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Survey of Conditions for Artificial Aurora Experiments at EISCAT

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Survey of Conditions for Artificial Aurora Experiments at EISCAT Tsuda et al. Earth, Planets and Space (2018) 70:40 https://doi.org/10.1186/s40623-018-0805-9 TECHNICAL REPORT Open Access Survey of conditions for artifcial aurora experiments at EISCAT Tromsø using dynasonde data T. T. Tsuda1* , M. T. Rietveld2,3, M. J. Kosch4,5,6, S. Oyama7,8, K. Hosokawa1, S. Nozawa7, T. Kawabata7, A. Mizuno7 and Y. Ogawa8,9 Abstract We report a brief survey on conditions for artifcial aurora optical experiments in F region heating with O-mode at the EISCAT Tromsø site using dynasonde data from 2000 to 2017. The results obtained in our survey indicate the follow- ing: The possible conditions for conducting artifcial aurora experiments are concentrated in twilight hours in both evening and morning, compared with late-night hours; the possible conditions appear in fall, winter, and spring, while there is no chance in summer, and the month-to-month variation among fall, winter, and spring is not clear. The year- to-year variation is well correlated with the solar cycle, and experiments during the solar minimum would be almost hopeless. These fndings are useful for planning future artifcial aurora optical experiments. Keywords: Artifcial aurora, Ionospheric heating, EISCAT, Tromsø, Dynasonde Background heating experiments with O-mode polarization during Many researchers have been working on ionospheric nighttime to detect optical emissions in artifcial auro- heating experiments using high frequency (HF) radio ras (e.g., Gustavsson et al. 2005; Bryers et al. 2013; Kosch waves to understand phenomenon such as the interac- et al. 2014a, b; Blagoveshchenskaya et al. 2014). Tese tion processes between radio waves and plasma particles, published papers are obviously based on successful heat- which is an essential part of plasma physics. A detailed ing experiments. On the other hand, a large number of overview on ionospheric heating experiments can be experiments might not have been successful, and they found in Kosch et al. (2007), Leyser and Wong (2009). were never published. Tere are several types of ionospheric heating experi- A main cause of such unsuccessful experiments would ments, but here we focus on artifcial aurora experiments be due to the ionospheric condition, which is not under using F region heating with the ordinary mode (O-mode) the control of researchers. Note that another important at the European Incoherent SCATter (EISCAT) heating factor would be the weather condition that limits opti- facility (Rietveld et al. 1993, 2016), to assist in the plan- cal observations, but we do not consider weather con- ning of such experiments in the future. ditions in the present study for simplicity. To be more Te EISCAT heating facility is one of several powerful precise, O-mode heating can only be induced at a condi- tools for such ionospheric heating experiments, which tion where the radio frequency of transmitted HF waves is a high-power HF transmitter system at the EISCAT is slightly lower than the maximum plasma frequency in Tromsø site (69.6°N, 19.2°E). Using the EISCAT heat- the heating region. Hence, if the radio frequency is higher ing system, many researchers have performed F region than the F region critical frequency in O-mode heating ( foF2), the HF waves cannot induce any plasma reso- nance in the ionosphere. In the case of the EISCAT heat- *Correspondence: [email protected] ing system, the minimum radio frequency is ∼4 MHz. 1 Department of Computer and Network Engineering, The University foF2 of Electro-Communications (UEC), Chofu, Japan Ten, of at least 4 MHz during nighttime is needed Full list of author information is available at the end of the article for successful artifcial aurora experiments. © The Author(s) 2018. This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. Tsuda et al. Earth, Planets and Space (2018) 70:40 Page 2 of 11 a 12 10 8 6 (MHz) 2 F o 4 f 2 0 00:00 06:00 12:00 18:00 00:00 19 Oct 2012 19 Oct 2012 19 Oct 2012 19 Oct 2012 20 Oct 2012 b 4 3 2 SD (MHz) 2 F o 1 f 0 00:00 06:00 12:00 18:00 00:00 19 Oct 2012 19 Oct 2012 19 Oct 2012 19 Oct 2012 20 Oct 2012 c ) 150 s e e r g 100 e d ( A 50 Z S 0 00:00 06:00 12:00 18:00 00:00 19 Oct 2012 19 Oct 2012 19 Oct 2012 19 Oct 2012 20 Oct 2012 d ) s 40 t n u o 30 c ( s 20 t n i o p 10 a t a 0 D 00:00 06:00 12:00 18:00 00:00 19 Oct 2012 19 Oct 2012 19 Oct 2012 19 Oct 2012 20 Oct 2012 Fig. 1 a Variation in foF2 on October 19, 2012. The black horizontal line corresponds to the threshold, i.e., 4 MHz. The shorter horizontal lines repre- sent the averaged values for each hour. b Variation in one standard deviation (SD) of foF2 for each hour. The black horizontal line corresponds to the threshold, i.e., 0.5 MHz. c Variation in the solar zenith angle (SZA). The black horizontal line corresponds to the threshold, i.e., 96°. The shorter hori- zontal lines represent the minimum values for each hour. d Variation in the number of foF2 data for each hour. The black horizontal line corresponds to the threshold, i.e., 5. Each value, which satisfed each threshold, is shown in blue, otherwise in gray. When all the four thresholds were satisfed at the same time, the values at that time are marked in red. Note that the time is written in UT (= LT 1 h (for winter time), at Tromsø) − Here, a vital question is when can such a condition would be relatively well known, observationally as well be satisfed. Tere are many publications on foF2 varia- as theoretically. However, this knowledge is not directly tion or F region electron density variation (e.g., Cai et al. relevant to conditions for artifcial aurora experiments 2007), and basic features of F region electron density because of missing information on the relationship Tsuda et al. Earth, Planets and Space (2018) 70:40 Page 3 of 11 a 12 10 8 6 (MHz) 2 F o 4 f 2 0 00:00 06:00 12:00 18:00 00:00 04 Mar 2017 04 Mar 2017 04 Mar 2017 04 Mar 2017 05 Mar 2017 b 4 3 2 SD (MHz) 2 F o 1 f 0 00:00 06:00 12:00 18:00 00:00 04 Mar 2017 04 Mar 2017 04 Mar 2017 04 Mar 2017 05 Mar 2017 c ) 150 s e e r g 100 e d ( A 50 Z S 0 00:00 06:00 12:00 18:00 00:00 04 Mar 2017 04 Mar 2017 04 Mar 2017 04 Mar 2017 05 Mar 2017 d ) s 40 t n u o 30 c ( s 20 t n i o p 10 a t a 0 D 00:00 06:00 12:00 18:00 00:00 04 Mar 2017 04 Mar 2017 04 Mar 2017 04 Mar 2017 05 Mar 2017 Fig. 2 Same as Fig. 1, but on March 4, 2017 between F region electron density (or foF2) and night- statistical dataset obtained by the dynasonde (Rietveld time hours [or solar zenith angle (SZA)], and it is not et al. 2008) at the EISCAT Tromsø site. much useful to answer the question. Several researchers may be able to answer the question based on their valu- Methods able experience in such experiments. However, there is For a statistical survey, we accumulated foF2 data from no investigation on this issue based on statistical data. To 2000 to 2017 (precisely to 06:06 UT on October 11, 2017), clarify this issue, in the present paper, we briefy report obtained by the dynasonde at the EISCAT Tromsø site on our survey for artifcial aurora experiments using a (69.6°N, 19.2°E). A sounding was made typically every Tsuda et al. Earth, Planets and Space (2018) 70:40 Page 4 of 11 a 24 2000 18 12 UT 6 0 01 Jan 01 Apr 01 Jul 01 Oct 01 Jan 24 b 2001 18 12 UT 6 0 01 Jan 01 Apr 01 Jul 01 Oct 01 Jan c 24 2002 18 12 UT 6 0 01 Jan 01 Apr 01 Jul 01 Oct 01 Jan d 24 2003 18 12 UT 6 0 01 Jan 01 Apr 01 Jul 01 Oct 01 Jan e 24 2004 18 12 UT 6 0 01 Jan 01 Apr 01 Jul 01 Oct 01 Jan f 24 2005 18 12 UT 6 0 01 Jan 01 Apr 01 Jul 01 Oct 01 Jan Fig. 3 Variations in possible UT-date for conducting artifcial aurora experiments from 2000 to 2005 (from a to f). The red region indicates periods under the possible condition, and the gray region indicates periods under the impossible condition. The white region corresponds to periods when there are no data. The solar zenith angle (SZA) of 96° is described by the black curve. Note that LT UT 1 h (for winter time), at Tromsø = + 6 min before February 2012, and every 2 min since then.
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