## 1 Introduction  
In order to mitigate the Radio Frequency (RF) technology limitations, over the past decades, there has been a growing interest in free space optical (FSO) communications. In the current scenario of limited radio spectrum, FSO can be a savior with its high speed over the secure free license optical wavelengths [1; 2]. However, the performance of FSO transmission is highly dependent on atmospheric conditions such as temperature, humidity, solar irradiance, etc. Fog is considered one of the most challenging environments for wireless optical transmissions [3]. Fog affects the transmission where wavelengths are in the visible and infrared range, as the fog particles and the wavelength range are of the same magnitude [4; 5]. Foggy weather leads to the appearance of scattering phenomena, which causes the optical signal degradation. On the other hand, there are other sources of impairments that highly affect the FSO behavior, such as the pointing errors caused by the building sways and mechanical vibrations which enhances the deviation of laser beam leading to the attenuation of the received light signal [6; 7]. Scintillation phenomenon is also one of the major sources affecting the performance of FSO communications, which is also known as atmospheric turbulence. Scintillation is caused by air turbulence leading to fluctuations in both the intensity and the phase of the received light signal causing impaired link performance [8]. In the literature, most of the experimental works were focused on the fog effect [2; 5; 8; 9; 10]. The effects of atmospheric turbulence have been also studied. Many researchers studied the strength of atmospheric turbulence called refractive index. In fact, in [11], the authors made some experimental tests related to the effect of scintillation on FSO link. They found that the refractive index is highly affected by the ambient temperature and by the time of day. In their work, they did not present how the fluctuations of refractive index affected the behavior of FSO link. Moreover, the path link is limited to 220 m. In [12], an indoor test to measure the refractive index was made. They have characterized the effects of these fluctuations on an ad-hoc FSO network. The dust and sandstorm effect on FSO link in the Gulf Cooperation Council (GCC) states was also studied in [12]. The authors made an experimental test of the performance of FSO under dusty weather. They found that the dust has a bigger effect than the fog. In all the work stated above, a detailed description of the test setup along with the sensors and detailed statistical analysis of the results from the test setup to show their effect on the performance of the FSO communication was missing. Studying extremely hot weather and moderate winter effects on FSO link in GCC countries can be considered as a major step towards a large-scale deployment of wireless optical communication technology in these countries. For this reason, in this work, we will briefly analyze the effects of some major environment parameters in Qatar on FSO link. Qatar's climate could be characterized as harsh sub-tropical desert climate with very dry and hot summer. The temperature is high throughout the year and is above 14 \({}^{\circ}\)C even in winter. The sun shines bright throughout most of the year. The period from December to February is considered as winter season with moderate temperature oscillating between 14 \({}^{\circ}\)C and 30 \({}^{\circ}\)C. The lowest temperature in the year is recorded during this period. On the other hand, the period from June to August is considered as the peak summer time in Qatar. The average summer's temperature is about 45 \({}^{\circ}\)C. During this period, it is extremely hot during the day, while the nights are warm but not as extreme as the day. The experimental tests were carried out throughout 2015 so that we can do an evaluation of the FSO performances during the prominent four seasons of Qatar.