Impacts from SSTs, ENSO, stratospheric QBO and global warming on Hurricanes over the North Atlantic

Processes affecting hurricane development over the North Atlantic like the El Niño Southern Oscillation (ENSO), the stratospheric Quasi-Biennial Oscillation (QBO) and Sea Surface Temperatures (SSTs) are discussed. Global coupled climate model simulations cannot answer directly the question on enhancement of hurricane activities (or its absence) under increased greenhouse gas concentrations because of their too coarse resolution. Therefore large-scale quantities that affect hurricane formation are investigated in a future warmer climate. More frequent or more intense hurricanes are expected from an increase in the local SST, from more latent heat flux from the ocean to the atmosphere, from more westerly winds in the tropical stratosphere that reduces the occurrence of strong easterly phases of the QBO and from a more moist-unstable stratification of the atmosphere. However, a stronger vertical wind shear similar to the difference between El Niño and La Niña events suggests fewer hurricanes in the northern Atlantic. Also a more dry-stable atmosphere would lead to fewer hurricanes. Of the various forcing factors, the impact of wind shear appears to be more decisive, i.e. with a strong wind shear over the tropical Atlantic like during El Niño events strong hurricanes hardly happen while impacts from SSTs over the tropical Atlantic are less significant. As there are some factors favouring an increase of hurricane activity in a future climate and others favouring a decrease, it remains so far difficult to estimate their joint effect and to suggest any decisive trend. The area of hurricane development is limited among others by an increase of vertical wind shear towards the north and south from a minimum at 5-10˚N. This wind shear pattern does not change in a future climate and has the potential of superseding impacts from ocean warming. A need for very long time series for obtaining robust results becomes obvious. Here at least 50 years of data were used

A preliminary analysis of variation of the Kuroshio axis during tropical cyclone

利用卫星高度计资料分析了热带气旋“艾碧“(AbE,9315)、“贝姬“(bECky,9316)、“莫拉克“(MOrAkOT,0309)和“茉莉“(MElOr,0319)对吕宋海峡及其附近海域黑潮流轴的影响。研究表明:1)吕宋海峡附近海域黑潮流轴容易受到热带气旋的影响而发生一定的变化。2)在热带气旋的作用下,黑潮流轴因中尺度涡的变异而变化;当吕宋海峡东侧的暖涡西移时,将使黑潮的流轴向西弯曲,有利于黑潮在该处的入侵。The impacts of tropical cyclones Abe(9315),Becky(9316),Morakot(0309) and Melor(0319) on the Kuroshio axis near the Luzon Strait are analyzed using satellite altimeter data.The results are as follows.1) As affected by tropical cyclone,the Kuroshio axis can be easily shifted.2) Under the influence of tropical cyclone,the Kuroshio axis changes due to the variation of mesoscale eddy.As the warm eddy in the east of the Luzon Strait moves westward,the Kuroshio axis bends to the west,which is conducive to the Kuroshio’s intrusion through the Luzon Strait.高等学校博士学科点专项科研基金项目(20090121110002);国家重点基础研究发展计划项目(2007CB411803、2009CB421208);国家自然科学基金项目(40976013、40821063);中国海洋大学物理海洋教育部重点实验室开放课题(200304

Dynamics of the Loop Current System and Its Effects on Surface and Subsurface Properties in the Gulf of Mexico

Surface circulation in the Gulf of Mexico is dominated by the Loop Current System (LCS), including the Loop Current (LC) and its associated eddies. The Gulf of Mexico (GoM) also displays long-term surface gradients of temperature and salinity due to climatological features including the intrusion of warm, saline waters from the Caribbean Sea and the seasonal deposition of freshwater from the Mississippi River System caused by seasonal increases in snow melt and precipitation over the watershed. This research aims to increase the understanding of the LCS through the investigation of its relationship with these surface gradients. A classification system of LCS interaction with seasonallypresent freshwater is developed to explore how the LCS can deform salinity gradients within the Gulf. Surface advective freshwater flux is calculated by combining satellitederived measurements of sea level anomalies with sea surface salinity from the recent satellite salinity missions, ESA’s Soil Moisture and Ocean Salinity (SMOS) and NASA’s Soil Moisture Active Passive (SMAP), in order to observe lateral movement of low-salinity water throughout the Gulf. Through interaction with the LCS, riverine-sourced freshwater can have numerous fates and redistribution patterns throughout the GoM. The LCS shares the GoM surface with a large mesoscale eddy field, which is investigated through the application of an automatic eddy-tracking algorithm to absolute dynamic topography derived from satellite altimetry and sea surface height from HYbrid Coordinate Ocean Model (HYCOM) simulations. The spatial distribution and temporal evolution of eddy properties, as well as the variation of these surface and subsurface properties between the eastern and western Gulf are analyzed. Surface eddy composite analysis reveals that long-term gradients present in the GoM greatly affect eddy salinity, temperature, and chlorophyll-a concentrations. HYCOM simulations are verified with insitu Argo profile data in order to investigate mean eddy vertical structure, which varies greatly between the eastern and western Gulf of Mexico. The classifications of LCS interaction with low-salinity water presented here offer a new explanation for the multiple fates of Mississippi River waters, and composite analysis of surface and subsurface eddy properties provides an innovative and complete picture of the GoM mesoscale eddy field