The long-term variations in f_oF2 at Hobart (52.88°S, 147.32°E), Canberra (35.28°S, 149.13° E) and Christchurch (43.53°S, 172.64°E) stations, located in the mid-latitude zone in the Southern Hemisphere were analyzed using 1947–2006 years of the data. The saturation, solar and geomagnetic activity and seasonal effects were removed mainly by using 12-month running mean, linear and multiple regression (twofold regression) methods to find possible signatures of climate change in long-term trends in the f_oF2. The solar activity proxies, sunspot number, R_Z, and F10.7 solar radio flux were used in regression to find the f_oF2 residuals at midday (12 LT) and midnight (00 LT) of the stations. The long-term trends obtained at 12 LT are more significant and consistent with the model results. The trends estimated with F10.7 solar flux are negative and the trends estimated with R_Z are positive (small and not significant). The f_oF2 decreased by 0.1–0.4 MHz for the 5 solar cycles period which could be mainly due to enhanced CO₂ in the troposphere that is cooling the upper atmosphere. Further research is needed to see if the f_oF2 trends are also affected by other factors such as thermospheric winds, neutral constituents, the secular variation of Earth's magnetic field, long-term changes in stratospheric ozone, solar and geomagnetic activities.

位于中纬度的霍巴特（52.88°S，147.32°E）、堪培拉（35.28°S，149.13°E）和基督城（43.53°S，172.64°E）站的f _o F2的长期变化使用 1947-2006 年的数据分析了南半球的区域。主要通过使用 12 个月的运行平均值、线性和多元回归（双重回归）方法来消除饱和度、太阳和地磁活动以及季节性影响，以在f _o F2的长期趋势中寻找气候变化的可能特征。太阳活动代理、太阳黑子数、R _Z和 F10.7 太阳射电通量用于回归以找到f _oF2 站点中午 (12 LT) 和午夜 (00 LT) 的残差。在12 LT处获得的长期趋势更为显着，并且与模型结果一致。用 F10.7 太阳通量估计的趋势为负，用R _Z估计的趋势为正（小且不显着）。所述˚F _Ô F2为5太阳周期期间这可能主要是由于增强的CO减少0.1-0.4兆赫₂在被冷却上层大气对流层。还需要进一步研究，看是否˚F _ØF2 趋势还受到其他因素的影响，例如热层风、中性成分、地球磁场的长期变化、平流层臭氧的长期变化、太阳和地磁活动。