An unprecedented cold wave intruded into East Asia in early January 2021 and led to record-breaking or historical extreme low temperatures over vast regions.This study shows that a major stratospheric sudden warming(S...An unprecedented cold wave intruded into East Asia in early January 2021 and led to record-breaking or historical extreme low temperatures over vast regions.This study shows that a major stratospheric sudden warming(SSW)event at the beginning of January 2021 exerted an important influence on this cold wave.The major SSW event occurred on 2 January 2021 and subsequently led to the displacement of the stratospheric polar vortex to the East Asian side.Moreover,the SSW event induced the stratospheric warming signal to propagate downward to the mid-to-lower troposphere,which not only enhanced the blocking in the Urals-Siberia region and the negative phase of the Arctic Oscillation,but also shifted the tropospheric polar vortex off the pole.The displaced tropospheric polar vortex,Ural blocking,and another downstream blocking ridge over western North America formed a distinct inverted omega-shaped circulation pattern(IOCP)in the East Asia-North Pacific sector.This IOCP was the most direct and impactful atmospheric pattern causing the cold wave in East Asia.The IOCP triggered a meridional cell with an upward branch in East Asia and a downward branch in Siberia.The meridional cell intensified the Siberian high and low-level northerly winds,which also favored the invasion of the cold wave into East Asia.Hence,the SSW event and tropospheric circulations such as the IOCP,negative phase of Arctic Oscillation,Ural blocking,enhanced Siberian high,and eastward propagation of Rossby wave eventually induced the outbreak of an unprecedented cold wave in East Asia in early January 2021.展开更多
Two supercold waves straddling 2020 and 2021 successively hit China and caused record-breaking extremely low temperatures.In this study,the distinct features of these two supercold waves are analyzed on the medium-ran...Two supercold waves straddling 2020 and 2021 successively hit China and caused record-breaking extremely low temperatures.In this study,the distinct features of these two supercold waves are analyzed on the medium-range time scale.The blocking pattern from the Kara Sea to Lake Baikal characterized the first cold wave,while the large-scale tilted ridge and trough over the Asian continent featured the second cold wave.Prior to the cold waves,both the northwest and hyperpolar paths of cold air contributed to a zonally extensive cold air accumulation in the key region of Siberia.This might be the primary reason why strong and extensive supercold waves occur even under the Arctic amplification background.The two cold waves straddling 2020 and 2021 exhibited distinct features:(1)the blocking circulation occurred to the north or the east of the Ural Mountains and was not confined only to the Ural Mountains as it was for the earlier cold waves;(2)the collocation of the Asian blocking pattern and the polar vortex deflection towards East Asia preferred the hyperpolar path of cold air accumulation and the subsequent southward outburst;and(3)both high-and low-frequency processes worked in concert,leading to the very intense cold waves.The cold air advance along the northwest path,which coincides with the southeastward intrusion of the Siberian High(SH)front edge,is associated with the high-frequency process,while the cold air movement along the hyperpolar path,which is close to the eastern edge of the SH,is controlled by the low-frequency process.展开更多
A nonhydrostatic numerical model was developed and numerical experiments performed on the interaction of an internal solitary wave （ISW） with a sill, for a two-layer fluid with a diffusive interface. Based on the bl...A nonhydrostatic numerical model was developed and numerical experiments performed on the interaction of an internal solitary wave （ISW） with a sill, for a two-layer fluid with a diffusive interface. Based on the blocking parameter （Br）, the flow was classified into three cases： （1） when bottom topography has little influence on the propagation and spatial structure of the ISW （Br〈0.5）, （2） where the ISW is distorted significantly by the blocking effect of the topography （though no wave breaking occurs, （0.5〈Br〈0.7）, and （3） where the ISW is broken as it encounters and passes over the bottom topography （0.7〈Br）. The numerical results obtained here are consistent with those obtained in laboratory experiments. The breaking process of the incident ISW when Br=0.7 was completely reproduced. Dissipation rate was linearly related to the blocking parameter when B,〈0.7, and the maximum dissipation rate could reach about 34% as Br raised to about 1.0. After that, instead of breaking, more reflection happened. Similarly, breaking induced mixing was also most effective during Br around 1.0, and can be up to 0.16.展开更多
In this paper,the WKB method is used to obtain the nonlinear Schrdinger equation satisfied by nonlinear Rossby wave in the rotational barotropic atmosphere.It is found that the nonlinear Schrdinger equation has an env...In this paper,the WKB method is used to obtain the nonlinear Schrdinger equation satisfied by nonlinear Rossby wave in the rotational barotropic atmosphere.It is found that the nonlinear Schrdinger equation has an envelope solitary wave solution under the condition 1≤m≤2(m the zonal wavenumber),and the phase speed of envelope solitary Rossby wave in the atmosphere is related to the square of its amplitude linearly,that is,the larger the amplitude of envelope solitary Rossby wave,the smaller its propagation speed.Farthermore, the blocking high and cut-off low pressures which are consistent with the observations of blocking in the atmo- sphere are obtained by calculating envelope solitary Rossby wave,and the blocking structures persist more than five days,the results demonstrate that the envelope solitary Rossby wave is a possible mechanism about the formation,maintenance and breakout of blocking in the atmosphere.展开更多
Ning et al. （2015） developed a 2D fully nonlinear potential model to investigate the interaction between focused waves and uniform currents. The effects of uniform current on focusing wave crest, focal time and foca...Ning et al. （2015） developed a 2D fully nonlinear potential model to investigate the interaction between focused waves and uniform currents. The effects of uniform current on focusing wave crest, focal time and focal position were given. As its extension, harmonic energy transfer for focused waves in uniform current is studied using the proposed model by Ning et al. （2015） and Fast Fourier Transformation （FFT） technique in this study. It shows that the strong opposing currents, inducing partial wave blocking and reducing the extreme wave crest, make the nonlinear energy transfer non-reversible in the focusing and defocusing processes. The numerical results also provide an explanation to address the shifts of focal points in consideration of the combination effects of wave nonlinearity and current.展开更多
Under conditions of atmospheric blocking, the presence of a quasi-stationary anticyclone of large amplitude disrupts the normal eastward progression of the synoptic systems. These blockings correspond mainly to a posi...Under conditions of atmospheric blocking, the presence of a quasi-stationary anticyclone of large amplitude disrupts the normal eastward progression of the synoptic systems. These blockings correspond mainly to a positive anomaly of the air pressure. As a result, in the regions affected by the blocking occur several consecutive dry days and temperatures above average. This paper aims to discuss synoptically the atmospheric blocking phenomenon occurred in January and February 2014 in the South Atlantic Ocean, affecting especially the Southeastern Brazil and sectors that depend on the quantity of water for their activities in the region, such as agriculture and electricity generation. The significant population concentration makes this area emphatically vulnerable to long periods of drought, especially during the summer, affecting the water supply for the population. In order to achieve this goal, data of geopotential height at 850/500 hPa, streamlines in 850/500 hPa, pressure, temperature, humidity and wind at surface were evaluated through NCEP/ NCAR reanalysis (CFSRv2—Climate Forecast System Reanalysis Version 2) with 0.2° × 0.2° resolution. The analysis showed that the stationary anticyclone was configured dynamically favorable to blocking in the lower and middle levels of the atmosphere. Thus, atmospheric pressure at mean sea level presented values above normal combined with high average air temperature. By the climatological analysis, it was noted that there were emphatic negative precipitation anomalies over Southeastern Brazil. This atmospheric blocking was characterized as anomalous due to its long duration in a considered rainy season.展开更多
Precipitation over southeastern Lake Baikal features a significant decreasing trend in July and August over 1979–2018 and is closely related to blocking occurrence over central Siberia(45°–70°N,75°–1...Precipitation over southeastern Lake Baikal features a significant decreasing trend in July and August over 1979–2018 and is closely related to blocking occurrence over central Siberia(45°–70°N,75°–115°E).This study investigates the formation and maintenance of anticyclonic and cyclonic wave-breaking(AWB and CWB)blocking events and their climate impacts on precipitation in the southeastern Lake Baikal area.Both AWB and CWB blocking events are characterized by a cold trough deepening from the sub-Arctic region and a ridge amplifying toward its north over central Siberia,as well as an evident Rossby wave train over midlatitude Eurasia.For AWB blocking events,the ridge and trough pair tilts clockwise and the wave train exhibits a zonal distribution.In contrast,ridge and trough pair associated with CWB blocking events leans anticlockwise with larger-scale,meridional,and more anisotropic signatures.Moreover,the incoming Rossby wave energy associated with CWB blocking events is more evident than for AWB blocking events.Therefore,CWB blocking events are more persistent.AWB blocking events produce more extensive and persistent precipitation over the southeastern Lake Baikal area than CWB blocking events,in which moderate above-normal rainfall is seen in the decaying periods of blockings.A significant decreasing trend is found in terms of AWB blocking occurrence over central Siberia,which may contribute to the downward trend of precipitation over southeastern Lake Baikal.展开更多
基金jointly supported by the National Natural Science Foundation of China (Grant Nos.41790471, 41991284, and 41875104)the Strategic Priority Research Program of the Chinese Academy of Sciences (Grant No.XDA20100304).
文摘An unprecedented cold wave intruded into East Asia in early January 2021 and led to record-breaking or historical extreme low temperatures over vast regions.This study shows that a major stratospheric sudden warming(SSW)event at the beginning of January 2021 exerted an important influence on this cold wave.The major SSW event occurred on 2 January 2021 and subsequently led to the displacement of the stratospheric polar vortex to the East Asian side.Moreover,the SSW event induced the stratospheric warming signal to propagate downward to the mid-to-lower troposphere,which not only enhanced the blocking in the Urals-Siberia region and the negative phase of the Arctic Oscillation,but also shifted the tropospheric polar vortex off the pole.The displaced tropospheric polar vortex,Ural blocking,and another downstream blocking ridge over western North America formed a distinct inverted omega-shaped circulation pattern(IOCP)in the East Asia-North Pacific sector.This IOCP was the most direct and impactful atmospheric pattern causing the cold wave in East Asia.The IOCP triggered a meridional cell with an upward branch in East Asia and a downward branch in Siberia.The meridional cell intensified the Siberian high and low-level northerly winds,which also favored the invasion of the cold wave into East Asia.Hence,the SSW event and tropospheric circulations such as the IOCP,negative phase of Arctic Oscillation,Ural blocking,enhanced Siberian high,and eastward propagation of Rossby wave eventually induced the outbreak of an unprecedented cold wave in East Asia in early January 2021.
基金jointly supported by the National Key Research and Development Project (Grant No. 2018YFC1505601)the National Natural Science Foundation of China (Grant No. 41975072)the Strategic Priority Research Program of Chinese Academy of Sciences (Grant No. XDA23090102).
文摘Two supercold waves straddling 2020 and 2021 successively hit China and caused record-breaking extremely low temperatures.In this study,the distinct features of these two supercold waves are analyzed on the medium-range time scale.The blocking pattern from the Kara Sea to Lake Baikal characterized the first cold wave,while the large-scale tilted ridge and trough over the Asian continent featured the second cold wave.Prior to the cold waves,both the northwest and hyperpolar paths of cold air contributed to a zonally extensive cold air accumulation in the key region of Siberia.This might be the primary reason why strong and extensive supercold waves occur even under the Arctic amplification background.The two cold waves straddling 2020 and 2021 exhibited distinct features:(1)the blocking circulation occurred to the north or the east of the Ural Mountains and was not confined only to the Ural Mountains as it was for the earlier cold waves;(2)the collocation of the Asian blocking pattern and the polar vortex deflection towards East Asia preferred the hyperpolar path of cold air accumulation and the subsequent southward outburst;and(3)both high-and low-frequency processes worked in concert,leading to the very intense cold waves.The cold air advance along the northwest path,which coincides with the southeastward intrusion of the Siberian High(SH)front edge,is associated with the high-frequency process,while the cold air movement along the hyperpolar path,which is close to the eastern edge of the SH,is controlled by the low-frequency process.
基金The National Natural Science Foundation of China under contract Nos 41528601 and 41376029the Youth Innovation Promotion Association of Chinese Academy of Sciences under contract No.Y4KY07103Lthe Strategic Priority Research Program of the Chinese Academy of Sciences under contract No.XDA11020101
文摘A nonhydrostatic numerical model was developed and numerical experiments performed on the interaction of an internal solitary wave （ISW） with a sill, for a two-layer fluid with a diffusive interface. Based on the blocking parameter （Br）, the flow was classified into three cases： （1） when bottom topography has little influence on the propagation and spatial structure of the ISW （Br〈0.5）, （2） where the ISW is distorted significantly by the blocking effect of the topography （though no wave breaking occurs, （0.5〈Br〈0.7）, and （3） where the ISW is broken as it encounters and passes over the bottom topography （0.7〈Br）. The numerical results obtained here are consistent with those obtained in laboratory experiments. The breaking process of the incident ISW when Br=0.7 was completely reproduced. Dissipation rate was linearly related to the blocking parameter when B,〈0.7, and the maximum dissipation rate could reach about 34% as Br raised to about 1.0. After that, instead of breaking, more reflection happened. Similarly, breaking induced mixing was also most effective during Br around 1.0, and can be up to 0.16.
文摘In this paper,the WKB method is used to obtain the nonlinear Schrdinger equation satisfied by nonlinear Rossby wave in the rotational barotropic atmosphere.It is found that the nonlinear Schrdinger equation has an envelope solitary wave solution under the condition 1≤m≤2(m the zonal wavenumber),and the phase speed of envelope solitary Rossby wave in the atmosphere is related to the square of its amplitude linearly,that is,the larger the amplitude of envelope solitary Rossby wave,the smaller its propagation speed.Farthermore, the blocking high and cut-off low pressures which are consistent with the observations of blocking in the atmo- sphere are obtained by calculating envelope solitary Rossby wave,and the blocking structures persist more than five days,the results demonstrate that the envelope solitary Rossby wave is a possible mechanism about the formation,maintenance and breakout of blocking in the atmosphere.
基金financially supported by the National Natural Science Foundation of China(Grant Nos.51679036 and 51490672)the Royal Academy of Engineering under the UK-China Industry Academia Partnership Programme(Grant No.UK-CIAPP\73)the Program for New Century Excellent Talents in University(Grant No.NCET-13-0076)
文摘Ning et al. （2015） developed a 2D fully nonlinear potential model to investigate the interaction between focused waves and uniform currents. The effects of uniform current on focusing wave crest, focal time and focal position were given. As its extension, harmonic energy transfer for focused waves in uniform current is studied using the proposed model by Ning et al. （2015） and Fast Fourier Transformation （FFT） technique in this study. It shows that the strong opposing currents, inducing partial wave blocking and reducing the extreme wave crest, make the nonlinear energy transfer non-reversible in the focusing and defocusing processes. The numerical results also provide an explanation to address the shifts of focal points in consideration of the combination effects of wave nonlinearity and current.
文摘Under conditions of atmospheric blocking, the presence of a quasi-stationary anticyclone of large amplitude disrupts the normal eastward progression of the synoptic systems. These blockings correspond mainly to a positive anomaly of the air pressure. As a result, in the regions affected by the blocking occur several consecutive dry days and temperatures above average. This paper aims to discuss synoptically the atmospheric blocking phenomenon occurred in January and February 2014 in the South Atlantic Ocean, affecting especially the Southeastern Brazil and sectors that depend on the quantity of water for their activities in the region, such as agriculture and electricity generation. The significant population concentration makes this area emphatically vulnerable to long periods of drought, especially during the summer, affecting the water supply for the population. In order to achieve this goal, data of geopotential height at 850/500 hPa, streamlines in 850/500 hPa, pressure, temperature, humidity and wind at surface were evaluated through NCEP/ NCAR reanalysis (CFSRv2—Climate Forecast System Reanalysis Version 2) with 0.2° × 0.2° resolution. The analysis showed that the stationary anticyclone was configured dynamically favorable to blocking in the lower and middle levels of the atmosphere. Thus, atmospheric pressure at mean sea level presented values above normal combined with high average air temperature. By the climatological analysis, it was noted that there were emphatic negative precipitation anomalies over Southeastern Brazil. This atmospheric blocking was characterized as anomalous due to its long duration in a considered rainy season.
基金supported by the National Science and Technology Support Program of China (Grant No. 2015BAC03B03)the National Natural Science Foundation of China (Grant Nos. 41861144014, 41630424 and 41875078)
文摘Precipitation over southeastern Lake Baikal features a significant decreasing trend in July and August over 1979–2018 and is closely related to blocking occurrence over central Siberia(45°–70°N,75°–115°E).This study investigates the formation and maintenance of anticyclonic and cyclonic wave-breaking(AWB and CWB)blocking events and their climate impacts on precipitation in the southeastern Lake Baikal area.Both AWB and CWB blocking events are characterized by a cold trough deepening from the sub-Arctic region and a ridge amplifying toward its north over central Siberia,as well as an evident Rossby wave train over midlatitude Eurasia.For AWB blocking events,the ridge and trough pair tilts clockwise and the wave train exhibits a zonal distribution.In contrast,ridge and trough pair associated with CWB blocking events leans anticlockwise with larger-scale,meridional,and more anisotropic signatures.Moreover,the incoming Rossby wave energy associated with CWB blocking events is more evident than for AWB blocking events.Therefore,CWB blocking events are more persistent.AWB blocking events produce more extensive and persistent precipitation over the southeastern Lake Baikal area than CWB blocking events,in which moderate above-normal rainfall is seen in the decaying periods of blockings.A significant decreasing trend is found in terms of AWB blocking occurrence over central Siberia,which may contribute to the downward trend of precipitation over southeastern Lake Baikal.
