Title Promjene u Zemljinoj termosferi tijekom geomagnetskih poremećaja u završnoj fazi 23. Sunčevog ciklusa Title (english) Changes in the Earth ' s Thermosphere during geomagnetic disturbances in the declining phase of Solar cycle No.23 Author Karmen Martinić Mentor Giuliana Verbanac (mentor)Committee member Giuliana Verbanac (predsjednik povjerenstva)Committee member Ivana Herceg Bulić (član povjerenstva)Committee member Ivica Sović (član povjerenstva)Committee member Maja Telišman Prtenjak (član povjerenstva)Committee member Snježana Markušić (član povjerenstva)Granter University of Zagreb Defense date and country 2020-07-16, Croatia Scientific / art field, NATURAL SCIENCES Abstract Kako bismo ispitali odgovor termosfere na pojačanu geomagnetsku aktivnost koja je posljedica brzih struja Sunčevog vjetra (engl. high-speed streams, HSS) i dodatno ga proučili, primijenjena je metoda poprečne korelacije. Promatrani vremenski period obuhvaća 100 dana u završnoj fazi 23. Sunčevog ciklusa; preciznije od 25. sijecnja do 5. svibnja 2005. godine. Poremećaji u geomagnetskom polju su iskazani trima geomagnetskim indeksima AE, ap i Dst. Korišteni su podaci neutralne gustoće termosfere duž putanje GRACE satelita normalizirani na visinu od 490 km. U cilju proučavanja odgovora dnevne i noćne strane termosfere na pojačanu geomagnetsku aktivnost, podaci su podijeljeni s obzirom na lokalno vrijeme (engl. skraćenica LT) u dvije skupine: LT=8-16 h i LT=20-4 h. Kako bismo eventualno uočili i kvantitativno opisali globalnu preraspodjelu energije podaci su podijeljeni s obzirom na latitudu, na tri pojasa: pojas visokih, srednjih i niskih latituda. Neovisno o LT-u i promatranom latitudinalnom pojasu najveća korelacija je izračunata za indeks Dst, a najmanja za indeks ap. Također, veće su korelacije dobivene za noćnu nego za dnevnu situaciju. Svi izračunati vremenski posmaci su pozitivni što ukazuje na to da ekspanzija termosfere nastaje kao posljedica povećane konvekcije plazme te povećanja Jouleove topline u polarnim predjelima za vrijeme pojačane geomagnetske aktivnosti. Za dnevnu situaciju vremenski posmaci su najmanji za korelaciju geomagnetskih indeksa i gustoće visokog latitudinalnog pojasa, a najveći za korelaciju geomagnetskih indeksa i gustoće niskog latitudinalnog pojasa što ukazuje na postojanje mehanizma globalne preraspodjele energije. S druge strane, vremenski posmaci za noćnu situaciju za srednji latitudinalni pojas su veći nego za niski pa ne možemo donositi zaključke o fenomenu premještanja poremećaja od polova prema ekvatoru. U skladu s time, zabilježeni putujući atmosferski poremećaji (engl. skraćenica TADs) su znatno vidljiviji na dnevnoj strani, a procijenjena brzina propagacije iznosi 700 m/s. Ovaj rad doprinosi boljem razumijevanju odaziva Zemljine termosfere na promjene u interplanetarnom prostoru, predikciji svemirskog vremena te poboljšanju postojećih modela termosfere i ionosfere.
Abstract (english) In order to confirm and further examine the correlation between increased geomagnetic activity induced by Solar wind high-speed stream events (HSS), the crosscorrelation method was performed. The focus was on the period between 25th of January 2005. and 5th of May 2005., which is a declining phase of the solar cycle No 23. Magnetic field disturbances were represented by three geomagnetic indices AE, ap and Dst. Furthermore, to represent the response of the thermosphere we used densities derived from the accelerometer measurements on the GRACE satellite, normalised to an average altitude of 490 km. To distinguish the differences in response to the increased geomagnetic activity between day-side and night-side thermosphere, the data was divided into two groups depending on their local time (LT): LT=8-16 h and LT=20-4 h. Moreover, the data was divided into three groups according to their geodetic latitudes: high, medium and low latitude range to eventually detect and quantitatively describe global energy redistribution, from a source in the polar region to the near equator region. The analysis showed the greatest correlation for Dst geomagnetic index and smallest correlation for ap geomagnetic index, regardless the LT and latitudinal range. Also, the greater correlation was calculated between the indices and the densities for night-side thermosphere then for the day-side thermosphere. Time lags calculated from cross-correlation analysis are positive for all correlation taken into consideration, which confirms our expectations. The thermospheric expansion is a result of enhanced plasma convection and great energy input of the Joule heating near the polar latitudes in times of increased geomagnetic activity. Furthermore, time lags for the day-side situation are the smallest for high latitude range and the greatest for the low latitude range, which suggests the existence of equatorward transport of density disturbances. Diversely, greater time lags are calculated for medium latitude range then for low latitude range for the night-side. Therefore, observed travelling atmospheric disturbances (TADs) are more distinct on the day-side, with the average propagation speed of 700 m/s. This study contributes to the better understanding of Earth’s thermospheric responce to changes in the interplanety space, aims towards improved space weather predictions and more accurate thermospheic-inospeheric models.
Keywords
geomagnetska aktivnost
metoda poprečne korelacije
Jouleova toplina
termosfera
putujući atmosferski poremećaji
Keywords (english)
increased geomagnetic activity
cross-correlation method
Joule heating
thermosphere
travelling atmospheric disturbances
Language croatian URN:NBN urn:nbn:hr:217:534939 Study programme Title: Graduate university study pf Physics - Geophysics; specializations in: Seismology and Physics of the Earth's Interior, Meteorology and Physical Oceanography Type of resource Text File origin Born digital Access conditions Open access Terms of use Created on 2020-07-24 09:29:13
