An exceptionally prolonged heavy snow event(PHSE)occurred in southern China from 10 January to 3 February 2008,which caused considerable economic losses and many casualties.To what extent any dynamical model can predi...An exceptionally prolonged heavy snow event(PHSE)occurred in southern China from 10 January to 3 February 2008,which caused considerable economic losses and many casualties.To what extent any dynamical model can predict such an extreme event is crucial for disaster prevention and mitigation.Here,we found the three S2S models(ECMWF,CMA1.0 and CMA2.0)can predict the distribution and intensity of precipitation and surface air temperature(SAT)associated with the PHSE at 10-day lead and 10−15-day lead,respectively.The success is attributed to the models’capability in forecasting the evolution of two important low-frequency systems in the tropics and mid-latitudes[the persistent Siberian High and the suppressed phase of the Madden−Julian Oscillation(MJO)],especially in the ECMWF model.However,beyond the 15-day lead,the three models show almost no skill in forecasting this PHSE.The bias in capturing the two critical circulation systems is responsible for the low skill in forecasting the 2008 PHSE beyond the 15-day lead.On one hand,the models cannot reproduce the persistence of the Siberian High,which results in the underestimation of negative SAT anomalies over southern China.On the other hand,the models cannot accurately capture the suppressed convection of the MJO,leading to weak anomalous southerly and moisture transport,and therefore the underestimation of precipitation over southern China.The Singular Value Decomposition(SVD)analyses between the critical circulation systems and SAT/precipitation over southern China shows a robust historical relation,indicating the fidelity of the predictability sources for both regular events and extreme events(e.g.,the 2008 PHSE).展开更多
A conceptual hydrological model that links the Xin＇anjiang hydrological model and a physically based snow energy and mass balance model, described as the XINSNOBAL model, was developed in this study for simulating ra...A conceptual hydrological model that links the Xin＇anjiang hydrological model and a physically based snow energy and mass balance model, described as the XINSNOBAL model, was developed in this study for simulating rain-on-snow events that commonly occur in the Pacific Northwest of the United States. The resultant model was applied to the Lookout Creek Watershed in the H. J. Andrews Experimental Forest in the western Cascade Mountains of Oregon, and its ability to simulate streamflow was evaluated. The simulation was conducted at 24-hour and one-hour time scales for the period of 1996 to 2005. The results indicated that runoffand peak discharge could be underestimated if snowpack accumulation and snowmelt under rain-on-snow conditions were not taken into account. The average deterministic coefficient of the hourly model in streamflow simulation in the calibration stage was 0.837, which was significantly improved over the value of 0.762 when the Xin＇anjiang model was used alone. Good simulation performance of the XINSNOBAL model in the WS 10 catchment, using the calibrated parameter of the Lookout Creek Watershed for proxy-basin testing, demonstrates that transplanting model parameters between similar watersheds can orovide a useful tool for discharge forecastin~, in un^au^ed basins.展开更多
Blowing snow is a typical natural hazard in high-altitude and snow-prone regions,and its impact could be significantly reduced by accurate forecasts.The empirical study on the conditions for blowing snow hazards on th...Blowing snow is a typical natural hazard in high-altitude and snow-prone regions,and its impact could be significantly reduced by accurate forecasts.The empirical study on the conditions for blowing snow hazards on the Sichuan-Xizang Highway in high-altitude mountainous areas are conducted in this paper.The study reveals that blowing snow events primarily occur from December to the following February,with the affected roads mainly located in mountainous areas above altitudes of 3000 m.Based on physical characteristics,snow cover is categorized into three types with different processes of snowdrifts:newly fallen or wind-transported snow,slightly consolidated snow,and compacted snow undergoing freeze-thaw cycles,each exhibiting distinct snowdrift formation processes.Field measurement results indicate that the average threshold wind speeds for initiating blowing snow are 9.65,14.77,and 23.15 m s^(-1)at the 10-m height for these three snow types,respectively.Additionally,analyzing the effects of temperature and snowfall timing on threshold wind velocity,a multi-tiered susceptibility model for blowing snow is developed.This model offers enhanced practical applicability for classifying different types of snow and provides more detailed insights into the variations in threshold wind speed during both the early and later stages of snowfall events,compared to models that rely solely on constant thresholds or temperature-based criteria.展开更多
In February 2022,a persistent low-temperature rain and snow event(LRSE)occurred in the central Pan-Pearl River Delta(CPPRD)region of southern China,causing severe damage and economic losses.During the LRSE,both the te...In February 2022,a persistent low-temperature rain and snow event(LRSE)occurred in the central Pan-Pearl River Delta(CPPRD)region of southern China,causing severe damage and economic losses.During the LRSE,both the temperature and precipitation fields exhibited quasi-biweekly oscillation(QBWO)signals over the CPPRD region.Circulation analysis revealed that the eastward propagation of Rossby waves at mid–high latitudes enhanced the Baikal blocking high and the Mongolian high,facilitating the continuous southward migration of cold air.The strengthening India–Burma trough(i.e.,the southern branch trough)brought abundant warm and humid airflow,converging with cold air from the north in the CPPRD region.Moreover,deep convective activity originating in the northern Indian Ocean became exceptionally active,propagating to southern China and providing dynamic lifting conditions for precipitation in the study region.The combined effects of tropical and extratropical weather systems resulted in the LRSE occurrence.Partial lateral forcing(PLF)experiments were performed to quantify the contributions of the QBWO signals from different boundaries of the region.The extratropical QBWO signal from the northern boundary led to a temperature decrease of 1.61℃,with 77.83%of the whole region experiencing cooling greater than 1℃,whereas the tropical QBWO signal from the southwestern boundary caused an increase in precipitation of 13.1 mm day^(−1),with more than 40%of the entire region experiencing a precipitation increase of over 5 mm day^(−1).This study provides quantitative evidence that the QBWO was a key factor contributing to the occurrence of the LRSE,which can be used as a precursor signal for extended-range forecasts of future LRSEs.展开更多
Based on the National Centers for Environmental Prediction and National Center for Atmospheric Research(NCEP/NCAR) daily reanalysis data and the upper-level objective analysis data provided by the Meteorological Infor...Based on the National Centers for Environmental Prediction and National Center for Atmospheric Research(NCEP/NCAR) daily reanalysis data and the upper-level objective analysis data provided by the Meteorological Information Comprehensive Analysis and Process System(MICAPS),the feature of the spatio-temporal variation of the East Asian jet stream(EAJS) in persistent snowstorm and freezing rain processes over southern China in January 2008 have been investigated.Each of the storm events was closely linked with the extraordinarily abnormal variations of East Asian subtropical jet(EASJ) and East Asian polar front jet(EAPJ) at that time.The stronger EASJ with abnormally northward position of the jet axis corresponded to the more intense storm event with broader ranges and longer duration time.The heavy freezing-rain-and-snow event occurred over the region where a strong southerly wind of EASJ prevailed.Meanwhile,the westerly and northerly winds of the EAPJ were significantly intensified,which were also closely related to the beginning,enhancement,and ending of the heavy snowfall.The meridional component of the EAPJ was dominated by the northerly wind during the snowstorm.Thus,the intensification of the snowstorm was attributed to both the strengthening of the meridional wind of EAPJ and the southerly wind of EASJ.Further analysis indicated that wind speed and the zonal wind of the two jets exhibited precursory signals about half a month prior to this extreme event,and the precursory signals were found in the meridional components of the two jets about 20 days preceding the event.The sudden weakening of the meridional component of EASJ and the zonal component of EAPJ signified the ending of this persistent snowstorm.展开更多
基金The authors greatly appreciate the professional and earnest review made by the anonymous reviewers which for sure improved the quality of our manuscript.This work was supported by the National Key R&D Program of China(Grant Nos.2018YFC1505905&2018YFC1505803)the National Natural Science Foundation of China(Grant Nos.42088101,41805048 and 41875069)Tim LI was supported by NSF AGS-1643297 and NOAA Grant NA18OAR4310298.
文摘An exceptionally prolonged heavy snow event(PHSE)occurred in southern China from 10 January to 3 February 2008,which caused considerable economic losses and many casualties.To what extent any dynamical model can predict such an extreme event is crucial for disaster prevention and mitigation.Here,we found the three S2S models(ECMWF,CMA1.0 and CMA2.0)can predict the distribution and intensity of precipitation and surface air temperature(SAT)associated with the PHSE at 10-day lead and 10−15-day lead,respectively.The success is attributed to the models’capability in forecasting the evolution of two important low-frequency systems in the tropics and mid-latitudes[the persistent Siberian High and the suppressed phase of the Madden−Julian Oscillation(MJO)],especially in the ECMWF model.However,beyond the 15-day lead,the three models show almost no skill in forecasting this PHSE.The bias in capturing the two critical circulation systems is responsible for the low skill in forecasting the 2008 PHSE beyond the 15-day lead.On one hand,the models cannot reproduce the persistence of the Siberian High,which results in the underestimation of negative SAT anomalies over southern China.On the other hand,the models cannot accurately capture the suppressed convection of the MJO,leading to weak anomalous southerly and moisture transport,and therefore the underestimation of precipitation over southern China.The Singular Value Decomposition(SVD)analyses between the critical circulation systems and SAT/precipitation over southern China shows a robust historical relation,indicating the fidelity of the predictability sources for both regular events and extreme events(e.g.,the 2008 PHSE).
基金supported by the National Natural Science Foundation of China (Grants No. 40901015 and41001011)the Major Program of the National Natural Science Foundation of China (Grants No. 51190090 and 51190091)+3 种基金the Fundamental Research Funds for the Central Universities (Grants No. B1020062 andB1020072)the Ph. D. Programs Foundation of the Ministry of Education of China (Grant No.20090094120008)the Special Fund of State Key Laboratories of China (Grants No. 2009586412 and 2009585412)the Programme of Introducing Talents of Disciplines to Universities of the Ministry of Education and State Administration of the Foreign Experts Affairs of China (the 111 Project, Grant No.B08048)
文摘A conceptual hydrological model that links the Xin＇anjiang hydrological model and a physically based snow energy and mass balance model, described as the XINSNOBAL model, was developed in this study for simulating rain-on-snow events that commonly occur in the Pacific Northwest of the United States. The resultant model was applied to the Lookout Creek Watershed in the H. J. Andrews Experimental Forest in the western Cascade Mountains of Oregon, and its ability to simulate streamflow was evaluated. The simulation was conducted at 24-hour and one-hour time scales for the period of 1996 to 2005. The results indicated that runoffand peak discharge could be underestimated if snowpack accumulation and snowmelt under rain-on-snow conditions were not taken into account. The average deterministic coefficient of the hourly model in streamflow simulation in the calibration stage was 0.837, which was significantly improved over the value of 0.762 when the Xin＇anjiang model was used alone. Good simulation performance of the XINSNOBAL model in the WS 10 catchment, using the calibrated parameter of the Lookout Creek Watershed for proxy-basin testing, demonstrates that transplanting model parameters between similar watersheds can orovide a useful tool for discharge forecastin~, in un^au^ed basins.
基金Supported by the National Natural Science Foundation of China(52278511)Innovative Development Special Project of China Meteorological Administration(CXFZ2025J071)“Leading the List”Project of Yunnan Meteorological Administration(YNJBGS202306)。
文摘Blowing snow is a typical natural hazard in high-altitude and snow-prone regions,and its impact could be significantly reduced by accurate forecasts.The empirical study on the conditions for blowing snow hazards on the Sichuan-Xizang Highway in high-altitude mountainous areas are conducted in this paper.The study reveals that blowing snow events primarily occur from December to the following February,with the affected roads mainly located in mountainous areas above altitudes of 3000 m.Based on physical characteristics,snow cover is categorized into three types with different processes of snowdrifts:newly fallen or wind-transported snow,slightly consolidated snow,and compacted snow undergoing freeze-thaw cycles,each exhibiting distinct snowdrift formation processes.Field measurement results indicate that the average threshold wind speeds for initiating blowing snow are 9.65,14.77,and 23.15 m s^(-1)at the 10-m height for these three snow types,respectively.Additionally,analyzing the effects of temperature and snowfall timing on threshold wind velocity,a multi-tiered susceptibility model for blowing snow is developed.This model offers enhanced practical applicability for classifying different types of snow and provides more detailed insights into the variations in threshold wind speed during both the early and later stages of snowfall events,compared to models that rely solely on constant thresholds or temperature-based criteria.
基金Supported by the National Key Research and Development Program of China (2018YFC1505602)National Natural Science Foundation of China (41705055)+2 种基金Graduate Innovation Project of Jiangsu Province (CXZZ11_0485)Innovation Teams of Jiangsu Qinglan ProjectPriority Academic Program Development of Jiangsu Higher Education Institutions (PAPD)
文摘In February 2022,a persistent low-temperature rain and snow event(LRSE)occurred in the central Pan-Pearl River Delta(CPPRD)region of southern China,causing severe damage and economic losses.During the LRSE,both the temperature and precipitation fields exhibited quasi-biweekly oscillation(QBWO)signals over the CPPRD region.Circulation analysis revealed that the eastward propagation of Rossby waves at mid–high latitudes enhanced the Baikal blocking high and the Mongolian high,facilitating the continuous southward migration of cold air.The strengthening India–Burma trough(i.e.,the southern branch trough)brought abundant warm and humid airflow,converging with cold air from the north in the CPPRD region.Moreover,deep convective activity originating in the northern Indian Ocean became exceptionally active,propagating to southern China and providing dynamic lifting conditions for precipitation in the study region.The combined effects of tropical and extratropical weather systems resulted in the LRSE occurrence.Partial lateral forcing(PLF)experiments were performed to quantify the contributions of the QBWO signals from different boundaries of the region.The extratropical QBWO signal from the northern boundary led to a temperature decrease of 1.61℃,with 77.83%of the whole region experiencing cooling greater than 1℃,whereas the tropical QBWO signal from the southwestern boundary caused an increase in precipitation of 13.1 mm day^(−1),with more than 40%of the entire region experiencing a precipitation increase of over 5 mm day^(−1).This study provides quantitative evidence that the QBWO was a key factor contributing to the occurrence of the LRSE,which can be used as a precursor signal for extended-range forecasts of future LRSEs.
基金National Natural Science Foundation of China(41130963)Industry research special funds for public welfare Meteorology projects(GYHY201006019)
文摘Based on the National Centers for Environmental Prediction and National Center for Atmospheric Research(NCEP/NCAR) daily reanalysis data and the upper-level objective analysis data provided by the Meteorological Information Comprehensive Analysis and Process System(MICAPS),the feature of the spatio-temporal variation of the East Asian jet stream(EAJS) in persistent snowstorm and freezing rain processes over southern China in January 2008 have been investigated.Each of the storm events was closely linked with the extraordinarily abnormal variations of East Asian subtropical jet(EASJ) and East Asian polar front jet(EAPJ) at that time.The stronger EASJ with abnormally northward position of the jet axis corresponded to the more intense storm event with broader ranges and longer duration time.The heavy freezing-rain-and-snow event occurred over the region where a strong southerly wind of EASJ prevailed.Meanwhile,the westerly and northerly winds of the EAPJ were significantly intensified,which were also closely related to the beginning,enhancement,and ending of the heavy snowfall.The meridional component of the EAPJ was dominated by the northerly wind during the snowstorm.Thus,the intensification of the snowstorm was attributed to both the strengthening of the meridional wind of EAPJ and the southerly wind of EASJ.Further analysis indicated that wind speed and the zonal wind of the two jets exhibited precursory signals about half a month prior to this extreme event,and the precursory signals were found in the meridional components of the two jets about 20 days preceding the event.The sudden weakening of the meridional component of EASJ and the zonal component of EAPJ signified the ending of this persistent snowstorm.
