This study investigated the regime-dependent predictability using convective-scale ensemble forecasts initialized with different initial condition perturbations in the Yangtze and Huai River basin(YHRB)of East China.T...This study investigated the regime-dependent predictability using convective-scale ensemble forecasts initialized with different initial condition perturbations in the Yangtze and Huai River basin(YHRB)of East China.The scale-dependent error growth(ensemble variability)and associated impact on precipitation forecasts(precipitation uncertainties)were quantitatively explored for 13 warm-season convective events that were categorized in terms of strong forcing and weak forcing.The forecast error growth in the strong-forcing regime shows a stepwise increase with increasing spatial scale,while the error growth shows a larger temporal variability with an afternoon peak appearing at smaller scales under weak forcing.This leads to the dissimilarity of precipitation uncertainty and shows a strong correlation between error growth and precipitation across spatial scales.The lateral boundary condition errors exert a quasi-linear increase on error growth with time at the larger scale,suggesting that the large-scale flow could govern the magnitude of error growth and associated precipitation uncertainties,especially for the strong-forcing regime.Further comparisons between scale-based initial error sensitivity experiments show evident scale interaction including upscale transfer of small-scale errors and downscale cascade of larger-scale errors.Specifically,small-scale errors are found to be more sensitive in the weak-forcing regime than those under strong forcing.Meanwhile,larger-scale initial errors are responsible for the error growth after 4 h and produce the precipitation uncertainties at the meso-β-scale.Consequently,these results can be used to explain underdispersion issues in convective-scale ensemble forecasts and provide feedback for ensemble design over the YHRB.展开更多
The characteristics of convective-scale downdrafts in the outer core of tropical cyclones in the lower-and upper-layer vertical wind shear(VWS)are investigated based on two high-resolution idealized numerical experime...The characteristics of convective-scale downdrafts in the outer core of tropical cyclones in the lower-and upper-layer vertical wind shear(VWS)are investigated based on two high-resolution idealized numerical experiments.Four types of outer-core downdrafts,originating from the lower troposphere,the midtroposphere,the upper level,and the tropopause,respectively,are found.The downdrafts originating from the lower and mid troposphere can penetrate down near the surface,and those originating from the tropopause in upper-layer VWS tend to penetrate more downward than in lower-layer VWS.Downdrafts tend to be located in the more upwind portion of the downshear-right quadrant in lower-layer VWS than in upper-layer VWS.The frequency of downdrafts outside and upwind of the parent updraft increases with the increasing downdraft top height.Vertical momentum budgets indicate that downward-oriented buoyancy due to the evaporational cooling of rainwater and precipitation drag mainly contribute to the occurrence of low-level downdrafts,and the midlevel and upper-level downdrafts originate due to precipitation drag and are strengthened by the downward-oriented,buoyancy-induced perturbation pressure gradient.The processes governing the downdrafts from the tropopause are different between the two experiments.More icy-type particles are produced and transported outward at upper levels in the lower-layer shear experiment,resulting in larger downward-oriented buoyancy due to the sublimational cooling of icy-type particles and contributing to the development/maintenance of the downdraft from the tropopause in that experiment.However,the downwardoriented perturbation pressure gradient leads to the development/maintenance of the downdraft from the tropopause in the upper-layer shear experiment.展开更多
Cold pools(CPs)significantly influence coastal heavy rainfall,but detailed observations of them are limited due to the lack of vertical measurement instruments.This study statistically characterizes CPs in the coastal...Cold pools(CPs)significantly influence coastal heavy rainfall,but detailed observations of them are limited due to the lack of vertical measurement instruments.This study statistically characterizes CPs in the coastal monsoon region of South China using unique data from the 356-m-high Shenzhen Meteorological Tower.CP occurrence correlates with convective activities influenced by the summer monsoon in the seasonal variations and land–sea breeze activities in the diurnal cycle.The CPs predominantly dry the atmosphere,highlighting the dominant role of dry entrainment through convective downdrafts in their formation,with a minor role of hydrometeor evaporation.The average CP depth is estimated at 668.0 m,deeper than tropical CPs but shallower than midlatitude counterparts.The CP properties exhibit diurnal variability,largely influenced by mesoscale convective system(MCS)activities.MCS-induced CPs are deeper and more intense than those from individual convective cells,while linear-MCS-produced CPs are the most intense.These observations from the coastal monsoon region contribute to a comprehensive global understanding of CP characteristics,complementing existing studies from midlatitude and tropical regions.展开更多
The quantitative precipitation forecast(QPF) in very-short range(0-12 hours) has been investigated in this paper by using a convective-scale(3km) GRAPES_Meso model. At first, a latent heat nudging(LHN) scheme to assim...The quantitative precipitation forecast(QPF) in very-short range(0-12 hours) has been investigated in this paper by using a convective-scale(3km) GRAPES_Meso model. At first, a latent heat nudging(LHN) scheme to assimilate the hourly intensified surface precipitation data was set up to enhance the initialization of GRAPES_Meso integration. And then based on the LHN scheme, a convective-scale prediction system was built up in considering the initial "triggering"uncertainties by means of multi-scale initial analysis(MSIA), such as the three-dimensional variational data assimilation(3DVAR), the traditional LHN method(VAR0LHN3), the cycling LHN method(CYCLING), the spatial filtering(SS) and the temporal filtering(DFI) LHN methods. Furthermore, the probability matching(PM) method was used to generate the QPF in very-short range by combining the precipitation forecasts of the five runs. The experiments for one month were carried out to validate the MSIA and PM method for QPF in very-short range.The numerical simulation results showed that:(1) in comparison with the control run, the CYCLING run could generate the smaller-scale initial moist increments and was better for reducing the spin-up time and triggering the convection in a very-short time;(2) the DFI runs could generate the initial analysis fields with relatively larger-scale initial increments and trigger the weaker convections at the beginning time(0-3h) of integration, but enhance them at latter time(6-12h);(3) by combining the five runs with different convection triggering features, the PM method could significantly improve the QPF in very-short range in comparison to any single run. Therefore, the QPF with a small size of combining members proposed here is quite prospective in operation for its lower computation cost and better performance.展开更多
基金supported by the National Key Research and Development Program of China(Grant No.2017YFC1502103)the National Natural Science Foundation of China(Grant Nos.41430427 and 41705035)+1 种基金the China Scholarship Councilthe Postgraduate Research&Practice Innovation Program of Jiangsu Province(Grant No.KYCX17_0876)。
文摘This study investigated the regime-dependent predictability using convective-scale ensemble forecasts initialized with different initial condition perturbations in the Yangtze and Huai River basin(YHRB)of East China.The scale-dependent error growth(ensemble variability)and associated impact on precipitation forecasts(precipitation uncertainties)were quantitatively explored for 13 warm-season convective events that were categorized in terms of strong forcing and weak forcing.The forecast error growth in the strong-forcing regime shows a stepwise increase with increasing spatial scale,while the error growth shows a larger temporal variability with an afternoon peak appearing at smaller scales under weak forcing.This leads to the dissimilarity of precipitation uncertainty and shows a strong correlation between error growth and precipitation across spatial scales.The lateral boundary condition errors exert a quasi-linear increase on error growth with time at the larger scale,suggesting that the large-scale flow could govern the magnitude of error growth and associated precipitation uncertainties,especially for the strong-forcing regime.Further comparisons between scale-based initial error sensitivity experiments show evident scale interaction including upscale transfer of small-scale errors and downscale cascade of larger-scale errors.Specifically,small-scale errors are found to be more sensitive in the weak-forcing regime than those under strong forcing.Meanwhile,larger-scale initial errors are responsible for the error growth after 4 h and produce the precipitation uncertainties at the meso-β-scale.Consequently,these results can be used to explain underdispersion issues in convective-scale ensemble forecasts and provide feedback for ensemble design over the YHRB.
基金jointly supported by the National Key Research and Development Program of China(Grant No.2017YFC1501601)the Key Program of the Ministry of Science and Technology of China(Grant No.2017YFE0107700)the National Natural Science Foundation of China(Grant Nos.41875054,41730961,41730960,and 41775065)
文摘The characteristics of convective-scale downdrafts in the outer core of tropical cyclones in the lower-and upper-layer vertical wind shear(VWS)are investigated based on two high-resolution idealized numerical experiments.Four types of outer-core downdrafts,originating from the lower troposphere,the midtroposphere,the upper level,and the tropopause,respectively,are found.The downdrafts originating from the lower and mid troposphere can penetrate down near the surface,and those originating from the tropopause in upper-layer VWS tend to penetrate more downward than in lower-layer VWS.Downdrafts tend to be located in the more upwind portion of the downshear-right quadrant in lower-layer VWS than in upper-layer VWS.The frequency of downdrafts outside and upwind of the parent updraft increases with the increasing downdraft top height.Vertical momentum budgets indicate that downward-oriented buoyancy due to the evaporational cooling of rainwater and precipitation drag mainly contribute to the occurrence of low-level downdrafts,and the midlevel and upper-level downdrafts originate due to precipitation drag and are strengthened by the downward-oriented,buoyancy-induced perturbation pressure gradient.The processes governing the downdrafts from the tropopause are different between the two experiments.More icy-type particles are produced and transported outward at upper levels in the lower-layer shear experiment,resulting in larger downward-oriented buoyancy due to the sublimational cooling of icy-type particles and contributing to the development/maintenance of the downdraft from the tropopause in that experiment.However,the downwardoriented perturbation pressure gradient leads to the development/maintenance of the downdraft from the tropopause in the upper-layer shear experiment.
基金supported by the National Key Research and Development Program of China (Grant No. 2024YFC3013003)the National Natural Science Foundation of China (Grant No. 42475002)+2 种基金the Innovation Group Project of Southern Marine Science and Engineering Guangdong Laboratory (Zhuhai) (Grant Nos. SML2024SP035, SML2024SP012, and 311024001)the Guangdong Basic and Applied Basic Research Foundation (Grant Nos. 2025A1515011974, 2024A1515510005 and 2020B0301030004)the Key Innovation Team of China Meteorological Administration (Grant No. CMA2023ZD08)
文摘Cold pools(CPs)significantly influence coastal heavy rainfall,but detailed observations of them are limited due to the lack of vertical measurement instruments.This study statistically characterizes CPs in the coastal monsoon region of South China using unique data from the 356-m-high Shenzhen Meteorological Tower.CP occurrence correlates with convective activities influenced by the summer monsoon in the seasonal variations and land–sea breeze activities in the diurnal cycle.The CPs predominantly dry the atmosphere,highlighting the dominant role of dry entrainment through convective downdrafts in their formation,with a minor role of hydrometeor evaporation.The average CP depth is estimated at 668.0 m,deeper than tropical CPs but shallower than midlatitude counterparts.The CP properties exhibit diurnal variability,largely influenced by mesoscale convective system(MCS)activities.MCS-induced CPs are deeper and more intense than those from individual convective cells,while linear-MCS-produced CPs are the most intense.These observations from the coastal monsoon region contribute to a comprehensive global understanding of CP characteristics,complementing existing studies from midlatitude and tropical regions.
基金National(Key)Basic Research and Development(973)Program of China(2013CB430106)the National Natural Science Foundation of China(41375108)
文摘The quantitative precipitation forecast(QPF) in very-short range(0-12 hours) has been investigated in this paper by using a convective-scale(3km) GRAPES_Meso model. At first, a latent heat nudging(LHN) scheme to assimilate the hourly intensified surface precipitation data was set up to enhance the initialization of GRAPES_Meso integration. And then based on the LHN scheme, a convective-scale prediction system was built up in considering the initial "triggering"uncertainties by means of multi-scale initial analysis(MSIA), such as the three-dimensional variational data assimilation(3DVAR), the traditional LHN method(VAR0LHN3), the cycling LHN method(CYCLING), the spatial filtering(SS) and the temporal filtering(DFI) LHN methods. Furthermore, the probability matching(PM) method was used to generate the QPF in very-short range by combining the precipitation forecasts of the five runs. The experiments for one month were carried out to validate the MSIA and PM method for QPF in very-short range.The numerical simulation results showed that:(1) in comparison with the control run, the CYCLING run could generate the smaller-scale initial moist increments and was better for reducing the spin-up time and triggering the convection in a very-short time;(2) the DFI runs could generate the initial analysis fields with relatively larger-scale initial increments and trigger the weaker convections at the beginning time(0-3h) of integration, but enhance them at latter time(6-12h);(3) by combining the five runs with different convection triggering features, the PM method could significantly improve the QPF in very-short range in comparison to any single run. Therefore, the QPF with a small size of combining members proposed here is quite prospective in operation for its lower computation cost and better performance.
