Occurrence Patterns And Numerical Simulations Of Strong Breeze And Strong Crosswind On The Jiangsu Section Of The Yangtze River Waterway

With the rapid development of economic society and the increasing traffic demand, modern transportation changes with each passing day. While the transportation capacity and efficiency improve continuously and create significant economic values,the impact of the various types of adverse weather on traffic restricts the safety and smooth of the transportation system increasingly. Strong breeze, especially strong crosswind is a huge threat to water traffic. In order to improve forecast accuracy and reduce the loss, it seems very import to ascertain occurrence, formation and maintain mechanism of strong breeze and strong crosswind scientifically, roundly and systematically.Based on the observed data of the Automatic Weather Monitoring System on Jiangsu Section of the Yangtze River Waterway during2009to2012, in this paper, the temporal and spatial distribution pattern of strong breeze and strong crosswind was analyzed to explore the impact of the atmospheric background, geographical environment on two kinds of wind, and the wind pressure grading warning mechanism applied to the waterway was established. The results showed as follows:(1) The diurnal and seasonal variations of the strong breeze and strong crosswind were similar. In a day, afternoon was a frequent occurring period of strong breeze and strong crosswind and in a year, spring and summer were the prevailing seasons of strong breeze and strong crosswind.(2) The local geographic environment had the different impact on the occurrence frequencies of strong crosswind in the different parts of Jiangsu Section of the waterway. There was the highest occurring frequencies in the middle part of the section, the east part took the second place, and the western part appeared the least frequencies.(3) Considering the temporal and spatial variations of wind direction and speed, an early-warning system of wind pressure in the transportation of this waterway was established preliminarily. The back substitutions displayed that the spatial distribution of wind pressure in this4years was closely related to the terrain. There was the highest wind pressure grades and the most early-warning times in the middle part, it took the second places in the east part and the least frequencies of strong crosswind in the western part and the lowest grades.Weather Research and Forecasting Model for Version3.4(WRF3.4), a non-hydrostatic mesoscale numerical forecasting combined with0.5°×0.5°meteorological reanalysis data were used to the simulations and diagnostic analysis of a strong crosswind event caused by strong cold air during29th to30th, December in2010. The results showed as follows:(1) There was a strong northwest airflow on upper air and strong wind shear. In addition, there was the coupling of the low-level divergence field and vorticity field with the upper-lever divergence field and vorticity field, combined with the downdraft. It was the downward transfering of momentum in the upper level and favorable dynamical conditions that resulted into the engendering of the surface strong wind.(2) Cold advection controlled the troposphere in the vertical direction, and atmospheric stratification became unstable. Besides, the strong cold advection strengthened the high pressure behind the cold front, inducing positive allobaric field and allobaric gradient turned larger. As a result, cold advection was one of the import reasons.(3) We had found that it was the height of terrain played a crucial role to form the special wind field of Jiangsu Section of the Yangtze River Waterway by conducting sensitivity tests of terrain and water-land distribution.Weather Research and Forecasting Model for Version3.4(WRF3.4), a non-hydrostatic mesoscale numerical forecasting combined with0.5°×0.5°meteorological reanalysis data were used to the numerical simulations of two strong crosswinds event caused by severe convection on14th, June in2009and13th, August in2011. Through the comparison and analysis, the results showed as follows:(1) Before the two events occurred, there was ascending motion in the lower troposphere, and then downdraft controlled the part of air. What is more, strong vertical wind shear and the downward transfering of momentum from the upper levels were the important conditions that triggered, maintained and strengthened the strong crosswinds. The divergence, vertical velocity and vertical wind shear of the previous event were larger than the latter.(2) There existed dry air in the upper atmosphere and wet air in the lower atmosphere in the two events. Such a vertical structure was likely to form convective unstable stratification. In addition, the moisture convergence in the lower air and the moisture divergence in the upper air developed and maintained severe convection weather.(3) The unstable energy was accumulated in the earlier stage of the two events. Besides, the vertical structure of cold air in the upper level and warm air in the lower level, and non-adiabatic heating played a role in the occurrence of the strong crosswinds.