Urbanization’s impact on pre-monsoon extreme rainfall in the Greater Bay Area(GBA),coastal South China(SC),and its relation to different synoptic systems remains understudied.This research investigates urbanization e...Urbanization’s impact on pre-monsoon extreme rainfall in the Greater Bay Area(GBA),coastal South China(SC),and its relation to different synoptic systems remains understudied.This research investigates urbanization effects on premonsoon rainfall using hourly station observations and Weather Research and Forecasting model with the Single Layer Urban Canopy Model(WRF-SLUCM)simulations.Observations show stronger pre-monsoon extreme rainfall in GBA cities than surrounding rural areas,with the urban heat island(UHI)intensifying the urban rainfall intensity and probability.Extreme cases were classified into frontal and shear-line warm-sector types.Enhanced urban rainfall due to UHI was more pronounced under shear-line and warm-sector systems.Four frontal and four shear-line cases were dynamically downscaled using WRF-SLUCM,and four parallel experiments were conducted:“Nourban”(urban areas replaced by cropland),“AH0”,“AH100”,and“AH300”[normal land use,with the diurnal maximum anthropogenic heat(AH)set to 0,100,and 300 W m^(−2)in SLUCM,respectively].In frontal cases,significantly reduced urban rainfall in AH0 is due to decreased(enhanced)surface evaporation(wind divergence)in cities compared to cropland.Strong northerly winds and cold-air intrusion suppress the UHI in AH0 and AH100 during the rainfall process;enhanced urban rainfall occurs only in AH300.In contrast,for shear-line cases,urban friction and UHI promote local convection and wind convergence,increasing urban rainfall significantly in all urban experiments compared to Nourban.Overall,urbanization’s influence on SC’s premonsoon extreme rainfall is highly sensitive to the type of synoptic systems,necessitating further investigation of urban rainfall in this season.展开更多
This paper discusses the stability structure and the bifurcation of phase path characteristics of synoptic scale system.The analytic results show that the catastrophe of the synoptic scale disturbance may be caused by...This paper discusses the stability structure and the bifurcation of phase path characteristics of synoptic scale system.The analytic results show that the catastrophe of the synoptic scale disturbance may be caused by the nonlinear effects of barotropic and baroclinic instability and advection of ambient large-scale flow.Also, foregoing nonlinear effects on the speed of development and decay of the system are presented in the processes deviating from or approaching to equilibrium state.It has been found that there is a resonance phenomenon between the time-oscillation of heat source and the atmospheric disturbance.展开更多
A record-breaking extreme heavy snowfall(EHS)event hit northern China during 6–8 November 2021,with two maximum snowfall centers in North China(NC)and Northeast China(NEC),which inflicted severe socioeconomic impacts...A record-breaking extreme heavy snowfall(EHS)event hit northern China during 6–8 November 2021,with two maximum snowfall centers in North China(NC)and Northeast China(NEC),which inflicted severe socioeconomic impacts.This paper compares the differences in the synoptic processes and moisture supply associated with the EHS event in NC and NEC,as well as the atmospheric circulation anomalies before the event,to provide a reference for better prediction and forecasting of EHS in northern China.Synoptic analyses show that a positively tilted,inverted 500-hPa trough channeled cold-air outbreaks into NC,while dynamic updrafts along the front below the trough promoted moisture convergence over this region.In NEC,the dynamic updraft south of the frontogenesis region firstly triggered a low-level Yellow–Bohai Sea cyclone,which then converged with the 500-hPa trough to ultimately form an NEC cold vortex.Calculation of the vorticity tendency indicates that absolute vorticity advection was a better indicator than absolute vorticity divergence for the movement of the trough/ridge at the synoptic scale.Moreover,NOAA’s HYSPLIT(Hybrid Single-Particle Lagrangian Integrated Trajectory)model results reveal that the moisture for the EHS over NC mainly originated from the mid-to-low levels over the Asian–African region and the Eurasian mid-to-high latitudes,accounting for 32%and 31%,respectively.In contrast,the source of water vapor for the EHS over NEC was mainly the Eurasian mid-to-high latitudes and East Asia,with contributions of 38%and 28%,respectively.The findings of this study shed some fresh light on the distinctive contributions of different moisture sources to local precipitation.Further analyses of the atmospheric circulation anomalies in October reveal that a phase shift in the Arctic Oscillation related to the weakening of the polar vortex could have served as a useful indicator for the cold-air outbreaks in this EHS event.展开更多
基金supported by CUHK Strategic Impact Enhancement Fund(project no.3135536)Guangdong Basic and Applied Basic Research Foundation(2023B1515020029).
文摘Urbanization’s impact on pre-monsoon extreme rainfall in the Greater Bay Area(GBA),coastal South China(SC),and its relation to different synoptic systems remains understudied.This research investigates urbanization effects on premonsoon rainfall using hourly station observations and Weather Research and Forecasting model with the Single Layer Urban Canopy Model(WRF-SLUCM)simulations.Observations show stronger pre-monsoon extreme rainfall in GBA cities than surrounding rural areas,with the urban heat island(UHI)intensifying the urban rainfall intensity and probability.Extreme cases were classified into frontal and shear-line warm-sector types.Enhanced urban rainfall due to UHI was more pronounced under shear-line and warm-sector systems.Four frontal and four shear-line cases were dynamically downscaled using WRF-SLUCM,and four parallel experiments were conducted:“Nourban”(urban areas replaced by cropland),“AH0”,“AH100”,and“AH300”[normal land use,with the diurnal maximum anthropogenic heat(AH)set to 0,100,and 300 W m^(−2)in SLUCM,respectively].In frontal cases,significantly reduced urban rainfall in AH0 is due to decreased(enhanced)surface evaporation(wind divergence)in cities compared to cropland.Strong northerly winds and cold-air intrusion suppress the UHI in AH0 and AH100 during the rainfall process;enhanced urban rainfall occurs only in AH300.In contrast,for shear-line cases,urban friction and UHI promote local convection and wind convergence,increasing urban rainfall significantly in all urban experiments compared to Nourban.Overall,urbanization’s influence on SC’s premonsoon extreme rainfall is highly sensitive to the type of synoptic systems,necessitating further investigation of urban rainfall in this season.
文摘This paper discusses the stability structure and the bifurcation of phase path characteristics of synoptic scale system.The analytic results show that the catastrophe of the synoptic scale disturbance may be caused by the nonlinear effects of barotropic and baroclinic instability and advection of ambient large-scale flow.Also, foregoing nonlinear effects on the speed of development and decay of the system are presented in the processes deviating from or approaching to equilibrium state.It has been found that there is a resonance phenomenon between the time-oscillation of heat source and the atmospheric disturbance.
基金Supported by the National Key Research and Development Program of China(2018YFC1505604)Innovation and Development Project of China Meteorological Administration(CXFZ2021J022).
文摘A record-breaking extreme heavy snowfall(EHS)event hit northern China during 6–8 November 2021,with two maximum snowfall centers in North China(NC)and Northeast China(NEC),which inflicted severe socioeconomic impacts.This paper compares the differences in the synoptic processes and moisture supply associated with the EHS event in NC and NEC,as well as the atmospheric circulation anomalies before the event,to provide a reference for better prediction and forecasting of EHS in northern China.Synoptic analyses show that a positively tilted,inverted 500-hPa trough channeled cold-air outbreaks into NC,while dynamic updrafts along the front below the trough promoted moisture convergence over this region.In NEC,the dynamic updraft south of the frontogenesis region firstly triggered a low-level Yellow–Bohai Sea cyclone,which then converged with the 500-hPa trough to ultimately form an NEC cold vortex.Calculation of the vorticity tendency indicates that absolute vorticity advection was a better indicator than absolute vorticity divergence for the movement of the trough/ridge at the synoptic scale.Moreover,NOAA’s HYSPLIT(Hybrid Single-Particle Lagrangian Integrated Trajectory)model results reveal that the moisture for the EHS over NC mainly originated from the mid-to-low levels over the Asian–African region and the Eurasian mid-to-high latitudes,accounting for 32%and 31%,respectively.In contrast,the source of water vapor for the EHS over NEC was mainly the Eurasian mid-to-high latitudes and East Asia,with contributions of 38%and 28%,respectively.The findings of this study shed some fresh light on the distinctive contributions of different moisture sources to local precipitation.Further analyses of the atmospheric circulation anomalies in October reveal that a phase shift in the Arctic Oscillation related to the weakening of the polar vortex could have served as a useful indicator for the cold-air outbreaks in this EHS event.
