Experimental Study On Meteorological Elements And Surface Fluxes Differences Between Urban And Suburban Areas In Hefei

Urbanization has not only led to huge differences in meteorological elements,radiation and surface energy balance,and heat storage in cities and suburbs,but also environmental problems such as urban heat islands.This paper mainly analyze the differences of meteorological elements,radiation and energy balance in different weather conditions in Hefei city and suburbs with the observation data of Eddy correlation system of the four seasons.The value of urban heat island(UHI)of Hefei is also given in this paper.In addition,the annual anthropogenic heat in the East Campus of University of science and technology of China in 2013 is calculated by the source list method.The differences of heat storage between Hefei city and suburb are analyzed with the formula energy balance.The main conclusions are as follows:(1)The differences in meteorological elements between the city and the suburbs are as follows:(a)The average value of solar short-wave radiation between the two sites in spring,summer and winter is no more than 10 W/m2,and the downward long wave radiation of the city site is 1-2 W/m2 higher than it in the suburb site.However,the suburban sites have more cloudy weather in the autumn.In the autumn sunny days,the value of the solar short-wave radiation in the urban site is 30.58 W/m2 higher than that in the suburbs,and average value of the downward long wave radiation of suburb site is 4.16 W/m2 higher than that in the urban site;(b)The relative humidity of the suburbs is always higher than that of the urban area.The difference of average relative humidity between the two stations during the day is no more than 2.5%.But the average value of the relative humidity of the suburb site at night is larger the urban site.The value of it can even reach 11.84%;(c)The average time of formation of unstable stratification in the.urban site is about 3 hours longer than that in the suburb site,and it is easy to form a strong stable stratification in the suburb site on winter,spring and autumn nights.The air temperature above the Dongpu reservoir is higher than that at the same altitude above the suburban site,and it is easy to form a local circulation.The suburban sites in these three seasons are prone to north wind at night.(2)The UHI at night is always higher than that in daytime.The mean value of the UHI in the four seasons at night is as follows:winter>autumn>spring>summer.The on the cloudy winter night can reach a maximum of 1.87?,but the UHI on the sunny summer night is only 0.69?.The UHI in the rain and snow days is very small,and the UHI on the snowy night is only 0.13?.Rain and snow have a significant weakening effect on urban heat islands.(3)The differences in energy dominance between urban and suburban areas are:the main way of energy domination in the city is the sensible heat flux,and the main way of energy domination in the suburbs is the latent heat flux.The daily average difference of sensible heat flux between the two stations can reach 58 W/m2 during the daytime of the sunny spring weather conditions.The daily average difference of latent heat flux between the two stations can reach the maximum value of 48.04 W/m2 during the daytime of the sunny autumn weather conditions.The Bowen ratio of the urban site is always higher than it in the suburb site;the relationship between the four seasons of the urban site is as follows:Winter>Spring>Summer>Autumn.The Bowen ratio of urban site Station has very big differences in Four Seasons.It can reach a maximum of 8.66 in sunny weather conditions in winter,and can reach a minimum of 0.95 in sunny weather conditions in autumn.The Bowen ratio of the urban site have a small fluctuation for four seasons.It reaches a maximum value of 1.65 in sunny weather conditions and reaches a minimum of 0.49 in sunny autumn weather conditions.(4)Compared with the suburb site,the urban site has a stronger heat storage capacity.The heat storage item(?QS)is the main source item in the energy balance of the urban underlying surface.The ?QS is larger than(H+LE)in urban site in the process of energy budget obviously;while(H+LE)is often larger than ?QS in the suburb site,which is the main performance difference of the thermal properties of the underlying surface of the city and suburbs.Man-made heat is a non-negligible item in calculating the heat storage of a city.