1. Introduction. 2. Materials and Methods

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1 A Study On The Detection Of Solar Flares And Its Effects On The Daytime Fluctuation Of VLF Amplitude And Geomagnetic Variation Using A Signal Of KHz Transmitted From England And Received At Kiel Longwave Monitor For 2015 Karan Bhatta 1, Bishnu Kumar Rayamajhi 2, Peter Wilhelm Schnoor 3, Mahesh Poudel Chhettri 4, Basu Dev Ghimire 5, Balaram Khadka 6 1,2,4 Students of M.Sc Physics at St. Xavier s College 3 Head of the Kiel Longwave Monitor 5,6 Assistant Professor of Physics, St. Xavier s College, Maitighar, Nepal Abstract: We studied the VLF signal of KHz (GQD) transmitted from Anthorn, England. Using the method in the amplitude fluctuation of the VLF signal, we detected several days of solar flares using the GQD signal and the flares ranged from C class to class X. These solar flares were then analyzed by using the method of daytime and night time fluctuation in the amplitude perturbation of the VLF signal of these days. The study of the DsT index and planetary K-index shows that the effects of the Solar flares were seen in the very days where solar flares were observed. We also studied the geomagnetic fluctuations associated with these months and found that there were some fluctuations in the geomagnetic for the particular days where the Solar flares were observed. 1. Introduction Several studies have shown that VLF waves can help us to detect solar flares and other ionospheric parameters [1,2,3,4]. Some studies have shown no major correlations between the geomagnetic storms and solar flares while some have hinted at a possibility [5,6,7,8]. The region where a considerable amount of activity is seen during Solar flare which results in the perturbation of electron density is the D-region of the atmosphere [9,10,11]. The X-ray flux during the onset of a Solar flare tends to have an effect on the different gases present in the atmosphere [12,13]. 2. Materials and Methods The of a signal of KHZ was received at the Kiel Longwave Monitor, Kiel, Germany. The was received in ASCII format as a one minute average spectrum as shown in figure 1. We adopted a variety of methods for the identification and study of the property of the Solar flares. Fig 1: Block diagram of Kiel Longwave Monitor Method 1 Identification of Solar flares First we noted the days which showed us the possible signatures of solar flares and compared it with the of GOES satellite for the detection of Hard as well as soft X-rays. We also checked if major perturbations were seen in the geomagnetic (in the particular times when Solar flare signatures were seen) as recorded in a geomagnetic observatory in Wingst, Germany, which is the nearest geomagnetic observatory from our receiver at Kiel, Germany. The change in amplitude caused by the Solar flare was recorded using the formula A-<A>, where <A> is the 4 day average amplitude of a non-flare day in the closest proximity (2 days before the flare as well as 2 days after) of a flare induced day[7]. Method 2 Daytime fluctuation in VLF amplitude For the daytime fluctuation method we used the same method that has been extensively used in studying the night time fluctuation as precursor to the seismo-ionospheric perturbation [14] as described in the following paragraph. But night time fluctuation in VLF amplitude has been used in other results also [15,16,17,18] For the daytime fluctuation we took the portion of the for time between the sunrise and sunset Page 2160

2 terminator times and found out the 3 day averaged of each day. A collection of the 3 day averaged for a month was taken and a monthly average was found, The individual averages of each day was compared with the monthly average and the days where the daily averages crossed the ±2σ lines were thrown out and a new average of the days where the 3day averaged did not cross the ±2σ were taken. This new average of the quietest days of the particular month was taken and compared with the raw. The number of raw points that crossed the standard ±2σ were noted the number of such counts was noted as the day time fluctuation. A similar method was applied for the night time fluctuation. Method 3 Daytime fluctuation in the geomagnetic We adopted a similar method as the day time fluctuation in the VLF amplitude for the fluctuation of the geomagnetic as obtained from INTERMAGNET for the geomagnetic observatory in Wingst, Germany. However, basic difference between the method of obtaining nighttime and daytime fluctuation of VLF waves and the dattime fluctuation in the geomagnetic is that is that we did not count the number of points that crossed the ±2σ lines(in the geomagnetic ) but determined visually if there were some anomalies recorded in the geomagnetic graphs at the same time when the Solar flares were recorded in the VLF signals. 3. Results and Discussions The cylindrical projection of the signal of is shown in Fig 2. The transmitting signal s location is at a distance of 837 km at a bearing of 278 degrees from the Kiel Longwave Monitor and is located at a distance of 54.7 North and 02.9West. Fig 2: cylindrical projection of the GQD signal for Identification of Solar flares We observed the days where the VLF signals were perturbed so that the static values of amplitude in the daytime abruptly went to a higher value for a considerable period of time and acted as a peak. We noted these days and compared the perturbations with the X-ray of GOES satellite and found out that the peaks in the VLF signal of GQD matched with the peaks in the GOES satellite, which included both the hard X-ray as well as the soft X-rays. We also visually analyzed whether the perturbations in the VLF corresponded in time with the perturbations in the geomagnetic of the observatories nearest to Kiel, Germany. We found a total of 20 days where the Solar flares were captured in the signal of GQD. The graphs that combine the VLF signal, Hard and Soft X-rays and the geomagnetic signals captured in Wingst, Germany are combined into a single one and shown through figure. Fig 3: A typical intensity profile of the VLF (top left) of April 10 is compared with the values of Hard X-ray and (top right), soft X-ray(bottom left) and the z-component of the geomagnetic flux obtained at Intermagnet geomagnetic observatory at Wingst, Germany. As shown in fig:3, the two corresponding peaks that we obtained at the daytime intensity of the VLF profile shows two peaks. (The daytime intensity of the VLF amplitude refers to the amplitude of the VLF waves as recorded by in the Kiel Longwave Monitor between the intervals of the Sunrise Terminator time and the Sunset Terminator time. This time is also referred to as the length of the VLF day). These two peaks have their counterparts at the flux as measured through the flux observed by the GOES satellite. The geomagnetic also shows some peak around that time but it is extremely difficult to know Page 2161

3 whether the peaks in the geomagnetic can be sole attributed to the Solar flares. We found other days where peaks in the daytime intensity of the VLF waves had a clear counterpart at the hard and soft X-rays in the GOES as shown in Fig 7: Solar flare of August 24 as observed in VLF Fig 4: Solar flare of April 12 as observed in VLF Fig 8: Solar flare of August 28 as observed in VLF Fig 5: Solar flare of August 9 as observed in VLF Fig 9: Solar flare of June 20 as observed in VLF Fig 6: Solar flare of August 22 as observed in VLF Page 2162

4 Fig 10: Solar flare of November 20 as observed in VLF signal, GOES X-ray and geomagnetic Fig 13: Solar flare of September 17 as observed in VLF signal, GOES X-ray and geomagnetic Fig 11: Solar flare of October 1 as observed in VLF Fig 14: Solar flare of September 27 as observed in VLF signal, GOES X-ray and geomagnetic Fig 12 : Solar flare of October 13 as observed in VLF signal, GOES X-ray and geomagnetic Fig 15: Solar flare of September 30 as observed in VLF signal, GOES X-ray and geomagnetic In some of the graphs we found more than one flare as in August 2, August 28 and a few other days. All Page 2163

5 of the salient features of this has been shown in table 1 indicating ΔA, time delay, the number of solar flares along with the timing of the Solar flare. interactions of the Sun and earth or due to extraterrestrial events such as GRB. 3.2 Daytime and Night time fluctuation in VLF amplitude There are no major deviations in the daytime fluctuations except for April 4 th where the daytime fluctuations were found to be a maximum for the days where Solar flare has not occurred. Fig 18: nighttime variation in the VLF amplitude fluctuation for March (top-left), April (top right), June (bottom left) and July (bottom right) Fig 16: daytime variation in the VLF amplitude fluctuation for March (top-left), April (top right), June (bottom left) and July (bottom right) Fig 19: nighttime variation in the VLF amplitude for August (top-left), September (top right), October (bottom left) and November (bottom right). Fig 17: daytime variation in the VLF amplitude for August (top-left), September (top right), October (bottom left) and November (bottom right). Therefore the effect of the Solar flares has not been well captured in the daytime fluctuations of the VLF amplitude. The peaks of the Solar flares in the Solar flare days did not readily correspond to the peaks in the daytime fluctuations in the VLF amplitude. The increase in the daytime fluctuations of the VLF amplitude in the das not corresponding to Solar flare days might be due to the other Since the effect of Solar flares is seen only in the amplitude fluctuation of the daytime, night time fluctuation cannot reveal features of the Solar flares for the particular day. There is no correlation between the days where the solar flares occurred and the nighttime fluctuations for the respective days. Night time fluctuations have been studied as indicators for tectonic activities in a particular location and since England is geologically a stable place, the anomalous behavior of night time fluctuations cannot be indicators of earthquakes either. Page 2164

6 Table 1: Table showing the various classes of the Solar flares, the times where they were observed, the amplitude fluctuation ( A) and the time delay Solar Flare Day Time (UTC) Class A Time Delay (min) :26 X :05 C :54 C :45 M :31 C :35 C :46 M :22 C :33 M :53 C :44 C :06 C :56 M :42 C :16 M :12 C :01 C :31 M :12 M :37 M :41 M :56 M :13 M :48 M :14 M :06 M :22 M :10 C :00 C Fig 20: Geomagnetic variation with respect to the ±2σ for April 10 Fig 21: Geomagnetic variation with respect to the ±2σ for August Daytime fluctuation in the geomagnetic The ±2σ lines drawn in the graph of the geomagnetic shows us that there a few days only where the time where the signatures of Solar flares was induced, a corresponding crossing of the geomagnetic of the ±2σ was seen. These are demonstrated in the figures to follow. Fig 22: Geomagnetic variation with respect to the ±2σ for August 23 Page 2165

7 Fig 23: Geomagnetic variation with respect to the ±2σ for August 26 Fig 26: Geomagnetic variation with respect to the ±2σ for November 29 Fig 24: Geomagnetic variation with respect to the ±2σ for June 20 Fig 27: Geomagnetic variation with respect to the ±2σ for October 2 Fig 25: Geomagnetic variation with respect to the ±2σ for June 21 Fig 28: Geomagnetic variation with respect to the ±2σ for October 13 Page 2166

8 fluctuations of the geomagnetic lines from the ±2σ lines at various days does seem to indicate that there is a correlation, a feeble one to that, between the impact of a Solar flare in the geomagnetic flux of observed in the place where the VLF receiver are placed. Fig 29: Geomagnetic variation with respect to the ±2σ for October 16 Fig 32: Planetary K-index from April- August of 2015 Fig 30: Geomagnetic variation with respect to the ±2σ for September 17 Fig 33: Planetary K-index from September- November Fig 31: Geomagnetic variation with respect to the ±2σ for September 26 Since the geomagnetic was affected by other factors (as shown by crossing of the ±2σ line in times where flare signatures have not been recorded), we cannot say that Solar flares captured in the VLF signals are the sole prerogative of the geomagnetic fluctuations. However, the Fig 34: DsT index for the months April to August Page 2167

9 4. Conclusions The VLF recording system of Kiel Longwave Monitor is good at capturing Solar flares of C, M and X classes. The solar flares of smaller classes need a resolution better than 1 minute average spectra. The effects of flares thus captured are not well recorded in the day time fluctuations. The variation observed in the geomagnetic indicated a slight co-relation between timings of solar flares and geomagnetic variations. 5. Acknowledgement Fig 35: DsT index for the months September, October and November The perturbations in the DsT and planetary K indices, which are plotted in hours but when converted in the units of days, match with the very days where the Solar flares were observed although not exclusively. However, in the months of April, August, September and Noember, there was strong co-relation between the days where the Solar flare was observed and the days where Dst index and the planetary K index were at their maximum values. Authors are grateful to Mr. Shreebar Acharya for giving his insights into the calculations. The results (related to geomagnetic variations) presented in this paper rely on collected at magnetic observatories. We thank the national institutes that support them and INTERMAGNET for promoting high standards of magnetic observatory practice ( 6. REFERENCES [1] Raulin, Jean Pierre, et al. "Solar flare detection sensitivity using the South America VLF Network (SAVNET)." Journal of Geophysical Research: Space Physics 115.A7 (2010). [2] Thomson, Neil R., Craig J. Rodger, and Mark A. Clilverd. "Large solar flares and their ionospheric D region enhancements." Journal of Geophysical Research: Space Physics 110.A6 (2005). [3] Thomson, Neil R., Craig J. Rodger, and Richard L. Dowden. "Ionosphere gives size of greatest solar flare." Geophysical research letters 31.6 (2004). [4] Pacini, Alessandra Abe, and Jean Pierre Raulin. "Solar X ray flares and ionospheric sudden phase anomalies relationship: A solar cycle phase dependence." Journal of Geophysical Research: Space Physics 111.A9 (2006). Fig 36. A graph showing the time delay versus the time of occurrence of the solar flares in UTC The time delay graph as shown in the figure 36 is indicative of the fact that the solar flares could only be studied if the perturbations in the average raw spectra obtained in the Kiel Longwave Monitor was seen between the sunrise terminator time and the sunset terminator times. The Solar flares observed in the earth at the times before the sunrise terminator time and after the sunset terminator time shoed no prominent effect in the perturbation in the amplitude fluctuation of the VLF sigal. [5] Newton, H. W. "Solar flares and magnetic storms." Monthly Notices of the Royal Astronomical Society (1943): [6] Russell, CT, and, and R. L. McPherron. "Semiannual variation of geomagnetic activity." Journal of geophysical research 78.1 (1973): [7] Selvakumaran, R., et al. "Solar flares induced D- region ionospheric and geomagnetic perturbations." Journal of Atmospheric and Solar- Terrestrial Physics 123 (2015): [8] Zhang, J., et al. "Identification of solar sources of major geomagnetic storms between 1996 and 2000." The Astrophysical Journal (2003): 520. [9] Webber, William. "The production of free electrons in the ionospheric D layer by solar and galactic cosmic Page 2168

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