The autumn Intertropical Convergence Zone(ITCZ)over the South China Sea(SCS)is typically held south of 10°N by prevailing northeasterly and weakening southwesterly winds.However,the ITCZ can move north,resulting ...The autumn Intertropical Convergence Zone(ITCZ)over the South China Sea(SCS)is typically held south of 10°N by prevailing northeasterly and weakening southwesterly winds.However,the ITCZ can move north,resulting in heavy rainfall in the northern SCS(NSCS).We investigate the mechanisms that drove the northward movement of the ITCZ and led to heavy non-tropical-cyclone rainfall over the NSCS in autumn of 2010.The results show that the rapid northward movement of the ITCZ on 1 and 2 October was caused by the joint influence of the equatorial easterlies(EE),southwesterly winds,and the easterly jet(EJ)in the NSCS.A high pressure center on the east side of Australia,strengthened by the quasi-biweekly oscillation and strong Walker circulation,was responsible for the EE to intensify and reach the SCS.The EE finally turned southeast and together with enhanced southwesterly winds associated with an anticyclone,pushed the ITCZ north.Meanwhile,the continental high moved east,which reduced the area of the EJ in the NSCS and made room for the ITCZ.Further regression analysis showed that the reduced area of the EJ and increased strength of the EE contributed significantly to the northward movement of the ITCZ.The enhancement of the EE preceded the northward movement of the ITCZ by six hours and pushed the ITCZ continually north.As the ITCZ approached 12°N,it not only transported warm moist air but also strengthened the dynamic field by transporting the positive vorticity horizontally and vertically which further contributed to the heavy rainfall.展开更多
This study reveals a significant positive connection between autumn non-tropical-cyclone heavy rainfall on Hainan Island and the intensity of Eastern Pacific(EP)El Ni?o events.That is,the amount of rainfall in super E...This study reveals a significant positive connection between autumn non-tropical-cyclone heavy rainfall on Hainan Island and the intensity of Eastern Pacific(EP)El Ni?o events.That is,the amount of rainfall in super EP El Ni?o years is more than that in normal EP El Ni?o years.Comparing EP El Ni?o years of different intensities,the cooler sea surface temperature in the northwestern Pacific during super EP El Ni?o years stimulates a negative surface latent heat flux(LHF)anomaly and abnormal anticyclonic circulation at 850 hPa.Under these conditions,an abnormal zonal vertical circulation develops in the northern South China Sea once a positive LHF anomaly and abnormal cyclonic circulation(ACC)at 850hPa occur in the Beibu Gulf.The abnormal zonal vertical circulation further strengthens the ascending motion over Hainan Island,as the critical factor that leads to excessive rainfall.Further analysis shows that the positive LHF anomaly,which can be attributed to the increased latent heat transfer which resulted from the increased surface wind speed,is an important trigger for the ACC.However,the ACC is also the supplier of favorable moisture conditions because it intensifies vapor convergence over Hainan Island and meridionally transports moisture from the South China Sea to northeastern Hainan Island,thereby generating heavy rainfall.This paper emphasizes that the impact of El Ni?o events,especially super El Ni?o events,on rainfall over Hainan Island cannot be ignored,even if the traditional view is that frequent rainfall occurs mainly in La Ni?a years.展开更多
Characterized by sudden changes in strength,complex influencing factors,and significant impacts,the wind speed in the circum-Bohai Sea area is relatively challenging to forecast.On the western side of Bohai Bay,as the...Characterized by sudden changes in strength,complex influencing factors,and significant impacts,the wind speed in the circum-Bohai Sea area is relatively challenging to forecast.On the western side of Bohai Bay,as the economic center of the circum-Bohai Sea,Tianjin exhibits a high demand for accurate wind forecasting.In this study,three machine learning algorithms were employed and compared as post-processing methods to correct wind speed forecasts by the Weather Research and Forecast(WRF)model for Tianjin.The results showed that the random forest(RF)achieved better performance in improving the forecasts because it substantially reduced the model bias at a lower computing cost,while the support vector machine(SVM)performed slightly worse(especially for stronger winds),but it required an approximately 15 times longer computing time.The back propagation(BP)neural network produced an average forecast significantly closer to the observed forecast but insufficiently reduced the RMSE.In regard to wind speed frequency forecasting,the RF method commendably corrected the forecasts of the frequency of moderate(force 3)wind speeds,while the BP method showed a desirable capability for correcting the forecasts of stronger(force>6)winds.In addition,the 10-m u and v components of wind(u_(10)and v_(10)),2-m relative humidity(RH_(2))and temperature(T_(2)),925-hPa u(u925),sea level pressure(SLP),and 500-hPa temperature(T_(500))were identified as the main factors leading to bias in wind speed forecasting by the WRF model in Tianjin,indicating the importance of local dynamical/thermodynamic processes in regulating the wind speed.This study demonstrates that the combination of numerical models and machine learning techniques has important implications for refined local wind forecasting.展开更多
In early February 2023,there was severe haze on the North China Plain(NCP)that was contemporaneous with heavy rainfall over southern China,which was known as southern rainfall-northern haze(SR-NH).Based on observation...In early February 2023,there was severe haze on the North China Plain(NCP)that was contemporaneous with heavy rainfall over southern China,which was known as southern rainfall-northern haze(SR-NH).Based on observational and reanalysis data,the meteorological causes of this SR-NH event are investigated in this study using correlation analysis,dynamic diagnostics and numerical experiments.The results show that the anticyclonic anomaly in the Pacific Northwest(also referred to as the northeast Asian anomalous anticyclone)is responsible for the SR-NH.On the one hand,this anticyclonic anomaly leads to persistent rainfall over southern China by causing strong ascending motion in conjunction with an anomalous cyclone over the Chinese mainland and transporting large amounts of water vapor there.On the other hand,it weakens the climatological northerly winds of the NCP through the southeasterly flow,worsening the horizontal diffusion conditions of pollutants.Additionally,the atmospheric stability and relative humidity over the NCP are significantly increased by this anticyclonic anomaly.These conditions result in higher PM2.5concentrations over the NCP.Additional results suggest that this anticyclonic anomaly is related to diabatic heating released by rainfall in southern China,which not only intensifies the rainfall process there(with a contribution of 11.5%)but also induces an anticyclonic anomaly in the upper troposphere of the Pacific Northwest(i.e.,200 hPa).The rainfall-related anticyclonic anomaly reinforces the anticyclonic anomaly in the Pacific Northwest caused by large-scale circulation(with a contribution of 27%)and thus affects haze over the NCP.This study provides a new reference for understanding the contribution of rainfall in southern China to haze over the NCP.展开更多
基金The research is supported by the Key Laboratory of South China Sea Meteorological Disaster Prevention and Mitigation of Hainan Province(Grant No.SCSF201906)the National Natural Science Foundation of China(Grant No.41975008)the Fundamental Research Funds for the Central Universities(Grant No.201861003).
文摘The autumn Intertropical Convergence Zone(ITCZ)over the South China Sea(SCS)is typically held south of 10°N by prevailing northeasterly and weakening southwesterly winds.However,the ITCZ can move north,resulting in heavy rainfall in the northern SCS(NSCS).We investigate the mechanisms that drove the northward movement of the ITCZ and led to heavy non-tropical-cyclone rainfall over the NSCS in autumn of 2010.The results show that the rapid northward movement of the ITCZ on 1 and 2 October was caused by the joint influence of the equatorial easterlies(EE),southwesterly winds,and the easterly jet(EJ)in the NSCS.A high pressure center on the east side of Australia,strengthened by the quasi-biweekly oscillation and strong Walker circulation,was responsible for the EE to intensify and reach the SCS.The EE finally turned southeast and together with enhanced southwesterly winds associated with an anticyclone,pushed the ITCZ north.Meanwhile,the continental high moved east,which reduced the area of the EJ in the NSCS and made room for the ITCZ.Further regression analysis showed that the reduced area of the EJ and increased strength of the EE contributed significantly to the northward movement of the ITCZ.The enhancement of the EE preceded the northward movement of the ITCZ by six hours and pushed the ITCZ continually north.As the ITCZ approached 12°N,it not only transported warm moist air but also strengthened the dynamic field by transporting the positive vorticity horizontally and vertically which further contributed to the heavy rainfall.
基金supported by the National Natural Science Foundation of China(Grant No.41975008)Key Laboratory of South China Sea Meteorological Disaster Prevention and Mitigation of Hainan Province(Grant No.SCSF201906)。
文摘This study reveals a significant positive connection between autumn non-tropical-cyclone heavy rainfall on Hainan Island and the intensity of Eastern Pacific(EP)El Ni?o events.That is,the amount of rainfall in super EP El Ni?o years is more than that in normal EP El Ni?o years.Comparing EP El Ni?o years of different intensities,the cooler sea surface temperature in the northwestern Pacific during super EP El Ni?o years stimulates a negative surface latent heat flux(LHF)anomaly and abnormal anticyclonic circulation at 850 hPa.Under these conditions,an abnormal zonal vertical circulation develops in the northern South China Sea once a positive LHF anomaly and abnormal cyclonic circulation(ACC)at 850hPa occur in the Beibu Gulf.The abnormal zonal vertical circulation further strengthens the ascending motion over Hainan Island,as the critical factor that leads to excessive rainfall.Further analysis shows that the positive LHF anomaly,which can be attributed to the increased latent heat transfer which resulted from the increased surface wind speed,is an important trigger for the ACC.However,the ACC is also the supplier of favorable moisture conditions because it intensifies vapor convergence over Hainan Island and meridionally transports moisture from the South China Sea to northeastern Hainan Island,thereby generating heavy rainfall.This paper emphasizes that the impact of El Ni?o events,especially super El Ni?o events,on rainfall over Hainan Island cannot be ignored,even if the traditional view is that frequent rainfall occurs mainly in La Ni?a years.
基金supported by the National Natural Science Foundation of China(42175137,41705130,41922037,and 71961137011)the National Key Research and Development Program of China(2021YFD1700902)+6 种基金the Chinese State Key Special Program on Severe Air Pollution Mitigation“Agricultural Emission Status and Enhanced Control Plan”(DQGG0208)the Shandong Provincial Natural Science Foundation(2022HWYQ-066)the Global International Nitrogen Management System(INMS)the High-level Team Project of China Agricultural Universitythe Beijing Advanced Discipline Fundingwas supported by the Fonds de la Recherche Scientifique(F.R.S.-FNRS)the Belgian State Federal Office for Scientific,Technical and Cultural Affairs(Prodex arrangement IASI.FLOW)。
基金Supported by the Open Project of Tianjin Key Laboratory of Oceanic Meteorology(2020TKLOMYB05)National Natural Science Foundation of China(42275191).
文摘Characterized by sudden changes in strength,complex influencing factors,and significant impacts,the wind speed in the circum-Bohai Sea area is relatively challenging to forecast.On the western side of Bohai Bay,as the economic center of the circum-Bohai Sea,Tianjin exhibits a high demand for accurate wind forecasting.In this study,three machine learning algorithms were employed and compared as post-processing methods to correct wind speed forecasts by the Weather Research and Forecast(WRF)model for Tianjin.The results showed that the random forest(RF)achieved better performance in improving the forecasts because it substantially reduced the model bias at a lower computing cost,while the support vector machine(SVM)performed slightly worse(especially for stronger winds),but it required an approximately 15 times longer computing time.The back propagation(BP)neural network produced an average forecast significantly closer to the observed forecast but insufficiently reduced the RMSE.In regard to wind speed frequency forecasting,the RF method commendably corrected the forecasts of the frequency of moderate(force 3)wind speeds,while the BP method showed a desirable capability for correcting the forecasts of stronger(force>6)winds.In addition,the 10-m u and v components of wind(u_(10)and v_(10)),2-m relative humidity(RH_(2))and temperature(T_(2)),925-hPa u(u925),sea level pressure(SLP),and 500-hPa temperature(T_(500))were identified as the main factors leading to bias in wind speed forecasting by the WRF model in Tianjin,indicating the importance of local dynamical/thermodynamic processes in regulating the wind speed.This study demonstrates that the combination of numerical models and machine learning techniques has important implications for refined local wind forecasting.
基金supported by the National Key R&D Program of China(Grant No.2019YFA0607002)the National Natural Science Foundation of China(Grant Nos.41721004&42275191)。
文摘In early February 2023,there was severe haze on the North China Plain(NCP)that was contemporaneous with heavy rainfall over southern China,which was known as southern rainfall-northern haze(SR-NH).Based on observational and reanalysis data,the meteorological causes of this SR-NH event are investigated in this study using correlation analysis,dynamic diagnostics and numerical experiments.The results show that the anticyclonic anomaly in the Pacific Northwest(also referred to as the northeast Asian anomalous anticyclone)is responsible for the SR-NH.On the one hand,this anticyclonic anomaly leads to persistent rainfall over southern China by causing strong ascending motion in conjunction with an anomalous cyclone over the Chinese mainland and transporting large amounts of water vapor there.On the other hand,it weakens the climatological northerly winds of the NCP through the southeasterly flow,worsening the horizontal diffusion conditions of pollutants.Additionally,the atmospheric stability and relative humidity over the NCP are significantly increased by this anticyclonic anomaly.These conditions result in higher PM2.5concentrations over the NCP.Additional results suggest that this anticyclonic anomaly is related to diabatic heating released by rainfall in southern China,which not only intensifies the rainfall process there(with a contribution of 11.5%)but also induces an anticyclonic anomaly in the upper troposphere of the Pacific Northwest(i.e.,200 hPa).The rainfall-related anticyclonic anomaly reinforces the anticyclonic anomaly in the Pacific Northwest caused by large-scale circulation(with a contribution of 27%)and thus affects haze over the NCP.This study provides a new reference for understanding the contribution of rainfall in southern China to haze over the NCP.
