Based on the data and method offered by Liu et al. （2009）, the direct wind and Stokes drift-induced energy inputs into the Ekman layer within the Antarctic Circumpolar Current （ACC） area are reestimated since the ...Based on the data and method offered by Liu et al. （2009）, the direct wind and Stokes drift-induced energy inputs into the Ekman layer within the Antarctic Circumpolar Current （ACC） area are reestimated since the results of the former have been proved to be underestimated. And the result shows that the total rate of energy input into the Ekman-Stokes layer within the ACC area is 852.41 GW, including 649.75 GW of direct wind energy input （76%） and 202.66 GW of Stoke drift-induced energy input （24%）. Total increased energy input, due to wave-induced Coriolis-Stokes forcing added to the classical Ekman model, is 52.05 GW, accounting for 6.5% of the wind energy input into the classical Ekman layer. The long-term variability of direct wind and Stokes drift-induced energy inputs into the Ekman layer within the ACC is also investigated, and the result shows that the Stokes drift hinders the decadal increasing trend of direct wind energy input. Meanwhile, there is a period of 4-5 a in the energy spectrums, as same as the Antarctic circumpolar wave.展开更多
This paper is concerned with the wave energy input into the Ekman layer, based on 3 observational facts that surface waves could significantly affect the profile of the Ekman layer. Under the assumption of constant ve...This paper is concerned with the wave energy input into the Ekman layer, based on 3 observational facts that surface waves could significantly affect the profile of the Ekman layer. Under the assumption of constant vertical diffusivity, the analytical form of wave energy input into the Ekman layer is derived. Analysis of the energy balance shows that the energy input to the Ekman layer through the wind stress and the interaction of the Stokes-drift with planetary vorticity can be divided into two kinds. One is the wind energy input, and the other is the wave energy input which is dependent on wind speed, wave characteristics and the wind direction relative to the wave direction. Estimates of wave energy input show that wave energy input can be up to 10% in high-latitude and high-wind speed areas and higher than 20% in the Antarctic Circumpolar Current, compared with the wind energy input into the classical Ekman layer. Results of this paper are of significance to the study of wave-induced large scale effects.展开更多
Based on the classical Ekman theory, a series of intermediate boundary layer models, which retain the nonlinear advective process while discard embellishments, have been proposed with the intention to understand the c...Based on the classical Ekman theory, a series of intermediate boundary layer models, which retain the nonlinear advective process while discard embellishments, have been proposed with the intention to understand the complex nonlinear features of the atmospheric boundary layer and its interaction with the free atmosphere. In this paper, the recent advances in the intermediate boundary-layer dynamic models are reviewed. Several intermediate models such as the boundary-layer models incorporating geostrophic momentum approximation, Ekman momentum approximation, and the weak nonlinear Ekman-layer model are a major theme. With inspection of the theoretical frameworks, the physical meaning and the limitations of each intermediate model axe discussed. It is found that the qualitative descriptions of the nonlinear nature in Ekman layer made by the intermediate models are fairly consistent though the details may be different. As the application of the intermediate models is concerned, the application of the intermediate models to the study of the topographic boundary layer, frontogenesis, low-level frontal structure, and low-level jet are especially summarized in this paper. It is shown that the intermediate boundary-layer models have great potential in illustrating the low-level structures of the weather and climate systems as they are coupled with the free atmospheric models. In addition, the important remaining scientific challenges and a prospectus for future research on the intermediate model are also discussed.展开更多
A heavy rainfall event caused by a mesoscale convective system(MCS),which occurred over the Yellow River midstream area during 7-9 July 2016,was analyzed using observational,high-resolution satellite,NCEP/NCAR reanaly...A heavy rainfall event caused by a mesoscale convective system(MCS),which occurred over the Yellow River midstream area during 7-9 July 2016,was analyzed using observational,high-resolution satellite,NCEP/NCAR reanalysis,and numerical simulation data.This heavy rainfall event was caused by one mesoscale convective complex(MCC)and five MCSs successively.The MCC rainstorm occurred when southwesterly winds strengthened into a jet.The MCS rainstorms occurred when low-level wind fields weakened,but their easterly components in the lower and boundary layers increased continuously.Numerical analysis revealed that there were obvious differences between the MCC and MCS rainstorms,including their three-dimensional airflow structure,disturbances in wind fields and vapor distributions,and characteristics of energy conversion and propagation.Formation of the MCC was related to southerly conveyed water vapor and energy to the north,with obvious water vapor exchange between the free atmosphere and the boundary layer.Continuous regeneration and development of the MCSs mainly relied on maintenance of an upward extension of a positive water vapor disturbance.The MCC rainstorm was triggered by large range of convergent ascending motion caused by a southerly jet,and easterly disturbance within the boundary layer.While a southerly fluctuation and easterly disturbance in the boundary layer were important triggers of the MCS rainstorms.Maintenance and development of the MCC and MCSs were linked to secondary circulation,resulting from convergence of Ekman non-equilibrium flow in the boundary layer.Both intensity and motion of the convergence centers in MCC and MCS cases were different.Clearly,sub-synoptic scale systems in the middle troposphere played a leading role in determining precipitation distribution during this event.Although mesoscale systems triggered by the sub-synoptic scale system induced the heavy rainfall,small-scale disturbances within the boundary layer determined its intensity and location.展开更多
基金The National Natural Science Foundation of China under contract Nos 40930844 and 40976005
文摘Based on the data and method offered by Liu et al. （2009）, the direct wind and Stokes drift-induced energy inputs into the Ekman layer within the Antarctic Circumpolar Current （ACC） area are reestimated since the results of the former have been proved to be underestimated. And the result shows that the total rate of energy input into the Ekman-Stokes layer within the ACC area is 852.41 GW, including 649.75 GW of direct wind energy input （76%） and 202.66 GW of Stoke drift-induced energy input （24%）. Total increased energy input, due to wave-induced Coriolis-Stokes forcing added to the classical Ekman model, is 52.05 GW, accounting for 6.5% of the wind energy input into the classical Ekman layer. The long-term variability of direct wind and Stokes drift-induced energy inputs into the Ekman layer within the ACC is also investigated, and the result shows that the Stokes drift hinders the decadal increasing trend of direct wind energy input. Meanwhile, there is a period of 4-5 a in the energy spectrums, as same as the Antarctic circumpolar wave.
基金the National Basic Research Program of China (973 program) (Grant Nos. 2005CB422302 and 2007CB411806)the Major Project of the National Natural Science Foundation of China (Grant No. 40490263)
文摘This paper is concerned with the wave energy input into the Ekman layer, based on 3 observational facts that surface waves could significantly affect the profile of the Ekman layer. Under the assumption of constant vertical diffusivity, the analytical form of wave energy input into the Ekman layer is derived. Analysis of the energy balance shows that the energy input to the Ekman layer through the wind stress and the interaction of the Stokes-drift with planetary vorticity can be divided into two kinds. One is the wind energy input, and the other is the wave energy input which is dependent on wind speed, wave characteristics and the wind direction relative to the wave direction. Estimates of wave energy input show that wave energy input can be up to 10% in high-latitude and high-wind speed areas and higher than 20% in the Antarctic Circumpolar Current, compared with the wind energy input into the classical Ekman layer. Results of this paper are of significance to the study of wave-induced large scale effects.
基金Supported jointly by the National Key Basic Research and Development Project of China: Research on Theories and Methods of Monitoring and Predicting of Heavy Rainfall hi South China (2004CB418301)the National Natural Science Foundation of China under Grant Nos. 40333025, 40325014, and 40333031
文摘Based on the classical Ekman theory, a series of intermediate boundary layer models, which retain the nonlinear advective process while discard embellishments, have been proposed with the intention to understand the complex nonlinear features of the atmospheric boundary layer and its interaction with the free atmosphere. In this paper, the recent advances in the intermediate boundary-layer dynamic models are reviewed. Several intermediate models such as the boundary-layer models incorporating geostrophic momentum approximation, Ekman momentum approximation, and the weak nonlinear Ekman-layer model are a major theme. With inspection of the theoretical frameworks, the physical meaning and the limitations of each intermediate model axe discussed. It is found that the qualitative descriptions of the nonlinear nature in Ekman layer made by the intermediate models are fairly consistent though the details may be different. As the application of the intermediate models is concerned, the application of the intermediate models to the study of the topographic boundary layer, frontogenesis, low-level frontal structure, and low-level jet are especially summarized in this paper. It is shown that the intermediate boundary-layer models have great potential in illustrating the low-level structures of the weather and climate systems as they are coupled with the free atmospheric models. In addition, the important remaining scientific challenges and a prospectus for future research on the intermediate model are also discussed.
基金National Natural Science Foundation of China(41475050)
文摘A heavy rainfall event caused by a mesoscale convective system(MCS),which occurred over the Yellow River midstream area during 7-9 July 2016,was analyzed using observational,high-resolution satellite,NCEP/NCAR reanalysis,and numerical simulation data.This heavy rainfall event was caused by one mesoscale convective complex(MCC)and five MCSs successively.The MCC rainstorm occurred when southwesterly winds strengthened into a jet.The MCS rainstorms occurred when low-level wind fields weakened,but their easterly components in the lower and boundary layers increased continuously.Numerical analysis revealed that there were obvious differences between the MCC and MCS rainstorms,including their three-dimensional airflow structure,disturbances in wind fields and vapor distributions,and characteristics of energy conversion and propagation.Formation of the MCC was related to southerly conveyed water vapor and energy to the north,with obvious water vapor exchange between the free atmosphere and the boundary layer.Continuous regeneration and development of the MCSs mainly relied on maintenance of an upward extension of a positive water vapor disturbance.The MCC rainstorm was triggered by large range of convergent ascending motion caused by a southerly jet,and easterly disturbance within the boundary layer.While a southerly fluctuation and easterly disturbance in the boundary layer were important triggers of the MCS rainstorms.Maintenance and development of the MCC and MCSs were linked to secondary circulation,resulting from convergence of Ekman non-equilibrium flow in the boundary layer.Both intensity and motion of the convergence centers in MCC and MCS cases were different.Clearly,sub-synoptic scale systems in the middle troposphere played a leading role in determining precipitation distribution during this event.Although mesoscale systems triggered by the sub-synoptic scale system induced the heavy rainfall,small-scale disturbances within the boundary layer determined its intensity and location.
