Ionospheric and Magnetic Signatures of a Space Weather Event on 25–29 August 2018: CME and HSSWs

Abstract

We present a study concerning a space weather event on 25–29 August 2018, accounting for its ionospheric and magnetic signatures at low latitudes and midlatitudes. The effects of a storm in several longitudinal sectors (Asia, Africa, America, and the Pacific) have been analyzed using various parameters such as total electron content (TEC), geomagnetic field, and column [O/N2] ratio. Positive ionospheric storms are found in all the longitudinal sectors having its maximum effects in the Asian sector, whereas the negative ionospheric storms have been observed in the summer hemisphere (Northern Hemisphere). A large decrease in [O/N2] ratio in the Northern Hemisphere is a possible cause of the observed negative storm effects. Ionospheric F2 region maximum electron density (NmF2) and TEC have shown a positive correlation during this storm. The study suggests that storm time‐generated wind does not have a uniform planetary extension and mainly affects dayside (America and Pacific) and duskside (Africa) sectors. During the space weather event, we observe an asymmetric variation of the magnetic field as a function of the longitude. On the other hand, the magnetic variations at midlatitudes are found to be symmetric in both hemispheres. A signature of the disturbance dynamo (anti‐Sq circulation) has been observed, mainly at low latitudes. We emphasize that the partial ring current (PRC), estimated by the ASYM‐H magnetic index, must also be taken into account along with the SYM‐H index for a better approximation of ionospheric currents. The study further suggests existence of several electric current cells in the ionosphere, which is consistent with the Blanc‐Richmond model.

Storm Time Effects on Latitudinal Distribution of Ionospheric TEC in the American and Asian‐Australian Sectors: August 25–26, 2018 Geomagnetic Storm

“…This is the origin of the interesting DHI reported in the works of Younas et al. (2020) at MGUE after the MP.…”

“…While it was upward directed around 13:00 LT–18:00 LT, it was a weaker one compared to that of the PC. Other geomagnetic conditions that signaled inhibition of fountain effect over the American dayside after the MP around 08:00 LT–17:00 LT are DDEF (Younas et al., 2020) and the varying Sym‐H attempting positive value (Figure 2, panel 5). Also, is a reduction in AE (not shown here but at http://wdc.kugi.kyoto-u.ac.jp/ae_realtime/201808/index_20180826.html) and PCN value (Figure 2, panel 4), which both signify a significant decrease in the number of energetic particles entering the atmosphere from the magnetosphere.…”

“…We corrected the latitudinal offset reported in the works of Younas et al. (2020). We observed a significant decrease in TEC over the northern middle‐low latitude stations compared to the southern ones in American sector during the storm's MP.…”

Magnetic Signatures of Ionospheric Disturbance Dynamo for CME and HSSWs Generated Storms

“…Whereas the D dyn is associated with DDEF (Bulusu et al., 2018; Fathy et al., 2014; Le Huy & Amory‐Mazaudier, 2005) and results in the anti‐Sq oscillations, which are often observed during the recovery phase. Moreover, the D iono has also contribution from other sources such as partial ring current during the early phase of a storm and sometime Sq‐like oscillations during the recovery phase, which cannot be associated D dyn (Younas et al., 2020). Hence, simply applying filters to D iono for the estimation of D dyn may not provide an accurate information.…”

“…Fejer et al (2017) summarized the recent progresses made to analyze the disturbance dynamo and its effect at middle and low latitudes. Nava et al (2016), Zaourar et al (2017), Bulusu et al (2018) and Younas et al (2020) studied the temporal variation of disturbance dynamo generated during different storms by applying the band pass filter techniques. However, the D iono can have Sq like variations, which may not be considered as an effect of DDEF.…”