Survey of conditions for artificial aurora experiments by the second electron gyro-harmonic at EISCAT Tromsø using dynasonde data

Survey of conditions for artificial aurora experiments by the second electron gyro-harmonic at... We report a brief survey of matching conditions for artificial aurora optical experiments utilizing the second electron gyro-harmonic (2.7-MHz frequency) in F region heating with O-mode at the EISCAT Tromsø site using dynasonde data from 2000 to 2017. Our survey indicates the following: The possible conditions for successful artificial aurora experi- ments are concentrated on 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 so clear; the year-to-year variation is well correlated with the solar activity. These characteristics in the case of 2.7-MHz frequency are basically similar to those previously reported in the case of 4-MHz frequency. However, the number of days meeting the possible condition in the case of 2.7-MHz frequency is obvi- ously large, compared with that in the case of 4-MHz frequency. In particular, unlike the 4-MHz frequency operation, the 2.7-MHz frequency operation can provide many chances for successful artificial aurora experiments even during the solar minimum. Keywords: Artificial aurora, Ionospheric heating, Second electron gyro-harmonic, EISCAT , Tromsø, Dynasonde some of heating experiments were successful (e.g., Gus- Background tavsson et  al. 2005; Bryers et  al. 2013; Kosch et  al. 2005, A large number of ionospheric heating experiments using 2007b, 2009, 2014a, b; Blagoveshchenskaya et  al. 2015), high-frequency (HF) radio waves have been performed but the others were unsuccessful. Thus, it is vitally impor - by many researchers. A detailed overview on iono- tant to understand when such successful conditions are spheric heating experiments can be found in, e.g., Kosch likely satisfied for planning heating experiments in cam - et  al. (2007a) and Leyser and Wong (2009). There are paigns. However, such surveys are not sufficiently carried restrictions for successful heating experiments. A main out. restriction in artificial aurora experiments is that the ion - Using observational data obtained by the dynasonde ospheric peak density drops below the lowest heater fre- (Rietveld et al. 2008) at the European Incoherent SCAT- quency too quickly after sunset. The weather condition is ter (EISCAT) Tromsø site, Tsuda et al. (2018) carried out another important factor affecting the optical observa - the first survey for artificial aurora experiments using F tions, but we do not treat the weather condition in the region heating with the ordinary mode (O-mode) by the present study for simplicity. Due to such restrictions, EISCAT heating facility (Rietveld et  al. 1993, 2016). In their survey, one of the required conditions for success- *Correspondence: takuo.tsuda@uec.ac.jp ful or possible artificial aurora experiments is that the F Department of Computer and Network Engineering, The University region critical frequency in O-mode ( f F ) is more than o 2 of Electro-Communications (UEC), Chofu, Japan Full list of author information is available at the end of the article © The Author(s) 2018. This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creat iveco mmons .org/licen ses/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) 70:94 Page 2 of 10 or equal to 4-MHz frequency, i.e., the minimum radio survey provides a strong scientific basis to re-introduce a frequency of the present EISCAT heating system. This is low-frequency capability to the EISCAT heating facility. because the electron energization by powerful O-mode It should be mentioned that originally the EISCAT heat- HF waves, which lead to electron heating and optical ing facility was able to transmit between 2.7 and 4 MHz emissions, can only occur when the radio frequency of from 1980 until October 1985 when a storm catastrophi- transmitted HF waves is slightly lower than the maxi- cally damaged the low-frequency antennas. That antenna mum plasma frequency in the heating region. In addi- array was rebuilt for higher frequencies, but a limited tion, darkness is needed to observe the optical emissions, modification for low frequencies may be feasible (see i.e., artificial aurora. Based on the survey, they suggested Rietveld et al. 2016). the following: The successful or possible conditions for the artificial aurora experiments are concentrated on Methods twilight hours in both evening and morning, compared The present survey is basically the same as that employed with late night hours; the possible conditions appear in by Tsuda et  al. (2018), but for the case of 2.7-MHz fre- fall, winter, and spring, while there is no chance in sum- quency (i.e., for the artificial aurora experiments utilizing mer, and the month-to-month variation among fall, win- the second electron gyro-harmonic). For a statistical sur- ter, and spring is not so clear; the year-to-year variation vey, we accumulated f F data from 2000 to 2017 (pre- o 2 is well correlated with the solar activity, and experiments cisely to 06:06 UT on October 11, 2017), obtained by the ◦ ◦ during the solar minimum would be almost hopeless. It dynasonde at the EISCAT Tromsø site ( 69.6 N, 19.2 E ). should be noted that the plasma frequency is sufficiently The data period covers more than one solar cycle. A high in summer but there is no chance in summer due to sounding was made typically every 6 minutes before the lack of darkness at the high latitude, i.e., the EISCAT February 2012 and every 2 minutes since then. Using Tromsø site. the dataset, we categorized each period of 1 h into three Another interest is a survey for artificial aurora experi - conditions: (a) possible nighttime heating condition; (b) ments utilizing the second electron gyro-harmonic (e.g., impossible nighttime heating condition; and (c) no data. Kosch et al. 2005, 2007b, 2009). Pumping the ionosphere To judge the conditions, we set four criteria: (1) number in the second electron gyro-harmonic frequency is spe- of f F data for each 1-h period is at least 5; (2) aver- o 2 cial, because on the second electron gyro-harmonic only aged f F for each period of 1  h is more than or equal o 2 there is a plasma resonance maximum. On all higher to 2.7  MHz; (3) one standard deviation of f F for each o 2 gyro-harmonic frequencies, there are plasma resonance period of 1  h is less than or equal to 0.5  MHz; (4) mini- minimums. The plasma resonance is found close to the mum of solar zenith angle (SZA) for each period of 1 h is gyro-frequency, but this is more difficult to achieve pre - more than or equal to 96 . If the criterion (1) is not satis- cisely because the ionosphere is not static, i.e., the plasma fied, the 1  h is categorized as the condition (c). If all the density varies and the height also varies, which varies the criteria are satisfied, the 1  h is categorized as the condi - magnetic field strength. Thus, the frequency regime on tion (a). Otherwise, the 1  h is categorized as the condi- the second electron gyro-harmonic allows more easily tion (b). Note that the criterion (2) is for O-mode heating the study of various plasma instabilities (e.g., parametric in the second electron gyro-harmonic, the criterion (3) decay instability for Langmuir, upper-hybrid, and elec- is for stable ionosphere or stable heating which would be tron Bernstein waves). Electron acceleration on the sec- important for, e.g., ON–OFF heating operation, and the ond gyro-harmonic is sufficiently intense that descending criterion (4) is for nighttime including both the nautical artificial ionization layers have been observed (e.g., Ped - twilight and the astronomical twilight to detect optical ersen et  al. 2010). The second gyro-harmonic frequency emissions, i.e., artificial aurora emissions. eB ( 2f ) can be calculated as: 2f = 2 × . Here, e is the ce ce 2πm −19 elementary charge (1.602 × 10 C), m is the electron Results and discussion −31 mass ( 9.109 × 10   kg), and B is the ionospheric mag- Local time variation netic field strength which is roughly 47,000–49,000 nT Figures  1, 2, 3 show UT-date variations in the possibility at 200–300  km heights above the EISCAT Tromsø site. for the artificial aurora experiments from 2000 to 2017. Hence, the second electron gyro-harmonic frequency It seems that the possible hours are fairly concentrated is roughly 2.6–2.7  MHz. Thus, in the present paper, we around the evening hours, i.e., a few hours after sunset, present a survey of conditions for artificial aurora experi - compared with the late night hours. Another interesting ments by 2.7-MHz frequency, i.e., the second electron characteristic is that a number of the possible hours can gyro-harmonic frequency, at the EISCAT Tromsø site be found in the morning hours, i.e., a few hours before using dynasonde data. This is an extension to the survey sunrise. These would indicate that relatively high elec - of Tsuda et  al. (2018). The information obtained in this tron density can be maintained at twilight hours due to Tsuda et al. Earth, Planets and Space (2018) 70:94 Page 3 of 10 a 2000 01 Jan 01 Apr 01 Jul 01 Oct 01 Jan b 2001 01 Jan 01 Apr 01 Jul 01 Oct 01 Jan c 2002 01 Jan 01 Apr 01 Jul 01 Oct 01 Jan d 2003 01 Jan 01 Apr 01 Jul 01 Oct 01 Jan e 2004 01 Jan 01 Apr 01 Jul 01 Oct 01 Jan f 2005 01 Jan 01 Apr 01 Jul 01 Oct 01 Jan Fig. 1 Variations in possible UT-date for conducting artificial 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 solar illumination in the F region. These characteristics Here, if there are no data in a day, we define the day as are basically similar to those by Tsuda et  al. (2018), but no data, marked by black. If there is the possible condi- the number of the possible hours seems to be large, com- tion of at least 1 h in a day, we define the day as the pos - pared with that by Tsuda et al. (2018). This would be due sible condition, marked by red. Otherwise, we define the to the change in the criterion (2) (i.e., 4–2.7 MHz in the day as the impossible condition, marked by gray. Obvi- averaged f F ). ously, there was no chance for the possible condition o 2 during summer, i.e., roughly May to July. This is because Month‑to‑month variation the criterion (4) for nighttime condition is never satisfied To see seasonal variation in detail, Figs.  4, 5, 6 show during the summer. On the other hand, we can find the month-to-month variations of the number of days for possible condition from August to April, i.e., fall, winter, possible artificial aurora experiments from 2000 to 2017. and spring. Of particular interest, we can find that there UT UT UT UT UT UT Tsuda et al. Earth, Planets and Space (2018) 70:94 Page 4 of 10 a 2006 01 Jan 01 Apr 01 Jul 01 Oct 01 Jan b 2007 01 Jan 01 Apr 01 Jul 01 Oct 01 Jan c 2008 01 Jan 01 Apr 01 Jul 01 Oct 01 Jan d 2009 01 Jan 01 Apr 01 Jul 01 Oct 01 Jan e 2010 01 Jan 01 Apr 01 Jul 01 Oct 01 Jan f 2011 01 Jan 01 Apr 01 Jul 01 Oct 01 Jan Fig. 2 Variations in possible UT-date for conducting artificial aurora experiments from 2006 to 2011 (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 were many chances for the artificial aurora experiments observed unclear seasonal variation. Again, these char- in winter. It seems that the number of days in the pos- acteristics are basically similar to those in Tsuda et  al. sible condition during winter is not much smaller than (2018), but the number of the possible days seems to be or is similar to those during spring as well as fall. Gen- large, compared with that in Tsuda et al. (2018). erally, there should be differences in the solar irradiation between winter and spring/fall. Such seasonal differences Year‑toy ‑ ear variation would be mainly due to different SZAs. However, in the Figure  7 shows year-to-year variations of the number of twilight hours, the SZA should be roughly the same in days with the possibility for the artificial aurora experi - any season. Hence, relatively high electron density can ments from 2000 to 2017, with 1-year average of the be maintained in the illuminated F region during the twi- solar radio flux index at 10.7  cm (2800  MHz), F . 10.7 light hours in any season. This would be a reason for the Note that the averaged F in 2017 is calculated using 10.7 UT UT UT UT UT UT Tsuda et al. Earth, Planets and Space (2018) 70:94 Page 5 of 10 a 2012 01 Jan 01 Apr 01 Jul 01 Oct 01 Jan b 2013 01 Jan 01 Apr 01 Jul 01 Oct 01 Jan c 2014 01 Jan 01 Apr 01 Jul 01 Oct 01 Jan d 2015 01 Jan 01 Apr 01 Jul 01 Oct 01 Jan e 2016 01 Jan 01 Apr 01 Jul 01 Oct 01 Jan f 2017 01 Jan 01 Apr 01 Jul 01 Oct 01 Jan Fig. 3 Variations in possible UT-date for conducting artificial aurora experiments from 2012 to 2017 (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 data to August 31, 2017. We can find a clear relationship minimum), the occurrence rates were very low (1–2%) in between the averaged F and the number of days in the the case of 4-MHz frequency [i.e., in the survey by Tsuda 10.7 possible condition in the case of 2.7-MHz frequency (see et al. (2018)], while those were 24–30% in the case of 2.7- Fig.  7a). This characteristic is similar to that in the case MHz frequency (i.e., in the present survey). of 4-MHz frequency (see Fig.  7b) by Tsuda et  al. (2018). u Th s, the results indicate that in the case of 2.7-MHz However, the number of the possible days during the frequency there are many chances for the artificial aurora solar minimum was obviously large, compared with that experiments even during the solar minimum. This would in the case of 4-MHz frequency. In Fig.  7c, we compare be a big advantage in the 2.7-MHz frequency operation. occurrence rates in the possible days for the artificial So, if an upgrade to the 2.7-MHz frequency operation in aurora experiments in the cases of 2.7- and 4-MHz fre- the EISCAT heating facility is realized, chances for the quencies. For example, during 2006–2009 (i.e., the solar artificial aurora experiments can be much enhanced even UT UT UT UT UT UT Tsuda et al. Earth, Planets and Space (2018) 70:94 Page 6 of 10 a 2000 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec b 2001 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec c 2002 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec d 2003 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec e 2004 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec f 2005 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Fig. 4 Month-to-month variations of the number of possible days for conducting artificial aurora experiments from 2000 to 2005 (from a to f). The red bars indicate the possible days, while the gray bars indicate days in which conducting the experiments is not possible, and the black bars indicate days when there are no data during the solar minimum. This means that we do not gyro-harmonic (e.g., various plasma instabilities such as have to wait for the next solar maximum, i.e., the maxi- parametric decay instability for Langmuir, upper-hybrid, mum of the cycle 25, which would be 2022–2023 accord- and electron Bernstein waves). ing to solar cycle predictions (e.g., Rigozo et  al. 2011; Historically, the EISCAT heating facility could operate Attia et al. 2013; Li et al. 2015). In addition, there would around the second electron gyro-harmonic frequency be much new science related to the second electron (2.76  MHz) in the early 1980s (e.g., Frey 1986), but this days days days days days days Tsuda et al. Earth, Planets and Space (2018) 70:94 Page 7 of 10 a 2006 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec b 2007 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec c 2008 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec d 2009 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec e 2010 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec f 2011 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Fig. 5 Month-to-month variations of the number of possible days for conducting artificial aurora experiments from 2006 to 2011 (from a to f). The red bars indicate the possible days, while the gray bars indicate days in which conducting the experiments is not possible, and the black bars indicate days when there are no data capability was not fully exploited then because of a lack the second electron gyro-harmonic frequency opera- of advanced diagnostic instruments and radar techniques tion, but there is no incoherent scatter radar near the available at that time. The HIgh-Power Auroral Stimula - HAARP. EISCAT has two incoherent scatter radars colo- tion (HIPAS) also had a capability of the operation for the cated with the EISCAT heating facility, which would be second electron gyro-harmonic frequency, but HIPAS a huge advantage if the EISCAT heating facility could stopped operating in 2007. The High-frequency Active get the 2.7-MHz capability back. Later, EISCAT_3D Auroral Research Program (HAARP) can be used for will also be a valuable diagnostic for a 2.7-MHz heating days days days days days days Tsuda et al. Earth, Planets and Space (2018) 70:94 Page 8 of 10 a 2012 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec b 2013 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec c 2014 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec d 2015 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec e 2016 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec f 2017 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Fig. 6 Month-to-month variations of the number of possible days for conducting artificial aurora experiments from 2012 to 2017 (from a to f). The red bars indicate the possible days, while the gray bars indicate days in which conducting the experiments is not possible, and the black bars indicate days when there are no data facility. EISCAT_3D and the heating facility will not be EISCAT Tromsø site using dynasonde data from 2000 colocated, but EISCAT_3D will be able to cover the iono- to 2017. This survey is an extended work of the survey sphere above the heating facility at Tromsø. Thus, we will in the case of 4-MHz frequency by Tsuda et  al. (2018). be able to perform multi-point observations along the Local time, month-to-month, and year-to-year variations local magnetic field line at heating facility with multiple in the possibility for the artificial aurora experiments by beams by EISCAT_3D. 2.7-MHz frequency are generally similar to those in the case of 4-MHz frequency. However, the number of days Conclusions with the right ionospheric condition in the case of 2.7- We carried out a statistical survey of conditions for MHz frequency was obviously much larger, compared artificial aurora experiments by 2.7-MHz frequency at with that in the case of 4-MHz frequency. In particular, in days days days days days days Tsuda et al. Earth, Planets and Space (2018) 70:94 Page 9 of 10 a 2.7 MHz 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 year b 4.0 MHz 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 year 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 year 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 year Fig. 7 a Year-to-year variations in the number of possible days for conducting artificial aurora experiments from 2000 to 2017, in the case of 2.7-MHz frequency. The red bars indicate possible days, the gray bars indicate days in which conducting the experiments is not possible, and the black bars indicate days when there are no data. b Same as a, but in the case of 4-MHz frequency ( Tsuda et al. 2018). c Year-to-year variation in the occurrence rate of possible days for conducting artificial aurora experiments from 2000 to 2017. The red indicates results in the case of 2.7-MHz frequency, and the black indicates results in the case of 4-MHz frequency. d Year-to-year variation in 1-year-averaged F from 2000 to 2017 10.7 the case of 2.7-MHz frequency, unlike the case of 4-MHz This would be an important advantage in the 2.7-MHz frequency, there would be many chances for the artifi - frequency operation by the EISCAT heating facility, if it cial aurora experiments even during the solar minimum. become a reality in the future. F days days 10.7 Occurrence rate (%) Tsuda et al. Earth, Planets and Space (2018) 70:94 Page 10 of 10 Abbreviations Bryers CJ, Kosch MJ, Senior A, Rietveld MT, Singer W (2013) A comparison EISCAT : European Incoherent SCATter; HAARP: high-frequency active auroral between resonant and nonresonant heating at EISCAT. J Geophys Res research program; HF: high frequency; HIPAS: high-power auroral stimula- Space Phys 118:6766–6776. https ://doi.org/10.1002/jgra.50605 tion; LT: local time; O-mode: ordinary mode; SD: standard deviation; SZA: solar Frey A (1986) The observation of HF-enhanced plasma waves with the EISCAT/ zenith angle; UT: universal time. UHF-radar in the presence of strong Landau-damping. Geophys Res Lett 13:438–441. https ://doi.org/10.1029/GL013 i005p 00438 Authors’ contributions Gustavsson B, Sergienko T, Kosch MJ, Rietveld MT, Brändström BUE, Leyser TTT conducted data analysis and wrote the first draft of the manuscript. MTR TB, Isham B, Gallop P, Aso T, Ejiri M, Grydeland T, Steen Å, LaHoz C, Kaila accumulated the dataset by operating the dynasonde and supported the data K, Jussila J, Holma H (2005) The electron energy distribution during HF analysis. MJK, SO, YO, KH, SN, TK, and AM contributed toward interpreting the pumping, a picture painted with all colors. Ann Geophys 23:1747–1754. results. All authors have contributed toward revising and improving the manu-https ://doi.org/10.5194/angeo -23-1747-2005 script. All authors have read and approved the final manuscript. Kosch MJ, Pedersen T, Hughes J, Marshall R, Gerken E, Senior A (2005) Artificial optical emissions at HAARP for pump frequencies near the third and Author details second electron gyro-harmonic. Ann Geophys 23:1585–1592. https ://doi. Department of Computer and Network Engineering, The University org/10.5194/angeo -23-1585-2005 of Electro-Communications (UEC), Chofu, Japan. European Incoherent SCAT- Kosch MJ, Pedersen T, Rietveld MT, Gustavsson B, Grach SM, Hagfors T (2007a) ter (EISCAT ) Scientific Association, Tromsø, Norway. Department of Physics Artificial optical emissions in the high-latitude thermosphere induced and Technology, University of Tromsø (UiT ) - The Arctic University of Norway, by powerful radio waves: an observational review. Adv Space Res Tromsø, Norway. South African National Space Agency (SANSA), Hermanus, 40:365–376. https ://doi.org/10.1016/j.asr.2007.02.061 South Africa. Department of Physics, Lancaster University, Lancaster, UK. Kosch MJ, Pedersen T, Mishin E, Oyama S, Hughes J, Senior A, Watkins B, Department of Physics and Astronomy, University of the Western Cape, Bristow B (2007b) Coordinated optical and radar observations of Bellville, South Africa. Institute for Space-Earth Environmental Research ionospheric pumping for a frequency pass through the second elec- (ISEE), Nagoya University, Nagoya, Japan. National Institute of Polar Research tron gyroharmonic at HAARP. J Geophys Res 112:A06325. https ://doi. (NIPR), Tachikawa, Japan. Ionosphere Research Unit, University of Oulu, Oulu, org/10.1029/2006J A0121 46 Finland. Department of Polar Science, Graduate University for Advanced Kosch MJ, Gustavsson B, Heinselman C, Pedersen T, Rietveld MT, Spaleta J, Studies (SOKENDAI), Tachikawa, Japan. Wong A, Wang W, Mutiso C, Bristow B, Hughes J (2009) First incoher- ent scatter radar observations of ionospheric heating on the second Acknowledgements electron gyro-harmonic. J Atmos Sol Terr Phys 71:1959–1966. https ://doi. We thank European Incoherent SCATter (EISCAT ) scientific association for org/10.1016/j.jastp .2009.08.007 providing dynasonde data. EISCAT is an international association supported Kosch MJ, Vickers H, Ogawa Y, Senior A, Blagoveshchenskaya N (2014) First by research organizations in China (CRIRP), Finland (SA), Japan (NIPR), Norway observation of the anomalous electric field in the topside ionosphere by (NFR), Sweden ( VR), and the UK (NERC). The dynasonde data can be available ionospheric modification over EISCAT. Geophys Res Lett 41:7427–7435. on request to M. T. Rietveld (mike@eiscat.uit.no) or can be accessed directly at https ://doi.org/10.1002/2014G L0616 79 the website, EISCAT Dynasonde (http://dynse rv.eisca t.uit.no/DD/login .php). Kosch MJ, Bryers C, Rietveld MT, Yeoman TK, Ogawa Y (2014) Aspect angle The 10.7-cm solar radio flux index data, F data, are provided at the Web site, sensitivity of pump-induced optical emissions at EISCAT. Earth Planets 10.7 National Centers for Environmental Information (NCEI), National Oceanic and Space 66:159. https ://doi.org/10.1186/s4062 3-014-0159-x Atmospheric Administration (NOAA) (ftp://ftp.ngdc.noaa.gov/STP/GEOMA Leyser TB, Wong AY (2009) Powerful electromagnetic waves for active envi- GNETI C_DATA/INDIC ES/KP_AP). This work was supported in part by MEXT/ ronmental research in geospace. Rev Geophys 47:RG1001. https ://doi. JSPS KAKENHI grants, JP26610157, JP15H05747, JP15H05815, JP16H01171, org/10.1029/2007R G0002 35 JP16H02230, JP16H06021, JP16H06286, JP16K05569, and JP17H02968, by the Li KJ, Feng W, Li FY (2015) Predicting the maximum amplitude of solar cycle 25 Sumitomo Foundation Basic Science Research grant, 150627, by National Insti- and its timing. J Atmos Sol Terr Phys 135:72–76. https ://doi.org/10.1016/j. tute of Polar Research (NIPR) through General Collaboration Project, 28-2, and jastp .2015.09.010 by the joint research program of the Institute for Space-Earth Environmental Pedersen T, Gustavsson B, Mishin E, Kendall E, Mills T, Carlson HC, Snyder AL Research (ISEE), Nagoya University. (2010) Creation of artificial ionospheric layers using high-power HF waves. Geophys Res Lett 37:L02106. https ://doi.org/10.1029/2009G L0418 Competing interests 95 The authors declare that they have no competing interests. Rietveld MT, Kohl H, Kopka H, Stubbe P (1993) Introduction to ionospheric heating at Tromsø—I. Experimental overview. J Atmos Terr Phys Ethics approval and consent to participate 55:577–599. https ://doi.org/10.1016/0021-9169(93)90007 -L Not applicable. Rietveld MT, Wright JW, Zabotin N, Pitteway MLV (2008) The Tromsø dynas- onde. Polar Sci 2:55–71. https ://doi.org/10.1016/j.polar .2008.02.001 Rietveld MT, Senior A, Markkanen J, Westman A (2016) New capabilities of the Publisher’s Note upgraded EISCAT high-power HF facility. Radio Sci 51:1533–1546. https :// Springer Nature remains neutral with regard to jurisdictional claims in pub- doi.org/10.1002/2016R S0060 93 lished maps and institutional affiliations. Rigozo NR, Souza Echer MP, Evangelista H, Nordemann DJR, Echer E (2011) Prediction of sunspot number amplitude and solar cycle length for cycles Received: 26 February 2018 Accepted: 16 May 2018 24 and 25. J Atmos Sol Terr Phys 73:1294–1299. https ://doi.org/10.1016/j. jastp .2010.09.005 Tsuda TT, Rietveld MT, Kosch MJ, Oyama S, Hosokawa K, Nozawa S, Kawabata T, Mizuno A, Ogawa Y (2018) Survey of conditions for artificial aurora experi- ments at EISCAT Tromsø using dynasonde data. Earth Planets Space 70:40. https ://doi.org/10.1186/s4062 3-018-0805-9 References Attia AF, Ismail HA, Basurah HM (2013) A Neuro-Fuzzy modeling for prediction of solar cycles 24 and 25. Astrophys Space Sci 344:5–11. https ://doi. org/10.1007/s1050 9-012-1300-6 Blagoveshchenskaya NF, Borisova TD, Kosch M, Sergienko T, Brändström U, Yeoman TK, Häggström I (2015) Optical and ionospheric phenomena at EISCAT under continuous X-mode HF pumping. J Geophys Res Space Phys 119:10483–10498. https ://doi.org/10.1002/2014J A0206 58 http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Earth, Planets and Space Springer Journals

Survey of conditions for artificial aurora experiments by the second electron gyro-harmonic at EISCAT Tromsø using dynasonde data

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Abstract

We report a brief survey of matching conditions for artificial aurora optical experiments utilizing the second electron gyro-harmonic (2.7-MHz frequency) in F region heating with O-mode at the EISCAT Tromsø site using dynasonde data from 2000 to 2017. Our survey indicates the following: The possible conditions for successful artificial aurora experi- ments are concentrated on 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 so clear; the year-to-year variation is well correlated with the solar activity. These characteristics in the case of 2.7-MHz frequency are basically similar to those previously reported in the case of 4-MHz frequency. However, the number of days meeting the possible condition in the case of 2.7-MHz frequency is obvi- ously large, compared with that in the case of 4-MHz frequency. In particular, unlike the 4-MHz frequency operation, the 2.7-MHz frequency operation can provide many chances for successful artificial aurora experiments even during the solar minimum. Keywords: Artificial aurora, Ionospheric heating, Second electron gyro-harmonic, EISCAT , Tromsø, Dynasonde some of heating experiments were successful (e.g., Gus- Background tavsson et  al. 2005; Bryers et  al. 2013; Kosch et  al. 2005, A large number of ionospheric heating experiments using 2007b, 2009, 2014a, b; Blagoveshchenskaya et  al. 2015), high-frequency (HF) radio waves have been performed but the others were unsuccessful. Thus, it is vitally impor - by many researchers. A detailed overview on iono- tant to understand when such successful conditions are spheric heating experiments can be found in, e.g., Kosch likely satisfied for planning heating experiments in cam - et  al. (2007a) and Leyser and Wong (2009). There are paigns. However, such surveys are not sufficiently carried restrictions for successful heating experiments. A main out. restriction in artificial aurora experiments is that the ion - Using observational data obtained by the dynasonde ospheric peak density drops below the lowest heater fre- (Rietveld et al. 2008) at the European Incoherent SCAT- quency too quickly after sunset. The weather condition is ter (EISCAT) Tromsø site, Tsuda et al. (2018) carried out another important factor affecting the optical observa - the first survey for artificial aurora experiments using F tions, but we do not treat the weather condition in the region heating with the ordinary mode (O-mode) by the present study for simplicity. Due to such restrictions, EISCAT heating facility (Rietveld et  al. 1993, 2016). In their survey, one of the required conditions for success- *Correspondence: takuo.tsuda@uec.ac.jp ful or possible artificial aurora experiments is that the F Department of Computer and Network Engineering, The University region critical frequency in O-mode ( f F ) is more than o 2 of Electro-Communications (UEC), Chofu, Japan Full list of author information is available at the end of the article © The Author(s) 2018. This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creat iveco mmons .org/licen ses/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) 70:94 Page 2 of 10 or equal to 4-MHz frequency, i.e., the minimum radio survey provides a strong scientific basis to re-introduce a frequency of the present EISCAT heating system. This is low-frequency capability to the EISCAT heating facility. because the electron energization by powerful O-mode It should be mentioned that originally the EISCAT heat- HF waves, which lead to electron heating and optical ing facility was able to transmit between 2.7 and 4 MHz emissions, can only occur when the radio frequency of from 1980 until October 1985 when a storm catastrophi- transmitted HF waves is slightly lower than the maxi- cally damaged the low-frequency antennas. That antenna mum plasma frequency in the heating region. In addi- array was rebuilt for higher frequencies, but a limited tion, darkness is needed to observe the optical emissions, modification for low frequencies may be feasible (see i.e., artificial aurora. Based on the survey, they suggested Rietveld et al. 2016). the following: The successful or possible conditions for the artificial aurora experiments are concentrated on Methods twilight hours in both evening and morning, compared The present survey is basically the same as that employed with late night hours; the possible conditions appear in by Tsuda et  al. (2018), but for the case of 2.7-MHz fre- fall, winter, and spring, while there is no chance in sum- quency (i.e., for the artificial aurora experiments utilizing mer, and the month-to-month variation among fall, win- the second electron gyro-harmonic). For a statistical sur- ter, and spring is not so clear; the year-to-year variation vey, we accumulated f F data from 2000 to 2017 (pre- o 2 is well correlated with the solar activity, and experiments cisely to 06:06 UT on October 11, 2017), obtained by the ◦ ◦ during the solar minimum would be almost hopeless. It dynasonde at the EISCAT Tromsø site ( 69.6 N, 19.2 E ). should be noted that the plasma frequency is sufficiently The data period covers more than one solar cycle. A high in summer but there is no chance in summer due to sounding was made typically every 6 minutes before the lack of darkness at the high latitude, i.e., the EISCAT February 2012 and every 2 minutes since then. Using Tromsø site. the dataset, we categorized each period of 1 h into three Another interest is a survey for artificial aurora experi - conditions: (a) possible nighttime heating condition; (b) ments utilizing the second electron gyro-harmonic (e.g., impossible nighttime heating condition; and (c) no data. Kosch et al. 2005, 2007b, 2009). Pumping the ionosphere To judge the conditions, we set four criteria: (1) number in the second electron gyro-harmonic frequency is spe- of f F data for each 1-h period is at least 5; (2) aver- o 2 cial, because on the second electron gyro-harmonic only aged f F for each period of 1  h is more than or equal o 2 there is a plasma resonance maximum. On all higher to 2.7  MHz; (3) one standard deviation of f F for each o 2 gyro-harmonic frequencies, there are plasma resonance period of 1  h is less than or equal to 0.5  MHz; (4) mini- minimums. The plasma resonance is found close to the mum of solar zenith angle (SZA) for each period of 1 h is gyro-frequency, but this is more difficult to achieve pre - more than or equal to 96 . If the criterion (1) is not satis- cisely because the ionosphere is not static, i.e., the plasma fied, the 1  h is categorized as the condition (c). If all the density varies and the height also varies, which varies the criteria are satisfied, the 1  h is categorized as the condi - magnetic field strength. Thus, the frequency regime on tion (a). Otherwise, the 1  h is categorized as the condi- the second electron gyro-harmonic allows more easily tion (b). Note that the criterion (2) is for O-mode heating the study of various plasma instabilities (e.g., parametric in the second electron gyro-harmonic, the criterion (3) decay instability for Langmuir, upper-hybrid, and elec- is for stable ionosphere or stable heating which would be tron Bernstein waves). Electron acceleration on the sec- important for, e.g., ON–OFF heating operation, and the ond gyro-harmonic is sufficiently intense that descending criterion (4) is for nighttime including both the nautical artificial ionization layers have been observed (e.g., Ped - twilight and the astronomical twilight to detect optical ersen et  al. 2010). The second gyro-harmonic frequency emissions, i.e., artificial aurora emissions. eB ( 2f ) can be calculated as: 2f = 2 × . Here, e is the ce ce 2πm −19 elementary charge (1.602 × 10 C), m is the electron Results and discussion −31 mass ( 9.109 × 10   kg), and B is the ionospheric mag- Local time variation netic field strength which is roughly 47,000–49,000 nT Figures  1, 2, 3 show UT-date variations in the possibility at 200–300  km heights above the EISCAT Tromsø site. for the artificial aurora experiments from 2000 to 2017. Hence, the second electron gyro-harmonic frequency It seems that the possible hours are fairly concentrated is roughly 2.6–2.7  MHz. Thus, in the present paper, we around the evening hours, i.e., a few hours after sunset, present a survey of conditions for artificial aurora experi - compared with the late night hours. Another interesting ments by 2.7-MHz frequency, i.e., the second electron characteristic is that a number of the possible hours can gyro-harmonic frequency, at the EISCAT Tromsø site be found in the morning hours, i.e., a few hours before using dynasonde data. This is an extension to the survey sunrise. These would indicate that relatively high elec - of Tsuda et  al. (2018). The information obtained in this tron density can be maintained at twilight hours due to Tsuda et al. Earth, Planets and Space (2018) 70:94 Page 3 of 10 a 2000 01 Jan 01 Apr 01 Jul 01 Oct 01 Jan b 2001 01 Jan 01 Apr 01 Jul 01 Oct 01 Jan c 2002 01 Jan 01 Apr 01 Jul 01 Oct 01 Jan d 2003 01 Jan 01 Apr 01 Jul 01 Oct 01 Jan e 2004 01 Jan 01 Apr 01 Jul 01 Oct 01 Jan f 2005 01 Jan 01 Apr 01 Jul 01 Oct 01 Jan Fig. 1 Variations in possible UT-date for conducting artificial 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 solar illumination in the F region. These characteristics Here, if there are no data in a day, we define the day as are basically similar to those by Tsuda et  al. (2018), but no data, marked by black. If there is the possible condi- the number of the possible hours seems to be large, com- tion of at least 1 h in a day, we define the day as the pos - pared with that by Tsuda et al. (2018). This would be due sible condition, marked by red. Otherwise, we define the to the change in the criterion (2) (i.e., 4–2.7 MHz in the day as the impossible condition, marked by gray. Obvi- averaged f F ). ously, there was no chance for the possible condition o 2 during summer, i.e., roughly May to July. This is because Month‑to‑month variation the criterion (4) for nighttime condition is never satisfied To see seasonal variation in detail, Figs.  4, 5, 6 show during the summer. On the other hand, we can find the month-to-month variations of the number of days for possible condition from August to April, i.e., fall, winter, possible artificial aurora experiments from 2000 to 2017. and spring. Of particular interest, we can find that there UT UT UT UT UT UT Tsuda et al. Earth, Planets and Space (2018) 70:94 Page 4 of 10 a 2006 01 Jan 01 Apr 01 Jul 01 Oct 01 Jan b 2007 01 Jan 01 Apr 01 Jul 01 Oct 01 Jan c 2008 01 Jan 01 Apr 01 Jul 01 Oct 01 Jan d 2009 01 Jan 01 Apr 01 Jul 01 Oct 01 Jan e 2010 01 Jan 01 Apr 01 Jul 01 Oct 01 Jan f 2011 01 Jan 01 Apr 01 Jul 01 Oct 01 Jan Fig. 2 Variations in possible UT-date for conducting artificial aurora experiments from 2006 to 2011 (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 were many chances for the artificial aurora experiments observed unclear seasonal variation. Again, these char- in winter. It seems that the number of days in the pos- acteristics are basically similar to those in Tsuda et  al. sible condition during winter is not much smaller than (2018), but the number of the possible days seems to be or is similar to those during spring as well as fall. Gen- large, compared with that in Tsuda et al. (2018). erally, there should be differences in the solar irradiation between winter and spring/fall. Such seasonal differences Year‑toy ‑ ear variation would be mainly due to different SZAs. However, in the Figure  7 shows year-to-year variations of the number of twilight hours, the SZA should be roughly the same in days with the possibility for the artificial aurora experi - any season. Hence, relatively high electron density can ments from 2000 to 2017, with 1-year average of the be maintained in the illuminated F region during the twi- solar radio flux index at 10.7  cm (2800  MHz), F . 10.7 light hours in any season. This would be a reason for the Note that the averaged F in 2017 is calculated using 10.7 UT UT UT UT UT UT Tsuda et al. Earth, Planets and Space (2018) 70:94 Page 5 of 10 a 2012 01 Jan 01 Apr 01 Jul 01 Oct 01 Jan b 2013 01 Jan 01 Apr 01 Jul 01 Oct 01 Jan c 2014 01 Jan 01 Apr 01 Jul 01 Oct 01 Jan d 2015 01 Jan 01 Apr 01 Jul 01 Oct 01 Jan e 2016 01 Jan 01 Apr 01 Jul 01 Oct 01 Jan f 2017 01 Jan 01 Apr 01 Jul 01 Oct 01 Jan Fig. 3 Variations in possible UT-date for conducting artificial aurora experiments from 2012 to 2017 (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 data to August 31, 2017. We can find a clear relationship minimum), the occurrence rates were very low (1–2%) in between the averaged F and the number of days in the the case of 4-MHz frequency [i.e., in the survey by Tsuda 10.7 possible condition in the case of 2.7-MHz frequency (see et al. (2018)], while those were 24–30% in the case of 2.7- Fig.  7a). This characteristic is similar to that in the case MHz frequency (i.e., in the present survey). of 4-MHz frequency (see Fig.  7b) by Tsuda et  al. (2018). u Th s, the results indicate that in the case of 2.7-MHz However, the number of the possible days during the frequency there are many chances for the artificial aurora solar minimum was obviously large, compared with that experiments even during the solar minimum. This would in the case of 4-MHz frequency. In Fig.  7c, we compare be a big advantage in the 2.7-MHz frequency operation. occurrence rates in the possible days for the artificial So, if an upgrade to the 2.7-MHz frequency operation in aurora experiments in the cases of 2.7- and 4-MHz fre- the EISCAT heating facility is realized, chances for the quencies. For example, during 2006–2009 (i.e., the solar artificial aurora experiments can be much enhanced even UT UT UT UT UT UT Tsuda et al. Earth, Planets and Space (2018) 70:94 Page 6 of 10 a 2000 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec b 2001 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec c 2002 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec d 2003 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec e 2004 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec f 2005 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Fig. 4 Month-to-month variations of the number of possible days for conducting artificial aurora experiments from 2000 to 2005 (from a to f). The red bars indicate the possible days, while the gray bars indicate days in which conducting the experiments is not possible, and the black bars indicate days when there are no data during the solar minimum. This means that we do not gyro-harmonic (e.g., various plasma instabilities such as have to wait for the next solar maximum, i.e., the maxi- parametric decay instability for Langmuir, upper-hybrid, mum of the cycle 25, which would be 2022–2023 accord- and electron Bernstein waves). ing to solar cycle predictions (e.g., Rigozo et  al. 2011; Historically, the EISCAT heating facility could operate Attia et al. 2013; Li et al. 2015). In addition, there would around the second electron gyro-harmonic frequency be much new science related to the second electron (2.76  MHz) in the early 1980s (e.g., Frey 1986), but this days days days days days days Tsuda et al. Earth, Planets and Space (2018) 70:94 Page 7 of 10 a 2006 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec b 2007 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec c 2008 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec d 2009 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec e 2010 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec f 2011 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Fig. 5 Month-to-month variations of the number of possible days for conducting artificial aurora experiments from 2006 to 2011 (from a to f). The red bars indicate the possible days, while the gray bars indicate days in which conducting the experiments is not possible, and the black bars indicate days when there are no data capability was not fully exploited then because of a lack the second electron gyro-harmonic frequency opera- of advanced diagnostic instruments and radar techniques tion, but there is no incoherent scatter radar near the available at that time. The HIgh-Power Auroral Stimula - HAARP. EISCAT has two incoherent scatter radars colo- tion (HIPAS) also had a capability of the operation for the cated with the EISCAT heating facility, which would be second electron gyro-harmonic frequency, but HIPAS a huge advantage if the EISCAT heating facility could stopped operating in 2007. The High-frequency Active get the 2.7-MHz capability back. Later, EISCAT_3D Auroral Research Program (HAARP) can be used for will also be a valuable diagnostic for a 2.7-MHz heating days days days days days days Tsuda et al. Earth, Planets and Space (2018) 70:94 Page 8 of 10 a 2012 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec b 2013 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec c 2014 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec d 2015 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec e 2016 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec f 2017 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Fig. 6 Month-to-month variations of the number of possible days for conducting artificial aurora experiments from 2012 to 2017 (from a to f). The red bars indicate the possible days, while the gray bars indicate days in which conducting the experiments is not possible, and the black bars indicate days when there are no data facility. EISCAT_3D and the heating facility will not be EISCAT Tromsø site using dynasonde data from 2000 colocated, but EISCAT_3D will be able to cover the iono- to 2017. This survey is an extended work of the survey sphere above the heating facility at Tromsø. Thus, we will in the case of 4-MHz frequency by Tsuda et  al. (2018). be able to perform multi-point observations along the Local time, month-to-month, and year-to-year variations local magnetic field line at heating facility with multiple in the possibility for the artificial aurora experiments by beams by EISCAT_3D. 2.7-MHz frequency are generally similar to those in the case of 4-MHz frequency. However, the number of days Conclusions with the right ionospheric condition in the case of 2.7- We carried out a statistical survey of conditions for MHz frequency was obviously much larger, compared artificial aurora experiments by 2.7-MHz frequency at with that in the case of 4-MHz frequency. In particular, in days days days days days days Tsuda et al. Earth, Planets and Space (2018) 70:94 Page 9 of 10 a 2.7 MHz 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 year b 4.0 MHz 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 year 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 year 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 year Fig. 7 a Year-to-year variations in the number of possible days for conducting artificial aurora experiments from 2000 to 2017, in the case of 2.7-MHz frequency. The red bars indicate possible days, the gray bars indicate days in which conducting the experiments is not possible, and the black bars indicate days when there are no data. b Same as a, but in the case of 4-MHz frequency ( Tsuda et al. 2018). c Year-to-year variation in the occurrence rate of possible days for conducting artificial aurora experiments from 2000 to 2017. The red indicates results in the case of 2.7-MHz frequency, and the black indicates results in the case of 4-MHz frequency. d Year-to-year variation in 1-year-averaged F from 2000 to 2017 10.7 the case of 2.7-MHz frequency, unlike the case of 4-MHz This would be an important advantage in the 2.7-MHz frequency, there would be many chances for the artifi - frequency operation by the EISCAT heating facility, if it cial aurora experiments even during the solar minimum. become a reality in the future. F days days 10.7 Occurrence rate (%) Tsuda et al. Earth, Planets and Space (2018) 70:94 Page 10 of 10 Abbreviations Bryers CJ, Kosch MJ, Senior A, Rietveld MT, Singer W (2013) A comparison EISCAT : European Incoherent SCATter; HAARP: high-frequency active auroral between resonant and nonresonant heating at EISCAT. J Geophys Res research program; HF: high frequency; HIPAS: high-power auroral stimula- Space Phys 118:6766–6776. https ://doi.org/10.1002/jgra.50605 tion; LT: local time; O-mode: ordinary mode; SD: standard deviation; SZA: solar Frey A (1986) The observation of HF-enhanced plasma waves with the EISCAT/ zenith angle; UT: universal time. UHF-radar in the presence of strong Landau-damping. Geophys Res Lett 13:438–441. https ://doi.org/10.1029/GL013 i005p 00438 Authors’ contributions Gustavsson B, Sergienko T, Kosch MJ, Rietveld MT, Brändström BUE, Leyser TTT conducted data analysis and wrote the first draft of the manuscript. MTR TB, Isham B, Gallop P, Aso T, Ejiri M, Grydeland T, Steen Å, LaHoz C, Kaila accumulated the dataset by operating the dynasonde and supported the data K, Jussila J, Holma H (2005) The electron energy distribution during HF analysis. MJK, SO, YO, KH, SN, TK, and AM contributed toward interpreting the pumping, a picture painted with all colors. Ann Geophys 23:1747–1754. results. All authors have contributed toward revising and improving the manu-https ://doi.org/10.5194/angeo -23-1747-2005 script. All authors have read and approved the final manuscript. Kosch MJ, Pedersen T, Hughes J, Marshall R, Gerken E, Senior A (2005) Artificial optical emissions at HAARP for pump frequencies near the third and Author details second electron gyro-harmonic. Ann Geophys 23:1585–1592. https ://doi. Department of Computer and Network Engineering, The University org/10.5194/angeo -23-1585-2005 of Electro-Communications (UEC), Chofu, Japan. European Incoherent SCAT- Kosch MJ, Pedersen T, Rietveld MT, Gustavsson B, Grach SM, Hagfors T (2007a) ter (EISCAT ) Scientific Association, Tromsø, Norway. Department of Physics Artificial optical emissions in the high-latitude thermosphere induced and Technology, University of Tromsø (UiT ) - The Arctic University of Norway, by powerful radio waves: an observational review. Adv Space Res Tromsø, Norway. South African National Space Agency (SANSA), Hermanus, 40:365–376. https ://doi.org/10.1016/j.asr.2007.02.061 South Africa. Department of Physics, Lancaster University, Lancaster, UK. Kosch MJ, Pedersen T, Mishin E, Oyama S, Hughes J, Senior A, Watkins B, Department of Physics and Astronomy, University of the Western Cape, Bristow B (2007b) Coordinated optical and radar observations of Bellville, South Africa. Institute for Space-Earth Environmental Research ionospheric pumping for a frequency pass through the second elec- (ISEE), Nagoya University, Nagoya, Japan. National Institute of Polar Research tron gyroharmonic at HAARP. J Geophys Res 112:A06325. https ://doi. (NIPR), Tachikawa, Japan. Ionosphere Research Unit, University of Oulu, Oulu, org/10.1029/2006J A0121 46 Finland. Department of Polar Science, Graduate University for Advanced Kosch MJ, Gustavsson B, Heinselman C, Pedersen T, Rietveld MT, Spaleta J, Studies (SOKENDAI), Tachikawa, Japan. Wong A, Wang W, Mutiso C, Bristow B, Hughes J (2009) First incoher- ent scatter radar observations of ionospheric heating on the second Acknowledgements electron gyro-harmonic. J Atmos Sol Terr Phys 71:1959–1966. https ://doi. We thank European Incoherent SCATter (EISCAT ) scientific association for org/10.1016/j.jastp .2009.08.007 providing dynasonde data. EISCAT is an international association supported Kosch MJ, Vickers H, Ogawa Y, Senior A, Blagoveshchenskaya N (2014) First by research organizations in China (CRIRP), Finland (SA), Japan (NIPR), Norway observation of the anomalous electric field in the topside ionosphere by (NFR), Sweden ( VR), and the UK (NERC). The dynasonde data can be available ionospheric modification over EISCAT. Geophys Res Lett 41:7427–7435. on request to M. T. Rietveld (mike@eiscat.uit.no) or can be accessed directly at https ://doi.org/10.1002/2014G L0616 79 the website, EISCAT Dynasonde (http://dynse rv.eisca t.uit.no/DD/login .php). Kosch MJ, Bryers C, Rietveld MT, Yeoman TK, Ogawa Y (2014) Aspect angle The 10.7-cm solar radio flux index data, F data, are provided at the Web site, sensitivity of pump-induced optical emissions at EISCAT. Earth Planets 10.7 National Centers for Environmental Information (NCEI), National Oceanic and Space 66:159. https ://doi.org/10.1186/s4062 3-014-0159-x Atmospheric Administration (NOAA) (ftp://ftp.ngdc.noaa.gov/STP/GEOMA Leyser TB, Wong AY (2009) Powerful electromagnetic waves for active envi- GNETI C_DATA/INDIC ES/KP_AP). This work was supported in part by MEXT/ ronmental research in geospace. Rev Geophys 47:RG1001. https ://doi. JSPS KAKENHI grants, JP26610157, JP15H05747, JP15H05815, JP16H01171, org/10.1029/2007R G0002 35 JP16H02230, JP16H06021, JP16H06286, JP16K05569, and JP17H02968, by the Li KJ, Feng W, Li FY (2015) Predicting the maximum amplitude of solar cycle 25 Sumitomo Foundation Basic Science Research grant, 150627, by National Insti- and its timing. J Atmos Sol Terr Phys 135:72–76. https ://doi.org/10.1016/j. tute of Polar Research (NIPR) through General Collaboration Project, 28-2, and jastp .2015.09.010 by the joint research program of the Institute for Space-Earth Environmental Pedersen T, Gustavsson B, Mishin E, Kendall E, Mills T, Carlson HC, Snyder AL Research (ISEE), Nagoya University. (2010) Creation of artificial ionospheric layers using high-power HF waves. Geophys Res Lett 37:L02106. https ://doi.org/10.1029/2009G L0418 Competing interests 95 The authors declare that they have no competing interests. Rietveld MT, Kohl H, Kopka H, Stubbe P (1993) Introduction to ionospheric heating at Tromsø—I. Experimental overview. J Atmos Terr Phys Ethics approval and consent to participate 55:577–599. https ://doi.org/10.1016/0021-9169(93)90007 -L Not applicable. Rietveld MT, Wright JW, Zabotin N, Pitteway MLV (2008) The Tromsø dynas- onde. Polar Sci 2:55–71. https ://doi.org/10.1016/j.polar .2008.02.001 Rietveld MT, Senior A, Markkanen J, Westman A (2016) New capabilities of the Publisher’s Note upgraded EISCAT high-power HF facility. Radio Sci 51:1533–1546. https :// Springer Nature remains neutral with regard to jurisdictional claims in pub- doi.org/10.1002/2016R S0060 93 lished maps and institutional affiliations. Rigozo NR, Souza Echer MP, Evangelista H, Nordemann DJR, Echer E (2011) Prediction of sunspot number amplitude and solar cycle length for cycles Received: 26 February 2018 Accepted: 16 May 2018 24 and 25. J Atmos Sol Terr Phys 73:1294–1299. https ://doi.org/10.1016/j. jastp .2010.09.005 Tsuda TT, Rietveld MT, Kosch MJ, Oyama S, Hosokawa K, Nozawa S, Kawabata T, Mizuno A, Ogawa Y (2018) Survey of conditions for artificial aurora experi- ments at EISCAT Tromsø using dynasonde data. Earth Planets Space 70:40. https ://doi.org/10.1186/s4062 3-018-0805-9 References Attia AF, Ismail HA, Basurah HM (2013) A Neuro-Fuzzy modeling for prediction of solar cycles 24 and 25. Astrophys Space Sci 344:5–11. https ://doi. org/10.1007/s1050 9-012-1300-6 Blagoveshchenskaya NF, Borisova TD, Kosch M, Sergienko T, Brändström U, Yeoman TK, Häggström I (2015) Optical and ionospheric phenomena at EISCAT under continuous X-mode HF pumping. J Geophys Res Space Phys 119:10483–10498. https ://doi.org/10.1002/2014J A0206 58

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