Numerical Modelling of VLF Radio Wave Propagation through Earth-Ionosphere Waveguide and its application to Sudden Ionospheric istur!ances Thesis submitted for the degree of octor of Philosoph# (Science% in Ph#sics (Theoretical) of the &niversity of 'alcutta Su(a# Pal Ma#8, )*+, CERTIFICATE FROM THE SUPERVISOR This is to certify that the thesis entitled "Numerical Modelling of VLF Radio Wave Propagation through Earth-Ionosphere waveguide and its application to !udden Ionospheric Distur#ances", submitted by Mr. Sujay Pal who got his name registered on $%&$'&%$(( for the award of Ph.D. )!cience* degree of the Universit, of Calcutta. absolutely based upon his own work under the supervision of Professor !andip K. Cha0ra#arti and that neither this thesis nor any part of it has been submitted for any degree/diploma or any other academic award anywhere before. Prof. !andip K. -ha0ra#arti Senior Professor & Head Department of #strophysics & Cosmology S. N. Bose National Centre for Basic Sciences JD Block, Sector())), Salt *ake, +olkata 7---./, India TO My PARENTS i ABSTRACT Very Low Frequency (VLF) radio waves with frequency in the range 3 30 kHz ∼ propagate within the Earth-ionosphere waveguide (EIWG) for#ed $y the Earth as the %ower $oundary and the %ower ionosphere (50 100 k#) as the upper $oundary ∼ of the waveguide. These waves are generated from #an-#ade transmitters as wel% as fro# lightnings or other natura% sources( *tudy of these waves is very i#portant since they are the only tool to diagnose the %ower ionosphere( Lower part of the Earth+s ionosphere ranging &0 90 km is known as the -- ∼ region of the ionosphere( *olar Lyman-α radiation at '.'./ n# and EUV radiation in 80 '''.& n# are #ain%y responsib%e for for#ing the --region through the ∼ ionization of 123N 23O 2 during day time( The VLF propagation takes p%ace $etween the Earth+s surface and the --region at the day time. -uring the night hours3 the --region disappears and the VLF waves reflect from a #uch higher region in the ionosphere known as the E-region (90 '.0 k#)( The cosmic rays are the on%y ∼ sources for regu%ar ionization of the ionosphere during the night ti#e. As a resu%t3 there is a diurna% (day-night) variation of ionization( nstead of these diurnal 4uctuations, activity on the *un or other Cosmic source can cause dramatic sudden changes to the ionosphere. When energy from solar 4ares or any other distur$ances (e.g.3 "am#a Ray 8ursts) reaches the Earth+s upper at#osphere, the ionization in the ionosphere increases suddenly( Hence, the electron-ion density and the height of the layer change( The ter# *udden Ionospheric -istur$ances (SIDs) is co##on%y app%ied to such pertur$ations which affect the ionosphere in a non-trivial way and the ionosphere takes ti#e (few seconds to severa% #inutes) to recover itself to nor#al condition( In this thesis, we theoretical%y predict the nor#al characteristics of VLF wave propagation through E !" corresponding to nor#a% $ehavior of the D-region iono- sphere. !e took the VLF narrow $and data fro# the receivers of Indian Centre for *pace Physics ( 6*:) to validate our #odel( 6*P-VLF receivers continuously #onitor the equatoria% low %atitude ionosphere through the recording of narrow $and data fro# several nu#$er of VLF transmitters and also the $road$and data for nat- ura% VLF sources( -etection of * -s is co##on to a%% the #easurements. !e app%y our theoretical #odels to infer the --region characteristics and to reproduce the observed VLF signal $ehavior corresponding to such * -s. !e develop a code $ased on ray theory to si#ulate the diurnal $ehavior of VLF signals over short propagation paths (.000 3000 km)( !e app%ied it for the ∼ propagation of VTX ('/.. kHz) transmitter signal over the Indian su$-continent( ii The day-night variation from this code are comparab%e to the variation obtained from a #ore general Long !ave Propagation Capa$i%ity (LWPC) code which is $ased on #ode theory approach( !e app%ied the L!:6 code to #odel the electron density variation in the --region during a <.(0 solar 4are si#u%taneously detected on two VLF paths (VTX-Kolkata and 1!C-Kolkata)( !e >nd that the short VLF path acts as a good detector for such solar distur$ances. !e si#u%ate the observational results obtained during the )ota% *olar Eclipse of Ju%y ..3 200, in India using the L!:6 code. As a >rst order approxi#ation3 the ionospheric parameters were assu#ed to vary according to the degree of solar obscuration on the way to the receivers. !e >nd that an assu#ption of A k# increase of %ower ionospheric height for p%aces going through totality in the propagation path reproduces the observations very wel% at =ath#andu and 7aiganB( !e >nd an increase of the VLF reflection height para#eter $yh � C 3.0 km for the VTX-<alda path andh � C '(/ k# for the VTX-Kolkata path respectively( !e also show the altitude variation of electron nu#$er density throughout the eclipse ti#e at RaiganB( !e report and analyze a historic event3 namely3 the lunar occu%tation of a solar 4are during the annu%ar solar eclipse of '&th January3 2010. !e use the data from a #u%tip%e nu#$er of satel%ite and ground $ased o$servations3 such as the "2ES-1A ($oth hard and soft X-ray light curves)3 "21" :roject (Magnetogram data)3 HIN- 2-E (i#ages of the 4are) RHES* (for X-ray %ight curves and i#age) for analysis of the event( !e extract the ti#e variation of the electron density pro>%e in the --region of the ionosphere due to the occu%ted solar 4are from the co#$ined effect of the eclipse and the 4are. iii ACKNOWLEDGMENTS am very #uch happy to write this page >na%ly at the comp%etion of #y thesis( It is a very pleasant task to express #y heartiest thanks to al% those peop%e who #ade this thesis possi$%e and an unforgetta$%e experience for #e( First of a%%3 would %ike to express #y sincere gratitude to #y thesis advisor Prof( *andip =( Chakrabarti for the continuous support during this research3 for his patience3 great power of #otivation3 enthusiasm and i##ense knowledge. feel proud to have the opportunity of having a supervisor %ike hi#( His guidance helped #e in al% the ti#e of research( would like to thank a%% the academic and non-academic sta9 of the *( 1( Bose National Centre for 8asic *ciences (*18168*) for their support during #y studies( It is great p%easure for #e to work there and could not forget the four years have spent at *18168*( It is great p%easure to thank a%% the co%%eagues and #y friends of *18168*3 Kolkata. wou%d %ike to #ention the name of <r( )ama% Basak3 -r( Hi#adri "hosh3 <r( *udip "arain3 Mr( Kinsuk "iri3 Mr( 5$hijit Chakrabarti for their helpfu% support during Ph(-( days. can not forget the #oments shared with them at *18168*( Most i#portant%y3 wou%d %ike to thank the President3 al% the #em$ers and #y friends of Indian Centre for *pace Physics ( 6*:)( a# attached with 6*: since #y initial days of :h(-( have attended so #any VLF workshops at 6*: and %earnt the detai%s a$out the VLF experi#entals fro# here. The VLF data that have $een used in this thesis are fro# 6*:-VLF network. deep%y appreciate al% the group #em$ers of the 6*P-VLF network for sharing so #any experiences. gratefu%ly acknowledge the assistance of Mr( *udipta *as#al3 Mr( *ushanta Monda%3 <r. -ebashish 8howmick3 <r( *u#an Ray3 Mr( *ourav :alit3 Mr( *urya =( <aji of 6*: during #y :h(-( period( Colla$orative works with them great%y helped #e to carry out this research( wou%d also %ike to thank Dr( Kenneth ?(!( Lynn of Austra%ia and -r. Desanka *ulic of *er$ia for their generous academic help through so#e successfu% discussions. take the opportunity to extend #y heartiest gratitude to al% of #y teachers special%y <r( Gurupada Nandi and <r( Bi#al 1aha for providing constant support and #otivation throughout #y life. !ords are short to express #y gratefu%ness to #y parents3 $rother3 sister and #y close friends for providing #e a great emotiona% support( iv Financial supports for this research were provided $y *18168* and part%y $y the Counci% for *cienti>c and Industrial 7esearch (6* 7) through fe%%owship( Final year of #y thesis work was supported $y <2ES through a grant to 6*:( v PUBLICATIONS IN REFEREED JOURNALS '( :a%it *(3 8asak )(3 <ondal *( =(3 Pal S. and 6hakrabarti *( =(3 D<odeling of the Very Low Frequency (VLF) radio wave signa% profi%e due to solar 4ares using the "EANT4 Monte Car%o si#u%ation coup%ed with ionospheric chem- istry”3 2013, 5t#os. Che#( Phys. Discuss.3 133 6007–6033, doi:'0.&',AJacpd- 13-6007-2013. .( S. Pal3 *( =( Maji and *( =( Chakra$arti3 “First Ever VLF Monitoring of Lunar Occu%tation of a *olar Flare during the 2010 Annu%ar *olar Eclipse and its effects on the --region Electron -ensity Profi%e”, 201.3 :lanetary and *pace *cience, doi:'0.101FJB(pss.201.(08.0'F( 3. *( =( 6hakrabarti, S. Pal3 *( *asmal et a%(3 “VLF campaign during the total eclipse of .2nd Ju%y3 .00,I 2$servations and interpretations”3 20'.3 Journal of 5t#ospheric and *olar-)errestria% :hysics, httpIJ/d@(doi(org/10('016JB(jastp(.012(06.00F( A( S.