The position of the South Asian High(SAH)over the Tibetan Plateau(TP)exhibits significant interannual variability.In this study,the criteria for defining the establishment and withdrawal of the SAH,as well as their ac...The position of the South Asian High(SAH)over the Tibetan Plateau(TP)exhibits significant interannual variability.In this study,the criteria for defining the establishment and withdrawal of the SAH,as well as their activities over the TP,are re-evaluated.The SAH is classified as“established over the TP”when the 1660 dagpm geopotential height contour covers 25%or more of the TP,and“withdrawn from the TP”when this contour covers less than 25%.Statistical analysis shows that,on average,the SAH establishes over the TP by the 4th pentad of May(28th pentad)and withdraws from the TP around the 2nd pentad of October(56th pentad).Over the past 50 years(1974–2023),the SAH has tended to establish over the TP earlier and withdraw later,resulting in a longer duration of control over the TP,with the rate of increase accelerating since 2017.The SAH exhibits a long-term linear trend of an eastward shift during both its establishment and withdrawal phases.The anomalous activity of the SAH over the TP is influenced by atmospheric heat sources.When there is anomalous warming(cooling)of atmospheric heating over the Bay of Bengal and the Indochina Peninsula,the SAH tends to establish and withdraw earlier and further westward(later and further eastward),with the westerly trough located over East Asia(the western part of the TP).展开更多
Black carbon (BC) aerosols are considered key factors that contribute to rapid climate warming and ice melt in the Arctic region.However,compared with long-term observations from land-based stations,observational data...Black carbon (BC) aerosols are considered key factors that contribute to rapid climate warming and ice melt in the Arctic region.However,compared with long-term observations from land-based stations,observational data over the Arctic Ocean remain relatively scarce.Four Arctic scientific expeditions were conducted in the summer and early autumn of 2010,2012,2016,and 2018 via the Chinese research vessel Xue Long,during which the BC concentrations along the routes were measured via light absorption methods.In this work,the spatiotemporal distribution characteristics of BC over the Arctic Ocean were examined on the basis of these observations.The potential sources of BC along the various routes were analyzed via the weighted potential source contribution function and weighted concentrationweighted trajectory methods of the hybrid single-particle Lagrangian integrated trajectory model in conjunction with Arctic transport potential climate model simulations.The analysis results indicated that wildfires in the western Aleutian Islands,Siberia,and Far East regions were the primary contributors to the BC aerosol concentration observed along the Arctic expedition routes in summer,identifying these regions as major potential source areas.展开更多
Subseasonal forecasting of extreme events is crucial for early warning systems.However,the forecast skills for extreme events are limited.Taking the extreme cold events in January 2018 as a specific example,and analyz...Subseasonal forecasting of extreme events is crucial for early warning systems.However,the forecast skills for extreme events are limited.Taking the extreme cold events in January 2018 as a specific example,and analyzing the 34 extreme cold events in East Asia from 1998 to 2020,the authors evaluated the forecast skills of the ECMWF model ensemble members on subseasonal time scales.The results show that while the ensemble mean has limited skills for forecasting extreme cold events at the 3-week lead time,some individual members demonstrate high forecast skills.For most extreme cold events,there are>10%of members among the total ensembles that can well predict the rapid temperature transitions at the 14-day lead time.This highlights the untapped potential of the ECMWF model to forecast extreme cold events on subseasonal time scales.High-skill ensemble members rely on accurate predictions of atmospheric circulation patterns(500-hPa geopotential height,mean sea level pressure)and key weather systems,including the Ural Blocking and Siberian High,that influence extreme cold events.展开更多
The Atmospheric Infrared Sounder(AIRS)on the Aqua satellite,along with the MWTS/MWHS Synergy(TSHS)sounding system and Atmospheric Vertical Sounder System(VASS)on the Fengyun-3D(FY-3D)satellite,provide highquality data...The Atmospheric Infrared Sounder(AIRS)on the Aqua satellite,along with the MWTS/MWHS Synergy(TSHS)sounding system and Atmospheric Vertical Sounder System(VASS)on the Fengyun-3D(FY-3D)satellite,provide highquality data for studying Arctic temperature change.The generalized cold bias of AIRS is confirmed through horizontal comparisons with Arctic land radiosonde stations.VASS corrects the warm bias of TSHS by incorporating the Hyperspectral Infrared Atmospheric Sounder-I(HIRAS-I).Vertical comparisons demonstrate that AIRS,TSHS,and VASS offer excellent temperature detection from the top of the boundary layer to the lower stratosphere(800–100 h Pa).However,the overestimation and errors of stratospheric temperatures by TSHS and VASS increase with altitude(pressures below60 h Pa).Specifically,the warm bias trends at 0.06 K hPa^(-1),reaching 2.87 K and 2.92 K at 10 h Pa.Similarly,RMSE values trend at 0.05?K h Pa^(-1),reaching 3.62?K and 3.69?K at 10 h Pa.The low correlation(R≥0.65)of TSHS near 250 h Pa in summer is significantly improved in VASS(R≥0.78)after adding HIRAS-I.The high vertical resolution due to infrared hyperspectral resolution facilitates the detection of complex temperature junctions.The retrieval error of AIRS in the boundary layer increases with cloudiness,while VASS combines microwave and infrared channel data to reduce the impact of cloud cover.Assessing the Arctic applicability of these three satellite temperature profile products will facilitate their widespread use in the Arctic region,enhance accurate climate change monitoring,and further reveal the mechanisms of Arctic warming.展开更多
In November 1984,China launched its first expedition to the Southern Ocean and the Antarctic continent,culminating in the establishment of its first year-round research station—Great Wall Station—on the Antarctic Pe...In November 1984,China launched its first expedition to the Southern Ocean and the Antarctic continent,culminating in the establishment of its first year-round research station—Great Wall Station—on the Antarctic Peninsula in February 1985.Forty years later,in February 2024,China’s fifth research station,Qinling Station,commenced operations on Inexpress-ible Island near Terra Nova Bay.展开更多
Based on the data(including radius of maximum winds) from the JTWC(Joint Typhoon Warning Center),the tropical cyclones(TCs) radii of the outermost closed isobar, TCs best tracks from Shanghai Typhoon Institute and the...Based on the data(including radius of maximum winds) from the JTWC(Joint Typhoon Warning Center),the tropical cyclones(TCs) radii of the outermost closed isobar, TCs best tracks from Shanghai Typhoon Institute and the Black Body Temperature(TBB) of the Japanese geostationary meteorological satellite M1 TR IR1, and combining13 tropical cyclones which landed in China again after visiting the island of Taiwan during the period from 2001 to2010, we analyzed the relationship between the number of convective cores within TC circulation and the intensity of TC with the method of convective-stratiform technique(CST) and statistical and composite analysis. The results are shown as follows:(1) The number of convective cores in the entire TC circulation is well corresponding with the outer spiral rainbands and the density of convective cores in the inner core area increases(decreases) generally with increasing(decreasing) TC intensity. At the same time, the number of convective cores within the outer spiral rainbands is more than that within the inner core and does not change much with the TC intensity. However, the density of convective cores within the outer spiral rainbands is lower than that within the inner core.(2) The relationship described above is sensitive to landing location to some extent but not sensitive to the structure of TC.(3) The average value of TBB in the inner core area increases(decreases) generally with increasing(decreasing) of TC intensity, which is also sensitive to landing situation to some extent. At the same time, the average value of TBB within the outer spiral rainbands is close to that within the entire TC circulation, and both of them are more than that within the inner core. However, they do not reflect TC intensity change significantly.(4) The results of statistical composite based on convective cores and TBB are complementary with each other, so a combination of both can reflect the relationship between TC rainbands and TC intensity much better.展开更多
Certain feasibilities and features were discussed in typhoon detection by radar with a negative elevation angle according to the relationship between the remote detecting range and the elevation angle of the new gener...Certain feasibilities and features were discussed in typhoon detection by radar with a negative elevation angle according to the relationship between the remote detecting range and the elevation angle of the new generation weather radar, in order to rectify the disadvantages of detecting capability for remote low-level echo with a lowest elevation angle of 0.5° in the common detecting mode. The data obtained from detecting the typhoon of Haitang and Changmi with radar for their negative elevation angles and the observed data for the common lowest elevation angle of 0.5° were compared to each other. The results showed that the detection of remote low level cloud system with radar could be improved by using the negative elevation angle, and the structure and the evolution trend of a typhoon could be better judged. The increasing degree of detection for negative elevation angles in the current volume scanning mode should be helpful for predicting the intensity and developing trend of windstorms, to further improve the capability of warning and nowcasting. The detection of negative elevation angle could also help reveal the development and change of typhoon＇s low level cloud system. As far as the typhoons of Haitang and Changmi were concerned, the detecting area of Changmi was increased by 1.09 times with the negative elevation angle of 0.31°, compared with the elevation angle of 0.48° if the threshold value for the sea echo within 100 km was eliminated. Several volume scans of Haitang were increased by 2.1%-7.9% for the negative elevation angle of 0.36° compared with the elevation angle of 0.49° . Therefore, the radar detecting capability of typhoons could be improved by the detection of negative elevation angles to some extent. This could make up for the disadvantages of a low detecting capability for remote low-level echo in the common detecting mode. At the same time, a negative elevation angle could be easily influenced by the ground clutter and the close sea wave clutter which interfered with the assessment of the typhoon structure at times. Assessing these advantages and disadvantages, some advantages for using negative elevation angle were discovered from the observation of the typhoons Haitang and Changmi, if the negative elevation angle with radar was selected reasonably in some conditions. As a result, a certain value arose for improving and monitoring the early warning system for typhoons, paying close attention to the detection of negative elevation angles.展开更多
Based on the global reanalysis data of the National Centers for Environmental Prediction(NCEP)/National Center for Atmospheric Research,the surface meteorological observation data,sounding data and satellite observati...Based on the global reanalysis data of the National Centers for Environmental Prediction(NCEP)/National Center for Atmospheric Research,the surface meteorological observation data,sounding data and satellite observation data,this paper comprehensively analyzes the evolution process and formation mechanism of a persistent severe dense fog process occurred on February 15–17,2015 in Yancheng,eastern China.Through the numerical simulation experiment of Weather Research and Forecast(WRF)model,we further analyze the impact of sea-land breeze on the formation and burst reinforcement of fog.Results show that the precipitation caused by the southwesterly airflow in front of the upper-level trough and the low-pressure inverted trough are conducive to the formation of early rain fog,while the nighttime clear radiance under the control of surface cold high and the infiltration of weak cold advection are conducive to the formation and development of later radiation-advection fog.The WRF model simulates the fog evolution process,which is basically consistent with the actual fog area,and the simulation results are credible to a certain extent.The simulation results show that the establishment of sea breeze has an advection cooling effect on the near surface layer,which is conducive to the formation and development of the inversion layer on the near surface,providing stable stratification conditions for the formation and burst reinforcement of fog.On one hand,the strengthening of sea breeze circulation can continuously transport water vapor to the study area.On the other,the occurrence of ultra-low level jet is favorable for the accumulation of low-level water vapor.At the same time,the inversion intensity further strengthens,which is in favor of the burst reinforcement and long-term maintenance of fog.展开更多
The Sichuan-Xizang Railway is an important part of the railway network in China, and geological disasters, such as mountain floods and landslides, frequently occur in this region. Precipitation is an important cause o...The Sichuan-Xizang Railway is an important part of the railway network in China, and geological disasters, such as mountain floods and landslides, frequently occur in this region. Precipitation is an important cause of these disasters;therefore,accurate simulation of the precipitation in this region is highly important. In this study, the descriptions for uncertain processes in the cloud microphysics scheme are improved;these processes include cloud droplet activation, cloud-rain autoconversion, rain accretion by cloud droplets, and the entrainment-mixing process. In the default scheme, the cloud water content of different sizes corresponds to the same cloud droplet concentration, which is inconsistent with the actual content;this results in excessive cloud droplet size, unreasonable related conversion rates of microphysical process(such as cloud-rain autoconversion), and an overestimation of precipitation. Our new scheme overcomes the problem of excessive cloud droplet size. The processes of cloudrain autoconversion and rain accretion by cloud droplets are similar to the stochastic collection equation, and the mixing mechanism of cloud droplets is more consistent with that occurred during the actual physical process in the cloud. Based on the new and old schemes, multiple precipitation processes in the flood season of 2021 along the Sichuan-Xizang Railway are simulated, and the results are evaluated using ground observations and satellite data. Compared to the default scheme, the new scheme is more suitable for the simulation of cloud physics, reducing the simulation deviation of the liquid water path and droplet radius from 2 times to less than 1 time and significantly alleviating the overestimation of precipitation intensity and range of precipitation center. The average root-mean-square error is reduced by 22%. Our results can provide a scientific reference for improving precipitation forecasting and disaster prevention in this region.展开更多
Based on wind profile radar data,this paper aims at different typhoon processes landed and affected Fujian from 2011 to 2019,according to the nature of typhoon rainstorm,it can be classified into outer precipitation b...Based on wind profile radar data,this paper aims at different typhoon processes landed and affected Fujian from 2011 to 2019,according to the nature of typhoon rainstorm,it can be classified into outer precipitation before typhoon landed,main body precipitation and precipitation at the rear of typhoon,the change of the characteristic quantities in approaching time of the occurrence of short-term heavy rainfall was analyzed,and the typhoon case in 2020 was back calculated.The results show that,the characteristics of low-level jet streams(maximum wind speed at low altitude,minimum height of jet streams,and low-level jet stream index),as well as the magnitude of vertical wind shear below 700 hPa,have important indicative significance for the occurrence of short-term heavy rainfall.(1)More than 80%of short-term heavy rainfall occurred 3 h before the low-level jet stream already existed.The maximum wind speed below 2 km was basically close to a normal distribution,and the occurrence of heavy precipitation showed a bimodal pattern.The percentage of wind speed between 8 and 32 m/s was the highest,exceeding 85%.The wind direction of the strong wind is mainly NE,SE,and SW.Classification analysis showed that the distribution characteristics of wind speed of the main precipitation were the same as before,but the wind direction SE was higher than NE.The wind speed of pre-landfall precipitation was basically skewed,and the occurrence time of heavy precipitation followed a normal distribution.The percentage of wind speed between 16 and 32 m/s was the highest,and the wind direction was the same as before classification.The maximum wind speed of precipitation in the rear was basically bimodal distribution,with a relatively even distribution,and the wind direction was mainly SE and SW.(2)In the 3 h before the occurrence of short-term heavy precipitation,there was an increase in the maximum wind speed value,a decrease in the minimum extension height,and an increase in the low-level jet stream index I.As short-term heavy rainfall approached,the intensity of the low-level jet stream remained high and its proportion increased.The minimum achievable extension height gradually decreased and remained stable at a low value.In the first 2 h of heavy rainfall,the wind speed reached its maximum,the extension height was the lowest,and the lowlevel jet stream index I was the highest.Classifying and discussing it,the precipitation in the rear was different,and the lowest height decreased to the lowest at the time of occurrence,at which point the I value reached its maximum.The characteristics of the other two categories were the same as before the classification.(3)The vertical wind shear from the ground to different isobaric surfaces gradually decreased with the increase of height.With the approach of short-term heavy rainfall,the vertical wind shear of each layer basically decreased gradually,after the beginning of heavy rainfall,which decreased to the minimum.The characteristics of main body precipitation were the same as before the classification.Pre-landfall precipitation,in addition to the gradual decrease of vertical wind shear from the ground to 925 hPa,both 850 hPa and 700 hPa increased first and then decreased,vertical wind shear decreased to the minimum after the beginning of heavy rainfall.Precipitation at rear of typhoon,vertical wind shear from ground to 700 hPa increased compared with that before the occurrence of heavy rainfall,while wind shear from ground to 925 hPa and 850 hPa showed the characteristics of decreasing when heavy rainfall occurred.(4)The median values of various physical quantities before the occurrence of typhoon short-term heavy rainfall were selected as the thresholds of short-term heavy rainfall will occur.The intensity of LLJ is about 21 m/s,the lowest height is about 0.65 km,the LLJ index I is about 36×10^(−3) s^(−1).Vertical wind shear from the ground to 925 hPa,850 hPa and 700 hPa are respectively about 15.9×10^(−3) s^(−1),11.2×10^(−3) s^(−1) and 5.1×10^(−3) s^(−1).展开更多
基金supported by the National Natural Science Foundation of China(Grant Nos.41930972 and 42475015)the Financial Meteorology Scientific and Technological Innovation Group of the China Meteorological Administration(Grant No.CMA2024ZD03).
文摘The position of the South Asian High(SAH)over the Tibetan Plateau(TP)exhibits significant interannual variability.In this study,the criteria for defining the establishment and withdrawal of the SAH,as well as their activities over the TP,are re-evaluated.The SAH is classified as“established over the TP”when the 1660 dagpm geopotential height contour covers 25%or more of the TP,and“withdrawn from the TP”when this contour covers less than 25%.Statistical analysis shows that,on average,the SAH establishes over the TP by the 4th pentad of May(28th pentad)and withdraws from the TP around the 2nd pentad of October(56th pentad).Over the past 50 years(1974–2023),the SAH has tended to establish over the TP earlier and withdraw later,resulting in a longer duration of control over the TP,with the rate of increase accelerating since 2017.The SAH exhibits a long-term linear trend of an eastward shift during both its establishment and withdrawal phases.The anomalous activity of the SAH over the TP is influenced by atmospheric heat sources.When there is anomalous warming(cooling)of atmospheric heating over the Bay of Bengal and the Indochina Peninsula,the SAH tends to establish and withdraw earlier and further westward(later and further eastward),with the westerly trough located over East Asia(the western part of the TP).
基金supported by the National Natural Science Foundation of China (No.42201151)the Basic Research Fund of the Chinese Academy of Meteorological Sciences (Nos.2023Z004 and 2024Z007)。
文摘Black carbon (BC) aerosols are considered key factors that contribute to rapid climate warming and ice melt in the Arctic region.However,compared with long-term observations from land-based stations,observational data over the Arctic Ocean remain relatively scarce.Four Arctic scientific expeditions were conducted in the summer and early autumn of 2010,2012,2016,and 2018 via the Chinese research vessel Xue Long,during which the BC concentrations along the routes were measured via light absorption methods.In this work,the spatiotemporal distribution characteristics of BC over the Arctic Ocean were examined on the basis of these observations.The potential sources of BC along the various routes were analyzed via the weighted potential source contribution function and weighted concentrationweighted trajectory methods of the hybrid single-particle Lagrangian integrated trajectory model in conjunction with Arctic transport potential climate model simulations.The analysis results indicated that wildfires in the western Aleutian Islands,Siberia,and Far East regions were the primary contributors to the BC aerosol concentration observed along the Arctic expedition routes in summer,identifying these regions as major potential source areas.
基金supported by the National Key Research and Development Program[grant number 2022YFC3004203]the S&T Development Fund of CAMS(Chinese Academy of Meteorological Sciences)[grant numbers 2023KJ040 and 2024KJ013].
文摘Subseasonal forecasting of extreme events is crucial for early warning systems.However,the forecast skills for extreme events are limited.Taking the extreme cold events in January 2018 as a specific example,and analyzing the 34 extreme cold events in East Asia from 1998 to 2020,the authors evaluated the forecast skills of the ECMWF model ensemble members on subseasonal time scales.The results show that while the ensemble mean has limited skills for forecasting extreme cold events at the 3-week lead time,some individual members demonstrate high forecast skills.For most extreme cold events,there are>10%of members among the total ensembles that can well predict the rapid temperature transitions at the 14-day lead time.This highlights the untapped potential of the ECMWF model to forecast extreme cold events on subseasonal time scales.High-skill ensemble members rely on accurate predictions of atmospheric circulation patterns(500-hPa geopotential height,mean sea level pressure)and key weather systems,including the Ural Blocking and Siberian High,that influence extreme cold events.
基金supported by the National Key R&D Program of China(Grant Nos.2022YFC2807204 and 2022YFE0106700)the Basic Research Fund of the Chinese Academy of Meteorological Sciences(Grant Nos.2023Z004,2023Z015,and 2023Y012)。
文摘The Atmospheric Infrared Sounder(AIRS)on the Aqua satellite,along with the MWTS/MWHS Synergy(TSHS)sounding system and Atmospheric Vertical Sounder System(VASS)on the Fengyun-3D(FY-3D)satellite,provide highquality data for studying Arctic temperature change.The generalized cold bias of AIRS is confirmed through horizontal comparisons with Arctic land radiosonde stations.VASS corrects the warm bias of TSHS by incorporating the Hyperspectral Infrared Atmospheric Sounder-I(HIRAS-I).Vertical comparisons demonstrate that AIRS,TSHS,and VASS offer excellent temperature detection from the top of the boundary layer to the lower stratosphere(800–100 h Pa).However,the overestimation and errors of stratospheric temperatures by TSHS and VASS increase with altitude(pressures below60 h Pa).Specifically,the warm bias trends at 0.06 K hPa^(-1),reaching 2.87 K and 2.92 K at 10 h Pa.Similarly,RMSE values trend at 0.05?K h Pa^(-1),reaching 3.62?K and 3.69?K at 10 h Pa.The low correlation(R≥0.65)of TSHS near 250 h Pa in summer is significantly improved in VASS(R≥0.78)after adding HIRAS-I.The high vertical resolution due to infrared hyperspectral resolution facilitates the detection of complex temperature junctions.The retrieval error of AIRS in the boundary layer increases with cloudiness,while VASS combines microwave and infrared channel data to reduce the impact of cloud cover.Assessing the Arctic applicability of these three satellite temperature profile products will facilitate their widespread use in the Arctic region,enhance accurate climate change monitoring,and further reveal the mechanisms of Arctic warming.
文摘In November 1984,China launched its first expedition to the Southern Ocean and the Antarctic continent,culminating in the establishment of its first year-round research station—Great Wall Station—on the Antarctic Peninsula in February 1985.Forty years later,in February 2024,China’s fifth research station,Qinling Station,commenced operations on Inexpress-ible Island near Terra Nova Bay.
基金National Natural Science Foundation of China(NSFC)(40875025,41175050,41475039 and41475041)Shanghai Natural Science Foundation of China(08ZR1422900)Public Sector(Meteorology)Research of China(GYHY201306012)
文摘Based on the data(including radius of maximum winds) from the JTWC(Joint Typhoon Warning Center),the tropical cyclones(TCs) radii of the outermost closed isobar, TCs best tracks from Shanghai Typhoon Institute and the Black Body Temperature(TBB) of the Japanese geostationary meteorological satellite M1 TR IR1, and combining13 tropical cyclones which landed in China again after visiting the island of Taiwan during the period from 2001 to2010, we analyzed the relationship between the number of convective cores within TC circulation and the intensity of TC with the method of convective-stratiform technique(CST) and statistical and composite analysis. The results are shown as follows:(1) The number of convective cores in the entire TC circulation is well corresponding with the outer spiral rainbands and the density of convective cores in the inner core area increases(decreases) generally with increasing(decreasing) TC intensity. At the same time, the number of convective cores within the outer spiral rainbands is more than that within the inner core and does not change much with the TC intensity. However, the density of convective cores within the outer spiral rainbands is lower than that within the inner core.(2) The relationship described above is sensitive to landing location to some extent but not sensitive to the structure of TC.(3) The average value of TBB in the inner core area increases(decreases) generally with increasing(decreasing) of TC intensity, which is also sensitive to landing situation to some extent. At the same time, the average value of TBB within the outer spiral rainbands is close to that within the entire TC circulation, and both of them are more than that within the inner core. However, they do not reflect TC intensity change significantly.(4) The results of statistical composite based on convective cores and TBB are complementary with each other, so a combination of both can reflect the relationship between TC rainbands and TC intensity much better.
基金funded by the Emphasis Opening Laboratory of Atmospheric Sounding, China Meteorological Administrationthe State Key Laboratory of Disaster Weather, Chinese Academy of Meteoro-logical Science (2007Y004)
文摘Certain feasibilities and features were discussed in typhoon detection by radar with a negative elevation angle according to the relationship between the remote detecting range and the elevation angle of the new generation weather radar, in order to rectify the disadvantages of detecting capability for remote low-level echo with a lowest elevation angle of 0.5° in the common detecting mode. The data obtained from detecting the typhoon of Haitang and Changmi with radar for their negative elevation angles and the observed data for the common lowest elevation angle of 0.5° were compared to each other. The results showed that the detection of remote low level cloud system with radar could be improved by using the negative elevation angle, and the structure and the evolution trend of a typhoon could be better judged. The increasing degree of detection for negative elevation angles in the current volume scanning mode should be helpful for predicting the intensity and developing trend of windstorms, to further improve the capability of warning and nowcasting. The detection of negative elevation angle could also help reveal the development and change of typhoon＇s low level cloud system. As far as the typhoons of Haitang and Changmi were concerned, the detecting area of Changmi was increased by 1.09 times with the negative elevation angle of 0.31°, compared with the elevation angle of 0.48° if the threshold value for the sea echo within 100 km was eliminated. Several volume scans of Haitang were increased by 2.1%-7.9% for the negative elevation angle of 0.36° compared with the elevation angle of 0.49° . Therefore, the radar detecting capability of typhoons could be improved by the detection of negative elevation angles to some extent. This could make up for the disadvantages of a low detecting capability for remote low-level echo in the common detecting mode. At the same time, a negative elevation angle could be easily influenced by the ground clutter and the close sea wave clutter which interfered with the assessment of the typhoon structure at times. Assessing these advantages and disadvantages, some advantages for using negative elevation angle were discovered from the observation of the typhoons Haitang and Changmi, if the negative elevation angle with radar was selected reasonably in some conditions. As a result, a certain value arose for improving and monitoring the early warning system for typhoons, paying close attention to the detection of negative elevation angles.
基金supported by the National Natural Science Foundation of China(Grant Nos.42075063&42075066)the Open Project of State Key Laboratory of Severe Weather(Grant No.2021LASW-A07)+3 种基金the Jiangsu Meteorological Youth Fund Project(Grant No.KQ202215)the Special Fund for Basic Scientific Research Business of China Academy of Meteorological Sciences(Grant No.2022Y025)the Bei Ji Ge Open Research Fund(Grant No.BJG202307)the Science and Technology Project of Yancheng Meteorological Administration(Grant No.YQK2021016)。
文摘Based on the global reanalysis data of the National Centers for Environmental Prediction(NCEP)/National Center for Atmospheric Research,the surface meteorological observation data,sounding data and satellite observation data,this paper comprehensively analyzes the evolution process and formation mechanism of a persistent severe dense fog process occurred on February 15–17,2015 in Yancheng,eastern China.Through the numerical simulation experiment of Weather Research and Forecast(WRF)model,we further analyze the impact of sea-land breeze on the formation and burst reinforcement of fog.Results show that the precipitation caused by the southwesterly airflow in front of the upper-level trough and the low-pressure inverted trough are conducive to the formation of early rain fog,while the nighttime clear radiance under the control of surface cold high and the infiltration of weak cold advection are conducive to the formation and development of later radiation-advection fog.The WRF model simulates the fog evolution process,which is basically consistent with the actual fog area,and the simulation results are credible to a certain extent.The simulation results show that the establishment of sea breeze has an advection cooling effect on the near surface layer,which is conducive to the formation and development of the inversion layer on the near surface,providing stable stratification conditions for the formation and burst reinforcement of fog.On one hand,the strengthening of sea breeze circulation can continuously transport water vapor to the study area.On the other,the occurrence of ultra-low level jet is favorable for the accumulation of low-level water vapor.At the same time,the inversion intensity further strengthens,which is in favor of the burst reinforcement and long-term maintenance of fog.
基金supported by the Second Tibetan Plateau Scientific Expedition and Research(STEP)Program(Grant No.2019QZKK0105)the Key Project of the National Natural Science Foundation of China(Grant No.42030611)+3 种基金the National Key Research and Development Program of China(Grant No.2022YFC3003903)the National Natural Science Foundation of China(Grant Nos.42205072&42305083)the Basic Research Fund of Chinese Academy of Meteorological Sciences(Grant No.2022Y024)the Key Research and Development Program of Science and Technology Department of Sichuan Province(Grant No.2022YFS0540)。
文摘The Sichuan-Xizang Railway is an important part of the railway network in China, and geological disasters, such as mountain floods and landslides, frequently occur in this region. Precipitation is an important cause of these disasters;therefore,accurate simulation of the precipitation in this region is highly important. In this study, the descriptions for uncertain processes in the cloud microphysics scheme are improved;these processes include cloud droplet activation, cloud-rain autoconversion, rain accretion by cloud droplets, and the entrainment-mixing process. In the default scheme, the cloud water content of different sizes corresponds to the same cloud droplet concentration, which is inconsistent with the actual content;this results in excessive cloud droplet size, unreasonable related conversion rates of microphysical process(such as cloud-rain autoconversion), and an overestimation of precipitation. Our new scheme overcomes the problem of excessive cloud droplet size. The processes of cloudrain autoconversion and rain accretion by cloud droplets are similar to the stochastic collection equation, and the mixing mechanism of cloud droplets is more consistent with that occurred during the actual physical process in the cloud. Based on the new and old schemes, multiple precipitation processes in the flood season of 2021 along the Sichuan-Xizang Railway are simulated, and the results are evaluated using ground observations and satellite data. Compared to the default scheme, the new scheme is more suitable for the simulation of cloud physics, reducing the simulation deviation of the liquid water path and droplet radius from 2 times to less than 1 time and significantly alleviating the overestimation of precipitation intensity and range of precipitation center. The average root-mean-square error is reduced by 22%. Our results can provide a scientific reference for improving precipitation forecasting and disaster prevention in this region.
基金funded by the Fujian Provincial Meteorological Bureau Open Research Fund Project(2020K05)Fujian Provincial Meteorological Bureau Open Research Fund Project(2021K01).
文摘Based on wind profile radar data,this paper aims at different typhoon processes landed and affected Fujian from 2011 to 2019,according to the nature of typhoon rainstorm,it can be classified into outer precipitation before typhoon landed,main body precipitation and precipitation at the rear of typhoon,the change of the characteristic quantities in approaching time of the occurrence of short-term heavy rainfall was analyzed,and the typhoon case in 2020 was back calculated.The results show that,the characteristics of low-level jet streams(maximum wind speed at low altitude,minimum height of jet streams,and low-level jet stream index),as well as the magnitude of vertical wind shear below 700 hPa,have important indicative significance for the occurrence of short-term heavy rainfall.(1)More than 80%of short-term heavy rainfall occurred 3 h before the low-level jet stream already existed.The maximum wind speed below 2 km was basically close to a normal distribution,and the occurrence of heavy precipitation showed a bimodal pattern.The percentage of wind speed between 8 and 32 m/s was the highest,exceeding 85%.The wind direction of the strong wind is mainly NE,SE,and SW.Classification analysis showed that the distribution characteristics of wind speed of the main precipitation were the same as before,but the wind direction SE was higher than NE.The wind speed of pre-landfall precipitation was basically skewed,and the occurrence time of heavy precipitation followed a normal distribution.The percentage of wind speed between 16 and 32 m/s was the highest,and the wind direction was the same as before classification.The maximum wind speed of precipitation in the rear was basically bimodal distribution,with a relatively even distribution,and the wind direction was mainly SE and SW.(2)In the 3 h before the occurrence of short-term heavy precipitation,there was an increase in the maximum wind speed value,a decrease in the minimum extension height,and an increase in the low-level jet stream index I.As short-term heavy rainfall approached,the intensity of the low-level jet stream remained high and its proportion increased.The minimum achievable extension height gradually decreased and remained stable at a low value.In the first 2 h of heavy rainfall,the wind speed reached its maximum,the extension height was the lowest,and the lowlevel jet stream index I was the highest.Classifying and discussing it,the precipitation in the rear was different,and the lowest height decreased to the lowest at the time of occurrence,at which point the I value reached its maximum.The characteristics of the other two categories were the same as before the classification.(3)The vertical wind shear from the ground to different isobaric surfaces gradually decreased with the increase of height.With the approach of short-term heavy rainfall,the vertical wind shear of each layer basically decreased gradually,after the beginning of heavy rainfall,which decreased to the minimum.The characteristics of main body precipitation were the same as before the classification.Pre-landfall precipitation,in addition to the gradual decrease of vertical wind shear from the ground to 925 hPa,both 850 hPa and 700 hPa increased first and then decreased,vertical wind shear decreased to the minimum after the beginning of heavy rainfall.Precipitation at rear of typhoon,vertical wind shear from ground to 700 hPa increased compared with that before the occurrence of heavy rainfall,while wind shear from ground to 925 hPa and 850 hPa showed the characteristics of decreasing when heavy rainfall occurred.(4)The median values of various physical quantities before the occurrence of typhoon short-term heavy rainfall were selected as the thresholds of short-term heavy rainfall will occur.The intensity of LLJ is about 21 m/s,the lowest height is about 0.65 km,the LLJ index I is about 36×10^(−3) s^(−1).Vertical wind shear from the ground to 925 hPa,850 hPa and 700 hPa are respectively about 15.9×10^(−3) s^(−1),11.2×10^(−3) s^(−1) and 5.1×10^(−3) s^(−1).
