This study examined the relationship between the boreal spring(April?May) Antarctic Oscillation(AAO) and the North American summer monsoon(NASM)(July?September) for the period of 1979?2008.The results show that these ...This study examined the relationship between the boreal spring(April?May) Antarctic Oscillation(AAO) and the North American summer monsoon(NASM)(July?September) for the period of 1979?2008.The results show that these two systems are closely related.When the spring AAO was stronger than normal,the NASM tended to be weaker,and there was less rainfall over the monsoon region.The opposite NASM situation corresponded to a weaker spring AAO.Further analysis explored the possible mechanism for the delayed impact of the boreal spring AAO on the NASM.It was found that the tropical Atlantic sea surface temperature(SST) plays an important role in the connection between the two phenomena.The variability of the boreal spring AAO can produce anomalous SSTs over the tropical Atlantic.These SST anomalies can persist from spring to summer and can influence the Bermuda High,affecting water vapor transportation to the monsoon region.Through these processes,the boreal spring AAO exerts a significantly delayed impact on the amount of NASM precipitation.Thus,information about the boreal spring AAO is valuable for the prediction of the NASM.展开更多
Even though the degree of damage inflicted by North Atlantic tropical cyclones (TCs) is highly dependent upon track location and proximity to land, the spatial characteristics of TCs are generally understudied. We inv...Even though the degree of damage inflicted by North Atlantic tropical cyclones (TCs) is highly dependent upon track location and proximity to land, the spatial characteristics of TCs are generally understudied. We investigated the spatial relationships between landfall locations and track patterns of all Cape Verde-type landfalling and coastal TCs that have affected the continental coastline of the western Atlantic Basin by region for the period 1851-2008. The degree of recurvature for these TCs increases progressively from the Central America/Caribbean coast (CA) through the Gulf of Mexico (GOM), Florida peninsula (FLOR), and Atlantic (ATL) coasts. The date (month) of occurrence shows similar increases from the GOM through ATL. These patterns for landfall location, track pattern, and occurrence date generally follow the intra-seasonal movement and intensity variations of the Bermuda High (BH), as represented by increasing North Atlantic Oscillation (NAO) index values from CA through FLOR. Analysis suggests that the region of landfall is primarily controlled by two factors: the amplitude of track recurvature and the longitude at which recurvature begins to dominate track shape. Both of these important steering controls are predominantly influenced by the strength and position of the BH, with increasing strength and/or more northeasterly position of the BH progressively driving landfall from Central America through the Gulf of Mexico and the Atlantic seaboard out to the open sea. The paleorecord suggests that the latitudinal position of the BH exerts an important control over the location of hurricane landfall along the western North Atlantic on millennial time scales. This suggests that global warming may result in a northern shift in TC tracks and increased frequency of landfalls in northern locations.展开更多
基金supported by the Key Program of theChinese Academy of Sciences (Grant No. KZCX2-YW-Q03-3)the Special Scientific Research Fund of Meteorological Public Welfare Profession of China (Grant No. GYHY200906018)the Na- tional Basic Research Program of China (Grant No. 2009CB421406)
文摘This study examined the relationship between the boreal spring(April?May) Antarctic Oscillation(AAO) and the North American summer monsoon(NASM)(July?September) for the period of 1979?2008.The results show that these two systems are closely related.When the spring AAO was stronger than normal,the NASM tended to be weaker,and there was less rainfall over the monsoon region.The opposite NASM situation corresponded to a weaker spring AAO.Further analysis explored the possible mechanism for the delayed impact of the boreal spring AAO on the NASM.It was found that the tropical Atlantic sea surface temperature(SST) plays an important role in the connection between the two phenomena.The variability of the boreal spring AAO can produce anomalous SSTs over the tropical Atlantic.These SST anomalies can persist from spring to summer and can influence the Bermuda High,affecting water vapor transportation to the monsoon region.Through these processes,the boreal spring AAO exerts a significantly delayed impact on the amount of NASM precipitation.Thus,information about the boreal spring AAO is valuable for the prediction of the NASM.
文摘Even though the degree of damage inflicted by North Atlantic tropical cyclones (TCs) is highly dependent upon track location and proximity to land, the spatial characteristics of TCs are generally understudied. We investigated the spatial relationships between landfall locations and track patterns of all Cape Verde-type landfalling and coastal TCs that have affected the continental coastline of the western Atlantic Basin by region for the period 1851-2008. The degree of recurvature for these TCs increases progressively from the Central America/Caribbean coast (CA) through the Gulf of Mexico (GOM), Florida peninsula (FLOR), and Atlantic (ATL) coasts. The date (month) of occurrence shows similar increases from the GOM through ATL. These patterns for landfall location, track pattern, and occurrence date generally follow the intra-seasonal movement and intensity variations of the Bermuda High (BH), as represented by increasing North Atlantic Oscillation (NAO) index values from CA through FLOR. Analysis suggests that the region of landfall is primarily controlled by two factors: the amplitude of track recurvature and the longitude at which recurvature begins to dominate track shape. Both of these important steering controls are predominantly influenced by the strength and position of the BH, with increasing strength and/or more northeasterly position of the BH progressively driving landfall from Central America through the Gulf of Mexico and the Atlantic seaboard out to the open sea. The paleorecord suggests that the latitudinal position of the BH exerts an important control over the location of hurricane landfall along the western North Atlantic on millennial time scales. This suggests that global warming may result in a northern shift in TC tracks and increased frequency of landfalls in northern locations.
