Climatologically, August is the month with the most tropical cyclone(TC) formation over the western North Pacific(WNP) during the typhoon season. In this study, the reason for abnormal TC activity during August is dis...Climatologically, August is the month with the most tropical cyclone(TC) formation over the western North Pacific(WNP) during the typhoon season. In this study, the reason for abnormal TC activity during August is discussed—especially August 2014, when no TCs formed. The large-scale background of August 2014 is presented, with low-level large-scale easterly anomalies and anticyclonic anomalies dominating over the main TC genesis region, a weak monsoon trough system,and a strong WNP subtropical high(WPSH), leading to significantly reduced low-level convergence, upper-level divergence,and mid-level upward motion. These unfavorable large-scale conditions suppressed convection and cyclogenesis. In August2014, equatorial waves were inactive within the negative phase of the Madden–Julian Oscillation(MJO), with fewer tropical disturbances. Although the low-level vorticity and convection of those disturbances were partly promoted by the convective envelopes of equatorial waves, the integral evolution of disturbances, as well as the equatorial waves, were suppressed when propagating into the negative MJO phase. Moreover, the upper-level potential vorticity(PV) streamers associated with anticyclonic Rossby wave breaking events imported extratropical cold and dry air into the tropics. The peripheral tropospheric dryness and enhanced vertical wind shear by PV streamer intrusion combined with the negative MJO phase were responsible for the absence of TC formation over the WNP in August 2014.展开更多
本文基于GRAPES全球模式的短期预报误差样本，利用赤道波动正规模态研究了热带风、压场平衡特征，并根据这些特征分析了线性平衡方程（LBE）在该区域应用时存在的问题。结果表明：（1）赤道波动能成功解释热带短期预报误差样本的大部分...本文基于GRAPES全球模式的短期预报误差样本，利用赤道波动正规模态研究了热带风、压场平衡特征，并根据这些特征分析了线性平衡方程（LBE）在该区域应用时存在的问题。结果表明：（1）赤道波动能成功解释热带短期预报误差样本的大部分分量，对流层中层为60%～80%，对流层顶和平流层低层为80%以上。（2）在可解释的误差方差中，赤道罗斯贝波（ER）占比仅为30%～55%，其他赤道波动的作用不可忽视。（3）在ER模态基础上引入其他赤道波动会大幅削弱原有风、压场平衡约束，重力惯性波与Kelvin波的作用最为显著。此时，对流层中层位势高度h与u风、v风间的约束接近于零，而平流层低层h–u的平衡特征由Kelvin波主导。（4）LBE主要表达了 ER 模态下的风、压场平衡特征，与实际情形相比高估了热带风、压场的耦合程度，进一步的改进中需削弱这一虚假平衡，使得热带风、压场分析变得更加独立。展开更多
The Chinese Academy of Meteorological Sciences developed a Climate System Model(CAMS-CSM) to participate in the upcoming Coupled Model Intercomparison Project phase 6(CMIP6). In this study, we assessed the model perfo...The Chinese Academy of Meteorological Sciences developed a Climate System Model(CAMS-CSM) to participate in the upcoming Coupled Model Intercomparison Project phase 6(CMIP6). In this study, we assessed the model performance in simulating the convectively coupled equatorial waves(CCEWs) by comparing the daily output of precipitation from a 23-yr coupled run with the observational precipitation data from Global Precipitation Climatology Project(GPCP). Four dominant modes of CCEWs including the Kelvin, equatorial Rossby(ER), mixed Rossby–gravity(MRG), tropical depression-type(TD-type) waves, and their annual mean and seasonal cycle characteristics are investigated respectively. It is found that the space–time spectrum characteristics of each wave mode represented by tropical averaged precipitation could be very well simulated by CAMS-CSM, including the magnitudes and the equivalent depths. The zonal distribution of wave associated precipitation is also well simulated, with the maximum centers over the Indian Ocean and the Pacific Ocean. However, the meridional distribution of the wave activities is poorly simulated, with the maximum centers shifted from the Northern Hemisphere to the Southern Hemisphere, especially the Kelvin, MRG, and TD waves. The seasonal cycle of each wave mode is generally captured by the model, but their amplitudes over the Southern Hemisphere during boreal winter are grossly overestimated. The reason for the excessive wave activity over the southern Pacific Ocean in the simulation is discussed.展开更多
By means of the numerical method,the tropical air-sea interaction waves are studied.The results show that when the Kelvin waves are filtered out and only the equatorial Rossby waves are reserved both in the atmosphere...By means of the numerical method,the tropical air-sea interaction waves are studied.The results show that when the Kelvin waves are filtered out and only the equatorial Rossby waves are reserved both in the atmosphere and in the ocean,the disturbances can also propagate eastward because of the air-sea interaction.The critical wavelength of the eastward propagating waves is related to the intensity of the air-sea interaction.The stronger the air-sea interaction,the larger the eastward propagating components of the air-sea interaction waves.The results of the numerical experiments are in good agreement with those of the theoretical analysis(Chao and Zhang,1988).展开更多
The effects of zonally varying mean state of equatorial Pacific on planetaryequatorial trapped waves were analytically investigated. A WKB approximation was used with the slowzonal variation hypothesis, acceptable in ...The effects of zonally varying mean state of equatorial Pacific on planetaryequatorial trapped waves were analytically investigated. A WKB approximation was used with the slowzonal variation hypothesis, acceptable in the context of equatorial trapped low-frequencyvariability, and a working space transformation was made to turn the meridional trappedlow-frequency variability, and a working space transformation was made to turn the meridional modeequation into the Weber-Hermite equation in the new space. The inhomoge-neous equatorial wave ductwas proposed and the theoretical results were compared with observation. It matches the real stateof the equatorial Pacific to a certain degree.展开更多
The quasi-biennial oscillation is the primary mode of variability of the equatorial mean zonal wind in the lower stratosphere, which is characterized by downward propagating easterly and westerly wind regimes from 10 ...The quasi-biennial oscillation is the primary mode of variability of the equatorial mean zonal wind in the lower stratosphere, which is characterized by downward propagating easterly and westerly wind regimes from 10 hPa level with a period approximately 28 months. The effects of the stratospheric quasi-biennial oscillation in zonal winds (SQBO) are not only confined to atmospheric dynamics but also seen in the chemical constituent (trace gases) anomalies such as ozone, water vapor, carbon monoxide and methane in the lower stratosphere. In this study, we examined the SQBO and associated ozone quasi-biennial oscillation (OQBO) using the chemistry-climate model CHASER (MIROC-ESM) simulations and ECMWF ERA-Interim ozone reanalysis for the period 2000-2015. We used lower stratospheric zonal wind from the radiosonde observations and total column ozone (TCO) from Aura Satellite (OMI Instruments) over Singapore to compare the SQBO and OQBO phases with model and reanalysis. The SQBO shows large variations in magnitude and periodicity during the period of study and the amplitude of OQBO also changes in accordance with the westerly (+ve ozone anomaly) and easterly (-ve ozone anomaly) phases of SQBO. During the Westerly phase of Ozone QBO (WQBO) corresponds to average positive total ozone anomaly of ~10 DU and in the Easterly phase of Ozone QBO (EQBO) corresponds to an average negative total ozone anomaly ~−10 DU in the tropical lower stratosphere. Since the SQBO phases were explained by the vertical propagations of Mixed-Ross by Gravity (MRG) waves and Kelvin waves, the correlation of ozone volume mixing ratio with zonal and vertical velocities gives quasi-biennial signals, which indicate the OQBO mechanism more related to dynamical transport than the stratospheric photochemical variations. Since the average amplitude of OQBO phases gives ~+/−10 DU from the observations during easterly and westerly phases SQBO, we need more research focused on the dynamical transport than the photochemical change展开更多
The characteristics of the response of equatorial Pacific upper ocean current to westerly wind bursts(WWB)were analyzed in the frequency domain by using wind and ADCP data collected by the Shiyan3 during TOGA-COARE IO...The characteristics of the response of equatorial Pacific upper ocean current to westerly wind bursts(WWB)were analyzed in the frequency domain by using wind and ADCP data collected by the Shiyan3 during TOGA-COARE IOP,1992-1993.The preliminary results showed that the response consistedof an eastward surface jet at shallower than 60m depth,a westward counter current centering near100m and a shear layer between them,with the variations of all three being nonlinear and nearlysynchronous.The oceanic responses in the frequency domain were characterized by occurrences of a remotely forced mixed Rossby-gravity wave with period of 8-10 days in the surface jet andcountercurrent at shallower than 110 m depth,and two locally forced waves with periods of 24 daysand 4-5 days limited in shallower than 70m depth.These fluctuations of the responses depended much more on zonal wind than meridional wind.The results also revealed that the oceanic response toWWB resulted from momentum transport and energy propagation展开更多
基金supported by the National Natural Science Foundation of China (Grant Nos. 41475074, 41775063 and 41475046)
文摘Climatologically, August is the month with the most tropical cyclone(TC) formation over the western North Pacific(WNP) during the typhoon season. In this study, the reason for abnormal TC activity during August is discussed—especially August 2014, when no TCs formed. The large-scale background of August 2014 is presented, with low-level large-scale easterly anomalies and anticyclonic anomalies dominating over the main TC genesis region, a weak monsoon trough system,and a strong WNP subtropical high(WPSH), leading to significantly reduced low-level convergence, upper-level divergence,and mid-level upward motion. These unfavorable large-scale conditions suppressed convection and cyclogenesis. In August2014, equatorial waves were inactive within the negative phase of the Madden–Julian Oscillation(MJO), with fewer tropical disturbances. Although the low-level vorticity and convection of those disturbances were partly promoted by the convective envelopes of equatorial waves, the integral evolution of disturbances, as well as the equatorial waves, were suppressed when propagating into the negative MJO phase. Moreover, the upper-level potential vorticity(PV) streamers associated with anticyclonic Rossby wave breaking events imported extratropical cold and dry air into the tropics. The peripheral tropospheric dryness and enhanced vertical wind shear by PV streamer intrusion combined with the negative MJO phase were responsible for the absence of TC formation over the WNP in August 2014.
文摘本文基于GRAPES全球模式的短期预报误差样本，利用赤道波动正规模态研究了热带风、压场平衡特征，并根据这些特征分析了线性平衡方程（LBE）在该区域应用时存在的问题。结果表明：（1）赤道波动能成功解释热带短期预报误差样本的大部分分量，对流层中层为60%～80%，对流层顶和平流层低层为80%以上。（2）在可解释的误差方差中，赤道罗斯贝波（ER）占比仅为30%～55%，其他赤道波动的作用不可忽视。（3）在ER模态基础上引入其他赤道波动会大幅削弱原有风、压场平衡约束，重力惯性波与Kelvin波的作用最为显著。此时，对流层中层位势高度h与u风、v风间的约束接近于零，而平流层低层h–u的平衡特征由Kelvin波主导。（4）LBE主要表达了 ER 模态下的风、压场平衡特征，与实际情形相比高估了热带风、压场的耦合程度，进一步的改进中需削弱这一虚假平衡，使得热带风、压场分析变得更加独立。
基金Supported by the National Key Research and Development Program of China(2018YFC1505801)National Natural Science Foundation of China(41705059)Startup Fund for Introduced Talents of Nanjing University of Information Science&Technology
文摘The Chinese Academy of Meteorological Sciences developed a Climate System Model(CAMS-CSM) to participate in the upcoming Coupled Model Intercomparison Project phase 6(CMIP6). In this study, we assessed the model performance in simulating the convectively coupled equatorial waves(CCEWs) by comparing the daily output of precipitation from a 23-yr coupled run with the observational precipitation data from Global Precipitation Climatology Project(GPCP). Four dominant modes of CCEWs including the Kelvin, equatorial Rossby(ER), mixed Rossby–gravity(MRG), tropical depression-type(TD-type) waves, and their annual mean and seasonal cycle characteristics are investigated respectively. It is found that the space–time spectrum characteristics of each wave mode represented by tropical averaged precipitation could be very well simulated by CAMS-CSM, including the magnitudes and the equivalent depths. The zonal distribution of wave associated precipitation is also well simulated, with the maximum centers over the Indian Ocean and the Pacific Ocean. However, the meridional distribution of the wave activities is poorly simulated, with the maximum centers shifted from the Northern Hemisphere to the Southern Hemisphere, especially the Kelvin, MRG, and TD waves. The seasonal cycle of each wave mode is generally captured by the model, but their amplitudes over the Southern Hemisphere during boreal winter are grossly overestimated. The reason for the excessive wave activity over the southern Pacific Ocean in the simulation is discussed.
文摘By means of the numerical method,the tropical air-sea interaction waves are studied.The results show that when the Kelvin waves are filtered out and only the equatorial Rossby waves are reserved both in the atmosphere and in the ocean,the disturbances can also propagate eastward because of the air-sea interaction.The critical wavelength of the eastward propagating waves is related to the intensity of the air-sea interaction.The stronger the air-sea interaction,the larger the eastward propagating components of the air-sea interaction waves.The results of the numerical experiments are in good agreement with those of the theoretical analysis(Chao and Zhang,1988).
文摘The effects of zonally varying mean state of equatorial Pacific on planetaryequatorial trapped waves were analytically investigated. A WKB approximation was used with the slowzonal variation hypothesis, acceptable in the context of equatorial trapped low-frequencyvariability, and a working space transformation was made to turn the meridional trappedlow-frequency variability, and a working space transformation was made to turn the meridional modeequation into the Weber-Hermite equation in the new space. The inhomoge-neous equatorial wave ductwas proposed and the theoretical results were compared with observation. It matches the real stateof the equatorial Pacific to a certain degree.
文摘The quasi-biennial oscillation is the primary mode of variability of the equatorial mean zonal wind in the lower stratosphere, which is characterized by downward propagating easterly and westerly wind regimes from 10 hPa level with a period approximately 28 months. The effects of the stratospheric quasi-biennial oscillation in zonal winds (SQBO) are not only confined to atmospheric dynamics but also seen in the chemical constituent (trace gases) anomalies such as ozone, water vapor, carbon monoxide and methane in the lower stratosphere. In this study, we examined the SQBO and associated ozone quasi-biennial oscillation (OQBO) using the chemistry-climate model CHASER (MIROC-ESM) simulations and ECMWF ERA-Interim ozone reanalysis for the period 2000-2015. We used lower stratospheric zonal wind from the radiosonde observations and total column ozone (TCO) from Aura Satellite (OMI Instruments) over Singapore to compare the SQBO and OQBO phases with model and reanalysis. The SQBO shows large variations in magnitude and periodicity during the period of study and the amplitude of OQBO also changes in accordance with the westerly (+ve ozone anomaly) and easterly (-ve ozone anomaly) phases of SQBO. During the Westerly phase of Ozone QBO (WQBO) corresponds to average positive total ozone anomaly of ~10 DU and in the Easterly phase of Ozone QBO (EQBO) corresponds to an average negative total ozone anomaly ~−10 DU in the tropical lower stratosphere. Since the SQBO phases were explained by the vertical propagations of Mixed-Ross by Gravity (MRG) waves and Kelvin waves, the correlation of ozone volume mixing ratio with zonal and vertical velocities gives quasi-biennial signals, which indicate the OQBO mechanism more related to dynamical transport than the stratospheric photochemical variations. Since the average amplitude of OQBO phases gives ~+/−10 DU from the observations during easterly and westerly phases SQBO, we need more research focused on the dynamical transport than the photochemical change
文摘The characteristics of the response of equatorial Pacific upper ocean current to westerly wind bursts(WWB)were analyzed in the frequency domain by using wind and ADCP data collected by the Shiyan3 during TOGA-COARE IOP,1992-1993.The preliminary results showed that the response consistedof an eastward surface jet at shallower than 60m depth,a westward counter current centering near100m and a shear layer between them,with the variations of all three being nonlinear and nearlysynchronous.The oceanic responses in the frequency domain were characterized by occurrences of a remotely forced mixed Rossby-gravity wave with period of 8-10 days in the surface jet andcountercurrent at shallower than 110 m depth,and two locally forced waves with periods of 24 daysand 4-5 days limited in shallower than 70m depth.These fluctuations of the responses depended much more on zonal wind than meridional wind.The results also revealed that the oceanic response toWWB resulted from momentum transport and energy propagation
