Investigating the attributes of the dual oasis effect and oasis–desert interactions is crucial for understanding the climatic and ecological effects of oases.In this study,oasis effect intensity(OEI)was used as an in...Investigating the attributes of the dual oasis effect and oasis–desert interactions is crucial for understanding the climatic and ecological effects of oases.In this study,oasis effect intensity(OEI)was used as an indicator to investigate the factors that contribute to the dual oasis effect.The oasis effect has two attributes:the surface oasis heating effect(OHE)occurred in winter,while the oasis cooling effect(OCE)occurred in the other three seasons,especially in summer.During the day,the OEI of the whole oasis was−12.8℃,−5.2℃,and−4.5℃ in summer,spring,and autumn,respectively,which indicated a strong OCE;and OEI was 0.5℃ in winter,which indicated a weaker OHE.In arid regions,the OCE dominated most of the time,but the OHE occurred in winter and cannot be ignored.In addition,through statistical analysis and energy balance analysis,high evapotranspiration of the oasis was the main factor leading to the occurrence of OCE in the summer,while low albedo to the occurrence of OHE in winter.展开更多
Oasis effect can improve the regional climate and habitability of an arid region. In this study, we explored the cold island effects of oases distributed along the edge of Tarim Basin by analyzing the oasis cold islan...Oasis effect can improve the regional climate and habitability of an arid region. In this study, we explored the cold island effects of oases distributed along the edge of Tarim Basin by analyzing the oasis cold island effect （OCIE） intensity, spatial-temporal variation of OCIE, factors influencing the OCIE and impacts of OCIE on air temperature using geographical statistics and GIS methods based on the MODIS land surface temperature, land use/cover change （LUCC） and observed air temperature data. Results showed that all the oases in the Tarim Basin exhibited cold island effects, with the OCIE intensity highest in summer （-9.08℃）, followed by autumn （-4.24℃） and spring （-3.85℃）. The total area of oasis cold island （OCI） and the comprehensive OCIE index showed the same seasonal change trend as the OCIE intensity. However, the changing trends in areas of OCI with strong, medium and weak OCIEs were inconsistent across different seasons. Farmland and water areas were found to be the key contributors that affected the OCIE, and the area and aggregation metrics of these two land use/cover types directly contributed to the OCIE. By contrast, natural vegetation, such as forest and grassland, almost had no contribution to the OCIE. Simulation of observed air temperature data showed that if farmland is replaced by forest or grassland in the oasis, the mean, maximum and minimum air temperatures will increase significantly. This heating effect will be higher in summer （reaching 1.14℃ to 2.08℃） and lower in spring and autumn. Moreover, the heating effect of farmland being replaced by forest will be higher than that of farmland being replaced by grassland. These results can provide a basis for understanding the cold island effect of oases in arid regions.展开更多
The kinetic energy variations of mean flow and turbulence at three levels in the surface layer were calculated by using eddy covariance data from observations at Jinta oasis in 2005 summer. It is found that when the m...The kinetic energy variations of mean flow and turbulence at three levels in the surface layer were calculated by using eddy covariance data from observations at Jinta oasis in 2005 summer. It is found that when the mean horizontal flow was stronger, the turbulent kinetic energy was increased at all levels, as well as the downward mean wind at the middle level. Since the mean vertical flow on the top and bottom were both negligible at that time, there was a secondary circulation with convergence in the upper half and divergence in the lower half of the column. After consideration of energy conversion, it was found that the interaction between turbulence and the secondary circulation caused the intensification of each other. The interaction reflected positive feedback between turbulence and the vertical shear of the mean flow. Turbulent sensible and latent heat flux anomaly were also analyzed. The results show that in both daytime and at night, when the surface layer turbulence was intensified as a result of strengthened mean flow, the sensible heat flux was decreased while the latent heat flux was increased. Both anomalous fluxes contributed to the cold island effect and the moisture island effect of the oasis.展开更多
基金This work was supported by the National Key R&D Program of China[2018YFA0606404]the National Natural Science Foundation of China[41601064]+1 种基金Strategic Priority Research Program of Chinese Academy of Sciences[XDA2009000001]Technology Basic Resource Investigation Program of China[2017FY101003].
文摘Investigating the attributes of the dual oasis effect and oasis–desert interactions is crucial for understanding the climatic and ecological effects of oases.In this study,oasis effect intensity(OEI)was used as an indicator to investigate the factors that contribute to the dual oasis effect.The oasis effect has two attributes:the surface oasis heating effect(OHE)occurred in winter,while the oasis cooling effect(OCE)occurred in the other three seasons,especially in summer.During the day,the OEI of the whole oasis was−12.8℃,−5.2℃,and−4.5℃ in summer,spring,and autumn,respectively,which indicated a strong OCE;and OEI was 0.5℃ in winter,which indicated a weaker OHE.In arid regions,the OCE dominated most of the time,but the OHE occurred in winter and cannot be ignored.In addition,through statistical analysis and energy balance analysis,high evapotranspiration of the oasis was the main factor leading to the occurrence of OCE in the summer,while low albedo to the occurrence of OHE in winter.
基金funded by the National Natural Science Foundation of China(41571109)
文摘Oasis effect can improve the regional climate and habitability of an arid region. In this study, we explored the cold island effects of oases distributed along the edge of Tarim Basin by analyzing the oasis cold island effect （OCIE） intensity, spatial-temporal variation of OCIE, factors influencing the OCIE and impacts of OCIE on air temperature using geographical statistics and GIS methods based on the MODIS land surface temperature, land use/cover change （LUCC） and observed air temperature data. Results showed that all the oases in the Tarim Basin exhibited cold island effects, with the OCIE intensity highest in summer （-9.08℃）, followed by autumn （-4.24℃） and spring （-3.85℃）. The total area of oasis cold island （OCI） and the comprehensive OCIE index showed the same seasonal change trend as the OCIE intensity. However, the changing trends in areas of OCI with strong, medium and weak OCIEs were inconsistent across different seasons. Farmland and water areas were found to be the key contributors that affected the OCIE, and the area and aggregation metrics of these two land use/cover types directly contributed to the OCIE. By contrast, natural vegetation, such as forest and grassland, almost had no contribution to the OCIE. Simulation of observed air temperature data showed that if farmland is replaced by forest or grassland in the oasis, the mean, maximum and minimum air temperatures will increase significantly. This heating effect will be higher in summer （reaching 1.14℃ to 2.08℃） and lower in spring and autumn. Moreover, the heating effect of farmland being replaced by forest will be higher than that of farmland being replaced by grassland. These results can provide a basis for understanding the cold island effect of oases in arid regions.
基金supported by the State Key Program of National Natural Science of China(Grant Nos.40233035 and 40633014)funded by one of National Basic Research Program of China(Grant No.2009CB421402)
文摘The kinetic energy variations of mean flow and turbulence at three levels in the surface layer were calculated by using eddy covariance data from observations at Jinta oasis in 2005 summer. It is found that when the mean horizontal flow was stronger, the turbulent kinetic energy was increased at all levels, as well as the downward mean wind at the middle level. Since the mean vertical flow on the top and bottom were both negligible at that time, there was a secondary circulation with convergence in the upper half and divergence in the lower half of the column. After consideration of energy conversion, it was found that the interaction between turbulence and the secondary circulation caused the intensification of each other. The interaction reflected positive feedback between turbulence and the vertical shear of the mean flow. Turbulent sensible and latent heat flux anomaly were also analyzed. The results show that in both daytime and at night, when the surface layer turbulence was intensified as a result of strengthened mean flow, the sensible heat flux was decreased while the latent heat flux was increased. Both anomalous fluxes contributed to the cold island effect and the moisture island effect of the oasis.
