<p>Free-space optical communication (FSOC), which utilises the unlicensed optical spectrum in the THz frequency range, is a promising technology that can meet the demands of high-speed, low-latency and secure communication applications. In this paper, we design and extensively analyse an FSO aerial communication (FSOAC) link between a high-altitude platform (HAP) and a ground-based optical terminal. The performance of the link is analysed for various bitrates across different link ranges to assess its reliability. The influence of the aperture size of the optical antennas on system performance is thoroughly investigated for varying transmitted power to understand its impact on signal quality and reception. Additionally, the performance is also evaluated for different weather conditions like rain and fog, which are the critical attenuating factors in FSOAC links, across different link ranges. The key performance metrics including the received optical power levels, Bit error rate (BER), Q-factor, and eye diagram have been studied. Finally, the key findings from these studies are discussed, which can support advancements in FSOAC system design and research. Such an FSOAC link finds applications in high-bandwidth backhaul connectivity, disaster and emergency recovery communications, aerial base stations for 5G/6G coverage, and high-throughput relay links for space communications.</p>