This paper presents observations of the F2-layer critical frequency (foF2) and height (hmF2) obtained at Phu Thuy (21.03°N, 105.95°E) and Bac Lieu (9.28°N, 105.73°E) observatories in Vietnam. The data have been examined for all seasons, during high and low solar activities, and compared with the foF2 and hmF2 of the International Reference Ionosphere model (IRI-2012, IRI-2016 two options: AMTB, SHU). Phu Thuy observatory is located at the Northern Crest of the EIA and Bac Lieu in the trough of the EIA, therefore the foF2 values at Phu Thuy are higher than at Bac Lieu. The results show that the IRI-2012 model estimates well the observed foF2 at both stations during high and low solar activities.

During high solar activity, models estimate well the calculated hmF2 in summer for both stations. At Phu Thuy in equinoxes AMTB reproduces the night peak better than IRI-2012 and SHU, but higher and later about 2–3 h, in winter the performance of AMTB is worst. At Bac Lieu, the IRI-2016 options reproduce the night peak and underestimates it, but IRI-2012 does not do it. The pre-noon peaks are underestimated by all the models, except IRI-2012 which overestimates the hmF2 pre-noon peaks at Bac Lieu. At Phu Thuy the pre-noon hmF2 peak is higher than the post-dusk one. At Bac Lieu the post-dusk peak is higher except in summer.

During low solar activity, the IRI models estimate relatively well the shape of the calculated hmF2 at both stations. The IRI-2012 models explained better the observed foF2 (deviation of 2.5%) during solstices than during equinoxes (14.2%) for high solar activity. The IRI-2012 model explained better the observed foF2 in spring (7.8%) than in autumn (19.9%), matched better the calculated hmF2 in solstice (5.4%) than during equinoxes (11.8%).

The performance of AMTB is worst at both stations for both the high and low solar activity periods except in autumn at Bac Lieu for the low solar year. IRI-2012 is best at the stations for both high and low solar activity periods, except in summer for the high solar activiy year when SHU is the best at Phu Thuy. These results can be used to improve the future IRI model.

本文介绍了在越南 Phu Thuy (21.03°N, 105.95°E) 和 Bac Lieu (9.28°N, 105.73°E) 天文台获得的 F2 层临界频率 (foF2) 和高度 (hmF2) 的观测结果。已对所有季节、高低太阳活动期间的数据进行了检查，并与国际参考电离层模型（IRI-2012、IRI-2016 两个选项：AMTB、SHU）的 foF2 和 hmF2 进行了比较。Phu Thuy 天文台位于EIA 的北顶和EIA 的低谷中的Bac Lieu，因此Phu Thuy 的foF2 值高于Bac Lieu。结果表明，IRI-2012 模型很好地估计了两个站点在高太阳活动和低太阳活动期间观测到的 foF2。

在高太阳活动期间，模型很好地估计了两个站夏季计算的 hmF2。在春分点的富翠，AMTB 比 IRI-2012 和 SHU 更好地再现了夜间高峰，但更高，更晚了大约 2-3 小时，在冬季，AMTB 的表现最差。在 Bac Lieu，IRI-2016 选项重现了夜间高峰并低估了它，但 IRI-2012 没有这样做。所有模型都低估了中午前的峰值，但 IRI-2012 高估了 Bac Lieu 的 hmF2 中午前的峰值。在 Phu Thuy，中午前的 hmF2 峰值高于黄昏后的峰值。在 Bac Lieu，除夏季外，黄昏后的高峰期更高。

在低太阳活动期间，IRI 模型相对较好地估计了两个站点计算出的 hmF2 的形状。对于高太阳活动，IRI-2012 模型更好地解释了在至点期间观察到的 foF2（偏差 2.5%）比在春分（14.2%）期间观察到的情况。IRI-2012 模型更好地解释了春季观察到的 foF2 (7.8%) 比秋季 (19.9%)，与计算的冬至 hmF2 (5.4%) 比在春分期间 (11.8%) 更好地匹配。

除了在低太阳年的薄寮秋季，AMTB 在两个站的表现在高太阳活动期和低太阳活动期都是最差的。IRI-2012 在高太阳活动期和低太阳活动期的观测站都是最好的，除了在夏季高太阳活动年，此时 SHU 在富水是最好的。这些结果可用于改进未来的 IRI 模型。