24th Pacific Science Congress (PSC-24)

Understanding the extent and impact of small-scale island wakes on the atmospheric boundary layer (ABL) is essential for advancing our comprehension of local meteorology. Using the high-resolution WRF-PALM nested model, we quantitatively evaluated the ABL disturbances caused by small-scale islands. The horizontal and vertical distribution characteristics of island wakes, their effects on near-surface meteorological variables, and the underlying physical mechanisms were investigated through sensitivity experiments with and without islands during the daytime and nighttime. The results reveal notable diurnal variations in the wake structure. At night, orographic dynamics dominate, creating a wind sheltering effect in the leeward area, reducing wind speed, and forming a weak wind wake with downward motion near the surface. This reduces upward turbulent heat flux, inhibiting latent heat flux from the sea. During the day, thermal and dynamic forces contribute to a more complex wake structure, with accelerated airflows flanking the low-speed wake on both sides. The convergence of wind streams induces upward motion and enhances wind-driven mixing, thereby increasing turbulent heat exchange within the wake zone. Even small islands induce substantial horizontal disturbances in the ABL, with the temperature wake at night extending 5.3 times the island's area and 5.9 times its length, reaching more than 15 km downstream of the island. Thermal effects dominate over dynamic effects in influencing vertical ABL disturbances, increasing the disturbance heights of wind speed, potential temperature, and water vapor to 445 m, 665 m, and 675 m, respectively.
 

WRF-PALM,atmospheric boundary layer,Island wake