STATISTICAL ANALYSIS AND NUMERICAL SIMULATION OF POYANG LAKE'S INFLUENCE ON TROPICAL CYCLONES

Based on the Tropical Cyclone(TC briefly thereafter)Yearbook 1980-2009,this paper first analyzes the number and intensity change of the TCs which passed directly over or by the side of Poyang Lake(the distance of TC center is less than 1°longitude or 1°latitude from the Lake)among all the landfalling TCs in China during the past 30 years.Two cases are examined in detail in this paper.One is severe typhoon Rananim with a speed of 3.26 m/s and a change of 1 hPa in intensity when it was passing the Lake.The other is super typhoon Saomai with a faster moving speed of 6.50 m/s and a larger change in intensity of 6 hPa.Through numerical simulation experiments,this paper analyzes how the change of underlying surface from water to land contributes to the differences in intensity,speed and mesoscale convection of the two TCs when they passed the Lake.Results show that the moisture and dynamic condition above the Lake were favorable for the maintenance of the intensity when Rananim was passing through Poyang Lake,despite the moisture supply from the ocean was cut off.As a result,there was strong convection around the lake which led to a rainfall spinning counter-clockwise as it was affected by the TC movement.However,little impact was seen in the Saomai case.These results indicate that for the TCs coming ashore on Poyang Lake with a slow speed,the large water body is conducive to the sustaining of the intensity and strengthening of the convection around the TC center and the subsequent heavy rainfall.On the contrary,a fast-moving TC is less likely to be influenced by the underlying surface in terms of intensity and speed.

Based on the Tropical Cyclone （TC analyzes the number and intensity change of the briefly thereafter） Yearbook 1980-2009, this paper first TCs which passed directly over or by the side of Poyang Lake （the distance of TC center is less than 1° longitude or 1° latitude from the Lake） among all the landfalling TCs in China during the past 30 years. Two cases are examined in detail in this paper. One is severe typhoon Rananim with a speed of 3.26 m/s and a change of 1 hPa in intensity when it was passing the Lake. The other is super typhoon Saomai with a faster moving speed of 6.50 m/s and a larger change in intensity of 6 hPa. Through numerical simulation experiments, this paper analyzes how the change of underlying surface from water to land contributes to the differences in intensity, speed and mesoscale convection of the two TCs when they passed the Lake. Results show that the moisture and dynamic condition above the Lake were favorable for the maintenance of the intensity when Rananim was passing through Poyang Lake, despite the moisture supply from the ocean was cut off. As a result, there was strong convection around the lake which led to a rainfall spinning counter-clockwise as it was affected by the TC movement. However, little impact was seen in the Saomai case. These results indicate that for the TCs coming ashore on Poyang Lake with a slow speed, the large water body is conducive to the sustaining of the intensity and strengthening of the convection around the TC center and the subsequent heavy rainfall. On the contrary, a fast-moving TC is less likely to be influenced by the underlying surface in terms of intensity and speed.