A Study On The Structure Evolution Of Strong Typhoon "Damrey" (2005) Through Hainan Island

Land-falling is an important turning point in the life history of a tropical cyclone. Landfall process which subjected to shallow continental shelf and coastal topography may change the TC structure, thus the structure-related intensity, track and precipitation changes. It is a key factor for the wind and precipitation forecast failure after TC landfall that the evolving structure change during the landfall process is lack of understanding.Tropical cyclone is the most severe tropical weather systems caused meteorological disasters in Hainan Island, and it is the most important defense objects and defensive difficulties in Hainan Province. A study on tropical cyclones over the Hainan Island process (TCOHIP) has an important practical significance in disaster prevention and mitigation. In addition, it is also concerned in scientific issue that the structural feature of tropical cyclones when it through a small island differs from land-falling inland.In this paper, the change of track, intensity and moving speed, as well as the convective rain-bands are analyzed when TCOHIP occurs, using the ((Typhoon Yearbook)) and ((Tropical Cyclones Yearbook)) data which are supplied by the China Meteorological Administration (CMA). It has demonstrated that the TCOHIP has some distinctive characteristics, such as the average time is 10 hours in the island activities, Hainan Island wind which caused by tropical cyclones shows the eastern and southern coast stronger, while the western inland weaker, resulting in two kinds of typical rainfall distribution patterns, that is the west and the east strong while the south and the north weak type and the north weak and south strong type. TO a westwards TC, the deep convective rain-bands moves from the center to the southwest quadran of the TC circulation through TCOHIP. To a northwards TC, it moves from the centre to the northern quadrant.Take strong typhoon Damrey (0518) as an example, as it has a typical TCOHIP stage concerned in this paper, its physical field changes in large-scale are diagnosed, and the meso-scale numerical model is applied to simulate the tropical cyclone landfall process, furthermore, terrain sensitivity experiments are designed to analyze the TCOHIP. The results indicate:(1) The symmetric structure shows damage to recovery when a symmetric strong typhoon through a TCOHIP. To the land-falling process, the wind speed near the land side of the boundary layer decreases, while near the ocean side increases, thus results in asymmetric wind field, the eye area and inner eye-wall destruct for the inflow wind. The upward current tilts to the land side, the secondary circulation destroyed. To the TC moving to the sea process, the asymmetric structure recovering, wind field tends to symmetry, the tilting upward current toward vertical, the eye-wall re-established in the sea.(2) Contrasting to land-falling China's mainland, the biggest difference is the water vapor will not be cut off when TCOHIP occurs, thus may cause water vapor flux convergence increases due to the impact of land surface friction, results in the vertical water vapor transport enhances, the convective activities in lower troposphere exhibits a short-term decay process during land-falling, but it will be re-strengthened after landing, as well as into the sea. When the strong typhoon moves on the island, eye wall convection intensifies into meso-scale rain cluster easily on Hainan Island's southern coast and mountain region, when it leaving Islands and into the sea, the spiral rain belt convective cells easily develop into meso-scale rain bands.(3) When a strong typhoon landfalls Hainan Island, the tangential wind, the radial wind and condensation heating rate decrease in the inner-core zone. When it leaves Hainan Island and moves into the sea, the tangential wind and the radial wind increase, and the condensation heating rate of the lower-middle troposphere increases as well.(4) A possible mechanism of the north weak and south strong precipitation type may include low-level cyclonic disturbances and high-level meso-scale divergence formatted in the rain area, the down shear left region which favorites to the development of convection has good consistency with the precipitation areas, and the uplift and convergence which caused by topography in central and southern Hainan Island contribute to convection intensitification.