Formation and Behavior of Es Layers Under the Influence of AGWs Evolving in a Horizontal Shear Flow

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Godfrey Lester
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1 Formatio ad Behavior of Es Layers Uder the Ifluece of AGWs Evolvig i a Horizotal Shear Flow Goderdzi G. Didebulidze 1, Giorgi Dalaishvili 1, Leva Lomidze 1,2 ad Giorgi Matiashvili 1 1 E. Kharadze Abastumai Astrophysical Observatory at Ilia State Uiversity; K. Choloashvili Ave 3/5; Tbilisi 0162; GEORGIA 2 Ceter for Atmospheric ad Space Scieces, Utah State Uiversity, Loga, USA ABSTRACT The formatio of mid-latitude sporadic E (Es) layer uder the ifluece of atmospheric gravity waves (AGWs), evolvig i the bacgroud horizotal wid with a horizotal liear shear (horizotal shear flow),is studied.the AGWs, which are i-situ excited i the horizotal shear flow, iteract with metallic ios through io-eutral collisios ad Loretz forcig, ifluece the io vertical motio ad lead to their covergece ito thi horizotal layers. I order to ivestigate the formatio of sporadic E, 2-D umerical simulatios are performed ad temporal evolutio of multilayered sporadic E is demostrated. It is foud that io/electro desity of Es layer depeds o the directio of bacgroud wid ad o the value of shear parameter. The icrease of the shear parameter value of the cycloic type shear icreases desity of coverged charged particles. It is show that the io/electro desity of Es layers also depeds o the horizotal ad vertical amplitudes of AGWs velocity perturbatios, ad spatial locatio of the layers is determied by the vertical wavelegth of atmospheric gravity waves. 1. INTRODUCTION The ioosphere sporadic E (Es layer) mostly are formed i the lower thermosphere. At this altitude, the behavior of the eutrals plays a importat role i the dyamics of the ios/electros [Kelley, 2009; Hultqvistet, et al., 2011]. It is assumed that the formatio of the mid-latitude Es is a result of eutral-io collisios ad Loretz force actig o the ios [Axford, 1963; Whitehead, 1989 ad refereces therei]. I the case of horizotal eutral wid, with vertical shear, the thi layer of coverged ios could occur i the viciity of the horizotal plae where wid velocity chages directio (zero wid-odes). Above metioed mechaism of Es formatio is ow as the widshear theory [Mathews, 1998 ad refereces therei; Haldoupis, 2012 ad refereces therei]. Appearace of ihomogeeous wid could be related to various dyamical processes i the lower thermosphere, the tidal motio is oe of the most importat pheomea at this regio. Atmospheric waves, such as plaetary waves, tidal motio, gravity waves ad the vortical perturbatios with same spatial scale [Chimoas, 1971; Shalimov ad Haldoupis, 2002; Arras, et al., 2009; Didebulidze ad Lomidze, 2008; 2010] could also ifluece the Es formatio. I the preseted wor we show that AGWs, excited i horizotal shear flow could lead to the formatio of Es. Icrease of shear parameter of the horizotal wid causes icrease i the AGW amplitudes ad trasformatio AGW ito the short-period oscilatios occurs ad velocity amplitude icreases sigificatly i vertical directio. I this case, cycloic type shear also causes the ios horizotal covergece, i additio high amplitude AGWs cause horizotal ad vertical 1

2 covergece of the ios at the odes of velocity perturbatios ad these circumstaces could lead to the formatio of sporadic E. I this case the formatio of sporadic Es movig dowward, the process importat for the quasiperiodic echoes, ad at certai meridioal locatios the formatio of almost horizotal thi layers is possible. The distace betwee these thi layers is approximately equal to the vertical wavelegth of AGWs. 2. SPORADIC E FORMATION AND EVOLUTION UNDER THE INFLUENCE OF AGW We cosider horizotal ( v i ) ad vertical ( w i ) drift of ios, whe eutrals velocity is composed of bacgroud horizotal wid velocity -u 0 a velocity perturbatio v produced by atmospheric waves i.e.: V Here u. (1) 0 v u, v, w are the horizotal x, y ad the vertical z compoets of perturbed velocity v ( u, v, w ), respectively. We assume that, horizotal (x) bacgroud wid velocity u 0 has liear shear i horizotal y directio: u o ( y) ay. (2) I our case velocity perturbatio v ( u, v, w ), correspods to the AGWs evolvig i the horizotal shear flow, Eq.(2). I order to ivestigated the formatio ad behavior of sporadic E iflueced by AGWs, evolvig i the horizotal shear flow, we have solved, equatio of cotiuity for ios/electros i the two dimesioal case (i.e., 0 ). The ios (maily Fe + ) horizotal ad vertical drift velocities are y z determied by their ambipolar diffusio ad by eutral velocities which are modified by AGWs evolvig i the shear flow [Didebulidze ad Lomidze, 2010]: I order to study ifluece of bacgroud shear flow ad ifluece of AGWs, evolvig i this shear flow, o the io/electro covergece process, as the first step we study behaviour of io/electro desity distributio uder ifluece of oly ambipolar diffusio ad the we ivestigate evolutio of io/electro desity uder ifluece of both factors-diffusio ad AGWs. I upper pael of Fig. 1 is demostrated that due to the ambibolar diffusio, the maximal desity of ios (10 4 cm -3 ) decreases ad becomes approximately half of iitial maximum after 1.8 hour. However, i this case the locatio of desity maximum does ot chage sigificatly. Presece of AGW chages process of evolutio of io/electro desity height distributio sigificatly. Bottom pael of Fig. 1 shows that AGWs, described o middle pael of Fig. 1, sigificatly iflueces height distributio of io/electro desity. I this case io/electro desity height distributio resembles quasi-periodic echoes (Hysell, et al., 2013 ad refereces therei). AGWs lead to the formatio of the thi layers, movig dowwards, i the viciity of iitial maximum ad the locatio of iitial desity maximum. Here we see that, durig 0.5 h, i the regio m Es type layers are formed. Tthe distace betwee these layers coicides with vertical wavelegth of AGW (12 m). I these layers, the io/electro desity is higher tha iitial maximal desity ad higher tha desity i the case whe desity chages uder ifluece of 2

3 oly ambipolar diffusio (upper pael Fig. 1). After certai time AGWs could lead to formatio of multilayered sporadic E. Figure 1. Upper pael shows evolutio of io/electro iitial distributio (Gaussia type distributio with maximum at height 100 m ad half width 16 m), i the lower thermosphere, uder ifluece of oly ambipolar diffusio. Middle pael represets time depedece of spatial Fourier harmoics (SFH) amplitudes of AGW velocity perturbatio compoets u, v u v (dashed lie ), ad w (solid lie), the bottom pael demostrates evolutio of io/electro desity i the case of presece of AGW ad diffusio without bacgroud wid ( u 0 i Eq. 1). Vertical wavelegth z 12 m ad horizotal wavelegths x y 120m. o 3

Figure 2. Upper pael show evolutio of the spatial Fourier amplitudes t u t (dashed lie), v t (dotted lie) ad w (solid lie) eutrals velocity perturbatios associated with AGWs.

4 Figure 2. Upper pael show evolutio of the spatial Fourier amplitudes t u t (dashed lie), v t (dotted lie) ad w (solid lie) eutrals velocity perturbatios associated with AGWs. Two cases are demostrated- left colum a) correspods to cycloe type shear of bacgroud wid velocity 4 1 a s (ad right colum b) demostrates case of aticycloe type shear. Sapshots illustrate behavior multilayered sporadic E uder ifluece of AGWs (show o upper paels). Middle sapshots correspod to meridioal coordiate y=65 m ad bottom paels demostrate case of meridial locatio y=115 m. Wave parameters are same as i Fig. 1 4

5 Figure 2 shows formatio of multilayered sporadic E after hours. The distace betwee these layers is about 12 m i our case ad maximal values of desity, which is more tha occurs at altitudes m. The electro/io desity i the coverged regios is higher tha iitial, maximal desity ad the desity i the regios evolved oly uder ifluece of the bacgroud shear flow. The above metioed layer are formed i the case of cycloe type bacgroud wid as well as i the case of aticycloe type shear flow. However, i the case of the cycloe type bacgroud wid the electro desity i the coverged regio is larger tha i the case of aticycloe type bacgroud wid. It is importat to ote that, i the case of cycloe typebacgroud wid, thi layer of coverged ios/lectros (sapshots i the left colum), at meridioal coordiates y=65 m ad y=115 m, move dowwards with lower velocitye tha thelayers of coverged charged particle at same emridioal locatio i the case of aticycloe bacgroud wid (sapshots i the right colum). As we see, icrease of cycloe type shear, attime iterval whe alog with covergece icreases amplitudes of horizotal ad vertival compoets of velocity perturbatios caused by AGWS, the additioal icrease of io/electro desity i the thi layers occurs. The chage of dowward motio of Es formed at certai meridioal regio, due to the chage AGW amplitudes at these regios ad uder ifluece of AGWs chages of evolutio of ios drift velocity horizotal ad vertical compoet. 3. CONCLUSIONS We have show that AGWs, evolvig i the horizotal shear flow, ca form midlatitude ighttime multilayered sporadic E. Existece of horizotal shear flow with cycloe type shear flow could lead to the horizotal covergece of the ios. Desity of the ios i the coverged regio icreases with icrease of shear a of the bacgroud horizotal wid. Such, horizotal covergece of ios/electros could help to formatio of thi, horizotal layers of electros/ios i the lower thermosphere uder ifluece of AGWs evolvig i the bacgroud shear flow. With icrease of shear parameter a, of the cycloe type shear flow leads to the icrease of amplitudes of horizotal ad vertical compoets, of the eutral velocity perturbatios associated with AGWs. I tur, eutrals motio (velocity) iflueces drift of the heavy, metallic ios ad cause their covergece i the thi horizotal layers. Distace betwee these locatios layers is approximately equal to the vertical wavelegth of AGW. We demostrated possibility of formatio, thi, horizotal sporadic E layers uder ifluece of AGWs evolvig i the horizotal shear flow. ACKNOWLEDGEMENTS This wor has bee supported by Shota Rustaveli Natioal Sciece Foudatio grats No 31/81 ad No 13/09. 5

6 REFERENCES Arras, C., Jacobi, C., Wicert, J. (2009). Semidiural tidal sigature i sporadic E occurrece rates derived from GPS radio occultatio measuremets at higher midlatitudes. Aales Geophysicae, 27, Axford,W.I., (1963). The formatio ad vertical movemet of dese ioized layers i the ioosphere., Joural of Geophysical Research 68, Chimoas, G. (1971). Ehacemet of sporadic-e by horizotal trasport withi the layer, Joural of GeophysicalResearch 76, Didebulidze,G.G. & Lomidze, L.N. (2008). The formatio of sporadic E layers by a vortical perturbatio excited i the horizotal wid shear flow, Aales Geophysicae, 26, Didebulidze, G. G. & Lomidze,L. N. (2010). Double atmospheric gravity wave frequecy oscillatios of sporadic E formed i a horizotal shear flow. Physics Letters A, 374(7), Haldoupis, C.,2012. Midlatitude Sporadic E. A Typical Paradigmof Atmosphere-Ioosphere Couplig, Space Sciece Review 168, Hultqvist, B., Abdu, M. A., Pacheva, D., Bhattacharyya, A. (Eds.), (2011). IAGA Special Sopro Boo Series, Aeroomy of the Earth s Atmosphere ad Ioosphere, Spriger Publisher. Hysell, D. L.,Nossa, E.,Aveiro, H. C.,Larse, M. F.,Muro, J., Sulzer, M. P.,Gozález,S. A. (2013). Fie structure i midlatitude sporadic E layers, Joural of Atmospheric ad Solar-Terrestrial Physics, 103, Kelley,M.C. (2009). The Earth s Ioosphere: Plasma Physics ad Electrodyamics, 2d ed. Academic Press, SaDiego. Mathews, J. D., Sporadic E: curret views ad recet progress, Joural of Atmospheric ad Solar-Terrestrial Physics, 60, Shalimov, S., ad Haldoupis, C. (2002). A model of mid-latitude E-regio plasma covergece iside a plaetary wave cycloic vortex, AalesGeophysicae, 20, Whitehead, J. D., (1989). Recet wor o mid-latitude ad equatorial sporadic-e. Joural of Atmospheric ad Terrestrial Physics, 51,

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