Windbreak Effect of Casuarina equisetifolia Main Shelterbelt on Typhoon"Doksuri"
In order to understand the protective effect of coastal defense forest on typhoon,the meteorological data of Typhoon"Doksuri"before and after landing collected by the monitoring station of Chihu State-owned Protective Forest Farm in Hui'an were used as materials to analyze the characteristic rules of wind speed,wind direction,tur-bulence intensity,windbreak effect and airflow acceleration rate in the near-ground layer before and after typhoon landing.The results showed as the following three aspects.(1)The time-history variation characteristics of the av-erage wind speed and wind direction before and after the landing of typhoon met the conditions of the typhoon eye area.The average wind speed curve showed a"M"-shaped bimodal distribution.The collection of the complete wind data of the typhoon eye area,the eye wall and the peripheral strong winds fully demonstrated the evolution process of wind speed and wind direction before and after the typhoon passing through the forest belt.(2)The overall trend of the time history of turbulence intensity showed the process of increasing-decreasing-surging-falling as the typhoon approached and departed.Especially in the area affected by the wind circle after the typhoon,the turbulence intensity increased sharply,and the intensity could increase by more than twice.(3)For the onshore wind,when it was in the vertical direction,the windbreak efficiency of weak wind or strong wind decreased with the increase of height,and at the same height,the windbreak efficiency of weak wind behind the forest belt was lower than that of strong wind;when it was in the horizontal direction,the windbreak efficiency in the forest and at the 1 H and 5 H behind the for-est belt was the best,the average windbreak efficiency was 49.57％-93.93％at the height of 3 m,and the aver-age windbreak efficiency was 44.04％-90.10％at the height of 9 m.For the offshore wind,when it was in the vertical direction,as the airflow was close to the forest belt,the airflow acceleration rate of weak wind or strong wind increased with the increase of height.At 1H behind the forest belt,the average airflow acceleration rates at the height of 3 m and 9 m were 0.219 3 and 0.324 2,respectively.And the airflow acceleration rate in the forest reached the lowest value.After the wind passed through the forest belt,the weak wind speed recovered to around 88％,and the strong wind airflow underwent an acceleration process.
万方数据
