Climatology of nocturnal low-level wind maxima at a topographically complex coastal site in Boseong

초록

We examined the characteristics of nocturnal low-level wind maximum (NLWM) at a topographically complex site in Boseong, South Korea. The study site is located on the southern coast of the Korean peninsula. Although the area within a few kilometers of the site is flat, it is surrounded by mountains and faces the ocean on the southeast side. We defined NLWM as the lowest wind speed maximum within the lowest 300 m of the atmosphere that is at least 2 m s(-1) greater than the next minimum above during nighttime. Climatology of NLWMs was derived from a 4-year half-hourly database of wind profiles (11 levels) obtained from a 300-m tower. The half-hourly data showed that NLWM occurred on approximately 18% of the nights. NLWMs were typically situated at 40 m above the ground. Half of the NLWMs had a speed of 3-5 m s(-1), and its direction was predominantly west-northwesterly regardless of the height or season. The occurrence of NLWM showed a maximum in October and a minimum in July. The cause of NLWM at this site was discussed. It was found that the NLWM at this site occurred in the presence of valley wind forcing on nights with weak northerly geostrophic winds at 850 hPa.

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