To investigate the impact of soil moisture uncertainty on summertime short-range ensemble forecasts(SREFs), a fivemember SREF experiment with perturbed initial soil moisture(ISM) was performed over a northern Chin...To investigate the impact of soil moisture uncertainty on summertime short-range ensemble forecasts(SREFs), a fivemember SREF experiment with perturbed initial soil moisture(ISM) was performed over a northern China domain in summertime from July to August 2014. Five soil moisture analyses from three different operational/research centers were used as the ISM for the ensemble. The ISM perturbation produced notable ensemble spread in near-surface variables and atmospheric variables below 800 h Pa, and produced skillful ensemble-mean 24-h accumulated precipitation(APCP24) forecasts that outperformed any single ensemble member. Compared with a second SREF experiment with mixed microphysics parameterization options, the ISM-perturbed ensemble produced comparable ensemble spread in APCP24 forecasts, and had better Brier scores and resolution in probabilistic APCP24 forecasts for 10-mm, 25-mm and 50-mm thresholds. The ISM-perturbed ensemble produced obviously larger ensemble spread in near-surface variables. It was, however, still under-dispersed, indicating that perturbing ISM alone may not be adequate in representing all the uncertainty at the near-surface level, indicating further SREF studies are needed to better represent the uncertainties in land surface processes and their coupling with the atmosphere.展开更多
Research on vertical motion in mesoscale systems is an extraordinarily challenging effort.Allowing for fewer assumptions,a new form of generalized vertical motion equation and a generalized Omega equation are derived ...Research on vertical motion in mesoscale systems is an extraordinarily challenging effort.Allowing for fewer assumptions,a new form of generalized vertical motion equation and a generalized Omega equation are derived in the Cartesian coordinate system(nonhydrostatic equilibrium)and the isobaric coordinate system(hydrostatic equilibrium),respectively.The terms on the right-hand side of the equations,which comprise the Q vector,are composed of three factors:dynamic,thermodynamic,and mass.A heavy rain event that occurred from 18 to 19 July 2021 in southern Xinjiang was selected to analyze the characteristics of the diagnostic variable in the generalized vertical motion equation(Qz)and the diagnostic variable in the generalized Omega equation(Qp)using high-resolution model data.The results show that the horizontal distribution of the Qz-vector divergence at 5.5 km is roughly similar to the distribution of the Qp-vector divergence at 500 hPa,and that both relate well to the composite radar reflectivity,vertical motion,and hourly accumulated precipitation.The Qz-vector divergence is more effective in indicating weak precipitation.In vertical cross sections,regions with alternating positive and negative large values that match the precipitation are mainly concentrated in the middle levels for both forms of Q vectors.The temporal evolutions of vertically integrated Qz-vector divergence and Qp-vector divergence are generally similar.Both perform better than the classical quasigeostrophic Q vector and nongeostrophic Q vector in indicating the development of the precipitation system.展开更多
A mathematical relation between deformation and vertical vorticity tendency is built by introducing the frontogenesis function and the complete vertical vorticity equation, which is derived by virtue of moist potentia...A mathematical relation between deformation and vertical vorticity tendency is built by introducing the frontogenesis function and the complete vertical vorticity equation, which is derived by virtue of moist potential vorticity. From the mathematical relation, it is shown that properly configured atmospheric conditions can make deformation exert a positive contribution to vortex development at rates comparable to other favorable factors. The effect of deformation on vortex development is not only related to the deformation itself, but also depends on the current thermodynamic and dynamic structures of the atmosphere, such as the convective stability, moist baroclinicity and vertical wind shear (or horizontal vorticity). A diagnostic study of a heavy-rainfall case that occurred during 20-22 July 2012 shows that deformation has the most remarkable effect on the increase in vertical vorticity during the rapid development stage of the low vortex during its whole life cycle. This feature is mainly due to the existence of an approximate neutral layer (about 700 hPa) in the atmosphere where the convective stability tends to be zero. The neutral layer makes the effect of deformation on the vertical vorticity increase significantly during the vortex development stage, and thus drives the vertical vorticity to increase.展开更多
A numerical experiment was performed using the Weather Research and Forecasting(WRF) model to analyze the generation and propagation of inertia-gravity waves during an orographic rainstorm that occurred in the Sichu...A numerical experiment was performed using the Weather Research and Forecasting(WRF) model to analyze the generation and propagation of inertia-gravity waves during an orographic rainstorm that occurred in the Sichuan area on 17 August 2014. To examine the spatial and temporal structures of the inertia-gravity waves and identify the wave types, three wavenumber-frequency spectral analysis methods(Fourier analysis, cross-spectral analysis, and wavelet cross-spectrum analysis)were applied. During the storm, inertia-gravity waves appeared at heights of 10-14 km, with periods of 80-100 min and wavelengths of 40-50 km. These waves were generated over a mountain and propagated eastward at an average speed of 15-20 m s^(-1). Meanwhile, comparison between the reconstructed inertia-gravity waves and accumulated precipitation showed there was a mutual promotion process between them. The Richardson number and Scorer parameter were used to demonstrate that the eastward-moving inertia-gravity waves were trapped in an effective atmospheric ducting zone with favorable reflector and critical level conditions, which were the primary causes of the long lives of the waves. Finally, numerical experiments to test the sensitivity to terrain and diabatic heating were conducted, and the results suggested a cooperative effect of terrain and diabatic heating contributed to the propagation and enhancement of the waves.展开更多
The stratospheric quasi-zero wind layer (QZWL) is a transition region with low zonal wind speeds in the lower stratosphere at an altitude of ~20 km. The zonal wind direction above the QZWL layer is opposite to that be...The stratospheric quasi-zero wind layer (QZWL) is a transition region with low zonal wind speeds in the lower stratosphere at an altitude of ~20 km. The zonal wind direction above the QZWL layer is opposite to that below the QZWL layer and the north –south wind component is small. The atmospheric wind field near the stratospheric QZWL is an important factor affecting the flight altitude and dynamic control of stratospheric airships. It is therefore necessary to study the stratospheric QZWL to provide better environmental information for these aircraft. High-resolution radiosonde data were used to analyze the characteristics of the stratospheric QZWL over Korla, Xinjiang Province, China. A weak wind layer in which the wind direction suddenly reversed from westerly to easterly was observed at ~20 km in the lower stratosphere, characteristic of the stratospheric QZWL. The Weather Research and Forecasting model was used to simulate the profiles of the horizontal wind speed and direction over Korla. The forcing effect of each diagnostic term in the equation on the zonal wind speed was analyzed. The results showed that the advection term was the dominant factor forcing the zonal wind speed. The wave term had a secondary forcing role, although the forcing effect of the wave term on the zonal wind speed was significant in some regions.展开更多
Short-duration snow bursts with heavy snow represent one type of hazardous weather in winter which can be easily missed by the winter weather warnings but often results in great hazards.In this paper,the mechanism for...Short-duration snow bursts with heavy snow represent one type of hazardous weather in winter which can be easily missed by the winter weather warnings but often results in great hazards.In this paper,the mechanism for the occurrence of such events was investigated with the aid of a localized terrain-influenced snow burst event in Northeast China.The snow burst was produced by an eastward-moving cold-frontal snowband which encountered the downstream complex terrain of the Changbai Mountains and intensified.To ascertain the role of orography on the snow burst,numerical experiments,together with a parallel sensitivity experiment removing Changbai Mountains,were performed to attempt to distinguish the contributions of cold-frontal system and orographic effects to produce the heavy snow.Diagnosis showed that without the influence of Changbai Mountains,the release of conditional instability(CI)and inertial instability(II)within a weak frontogenetical environment was responsible for the snowband maintenance.Orographic effects played important roles in enhancing the snowband and increasing the snowfall intensities.The enhancement mechanism was related to the interactions of the cold-frontal snowband and the topography.On the one hand,orographic frontogenesis and persistent ascent,created by orographic gravity waves over the terrain,greatly enhanced the orographic lifting.The intensification of the lifting promoted the release of CI and thus enhanced the snowfall.On the other hand,pre-existing orographic instabilities were released due to the passing of the cold-frontal snowband,which could also serve to intensify the snowband over terrain and thus increase the snowfall.展开更多
A three-dimensional transformed Eulerian-mean(3D TEM) equation under a non-hydrostatic and non-geostrophic assumption is deduced in this study. The vertical component of the 3D wave activity flux deduced here is the p...A three-dimensional transformed Eulerian-mean(3D TEM) equation under a non-hydrostatic and non-geostrophic assumption is deduced in this study. The vertical component of the 3D wave activity flux deduced here is the primary difference from previous studies, which is suitable to mesoscale systems. Using the 3D TEM equation, the energy propagation of the inertia–gravity waves and how the generation and dissipation of the inertia–gravity waves drive the mean flow can be examined. During the mature stage of a heavy precipitation event, the maximum of the Eliassen–Palm(EP) flux divergence is primarily concentrated at the height of 10–14 km, where the energy of the inertia–gravity waves propagates forward(eastward) and upward. Examining the contribution of each term of the 3D TEM equation shows that the EP flux divergence is the primary contributor to the mean flow tendency. The EP flux divergence decelerates the zonal wind above and below the high-level jet at the height of 10 km and 15 km, and accelerates the high-level jet at the height of 12–14 km. This structure enhances the vertical wind shear of the environment and promotes the development of the rainstorm.展开更多
The unique geographical location and high altitude of the Tibetan Plateau can greatly influence regional weather and climate.In particular, the Asian summer monsoon(ASM) anticyclone circulation system over the Tibetan...The unique geographical location and high altitude of the Tibetan Plateau can greatly influence regional weather and climate.In particular, the Asian summer monsoon(ASM) anticyclone circulation system over the Tibetan Plateau is recognized to be a significant transport pathway for water vapor and pollutants to enter the stratosphere. To improve understanding of these physical processes, a multi-location joint atmospheric experiment was performed over the Tibetan Plateau from late July to August in 2018, funded by the fiveyear(2018–2022) STEAM(stratosphere and troposphere exchange experiment during ASM) project, during which multiple platforms/instruments—including long-duration stratospheric balloons, dropsondes, unmanned aerial vehicles, special sounding systems, and ground-based and satellite-borne instruments—will be deployed. These complementary methods of data acquisition are expected to provide comprehensive atmospheric parameters(aerosol, ozone, water vapor, CO_2, CH_4, CO, temperature, pressure,turbulence, radiation, lightning and wind); the richness of this approach is expected to advance our comprehension of key mechanisms associated with thermal, dynamical, radiative, and chemical transports over the Tibetan Plateau during ASM activity.展开更多
Many observational studies have shown that deformation, like vertical vorticity and divergence, is closely related to the occurrence and distribution of strong precipitation. In this paper, to involve deformation in p...Many observational studies have shown that deformation, like vertical vorticity and divergence, is closely related to the occurrence and distribution of strong precipitation. In this paper, to involve deformation in precipitation diagnosis, a new parameter called potential deformation(PD) is derived and then applied to precipitation detection within a simulated mesoscale convective system(MCS). It is shown that PD includes both stretching deformation and shearing deformation and shares similar characteristics with deformation insofar as it does not change with the rotating coordinate. Diagnosis of the simulated MCS reveals that PD performs well in tracing the MCS' precipitation. In terms of their distributional pattern, the large-value areas of PD are similar to the precipitation in the different development stages of the MCS. A detailed analysis of the physical processes contained within the PD shows that it can reflect the three-dimensional moisture variation,vertical wind shear and wind deformation within the MCS. These structures are usually a comprehensive reflection of the characteristics of the surface cold pool, rear inflow jet, downward cold air flow and upward warm moist flow within the precipitating convective cells. For this reason, the PD shows much stronger anomalies in the precipitating atmosphere than the non-precipitating atmosphere, which implies considerable potential for its application in detecting heavy precipitation within MCSs.展开更多
The non-hydrostatic wave equation set in Cartesian coordinates is rearranged to gain insight into wave generation in a mesoscale severe convection system. The wave equation is characterized by a wave operator on the l...The non-hydrostatic wave equation set in Cartesian coordinates is rearranged to gain insight into wave generation in a mesoscale severe convection system. The wave equation is characterized by a wave operator on the lhs, and forcing involving three terms—linear and nonlinear terms, and diabatic heating—on the rhs. The equation was applied to a case of severe convection that occurred in East China. The calculation with simulation data showed that the diabatic forcing and linear and nonlinear forcing presented large magnitude at different altitudes in the severe convection region. Further analysis revealed the diabatic forcing due to condensational latent heating had an important influence on the generation of gravity waves in the middle and lower levels. The linear forcing resulting from the Laplacian of potential-temperature linear forcing was dominant in the middle and upper levels. The nonlinear forcing was determined by the Laplacian of potential-temperature nonlinear forcing. Therefore, the forcing of gravity waves was closely associated with the thermodynamic processes in the severe convection case. The reason may be that, besides the vertical component of pressure gradient force, the vertical oscillation of atmospheric particles was dominated by the buoyancy for inertial gravity waves. The latent heating and potential-temperature linear and nonlinear forcing played an important role in the buoyancy tendency. Consequently, these thermodynamic elements influenced the evolution of inertial-gravity waves.展开更多
NCEP-NCAR reanalysis data were used to analyze the characteristics and evolution mechanism of convective and symmetric instability before and during a heavy rainfall event that occurred in Beijing on 21 July 2012.Appr...NCEP-NCAR reanalysis data were used to analyze the characteristics and evolution mechanism of convective and symmetric instability before and during a heavy rainfall event that occurred in Beijing on 21 July 2012.Approximately twelve hours before the rainstorm,the atmosphere was mainly dominated by convective instability in the lower level of 900-800 hPa.The strong southwesterly low-level jet conveyed the moist and warm airflow continuously to the area of torrential rain,maintaining and enhancing the unstable energy.When the precipitation occurred,unstable energy was released and the convective instability weakened.Meanwhile,due to the baroclinicity enhancement in the atmosphere,the symmetric instability strengthened,maintaining and promoting the subsequent torrential rain.Deriving the convective instability tendency equation demonstrated that the barotropic component of potential divergence and the advection term played a major role in enhancing the convective instability before the rainstorm.Analysis of the tendency equation of moist potential vorticity showed that the coupled term of vertical vorticity and the baroclinic component of potential divergence was the primary factor influencing the development of symmetric instability during the precipitation.Comparing the effects of these factors on convective instability and symmetric instability showed some correlation.展开更多
In this study,the ability of the Weather Research and Forecasting(WRF)model to generate accurate near-surface wind speed forecasts at kilometer-to subkilometer-scale resolution along race tracks(RTs)in Chongli during ...In this study,the ability of the Weather Research and Forecasting(WRF)model to generate accurate near-surface wind speed forecasts at kilometer-to subkilometer-scale resolution along race tracks(RTs)in Chongli during the wintertime is evaluated.The performance of two postprocessing methods,including the decaying-averaging(DA)and analogy-based(AN)methods,is tested to calibrate the near-surface wind speed forecasts.It is found that great uncertainties exist in the model’s raw forecasts of the near-surface wind speed in Chongli.Improvement of the forecast accuracy due to refinement of the horizontal resolution from kilometer to subkilometer scale is limited and not systematic.The RT sites tend to have large bias and centered root mean square error(CRMSE)values and also exhibit notable underestimation of high-wind speeds,notable overestimation or underestimation of the near-surface wind speed at high altitudes,and notable underestimation during daytime.These problems are not resolved by increasing the horizontal resolution and are even exacerbated,which leads to great challenges in the accurate forecasting of the near-surface wind speed in the competition areas in Chongli.The application of postprocessing methods can greatly improve the forecast accuracy of near-surface wind speed.Both methods used in this study have comparable abilities in reducing the(positive or negative)bias,while the AN method is also capable of decreasing the random error reflected by CRMSE.In particular,the large biases for high-wind speeds,wind speeds at high-altitude stations,and wind speeds during the daytime at RT stations can be evidently reduced.展开更多
As part of“The Earth Summit Mission-2022”during the second Tibetan Plateau Scientific Expedition and Research(STEP)in April and May 2022,we conducted the ozone sounding experiment(an ozonesonde mated to a radiosonde...As part of“The Earth Summit Mission-2022”during the second Tibetan Plateau Scientific Expedition and Research(STEP)in April and May 2022,we conducted the ozone sounding experiment(an ozonesonde mated to a radiosonde)at Mt.Qomolangma Base Camp(MQBC;86.85°E,28.14°N;5200 m),a location at an extremely high altitude.A total of ten sounding profiles were obtained between April 30 and May 06,2022,of which seven profiles were above35 km in altitude,with a maximum detection altitude up to 39.0 km.This study presents the temporal variation and vertical distributions of atmospheric temperature,humidity,and ozone during the MQBC campaign.The averaged ozone concentration was high(68.3 ppbv)at the surface and then increased smoothly until peaking(~110 ppbv)in the middle troposphere(approximately 10 km),and afterward,the ozone concentration increased rapidly from the upper troposphere to a maximum of~10 ppmv at~30 km.The enhanced ozone concentration in the middle troposphere was associated with the blocking high pressure,and transport from the southern flank of the Himalayas occurred during the campaign period.The average total ozone column was 291.9±21.4 DU for the seven profiles exceeding 35km in altitude.The ozonesonde measurements were also compared with the vertical ozone profiles retrieved from the space-borne ozone products from the Microwave Limb Sounder(MLS)onboard the Aura satellite and the Atmospheric Infrared Sounder(AIRS)onboard the Aqua satellite.展开更多
The characteristics of the mesoscale gravity waves during a snowfall event on November 30,2018 over the Ili Valley and the northern slope of the Tianshan Mountains are analyzed based on the Weather Research and Foreca...The characteristics of the mesoscale gravity waves during a snowfall event on November 30,2018 over the Ili Valley and the northern slope of the Tianshan Mountains are analyzed based on the Weather Research and Forecasting model simulation.The vertical distribution of Ro is similar to that of the residual of the nonlinear balance equation(△NBE),with their high-value areas located over the leeward slope and the fluctuations extending upwardly with time,indicating the characteristics of strong ageostrophy and non-equilibrium of atmospheric motions.In addition,the Ro and(△NBE)are first developed in the lower layers over the leeward slope,revealing that the generation of the gravity waves is closely related to the topography.Thus,the topographic uplifting greatly affects this snowfall,and the ageostrophic motion in the whole troposphere and the lower stratosphere,as well as the unbalanced motions between convergence and divergence over the peak and the leeward slope are conductive to the development of the inertia-gravity waves.In terms of the horizontal scale of the gravity waves,the Barnes’bandpass filter is applied to separate the mesoscale waves and the synoptic-scale basic flow.The vertical distributions of the vorticity and divergence perturbations have a phase difference ofπ/2,indicating the polarization state of gravity waves.The analyses on the sources and sinks of gravity waves by the non-hydrostatic wave equation show that the main forcing term for orographic gravity waves is the second-order nonlinear term,whose magnitude mainly depends on the nonlinear thermal forcing.This term is mainly related to the vertical transport of potential temperature perturbations.During the snowfall,the potential temperature perturbations are mainly caused by the topographic relief and the release of condensation latent heat.Therefore,the gravity waves in this snowfall are caused by the topographic forcing and condensation latent heating.展开更多
Based on multiresource high-resolution in situ and satellite merged observations along with model simulations from the Coordinated Regional Climate Downscaling Experiment(CORDEX),this study first investigated historic...Based on multiresource high-resolution in situ and satellite merged observations along with model simulations from the Coordinated Regional Climate Downscaling Experiment(CORDEX),this study first investigated historical changes in extreme temperature and precipitation during the period of 1979-2018 in areas along the Sichuan-Tibet Railway,and then projected the future changes in the frequency and intensity of extreme temperature and precipitation under the RCP(Representative Concentration Pathway)4.5 and 8.5 scenarios.This paper is expected to enhance our understanding of the spatiotemporal variability in the extreme temperature and precipitation along the Sichuan-Tibet Railway,and to provide scientific basis to advance the Sichuan-Tibet Railway construction and operation.The results show that temperatures in the Sichuan-Tibet region display a noticeable warming trend in the past 40 years,and the increase of minimum temperature is significantly higher than that of maximum temperature in the northwest of the region.Significant increase of precipitation is found mainly over the northwest of the Tibetan Plateau.Except for Lhasa and its surrounding areas,precipitation over other areas along the Sichuan-Tibet Railway shows no significant change in the past 40 years,as indicated in five datasets;however,precipitation along the railway has shown a remarkable decrease in the past 20 years in the TRMM satellite dataset.The warm days and nights have clearly increased by 6 and 5 day decade1-for 1979-2019,while cold days and nights have markedly decreased by about 6.6 and 3.6 day decade-1,respectively.In the past 20 years,the areas with increased precipitation from very wet days and extremely wet days are mainly distributed to the north of the Sichuan-Tibet Railway,while in the areas along the railway itself,the very wet days and extremely wet days are decreasing.Under RCPs 4.5 and 8.5,the temperature in the Sichuan-Tibet region will increase significantly,and the frequency of extreme high(low)temperature events in the late 21 st century(2070-2099)will greatly increase(decrease)by about 50%-80%(10%)compared with occurrences in the late 20 th century(1970-1999).Meanwhile,the frequency of very wet days and extremely wet days in the Sichuan-Tibet region will increase by about 2%-19% and 2%-5%,respectively,and the areas along the Sichuan-Tibet Railway will be affected by more extreme high temperature and extreme precipitation events.展开更多
基金supported by the Basic Scientific Program of the Institute of Atmospheric Physics supporting the 14th Five-Year Plan[Grant No.7-224151]Youth Innovation Team of China Meteorological Administration[Grant No.CMA2023QN10]+4 种基金the National Natural Science Foundation of China[Grant Nos.42175010,41965010,U223321842275010]Beijing Municipal Science and Technology Commission[Grant No.Z221100005222012]the Department of Science and Technology of Hebei Province[Grant No.22375404D]the Open subjects of the Key Open Laboratory of Cloud Physical Environment,China Meteorological Administration[Grant No.2020Z00715]。
基金supported by the National Key R&D Program on Monitoring, Early Warning and Prevention of Major Natural Disaster (2017YFC1502103)the National Natural Science Foundation of China (Grant Nos. 41305099 and 41305053)
文摘To investigate the impact of soil moisture uncertainty on summertime short-range ensemble forecasts(SREFs), a fivemember SREF experiment with perturbed initial soil moisture(ISM) was performed over a northern China domain in summertime from July to August 2014. Five soil moisture analyses from three different operational/research centers were used as the ISM for the ensemble. The ISM perturbation produced notable ensemble spread in near-surface variables and atmospheric variables below 800 h Pa, and produced skillful ensemble-mean 24-h accumulated precipitation(APCP24) forecasts that outperformed any single ensemble member. Compared with a second SREF experiment with mixed microphysics parameterization options, the ISM-perturbed ensemble produced comparable ensemble spread in APCP24 forecasts, and had better Brier scores and resolution in probabilistic APCP24 forecasts for 10-mm, 25-mm and 50-mm thresholds. The ISM-perturbed ensemble produced obviously larger ensemble spread in near-surface variables. It was, however, still under-dispersed, indicating that perturbing ISM alone may not be adequate in representing all the uncertainty at the near-surface level, indicating further SREF studies are needed to better represent the uncertainties in land surface processes and their coupling with the atmosphere.
基金supported by the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant No.XDA17010105)National Key Research and Development Program(Grant No.2018YFC1507104)+2 种基金Science and Technology Development Plan Project of Jilin Province(20180201035SF)Flexible Talents Introducing Project of Xinjiang(2019)the National Key Scientific and Technological Infrastructure project“Earth System Numerical Simulation Facility”(EarthLab)。
文摘Research on vertical motion in mesoscale systems is an extraordinarily challenging effort.Allowing for fewer assumptions,a new form of generalized vertical motion equation and a generalized Omega equation are derived in the Cartesian coordinate system(nonhydrostatic equilibrium)and the isobaric coordinate system(hydrostatic equilibrium),respectively.The terms on the right-hand side of the equations,which comprise the Q vector,are composed of three factors:dynamic,thermodynamic,and mass.A heavy rain event that occurred from 18 to 19 July 2021 in southern Xinjiang was selected to analyze the characteristics of the diagnostic variable in the generalized vertical motion equation(Qz)and the diagnostic variable in the generalized Omega equation(Qp)using high-resolution model data.The results show that the horizontal distribution of the Qz-vector divergence at 5.5 km is roughly similar to the distribution of the Qp-vector divergence at 500 hPa,and that both relate well to the composite radar reflectivity,vertical motion,and hourly accumulated precipitation.The Qz-vector divergence is more effective in indicating weak precipitation.In vertical cross sections,regions with alternating positive and negative large values that match the precipitation are mainly concentrated in the middle levels for both forms of Q vectors.The temporal evolutions of vertically integrated Qz-vector divergence and Qp-vector divergence are generally similar.Both perform better than the classical quasigeostrophic Q vector and nongeostrophic Q vector in indicating the development of the precipitation system.
基金supported by a National Program on Key Basic Research project(Grant No.2013CB 430105)the Key Program of the Chinese Academy of Sciences (Grant No.KZZD-EW-05)+2 种基金the National Key Technology Support Program(Grant No.2015BAC03B04)the Special Scientific Research Fund of the Meteorological Public Welfare of the Ministry of Sciences and Technology(Grant No.GYHY200906004)the National Natural Science Foundation of China(Grant Nos. 41175060,41505040)
文摘A mathematical relation between deformation and vertical vorticity tendency is built by introducing the frontogenesis function and the complete vertical vorticity equation, which is derived by virtue of moist potential vorticity. From the mathematical relation, it is shown that properly configured atmospheric conditions can make deformation exert a positive contribution to vortex development at rates comparable to other favorable factors. The effect of deformation on vortex development is not only related to the deformation itself, but also depends on the current thermodynamic and dynamic structures of the atmosphere, such as the convective stability, moist baroclinicity and vertical wind shear (or horizontal vorticity). A diagnostic study of a heavy-rainfall case that occurred during 20-22 July 2012 shows that deformation has the most remarkable effect on the increase in vertical vorticity during the rapid development stage of the low vortex during its whole life cycle. This feature is mainly due to the existence of an approximate neutral layer (about 700 hPa) in the atmosphere where the convective stability tends to be zero. The neutral layer makes the effect of deformation on the vertical vorticity increase significantly during the vortex development stage, and thus drives the vertical vorticity to increase.
基金supported by Study on Key Techniques of convective gale monitoring and forecasting in spring in Southern China (GYHY201406002)the National Natural Science Foundation of China (41705027,41775140,41175060,91437215,and 41575047)+1 种基金the research project of Heavy Rain and Drought-Flood Disasters in Plateau and Basin Key Laboratory of Sichuan Province (SZKT2016002)Open projects of Plateau Atmosphere and Environment Key Laboratory of Sichuan Province (PAEKL-2015-K2)
文摘A numerical experiment was performed using the Weather Research and Forecasting(WRF) model to analyze the generation and propagation of inertia-gravity waves during an orographic rainstorm that occurred in the Sichuan area on 17 August 2014. To examine the spatial and temporal structures of the inertia-gravity waves and identify the wave types, three wavenumber-frequency spectral analysis methods(Fourier analysis, cross-spectral analysis, and wavelet cross-spectrum analysis)were applied. During the storm, inertia-gravity waves appeared at heights of 10-14 km, with periods of 80-100 min and wavelengths of 40-50 km. These waves were generated over a mountain and propagated eastward at an average speed of 15-20 m s^(-1). Meanwhile, comparison between the reconstructed inertia-gravity waves and accumulated precipitation showed there was a mutual promotion process between them. The Richardson number and Scorer parameter were used to demonstrate that the eastward-moving inertia-gravity waves were trapped in an effective atmospheric ducting zone with favorable reflector and critical level conditions, which were the primary causes of the long lives of the waves. Finally, numerical experiments to test the sensitivity to terrain and diabatic heating were conducted, and the results suggested a cooperative effect of terrain and diabatic heating contributed to the propagation and enhancement of the waves.
基金supported by the Strategic Priority Research Program of the Chinese Academy of Sciences (Grant No. XDA17010105)
文摘The stratospheric quasi-zero wind layer (QZWL) is a transition region with low zonal wind speeds in the lower stratosphere at an altitude of ~20 km. The zonal wind direction above the QZWL layer is opposite to that below the QZWL layer and the north –south wind component is small. The atmospheric wind field near the stratospheric QZWL is an important factor affecting the flight altitude and dynamic control of stratospheric airships. It is therefore necessary to study the stratospheric QZWL to provide better environmental information for these aircraft. High-resolution radiosonde data were used to analyze the characteristics of the stratospheric QZWL over Korla, Xinjiang Province, China. A weak wind layer in which the wind direction suddenly reversed from westerly to easterly was observed at ~20 km in the lower stratosphere, characteristic of the stratospheric QZWL. The Weather Research and Forecasting model was used to simulate the profiles of the horizontal wind speed and direction over Korla. The forcing effect of each diagnostic term in the equation on the zonal wind speed was analyzed. The results showed that the advection term was the dominant factor forcing the zonal wind speed. The wave term had a secondary forcing role, although the forcing effect of the wave term on the zonal wind speed was significant in some regions.
基金the Chinese Academy of Sciences(Grant No.XDA17010105)the National Key Research and Development Project(Grant No.2018YFC1507104)+2 种基金The Key Scientific and Technology Research and Development Program of Jilin Province(Grant No.20180201035SF)the National Natural Science Foundation of China(Grant Nos.41875056,41575065 and 41790471,42075013)Chongqing Technology Innovation and Application Development Special Key Project(Grant No.cstc2019jscxtjsbX0007).
文摘Short-duration snow bursts with heavy snow represent one type of hazardous weather in winter which can be easily missed by the winter weather warnings but often results in great hazards.In this paper,the mechanism for the occurrence of such events was investigated with the aid of a localized terrain-influenced snow burst event in Northeast China.The snow burst was produced by an eastward-moving cold-frontal snowband which encountered the downstream complex terrain of the Changbai Mountains and intensified.To ascertain the role of orography on the snow burst,numerical experiments,together with a parallel sensitivity experiment removing Changbai Mountains,were performed to attempt to distinguish the contributions of cold-frontal system and orographic effects to produce the heavy snow.Diagnosis showed that without the influence of Changbai Mountains,the release of conditional instability(CI)and inertial instability(II)within a weak frontogenetical environment was responsible for the snowband maintenance.Orographic effects played important roles in enhancing the snowband and increasing the snowfall intensities.The enhancement mechanism was related to the interactions of the cold-frontal snowband and the topography.On the one hand,orographic frontogenesis and persistent ascent,created by orographic gravity waves over the terrain,greatly enhanced the orographic lifting.The intensification of the lifting promoted the release of CI and thus enhanced the snowfall.On the other hand,pre-existing orographic instabilities were released due to the passing of the cold-frontal snowband,which could also serve to intensify the snowband over terrain and thus increase the snowfall.
文摘A three-dimensional transformed Eulerian-mean(3D TEM) equation under a non-hydrostatic and non-geostrophic assumption is deduced in this study. The vertical component of the 3D wave activity flux deduced here is the primary difference from previous studies, which is suitable to mesoscale systems. Using the 3D TEM equation, the energy propagation of the inertia–gravity waves and how the generation and dissipation of the inertia–gravity waves drive the mean flow can be examined. During the mature stage of a heavy precipitation event, the maximum of the Eliassen–Palm(EP) flux divergence is primarily concentrated at the height of 10–14 km, where the energy of the inertia–gravity waves propagates forward(eastward) and upward. Examining the contribution of each term of the 3D TEM equation shows that the EP flux divergence is the primary contributor to the mean flow tendency. The EP flux divergence decelerates the zonal wind above and below the high-level jet at the height of 10 km and 15 km, and accelerates the high-level jet at the height of 12–14 km. This structure enhances the vertical wind shear of the environment and promotes the development of the rainstorm.
基金supported by the Strategic Priority Research Program of the Chinese Academy of Sciences (Grant Nos. XDA17010101, XDA17010102, XDA17010103, XDA17010104 and XDA17010105)
文摘The unique geographical location and high altitude of the Tibetan Plateau can greatly influence regional weather and climate.In particular, the Asian summer monsoon(ASM) anticyclone circulation system over the Tibetan Plateau is recognized to be a significant transport pathway for water vapor and pollutants to enter the stratosphere. To improve understanding of these physical processes, a multi-location joint atmospheric experiment was performed over the Tibetan Plateau from late July to August in 2018, funded by the fiveyear(2018–2022) STEAM(stratosphere and troposphere exchange experiment during ASM) project, during which multiple platforms/instruments—including long-duration stratospheric balloons, dropsondes, unmanned aerial vehicles, special sounding systems, and ground-based and satellite-borne instruments—will be deployed. These complementary methods of data acquisition are expected to provide comprehensive atmospheric parameters(aerosol, ozone, water vapor, CO_2, CH_4, CO, temperature, pressure,turbulence, radiation, lightning and wind); the richness of this approach is expected to advance our comprehension of key mechanisms associated with thermal, dynamical, radiative, and chemical transports over the Tibetan Plateau during ASM activity.
基金supported by the Special Scientific Research Fund of the Meteorological Public Welfare of the Ministry of Sciences and Technology (Grant No. GYHY201406002, GYHY201406001)National Key Technology Support Program (Grant No. 2015BAC03B04)+4 种基金a National Program on Key Basic Research project (Grant No. 2013CB430105)the Major Research Plan of the National Natural Science Foundation of China (Grant No. 91437215)the National Natural Science Foundation of China (Grant Nos. 41505040, 41375052 41405055 and 41575065)the Open Project of the State Key Laboratory of Severe Weather (La SW), the Chinese Academy of Meteorological Sciences (CAMS) (Grant No. 2015LASW-B05)the Beijing Natural Sciences Foundation (Grant No. 8142035)
文摘Many observational studies have shown that deformation, like vertical vorticity and divergence, is closely related to the occurrence and distribution of strong precipitation. In this paper, to involve deformation in precipitation diagnosis, a new parameter called potential deformation(PD) is derived and then applied to precipitation detection within a simulated mesoscale convective system(MCS). It is shown that PD includes both stretching deformation and shearing deformation and shares similar characteristics with deformation insofar as it does not change with the rotating coordinate. Diagnosis of the simulated MCS reveals that PD performs well in tracing the MCS' precipitation. In terms of their distributional pattern, the large-value areas of PD are similar to the precipitation in the different development stages of the MCS. A detailed analysis of the physical processes contained within the PD shows that it can reflect the three-dimensional moisture variation,vertical wind shear and wind deformation within the MCS. These structures are usually a comprehensive reflection of the characteristics of the surface cold pool, rear inflow jet, downward cold air flow and upward warm moist flow within the precipitating convective cells. For this reason, the PD shows much stronger anomalies in the precipitating atmosphere than the non-precipitating atmosphere, which implies considerable potential for its application in detecting heavy precipitation within MCSs.
基金supported by the Key Program of the Chinese Academy of Sciences (KZZD-EW05)the National Basic Research Program of China (Grant No. 2013CB430105)+1 种基金the Beijing Natural Sciences Foundation (Grant No. 8142035)the National Natural Sciences Foundation of China (Grant No. 41575065)
文摘The non-hydrostatic wave equation set in Cartesian coordinates is rearranged to gain insight into wave generation in a mesoscale severe convection system. The wave equation is characterized by a wave operator on the lhs, and forcing involving three terms—linear and nonlinear terms, and diabatic heating—on the rhs. The equation was applied to a case of severe convection that occurred in East China. The calculation with simulation data showed that the diabatic forcing and linear and nonlinear forcing presented large magnitude at different altitudes in the severe convection region. Further analysis revealed the diabatic forcing due to condensational latent heating had an important influence on the generation of gravity waves in the middle and lower levels. The linear forcing resulting from the Laplacian of potential-temperature linear forcing was dominant in the middle and upper levels. The nonlinear forcing was determined by the Laplacian of potential-temperature nonlinear forcing. Therefore, the forcing of gravity waves was closely associated with the thermodynamic processes in the severe convection case. The reason may be that, besides the vertical component of pressure gradient force, the vertical oscillation of atmospheric particles was dominated by the buoyancy for inertial gravity waves. The latent heating and potential-temperature linear and nonlinear forcing played an important role in the buoyancy tendency. Consequently, these thermodynamic elements influenced the evolution of inertial-gravity waves.
基金supported by the National Natural Science Foundation of China (Grant Nos. 41175060 and 41375052)the Key Program of the Chinese Academy of Sciences (Grant No. KZZD-EW-05)+1 种基金the National Basic Research Program of China (Grant No. 2013CB430105)the State Key Laboratory of Severe Weather (LASW),Chinese Academy of Meteorological Sciences (Grant No. 2013LASW-A06)
文摘NCEP-NCAR reanalysis data were used to analyze the characteristics and evolution mechanism of convective and symmetric instability before and during a heavy rainfall event that occurred in Beijing on 21 July 2012.Approximately twelve hours before the rainstorm,the atmosphere was mainly dominated by convective instability in the lower level of 900-800 hPa.The strong southwesterly low-level jet conveyed the moist and warm airflow continuously to the area of torrential rain,maintaining and enhancing the unstable energy.When the precipitation occurred,unstable energy was released and the convective instability weakened.Meanwhile,due to the baroclinicity enhancement in the atmosphere,the symmetric instability strengthened,maintaining and promoting the subsequent torrential rain.Deriving the convective instability tendency equation demonstrated that the barotropic component of potential divergence and the advection term played a major role in enhancing the convective instability before the rainstorm.Analysis of the tendency equation of moist potential vorticity showed that the coupled term of vertical vorticity and the baroclinic component of potential divergence was the primary factor influencing the development of symmetric instability during the precipitation.Comparing the effects of these factors on convective instability and symmetric instability showed some correlation.
基金supported by the National Key Research and Development Program on the Monitoring,Early Warning and Prevention of Major Natural Disasters[grant number 2018YFC1507104]the National Natural Science Foundation of China[grant numbers 41875079,41875056,and 41975137]a Key Technology Research project on multi-source meteorological data fusion in medium and small basins[grant number DSJ-KY-2021-004].
基金The authors were supported by the National Key Research and Development Program on the Monitoring,Early Warning and Prevention of Major Natural Disasters[grant number 2018YFC1507104]the Flexible Talents Introducing Project of Xinjiang(2019).
基金supported by the Strategic Priority Research Program of the Chinese Academy of Sciences grant number XDA17010105the National Key Research and Development Program grant number2018YFC1507104+3 种基金the Key Scientific and Technology Research and Development Program of Jilin Province grant number 20180201035SFthe National Natural Sciences Foundation of China grant numbers417751404157506541790471。
基金the Strategic Pilot Science and Technology Special Program of the Chinese Academy of Sciences(Grant No.XDA17010105)the National Key Research and Development Project(Grant No.2018YFC1507104)+1 种基金the Key Scientific and Technology Research and Development Program of Jilin Province(Grant No.20180201035SF)the National Natural Science Foundation of China(Grant Nos.41875056,41775140,42075013 and 41575065).
文摘In this study,the ability of the Weather Research and Forecasting(WRF)model to generate accurate near-surface wind speed forecasts at kilometer-to subkilometer-scale resolution along race tracks(RTs)in Chongli during the wintertime is evaluated.The performance of two postprocessing methods,including the decaying-averaging(DA)and analogy-based(AN)methods,is tested to calibrate the near-surface wind speed forecasts.It is found that great uncertainties exist in the model’s raw forecasts of the near-surface wind speed in Chongli.Improvement of the forecast accuracy due to refinement of the horizontal resolution from kilometer to subkilometer scale is limited and not systematic.The RT sites tend to have large bias and centered root mean square error(CRMSE)values and also exhibit notable underestimation of high-wind speeds,notable overestimation or underestimation of the near-surface wind speed at high altitudes,and notable underestimation during daytime.These problems are not resolved by increasing the horizontal resolution and are even exacerbated,which leads to great challenges in the accurate forecasting of the near-surface wind speed in the competition areas in Chongli.The application of postprocessing methods can greatly improve the forecast accuracy of near-surface wind speed.Both methods used in this study have comparable abilities in reducing the(positive or negative)bias,while the AN method is also capable of decreasing the random error reflected by CRMSE.In particular,the large biases for high-wind speeds,wind speeds at high-altitude stations,and wind speeds during the daytime at RT stations can be evidently reduced.
基金supported by the Strategic Priority Research Program of the Chinese Academy of Sciences grant numbers XDA17010105and XDA20100304the National Key Research and Development Program grant numbers 2018YFC1507104 and 2019YFC1510400+1 种基金the Key Projects of Jilin Province Science and Technology Development Plan grant numbers 20180201035SFthe National Natural Science Foundation of China grant numbers 41775140 and 41790471。
基金supported by the second Tibetan Plateau Scientific Expedition and Research Program (STEP,2019QZKK0606,2019QZKK0604)the National Natural Science Foundation of China (Grant No.41875183)。
文摘As part of“The Earth Summit Mission-2022”during the second Tibetan Plateau Scientific Expedition and Research(STEP)in April and May 2022,we conducted the ozone sounding experiment(an ozonesonde mated to a radiosonde)at Mt.Qomolangma Base Camp(MQBC;86.85°E,28.14°N;5200 m),a location at an extremely high altitude.A total of ten sounding profiles were obtained between April 30 and May 06,2022,of which seven profiles were above35 km in altitude,with a maximum detection altitude up to 39.0 km.This study presents the temporal variation and vertical distributions of atmospheric temperature,humidity,and ozone during the MQBC campaign.The averaged ozone concentration was high(68.3 ppbv)at the surface and then increased smoothly until peaking(~110 ppbv)in the middle troposphere(approximately 10 km),and afterward,the ozone concentration increased rapidly from the upper troposphere to a maximum of~10 ppmv at~30 km.The enhanced ozone concentration in the middle troposphere was associated with the blocking high pressure,and transport from the southern flank of the Himalayas occurred during the campaign period.The average total ozone column was 291.9±21.4 DU for the seven profiles exceeding 35km in altitude.The ozonesonde measurements were also compared with the vertical ozone profiles retrieved from the space-borne ozone products from the Microwave Limb Sounder(MLS)onboard the Aura satellite and the Atmospheric Infrared Sounder(AIRS)onboard the Aqua satellite.
基金supported by the National Key Research and Development Project(No.2018YFC1507104)Strategic Priority Research Program of the Chinese Academy of Sciences(No.XDA17010105)+1 种基金The Key Scientific and Technology Research and Development Program of Jilin Province(No.20180201035SF)National Natural Science Foundation of China(Grant No.41775140).
文摘The characteristics of the mesoscale gravity waves during a snowfall event on November 30,2018 over the Ili Valley and the northern slope of the Tianshan Mountains are analyzed based on the Weather Research and Forecasting model simulation.The vertical distribution of Ro is similar to that of the residual of the nonlinear balance equation(△NBE),with their high-value areas located over the leeward slope and the fluctuations extending upwardly with time,indicating the characteristics of strong ageostrophy and non-equilibrium of atmospheric motions.In addition,the Ro and(△NBE)are first developed in the lower layers over the leeward slope,revealing that the generation of the gravity waves is closely related to the topography.Thus,the topographic uplifting greatly affects this snowfall,and the ageostrophic motion in the whole troposphere and the lower stratosphere,as well as the unbalanced motions between convergence and divergence over the peak and the leeward slope are conductive to the development of the inertia-gravity waves.In terms of the horizontal scale of the gravity waves,the Barnes’bandpass filter is applied to separate the mesoscale waves and the synoptic-scale basic flow.The vertical distributions of the vorticity and divergence perturbations have a phase difference ofπ/2,indicating the polarization state of gravity waves.The analyses on the sources and sinks of gravity waves by the non-hydrostatic wave equation show that the main forcing term for orographic gravity waves is the second-order nonlinear term,whose magnitude mainly depends on the nonlinear thermal forcing.This term is mainly related to the vertical transport of potential temperature perturbations.During the snowfall,the potential temperature perturbations are mainly caused by the topographic relief and the release of condensation latent heat.Therefore,the gravity waves in this snowfall are caused by the topographic forcing and condensation latent heating.
基金Supported by the Strategic Priority Research Program of Chinese Academy of Sciences(XDA20020201)Breakthrough Project of Strategic Priority Program of Chinese Academy of Sciences(KFZD-SW-426)+2 种基金National Natural Science Foundation of China(41675094 and 41975115)Natural Science Foundation of Shaanxi Province(2021JQ-166)Open Research Fund of Key Laboratory of the Loess Plateau Soil Erosion and Water Process and Control,Ministry of Water Resources of China(HTGY202002)。
文摘Based on multiresource high-resolution in situ and satellite merged observations along with model simulations from the Coordinated Regional Climate Downscaling Experiment(CORDEX),this study first investigated historical changes in extreme temperature and precipitation during the period of 1979-2018 in areas along the Sichuan-Tibet Railway,and then projected the future changes in the frequency and intensity of extreme temperature and precipitation under the RCP(Representative Concentration Pathway)4.5 and 8.5 scenarios.This paper is expected to enhance our understanding of the spatiotemporal variability in the extreme temperature and precipitation along the Sichuan-Tibet Railway,and to provide scientific basis to advance the Sichuan-Tibet Railway construction and operation.The results show that temperatures in the Sichuan-Tibet region display a noticeable warming trend in the past 40 years,and the increase of minimum temperature is significantly higher than that of maximum temperature in the northwest of the region.Significant increase of precipitation is found mainly over the northwest of the Tibetan Plateau.Except for Lhasa and its surrounding areas,precipitation over other areas along the Sichuan-Tibet Railway shows no significant change in the past 40 years,as indicated in five datasets;however,precipitation along the railway has shown a remarkable decrease in the past 20 years in the TRMM satellite dataset.The warm days and nights have clearly increased by 6 and 5 day decade1-for 1979-2019,while cold days and nights have markedly decreased by about 6.6 and 3.6 day decade-1,respectively.In the past 20 years,the areas with increased precipitation from very wet days and extremely wet days are mainly distributed to the north of the Sichuan-Tibet Railway,while in the areas along the railway itself,the very wet days and extremely wet days are decreasing.Under RCPs 4.5 and 8.5,the temperature in the Sichuan-Tibet region will increase significantly,and the frequency of extreme high(low)temperature events in the late 21 st century(2070-2099)will greatly increase(decrease)by about 50%-80%(10%)compared with occurrences in the late 20 th century(1970-1999).Meanwhile,the frequency of very wet days and extremely wet days in the Sichuan-Tibet region will increase by about 2%-19% and 2%-5%,respectively,and the areas along the Sichuan-Tibet Railway will be affected by more extreme high temperature and extreme precipitation events.