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Study on the Wavelet Characteristics of Water and Heat Fluxes in Urban Park Green Space

WANG Xiu-xin1,2,3,4,CHEN Sheng-hai1,2,3,LIU Xin1,2,3,ZHU Qi-jiang1,2,3,HU Yu-mei1,2,3 (1.Research Center for Remote Sensing and GIS,College of Geography and Remote Sensing Science,Beijing Normal University,Beijing 100875,China;2.State key Laboratory of Remote Sensing Science,Beijing 100875,China;3.Beijing Key Laboratory for Remote Sensing of Environment and Digital Cities,Beijing 100875,China;4.College of Computer Science and Information Technology,Guangxi Normal University,Guilin 541004,China)  
Urban park green space is one of the important factors affecting urban microclimate.Water and heat fluxes on land surface affect urban microclimate directly.So the fluxes are the important factors used to evaluate the ecological benefits of urban green space.Therefore,in this study an eddy covariance system in Haidian Park in the Beijing urban area is developed,and the fluxes latent heat and sensible heat between underlaying surface and atmosphere were continuously measured in the park.The flux values were measured on a sunny day and a cloudy day in growing season and a sunny day in non-growing season.The fluctuations of the fluxes are processed with continue wavelet transform.Finally,the isolines of wavelet coefficients are drawn,and the temporal structure of the fluxes and its change characteristics are analyzed.The results show that there are the multiple temporal scales of the fluxes affecting urban microclimate,and there are also the quasi-periodic components of different temporal scales in their fluctuations.In growing season,there are the quasi-periodic components about 20 minutes and varying from 40 minutes to 80 minutes for latent heat flux.For sensible heat flux,however,there are the same quasi-periodic components as that of latent heat flux on sunny day but the large quasi-periodic components on cloudy day.In non-growing season,there are the quasi-periodic components varying from 30 minutes to 180 minutes for both latent heat and sensible heat fluxes.The temporal scales of the quasi-periodic components are greater in growing season than that in non-growing season.The more seriously the fluxes fluctuate,the smaller the temporal scales of the quasi-periodic components will be.There is no the significant difference for quasi-periodic components of latent heat flux between sunny day and cloudy day.But for sensible heat flux there are only great temporal scales for quasi-periodic components on cloudy day because sensible heat flux varies less seriously on cloudy day than on sunny day.
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