Using NCEP/NCAR reanalysis, the structure of a wintertime typhoon named Nanmadol that landed on Taiwan 4 December, 2004 has been examined in this paper. It is found that Nanmadol looks similar in structure and time ev...Using NCEP/NCAR reanalysis, the structure of a wintertime typhoon named Nanmadol that landed on Taiwan 4 December, 2004 has been examined in this paper. It is found that Nanmadol looks similar in structure and time evolution to summer typhoons;the central part of it is warm and humid, and the convergence is observed in the lower troposphere while there is divergence in the upper troposphere. The differences between wintertime and summertime typhoons are found. The southwest stream flow in the lower troposphere and cyclonic disturbance in the upper troposphere seem significantly weaker in Nanmadol than in summertime typhoons. The EOF analysis performed for sea level pressure (SLP) of Nanmadol shows that about 90% of the total variance of temporal changes in typhoon circulation can be explained by two leading EOF modes of EOF1 and EOF2. EOF1 shows the structure and intensity variations of Nanmadol while EOF2 shows the changes in environmental SLP distributions that influences the moving direction of Nanmadol.展开更多
To investigate whether the Asian monsoon influences tropical cyclone (TC) activity over the South China Sea (SCS), TCs (including tropical storms and typhoons) over the SCS are analyzed using the Joint Typhoon Warning...To investigate whether the Asian monsoon influences tropical cyclone (TC) activity over the South China Sea (SCS), TCs (including tropical storms and typhoons) over the SCS are analyzed using the Joint Typhoon Warning Center dataset from 1945 to 2009. Results show an increasing trend in the frequencies of TC-all (all TCs over the SCS) and TY-all (all typhoons over the SCS), due mainly to an increase in the number of TCs moving into the SCS after development elsewhere. Little change is seen in the number of TCs that form in the SCS. The results of wavelet analysis indicate that the frequency of typhoons (TY) shows a similar oscillation as that of TCs, i.e., a dominant periodicity of 8-16 years around the 1970s for all TC activity, except for TC-mov (TCs that moved into the SCS from the western North Pacific). To examine the relationship between typhoon activity and the summer monsoon, a correlation analysis was performed that considered typhoons, TCs, and five monsoon indexes. The analysis reveals statistically significant negative correlation between the strength of the Southwest Asian summer monsoon and typhoon activity over the SCS, which likely reflects the effect of the monsoon on TC formation in the western North Pacific (WNP) and subsequent movement into the SCS. There is a statistically significant negative correlation between TY-loc (typhoons that developed from TCs formed over the SCS) and the South China Sea summer monsoon and Southeast Asian summer monsoon.展开更多
By using data of serially numbered typhoons in northwestem Pacific and NOAA OLR data and NCEP/NCAR reanalysis data of wind field, based on the statistics and study of the relationship between the calendar years with m...By using data of serially numbered typhoons in northwestem Pacific and NOAA OLR data and NCEP/NCAR reanalysis data of wind field, based on the statistics and study of the relationship between the calendar years with more （or fewer） summer typhoons and ENSO events, we compared the composites of OLR eigenvectors and tropical summer wind fields during E1 Nino and La Nino events with more or fewer than normal summer typhoons, respectively. The results show that, in summer, without remarkable systematic anomalies of Mascarene High and Australia High in South Hemisphere, the anomaly of Walker circulation will dominate and follow the rule of ENSO impacts to atmospheric circulation and typhoon frequency. Otherwise, when systematic anomalies of Australia High appear during the El Nino events, circulation anomalies in the South Hemisphere will dominate, and many more typhoons will occur. In 1999, which is a special year of La Nina events, northward and eastward monsoon was induced by the stronger Mascarene High, and fewer typhoons arose. The typhoon source are regions where weak vertical wind shear, warm pool in westem Pacific and the area with monsoon troughs are overlapping with each other. Finally, this paper analyzes and compares the source locations and ranges of more （fewer） typhoons in the events of El Nino and La Nino, respectively.展开更多
To improve current understanding of the water cycle,energy partitioning and CO2 exchange over hilly zone vegetative land surfaces in the subtropical monsoon environment of southern China,a long-term field experiment o...To improve current understanding of the water cycle,energy partitioning and CO2 exchange over hilly zone vegetative land surfaces in the subtropical monsoon environment of southern China,a long-term field experiment observatory was set up at Ningxiang,eastern Hunan Province.This paper presents a preliminary analysis of the field observations at the observatory collected from August to November 2012.Results show that significant diurnal variations in soil temperature occur only in shallow soil layers(0.05,0.10,and 0.20 m),and that heavy rainfall affects soil moisture in the deep layers(≥ 0.40 m).During the experimental period,significant diurnal variations in albedo,radiation components,energy components,and CO2 flux were observed,but little seasonal variation.Strong photosynthesis in the vegetation canopy enhanced the CO2 absorption and the latent heat released in daylight hours;Latent heat of evaporation was the main consumer of available energy in late summer.Because the field experiment data are demonstrably reliable,the observatory will provide reliable long-term measurements for future investigations of the land-atmosphere interaction over hilly land surfaces in the subtropical monsoon region of southern China.展开更多
The association of typhoon tracks over the western Pacific with the low-frequency wind-field pattern of atmospheric intraseasonal (30-60 days) oscillation at 850 hPa is further studied by using observational data anal...The association of typhoon tracks over the western Pacific with the low-frequency wind-field pattern of atmospheric intraseasonal (30-60 days) oscillation at 850 hPa is further studied by using observational data analyses. Comparative analyses of the composite wind fields at 850 hPa, contrasting the atmospheric intraseasonal oscillation (ISO) with the original circulation, show that the typhoon tracks are closely related to the wind pattern of the ISO but are not obviously related to the original wind fields. Case studies of two typhoons in 2006 also show that the low-frequency wind-field pattern, particularly the maximum-value line (belt) of low-frequency cyclonic vorticity at 850 hPa, is closely related to the typhoon track. Therefore, the lowfrequency circulation pattern and the maximum-value line (belt) of low- frequency cyclonic vorticity at 850hPa can be used to predict typhoon tracks over the northwestern Pacific.展开更多
This study documents the decadal changes of the spring meridional circulation （SMC） over 110°E- 165°E and the relationship between the SMC and summer （June-July-August-September） typhoon activity over th...This study documents the decadal changes of the spring meridional circulation （SMC） over 110°E- 165°E and the relationship between the SMC and summer （June-July-August-September） typhoon activity over the Western North Pacific （WNP） during 1948-2010. The authors found that the SMC was changed after 1969. Before its change, the SMC had no clear relation with the summer typhoon number over the WNP （TNWNP）, but after the change, it has become positively correlated with the TNWNP, with a correlation coefficient of 0.57 be- tween them （above the 99% confidence level）. It was ob- served that after the SMC was changed, the positive tropical sea surface temperature anomaly associated with the SMC was shifted from the Equatorial Eastern Pacific （El Nifio） to the equatorial middle Pacific （El Nifio Mo- doki）; at the same time, the Pacific decadal oscillation （PDO） pattern over the North Pacific, which is associated with the SMC, was enhanced. The SMC and the TNWNP are both modulated by the E1 Nifio Modoki after 1969, so the relationship between them becomes significant.展开更多
The effects of typhoon intrusion on the Guangdong coastal upwelling system were investigated on the basis of in situ CTD （conductivity-temperature-depth） cruise observations and especially upward-looking ADCP （Acou...The effects of typhoon intrusion on the Guangdong coastal upwelling system were investigated on the basis of in situ CTD （conductivity-temperature-depth） cruise observations and especially upward-looking ADCP （Acoustic Doppler Current Profilers） measurements obtained from a comprehensive survey of the Guangdong coastal region carded out by the Chinese Off- shore Investigation and Assessment Project in the summer of 2006. It was found that northeastward geostrophic advection driven by the summer monsoon has a significant near-seabed onshore component adjacent to Shantou, which in conjunction with upper-level offshore Ekman flow, constitutes the canonical Guangdong coastal upwelling system. Further analyses suggested that the Guangdong coastal upwelling system is sensitive to subtle changes in the typhoon intensity and migration pathway. On one hand, as a typhoon approaches from north of the upwelling system （e.g. Typhoon 0604 （Bilis） and Typhoon 0605 （Kaemi）） in the early phase of inmasion, the enhanced southwesterly leads to exceptional enhancement of the onshore flow; i.e., enhanced upwelling. Afterward, irrespective of the forced ocean responses resulting from the stronger local winds （Typhoon 0604） or the moderate typhoon-induced inertial oscillations （Typhoon 0605）, the situation is not conducive to sustaining a stable, persistent upwelling system. On the other hand, when there is typhoon intrusion south of the upwelling system （e.g. Typhoon 0606 （Prapiroon））, the favorable southwesterly tends to be substituted by an anomalous northeasterly, which destroys the traditional coastal upwelling pattern. However, the canonical upwelling system tends to recover within 1-2 days of the typhoon passing.展开更多
As an important channel connecting the East and South China Seas, circulations in the Taiwan Strait are strongly influenced by the East Asian monsoon and the topography of the strait, especially the Taiwan Bank(TWB), ...As an important channel connecting the East and South China Seas, circulations in the Taiwan Strait are strongly influenced by the East Asian monsoon and the topography of the strait, especially the Taiwan Bank(TWB), which is a remarkable topographic feature located at the southern entrance to the strait. Based on a series of pressure gauges deployed roughly 40 km offshore along the western Strait, subtidal sea-level variability under the combined impact of winter monsoon and topography was studied. The analyses show significant along-strait coherences of subtidal sea levels and their coherences with the large-scale monsoon wind for periods from 2 to 14 days. It is suggested that these fluctuations are mainly forced waves driven by the large-scale winds. In addition to the normal cross-shore wind setup, a sea-level setup in the along-strait direction is confirmed, which is induced by the combined forcing of the fluctuating winter monsoon and the blocking of the TWB. A southward current surge driven by a northerly wind event will cause a rising sea level over the TWB inducing a southward alongshore slope anomaly to the north of the TWB and a reversed slope anomaly to the south The subtidal current through the channel to the west of the TWB is found to be influenced by the reversed slope anomalies generated via the along-shore setup.展开更多
基金2006BAC02B, Guangxi meteorologyical bureau research foundation (QK200603)
文摘Using NCEP/NCAR reanalysis, the structure of a wintertime typhoon named Nanmadol that landed on Taiwan 4 December, 2004 has been examined in this paper. It is found that Nanmadol looks similar in structure and time evolution to summer typhoons;the central part of it is warm and humid, and the convergence is observed in the lower troposphere while there is divergence in the upper troposphere. The differences between wintertime and summertime typhoons are found. The southwest stream flow in the lower troposphere and cyclonic disturbance in the upper troposphere seem significantly weaker in Nanmadol than in summertime typhoons. The EOF analysis performed for sea level pressure (SLP) of Nanmadol shows that about 90% of the total variance of temporal changes in typhoon circulation can be explained by two leading EOF modes of EOF1 and EOF2. EOF1 shows the structure and intensity variations of Nanmadol while EOF2 shows the changes in environmental SLP distributions that influences the moving direction of Nanmadol.
基金Supported by the Knowledge Innovation Program of Chinese Academy of Sciences (No. KZCX2-YW-Q11-02)
文摘To investigate whether the Asian monsoon influences tropical cyclone (TC) activity over the South China Sea (SCS), TCs (including tropical storms and typhoons) over the SCS are analyzed using the Joint Typhoon Warning Center dataset from 1945 to 2009. Results show an increasing trend in the frequencies of TC-all (all TCs over the SCS) and TY-all (all typhoons over the SCS), due mainly to an increase in the number of TCs moving into the SCS after development elsewhere. Little change is seen in the number of TCs that form in the SCS. The results of wavelet analysis indicate that the frequency of typhoons (TY) shows a similar oscillation as that of TCs, i.e., a dominant periodicity of 8-16 years around the 1970s for all TC activity, except for TC-mov (TCs that moved into the SCS from the western North Pacific). To examine the relationship between typhoon activity and the summer monsoon, a correlation analysis was performed that considered typhoons, TCs, and five monsoon indexes. The analysis reveals statistically significant negative correlation between the strength of the Southwest Asian summer monsoon and typhoon activity over the SCS, which likely reflects the effect of the monsoon on TC formation in the western North Pacific (WNP) and subsequent movement into the SCS. There is a statistically significant negative correlation between TY-loc (typhoons that developed from TCs formed over the SCS) and the South China Sea summer monsoon and Southeast Asian summer monsoon.
基金Science and Technology Bureau of Xiamen (40275016)
文摘By using data of serially numbered typhoons in northwestem Pacific and NOAA OLR data and NCEP/NCAR reanalysis data of wind field, based on the statistics and study of the relationship between the calendar years with more （or fewer） summer typhoons and ENSO events, we compared the composites of OLR eigenvectors and tropical summer wind fields during E1 Nino and La Nino events with more or fewer than normal summer typhoons, respectively. The results show that, in summer, without remarkable systematic anomalies of Mascarene High and Australia High in South Hemisphere, the anomaly of Walker circulation will dominate and follow the rule of ENSO impacts to atmospheric circulation and typhoon frequency. Otherwise, when systematic anomalies of Australia High appear during the El Nino events, circulation anomalies in the South Hemisphere will dominate, and many more typhoons will occur. In 1999, which is a special year of La Nina events, northward and eastward monsoon was induced by the stronger Mascarene High, and fewer typhoons arose. The typhoon source are regions where weak vertical wind shear, warm pool in westem Pacific and the area with monsoon troughs are overlapping with each other. Finally, this paper analyzes and compares the source locations and ranges of more （fewer） typhoons in the events of El Nino and La Nino, respectively.
基金supported by the Strategic Priority Research Program of Chinese Academy of Sciences(Grant No.XDA05110102)the National Natural Science Foundation of China (Grant No.41075062)the National Basic Research Program of China (Grant No. 2010CB951001)
文摘To improve current understanding of the water cycle,energy partitioning and CO2 exchange over hilly zone vegetative land surfaces in the subtropical monsoon environment of southern China,a long-term field experiment observatory was set up at Ningxiang,eastern Hunan Province.This paper presents a preliminary analysis of the field observations at the observatory collected from August to November 2012.Results show that significant diurnal variations in soil temperature occur only in shallow soil layers(0.05,0.10,and 0.20 m),and that heavy rainfall affects soil moisture in the deep layers(≥ 0.40 m).During the experimental period,significant diurnal variations in albedo,radiation components,energy components,and CO2 flux were observed,but little seasonal variation.Strong photosynthesis in the vegetation canopy enhanced the CO2 absorption and the latent heat released in daylight hours;Latent heat of evaporation was the main consumer of available energy in late summer.Because the field experiment data are demonstrably reliable,the observatory will provide reliable long-term measurements for future investigations of the land-atmosphere interaction over hilly land surfaces in the subtropical monsoon region of southern China.
基金supported by the National Natural Science Foundation of China (Grant No. U0833602)the National Basic Research Program of China (Grant No. 2007CB411805)
文摘The association of typhoon tracks over the western Pacific with the low-frequency wind-field pattern of atmospheric intraseasonal (30-60 days) oscillation at 850 hPa is further studied by using observational data analyses. Comparative analyses of the composite wind fields at 850 hPa, contrasting the atmospheric intraseasonal oscillation (ISO) with the original circulation, show that the typhoon tracks are closely related to the wind pattern of the ISO but are not obviously related to the original wind fields. Case studies of two typhoons in 2006 also show that the low-frequency wind-field pattern, particularly the maximum-value line (belt) of low-frequency cyclonic vorticity at 850 hPa, is closely related to the typhoon track. Therefore, the lowfrequency circulation pattern and the maximum-value line (belt) of low- frequency cyclonic vorticity at 850hPa can be used to predict typhoon tracks over the northwestern Pacific.
基金supported by the National Natural Science Foundation of China(Grant No.41130103)
文摘This study documents the decadal changes of the spring meridional circulation （SMC） over 110°E- 165°E and the relationship between the SMC and summer （June-July-August-September） typhoon activity over the Western North Pacific （WNP） during 1948-2010. The authors found that the SMC was changed after 1969. Before its change, the SMC had no clear relation with the summer typhoon number over the WNP （TNWNP）, but after the change, it has become positively correlated with the TNWNP, with a correlation coefficient of 0.57 be- tween them （above the 99% confidence level）. It was ob- served that after the SMC was changed, the positive tropical sea surface temperature anomaly associated with the SMC was shifted from the Equatorial Eastern Pacific （El Nifio） to the equatorial middle Pacific （El Nifio Mo- doki）; at the same time, the Pacific decadal oscillation （PDO） pattern over the North Pacific, which is associated with the SMC, was enhanced. The SMC and the TNWNP are both modulated by the E1 Nifio Modoki after 1969, so the relationship between them becomes significant.
基金supported by the Chinese Offshore Physical Oceanography and Marine Meteorology Investigation and Assessment Project (Grant No.908-ZC-I-01)the Chinese Main Estuarine Dynamic Sedimentary Processand Its Impacts on Coastal Economic Development (Grant No.908-02-01-04)+2 种基金the Chinese Main Estuarine and the Adjacent Sea Environmental Quality Evaluation (Grant No. 908-02-02-02)the National Natural Science Foundation of China (Grant Nos. 40806013 and 41176031)the China Ocean University Physical Oceanography Key Laboratory Open Fund (Grant No. 200904)
文摘The effects of typhoon intrusion on the Guangdong coastal upwelling system were investigated on the basis of in situ CTD （conductivity-temperature-depth） cruise observations and especially upward-looking ADCP （Acoustic Doppler Current Profilers） measurements obtained from a comprehensive survey of the Guangdong coastal region carded out by the Chinese Off- shore Investigation and Assessment Project in the summer of 2006. It was found that northeastward geostrophic advection driven by the summer monsoon has a significant near-seabed onshore component adjacent to Shantou, which in conjunction with upper-level offshore Ekman flow, constitutes the canonical Guangdong coastal upwelling system. Further analyses suggested that the Guangdong coastal upwelling system is sensitive to subtle changes in the typhoon intensity and migration pathway. On one hand, as a typhoon approaches from north of the upwelling system （e.g. Typhoon 0604 （Bilis） and Typhoon 0605 （Kaemi）） in the early phase of inmasion, the enhanced southwesterly leads to exceptional enhancement of the onshore flow; i.e., enhanced upwelling. Afterward, irrespective of the forced ocean responses resulting from the stronger local winds （Typhoon 0604） or the moderate typhoon-induced inertial oscillations （Typhoon 0605）, the situation is not conducive to sustaining a stable, persistent upwelling system. On the other hand, when there is typhoon intrusion south of the upwelling system （e.g. Typhoon 0606 （Prapiroon））, the favorable southwesterly tends to be substituted by an anomalous northeasterly, which destroys the traditional coastal upwelling pattern. However, the canonical upwelling system tends to recover within 1-2 days of the typhoon passing.
基金supported by National Natural Science Foundation of China(Grant Nos.41476005&U1305231)supported by Chinese Offshore Physical Oceanography and Marine Meteorology Investigation and Assessment Project(Grant No.908-ZC-I-01)
文摘As an important channel connecting the East and South China Seas, circulations in the Taiwan Strait are strongly influenced by the East Asian monsoon and the topography of the strait, especially the Taiwan Bank(TWB), which is a remarkable topographic feature located at the southern entrance to the strait. Based on a series of pressure gauges deployed roughly 40 km offshore along the western Strait, subtidal sea-level variability under the combined impact of winter monsoon and topography was studied. The analyses show significant along-strait coherences of subtidal sea levels and their coherences with the large-scale monsoon wind for periods from 2 to 14 days. It is suggested that these fluctuations are mainly forced waves driven by the large-scale winds. In addition to the normal cross-shore wind setup, a sea-level setup in the along-strait direction is confirmed, which is induced by the combined forcing of the fluctuating winter monsoon and the blocking of the TWB. A southward current surge driven by a northerly wind event will cause a rising sea level over the TWB inducing a southward alongshore slope anomaly to the north of the TWB and a reversed slope anomaly to the south The subtidal current through the channel to the west of the TWB is found to be influenced by the reversed slope anomalies generated via the along-shore setup.
