Effect of Solar Flare X-Rays on digisonde fmin values. S. C. Tripathi H. Haralambous

Size: px

Start display at page:

Download "Effect of Solar Flare X-Rays on digisonde fmin values. S. C. Tripathi H. Haralambous"

Coral Oliver
5 years ago
Views:

1 Effect of Solar Flare X-Rays on digisonde fmin values S. C. Tripathi H. Haralambous

SOLAR FLARE Solar flares occur when the sun's magnetic field twists up and reconnects, blasting energy outward and superheating the solar surface.

2 SOLAR FLARE Solar flares occur when the sun's magnetic field twists up and reconnects, blasting energy outward and superheating the solar surface. X-class solar flares can cause radiation storms in Earth's upper atmosphere and trigger radio blackouts lasting from min to hours, occurs in localized active regions of the Sun, usually near a complex group of sunspots, arrives almost immediately in the geospace (around 9 min), following an eruption on the Sun s surface, usually coupled with Coronal Mass Ejection (CME)

3 IMPACT OF SOLAR FLARES ON THE LOWER IONOSPHERE Solar flares abruptly emit large amounts of electromagnetic energy at a wide range of wavelengths, particularly X-ray and Extreme Ultra Violet (EUV), for a very short duration. Solar EUV and X-rays are the primary energy sources of ionisation in the earth s ionosphere. The sudden increase in X-ray and EUV fluxes during solar flares causes extra ionisation of the D, E and F regions of the earth s ionosphere in the sunlit hemisphere within short intervals of time. The solar EUV spectrum of the range nm ionises the peak density F region of the ionosphere, while the soft X-rays with wavelengths less than 15 nm are responsible for the E region ionisation, and the Lyman-α ionises the D- region (Rishbeth and Garriott 1969). Solar flares may cause a sudden increase of total electron content (SITEC), short-wave fadeouts (SWF) and sudden D region absorption (SDA) (Donnelly 1971; Davies 1990; Liu et al. 1996, 2004, 2006). Many researchers have studied the effect of solar flares in the past and found that the earth s ionosphere in the sunlit hemisphere is significantly affected by solar flares (e.g., Mitra 1974; Davies 1990).

4 IMPACT OF SOLAR FLARES ON THE LOWER IONOSPHERE Ionization of the lower ionosphere (D-, E region) D region: L-alpha (121.6 nm), solar ultraviolet (UV) radiation ( λ < nm), solar X-rays (<0.8 nm), and galactic cosmic rays; E region: X- rays in the nm range and UV radiation from 80 nm to L-beta (102.6 nm) Particle ionization: solar cosmic rays, solar protons of MeV, and possibly solar electrons of energy >10 kev V. Bothmer & I Daglis, Space Weather, Physics and Effects, 7.2 Chapter B. Zolesi & L. Cander, Ionospheric Prediction and Forecasting, 2014

5 RADIO SYSTEM CONCERNS The penetration of X-rays down to the D-region of the ionosphere following solar flare event increases significantly the electron density The chief effect of the ionization in the D-region is to cause attenuation of the field intensity of HF (3-30 MHz) radio waves and to cause complete absorption of low (LF) and medium (MF) radio waves (below 3 MHz) Another phenomenon is polar cap absorption (PCA) which is generally preceded by a major solar flare seems to ionize molecular (O2, N2) protons in the D-region. PCA primarily takes place in the higher latitudes, appears an hour or two after the flare and can last from as few as five hours to as long as nearly two weeks. PCA simultaneously lowers the Maximum Usable Frequency (MUF) and raises the Lowest Usable Frequency (LUF) narrowing the usable frequency spectrum. As a result of solar activity LF, MF, and HF radio waves are not only absorbed but also cause fading, noise, and interference. Specially, HF Radio System operating in the mid-latitudes may experience depression of their MUF (up to 50%). Although not severely affected, VHF, UHF, microwave, and even satellite communication systems may experience enhanced phase and amplitude scintillations.

GSFLAI (GNSS SOLAR FLAREINDICATOR) The availability of extensive networks of Global Navigation Satellite Systems (GNSS) dual frequency receivers monitoring simultaneously the daylight and night

6 GSFLAI (GNSS SOLAR FLAREINDICATOR) The availability of extensive networks of Global Navigation Satellite Systems (GNSS) dual frequency receivers monitoring simultaneously the daylight and night hemispheres, makes it feasible to detect major solar flares as they cause rapid strong ionisation in the dayside ionosphere. GSFLAI (ESA SSA) product is developed and operated by the Universitat Politècnica de Catalunya.It is based on the impact of the ionospheric electron content as a response to solar flare activity. The ionospheric response appears as a change in the Vertical Total Electron Content (VTEC) whose time derivative has a linear dependency on the cosine of the Solar Zenith Angle (SZA). The slope of this linear trend can be used as a proxy for the time derivative of Solar EUV flux (in the spectral band of nm).

SOLAR FLARE CLASSIFICATION X : >100µW/m 2 M : 10 100µW/m 2 C : 1 10µW/m 2 B : 0.

7 SOLAR FLARE CLASSIFICATION X : >100µW/m 2 M : µW/m 2 C : 1 10µW/m 2 B : µw/m 2 A : µw/m 2 M4.5 X1.1 Χ28 (2800 μw/m 2 ) GOES greatest, Nov 4, 2003

8 IONOGRAMSDURING SOLAR FLARE Violent sun activity during intense solar flare produces X-ray radiations those can penetrate further into the ionosphere and ionize the D-layer much higher than normal. Such a high D-layer ionization can blank off a lot of the radio-wave spectrum. As a result, the lack of ionograms or partial ionograms may appear. This indicates no echoes or partial echoes of the transmitted digital ionosonde signals.

9 occurred beginning at 12:00:00 attaining its peak at 12:17:00 and ending at

9 IONOGRAMSDURING SOLAR FLARE Figure shows series of ionograms during a solar flare of class M5.9 occurred beginning at 12:00:00 attaining its peak at 12:17:00 and ending at 12:25:00. Note that at 12:20 the F layer is about to vanish indicating sudden ionospheric disturbances and recovering slowly after the flare has been over.

10 IMPACT OF OF SOLAR FLARES X-RAYS ON fmin VALUES The f min parameter, representing the lowest recorded ionosonde echo, is usually considered as a qualitative measure of the so called nondeviative radio wave absorption in the ionosphere (Risbeth and Gariott, 1960). It has been widely used to measure the absorption of D region (Lusignan, 1960; Oksman et al., 1981; Kokourov, 2006; Sharma et al, 2010; Schimmer et al, 2011). But this parameter is dependent on the radar instrumental characteristics and radio-noise level.

11 QUIET TIME FLARE TIME The practical significance of the increase in D-region electron density caused by solar flares lies on the increase of signal absorption that it produces causing limited window of operating frequencies for HF communications.

12 Day time Event 10 June 2014 Two solar flare of class X1.1 and X1.5 occurred Peaks are at 11:42 and 12:52:00 Figure shows the temporal variation of f min and f O F2 and the X-ray flux. There exists a very good correlation between f min and X-ray flux. At 13:00 hours UT, f min peaked to about 8.25 MHz. Later, a sharp decrease occurred in X-ray intensity and values reached to its background. f min follows the same trend. The X-ray intensity variation are similar to variations in f min but the decrease in X-ray intensity is slightly sharper. The variation of f 0 F2 does not follow the similar pattern as of X-ray flux. The value of f 0 F2 peaks around 12:20 hours at noon and the maximum value is MHz. Thereafter the value of f 0 F2 gradually decreases to 7.2 MHz at 15:50:00 and again gradually increases to MHz around 18:15 hours long time after the X-ray flux has reached to its quiet value.

13 Night time Event 20 December 2014 A solar flare of class X1.8 occurred Begun at 00:11 attained peak at 00:28 and ended at 00:55. Figure shows the temporal variations of f min and f O F2 duringsolar flare event which are not responsive to the X-ray flux intensity. The event exhibits poor correlation between f min and X-ray flux intensity. The correlation between N m F2and X-ray flux is also poor. X-ray flux intensity attains peak at 00:28, but despite that fact, both f min and N m F2rather show clear diurnal variation by attaining maxima during noon.

X-class Flares and Solar Particle Events of September 2017 The largest solar

3, took place on at 12:24 UTC on 6th September 2017.

a Coronal Mass Ejection (CME) and an associated interplanetary shock

Earth known as a Solar Particle Event (SPE).

14 X-class Flares and Solar Particle Events of September 2017 The largest solar X-ray flare seen in 12 years, class X9.3, took place on at 12:24 UTC on 6th September This eruption was accompanied by a fast expulsion of coronal plasma known as a Coronal Mass Ejection (CME) and an associated interplanetary shock accelerating particles resulting in an enhancement of radiation seen near the Earth known as a Solar Particle Event (SPE). This was followed by another huge X8.2 flare which took place at 16:06 UTC on Sunday 10th September 2017 with another very fast CME this time resulting in a stronger high-energy SPE.

15 Impact of the September 2017 solar flares over European ionosphere European ionosonde stations

16 Impact of the 6 th September 2017 solar flare over European ionosphere

17 Impact of the 10 th September 2017 solar flare over European ionosphere

18 Impact of the 7 th September 2017 solar flare over European ionosphere

19 Quantitative assessment of the impact of of Solar Flare X- Rays on digisonde fmin values from Global Ionospheric Radio Observatory (GIRO)

20 GIRO available data- American Sector

21 GIRO available data- Asian Sector

22 OUR STUDY We examined the behavior of lower ionosphere over a number of GIRO stations with a sounding time-resolution of 5-8 min during a number of solar flares (total seventy one x-flare-station cases) that occurred during The time series of the fmin and x-ray flux, recorded at meridionally-distributed stations over the globe, were analyzed during these intense solar events after manually scaling fmin values from each corresponding ionogram. In order to minimize and compensate for the instrumental errors, a df min parameter (difference between the value of the f min and the mean f min for a number of reference quiet days (10 geomagnetically quiet days around the events) was used during the analysis.

23 OUR STUDY Main aim was to determine whereas fmin can be used to carry out solar flare effects investigation similar to those based on dtec measurements (K. K. Mahajanet al. 201JGR for several solar flare events), (S. Sripathi et al JGR for a single solar flare events)

24 RESULTS

25 RESULTS

26 RESULTS

27 RESULTS

28 CONCLUSIONS Extreme increases of the fmin values (2-7 MHz) were observed at almost every GIRO station considered in this investigation during most X-class solar flares. The enhanced peak fmin was correlated with the enhanced peak X-ray flux. In some cases the relatively poor correlation with X-ray flux improved when the central meridian distance (CMD) of the solar flare location was considered. High time resolution is required to capture fmin transients during solar flare events.

29 THANK YOU

Introduction to Space Weather and Propagation

Introduction to Space Weather and Propagation Carl Luetzelschwab K9LA ARRL Vice Director, Central Division k9la@arrl.net https://k9la.us K9LA 1 What Is Space Weather? Space weather is the quiet Sun Electromagnetic