## 1 Introduction
The latter is a complex effect that generates the so-called scintillation effect which results, in turn, in rapid fluctuations of the intensity of the signal at the receiver side, analogous to fading in RF systems [2; 20; 21; 22; 23]. Although THz transmissions are generally less vulnerable to atmospheric turbulence than FSO transmissions, turbulence-induced THz performance degradations are not negligible and should be taken into consideration, especially in a long-path propagation that emerging THz links are expected to accommodate [19]. Another concern in THz links is the pointing errors effect that mainly arises from building sway. Thermal expansion, dynamic wind loads as well as weak earthquakes bring about the sway of high-rise building structures where THz terminals are usually placed. The latter results in random vibrations of the transmitted information-bearing beam and consequently in stochastic misalignments between transmitter and receiver antenna terminals. These unavoidable misalignments, which are commonly known as pointing errors, generate random intensity variations of the propagated signal arriving at the receiver aperture which strongly degrades the THz performance and availability [24; 25; 26; 27]. More precisely, pointing errors consist of both boresight and jitter components [22]. The former is the fixed displacement between the beam and the detector center, while the latter is the random offset of the beam center at the detector plane [28]. In short, while line of sight (LOS) THz links exhibit concrete advantages that make them a prime candidate to reach the growing demands of the emerging wireless communications, their deployment is impaired by attenuations due to weather effects and especially rain, attenuations due to molecular absorption and especially water vapor, attenuations due to FSPL, atmospheric turbulence and pointing errors. It therefore becomes evident that a generalized LOS channel model that evaluates the joint impact of all the above detrimental effects could be a very useful tool for the design and the establishment of such LOS THz links. Still, this research gap remains in the open technical literature. Specifically, a good approximation for the attenuation of the lower frequency band of THz waves (0.1-1 THz) due to molecular absorption is the ITU-R model [19]. In this respect, the authors of [29; 30], by using time domain spectroscopy, investigated attenuation due to water vapor from 0.2-2 THz, while in [18] they confirmed four transparent windows at 0.41 THz, 0.46 THz, 0.68 THz and 0.85 THz. Recently, attenuation due to water vapor in the presence of dry air has been assessed for practical outdoor THz links in [31]. Additionally, based on the model proposed in [32], the authors of [33] proposed an alternative channel model including path loss, transceiver parameters and molecular absorption. The above results demonstrate that in terms of molecular attenuation, attenuation due to water vapor is more significant than attenuation due to oxygen within the frequency regions in which emerging THz links operate. Attenuation due to fog, cloud or rain has been evaluated through the Laser Environmental Effects Definition and Reference (LEEDR) computation tool in [34] as well as through a theoretical framework and/or experimentally in a laboratory or a real outdoor environment in [5; 11; 12; 13; 15; 16; 17; 36; 37]. Apart from the feasibility of establishing realistic THz links, their findings reveal that experimental results are in good agreement with the predicted attenuation due to weather effects, with rain being the most destructive effect for the emerging THz transmissions. Moreover, it is highlighted that attenuation due to weather effects must be taken into consideration, especially for longer THz link lengths, while THz outperforms FSOs under fog conditions and thus THz can be a promising alternative for many wireless applications in fog.