###### Abstract  
Due to the advantages of high transmission rate, lower power consumption, high security, etc., underwater wireless optical communication (UWOC) has been widely studied and considered as a potential technique for underwater communication. However, its performance is severely degraded by oceanic turbulence due to refractive index fluctuations, which is caused by the change of inhomogeneous ocean environment. Within our derived spatial power spectrum model under anisotropic oceanic turbulence, we conducted a detailed investigation for a spherical wave propagating in weak anisotropic turbulence in this paper. Based on the derived oceanic spectrum, we proposed a scintillation index model for spherical wave in anisotropic oceanic turbulence considering the aperture averaging effect at non-zero inner scale and limited outer scale. Besides, we analyze the aperture averaging scintillation index under the influence of channel parameters such as inner and outer scales. Simulation results reveal that the scintillation index increases with the increase of the outer scale, while the inner scale induces an opposite trend on the scintillation index. Moreover, the inner scale exhibits a larger impact than the outer scale on the UWOC system over weak oceanic turbulence. s 2022 9 458 0000-0001-9232-4500-0000-0000-00000-00000-0000-00000-00000-00000-00000-00000-00000-00000-00000-000000-00000-00000-00000-000000-000000-000  
the underwater environment, which restrict them to a certain extent. The performance of UWOC can be severely damaged by absorption, scattering and underwater turbulence. Therefore, photons inevitably interact with water molecules and other particulate matter in the water, leading to absorption and scattering. In addition, many undesired effects, such as beam expansion, jitter and intensity fluctuations, can result in a severe drop in beam quality due to the influence of oceanic turbulence when the wave propagates in seawater [7; 8]. The statistical characteristics of the rectangular cusped random beams, which maintain the rectangular tip profile under the weak load, propagating in oceanic turbulence were studied by [PERSON] and [PERSON] [9]. It was proved that the spectral density and the degree of spectral consistency are significantly affected by various turbulence parameters. A more realistic environment where the eddy diffusivity of temperature and salt were not equal was futher considered by [PERSON] et al. [10]. The scintillation index of both plane and spherical waves under weak oceanic turbulence was obtained. [PERSON] et al. proposed a new ocean spectrum to study the influence of oceanic turbulence in the unstable stratification on the Gaussian beam scintillation index [11]. The results show that the fluctuation of temperature and salinity in ocean turbulence significantly impacts the scintillation index, and weak ocean turbulence with larger kinematic viscosity can obtain a smaller scintillation index. Moreover, the asymmetric oceanic turbulence will affect the phase broadening and the received probability of the OAM modes in the Lommel-Gaussian pulsed beams [12]. Most studies described above treated the seawater as isotropic turbulence while ignoring its anisotropic property. The difference from isotropic is that the physical properties of anisotropic turbulence are closely related to the orientation. In addition, the measurement results of various orientations are very different. The turbulence vortex is isotropic only in the inertial sub-interval [13]. In reality, oceanic turbulence exhibits asymmetric spatial frequencies in various directions, resulting in an anisotropic spatial power spectral density due to the rotation of the Earth [14]. The effect of anisotropic oceanic turbulence on the intensity fluctuations was discussed by [PERSON] [15; 16]. Thereafter, the effect of anisotropic turbulence on the average bit error rate (BER) was further investigated when an asymmetrical Gaussian beam propagates in anisotropic turbulence [17].