Thunderstorm activity dynamics during hurricanes

783

ISSN 0016-7932, Geomagnetism and Aeronomy, 2006, Vol. 46, No. 6, pp. 783–795. © Pleiades Publishing, Inc., 2006.Original Russian Text © Yu.M. Mikhailov, G.I. Druzhin, G.A. Mikhailova, O.V. Kapustina, 2006, published in Geomagnetizm i Aeronomiya, 2006, Vol. 46, No. 6, pp. 825–838.

1. INTRODUCTION

A large volume of observations of anomalies in theEarth’s natural electromagnetic field before earth-quakes in a broad band of frequencies (from tens ofhertz to tens of kilohertz) has been accumulated to date.The most complete reviews of these results before 1990were published in [

Catalog

…, 1991; Remisov, 1991].These anomalies manifested themselves in enhance-ment of fluxes of output pulsed signals registered withbroadband ELF and VLF receivers and in intensifica-tion of emissions at the indicated frequencies in theregime of narrowband registration. Anomaliesobserved in seismic regions made it possible to con-sider them as earthquake precursors [

Electromag-netic…,

1982; Druzhin, 2002]. Pulse flux intensity perhour was considered as the main indication in almost allprevious works. Broadband records of isolated discretesignals, supplemented with data on direction toward asource, made it possible to control location of thesesources. It turned out that an increased flux of pulsedsignals does not coincide with direction toward anearthquake epicenter, and the time form of these signalsis close to the form of ordinary atmospherics generatedby distant thunderstorm sources [Sadovskii et al., 1979;Migunov et al., 1983]. Moreover, the registration ofelectromagnetic signals before strong earthquakes onKamchatka [Migunov et al., 1983] indicated that thesources of these signals do not coincide with the epi-central zone, are located at large distances in the Pacific

water area, and move from east to west. This fact sug-gested that pulsed signal flux intensification couldapparently be caused by hurricanes.

It is known that active cumulonimbus clouds,formed during origination and development of hurri-canes, cause powerful lightning strokes. Giant pulsedsignals generated in this case can propagate over largedistances even in daytime, when the upper wall of theEarth–ionosphere waveguide considerably suppressespropagation of ELF and VLF electromagnetic waves. Ifwe assume that anomalous electromagnetic radiation ofa lithospheric origin is generated in the same frequencyband before earthquakes in seismic regions (and such aviewpoint exists [

Electromagnetic…,

1982], than thenatural electromagnetic radiation during hurricanescreates a certain parasitic effect masking this anoma-lous radiation.

The aim of the present work is to study the dynamicsof thunderstorm activity during hurricanes in the north-western Pacific by means of broadband registration ofatmospherics on Kamchatka. The traditional parame-ter—the number of pulsed signals per minute at simul-taneously determined azimuths of their sources—wasused as the level of thunderstorm activity. The fluxes ofatmospherics in August and October 2002 (during theseasonal maximum of hurricanes in this region) areanalyzed in the work.

Thunderstorm Activity Dynamics during Hurricanes

Yu. M. Mikhailov

a

, G. I. Druzhin

b

, G. A. Mikhailova

a

, and O. V. Kapustina

a

a

Pushkov Institute of Terrestrial Magnetism, Ionosphere, and Radiowave Propagation, Russian Academy of Sciences, Troitsk, Moscow oblast, 142190 Russia

b

Institute of Cosmophysical Research and Radiowave Propagation, Far East Division, Russian Academy of Sciences, Mirnaya ul. 7, Paratunka, Elizovo raion, Kamchatka oblast, 684034 Russia

Received November 24, 2005; in final form, April 13, 2006

Abstract

—Results of studying the thunderstorm activity dynamics during the Pacific hurricanes in August andOctober 2001, using broadband recording of the time forms of atmospherics on Kamchatka, have been pre-sented. The number of atmospherics per minute at simultaneously determined azimuths of their sources hasbeen used as an example of thunderstorm activity. An analysis of data processing results has indicated (a) in theabsence of hurricanes, the maximal atmospheric flux level (

10

±

4

pulse/min) was observed at night, and thedaylight level was

3

±

1

pulse/min; (b) thunderstorm activity increases at the stage of tropical depression regard-less of depression development into hurricane; in this case the flux of atmospherics can increase to 250pulse/min at night and can be widely variable (5–100 pulse/min) in daytime; (c) in the sate of hurricane matu-rity, the thunderstorm activity level is not higher than the background level. It has been indicated that IGWs inthe Earth’s atmosphere and the lower ionosphere are caused by lightning strokes accompanied by shock wavesduring expansion of the lightning channel. The results obtained are of interest in studying anomalous effects inthe natural electromagnetic field in the VLF band during increased seismic activity on Kamchatka.

PACS numbers: 92.60.Qx

DOI:

10.1134/S0016793206060144

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2. METHODS OF REGISTRATION AND EXPERIMENTAL DATA PROCESSING

To register the flux of pulsed signals at Paratunkaobservatory (

ϕ

= 53.0°

N

,

λ

= 158.3° E

), we used theONCh-Pelengator facility designed and manufacturedat Institute of Cosmophysical Research and RadiowavePropagation, DVO RAN [Druzhin et al., 2001]. Thisfacility makes it possible to simultaneously record threecomponents of the electromagnetic field (

E

z

,

H

x

,

H

y

) inthe frequency band 3–60 kHz. Two mutually transversemagnetic loops oriented N–S and E–W and toward thevertical antenna are used to receive signals. Analog out-put signals from broadband amplifiers through an ana-log-digital converter come to personal computer, wherepulsed signals with the intensity exceeding the speci-fied threshold are sought according to the correspond-ing algorithm. The time form of all three components inarbitrary units, date, no. from the beginning of day, timeof the first reading, and reading number are filed foreach detected pulse. The direction toward a pulsed sig-nal source is determined from the formula:

ϕ

=

H

M–S

/

H

E–W

)

, where

H

N–S

and

H

E–W

are the rmsvoltages of amplified output signals of the loop anten-nas. Ambiguity in detecting the azimuth toward asource is eliminated by using a signal received from thevertical antenna (see in more detail in [Druzhin et al.,2001; Mikhailov et al., 2005]). A new file is created fordata on angles of pulsed signal arrival together withhousekeeping information. Figure 1a illustrates thetime forms of three components of the detected pulsedsignal, coincident with the traditional time form ofatmospherics from remote sources. Figure 1b shows thediurnal variations in the number of atmospherics perminute. Fig. 1c demonstrates the daily azimuth distri-bution of atmospherics in rectangular coordinates, andthe same azimuth distribution but in polar coordinatesis shown in the lower panel of Fig. 1c for four periodsof day. Zero angle value corresponds to the northwarddirection, and azimuths are counted off from zeroclockwise. Gaps in the distribution for angles of 90

°

,180

°

, and 270

°

are related to singularities of the function. Here, the radius of any point is the

reciprocal of the average square of the signal magneticcomponent intensity.

The algorithm for processing data on the signalthree components makes it possible to detect individualazimuths in the distinguished time intervals in the dailydistribution of fluxes of atmospherics in order to ana-lyze in detail the dynamics of thunderstorm activitydevelopment. The proposed data processing methodwas used to register thunderstorm activity whencyclones crossed Kamchatka and during the hurricanesin the Pacific [Mikhailov et al., 2005]. In the presentwork, this technique is used to analyze thunderstormactivity during the same hurricanes in August and Octo-ber 2002.

(arctan

ϕarctan

3. MAIN RESULTS

Let us consider specific features of thunderstormactivity during these cyclones.

3.1. Flux Background Level of Atmosphericsin the Absence of Hurricanes

Under these conditions, thunderstorms above thePacific are observed extremely rarely, especially in day-time, and the level of atmospheric noise above theocean and on Kamchatka is governed by continentalsources [Terina, 1965]. The number of such quiet daysduring observations was insignificant: August 6–9, 20,and 21; October 5, 6, 21, 22, and 31. Figure 2a showsthe daily average distribution of the number of atmo-spherics per minute, which came to the observationpoint from all directions in August. Figure 2c demon-strates the corresponding everyday polar diagrams. Thepolar diagrams indicate the directions of arrival ofatmospherics in a wide range of azimuths:

ϕ

~ 40°–300°

, including sources in the northeastward and north-westward directions with the predominant direction inthe range 200

°

–230

°

. The daily average distribution ofthe number of atmospherics in this direction is shownin Fig. 2b. It is clear that the number of atmospherics ismaximal (

10

±

4

pulse/min) at local midnight (1200–1300 UT) and is minimal (

3

±

1

pulse/min) at localnoon (0000–0100 UT). This distribution was acceptedas a background flux level for further studying thedynamics of thunderstorm activity during hurricanes.In October this level was slightly lower owing to theseasonal variations in thunderstorm activity.

3.2. The maximum in the distribution of the occur-rence frequency

and intensity of hurricanes and theirseasonal distribution in the Pacific water area falls onAugust–October, when the ocean surface is sufficientlywarm. Data on the hurricanes were obtained fromhttp://www.npmoc.navy.mil/jtwc/atcr. Several stronghurricanes and tropical depressions occurred duringthose period of 2002 in the western Pacific: TS 16WKammuri, August 2–5; TD 17W, August 5; TS 18W,August 10–13; ST 19W Phanfone, August 11–20; T21W Rusa, August 22–September 1; T 22W Sinlaku,August 28–September 8; T 26W Bavi, October 9–14; T29W Maysak, October 25–30; TD 27W, October 17–19; and TD 28W, October 18–19. The dynamics ofthunderstorm activity during these events is consideredin detail below.

Tropical storm 16W Kammuri of August 2–5,2002.

The upper panel in Fig. 3 shows the motion tra-jectory of the typhoon center where the pressure is min-imal and the wind velocity is maximal. These data aremarked on the trajectory at an interval of 6 h. As fol-lows from meteorological satellite photographs, hurri-cane is actually a giant meteorological phenomenon,very extensive in both latitude and longitude [Dobrysh-man, 1994]. The azimuth distribution of the sources ofatmospherics at an interval of 6 h on August 2–5 is


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THUNDERSTORM ACTIVITY DYNAMICS DURING HURRICANES 785

100

t

,

µ

s

E

z

,

H

N–S

,

H

E–W

, arb. units

400

–400

0

200

0

–200

200 300 400 500

2N_0000:38(‡)

0600 UT, h

N

,

pulse/min

0000

50

1200 1800

(b)

0600 UT, h0000

270

1200 1800

(c)360

180

90

0000–0600 060–1200 1200–1800 1800–2400

030

60

90

120

160180

210

240

270

300

3300

30

60

90

120

160180

210

240

270

300

3300

30

60

90

120

160180

210

240

270

300

3300

30

60

90

120

160180

210

240

270

300

330

12 3

(d)

Fig. 1.

Examples of (a) three time forms—

E

z

(

1

),

H

E–W

(

2

), and

H

N–S

(

3

)—of detected atmospheric; (b) the diurnal variations inthe signal flux per minute; and the diurnal distribution of the azimuths (in degrees) and their sources (c) in rectangular coordinatesand (d) in polar coordinates at an interval of 6 h.

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N

,

2RMSD

pulse/min

0

40 (‡)

35

30

25

20

15

10

5

45

Background for all

ϕ

0600 UT, h0000 1200 1800

(b)15

10

5

Background for

ϕ

= 200°–230°

0N

30

60

90 E

120

150180S

210

240

270W

300

3600N

30

60

90 E

120

150180S

210

240

270W

300

3600N

30

60

90 E

120

150180S

210

240

270W

300

3600N

30

60

90 E

120

150180S

210

240

270W

300

360

0N

30

60

90 E

120

150180S

210

240

270W

300

360

0N

30

60

90 E

120

150180S

210

240

270W

300

360

06 07 08 09

20 21

(c)

Fig. 2.

The average background level of the flux of atmospherics that came to the registration point (a) from all directions and(b) from the sources with the azimuths

ϕ

= 200°–230°

; (c) the polar diagram of azimuths for August 6–9, 20, and 21. The verticalbars are the rms deviations.


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2006


ϕ

= 170°–205° (TD17)

N

,

pulse/min

0

50

100

2 3 4 Days

0518Z 9 2

28N

110E

Legend24-hr best track positionTropical disturbanceTropical depression

Tropical stormTyphoon/super typhoon

DTGXXXXZ

SPD(KT)XX

INT(KT)XX

Tropical storm 16W (Kammuri) August 2–5, 2002

00–06

06–12

18–24

12–18

02

26N

24N

22N

20N

18N

16N

0500Z 9 50

0400Z 3 45

0300Z 11 30

0200Z N/A 25

114E 118E 122E 135E



DTGXXXXZ

SPD(KT)XX

INT(KT)XX

40N

35N

30N

25N

0606Z 6 25

140E 145E 150E

0600Z 6 25

0500Z 10 200400Z 7 20

0300Z 9 15

0218Z N/A 15

24-hr best track positionidentification

Tropical depression 17W August 5, 2002

155E 160E

00–06 00–06 00–06

06–12 06–12 06–12

12–18

12–18 12–18

18–24 18–24 18–24

03 04 05

5

0

50

100

ϕ

= 225*–240° (TS16)

Fig. 3.

Trajectories of the Kammuri 16W tropical storm and the 17W tropical depression on August 2–5; the azimuthal distributionsof the directions toward the signal sources and the daily distributions of the flux of atmospherics in the sectors 225

°

–240

°

(TS16)and 170

°

–205

°

(TD17) during this period. Four figures on the trajectories near arrows indicate the date and time 00Z (0000 UT);two and three numerals (the closest to a trajectory), the wind velocity in knots (1 knot = 1.87 km/h).

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shown in the second panel from above in Fig. 3. Thenumber of atmospherics is maximal in the sectors185

°–225° and 225°–240°. These directions coincidewith the directions toward the sources during the tropi-cal depression 17W and the tropical storm Kammuri16W. The diurnal curves of the fluxes of atmosphericsare shown independently for the sources in the distin-guished sectors (the third and fourth panels of Fig. 3).It is evident that, in the course of the depression, thegeneral level during the entire day was much higherthan the background, reached its maximum at midnighton August 3, and slowly decreased during August 4 and5, remaining higher then the background level. In theazimuthal sector 225°–240°, the diurnal distribution ofthe flux of atmospherics was slightly different from theprevious distribution: at 0600 UT on August 2, the levelwas lower than during TD17; the maximum wasobserved at midnight on August 2 and 3 and coincidedwith the state of cyclone depression according to theTS16 trajectory. A sharp decrease in the pulse flux tothe background level on August 4 and 5 coincided withthe tropical storm state, when the wind velocityincreased almost twice as compared to such a velocityon August 2 and 3. As follows from the TS16 trajectory,the emission of atmospherics was maximal at the stateof depression fro the Kammuri typhoon and subse-quently sharply decreased to the background level atthe state of tropical storm.

Tropical storm 18W of August 10–13, 2002, andsuper-typhoon Phanfone 19W of August 11–20,2002. The polar diagrams of azimuths in Fig. 4 indicatethat, on August 10–14, the maximal signal flux was reg-istered from the sources in the sectors 175°–230° and210°–230°. These azimuths correspond to the direc-tions toward ST19 and TS18. The daily distribution ofthe flux of atmospherics from the sources in these sec-tors is shown in the lower fragment of Fig. 4, during theentire considered period, an anomalously large N value(pulse/min) was observed at 0600 UT. On August 12and 13, this value was even larger than the nighttimevalues and increased from 30 to 60 pulse/min beginningfrom August 10. That is, an anomalous flux enhance-ment (as follows from the trajectory of cyclone devel-opment) began at the stage of storm and typhoondepression, and N reached its maximum on August 13at the stage of TS18 depression and when the 19Wcyclone changed into the initial stage of typhoon.

Typhoon Rusa 21W of August 22–September 1.Figure 5 presents the trajectory of the typhoon centermotion, the series of polar diagrams toward the sourceof signals at an interval of 6 h for the first four days oftyphoon development, and the diurnal variations in theflux of atmospherics in the detected interval of azi-muths 170°–205°. The lower fragment of Fig. 5 indi-cates that the diurnal variations N(t) is close in shape tothe traditional background behavior but has a higher Nlevel. In contrast to the previous events, the daytimelevel of activity was increased (up to 20 pulse/min) onlyon August 22 and was equal to the background level on

the remaining days. A nighttime enhancement was reg-istered only on August 22–24. On the following days,beginning from August 25, a substantial increase in theflux of signals was not observed during this typhoon;therefore, these data are absent in Fig. 5. According tothe typhoon development trajectory, the period August22–24 coincides with the stage of depression at a mini-mal wind velocity.

Typhoon Sinlaku 22W of August 28–September 8.The trajectory of the center of this typhoon is shown inFig. 6. This typhoon began on August 28, coincidedwith the Rusa typhoon in both time and space, but dif-fered from it in thunderstorm activity. The lower frag-ment of Fig. 6 indicates that the level of thunderstormactivity was close to the background level (see Fig. 2)in the distinguished sector of azimuths (180°–210°),coincident with the direction toward the typhoon, onAugust 28–September 1 (except August 29). This levelreached ~30–40 pulse/min only on August 29 but wasonly slightly higher than the background level duringthe Rusa typhoon (see the lower fragment in Fig. 5). Asfollows from the trajectory of motion of the typhooncenter (the upper fragment in Fig. 6), August 29 corre-sponded to the stage of depression. The consideredtyphoon became mature, with a maximal wind velocityof 105 knots per hour (1 knot = 1.87 km/h), on Septem-ber 1, when the level of thunderstorm activity increasedbut did not reach the level observed on August 29. Thus,as during the typhoons considered above, the thunder-storm activity maximum is observed at the stage oftropical depression.

Typhoon Bavi 26W of October 9–14. The corre-sponding fragments, similar to Fig. 3, for this typhoonare presented in Fig. 7. The lover fragment of Fig. 7indicates that the flux of atmospherics was most intenseon October 9 and 10, when the typhoon was in the stateof tropical depression. However, the value of N(pulse/min) was only a factor of 1.5 as large as thebackground level both in daytime and at night. In thestate of typhoon maturity on October 12 and 13, the fluxvalue was on the background level and, therefore, is notshown in Fig. 7.

Tropical storm Maysak 29W of October 25–30developed against a background of the magnetic storm(ΣKp = 36–44), which, as is known, results in a strongdecay of VLF electromagnetic waves in the Earth–lower ionosphere waveguide. Therefore, the flux ofatmospherics was even lower than the backgroundlevel. However, in this case (as well as for the typhoonsconsidered above) the flux of atmospherics was alsomost intense at the stage of typhoon depression.

This conclusion was confirmed during the TD 27Wand TD 28D tropical depressions: on October 18, theflux of atmospherics increased to 10 ± 5 pulse/min indaytime and to (40–100) ± 10 pulse/min at night, whichis considerably higher than the background level.

GEOMAGNETISM AND AERONOMY Vol. 46 No. 6 2006


ϕ = 175°–230° (ST19–175°–230°, TS18–210°–230°)

N, pulse/min

0

50

10 11 12 Days

1418Z 9 20



DTGXXXXZ

SPD(KT)XX

INT(KT)XX

Tropical storm 18W August 10–13, 2002

00–06

10

24N

22N

20N

18N

16N

1006Z N/A 20

114E 118E 122E 135E



DTGXXXXZ

SPD(KT)XX

INT(KT)XX

40N

35N

30N

25N

145E

2000Z 24 50

1018Z N/A 20


Super tuphoon 19W (Phanfone) August 11–20, 2002

155E

06–12

12–18

18–24

13

14N

12N

10N

8N

126E 130E 134E


1400Z 11 20

1300Z 15 25

1200Z 9 30

1100Z 3 30

45N

20N

15N

10N

5N0

1900Z 9 85

1800Z 7 105

1700Z 10 115

1600Z 15 130

1500Z 14 100

1400Z 16 75

1300Z 11 601200Z 4 40

1100Z 7 25

2018Z 36 35

165E 175E125E00–06 00–06 00–06 00–06

06–12 06–12 06–12 06–12

12–18 12–18 12–18 12–18

18–24 18–24 18–24 18–24

11 12 13 14

14

Fig. 4. The same as in Fig. 3 but for the 18W tropical storm in the sector ϕ = 210°–230° and for the Phanfone 19W super-typhoonin the sector ϕ = 175°–230°.

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MIKHAILOV et al.

0106Z 12 35

2200ZN/A 20

40N

35N

30N

25N

20N

15N

10N

5N

0135E 145E 155E 165E




DTGXXXXZ

SPD(KT)XX

INT(KT)XX

Typhoon 21W (Rusa) August 22–September 1

125E115E

45N

0100Z 14 45

3100Z 11 70

3000Z 7 80

2900Z 12 85

2800Z 13 95

2600Z 12 100

2400Z 13 652300Z 10 45

2700Z 11 115

2500Z 15 75

00–0600–06

06–12

12–18

18–24

22

00–06 00–06

06–12 06–12 06–12

12–18 12–18 12–18

18–2418–24

18–24

23 24 25

ϕ = 170°–205° (TY21)

N, pulse/min

50

22 23 Days

100

150

0

200

24 25

Fig. 5. The same as in Fig. 3 but for the Rusa 21W tropical storm in the sector ϕ = 170°–205°.



2806ZN/A 20

50N

40N

30N

20N

10N

130E 140E 150E 160E 170E




DTGXXXXZ

SPD(KT)XX

INT(KT)XX

Typhoon 21W (Sinlaku) August 28–September 8, 2002

00–06

06–12

12–18

18–24

28

120E110E

2900Z 5 30

3000Z 9 55

3100Z 10 95

0100Z 9 105

0200Z 12 1000600Z 3 90

0700Z 10 70

0800Z 16 30

0500Z 6 95

0400Z 12 90

0300Z 14 90

29

00–06 00–06 00–06 00–06

06–12 06–12 06–12 06–12

12–18 12–18 12–18 12–18

18–24 18–24 18–24 18–24

30 31 01

ϕ = 180° –210° (TY22)

N, pulse/min

29 30 Days

20

40

031 0128

Fig. 6. The same as in Fig. 3 but for the Sinlaku 22W tropical storm in the sector ϕ = 180°–210°.

792


MIKHAILOV et al.

ϕ = 170°–205°

N, pulse/min

10

20

Days

1400Z 32 35

1300Z 13 65

1200Z 13 65

1100Z 8 55

1000Z 8 30

0900Z 20 25

0712ZN/A 15

0800Z 10 25

50N

45N

40N

35N

30N

25N

20N

15N

10N

5N

0125E 130E 135E 140E 145E 150E 155E 160E 165E 170E 175E 180




DTGXXXXZ

SPD(KT)XX

INT(KT)XX

Typhoon 26W (Bavi) October 9–14, 2002

00–06

06–12

00–0600–0600–0600–06

06–1206–1206–1206–12

18–24

18–24

12–18

12–18

18–2418–24

18–24

12–1812–18

18–24

07 08 09 10 11

1406Z 37 30

80

9 10 117

Fig. 7. The same as in Fig. 3 but for the Bavi 26W tropical storm in the sector ϕ = 170°–205°.



4. COMPARISON BETWEEN DIURNAL VARIATIONS IN THE FLUX OF ATMOSPHERICS

AND ATMOSPHERIC RADIO NOISE DURING HURRICANES

Mikhailov et al. [2005] performed the temporal–spectral analysis of the diurnal variations in atmo-spheric radio noise at a frequency of 4.65 kHz,

observed on Kamchatka in August and October 2002during hurricanes. The oscillation band T = 0.5–3 hwith the maximum T = 2–3 h was distinguished in thepower spectra of these variations. As is known, theseperiods coincide with the periods of atmospheric inter-nal gravity waves. The intensity of these spectral com-ponents is a factor of 1.5–2 as high as the backgroundlevel and pronouncedly changes during cyclone devel-

N, pulse/min

13 14 Days

50

012

(a)

20 t, h

1600

1510

141312

5015105020155 100

800

Ä

August 2002

20

T, h0431 20

3E+10S2

2E+10

1E+10

0431 2 0 31 2

Fig. 8. (a) Diurnal variations in the flux of atmospherics, N, pulse/min (upper fragment), intensity of atmospheric radio noise at afrequency of 4.65 kHz (middle fragment), and power spectra of radio noise in the band of periods 0.5–3 h (lower fragment) for thePhanfone typhoon of August 12–14, 2002; (b) the corresponding curves for the Rusa typhoon of August 22–25 (on the left) and theSinlaku typhoon of August 28–September 1, 2002 (on the right).

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MIKHAILOV et al.

opment. The present work has studied the dynamics ofthunderstorm activity accompanying the same hurri-canes. It was interesting to elucidate what stage in thedevelopment of hurricanes cause enhancement ofIGWs in the Earth’s atmosphere and lower ionosphere.For this purpose, we compared the diurnal variations inthe flux of atmospherics and atmospheric radio noiseduring the cyclone development. We obtained that themaximal intensity of the spectral components in theband of periods T = 0.5–3 h coincides with the maxi-mum in the daily distribution of the flux of atmospher-ics. The N curves (upper fragment), diurnal variationsin the atmospheric radio noise intensity (middle frag-ment), and power spectra of these variations (lowerfragment) for the Phanfone typhoon of August 12–14,2002, are presented in Fig. 8a as an example. Figure 8b

shows the corresponding curves for the Rusa typhoonof August 22–25 (on the left) and for the Sinlakutyphoon of August 28–September 1 (on the right). In afinal analysis, we can conclude that IGWs in the Earth’satmosphere and lower ionosphere are caused by power-ful lightning strokes at the stage of hurricane depres-sion and origination rather than by gusts reaching theirmaximal intensity at the center of cyclones.

5. DURATION OF ANOMALOUS INCREASE IN THUNDERSTORM ACTIVITY

DURING HURRICANES

The middle fragment of Fig. 2 demonstrates thedaily distribution of the mean flux of atmospherics inthe sector of azimuths coincident with the possible

N, pulse/min

23 24 Days

200

022

(b)

2000

252423220

500

Ä

T, h0 431 20

4E+10S2

2E+10

25

150

100

50

1000

1600

0 431 2 0 431 2 0 431 2

N, pulse/min

29 30

40

028

Aug. 313029280

0 431 2

31

20

0 431 2 0 431 2 0 431 2

01

Sept. 1, 2002

0 31 2

Fig. 8. Contd.



direction toward hurricanes but during the period whenthe latter are absent. Such a character of the diurnalcurve coincides with the classical variations in the levelof atmospheric radio noise above ocean, caused by dis-tant sources, and depends on the conditions of propaga-tion of VLF electromagnetic waves in the Earth–iono-sphere waveguide [Terina, 1965]. As was indicatedabove, during hurricanes, these diurnal variations areviolated due to the appearance of anomalously highfluxes of atmospherics in daytime. It was interesting toestimate the duration (τ) and intensity (N, pulse/min) ofan anomalous increase in the flux of atmospherics ascompared to the background level. It is clear that theaverage duration of anomalous fluxes of atmosphericsmakes up several hours in different time of day (4, 7,8 h), and the intensity of these fluxes is very widelyvariable: form 5 to 70–100 pulse/min in daytime andfrom 20 to 250 pulse/min at night. These data are ofinterest when anomalous effects in the natural electro-magnetic field in the VLF band are studied during theperiod of increased seismic activity on Kamchatka.

6. CONCLUSIONS

An analysis of the entire set of data on the fluxes ofatmospherics on Kamchatka, as a measure of thunder-storm activity during hurricanes in the western Pacific,indicated the following:

(1) In the absence of cyclones, the maximal level of theflux of atmospherics above the ocean (10 ± 4 pulse/min)was observed at local night (1300 UT = 0000 LT); in thedaytime, except the postnoon burst (4 ± 2 pulse/min),the average flux was 3 ± 1 pulse/min.

(2) Thunderstorm activity increased mostly at thestage of tropical depression regardless of depressiondevelopment into hurricane.

(3) In the state of hurricane maturity, when the windvelocity becomes maximal, the level of thunderstormactivity was mainly not higher than the backgroundlevel.

(4) At local night during hurricanes, the average fluxof atmospherics increased by a factor of approximately8, sometimes approaching 250 pulse/min at a back-ground value of 10 pulse/min. In this case the durationof the anomalous period varied differently, increasingor decreasing as compared to the duration of the back-ground maximum.

(5) In daytime during cyclones, the anomalousbursts in the fluxes of atmospherics were most pro-nounced. The average duration of these bursts was 7 h,and the burst intensity was very widely variable (5–100 pulse/min) with abrupt beginning and end.

(6) A comparison of the daily distribution of the fluxof atmospherics during tropical storms and the powerspectra of the daily distribution of atmospheric radionoise, simultaneously measured during hurricanes,

indicated that the intensity of the components in theband 0.5–3 h (during atmospheric IGWs) is maximal athigh thunderstorm activity. This result makes it possi-ble to state that the sources of these waves in the Earth’satmosphere and lower ionosphere are lightning strokesaccompanied by shock waves at an expansion of thelightning channel, rather than gusts.

7. ACKNOWLEDGMENTSThis work was supported by the Russian Founda-

tion for Basic Research, project nos. 02-05-79066 and04-05-65100.

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Thunderstorm activity dynamics during hurricanes