Numerical Simulations and Trajectory Analyses of Local "Karakkaze" Wind: A Case That Could Have Contributed to an Aircraft Accident at Narita Airport on 23 March 2009

Abstract

We conducted numerical simulations on a case of local "Karakkaze wind on 23 March 2009. On this day, an aircraft crashed on landing at Narita Airport in the eastern Kanto Plain in Japan in the early morning when surface winds were significantly strengthened. Numerical simulations were used to elucidate the characteristics and mechanism of the strong wind over the Kanto Plain. This strong wind was identified as the Karakkaze wind, which occurs in the lee of the convex mountain range northwest of the Kanto Plain. The vertical shear associated with the Karakkaze wind could cause strong turbulence near the surface. The results of a sensitivity experiment suggest that the presence of the mountain convexity is essential for the development of the Karakkaze wind. Backward trajectory analyses reveal the area where the Karakkaze wind originated upstream of the mountain range. The horizontal wind speed in this area is even weaker than in the northern area. However, unlike in the northern area, the air with large momentum descends from altitudes much higher than the height of the dividing streamline owing to the mountain convexity, thereby driving strong surface winds in the leeward area. was stronger than the case of Nishi and Kusaka(2019d). This case could have impacts on aviation: an aircraft accident at Narita Airport occurred at 0649 Japan Standard Time (JST: +0900 UTC) on 23 March 2009. A cargo plane failed to land and burst into flames, causing the fatalities of two pilots. The official report of the accident (JTSB 2013) describes that the presence of a strong low-level wind shear could be one of the factors of the accident, although it does not mention the local Karakkaze wind. After the midnight on 23 March, the surface temperature over the Kanto Plain dropped significantly following the passage of a cold front (Figs, lb, Id, and Sla). At observatories of the Japan Meteorological Agency (JMA) on the Kanto Plain (AMeDAS at Haneda, Narita, and Kumagaya), wind directions changed to northwest, and the wind speed significantly increased in the early morning (Figs, lc, le and Sib). Later than the other observatories, the wind speed at Narita increased remarkably after 0600 JST (Fig. lc). The strong northwesterlies appeared to contribute to the aircraft accident that occurred at 0649 JST. In the present study, we conduct numerical simulations on the case on 23 March 2009 when the strong Karakkaze wind occurred. Sensitivity experiments examine the mechanism of the Karakkaze wind and effect of small scale topography. Trajectory analyses, which have not been conducted for the Karakkaze wind, reveal upstream conditions and strengthen confidence about the mechanism of the wind. The rest of this paper is organized as follows. Section 2 describes the numerical simulations. Section 3 overviews results of the simulations. Section 4 elucidates the mechanism and factors affecting the strength. Section 5 gives conclusions.