We propose a theoretical model for spatial variations of the temperature varianceσ2(z,r)(z is the dis-tance from the sample bottom and r the radial coordinate)in turbulent Rayleigh-Bénard convection(RBC).Adaptin...We propose a theoretical model for spatial variations of the temperature varianceσ2(z,r)(z is the dis-tance from the sample bottom and r the radial coordinate)in turbulent Rayleigh-Bénard convection(RBC).Adapting the“attached-eddy”modelofshearflowtothe plumesofRBC,wederivedanequationforσ2 which is based on the universal scaling of the normalized RBC temperature spectra.This equation in-cludes both logarithmic and power-law dependences on z/λth,whereλth is the thermal boundary layer thickness.The equation parameters depend on r and the Prandtl number Pr,but have only an extremelyweak dependence on the Rayleigh number Ra Thus our model provides a near-universal equation for thetemperature variance profile in turbulent RBC.展开更多
In the summer of 2022,an unprecedented and long-lasting high temperature swept central-eastern China,causing significant societal effects.However,the sub-seasonal characteristics,causes and predictability of this extr...In the summer of 2022,an unprecedented and long-lasting high temperature swept central-eastern China,causing significant societal effects.However,the sub-seasonal characteristics,causes and predictability of this extreme high temperature event are not well explored.Based on the locations,intensities and causes of the high temperature,we divided it into three stages:early(13 June-3 July),sustained(4-28 July),and enhancement(29 July-30 August)stages.The high temperature during the early stage mainly occurred in north-central China with an anomaly of 2.5℃compared with climatology(1981-2010),while the last two stages occurred in the middle and lower Yangtze River Basin with anomalies of 2.8 and 3.8℃respectively.The high temperature during the three stages were all regulated by the strengthening and westward extension of the western Pacific subtropical high(WPSH)but involved different physical process.In the early stage,it was mainly caused by the anticyclones over the Mongolia and Northwest Pacific and enhanced by the minor impact of WPSH.In the sustained stage it was influenced by relatively more stronger WPSH and South Asia high(SAH)and the relatively minor impact of the anticyclone over the north-western South Asia.In the enhancement stage,the high temperature was mainly caused by a combination of the record-breaking WPSH and SAH and the strong European blocking high.Inside,the exceptionally powerful WPSH was well correlated with the sea surface temperature gradient induced by the developing La Niña.The ECMWF and NCEP models reasonably predicted the location and intensity of the high temperature in the early stage,but poorly predicted that in the sustained and enhancement stages partly because of the failure prediction of the WPSH's enhancement and westward extension.The ECMWF model's more accurate prediction of the WPSH may contribute to its better forecasting of the heatwaves.展开更多
基金the National Natural Science Foundation of China(Grants 11772111 and91952101)the Max Planck Partner Group.
文摘We propose a theoretical model for spatial variations of the temperature varianceσ2(z,r)(z is the dis-tance from the sample bottom and r the radial coordinate)in turbulent Rayleigh-Bénard convection(RBC).Adapting the“attached-eddy”modelofshearflowtothe plumesofRBC,wederivedanequationforσ2 which is based on the universal scaling of the normalized RBC temperature spectra.This equation in-cludes both logarithmic and power-law dependences on z/λth,whereλth is the thermal boundary layer thickness.The equation parameters depend on r and the Prandtl number Pr,but have only an extremelyweak dependence on the Rayleigh number Ra Thus our model provides a near-universal equation for thetemperature variance profile in turbulent RBC.
基金the support of National Natural Science Foundation of China(42275097)the Key Program of the National Natural Science Foundation of China(42130610)+1 种基金National Natural Science Foundation of China(42075091)the CAS Light of West China Program.
文摘In the summer of 2022,an unprecedented and long-lasting high temperature swept central-eastern China,causing significant societal effects.However,the sub-seasonal characteristics,causes and predictability of this extreme high temperature event are not well explored.Based on the locations,intensities and causes of the high temperature,we divided it into three stages:early(13 June-3 July),sustained(4-28 July),and enhancement(29 July-30 August)stages.The high temperature during the early stage mainly occurred in north-central China with an anomaly of 2.5℃compared with climatology(1981-2010),while the last two stages occurred in the middle and lower Yangtze River Basin with anomalies of 2.8 and 3.8℃respectively.The high temperature during the three stages were all regulated by the strengthening and westward extension of the western Pacific subtropical high(WPSH)but involved different physical process.In the early stage,it was mainly caused by the anticyclones over the Mongolia and Northwest Pacific and enhanced by the minor impact of WPSH.In the sustained stage it was influenced by relatively more stronger WPSH and South Asia high(SAH)and the relatively minor impact of the anticyclone over the north-western South Asia.In the enhancement stage,the high temperature was mainly caused by a combination of the record-breaking WPSH and SAH and the strong European blocking high.Inside,the exceptionally powerful WPSH was well correlated with the sea surface temperature gradient induced by the developing La Niña.The ECMWF and NCEP models reasonably predicted the location and intensity of the high temperature in the early stage,but poorly predicted that in the sustained and enhancement stages partly because of the failure prediction of the WPSH's enhancement and westward extension.The ECMWF model's more accurate prediction of the WPSH may contribute to its better forecasting of the heatwaves.
