Diurnal and Seasonal Variation of Critical Frequency in Malaysia from 2005 to 2007

Abstract

Ionospheric layer plays an important role as the main medium for communication of wireless radio in the High Frequency (HF) band. Critical frequencies are important parameters of the ionosphere. Critical frequencies vary diurnally following the pattern of day and night due to the activities of the sun. The critical frequency for Parit Raja station is determined using an ionosonde at latitude 1° 52' N and longitude 103° 48' E, which are close to the geomagnetic equator at geographic latitude 5° N. This work analyses the dependence of the critical frequency during the solar minimum of Solar Cycle 23. From the observations, the critical frequency observed in 2005 was the highest, corresponding to a higher sunspot number of between 11 and 192. The general trend of the daily critical frequency was 6.8 MHz to 12.0 MHz from 00:00 to 17:30 Coordinated Universal Time (UTC) and decreasing to 7.0 MHz from 18:00 to 23:00 UTC. The average value of the critical frequency for 2005 to 2007 was 7.5 MHz, with a minimum of 1.8 MHz and a maximum of 11.0 MHz. The results showed a slow decrease from 2006 to 2007 for the critical frequencies in 2006 and 2007.

Variations of ionospheric F2 layer critical frequency in Malaysia during different solar phases

“…The researchers in [4] agree with the findings of [3]. In [4] The researchers in [5] and [6] studied the monthly median values of foF2 in Okinawa (26.30° N, 127.80° E).…”

“…The F2 layer critical frequency, foF2, is an important ionospheric parameter influenced by local time, geographical latitude, solar and magnetic activities, atmospheric background wind and other factors [1]. Several studies have been conducted to observe the changes in critical frequency and related them to other parameters, including solar activities [2][3][4][5][6][7]. The SSN appears on the sun's surface with an average cycle of approximately 11 years.…”

“…Solar radio flux at 10.7 (F10.7) and SSN are common solar activity indices used by many researchers in [2][3][4][5][6][7]. This study only focuses on the SSN.…”

The influence of sunspot number on high frequency radio propagation

“…Basically, MUF reflection is dependen parameters, namely critical frequency a Previous researches of these parameters in th carried out by [13][14][15] Sunspot is crucially important in predicting the HF frequencies. Sunspots according to the 11-year solar cycle and it smoothed sunspot number (SSN).…”

Determination of gyro frequency from critical frequency measurements over Parit Raja, Malaysia

“…The critical frequency is also called plasma frequency. It varies according to the electron density of the ionosphere with values f o E < f o F 1 < f o F 2 where f o E, f o F 1 and f o F 2 denote the E-, F1-and F2-regions critical frequencies respectively [1].…”