Perturbations of the terrestrial low ionosphere caused by

Perturbations of the terrestrial low ionosphere caused by solar flares Aleksandra Nina Institute of Physics, Belgrade, Serbia

Contents • Ionosphere • Significance of its study • VLF signals – “ionospheric probes” • Belgrade VLF station • Analyze of low ionosphere response to the solar X-flares

Introduction • Terrestrial ionosphere • Methods • This talk: experimental and theoretical research of the perturbations of low ionosphere (D region)

Significance • Science - ionospheric diagnostics - study of physical and chemical processes - detection of different pure natural and man-induced events: 1. processes in the Sun 2. processes in the outer spaces 3. processes in the Earth • Telecommunications • - radio communications, • • - planned networks of mobile communications satellites, - high precision applications of global navigation satellite systems, etc. Earthquakes Lightning Solar flares and CME GRB Vulcan eruptions Nuclear tests Terrestrial Gamma-Ray Flashes

VLF signals – “ionospheric probes” • Numerical programs: LWPC, LWPC Mode. Finder • Advantage: - continual emission - large space that can be analyzed • VLF networks -transmitters -receivers: AWESOME, AWESOME Abs. PAL, Abs. PAL SAVNET, SAVNET AARDDVARK

Belgrade VLF station on Institute of Physics • Abs. Pal - electrical antenna - works as of 2004 - simultaneously records 6 signals • AWESOME (Atmospheric Weather Electromagnetic System for Observation Modeling and Education) - two magnetic loop antennas - works as of 2008 - simultaneously records 15 signals Abs. PAL AWESOME VLF receiver systems at Belgrade station

Solar X-flare perturbations • Theoretical model: Wait’s model of ionosphere: reflection height H’ and sharpness β • Case: Numerical program for simulation VLF signal propagation: -February 18 th, 2011 LWPC (Long-Wave Propagation Capability): -- Recording: Input parameters: β and H’ - Output: ALWPC and PLWPC - GOES-15 satellite AWESOME receiver -- Belgrade Unperturbed ionosphere: - DHO (Germany) transmitter -1 β = 0. 3 km H’=74 km (23. 4 k. Hz) - Perturbed ionosphere: determination of β and H’

Ionospheric response (preliminary results) G(t) – electron gain rate L(t) – electron loss rate Upper half of D region: I - Quasi equilibrium regime P(t) – photo-ionization rate II - Photo-ionization regime R(t) – recombination rate I(t) – radiation flux by satellite III - Recombination regime αeff – effective recombination coefficient Ks – coefficient (dependent on energy interval of data registered by satellite)

Conclusions • The applications of the low ionospheric investigations in science and information technologies • Research of low ionosphere by VLF waves • Presentation of Belgrade VLF station • Experimental and theoretical analyzes of the low ionospheric response to particular solar X-flares - electron concentration - electron gain and electron loss rates (preliminary results)

Perturbers • Solar radiation - regular variation - transient variations • Outer space • Terrestrial SGR 1806 -20 HESSI