This study deals with a unusual cooling event after Typhoon Mujigea passed over the northern South China Sea(SCS) in October 2015. We analyze the satellite sea surface temperature(SST) time series from October 3 to 18...This study deals with a unusual cooling event after Typhoon Mujigea passed over the northern South China Sea(SCS) in October 2015. We analyze the satellite sea surface temperature(SST) time series from October 3 to 18,2015 and find that the cooling process in the coastal ocean had two different stages. The first stage occurred immediately after typhoon passage on October 3, and reached a maximum SST drop of –2℃ on October 7 as the usual cold wake after typhoon. The second stage or the unusual extended cooling event occurred after 7d of the typhoon passage, and lasted for 5d from October 10 to 15. The maximum SST cooling was –4℃ and occurred after 12d of typhoon passage. The mechanism analysis results indicate that after landing and moving northwestward to the Yunnan-Guizhou Plateau(YGP), Typhoon Mujigea(2015) met the westerly wind front on October 5. The lowpressure and positive-vorticity disturbances to the front triggered meridional air flow and low-pressure trough,thus induced a katabatic cold jet downward from the Qinghai-Tibet Plateau(QTP) passing through the YGP to the northwestern SCS. The second cooling reached the maximum SST drop 4d later after the maximum air temperature drop of –9℃ on October 11. The simultaneous air temperature and SST observations at three coastal stations reveal that it is this katabatic cold jet intrusion to lead the unusual SST cooling event.展开更多
A new simulation method for solving dynamic equations for stationary katabatic wind is suggested by the assumption that the turbulent exchange coefficient is a function of height and the effect of the cold sloping sur...A new simulation method for solving dynamic equations for stationary katabatic wind is suggested by the assumption that the turbulent exchange coefficient is a function of height and the effect of the cold sloping surface is a multinomial function of height. Calculated wind profiles agree with observational data at Mizuho Station, Antarctica.展开更多
The Regional Atmospheric Modeling System （RAMS）, which is a non-hydrostatic numerical model, has been used to investigate the impact of terrain shape and large-scale forcing on the Antarctic surface-wind regime, foc...The Regional Atmospheric Modeling System （RAMS）, which is a non-hydrostatic numerical model, has been used to investigate the impact of terrain shape and large-scale forcing on the Antarctic surface-wind regime, focusing on their roles in establishing favorable flow conditions for the formation of katabatic flow jumps. A series of quasi-2D numerical simulations were conducted over idealized slopes representing the slopes of Antarctica during austral winter conditions. Results indicate that the steepness and variations of the underlying slope play a role in the evolution of near-surface flows and thus the formation of katabatic flow jumps. However, large-scale forcing has a more noticeable effect on the occurrence of this small-scale phenomenon by establishing essential upstream and downstream flow conditions, including the upstream supercritical flow, the less stably stratified or unstable layer above the cold katabatic layer, as well as the cold-air pool located near the foot of the slope through an interaction with the underlying topography. Thus, the areas with steep and abrupt change in slopes, e.g. near the coastal areas of the eastern Antarctic, are preferred locations for the occurrence of katabatic flow jumps, especially under supporting synoptic conditions.展开更多
The vertical velocity at the top of Ekman layer caused by katabatic winds is proposed and deduced. By computing actual data we get a distribution of the velocities over Antarctica. The distribution plays a positive ro...The vertical velocity at the top of Ekman layer caused by katabatic winds is proposed and deduced. By computing actual data we get a distribution of the velocities over Antarctica. The distribution plays a positive role in maintaining the cyclone and anticyclone over Antarctica.展开更多
We show that low-level jets(LLJs)occurred in 11 out of 22 radiosonde profiles in late austral summer over the coastal region of the Amundsen Sea Embayment,with ten of the LLJs directed offshore.The LLJs had core speed...We show that low-level jets(LLJs)occurred in 11 out of 22 radiosonde profiles in late austral summer over the coastal region of the Amundsen Sea Embayment,with ten of the LLJs directed offshore.The LLJs had core speeds from 9 to 32 m s^(-1),jet core heights from 80 to 800 m,and were associated with strong,low-level temperature inversions.Seven of the observed offshore LLJs were reasonably simulated by the polar-optimized Weather Research and Forecasting(Polar WRF)model,with output from the model subsequently used to elucidate their generation mechanisms.This study shows that one of the offshore LLJs simulated by the Polar WRF was caused by katabatic winds,while the remaining six were caused by the enhancement of katabatic winds by synoptic forcing in response to a low-pressure system over the Bellingshausen Sea,i.e.,the offshore wind component associated with this system plays a crucial role in the enhancement of the katabatic LLJ.Examination of the Polar WRF output further shows that the LLJs extended over large areas of the Amundsen Sea Embayment,resulting in substantially enhanced near-surface wind speeds over both the Thwaites and Pine Island ice shelves,as well as the open ocean over the continental shelf.The wind-driven forcing associated with the LLJs could perhaps have important impacts on the redistribution of snow over the ice shelves significantly,as well as to affecting sea-ice and ocean circulation variability,including the transport of relatively warm water over the continental shelf to the ice shelf cavities and extension basal melting.展开更多
Analysis of sensible heat flux （ Qh ）, latent heat flux （ Qe ）, Richardson number （Ri） ,bulk transport coefficient （Cd） and katabatic windsare presented by using the meteorological data in the near surface lay...Analysis of sensible heat flux （ Qh ）, latent heat flux （ Qe ）, Richardson number （Ri） ,bulk transport coefficient （Cd） and katabatic windsare presented by using the meteorological data in the near surface layer from an automatic weather station （AWS） in Princess Elizabeth Land, East Antarctica ice sheet and the data of corresponding period at Zhongshan station in 2002. It shows that annual mean air temperature at LGB69 is -25.6℃, which is 16.4℃ lower than that at Zhongshan, where the elevation is lower and located on the coast. The temperature lapse rate is about 1.0℃/110 m for the initial from coast to inland. The turbulence heat flux at LGB69 displays obvious seasonal variations with the average sensible heat flux -17.9 W/m^2 and latent heat flux -0.9 W/m^2. The intensity （Qh ＋ Qe ） of coolling source is - 18.8 W/m^2 meaning the snow surface layer obtains heat from atmosphere. The near surface atmosphere is near-neutral stratified with bulk transport coefficients （Cd） around 2.8 ×10^-3 ,and it is near constant when the wind speed higher than 8 m/s. The speed and the frequency of easterly Katabatic winds at LGB69 were higher than that at Zhongshan Station.展开更多
The net surface snow accumulation on the Antarctic ice sheet is determined by a combination of precipitation, sublimation and wind redistribution. We present a one-year record of hourly snow-height measurements at LGB...The net surface snow accumulation on the Antarctic ice sheet is determined by a combination of precipitation, sublimation and wind redistribution. We present a one-year record of hourly snow-height measurements at LGB69 (70°50'S, 77°04'E, 1850 m a.s.l.). east side of Lambert Glacier basin (LGB), and 4 year record at G3 (70°53'S, 69°52'E, 84 m a.s.l.), Amery Ice Shelf (AIS). The measurements were made with ultrasonic sensors mounted on automatic weather stations installed at two sites. The snow accumulation at LGB69 is approximately 70 cm. Throughout the winter, between April and September, there was little change in surface snow height (SSH) at the two sites. The negative SSH change is due to densification at LGB69, and is due to both ablation and densification at G3. The strongest accumulation at two sites occurred during the period between October and March (accounting for 101.6% at LGB69), with four episodic increasing events occurring during 2002 for LGB69, and eight events during 1999-2002 for G3 (2 to 3 events per year). At LGB69, these episodic events coincided with obvious humidity 'pulses' and decreases of incoming solar radiation as recorded by the AWS. Observations of the total cloud amount at Davis station, 160 km NNE of LGB69, showed good correlation with major accumulation events recorded at LGB69. There was an obvious anti-correlation between the lowest cloud height at Davis and the daily accumulation rate at LGB69. Although there was no correlation over the total year between wind speed and accumulation at LGB69, large individual accumulation events are associated with episodes of strong wind (>7 m/s), we estimate drift snow may contribute to total SSH up to 35%. Strong accumulation events at LGB69 are associated with major storms in the region and inland transport of moist air masses from the coast.展开更多
基金The National Natural Science Foundation of China under contract Nos 41776034,41476009 and41706025the GASI Project under contract Nos GASI-IPOVAI-01-02 and GASI-02-SCS-YGST2-02+1 种基金the Natural Key Research and Development Program of China under contract No 2016YFC1401403the Foundation of Guangdong Province for Outstanding Young Teachers in University under contract No.YQ201588
文摘This study deals with a unusual cooling event after Typhoon Mujigea passed over the northern South China Sea(SCS) in October 2015. We analyze the satellite sea surface temperature(SST) time series from October 3 to 18,2015 and find that the cooling process in the coastal ocean had two different stages. The first stage occurred immediately after typhoon passage on October 3, and reached a maximum SST drop of –2℃ on October 7 as the usual cold wake after typhoon. The second stage or the unusual extended cooling event occurred after 7d of the typhoon passage, and lasted for 5d from October 10 to 15. The maximum SST cooling was –4℃ and occurred after 12d of typhoon passage. The mechanism analysis results indicate that after landing and moving northwestward to the Yunnan-Guizhou Plateau(YGP), Typhoon Mujigea(2015) met the westerly wind front on October 5. The lowpressure and positive-vorticity disturbances to the front triggered meridional air flow and low-pressure trough,thus induced a katabatic cold jet downward from the Qinghai-Tibet Plateau(QTP) passing through the YGP to the northwestern SCS. The second cooling reached the maximum SST drop 4d later after the maximum air temperature drop of –9℃ on October 11. The simultaneous air temperature and SST observations at three coastal stations reveal that it is this katabatic cold jet intrusion to lead the unusual SST cooling event.
文摘A new simulation method for solving dynamic equations for stationary katabatic wind is suggested by the assumption that the turbulent exchange coefficient is a function of height and the effect of the cold sloping surface is a multinomial function of height. Calculated wind profiles agree with observational data at Mizuho Station, Antarctica.
文摘The Regional Atmospheric Modeling System （RAMS）, which is a non-hydrostatic numerical model, has been used to investigate the impact of terrain shape and large-scale forcing on the Antarctic surface-wind regime, focusing on their roles in establishing favorable flow conditions for the formation of katabatic flow jumps. A series of quasi-2D numerical simulations were conducted over idealized slopes representing the slopes of Antarctica during austral winter conditions. Results indicate that the steepness and variations of the underlying slope play a role in the evolution of near-surface flows and thus the formation of katabatic flow jumps. However, large-scale forcing has a more noticeable effect on the occurrence of this small-scale phenomenon by establishing essential upstream and downstream flow conditions, including the upstream supercritical flow, the less stably stratified or unstable layer above the cold katabatic layer, as well as the cold-air pool located near the foot of the slope through an interaction with the underlying topography. Thus, the areas with steep and abrupt change in slopes, e.g. near the coastal areas of the eastern Antarctic, are preferred locations for the occurrence of katabatic flow jumps, especially under supporting synoptic conditions.
文摘The vertical velocity at the top of Ekman layer caused by katabatic winds is proposed and deduced. By computing actual data we get a distribution of the velocities over Antarctica. The distribution plays a positive role in maintaining the cyclone and anticyclone over Antarctica.
基金support from the European Union’s Horizon 2020 research and innovation framework program under Grant No.101003590(PolarRES)funding from the Indian Institute of Technology Kharagpur and the Ministry of Education,Government of India。
文摘We show that low-level jets(LLJs)occurred in 11 out of 22 radiosonde profiles in late austral summer over the coastal region of the Amundsen Sea Embayment,with ten of the LLJs directed offshore.The LLJs had core speeds from 9 to 32 m s^(-1),jet core heights from 80 to 800 m,and were associated with strong,low-level temperature inversions.Seven of the observed offshore LLJs were reasonably simulated by the polar-optimized Weather Research and Forecasting(Polar WRF)model,with output from the model subsequently used to elucidate their generation mechanisms.This study shows that one of the offshore LLJs simulated by the Polar WRF was caused by katabatic winds,while the remaining six were caused by the enhancement of katabatic winds by synoptic forcing in response to a low-pressure system over the Bellingshausen Sea,i.e.,the offshore wind component associated with this system plays a crucial role in the enhancement of the katabatic LLJ.Examination of the Polar WRF output further shows that the LLJs extended over large areas of the Amundsen Sea Embayment,resulting in substantially enhanced near-surface wind speeds over both the Thwaites and Pine Island ice shelves,as well as the open ocean over the continental shelf.The wind-driven forcing associated with the LLJs could perhaps have important impacts on the redistribution of snow over the ice shelves significantly,as well as to affecting sea-ice and ocean circulation variability,including the transport of relatively warm water over the continental shelf to the ice shelf cavities and extension basal melting.
文摘Analysis of sensible heat flux （ Qh ）, latent heat flux （ Qe ）, Richardson number （Ri） ,bulk transport coefficient （Cd） and katabatic windsare presented by using the meteorological data in the near surface layer from an automatic weather station （AWS） in Princess Elizabeth Land, East Antarctica ice sheet and the data of corresponding period at Zhongshan station in 2002. It shows that annual mean air temperature at LGB69 is -25.6℃, which is 16.4℃ lower than that at Zhongshan, where the elevation is lower and located on the coast. The temperature lapse rate is about 1.0℃/110 m for the initial from coast to inland. The turbulence heat flux at LGB69 displays obvious seasonal variations with the average sensible heat flux -17.9 W/m^2 and latent heat flux -0.9 W/m^2. The intensity （Qh ＋ Qe ） of coolling source is - 18.8 W/m^2 meaning the snow surface layer obtains heat from atmosphere. The near surface atmosphere is near-neutral stratified with bulk transport coefficients （Cd） around 2.8 ×10^-3 ,and it is near constant when the wind speed higher than 8 m/s. The speed and the frequency of easterly Katabatic winds at LGB69 were higher than that at Zhongshan Station.
基金This work was supported by the National Natural Science Foundation of China(Grant No.40305007)Ministry of Science and Te chnology of China(2001CB711003)the Chinese Academy of Sciences(Grant No.KZCX2-303).
文摘The net surface snow accumulation on the Antarctic ice sheet is determined by a combination of precipitation, sublimation and wind redistribution. We present a one-year record of hourly snow-height measurements at LGB69 (70°50'S, 77°04'E, 1850 m a.s.l.). east side of Lambert Glacier basin (LGB), and 4 year record at G3 (70°53'S, 69°52'E, 84 m a.s.l.), Amery Ice Shelf (AIS). The measurements were made with ultrasonic sensors mounted on automatic weather stations installed at two sites. The snow accumulation at LGB69 is approximately 70 cm. Throughout the winter, between April and September, there was little change in surface snow height (SSH) at the two sites. The negative SSH change is due to densification at LGB69, and is due to both ablation and densification at G3. The strongest accumulation at two sites occurred during the period between October and March (accounting for 101.6% at LGB69), with four episodic increasing events occurring during 2002 for LGB69, and eight events during 1999-2002 for G3 (2 to 3 events per year). At LGB69, these episodic events coincided with obvious humidity 'pulses' and decreases of incoming solar radiation as recorded by the AWS. Observations of the total cloud amount at Davis station, 160 km NNE of LGB69, showed good correlation with major accumulation events recorded at LGB69. There was an obvious anti-correlation between the lowest cloud height at Davis and the daily accumulation rate at LGB69. Although there was no correlation over the total year between wind speed and accumulation at LGB69, large individual accumulation events are associated with episodes of strong wind (>7 m/s), we estimate drift snow may contribute to total SSH up to 35%. Strong accumulation events at LGB69 are associated with major storms in the region and inland transport of moist air masses from the coast.
