Total electron content (TEC) is an important parameter in the ionosphere that is extensively used to study the variability of the ionosphere as it significantly affects radio wave propagations, causing delays on GPS signals. Therefore, evaluating the performance of ionospheric models is crucial to reveal the variety of ionospheric behaviour in different solar activity periods during geomagnetically quiet and disturbed periods for further improvements of the IRI model performance over the equatorial region. This research aimed to investigate the variations of ionospheric VTEC and observe the improvement in the performance of the IRI-2016 (IRI-2001, IRI01-corr, and NeQuick). The IRI-2016 was evaluated with the IRI-2012 using NeQuick, IRI-2001, and IRI01-corr topside electron density options. The data were obtained using a dual-frequency GPS receiver installed at the Universiti Utara Malaysia Kedah (UUMK) (geographic coordinates 4.62° N–103.21° E, geomagnetic coordinates 5.64° N–174.98° E), Mukhtafibillah (MUKH) (geographic coordinates 6.46° N–100.50° E, geomagnetic coordinates 3.32° S–172.99° E), and Tanjung Pengerang (TGPG) (geographic coordinates 1.36° N–104.10°E, geomagnetic coordinates 8.43° S–176.53° E) stations, during ascending to high solar activity at the geomagnetically quiet and disturbed periods in October 2011, March 2012, and March 2013. The maximum hourly ionospheric VTEC was observed during the post-noon time, while the minimum was during the early morning time. The ionospheric VTEC modelled by IRI-2016 had a slight improvement from the IRI-2012. However, the differences were observed during the post-noon and night-time, while the modelled VTEC from both IRI models were almost similar during the early morning time. Regarding the daily quiet and disturbed period’s prediction capability of the IRI-2016 and IRI-2012, IRI-2016 gave better agreement with the measured VTEC. The overall results showed that the model’s prediction performance during the high solar activity period in 2013 was better than the one during the ascending solar activity period. The results of the comparison between IRI-2016 and IRI-2012 in high solar activity exhibited that during quiet periods, all the IRI models showed better agreement with the measured VTEC compared to the disturbed periods.

中文翻译：

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使用 GPS-TEC 测量在赤道地区评估 IRI-2016 的性能

总电子含量 (TEC) 是电离层中的一个重要参数，广泛用于研究电离层的可变性，因为它会显着影响无线电波传播，从而导致 GPS 信号延迟。因此，评估电离层模型的性能对于揭示地磁平静和扰动期间不同太阳活动期间电离层行为的多样性至关重要，以进一步改善赤道地区的 IRI 模型性能。本研究旨在调查电离层 VTEC 的变化并观察 IRI-2016（IRI-2001、IRI01-corr 和 NeQuick）性能的改进。IRI-2016 与 IRI-2012 一起使用 NeQuick、IRI-2001 和 IRI01-corr 顶部电子密度选项进行评估。数据是使用安装在马来西亚吉打北方大学 (UUMK)（地理坐标 4.62° N–103.21° E，地磁坐标 5.64° N–174.98° E）、Mukhtafibillah (MUKH)（地理坐标）的双频 GPS 接收器获得的6.46° N–100.50° E，地磁坐标 3.32° S–172.99° E) 和 Tanjung Pengerang (TGPG)（地理坐标 1.36° N–104.10°E，地磁坐标 8.43° S–176.53° E）站，上升期间2011 年 10 月、2012 年 3 月和 2013 年 3 月的地磁平静和干扰时期的高太阳活动。在中午之后观测到每小时电离层 VTEC 的最大值，而在清晨时间观测到最小值。IRI-2016 建模的电离层 VTEC 比 IRI-2012 略有改进。然而，在中午和夜间观察到差异，而来自两个 IRI 模型的建模 VTEC 在清晨时间几乎相似。关于IRI-2016和IRI-2012的每日安静和扰动期的预测能力，IRI-2016与实测的VTEC更加吻合。总体结果表明，该模型在2013年太阳高活动期的预测性能优于太阳活动上升期。IRI-2016 和 IRI-2012 在高太阳活动下的比较结果表明，在安静时期，与受干扰时期相比，所有 IRI 模型与测量的 VTEC 表现出更好的一致性。关于IRI-2016和IRI-2012的每日安静和扰动期的预测能力，IRI-2016与实测的VTEC更加吻合。总体结果表明，该模型在2013年太阳高活动期的预测性能优于太阳活动上升期。IRI-2016 和 IRI-2012 在高太阳活动下的比较结果表明，在安静时期，与受干扰时期相比，所有 IRI 模型与测量的 VTEC 表现出更好的一致性。关于IRI-2016和IRI-2012的每日安静和扰动期的预测能力，IRI-2016与实测的VTEC更加吻合。总体结果表明，该模型在2013年太阳高活动期的预测性能优于太阳活动上升期。IRI-2016 和 IRI-2012 在高太阳活动下的比较结果表明，在安静时期，与受干扰时期相比，所有 IRI 模型与测量的 VTEC 表现出更好的一致性。