## 1 Introduction  
To meet the growing demands for wireless communication in the real world, forthcoming wireless communication systems will require higher data rates, increased carrier frequency, and greater system capacity and bandwidth [1]. After the fifth-generation (5G) wireless communication system adopted millimeter-wave (mmWave) bands, the sixth-generation (6G) wireless communication system are working toward adopting the terahertz (THz) band (0.1-10 THz), which offers abundant spectrum resources, being situated between microwaves and optical waves [2]. Terahertz communication is a technology that takes the terahertz band as a carrier to realize wireless communication. It is characterized by a high transmission rate, extensive capacity, and large bandwidth, which position terahertz communication technology as one of the vital technologies for the development of 6G [3; 4; 5]. Terahertz communication technology is expected to be applied in high-precision positioning, three-dimensional perception imaging, holographic communication, micro-sized communication, ultra-large-capacity data backhaul, and short-distance ultra-high-speed transmission [6; 7; 8; 9; 10; 11]. Terahertz waves have a higher frequency and experience more significant path loss than millimeter waves. Additionally, terahertz waves are prone to blockage by buildings and objects and can be easily absorbed and scattered by atmospheric molecules during transmission, which leads to signal attenuation. In addition to the atmosphere, the terahertzsignal is affected by weather, such as rain and fog [12; 13]. The large-sized raindrops and fog droplets on rainy and foggy days can strongly absorb and scatter terahertz waves and thus cause more significant signal attenuation. Moreover, due to the increase in the frequency band, weather conditions have increasing influences on terahertz waves. Hence, conducting intensive research on the propagation characterization of terahertz waves in atmospheric particles such as fog droplets and raindrops is crucial. In recent years, the propagation characterization of terahertz waves in the atmosphere and under diverse weather conditions has been extensively investigated. Regarding atmospheric attenuation, in [14; 15], the authors studied the influence of the atmosphere on terahertz waves, analyzed the feasibility of outdoor terahertz communication systems, and demonstrated the potential of line-of-sight terahertz communication, sensing, and imaging. Regarding fog attenuation, in [16], the transmission rate of terahertz wireless links in the frequency range of 300-900 GHz in sunny, foggy, and rainy days was investigated. In the transmission windows of 300-376 GHz and 376-434 GHz, even under the worst rainy days with a rainfall intensity of 50 mm/h, the upper limit of the data rate surpassed 10 Gbps (per 1 GHz channel bandwidth). Researchers [17] considered the attenuation of terahertz waves caused by different particles, such as fog droplets, haze particles, and raindrops, where the optical parameters of these particles were given by the analysis of meteorological data, and the scattering characteristics of THz waves were explored. In addition, it was observed that the factors, including visibility and rainfall rate, had a significant impact on the scattering characteristics of terahertz waves. In [13; 18; 19; 20], propagation characteristics were investigated through theory and experimentation with terahertz waves in fog. The authors of [19; 20] conducted fog attenuation experiments using a controllable fog testing chamber, in which the attenuation of terahertz waves was analyzed based on the millimeter-wave propagation model (MPM), Rayleigh approximation [21; 22], and Mie theory. Furthermore, the experimental results were consistent with the model predictions, and the increase in attenuation with the decrease in the optical visibility conformed to the predicted values.