## 2 Measurements
### Measurements  
To make the results of the observation experiments more accurate and meaningful, before the Antarctic and Beijing measurement experiments were conducted, we carried out a laboratory experiment in Beijing, China. In this experiment, the researchers applied an adjustable DC voltage to two metal pole plates with a radius of 54 cm (the radius of the probe was 4.5 cm), and the height between the two plates was fixed (measured value was 24.6 cm). During the laboratory experiment, researchers set the voltage values to approximately 111, 80, 40, and 0 V to check the stability and accuracy of the probe (during the production of the probe, they completed calibration experiments). Each voltage value was retained for 5 min to determine whether the AEF value was stable.  
The laboratory experimental results are shown in Figure 2, where the horizontal axis is the voltage value, and the vertical axis represents the AEF. The red line and blue line represent the standard curve fitting curve, and the black squares indicate the sampling points obtained in Figure 2. Figure 2 clearly shows that the measured value does not change more than 8 V/m within 5 min for the same voltage, and the stability and linearity of this probe are excellent. However, the difference between the fitting line and the standard line is clear, which means that the theoretical value is 5-20 V/m greater than the measured value under the same voltage. This error (5-20 V/m) accounts for \(<\)5% of the standard AEF values and may be caused by the interference of the laboratory environment, the inevitable measurement system error, and the limitation of the probe measurement accuracy. These possible causes can result in the actual voltage added to the probe terminals being less than the theoretical values, or result in the actual measured voltage being lower, so that the measured values of AEF are 5-20 V/m lower than the theoretical values.  
Figure 2: Results of the laboratory experiments (black squares indicate the sampling points obtained; the red line and blue line represent the standard curve and fitting curve, respectively).  
The topographic relief, buildings or communication base stations and other protrusions can affect the distribution of the AEF, making the atmospheric equipotential surface a changing surface, which in turn affects the measurement error of the AEF. Therefore, in the practical application of an AEF meter, it is generally required that it be installed in a certain elevation range where there are no protrusions, trees, signal towers, sharp objects, human activities, or other sources of interference. A photo of the observation scene at the Antarctic Chinese Zhongshan Station is shown in Figure 3. The yellow arrow points to the EFM, while the other two instruments are used to observe other relevant physical parameters. The EFM is constructed with the probe at the top, which contains the motor, stator, rotor, and circuitry, and the electrical box in the middle, which contains the power supply and data processing and data transmission equipment. The instrument is powered by main electricity and will not be interrupted by weather or external factors. The height of the mast is 1.5 m, and it serves as a support. This mast is made in bulk by the manufacturer, and its exterior is fully insulated and does not interfere with the measured value of the AEF. Due to the impact of the station, it must be placed relatively close to snow, ice, and water sources, which can cause unavoidable interference to the AEF measurements [44]. The area surrounding the AEF meter is empty, with no high buildings, sharp objects, grass or trees, or other sources of interference except for the other two nearby instruments. Therefore, this location is a long-term observatory station for studying the differences in the atmospheric electric environment at different latitudes and the interaction of solar activity with the Earth's near-surface atmosphere.