Journal of Geophysical Research Atmospheres - 1997 - Krasilnikov - Electromagnetohydrodynamic nature of tropical cyclones
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Journal of Geophysical Research Atmospheres - 1997 - Krasilnikov - Electromagnetohydrodynamic nature of tropical cyclones
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JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 102, NO. D12, PAGES 13,571-13,580,JUNE 27, 1997 Electromagnetohydrodynamic nature of tropical cyclones, hurricanes, and tornadoes EvgenyY. Krasilnikov MoscowStateAviation Institute,TechnologicalUniversity, Moscow, Russia Abstract. The problemof genesis and imensification of tropicalcyclones,hurricanes, andtornadoes is highly importantin meteorology andto date hasnot been solved.At the sametime, practicallyall researches madeconcerning thesephenomena fail to take into account that the origin and intensification of tropicalcyclones, hurricanes, and tornadoes take placeunderconditions of an abnormally strongelectricfield which together with electromagnetohydrodynamic interaction occupies a key positionin the intensification process. The detailed description of the electromagnetohydrodynamic modelexplaining the processes of energyconversion in tropicalcyclones, hurricanes, andtornadoes is presented. 1.Introduction It hasbeenover 150 years, starting,perhaps,from the research performedby Hare [1837], since the problems relatedwith ascertaining the natureof tropicalcyclones, destructive hurricanes, and tornadoes were first discussed, andthey still remaina subject of intense attention for many specialists engaged in studies of these rathercomp- lex phenomena of nature. By carrying out multiple and systematic studiesof these phenomena in recemdecades (for obviousreasons onlya minorpan of these studies are citedin thisarticle) and using satellite,aircraft, sound, and ground-based observation facilities extensive statistical data have been accumulated and considerable progress hasbeenachieved in revealing factors which determine the genesis of these formidable naturalphenomena. Considerable research ef- fort has been directedto finding out the causes which result in intensification of thesevorticesand building mathematical modelsof them as well as to simulating them in laboratories. As for tropical cyclonesand hurricanes,the above givenanalysis of their origin and development has not yet given an exhaustiveanswer in terms of nature but, nevertheless, it hashelpedto disclose somefactorswhich are of primary significance for the process of intensifi- cationand they are as follows' power supplyto tropical cyclones and hurricanes at the expenseof sensibleand latent heat of moist air lifted upward from the ocean surface,the secondary circulationin the vertical plane, the lowering of cooled air in rainbandcloud-linesat the tropicalcyclone peripheryand coolingof incomingair. At the sametime there has been, to date, no compre- hensiveunderstanding of the mechanismwhich trans- Copyright 1997 by the American GeophysicalUnion. Paper number 97JD00146. 0148-0227/97/97JD-00146509.00 formsthe heat energyof moist air lifted upward from the oceansurface to an imensivekineticenergyof vortex motion(the primary circulation)of a developing tropical cyclone. The results of tornado research leave still fewer groundsfor optimism. Till recemly there has been no clear idea about the origin and rapid imensificationof tornadoesfrom the primary vertical and especially horizontal vorticity. Anotherphenomenon which remains unexplained is the mechanism that providestransmission andenergyconversion of a strongthunderstorm, at times, to the abnormally intensive kineticenergyof the air rota- ry motionin a tornado. It mightbe a paradox,but an overwhelming majority of researches madelately in analyzingthe intensification processes of tropicalcyclones,hurricanes, and tornadoes have consideredthermodynamic,hydrodynamic, heat transfer processes, and aqueous phase change only, taking no accountof processes occasioned by the action of an abnormallystrong electric field. Meanwhile, the cloud structures of tropical cyclones,hurricanes,and thunder- storms forming a tornado display abnormal electrical properties obviously observed nowhereelsein nature.So, for ex_ample, the maximumpotemialgradientvaluesreach 105-106 V m 4, whilethetotalelectric charge of a hur- ricane is many times as large as Eaxth's total electric charge.For all that, the values of electric and electro- magneticforcescould happento be greaterthan all other acting forces, which explains their decisiverole in the intensification of these vortices. It is evident that a one- sidedapproach to the analysis of physicalphenomena in tropicalcyclones,hurricanes, and tornadoes, taking no account of electromagnetohydrodynamic effects, can not providea correct and comprehensive understanding of theseprocesses which accountfor their intensification and withoutwhich, in turn, it would be impossible to construct applicable mathematical models. Meanwhile, we can refer to Hare [1837], who 160 years ago poimed out the possiblerole of effects con- nectedwith a strongelectricfield in the formationof a 13,571
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13,572 KRASILNIKOV: ELECTROMAGNETOHYDRODYNAMIC NATURE OFPOWERFUL STORMS tornado. Similarassumptions havenot oncebeenmadein recem decades.Let us, for example, refer to the as- sumptions madeby Riehl [ 1979, p.549], "...someform of rotational mechanism appears to offer a viable solutionon the large scaleof the atmosphere; magneticfields, for instance,do not enterin tropospheric balancesof for- ces" , and by Vonnegut [1960, p.203], "It is suggested that there is sufficiem electrical energy in an intense thunderstorm to power a tornadoand that the electri- ficationcouldcause extraordinarily intense winds...". Basedon the _analysis of multiple studieson electro- physical properties of cloud structures in the troposphere and numerousobservationaldata on the genesis and intensification of tropical cyclones,hurricanes, and tor- nadoes, this papergives a description of an electromag- netohydrodynamic (EMHD) mechanism which does ac- countfor the formationand intensification of the primary circulation in thesevortices.According to this model the heat energy of moist air lifted upward from the ocean surfaceis converted to the electric field energy which through the EMHD mechanism is converted to the kinetic energyof intensive vortex motion of a tropicalcyclone and a hurricane,while the electricenergyof a powerful thunderstorm as a restfit of EMHD mechanism action is convertedto the kinetic energy of the intensiverotary motionof a tornado.In view of the principaldifferences betweentropical cyclonesand tornadoes under the con- difions of genesisand development,this paper gives separate analyses of the EMHD mechanism actionin the processes of their imensification. 2. Electromagnetohydrodynamic(EMHD) Model The developed tropical cycloneand hurricane moving over the oceansurface represem a powerfulcloudsystem, the radius of which can exceed 500 km or more. The altitudeof this cloudaccumulation extended upwardfight up to the tropopause can reach 17 kin. Tornadoesare generatedonly by very powerfid thunderstorms. The dimensions of a thunderstorm often exceed 10-20 km in the horizontal direction and 15-17 km in the vertical direction fight up to the tropopause. So, tropicalcyclones and hurricanesrepresentunique meteorologicalform- ations. Tornadoes,as well, are connectedwith unique thunderstorms. The uniqueness of thesecloudsystems (as distinguished from other types observedin nature) is determined by the highestaltitudeand by the hugemass of water accumulated in them, and what is more im- portant, by the maximum possible waterconcernration in themper unit of volume in the form of vapor, dropsand ice crystals.The estimates show that in a hurricaneof averageintensitythe energy of latent heat releasedper dayis of the orderof 4x10 •9 J, and thewater coment needed for that is 16km 3, whichisequivalent to the Colorado River annual runoff [Riehl, 1979]. This circumstance is very important, since it is exactly such concentrated cloud accumulations with which the abnor- mal strongelectricfieldsare related. The electric field in Earth's atmosphere is known to exist in the absenceof clouds. So, the measurement data at an altitude of 6 km [Clark, 1957] show that the potential makes upa value of theorder of 2.2xl0sV. But during emergence and development of any clouda local electric field related with it is being formed and increased. Quite a great numberof investigations have been made on the nature of this electric field. This problem includesthree main aspects.The first one is connectedwith the process of formation of electric charges in a cloud.The second one concernsthe process of charge separation,and the third one concernsthe electric structure of clouds.As for the first two aspects, in spite of extensiveand prolongedstudies [e.g., Workman and ReynoMs, 1950; Vonnegut, 1953; Chalmers, 1967]thereis till now no common viewpoint both with respect to the mechanism of electriccharge formation duringcloudformingand with respect to the process of their separation. However, numerous studies of the third aspect showed that the electric structureof mature powerful thunderstormsis the tripole one [Chalmers,1967; Williams, 1989; Byrne et al., 1989]. The electric structure scheme of the mature thunderstorm is givenin Figure 1. In the centralpart of the cloudat an altitudeof about6 km abovethe Earth's surface (by data of different authorsfrom 3 to 8 km [Chalmers, 1967]) where airtemperature is about-15øC is thecenter of the negative chargelayer. The height of this layer, as a role, does not exceed 1 km, and in the horizontal direction its size could coincide with the size of the thunderstorm. The maximumvaluesof the electric field potentialgradient correspond to the upper and lower boundariesof this layer. It is in this layer that a maximumvalue of the volumecharge densityis observed. A positivelycharged area occupiespractically the whole upper part of a thunderstorm, sometimes extending up to the tropopause. The electric volumechargeconcentration is lesshere than in the negativechargelayer. Another area of a positive charge is in the very lower part of a thunderstorm, just at its basis. This area(the reason for its formation is not yet established) is not very large and, as assumed, does not play any essentialrole in the formation of an electric field. Besides, in the very upperpart of a thunderstorm there is a rather thin layer which containsnegative charges. The Earth's surfaceunder a thunderstorm has an induced positivecharge,the intensive coronadischarge beingformeddirectlyover the surface (over the objects in the form of a cusp). There are virtually no measurement data of electric parameters in hurricanes and tornadoes. Hence, we refer to the data of numerous measurements of the most sig- nificant electricparameters of maturepowerful thunder- storms. The potential difference between the negatively charged layer andtheground surface is 109 V [Schon- land, 1964], and betweenthe negativelychargedlayer and the upper part of a thunderstorm is 108 V. Inside of a thunderstorm the largestmeasured valuesof the potential gradient change from1.5x l0s to2x106 V m 4 [Marshall and Rust, 1995; Ziegler and MacGorman, 1994; Norinder and Salka, 1951; Imianitov et al. , 1971]. These values correspond to the conditions at whichlight- ning takesplace, but as observations show, both hurri- canesand tornadoes are accompanied by frequentand strong lightning [Chalmers, 1967; Ziegler and Mac 21562202d, 1997, D12, Downloaded from https://agupubs.onlinelibrary.wiley.com/doi/10.1029/97JD00146, Wiley Online Library on [08/03/2026]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License
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KRASILNIKOV: ELECTROMAGNETOHYDRODYNAMIC NATURE OF POWERFUL STORMS 13,573 Gorman,1994; Molinari et al., 1994]. The presence of a strong electric field and electric conduction of the medium determinesthe presenceof electric currents flowingboth insideof a thunderstorm and betweenit and the Earthsurface. So, the conduction currentdensityin a powerful thunderstorm canreach a value of 10 -8A m -• [Irnianitov et al., 1971]. Diffusion current can have the same value. The precipitationvertical current reaches values of 10 -8-10 -5 A m -2 [Chalmers, 1967; Imianitov et al., 1971]. However, the convective current causedby flow turbulence andby the actionof a strongelectricfield can be many times as large as the above mentioned currents. Still another principallyimportantparameter is the volumeelectricchargedensityPE. Data of measure- mentsand estimates of maximumvolume electriccharge density in thunderstorms attain valuesin the range of 10-9-10• C m -3 [Byrne et al., 1989; Ziegler andMac Gorman, 1994; Imianitov et al., 1971; Matveev, 1984]. The total chargevalue of any sign in a thunderstorm of the size 5x5 km in the horizontalplane following the estimatesof Wormell [1953] amounts to about 1400 C. Then the total chargeof any sign in a hurricanewith a radius of 500kmshould have a value of 4.4x10 7C, although taking into accourn that a hurricanecontainsan abnormally largearnourn of water simultaneously in three phases (and this is the very circumstance determining the charge value), this inconceivably large chargevaluecould actuallybe an underestimate. So, if we assume a value of the volumeelectricchargeaveragedensityin a hurricane of PE = 10-5 C m -3and theheight of thenegative charge layer is 1000 m, the value of total negativechargewill be -q•10•ø C. It should betaken imoaccourn that thecharge average value neutralized by one lightningflash is about 30 C and in very stronglightning it can be over 100 C [Chalmers, 1967]. Thus, with a considerable frequency of lightningflashes in powertiffthunderstorms and tropical cyclones, a process of the total electricchargerecovery shouldtake place. The estimates [Schonland,1964; Mar- shall and Rust, 1995] give a value of charge formation velocity in a thunderstorm of average sizeas 1 C min -• km -3[Latham andMason, 1961]. The valuesof electricparameters presented relatedto cloudsystems of tropicalcyclones and hurricanes as well as to thunderstorms which generate a tornado(especially with respect to the electricpotentialgradientand a total electric charge valueof a hurricane) are evidentlyunique phenomena and haveno analogue in natureon the Earth. This circumstance determines the high intensity of elec- tromagnetohydrodynamic effectswhich represent the fun- damentalreasonfor the primary circulationand inten- sification of tropicalcyclones, hurricanes andtornadoes. Consider an electromagnetohydrodynamic (EMHD) mechanism for the example of a developedhurricane and a tornado, not touchingfor the time being upon questions connected with their genesis and the principal difference between them. Figure 2 presems the schematic depictionof the sectionalview of the developedcloud structure cyclonicallyrotating with respectto a vertical axis. This rotatingcloud structure can be the centralpart of a hurricaneor a large tornado. Rotation of concen- trationregions of negative andpositivecharges initiatesa concemric electric current j•, whichin mm induces in the Earth-relatedreferencesystema magnetic field Bi, the lines of force of which are shown in the figure (the directions of currents and magnetic fields in Figures2 and 3 agreewith thoseaccepted in the theoryof electro- 18 16 14 12 10 8 6 4 2 0 H, km Stratosphere . Mature Thundercloud Tropopause •t•-65øC) / ' • + + + + + + + + Negative Screening Layer_ /-+ + + + +-t, ] ' - /- + + + • -• /- + + + + + + + + •1,-.•........,.• Upper Pos'it-ive / + • Charge Region - O • • + + + + + \ R . I o • IE tE ] Negative Charge Layer . 0 ! , ,l, - - , •-U•10 V . E + + E + + + +-•-••-• Sm• 1 Lower Positive • , - • ChaPge Region Corona Charge •"Thi ders•orm Base ! + + + + + + + + + + ,, Ground Figure 1. The structureschemeof a mature thunderstorm. 21562202d, 1997, D12, Downloaded from https://agupubs.onlinelibrary.wiley.com/doi/10.1029/97JD00146, Wiley Online Library on [08/03/2026]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License
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13,574 KRASILNIKOV: ELECTROMAGNETOHYDRODYNAMIC NATUREOFPOWERFUL STORMS magnetism). The magnetic field induction in the areaof negative charge considerably exceeds the corresponding valuein the areaof positivecharge because of the higher concentration of electriccharges in the layer of negative charge. Withinthe bounds of eachlayera magnetic field increases linearly (on the assumption of homogeneity of electricchargedistribution in the layer volume) from a zero value in its middle to maximum values at the upper andlower boundaries of the layer. The distribution of the horizontal component of the magnetic field induction in the vertical directionis shownin Figure 2. Upward and downwardfrom the boundsof eachlayer (in areasI, III, V) the magneticfield inductionshoulddecrease pro- portionally as 1/h (h is the distance measuredfrom a layer bound),but actuallythe magneticfield in these areaswill have greatervaluesthan thosedetermined by this law. The intensive convective electric currents, movingin a spiral trajectoryin areasI, III, and V and havinga verticalcomponent Jh,alsogenerate a magnetic field, thusstrengthening the magnetic field induced by rotatinglayers II and VI. The mechanism of vertical current emergence jh is connected with a very highdegree of eddyflow turbulence. The Reynolds number valuesfor a tornadoand a hurricane(found, e.g., using the layer height of negative chargeor the vortex diameter) are higher than 10 8 and10 •ø,respectively, thus determining an extremely high intensity of turbulence. Theseinten- sivedisturbances carrythe particles with negative charge awayfromthe layerbounds II andVI. Unlike the situ- ation presented in Figure 1, where the whole set of electric charges is in a state of static equilibrium under the action of the vertical electric field and the gravitational field, in this caseonly the charged particles insidelayers II andIV are statically balanced in the verticaldirection. These negatively charged particles movein the areawith the maximum electricalfield strength value, and the ver- tical convective electriccurrentjh is thus generated. The interaction of convective electriccurrents jh andj, with the inducedmagneticfield Bi gives rise to volume electromagnetic forces F,=jhXBi and Fh=j,xBi, the directionsof whichare shownin Figure2. The forceF, is theveryonewhichdetermines theintensive vorticity of tropical cyclones, hurricanes, and tornadoes. It is neces- sary to emphasize that a high intensity of the EMHD mechanism is conditioned by a large value of convection currents jh and j, whicharemanytimesas largeas cur- rent valuesof conduction, diffusion, and precipitation. Thus, the mechanism of current formationjh, as was alreadymentioned, is connected with a removalof the volumes,for example,of the negativelychargedlayer 17 H, km Stratosphere ' Overshooting Top Tropo_••.• ' • V ' Magnetic••Fh••• Positive Charge Re•0n • ••;;;'• •E •jh ' Negative Charge •yer _' Thundercloud Base , .... Ocean or Ground Surface Figure2. The scheme of the sectional view of a developed cyclonically rotating cloudstructure (the central partof a tropical cyclone, a hurricane, or a tornado). Here, thecirclewith a pointdenotes a vectordirected upwardwith respect to the planeof the page,and the circlewith a crossdenotes a vectordirected downward. The distribution of the induced magnetic field Bi (the radialcomponent) is shown. 21562202d, 1997, D12, Downloaded from https://agupubs.onlinelibrary.wiley.com/doi/10.1029/97JD00146, Wiley Online Library on [08/03/2026]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License
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KRASILNIKOV: ELECTROMAGNETOHYDRODYNAMIC NATUREOF POWERFUL STORMS 13,575 containing charged particles.As a result, thesevolumes are acted upon by the vertically directed electric force FE=q-E (q is the total electricchargeof somevolume). The valueof thisforcemightbe very significant. So, for example, nearthe upperandlowerbounds of a negatively charged layerat an altitudeof 6 km with electriccharges ofvolume density pE= 10 -4C m-3atE= 105V m-• there is an actingforceF•.= 10 N per cubicmeterof air whichim- parts toit anacceleration •15 m s -2,and atp•.=10 -3 C m -3 and E-10 s V m 4 theforce F•.=100 N andtheacce- leration is• 150 m s -2.It isobvious that thegiven values of the electric force and the acceleration demonstrate an exclusively importantrole which this force plays in the processes of formation and intensification of tropical cyclones andtornadoes. It is this forceand the forceF, actingup to the Earth surface that form the quick rotating cone or column with very high downward vertical velo- city of a tornadoandintensive rotatingair in a hurricane. The maximum valueof the forceF, occurs in areasbor- deringon the lower andupperboundaries of a negatively chargedlayer, since it is proportionalto the magnetic field induction Bi, volumeelectriccharge densityandver- tical velocityvalue Vh. Estimates showthat the maximum value of the force F, for a developing tropicalcyclone gradually beingtransformed into the stageof a hurricane vanes w•thin thel•m•ts of 10 to 10 N m-3,andfor a tornado from 10 -2to 104 N m -3.Tothese values, depend- ing on differentinitial conditions, correspond the time of tropicalcyclonedevelopment from the initial disturbance to hurricane stage within 5-8 daysand the time of tornado intensification,from severalminutesto dozensof min- utes. The force Fh also plays a considerable role in the for- mationand intensification of tropical cyclonesand tor- nadoes. The actionof this force, causing compression of layers containingelectric charges,in the vertical direc- tion increases the volumeelectriccharge densityp•., that, in ram, resultsin the growth of Bi, F,, F•. and the tangential velocityof eddymotion,and, finally, the force Fh increases again. This process,which is of principal significance,should in the end lead to a considerable increase of electricchargeconcentration in eddy struc- turesof tropicalcyclones, hurricanes, and especially tor- nadoes, which is in close relation with the maximum valuesof velocity of air eddy motion. One more effect mostclearlyconnected with the actionof the force Fh is that in the upperpart of a thunderstorm where a tornado is generated an overshooting top is formed,oftenpro- truding beyond the tropopause. Its size is comparable with the size of a tornado. A similarphenomenon, but of muchlargerscale,accomp- aniesa hurricane whenits upperpart risesbeyondthe tropopause. Rotation and a high degree of turbulence resultin lifting air volumes containing positivelycharged particlesupwardbeyondthe boundsof the positively chargedlayer. Volumes of air in the upward directed electricfield E are transferred upwardunderthe actionof forceFh,formingan overshooting top anda lift-off of the upperpartof a hurricane beyond the tropopause. It shouldbe especiallyemphasized that while speci- fying the decisiverole of the EMHD mechanismin the formationand intensification of tropical cyclonesand tornadoes we do not diminish in any way the role of other processes (hydrodynamic, thermodynamic, heat transfer, water phasechange,etc.). Moreover, we believe that the EMHD mechanism is the missinglink in the chain of processes of energy conversion in a tropical cyclone, a hurricane,and a tornado, without which construction of a logicallysubstantiated and to a large extentadequate model of their formation and intensification has not been possible. No doubt that the processes of genesis,form- ationand intensification of a tropicalcyclone differ from the similar processes resultingin the development of a tornado. The conditions under which their intensification takesplacediffer substantially as well. It is obviousthat the role of the EMHD processes and of this mechanism differsconsiderably in the development of tropicalcy- clones andhurricanesfrom similareffectswith respect to a tornado.Thus we shall discuss separately the action of the EMHD mechanism in the development of tropical cyclones andhurricanes and its actionin the development of tornadoes. 3. Tropical Cyclones and Hurricanes Tropical cyclones,which in their developmentcan build up into destructive tropical stormscalledhurricanes in the Atlantic and typhoonsin the westernpart of the Pacific Ocean, usually emerge out of quite weak dis- mrbances.This problem has inspired much research [e.g., Riehl, 1954, 1979; Malcus and Riehl, 1960; Charney and Eliassen, 1964; McBride, 1981; Gray, 1982; Maxworthy, 1982; Ooyama, 1982; Pearce, 1982; Sheets, 1982; GoMen and Snow, 1991; Molinari at al., 1994]. The main conditions necessary for emergence and development of a tropical cyclone were formulatedby Riehl [ 1954]. As for the EMHD mechanismwhich provides the primary circulation, we can formulate at least three additionalconditions for emergence and intensification of a tropical cyclone. First, it is necessary that the initial cyclonicdisturbance could emergein a powerfulenough cumuluscontaininglayers of chargedparticlesof high volume electric chargedensity. The secondconditionis that the initial cyclonicdisturbance shouldbe localizedin the middle troposphere, at an altitude where the nega- tively charged layer is, sincethis is the very areain which the EMHD mechanism is realized to a maximum. Note that the resultsof observations [e.g., Miller, 1967] con- firm this condition. Third, the initial cyclonic disturb- ance should not be too weak. So, the estimatesbased on the EMHD mechanism for the area of the negatively charged layer show that the initial value of the tangential velocity Vo-5 m s 4 is insufficient fordevelopment of a tropical cyclone. Intensificationof a tropical cyclone from Vo = 10m s 4 to a velocity of 80m s -1 (288kmh-1) takes 16days' the time re•quired toincrease the velocity from 10 ms4'to 20ms-isover 11 days. If the initial velocity Vo=20m s -1,a tropical cyclone will be inten- sified uptothe velocity 80m s -x within 4.6days. Theseadditional conditions are necessary to initiate the EMHD mechanism. Perhaps,the low probabilityof the simultaneous realization of all favorable conditions, includingthe additionalones, explainsthe comparative rarity of tropicalcyclone emergence and development, at 21562202d, 1997, D12, Downloaded from https://agupubs.onlinelibrary.wiley.com/doi/10.1029/97JD00146, Wiley Online Library on [08/03/2026]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License
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13,576 KRASILNIKOV:ELECTROMAGNETOHYDRODYNAMIC NATURE OF POWERFUL STORMS least in comparison with the frequencyof extratropical cyclone formation. However, after the emergenceand initial cyclonicvorticity and EMHD mechanism initiation the factors facilitatingformationof the initial vorticityno longer play any apparentrole. Further, a unique closed cycleof energy conversion beginsdeveloping in a tropical cyclone,providingfor its intensification when the exter- nal conditions do not exert any practical influence on thisprocess. The EMHD mechanism beginsdeveloping in the area of the negatively charged layer, in which the volume electric charge density and the electric field potential gradient are maximum.Here the actionof the forcesF, and Fh resultsin the amplificationof vorticity and its propagation verticallyupwardin the areaof the positively charged layer wherethe EMHD mechanism develops, and the vorticityis amplified as well verticallydownward to the ocean surface.Amplification of the primary circu- lation and action of the centrifugal inertial force, the Coriolis force and the pressure gradientforce will result in pressure reduction in the centralpart of circulation and later in deepening of a tropical cyclone. This, in turn, causes amplification of radial (in the lower layersof the troposphere) and vertical (in the center of a cyclone) flows by the scheme "in-up-out". This process called"the secondary circulation"plays a uniquelyimportantrole in intensification of a tropicalcycloneand a hurricanesince it providesan energy supply to them at the expense of sensible and latent heat of moist air lifted upward from the oceansurface.In the middle troposphere a conside- rable part of this energyis converted to the electricfield energyas a resultof processes of water phasetransition. The electricfield energyvia the EMHD mechanism is convertedto the kinetic energy of eddy motion in the horizontalplane, consistingof the primary circulation, the intensification of which resultsin further deepening of a cyclone, and the secondarycirculation amplification. Intensificationof the secondarycirculation in the end causes a furtherenergyincrease of the electricfield and EMHD mechanism amplification,etc. Continuous repe- tition of these processes results in a constantgain of water mass(in three phases) and air involved in a rotary motionin a tropicalcycloneand alsoin the growthof its size. Finally, the diameterof a tropical cyclonereaches severalhundreds of kilometers;by its height it occupies practicallythe entire depthof troposphere, its upperpart as a resultof Fh forceaction risesup beyondthe tropo- pause. The sequence of these processes in the frame of a closed cycle of energy conversionin the intensifying tropicalcycloneand hurricanemeansthat thesemeteoro- logical systems developto a large extent independently, i.e., practically independent of externalconditions. First of all, it follows from this that a sourceof the primary circulation(the EMHD mechanism) existsand actsinside the very meteorological systems.The assumption about independence of a tropical cyclone and a hurricaneis confirmedby the fact that their development and motion over the ocean ran, as a role, in conditionsof good weather around them (i.e., in the absenceof powerful cloud systemsin the troposphere). Once the EMHD mechanism has developed,the remainingconditionsof principalimportance for tropical cycloneintensification are a sufficiently _hightemperature of the oceansurface (no lessthan26ø-27øC) anda considerably lowerair temperature inflowing over the ocean surfacefrom the peripheryto the centerof a tropical cyclone.However, the latter factorto a large extent is providedby the tro- pical cyclone itself (well-developed already) at the expense of cool air loweringin the rainband zone and the coolingin the samezoneof the air inflowing in the radial directionfrom the cycloneperipheryin the lower tropo- sphere. 4. Tornadoes Tornadoes are the most intensivemeteorological vor- tices, which are always generatedby very powerful thunderstorms. A specificsize of thesethunderstorms in the horizontal direction can exceed 15-20 km and in ver- tical 15-17 km; their upper boundarycan coincidewith the tropopause. Very often the tornadoes accompany hurricanes overflowingto a coast. Incidentsare known when dozens of destructive tornadoes were formed. The problem of tornadoeshas inspired a great deal of research[e.g., Hare, 1837; Vonnegut,1960; Vonnegut and Weyer, 1966; Brook, 1967; Brandes, 1977; Watkins et al., 1978; Fujita, 1981; Davies-Jones, 1982; Klemp and Rotunno, 1982; Maxworthy, 1982; Simpson,1982; Snow,1984, 1987; Goldenand Snow, 1991; Zieglerand MacGorman,1994]. The mostvaluableresults,perhaps, are connectedwith revealing of the conditionswhich determinethe genesisof a tornado. Nonetheless, to date therehasbeenno clearunderstanding of what the proces- ses are that determine the formation and intensification of a tornado.However,it is possible to give an explanation for theseprocesses within the frame of the presented EMHD mechanism but taking into account thosespecial features which distinguish a tornadofrom a tropicalcy- clone. First of all, let us formulate two principally important conditions under which formation and intensification of a tornado is possible. The first condition is connected with the presence of a very powerfulmature thunderstorm occupying in height practically the wholetroposphere up to the tropopause. In such a thunderstorm thereare alreadypowerfulnegatively andpositively charged layerswith a high volumeelectric chargedensityand a maximumvalue of the potential gradient of 105-10 • V m -• which isnecessary forthede- velopmentof the EMHD mechanism. According to the second conditionthe emergence and intensification of a tornado is possible only in the presence of a ratherstronginitial disturbance in the form of vorticity. Here, as observations show, there are two typesof initial vorticity which are usuallyrealizedand whichare shown in Figure3. The first type refersto an intensive initial vorticity with a vertical axis which canbe conditioned, for example,by the actionof a gust front. The second typeof initial vorticityis usually a very inten- sivevortexwith thehorizontal axisrapidlypropagating in the upperor middle troposphere, which, however, later bends andbecomes verticalin the lower troposphere. The emergence of this type of initial vorticity can be con- nected,for example,with a jet stream.These, as well as otherpossible reasons of emergence of a powerfulinitial vorticity, are analyzedin detail in the abovereferenced 21562202d, 1997, D12, Downloaded from https://agupubs.onlinelibrary.wiley.com/doi/10.1029/97JD00146, Wiley Online Library on [08/03/2026]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License
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KRASILNIKOV' ELECTROMAGNETOHYDRODYNAMIC NATURE OF POWERFUL STORMS 13,577 17 + + + ++ + + + + + + + + + + + ++ + + + Stratosphere Overshooting Top Tropopause + + + + + + + + + PositiveChargeRegion + + + + + + + + Horizontal Vortex + + + + + W + + • + Magnetic Lines I E of Force NegativeCharge Layer E Thunderstorm Base Funnel + + + + + + + + + + + + + + + + + + + Ground Figure 3. The schemeof tornado formation. The left side shows formation of a tornado with the vertical axis,andthe fight sidedemonstrates tiltingof an initialhorizontal vortexmovingwith a velocityW into a verticalvortex in the process of tornadoformation (arrowsindicatedirections of vorticity spreading). studies.The changeof the horizontalpositionof the initialvorticityaxisto the final verticalpositionis caused by the fact thatif, for example, a vorticityis propagated in the lower part of a positivelycharged layer, this will lead to a concentration of electriccharges in the vortex periphery layer and to a force actionon the part of the electricfield. The vertical downwardpowerful electric field will inevitablycausea bendingof the vortex axis towardthe ground,and finally the axis will be in vertical positionparallelto the electricfield direction. It is alsonecessary that the initial vorticityin the hori- zontal plane should be localized in the area of the negativelychargedlayer in which the volume electric chargedensityis maximum. Observations confirm that thiscondition is actually realized: "Doppler radarobser- vationshave shownthat the rotationbeginsin the mid- troposphere, at altitudes of four to eightkilometers", and "Doppler radar observations again suggestthat the intensification of spinbegins aloft, at altitudes of several kilometers,and then quickly builds down toward the ground"[Snow, 1984, pp. 60, 61]. The estimate of the role of the initial disturbance in- tensity in theareaof the negatively charged layershows that the time of tornado intensification from the initial tangential velocity Vo=25m s -1 to a velocity V-100 -1 m s is 31min andat Vo-50 ras -1 it decreases to 8 min. The most importantspecialfeatureof the EMHD me- chanismwith respectto tornadoes(as distinct from tro- pical cyclonesand hurricanes)is that the initial rather powerful eddy disturbanceappearsin a very powerful mature thunderstorm in which there are already highly concentrated negatively and positively charged layers. The initial vorticity with a vertical axis in the area of the negatively charged layer causes a considerable increase of electric chargeconcentration (due to the action of the forceFh) in the narrow rotatingannularlayer. Formation and amplificationof the magnetic field Bi and its inter- action with convective currents j, andJh concentrated in the narrowannular zonecause the actionof forcesF, and Fh. The intensive initial vorticity resultsin a sharpinc- reaseof PE for two reasons.First, becauseof the action of the centrifugal inertiaforce, the charged particles are displacedfrom the vortex central part to the periphery annular area, and second, the intensive rotation and the EMHD interaction result in a considerable increase of the force Fh. In addition, a strong initial vorticity and a subsequent much strongerintensiveair rotation with a highdegree of turbulence cause a removalof charged par- ticlesbeyondthe layerscontaining electriccharges in the vertical direction, with the result that they occur in the zone of actionof the strongelectricfield. Here the force F•. can reach very high values.So,if E= 105 V m-1 and p•.=10-3C m-3,F•= 100N m-3,andtheacceleration 21562202d, 1997, D12, Downloaded from https://agupubs.onlinelibrary.wiley.com/doi/10.1029/97JD00146, Wiley Online Library on [08/03/2026]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License
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13,578 KRASILNIKOV: ELECTROMAGNETOHYDRODYNAMIC NATURE OF POWERFUL STORMS given bythe action of this force to 1 m 3of airataltitude 6 kmwill be•150 m s -2.Thus,asa result of theaction of the force F,, the intensiverotatingmotion in the horizontalplane in the area of the negativelycharged layerandbeneath it is transformed undertheaction of the very large force FE into motiondirected to the ground surface with a very high velocity.In thismotion,air with negatively charged particlesmovesalong the downward directedspiral. A large vertical velocity value makesit possibleto transferthe convectivecurrent (negatively charged particles whichin the negatively charged layer at analtitude about 6 kmhavetemperature -15øC) from the negatively charged layer up to the Earth surface.Tereby, the motion of negativelychargedparticlesoccursin the magnetic field Bi and the EMHD mechanism is activeup to the Earth surface. These are the very features of EMHD mechanism action in a tornado which determine the observed maximum values of both horizontal and verticalcomponents of wind velocity in a tornado.Per- haps,it is the transfer in the tornado's rotating periphery zone of the convectiveelectric current up to the Earth's surfacethat causesnumerousobservedspecificeffects, for example, luminous phenomena in nocturnal tornadoes, electricaldischarges inside tornadoes, and a magnetic field [Hare, 1837; Vonnegutand Weyer, 1966; Brook, 1967; Chalmers, 1967; Watkinset al., 1978; Ziegler and MacGorman, 1994]. In the areaof the positivelycharged layerandaboveit a rotatingmotion as a result of actionof the force FE acquires a verticalvelocity component pointedupward. And this is the reasonfor the formationof the rotating overshooting top in the upperpart of a thunderstorm. So, the actionof the EMHD mechanism in the process of tornado intensification results in the formation of a very intensiverotation only in a rather narrow annular zoneof width AR (Figure 3) at the peripheryof a cylin- dricalvolume, occupying in heightalmostthe whole tro- posphere. In the tornado's central part, pressure is stron- gly reduced,andthe air near the Earth surface flows into the lower part of a tornado andrisesupwardin its central part, forminga circulation in the verticalplane.However, for a tornadothis secondary circulation is not of the same significance as it is for a tropicalcyclone,sincea power source feeding the EMHD mechanism andproviding huge kinetic energy of air in a tornado is the electric field energy stored at the expense of accumulatedelectric chargein a thundercloud. In this case there is no con- tinuousand closedenergyconversion process, and a lim- ited (throughvery large, sometimes) storeof energyin a thundercloud determines the comparatively short activity cycleof a tornado,from severalminutesto severalhours. So, an approximate estimate of the power of a tornadoof average intensity gives a value of theorder of 108 kW [Vonnegut,1960], while the energy of a single average thunderstorm cell makes upabout 10 •5J. The process of energyconversion in a tornadocan be presented as follows: the electric field energyof a thun- dercloud via the EMHD mechanism is converted to the kineticenergyof intensive rotary motionanddirectlyto a very intensive verticalair motion. Tornado funnels, as observationsshow, can take the forms of a cylinder (usually very intensiveand long- actingtornadoes), a coneor a very thin vortex. The form of a funnel, perhaps,depends on a characteristic size of the initial disturbance, on the electric field energy of a thundercloud(total accumulated charge) and on the conditionsin the lower troposphere,in particular, on temperature, humidity,and wind velocity. So, in the case of sufficientlyhigh temperature the convectiveelectric currentin the annulararea during motion to the Earth surface will decrease and can disappear if thereis a phase transition of negative electricchargecarders. Obviously, all typesof tornadoes underobservation (from "weak" to "strong" (according to the T.Fujita scale), waterspouts, and dust devils) are of one and the same nature determinedby the EMHD mechanism.Their external distinctions are determined by the above listed reasons and properties of underlyingsurfaces. It shouldbe also notedthat the proposedEMHD mechanism describes not only the cyclonicallyrotating tornadoesbut in equal measure the sometimes observed tornadoes with anti- cyclonic rotation [Goldenand Snow, 1991]. 5. Conclusions 1. Numerous investigations of tropicalcyclones, hurri- canes, andtornadoes cardedout for the last centuryand a half have led to the accumulation of extensive statistical materialabouttheir genesis andintensification. A number of important processes havebeenrevealed whichfacilitate intensification of tropicalcyclones and hurricanes. At the sametime, to date we do not know the processes deter- miningtheheatenergyconversion of the moistair rising up from the oceansurface in the intensivekinetic energy of eddymotion(the primary circulation)of tropicalcyc- lones and hurricanes. Thereis alsono understanding of how the energyof a powerfulthunderstorm is converted at timesto the abnor- mally intensive kinetic energyof air eddy motion in a tornado.Furthermore,in analyzingthe physicalproces- ses causingintensificationof tropical cyclones,hurri- canes, andtornadoes as well as in developing their mathe- maticalmodels,in the overwhelming majorityof investi- gations performed therehasbeenno account of the action of abnormally strongelectricfields relatedwith powerfid cloudstructures of tropicalcyclones and hurricanes, and thunderstorms generating the tornadoes. However, it is theelectric field energy via the EMHD mechanism that is converted to the intensivekinetic energyof eddyair mo- tion (the primary circulation)in tropicalcyclones, hurri- canes,and tornadoes. 2. Basedon the analysis of multiple investigations of electrophysical properties of cloudstructures in the tropo- sphereand multiple data on the genesisand intensifi- cationof tropical cyclones,hurricanes,and tornadoes a description is given of the electromagnetohydrodynamic mechanism which determines formation and intensifica- tion of the primary circulationin theseeddy structures. According to this modelthe heat energyof the moistair uprisingfrom the ocean surfaceis convenedinto the electricfield energy,whichvia the EMHD mechanism is convenedto the kinetic energy of the intensive eddy motion of a tropical cycloneand a hurricane,and the energyof a powerfidthunderstorm is convened as a re- sult of the EMHD mechanism actionto the kinetic energy of intensive rotary air motion in a tornado.Because of 21562202d, 1997, D12, Downloaded from https://agupubs.onlinelibrary.wiley.com/doi/10.1029/97JD00146, Wiley Online Library on [08/03/2026]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License
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