The “Karakkaze” Local Wind as a Convexity Wind: A Case Study using Dual-Sonde Observations and a Numerical Simulation

Abstract

In the present study, we conducted dual-sonde observations and a numerical simulation when the “Karakkaze”, a local wind in Japan, blew. The result showed that the basic features of the Karakkaze coincide closely with the characteristics of convexity wind defined as “strong winds in the leeward region of a convex-shaped mountain range”.

Firstly, we investigated the horizontal distribution of surface winds during the Karakkaze event on January 24, 2019. The results showed that the Karakkaze blows in the downwind plain of the convexity of the mountain range.

Secondly, we compared the vertical distribution of the winds inside and outside the Karakkaze region, using the results of dual-sonde observations and a numerical simulation. Our results showed that strong winds blew from near ground level to a height of 1.8 km above mean sea level (AMSL) in the Karakkaze region. In contrast, weaker winds were observed and simulated outside the Karakkaze region. The reason of the weaker winds is that a hydraulic jump occurs on the slope of the mountain range and that the area outside the Karakkaze region is located in a more leeward direction than the hydraulic jump. These features closely match the characteristics of convexity winds.