to-ground strikes are placed along the prescribed directions, that reproduce the loading structure of the Earth's core. This corresponds to the well-known data about the relation between lightning activity and anomalies of the Earth's core conductivity. The most intriguing fact is that observed sprites axe grouped together at the intersection of loading directions, reproducing the zone of maximum stress of the core. The Sprite'98 campaign data on lightning reproduces the stripe structure of the core stress in the California

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region. Such correlation allows us to propose the hypothesis that the optical events may be connected with the processes in the core. Among the last we can mark the following: (1) strong local changing of the Earth's core conductivity; (2) local increasing of electric field over the breaks during their shift; (3) exhausting of radon or other chemicals from the breaks, causing sufficient pre-ionization, and change of electrical properties of an atmosphere. ACKNOWLEDGEMENTS We thank Prof. Yu. Shukin of Institute of Geospheres Dynamics for the help and discussion in evaluating the comparison with geological survey data. REFERENCES Barrington-Leigh, C.P., U.S. Inan, M. Stanley and S.A. Cummer, Sprites triggered by negative lightning discharges, Geophys. Res. Lett., 26, 3605-3608, 1999. Borisov, N., S. Kozlov and N. Smirnova, Changes in the chemical composition of the middle atmosphere during multiple microwave pulse discharge in the air, Cosmic. Res, 31(2),177-186, 1993. Davidson, G., and O'Neil, R, Optical radiation from nitrogen and air at high pressure excited by energetic electrons, J. Chem. Phys.,41, 3946-3955, 1964. Hampton, D.L., M.J. Heavner, E.M.Wescott, and D.D. Sentman, Optical spectral characteristics of sprite, Geophys. Res. Lett., 23, 89-92, 1996. Pasko V.P., U. S. Inan and T. F.Bell, Blue Jets produced by quasi-electrostatic pre~dischaxge thundercloud fields, Geophys. Res. Lett.,23, 301-304, 1996. Pasko, V.P., U.S. Inan, T.F. Bell and Y.N. Taranenko, Sprites produced by quasi-electrostatic heating and ionization in the lower ionosphere, J. Geophys. Res, 102, 4529-4561, 1997. Pasko, V.P., U. S. Inan and T. F.Bell, Mesospheric electric field transients due to tropospheric lightning discharges, Geophys. Res. Lett.,26,1247-1250, 1999. Rowland, H.L., Theories and simulations of elves, sprites and blue jets, J. Arm. Terr. Phys., 60,831-844, 1998. Sentman, D.D., E.M. Wescott, D.L.Osborne, D.L.Hampton and M.J.Heavner, Preliminary results from the Sprites94 aircraft campaign: 1. Red Sprites, Geophys. Res. Lett., 22, 1205-1208, 1995a Sentman, D.D., E.M. Wescott, D.L.Osborne, D.L.Hampton and M.J.Heavner, Preliminary results from the Sprites94 aircraft campaign: 2. Blue Jets, Geophys. Res. Lett., 22, 1205-1208, 1995b Sentman, D.D. and E.M. Wescott, Red sprites and blue jets: Thunderstorm-excited optical emissions in the stratosphere, mesosphere and ionosphere, Phys. Plasm., 39, 2514-2522, 1995. Smirnova, N.V., A.N.Lyakhov and S.I.Kozlov, Lower stratosphere responce to electric field pulse. Int. J. Geom. Aer., 2000. Geophysics Papers Online (http://eos. wdcb.ru/gpo/1999/gai99323/gai99323.htm) Sukhorukov, A. and P. Stubbe, Problems of the blue jet theory, J. Arm. Terr. Phys, 60, 725-732, 1998. Taranenko, Y.N., U.S. Inan and T.F.Bell, Interaction with the lower ionosphere of electromagnetic pulses from lightning: Heating, attachement, ionization, Geophys. Res. Lett., 20,1539-1543, 1993. Uman, M.A. Lightning Return Stroke Electric and Magnetic Fields, J. Geophys. Res. ser.D., 90, 6121-6130, 1985.