The sunspot group continues to evolve, causing flares to erupt under the action of the atmospheric magnetic field. After the flare erupts, the ejected X-rays cause the electron concentration in the ionosphere to increase, and the equivalent reflection height of the ionosphere decreases. We investigate the correlation between the series of flares erupted by sunspot groups and the propagation of VLF signals. We used NOAA sunspot activity area data and solar flare data released by GOSE satellite, counted the series of flares erupted by sunspot group in 2000, and analyzed the size of the flare. Among them, the sunspot group numbered AR9077 erupted continuously with 15 M-level and above flares, X Level 3 flares. Received data from the Alpha VLF navigation station in Haikou, and observed a series of large flares erupted by AR9077. After the flare disk erupted, the phase anomaly of the VLF signal in the ground-ionosphere was caused. Analyze the flare according to the phase anomaly change, calculate the phase velocity when the flare occurs, the equivalent reflection height change, and the X-ray flux to predict the size of the flare. The calculations are consistent with the comparison of data published by the GOSE satellite. The observations show that the VLF signal correlates well with solar flares and sunspots. The VLF signal can be used as a reliable solution for predicting sunspots and solar flares, avoiding the impact of continuous flares of sunspots.
Research Article
Effects of a series of large flares from a sunspot group eruption on VLF propagation
https://doi.org/10.21203/rs.3.rs-1647653/v1
This work is licensed under a CC BY 4.0 License
Version 1
posted
You are reading this latest preprint version
Sunspot group
Solar flare
VLF signal
Phase changes
Solar activity is the source of space weather. The outburst of solar activity causes sudden and short-term changes in the space environment of the earth's magnetosphere, ionosphere and thermosphere in solar terrestrial space, which is harmful to the space weather (Cander, 2008). Solar activity affects the whole solar atmosphere, and flares are usually accompanied by sudden and drastic changes in brightness. Prediction of the space environment is the timely and effective prediction of outbursts of solar activity. The parameters of the active region constituted by the sunspot groups are important indicators of solar activity outbursts, and the characteristics of sunspot groups are important factors for forecasting solar flares (Fang, Cui and Ao, 2019). The evolution of sunspot groups is closely related to solar flare outbursts. The movement of sunspot groups can help the solar atmosphere to accumulate the energy required for solar flare outbursts (Nagovitsyn and Kuleshova, 2013). Jiang et al. (2011) Studied the sunspot activity region AR11158 in 2012 and it was found that the rapid shearing and rotational motion of sunspots causes the outbreak of X2.2 class solar flares. Ruan et al. (2014) Study found that the rapid rotation of sunspots in the sunspot activity region AR11283 led to the outburst of a X2.1 solar flare. Yan et al. (2015) Study found that the filament formation event in the sunspot active region AR11884, due to the non-short rotation of sunspots, caused the solar filament to be more twisted, resulting in the eruption of the filament and the eruption of M-class solar flares. Wheatland (2001) Study of flares in the solar active regions between 1981 and 1999 found that 61.5% of the flares above C-class corresponded to independently numbered sunspot group active regions, compared to 94% and 82% for X-class and M-class flares respectively. Bornmannn and Shaw (1994) used multiple linear regression (MLR) to analyze the relationship between the McIntosh classification of sunspot active regions and the M and X flare yields observed by GOSE satellites. The evolution of the sunspot groups is driven by the Sun's interior, where the magnetic field of the Sun's atmosphere causes solar flares to erupt. In terms of the causality of solar activity, the evolution of the sunspot groups is the cause and the eruption of solar flares is the effect. If the sunspot group gains enough momentum, the group will keep moving, causing a series of flare eruptions (Grimes, Pintér and Morgan, 2020). Solar flare is the most violent solar activity. When a solar flare erupts, a large amount of radiation such as X-rays, charged particles, and UV (ultraviolet) are emitted. Various types of electromagnetic radiation reaching near-Earth space affect the ionosphere, disturb the relatively calm environment of near-Earth space, and have a large impact on satellites in space, threatening the lives of astronauts carrying out space activities, causing damage to power systems, deterioration in the quality of mobile phone communications, failure of navigation and positioning systems, and having an impact on our productive lives. Many scientists have made great efforts to predict the space weather and made some progress. Many scholars have studied the prediction methods of space weather, but it is very difficult to directly measure the upper magnetic field of the solar atmosphere. Many flare prediction methods are based on the observation of the active area (Barnes et al., 2016; Florios et al., 2018; Kontogiannis et al., 2018; Kim et al., 2019; Korsós et al., 2019).
Very Low Frequency (VLF) signals propagation attenuation is small, long action distance, have stable amplitude and phase propagation and are well predictable. The VLF signal propagations in the earth-ionosphere waveguide and is influenced by the ground surface and the ionosphere as it propagates within the waveguide (Šulić, Srećković and Mihajlov, 2016). Sudden ionospheric disturbance (SID) causes abnormal propagation of VLF signal. The X-rays emitted after the eruption of the solar flare first reached the near-Earth space, causing an increase in ionospheric electron density resulting in the SID phenomenon (Thomson and Clilverd, 2001). Kolarski and Grubor (2014) used VLF signals to detect the Earth's lower ionosphere during solar flares. Hayes et al. (2021) used VLF and GOES X-ray sensors to observe the solar flare events, and statistically studied its influence on ionospheric D region. Kumar and Kumar (2018) used VLF to observe the effect of solar flare on ionospheric D-depletion in the 24th solar cycle. There is a good correlation between the VLF signal and solar flares in terms of time and grade (Gu et al., 2021). Therefore, we can monitor the solar flare by observing the abnormal phenomena of VLF signal propagation, and then forecast the space weather. This method is economical and convenient.
Many scholars have studied the identification and classification of sunspot groups, the yield of sunspot groups and flares, the relationship between solar flares and the area of sunspot groups, and the prediction of solar flares by using the morphological characteristics of sunspots (Wu, Zhao and Song, 200; Lee, et al. 2012; Zhao et al, 2014; Mariachiara, Costa and Romano, 2019). However, the effect of sunspot group eruption series flares in the active region on the VLF signal has been less studied. In this paper, we observe the effect of a series of large solar flares emitted by sunspot group number AR9077 on the propagation of VLF signals at Haikou station, analyzes and processes the VLF signal data with phase anomalies. Predicting the grade of the sunspot group's continuous solar flare, and monitoring the energy change of the sunspot group according to the flare size. Provide a basis for monitoring of the space environment to avoid larger losses.
1.1 Observation system
Figure 1 shows the block diagram of the VLF signal observation system. The design idea of the system is based on software radio technology, using software to implement the functions of the hardware. The observation system consists of a single whip antenna, a digital VLF signal software radio receiver, a Rb Atomic Frequency Reference and computer. The single whip antenna is connected to a digital VLF software radio receiver and receives data on the amplitude, phase and signal-to-noise ratio and other data of the VLF signals from the three stations of the Alpha VLF navigation system. Rb Atomic Frequency Reference has high stability, provides the observation system with a 5MHz sine wave with an accuracy higher than 1×10− 11 as the local frequency standard of the observation system (Niu et al., 2009; Niu et al., 2014; Niu and Bi, 2016). The computer processes and displays the amplitude, phase and signal-to-noise ratio change curve of the VLF signals and records and stores the VLF data in real time.
Figure 2 shows the propagation path of the Alpha VLF navigation system to Haikou, where the main station is located in Novosibirsk (NOV), the eastern sub-station in Khabarovsk (HAB) and the western sub-station in Krasnodar (KRA) (Němec, Santolík and Parrot, 2021). Each station has three frequencies: 11.904 kHz, 12.649 kHz and 14.881 kHz. Haikou Station is in the northern part of Hainan Island and its geographical coordinates are\(({22^ \circ }02^{\prime}45.97^{\prime\prime}N,{110^ \circ }11^{\prime}38.39^{\prime\prime}E)\). The observation system receives VLF signals at 11.904 kHz, 12.649 kHz and 14.881 kHz operating frequencies from the Alpha VLF Navigation System West (KRA), Main (NOV) and East (HAB) stations in Haikou, Hainan Province. The data is recorded and monitored every 3 min by the digital VLF software radio receiver designed in Fig. 1, and the VLF signal is received uninterruptedly throughout the day.
1.2 Observation Principles
The working frequency of VLF is between 3 and 30 kHz. VLF signals are widely used in long-distance radio communication, earthquake prediction, undersea communication, ground exploration engineering, navigation system and astronomical prediction because of their long wavelength, low attenuation, and good phase stability. In recent years, many data show that the phase variation of VLF is very sensitive to SID caused by X-rays (Selvakumaran et al., 2015) and high-energy particles (Peter, Chevalier and Inan, 2006) erupting from solar activities. By analyzing the abnormal VLF phase, the correlation between solar flare, high-energy particle deposition and VLF signal is studied, and then the energy change of sunspot group is monitored.
The wavelength of the VLF signal emitted by the VLF antenna is comparable to the distance between the ground and the ionosphere. VLF signal propagates in the earth-ionosphere waveguide composed of the earth and the ionosphere, which is usually analyzed by the concept of "waveguide mode". The propagation mode is shown in Fig. 3. Ionosphere is usually divided into three regions, from top to bottom, F layer, E layer and D layer. Layer D is about 70km away from the earth's surface. It absorbs the short-wave of radio wave, and the electron density is large during the day, and basically disappears at night. Within the range of about 90km from the earth's surface in the E layer, the electron density has diurnal and seasonal changes. The electron density can reach during the day, and it decreases by an order of magnitude at night compared with that during the day. At night, E layer will rise in height. The F layer is about 130km away from the earth's surface. There are irregular and abnormal changes in the F layer, which exists day and night. It is divided into F1 layer and F2 layer during the day, and the nigh is combined into one layer. The upper wall of the earth-ionospheric waveguide is the ionospheric D layer during the day, the D layer disappears at night, and the reflective upper wall is the E layer (Devi, Khan and Rao, 2008). The geomagnetic field causes the ionosphere to become an anisotropic medium, which changes periodically with the latitude and longitude of sunspots, seasons, and 11 years. When the VLF signal propagates in the waveguide space between the transmitting station and the receiving station, it undergoes multiple refractions in the ground-ionospheric waveguide and propagates forward in the waveguide cavity
Ionosphere D is mainly formed by the atmosphere ionized by Lyman-α rays of solar radiation and X rays. When a solar flare erupts, the change of Lyman-α ray flux is small, while the X-ray flux tends to increase by 2 ~ 3 orders of magnitude in a short time. A large number of X-rays emitted travel at the speed of light, reaching the near-earth space in about 8.3min. As the electron concentration in the ionosphere increases, the equivalent reflection height will decrease, resulting in the phase anomaly of VLF signal. The offset \(\Delta \varphi\) of VLF signal phase anomaly is related to propagation direction, great circle distance of path, working frequency, ground conductivity, solar zenith angle and equivalent reflection height of low ionosphere, etc. Given the working frequency, time and propagation path, the offset \(\Delta \varphi\) of the phase anomaly is only related to the change of the equivalent reflection height of the low ionosphere. The distance between the transmitting station and the receiving station of VLF signal is relatively far. If part of the propagation path is on the sunshine surface, the outbreak of solar flare can be observed. If more than two propagation paths exist, the solar activity can be observed all day. VLF signal can conveniently monitor and forecast solar flares, and then predict the strength of sunspot groups according to the size of a series of solar flares, thus reducing the impact of strong sunspot movement on the space environment and people's production and life.
In the process of VLF signal propagating in the ground-ionosphere waveguide, the transmitting antenna will excite multi-order modes when it is relatively close to the transmitting station, and the phenomenon of multi-order wave mode propagation will occur in the waveguide, and the attenuation of high-order modes will increase with the propagation distance. In this paper, when the VLF signal receiving antenna is located in Haikou City far from the transmitting antenna it is mainly the first-order wave mode propagation. For the first-order mode, the phase velocity \({v_p}\) of the VLF signal when propagating within the waveguide is (Zhao and Wang 1990):
$${v_P} \approx {v_c}(1 - \frac{{0.36{h_0}}}{a}+\frac{{v_{c}^{2}}}{{32{f^2}h_{0}^{2}}})$$
1
Where: \({v_c}\) is the propagation speed of light in space, which is about\(3 \times {10^8}m/s\); \({h_0}\) is the equivalent reflection height of the ionosphere, which is about 72km in summer and autumn, 70km in winter and spring, and 90km at night; f is the frequency of VLF signal. Each transmitting station of Alpha VLF navigation system has three frequencies of 11.904kHz, 12.649 kHz and 14.881 kHz, and the corresponding value of fis selected according to different transmitting stations; a is the average radius of the earth, about 6371km.
When the VLF signal is abnormal, the phase change \(\Delta \varphi\) is:
$$\Delta \varphi =D(\frac{1}{{{v_p}^{\prime }}} - \frac{1}{{{v_p}}})$$
2
From (1) and (2), the phase velocity of VLF can be obtained when a sunspot group erupts into a solar flare.
$${v_p}^{\prime }=\frac{{D{v_p}}}{{D+\Delta \varphi {v_p}}}$$
3
Where: D is the great circle path distance; Through programming calculation, the great circle distance from Russian Alpha navigation station KRA to Haikou receiving station in Hainan province is 7060.98km; the distance from NOV to Haikou receiving station in Hainan Province is 4508.875km; the distance from HAB to Haikou receiving station in Hainan Province is 4066.35km.
After sunspot group erupts solar flare, the decrease of ionospheric equivalent height \(\Delta {h_0}\) is:
$$\Delta {h_0}=\frac{{{h_0}\lambda }}{{2\pi \cdot D\left[ {0.36\frac{{{h_0}}}{a}+{{\left( {\frac{\lambda }{{4{h_0}}}} \right)}^2}} \right]}}\cdot \Delta \varphi ^{\prime}$$
4
Where: \(\Delta \varphi ^{\prime}\) is the arc system, \(\Delta \varphi ^{\prime}=2\pi f\cdot \Delta \varphi\), the phase change is expressed in radians; the wavelength of VLF signal\(\lambda ={{{v_c}} \mathord{\left/ {\vphantom {{{v_c}} f}} \right. \kern-0pt} f}\); the relationship between \(\Delta {h_0}\) and phase \(\Delta \varphi\) (Unit S) can be obtained by introducing the above formula:
$$\Delta {h_0}=\frac{{{h_0}}}{{D\left[ {0.36\frac{{{h_0}}}{a}+{{\left( {\frac{{{v_c}}}{{4{h_0}f}}} \right)}^2}} \right]}}\cdot \Delta \varphi$$
5
Therefore, through the phase change \(\Delta \varphi\) of VLF when the solar flare breaks out, the phase velocity \({v_p}^{\prime }\) when the solar flare breaks out and the equivalent height drop \(\Delta {h_0}\) of the low ionosphere are calculated.
Solar activity reaches a peak every 11 years. The peak years of solar activity in the 23rd solar activity week (1996–2008) were in 2000–2001 (Xiong et al., 2021). At this time, the Sun radiated a lot of material outwards, and solar flares were the most intense solar activities. Due to the relatively small impact of flares of small magnitude (A, B, C) on the space environment, the statistical analysis in this paper does not include flare events of small magnitude, but only flare events of M magnitude and above. In this paper, a total of 223 flares of M-level and above in the solar activity peak year 2000, of which 180 flares corresponding to sunspot groups accounted for 80.7% of the total number of flares and 43 flares without corresponding sunspot groups accounted for 19.3% of the total number of flares.
In 2000, a total of 62 sunspot groups erupted large flares of M-level or above. As shown in Fig. 4, the number of flares corresponding to the eruption of each sunspot group can be observed in the graph, with the number of black subgroup eruption flares of five or more represented by the red bar graph. The sunspot cluster numbered AR9077 in this picture has erupted in a total of 15 large flares. Figure 5 shows the corresponding relationship between sunspots extinction and flare grade. In the figure, the blue circle indicates the grade of flare M series, and the red circle indicates the size of flare X series. Among the large flares, M-class flares account for the vast majority, and it can be seen from the figure that the flares erupted by the sunspot group AR9077 are numerous and high-class, which is conducive to analyzing the impact of a series of flares erupted by sunspot groups on VLF.
In Table 1, statistics are made on a series of solar flares erupted by the sunspot group with the number of AR9077. There are 15 solar flares above M in total. Among them, there are 3 large flares above X level and 12 large flares above M level. The largest flare was X5.7, and the eruption time was 10: 03 am (UT) on July 14th, 2000.
|
NOAA/USAF |
Start |
Max |
End |
|||
|---|---|---|---|---|---|---|
|
Month |
Day |
Group |
Xray |
(UT) |
(UT) |
(UT) |
|
07 |
09 |
9077 |
M5.7 |
07:15 |
07:23 |
07:26 |
|
10 |
M1.1 |
10:26 |
10:56 |
11:43 |
||
|
10 |
M1.4 |
14:16 |
14:26 |
14:37 |
||
|
10 |
M5.7 |
21:05 |
21:42 |
22:27 |
||
|
11 |
M4.2 |
11:32 |
11:41 |
11:52 |
||
|
11 |
X1.0 |
12:12 |
13:10 |
13:35 |
||
|
12 |
M1.2 |
04:55 |
05:02 |
05:09 |
||
|
12 |
X1.9 |
10:18 |
10:37 |
10:46 |
||
|
13 |
M1.2 |
18:32 |
18:42 |
19:04 |
||
|
14 |
X5.7 |
10:03 |
10:24 |
10:43 |
||
|
14 |
M3.7 |
13:44 |
13:52 |
14:00 |
||
|
15 |
M1.3 |
08:20 |
08:33 |
08:48 |
||
|
16 |
M1.4 |
23:37 |
00:04 |
00:15 |
||
|
18 |
M1.9 |
04:59 |
05:15 |
05:38 |
||
|
18 |
M3.3 |
19:34 |
19:45 |
20:14 |
||
Select three representative large flares from a series of flares erupted by a sunspot group counted in the above table, and analyze the influence of flare eruption on the propagation path of VLF signal. Figure 6 shows the VLF data of 11.904kHz, 12.649kHz and 14.881kHz received from Alpha VLF navigation system in Haikou on July 9, 2000. Figure 6 shows the VLF data of Alpha VLF navigation system KRA 11.904kHz, 12.649kHz and 14.881kHz received in Haikou on July 9, 2000. To clearly observe the abnormal phase change caused by the flare with sunspot group eruption, the green circle is used in the figure to circle the area with obvious phase advance phenomenon, and the abnormal phase change of VLF propagation is calculated. According to the relationship between local time (LT) and universal time (UT), LT = UT + 8, and according to the time of VLF phase advance in Fig. 6, it can be estimated that the time of flare burst is from 07: 15 to 08: 02 UT on July 9, 2000.
Figure 7 shows the VLF amplitude and phase curves of three frequencies in the Alpha VLF navigation system KRA received in Haikou on July 12th, 2000. It is found that at 12:55 − 13:30 LT and 18:18–20:00 LT on the same day, the phase of VLF signal is abnormally advanced, and the change range is large. According to the changing relationship between LT and UT, it is speculated that the phase anomaly of large flare occurred at 04:55 − 5:30 UT and 10:18 − 12:00 UT.
Figure 8 shows the VLF amplitude and phase curves of three frequencies in the Alpha VLF navigation system KRA received in Haikou on July 14th, 2000. It is observed that at 18:03–18:48 LT on the same day, that is, the green circle in Fig. 8, the VLF signal propagation leads to abnormal phase advance. According to the conversion relationship between local time and universal time, it is predicted that there will be a big flare at 10:03–10:18 UT, which will cause the phase propagation anomaly.
The VLF phase change curves of July 9, 12 and 14, 2000 were observed by receiving the VLF data of sunspot group AR9077 from the east sub-station and the west sub-station of Alpha VLF navigation system to Haikou station, and the abnormal phase advance was found. The phase change was inferred according to the conversion relationship between local time and universal time, and compared with the X-ray flow chart released by GOSE satellite in the United States. The duration of flare observed by VLF method is based on the time from when the phase of flare starts to suddenly change to when the phase returns to normal, while the duration of flare released by GOSE satellite is calculated according to the X-ray streamline, so the duration of flare observed by VLF method is longer than that in the X-ray flow chart released by GOSE satellite. Although the two methods calculate flare time differently, they do not affect the accuracy of VLF observation. As shown in Fig. 9, Fig. 9 shows the X-ray flux on July 9th, 12th and 14th, 2000, respectively. In the figure, the curve of the big flare caused by the sunspot group AR9077 in three days is marked with a green circle. The observed flare outbreak time is consistent with the release time of GOSE satellite.
According to the X-ray flux, flare grades can be divided into five grades (Niu et al., 2014), as shown in Table 2. Among them, each grade in A, B, C, M is divided into 1 to 9 grades according to intensity, while grade X has no upper limit.
In Fig. 9, according to the X-ray flux released by GOSE satellite, the levels of X-rays are M5.7, M1.2, X1.9 and X5.7 on the day of the outbreak. From the observed VLF phase change curves as shown in Fig. 6, Fig. 7 and Fig. 8, the abrupt phase change \(\Delta \varphi\)is calculated as 25cec, 21cec, 57cec and 68cec according to the abnormal phase change of the black curve. Based on the theoretical analysis above, the equivalent reflection height \(\Delta {h_0}\) of the ionosphere is calculated as 8.996km, 4.342km, 11.812km and 14.092km.
Table 2 Solar flare level
The observation site selected in this paper is different from the previous observation sites, and the propagation path is also different (Niu et al., 2014). It is necessary to re-fit the relationship between the solar X-ray flux density and the equivalent descent height of the ionosphere. The fitting solution of the West Sub-station is carried out by a large amount of observation data and the least square method. From the variation of VLF phase and the variation of equivalent reflection height of ionosphere, a new fitting formula is obtained:
West substation fitting formula: \(F=3.271{e^{0.2602\Delta {h_0}}} \times {10^{ - 3}}\) (6)
Where: F is the solar X-ray flux density, the unit is \({\text{erg}}/c{m^2}\cdot s\), The zenith angle is the angle between the incident direction of the sun's rays and the vertical direction of the zenith (Cronin, 2014).The change of the sun's zenith angle will affect the equivalent reflection height of the ionosphere. From sunrise to noon to sunset, the sun's zenith angle first decreases to a minimum and then gradually increases, and the equivalent reflection height of the ionosphere will change to some extent (Han and Cummer, 2010). The series of flares erupted by AR9077 were observed in summer, and the time of sunrise and sunset was almost the same as the change of zenith angle. The daily change was regarded as consistency, and the middle day of observation was selected as the reference value. Divide the zenith angle of the sun at each moment at the receiving station. As shown in Fig. 10, the zenith angle of the sunrise and sunset changes with time, and calculate the zenith angle of the sun at the whole point. The zenith angle is the smallest when the sunlight is vertically incident between 12:00–13:00 LT. Because of the influence of solar zenith angle on the ionosphere, the prediction accuracy of flare in this paper will be wrong, so the prediction system needs to be further revised. In this paper, the effect of the solar zenith angle is reduced by correcting the equivalent height of the ionosphere. According to the change of solar zenith angle, the ionospheric equivalent height is corrected, and the correction coefficient is \(co\). The corresponding values of the change of zenith angle and the correction coefficient \(co\) are shown in Table 3. From 11: 00 to 14: 00LT, the small change of the solar zenith angle has little impact on the ionosphere, and the correction coefficient \(co=1\). When calculating, the corresponding coefficient can be selected according to the zenith angle corresponding to the time change to reduce the error. The X-ray flux density F calculated by formula (6) is compared with the flare grade classification in Table 2, and the flare grade can be predicted.
|
Time (LT) |
Sun zenith angle |
\(co\) |
|---|---|---|
|
07:00 |
78.77 |
1.46 |
|
08:00 |
65.46 |
1.35 |
|
09:00 |
51.09 |
1.28 |
|
10:00 |
38.18 |
1.20 |
|
11:00 |
24.35 |
1.0 |
|
12:00 |
10.46 |
1.0 |
|
13:00 |
3.49 |
1.0 |
|
14:00 |
17.38 |
1.0 |
|
15:00 |
31.25 |
1.16 |
|
16:00 |
45.03 |
1.25 |
|
17:00 |
58.68 |
1.33 |
|
18:00 |
72.13 |
1.42 |
|
19:00 |
85.27 |
1.50 |
In this paper, after observing the series of flares erupted by the sunspot group AR9077, the flare level is predicted by calculation to obtain the observed flare data in Table 4. The VLF data of 11.904kHz from Alpha West Sub-station to Haikou are monitored in Table 4. In the table, when the flares of M1.4 and M5.7 on 10th, M1.2 on 13th, M3.7 on 14th, M1.4 on 16th and M3.3 on 18th occur, the propagation paths are all in the dark, so VLF data can't observe the big flares completely at night, so there is a data gap. The prediction of flare level in daytime or part of daytime in the propagation path is consistent with the flare level released by GOSE satellite, which confirms the correctness of the observed data. At the same time, we should pay attention to the errors in the calculation results caused by various factors when VLF signals propagate in the earth-ionosphere waveguide, and further correct them.
|
Month |
Day |
Sunspot group |
Start |
Max |
End |
\(\Delta \varphi\) |
\(\Delta {h_0}\) |
\(co\) |
VLF phase-based flare magnitude |
GOES-based flare magnitude |
|---|---|---|---|---|---|---|---|---|---|---|
|
(LT) |
(LT) |
(LT) |
\((cec)\) |
\((km)\) |
||||||
|
07 |
09 |
9077 |
15:15 |
15:23 |
16:06 |
40.3 |
8.289 |
1.3 |
M5.5 |
M5.7 |
|
10 |
18:26 |
18:56 |
19:43 |
20 |
4.145 |
1.4 |
M1.4 |
M1.1 |
||
|
10 |
— |
— |
— |
— |
— |
— |
— |
M1.4 |
||
|
10 |
— |
— |
— |
— |
— |
— |
— |
M5.7 |
||
|
11 |
19:32 |
19:41 |
19:52 |
31 |
6.424 |
1.5 |
M4.0 |
M4.2 |
||
|
11 |
20:12 |
21:10 |
21:35 |
42 |
8.704 |
1.5 |
X1.0 |
X1.0 |
||
|
12 |
12:55 |
13:02 |
13:30 |
21 |
4.342 |
1.0 |
M1.0 |
M1.2 |
||
|
12 |
18:18 |
18:37 |
20:00 |
57 |
11.812 |
1.4 |
X2.4 |
X1.9 |
||
|
13 |
— |
— |
— |
— |
— |
— |
— |
M1.2 |
||
|
14 |
18:03 |
18:24 |
18:48 |
68 |
14.092 |
1.4 |
X5.6 |
X5.7 |
||
|
14 |
— |
— |
— |
— |
— |
— |
M3.7 |
|||
|
15 |
16:20 |
16:33 |
16:48 |
27 |
5.595 |
1.3 |
M2.1 |
M1.3 |
||
|
16 |
— |
— |
— |
— |
— |
— |
M1.4 |
|||
|
18 |
12:59 |
13:15 |
13:38 |
29 |
6.100 |
1.0 |
M1.6 |
M1.9 |
||
|
18 |
— |
— |
— |
— |
— |
— |
M3.3 |
This paper based on NOAA sunspot activity area data and solar flare data released by GOSE satellite, a series of flares erupted by sunspot groups in 2000 are counted. In 2000, there were 223 flares of M-class and above, of which 80.7% were related to sunspot groups. According to statistics, M-class flares accounted for most of flares. In this paper, a series of large flares with the number AR9077 were selected. By receiving the VLF data of Alpha VLF navigation system in Haikou, the influence of the series of large flares with sunspots on the propagation of VLF signals was analyzed. After the flare broke out, a large number of X-rays reached the near-earth space, resulting in an increase in the electron concentration of the ionosphere and a decrease in the equivalent reflection height of the ionosphere, which resulted in the phase advance of VLF signals in the propagation process, and the abnormal change of phase was proportional to the flare level. According to the phase variation of VLF signal, the variation of ionospheric equivalent height is calculated, and the flare size is calculated according to the fitting equation of X-ray flux and the classification of flare grade. By being consistent with the data released by GOSE satellite, we can know the validity of our observed data. In this paper, there are still some errors between the time of VLF signal phase anomaly and the time of flare burst released by GOSE satellite, so it is necessary to correct the observation system, propagation path and other parameters. A sunspot group has different flares depending on the amount of energy obtained. A sunspot group with higher energy can continuously erupt a series of large flares, thus causing a great impact on the space environment, navigation systems, short-wave communications, and power systems.. Therefore, solar flares are monitored, and then the energy of sunspots is predicted to judge the impact on us, so as to avoid property damage.
Acknowledgments
This research was supported by the National Natural Science Foundation of China (U1704134) and key scientific and technological key projects of Henan Province (162102210263, 172102310238). The sunspot group data and X-ray flux used in this paper are from the website of the National Oceanic and Atmospheric Administration (NOAA): https://satdat.ngdc.noaa.gov/sem/goes/data/full/。The VLF data used in this paper were collected from observations made by Professor Niu Youtian while working in China Institute of Radio Wave Propagation.
- Bornmann, P.L., Shaw, D.: 1994, Flare rates and the McIntosh active-region classifications. Solar. Phys. 105, 127. Doi:10.1007/BF00712882.
- Barnes, G., Leka, K.D., Schrijver, T.C., Qahwaji, R., Ashamari, O.W., YUAN, Y., Zhang, J., Mcateer, R.T., Bloomfield, D.S., Higgins, P.A., Gallagher, P.T., Falconer, D.A., Georgoulis,. M.K., Wheatland, M.S., Balch, C., Dunn, T., Wagner, E.L.: 2016, A Comparison of Flare Forecasting Methods. I. Results from the “All-Clear” Workshop. Astrophys J. 829, 89. Doi:10.3847/0004-637X/829/2/89.
- Cander, L.R.:2008, Ionospheric research and space weather services. J Atmos Sol-Terr Phy. 70, 1870. Doi:10.1016/j.jastp.2008.05.010.
- Cronin, T.W.: 2014, On the choice of average solar zenith angle. J Atmos Sci. 71, 2994. Doi:10.1175/jas-d-13-0392.1.
- Devi, M.I., Khan, I., Rao, D.M.: 2008, A study of VLF wave propagation characteristics in the earth-ionosphere waveguide. Earth Planets Space. 60, 737. Doi:10.1186/bf03352822.
- Fang, Y.H., Cui, Y.M., Ao, X.Z.: 2019, Deep learning for automatic recognition of magnetic type in sunspot groups. Adv Astron. 2019, 9196234. Doi:10.1155/2019/9196234.
- Florios, K., Kontogiannis, I., Park, S.H., Guerra, J.A., Benvenuto, F., Bloomfield, D.S., Georgoulis, M.K.: 2018, Forecasting Solar Flares Using Magnetogram-based Predictors and Machine Learning. Solar Phys. 293, 2. Doi:10.1007/s11207-018-1250-4.
- Grimes, R., Pintér, B., Morgan, H.: 2020, Observation of Differential Rotation Within a Sunspot Umbra During an X-Class Flare. Solar Phys. 295, 87. Doi:10.1007/s11207-020-01657-5.
- Gu, X.D., Luo, F., Peng, R., et al. 2021.Response characteristics of very low frequency signals from JJI transmitter to solar flare events (in Chinese). Chin J Geophys. 64, 1508. Doi:10.6038/cjg2021O0422.
- Hayes, L.A., O’Hara, O.S.D., Murray, S.A., Gallagher, P.T.: 2021, Solar Flare Effects on the Earth’s Lower Ionosphere. Solar Phys. 296, 157. Doi:10.1077/s11207-021-01898-y.
- Han, F., Cummer, S.A.: 2010, Midlatitude daytime D region ionosphere variations measured from radio atmospherics. J Geophys Res: Space Phy. 115, 10314. Doi:10.1029/2010JA015715.
- Jiang, Y., Zheng, R., Yang, J., Hong, J., Yi, B., Yang, D.: 2012, Rapid Sunspot Rotation Associated with the X2.2 Flare on 2011 February 15. Astrophys J. 744, 50. Doi:10.1088/0004-637X/744/1/50.
- Kontogiannis, I., Georgoulis, M.K., Park, S-H., Guerra, J.A.: 2018, Testing and improving a set of morphological predictors offlaring activity. Solar Phys. 293, 96. Doi:10.1007/s11207-018-1317-2.
- Kim, T., Park, E., Lee, H., Moon, Y.J., Bae, S.H., Lim, D., Jang, S., Kim, L., Cho, I.H., Choi, M., Cho, K.S.: 2019, Solar farside magnetograms from deep learning analysis of STEREO/EUVI data. Nat Astron. 3, 397. Doi:10.1038/s41550-019-0711-5.
- Korsós, M.B., Yang, S., Erdélyi, R.: 2019, Investigation of pre-flare dynamics using the weighted horizontal magnetic gradient method: From small to major flare classes. J Space Weather Space Clim. 9, A6. Doi:10.1051/swsc/2019002.
- Kolarski, A., Grubor, D.: 2014, Sensing the Earth’s low ionosphere during solar flares using VLF signals and goes solar X-ray data. Ad Space Res, 53, 1595. Doi:10.1016/j.asr.2014.02.022.
- Kumar, A., Kumar, S.: 2018, Solar flare effects on D-region ionosphere using VLF measurements during low- and high-solar activity phases of solar cycle 24. Earth Planets Space. 70, 29. Doi:10.1186/s40623-018-0794-8.
- Lee, K.J., Moon, Y.J., Lee, J.Y., Lee, K.S., Na, H.: 2012, Solar Flare Occurrence Rate and Probability in Terms of the Sunspot Classification Supplemented with Sunspot Area and Its Changes. Solar Phys. 281, 639. Doi:10.1007/s11207-012-0091-9.
- Mariachiara, F., Costa, P., Romano, P.: 2019, Solar flare forecasting using morphological properties of sunspot groups. J Space Weather Space. 9, 22. Doi:10.1051/swsc/2019019.
- Nagovitsyn, Y.A., Kuleshova, A.I.: 2013, Recurrence of flare energy releases in solar active regions (Cycle 23). Geomagn Aeron. 53, 985. Doi:10.1134/S0016793213080173.
- Niu, Y.T., Bi, Y.: 2016, VLF Method Prospecting Receiver Based on Software Radio (in Chinese). J Henan Normal Univ (Nat Sci Ed). 44, 70. Doi:10.16366/j.cnki.1000-2367.2016.01.013.
- Niu, Y.T., Li, L., Zhao. X.Z., Li, D.D., Wei, S.J., Bi Y.X.: 2014, Observation and Analysis of the Effect of Two Consecutive Extra-large Particles Sedimentation on VLF Signal Propagation in Antarctic (in Chinese). Sci Tech Engrg. 14, 203.
- Niu, Y.T., Chen, J.F., Hao, H.Z., Wang, H.B., Zhang, Z.Y.: 2009, Observation and Analysis of Total Solar Eclipse of 1997 March 9 Using VLF Signal. J Henan Normal Univ (Nat Sci Ed). 37, 64. Doi:10.16366/j.cnki.1000-2367-2009.02.045.
- Němec, F., Santolík, O., Parrot, M.:2021, Doppler Shifted Alpha Transmitter Signals in the Conjugate Hemisphere: DEMETER Spacecraft Observations and Raytracing Modeling. J Geophys Res-Space. 126, 029017. Doi:10.1029/2020ja029017.
- Niu, Y.T., Li, L., Zhao, X.Z., Li, D.D., Wei, S.J., Bi Y.X.: 2014. Correlation between extra-large solar flare and phase of VLF on February 25, 1991 in Antarctic (in Chinese). Prog Geophys. 29, 2526. Doi:10.6038/pg20140607.
- Niu, Y.T., Zhang, Y.X., Xie, Y.T., Li, D.D., Li, L.: 2014, Forecast on solar activity during the launch of ”ShenzhouII” by the VLF method (in Chinese). Prog Geophys. 29, 1426. Doi:10.6038/pg20140359.
- Peter, W.B., Chevalier, M.W., Inan, U. S.: 2006, Perturbations of midlatitude subionospheric VLF signals associated with lower ionospheric disturbances during major geomagnetic storms. J Geophys Res: Space Phy. 111, 03301. Doi:10.1029/2005JA011346.
- Ruan, G.P., Chen, Y., Wang, S., Zhang, H.Q., Li, G., Jing, J., Su, J.T., Li, H.Q., Du, G.H., Wang, H.M.: 2014, A Solar Eruption Driven by Rapid Sunspot Rotation. Astrophys J. 784, 165. Doi:10.1088/0004-637X/784/2/165.
- Šulić, D.M., Srećković, V.A., Mihajlov, A.A.: 2016, A study of VLF signals variations associated with the changes of ionization level in the D-region in consequence of solar conditions. Adv Space Res. 57,1029. Doi:10.1016/j.asr.2015.12.025.
- Selvakumaran, R., Maurya, A.K., Gokani, S.A., Veenadhari, B., Kumar, S., Venkatesham, K., Phanikumar, D.V., Singh, A.K., Siingh, D., Singh, R.: 2015, Solar flares induced D -region ionospheric and geomagnetic perturbations. J Atmos Sol-Terr Phy. 123, 102. Doi:10.1016/j.jastp.2014.12.009.
- Thomson, N.R., Clilverd. M.A.: 2001, Solar flare induced ionospheric D-region enhancements from VLF amplitude observations. J Atmos Sol-Terr Phy. 63, 1729. Doi:10.1016/S1364-6826(01)00048-7.
- Wheatland, M.S.: 2001, Rates of Flaring in Individual Active Regions. Solar Phys. 203, 87. Doi:10.1023/A:1012749706764.
- Wu, Q.D., Zhou, S.R., Song, Y.: 2000, Relations between the solar flares and the areas of sunspot groups (in Chinese). Publications of purple mountain observatory. 19, 10.
- Xiong, B., Wang, T., Li, X.L., Yin, Y.X.:2021, Statistical analysis of soft X-ray solar flares during solar cycles 22, 23, and 24. Astrophys Space Sci. 366, 1. Doi:10.1007/s10509-020-03909-z.
- Yan, X.L., Xue, Z.K., Pan, G.M., Wang, J.C., Xiang, Y.Y., Kong, D.F., Yang, L.H.: 2015, The Formation and Magnetic Structures of Active-region Filaments Observed by NVST, SDO, and Hinode. Astrophys J Suppl. S. 219, 17. Doi:10.1088/0067-0049/219/2/17.
- Zhao, M.Y., Chen, J.Q., Liu, Y., Ahmed, I., Yan, X.L., Guo, J.P.: 2014, Statistical analysis of sunspot groups and flares for so1ar maximum and minimum (in Chinese). Sci Sin-Phys Mech Astron. 44, 109. Doi:10.1360/132012-809.
- Zhao, X.Z., Wang, X.J.: 1990, The study of correlation between VLF phase anomalies and solar X-Ray fluxes during solar flares (in Chinese). Chin J Radio. 05, 35. Doi:10.13443/j.cjors.1990.02.05.
No competing interests reported.