Very low frequency EM wave studies of transient luminous events in the lower ionosphere

Abstract

First of all, I would like to express my gratitude to my supervisor, Christos Haldoupis, for his guidance with my thesis work during my three and a half years at the University of Crete. We shared many hours of stimulating discussions which have also provided me with new ways of looking at scientific problems. I am also very thankful for his hospitality and kindness which made my stay on Crete even more enjoyable. I thank to the Physics Department of the University of Crete and my professors for the graduate courses which enriched my knowledge, and also for generously placing at my disposal the facilities needed for my work. I also thank to the computer centre personnel who provided me with continuous help and support. My PhD studies were sponsored by the CAL (Coupling of Atmospheric Layers) network, under the European Union Research Training Network contract HPRN-CT-2002-00216. I wish to thankTorsten Neubert, the PI of the network for his scientific leadership in this project which benefited everyone, including myself. CAL provided me with the opportunity to obtain high quality research training and a PhD degree, while also having made my attendance of a number of memorable meetings and conferences possible. Working together with the CAL young scientists during the long sprite-watch nights and writing joint publications added a lot to my abilities to work as a member of a team. I wish to thank in particular to Oscar A. van der Velde for our inspiring discussions and collaboration which resulted in some joint publications. Umran S. Inan, our collaborator from Stanford University, advised me all along the way and provided me with lots of discussions which have enriched my knowledge significantly. Craig J.Rodger from the University of Otago has never gotten tired of helping me to improve my understanding of the field. János Lichtenberger from the Eötvös Loránd University clarified many of the technical issues behind VLF measurements to me and guided me in setting up the OmniPAL VLF receiver. David Nunn from the University of Southampton guided my efforts to model VLF scattering. Robert A. Marshall from Stanford University has never run out of patience to answer my numerous requests for help with our Stanford receiver and VLF data analysis. Tilmann Bösinger has helped me a lot with both scientific and personal matters, and I am greatly indebted to him for having made my attendance of the 2 nd VERSIM meeting in Sodankylä, Finland, possible. Sergei S. Shalimov provided guidance with some parts of my work and fruitful scientific advice. Many special thanks go to René J. Steiner who introduced me to emacs and L A T E X, saving me a huge amount of time and fuming when writing up my thesis.Last, but not least, I thank to my family for their love and support on which I could always count.

Thunderstorms, Lightning, Sprites and Magnetospheric Whistler-Mode Radio Waves

“…The sprite related VLF waves had long recovery times (~ 30 -300 s), which suggests spatially extended and diffuse regions of electron density increases at altitudes higher than 75 km. This agrees with the theoretical prediction of air breakdown in the upper D-region during sprite occurrence triggered by strong quasi-static electric fields Mika (2007). has discussed experimental data in which the incident VLF transmitter signal seems to be scattered from horizontally extended diffuse regions of electron density enhancements, most likely associated with halos or diffuse regions of the upper part of carrot sprites, rather than small scale streamers observed at lower altitudes.…”

Recent Results from Studies of Electric Discharges in the Mesosphere

“…Good agreement with the observed recovery times of 20 to 250 s was obtained assuming electron density increases at altitudes of 75 to 85 km by factors from 10 2 to 10 4 times the unperturbed densities. This, in addition to the strong forward scattering pattern observed in relation to the VLF events recorded on Crete, leads to the conclusion that the incident VLF transmitter signals underwent scattering from horizontally extended diffuse regions of electron density enhancements, most likely associated with halos or the diffuse region of the upper part of carrot sprites, rather than small-scale streamers observed at lower altitudes (Mika 2007).…”

A Study of Early/Slow VLF Perturbations Observed at Agra, India

“…Haldoupis et al (2006) reported a new category of early VLF, namely "early/slow" events having the longer onset duration, of < 100 ms to couples of seconds, with similar signatures of recovery. Mika (2007) have done the detailed work on these events. Mika and Haldoupis (2008) from EuroSprite-2003 campaign data show that there is one-to-one correlation between sprite and early/fast events.…”