| In order to explore the impact of road thermal condition on road traffic,explain the physical mechanism of high-temperature and low-temperature events on road surface and provide meteorological support for road traffic,in this paper, the observed data of the Automatic Weather Monitoring System on the Shanghai-Nanjing Expressway during2010to2012and the recent basic geographical information in Jiangsu Province were collected to analyze the temporal and spatial pattern of road surface on the expressway, the differences between the temperature of the road surface, the base temperature at10cm below the road surface and the air temperature at3m level above the road surface were compared and the impact of topographic environment on the road surface temperature was discussed. On this basis, firstly, analyze the historical process of the high/low-temperature events over the surface of Shanghai-Nanjing Expressway and the characteristic of high/low temperature extreme events. Secondly, apply the WRF model for different types of high and low temperature process in numerical simulation; analysis the change of the road surface heat flux based on the radiation balance equation and heat balance equation during the process of high and low temperature on road surface;explore the mechanism of formation in the different sections of high/low temperature process on shanghai-nanjing expressway.At last, estimate the road surface heat flux based on the results of the numerical simulation; set up the model of high/low temperature on road surface combined with the road temperature for realizing the prediction of high/low temperature process on road surface of hanghai-nanjing expressway1.The results showed as follows:(1) In general, the daily maximum value of road surface temperature appeared at13:00pm (BST), the daily minimum value occurred at5:00am (BST). The average daily range of road surface temperature was20.5℃and it was obviously higher than the average daily ranges of the base temperatures at10cm below the road surface and the air temperature at3m level above the road surface.The extreme values phase of the road surface temperature was1hour before the extreme values phase of the air temperature at3m above the road surface and2hours before the extreme values phase of the base temperature at10cm below the road surface.(2) For a whole year, the daily range of the road surface temperature in summer was largest, it was least in winter and it was placed in between the largest value and the least value in spring and autumn.(3) In a year, August was the highest month of monthly average road surface temperature and January was the lowest month. The extreme maximum surface temperature appeared in August and the extreme minimum value was in January. In the vertical direction, the annual range of the road surface temperature was largest, the annual range of the base temperature at10cm below the road surface taked the second place and the annual range of the air temperature at3m level above the road surface was least.(4) The surrounding thermal environment and undulated terrain had obvious effect on the variations of road surface temperature and there were some obvious differences between the road surface temperatures of the different road parts. The daily and annual ranges of surface temperature decreased from west to east. Suzhou Industrial Park Station in the east part of the expressway occurred the high road surface temperatures usually for the influence of the deposed industrial heat discharge and the urban heat island (UHI) in summer. Tangshan Station in the west part of the expressway appeared the low road surface temperatures frequently for the low-lying and concave terrains and the accumulation of the cold air.(5) The basic variation characteristic of road surface temperature on the Shanghai-Nanjing taked shape from the interaction of the large scale climate background and the local microclimate environment.The periodic change pattern is decided by the large scale climate background and the difference between the road surface temperatures in the different sections of the expressway is resulted from the local microclimate environment.2. In2010-2012high and low temperature process is happening on the shanghai-nanjing expressway and the road surface extreme high and low temperature events after statistical analysis found that:(1) The high temperature process averaged6hours a day, the longest duration of which lasted12days. Besides, the high temperature process could be classified as damp-heat type and dry-heat type, both of which had a common of daily maximum temperature of air(above32℃) and pavement (above55℃). But the dry-type was more frequent, stronger, higher surface temperature and longer lasting time. The two types also had a difference in occurring time. The damp-heat type happened from the end of June to early July, when was plum rain season happening. Though the dry-type lasted two periods, late July to early August, when midsummer was influenced by subtropical high, and late August to the end of August, when the weather was controlled by stronger subtropical high and continental high.(2) The low-temperature process of pavement, which could last for17hours, could divide into damp-cold type and dry-cold type. Both types had a common of minimum temperature of air and pavement, which were below0℃. However, the dry-cold type happened more frequently. And the damp-cold type usually accompanied by the rainfall and snow, where the roads were icy.(3) The high temperature process occurred most in the eastern section of Shanghai-Nanjing Expressway, while the western part was where the low temperature process easily happened.3.In Shanghai-Nanjing Expressway typical high and low temperature process has carried on the example analysis, numerical simulation and mechanism analysis and prediction model, get the following conclusions:(1) The simulation values of the temperature at2m is the most close to the measured values of the temperature at3m; the measured values of the temperature at2m, soil temperature and the surface temperature is linear relation with the simulation values of the temperature at3m, the base temperature at10cm and road surface temperature (2)The income net radiation flux on the road surface is the crucial factor of the high/low temperature process;the more net radiation flux, the road surface temperature is higher; on the other hand, the lower road surface temperature. The atmospheric counter radiation and the sensible heat, latent heat between surface (road) to high atmosphere in the radiation balance equation form the spatial difference of road surface temperature on Shanghai-Nanjing Expressway.(3) Matching the road surface heat flux with the road surface temperature.The Gaussian is the best to road surface high temperature process and the Polynomial is to low.At the results, the road surface heat flux show the road surface temperature,the estimate of error between simulation and measured values is2℃. |
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