High-frequency trend during intense solar activity in September 2017: equatorial studies
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ORIGINAL PAPER
High-frequency trend during intense solar activity in September 2017: equatorial studies S Abdullah*
and J Talib
Space Science Center, Institute of Climate Change, Universiti Kebangsaan Malaysia, Bangi, Malaysia Received: 02 December 2019 / Accepted: 19 June 2020
Abstract: Various solar flares and coronal mass ejections were associated with the intense solar activity located at RGN 2673 based on NASA’s record. The effects of solar activity change the condition of the ionosphere leading to fading or loss of signal. The duration of signal loss may last for a few minutes or more than an hour depending on the scale of the solar flare. Having said that, such an event disturbed the HF (high-frequency) radio communication with high sunspot number (SSn) from 4th to 10th September 2017. The R1–R2 (minor moderate) and R3 (strong) radio blackouts occurred on 4th, 6th and 10th of September 2017. Therefore, this study aims to investigate and analyse the effects of intense solar activity towards HF radio communication based on the observations of Jicamarca (11.571° S, 76.525° W) and Fortaleza (3.7327° S, 38.527° W) ionosondes located at low latitudes and an amateur radio application executed at a ground station in UKM (2.92° N, 101.77° E). According to the data coverage from both the ionosondes on the specific dates, an increased value of critical frequency of F2 layer (foF2) during HF radio blackout was identified to be associated with high SSn. The X-class flares recorded on all three dates in September 2017 caused the foF2 to enhance with recovery times of tens of minutes to hours, based on the decay time of the flare. Moreover, HF selection for amateur radios experienced an increase of more than 8 MHz during the day compared to around 7 MHz on a normal day. This result is essential for frequency planning, especially for HF amateur radio users in and around Malaysia. Keywords: Critical frequency; High frequency; Solar activity; Ionosphere; Low latitude
1. Introduction High frequency (HF) is a communication frequency that utilises the ionosphere layer as the main medium for overhorizon communications. As for the radio communication systems, HF uses the earth–ionosphere layer for waveguiding. It is a valuable method of electronic communication that does not require man-made infrastructure to relay messages over the horizon and ranges between 3 and 30 MHz [1]. HF, which is a dependent wave signal that relies on ‘‘skywave’’ reflected in the ionosphere region [2], also travels in-ground and direct or line-of-sight wave. HF radio waves reflected by the ionosphere can be accessed up to a considerable distance, with changes in amplitude, phase and frequencies [3]. The ionosphere condition can be measured and analysed by several methods and instruments using the HF band, namely ionosonde, riometer and
*Corresponding author, E-mail: [email protected]
satellite observations [4]. For instance, Elias et al. [5] adapted the scale from ionograms using a standard graphical method for their research. Conteira et al.
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