Classification of X-ray solar flares regarding their effects on the lower ionosphere electron density profile

Abstract

Abstract. The classification of X-ray solar flares is performed regarding their effects on the Very Low Frequency (VLF) wave propagation along the Earth-ionosphere waveguide. The changes in propagation are detected from an observed VLF signal phase and amplitude perturbations, taking place during X-ray solar flares. All flare effects chosen for the analysis are recorded by the Absolute Phase and Amplitude Logger (AbsPal), during the summer months of 2004-2007, on the single trace, Skelton (54.72 N, 2.88 W) to Belgrade (44.85 N, 20.38 E) with a distance along the Great Circle Path (GCP) D≈2000 km in length.The observed VLF amplitude and phase perturbations are simulated by the computer program Long-Wavelength Propagation Capability (LWPC), using Wait's model of the lower ionosphere, as determined by two parameters: the sharpness (β in 1/km) and reflection height (H in km). By varying the values of β and H so as to match the observed amplitude and phase perturbations, the variation of the D-region electron density height profile N e (z) was reconstructed, throughout flare duration. The procedure is illustrated as applied to a series of flares, from class C to M5 (5×10 −5 W/m 2 at 0.1-0.8 nm), each giving rise to a different time development of signal perturbation.The corresponding change in electron density from the unperturbed value at the unperturbed reflection height, i.e. N e (74 km)=2.16×10 8 m −3 to the value induced by an M5 class flare, up to N e (74 km)=4×10 10 m −3 is obtained. The β parameter is found to range from 0.30-0.49 1/km and the reflection height H to vary from 74-63 km. The changes in N e (z) during the flares, within height range z=60 to 90 km are determined, as well.

Modeling solar flare induced lower ionosphere changes using VLF/LF transmitter amplitude and phase observations at a midlatitude site

“…8 in Han and Cummer (2010), the h = 3.5-5 km per X sh -flux decade can be read. To compare our calculated h vs. X sh relation and results of different authors (Thomson et al, 2005;Grubor et al, 2008), we have to map X sh to X lo , because these results are mostly listed with respect to the lower energy (longer wavelength, 0.1-0.8 nm) band which is also used for the usual B, C, M, X flare classification.…”

Modeling of very low frequency (VLF) radio wave signal profile due to solar flares using the GEANT4 Monte Carlo simulation coupled with ionospheric chemistry

“…It uses the exponential D-region ionosphere defined by Wait and Spies (1964) and wave guide mode formulations developed by Budden (1951). This program has been used by many workers and is quiet successful for modeling of long-range propagation of VLF signals even in presence of ionospheric anomalies (Grubor et al, 2008;Rodger et al, 1999;Chakrabarti et al, 2012;Pal et al, 2012a, b). Instead of Wait's model for the D-region ionosphere, we used our own result for that part of the ionosphere, by incorporating the results from the GEANT4 Monte Carlo simulation and the GPI scheme in the LWPC program.…”

The responses of low-latitude D region ionosphere to solar flares during 2014

“…Từ đó, các giá trị biên độ nhiễu loạn (A), pha nhiễu loạn (P) được tính như sau (Grubor et al, 2008):…”

“…Khoảng thời gian trễ này là cần thiết cho quá trình tái hợp và ion hóa để hồi phục lại sự cân bằng dưới tác dụng của bức xạ tia X khi có BNSCMT (Zigman et al, 2007). Sử dụng sóng VLF từ trạm phát GQD, Grubor và các cộng sự ghi nhận BNSCMT từ lớp C đến M5 trong suốt các tháng mùa hè từ năm 2004 -2007, tại Belgrade (44,85°B; 20,38°Đ) Serbia và tìm thấy  tăng từ 0,3 đến 0,49 km -1 trong khi đó h' giảm từ 74 km đến 63 km (Grubor et al, 2008). Basak & Chakrabarti phân tích 22 sự kiện BNSCMT từ C1.5 đến M9.31 ghi nhận bởi sóng NWC/19,8 kHz trong suốt tháng 1 -9 năm 2011 tại Sitapur (22,45° B; 87,75° Đ), India với góc thiên đỉnh trong khoảng 14-33 (Basak & Chakrabarti, 2013 …”