Topography Effect Of Second Island Chain On Mesoscale Eddies In The North Pacific Subtropical Countercurrent Region

HYCOM global assimilation run (2004-2011) and AVISO satellite sea-surface height(SSH) data are analyzed to investigate mesoscale eddy characteristics in the NorthPacific Subtropical Counter Current (STCC) region. Automate eddy detection methodis used to identify and track mesoscale eddies. In addition, the changes in vortextrajectory, shape, intensity and Rossby number of eddies encountering with the secondIsland chain are investigated. The conclusions demonstrate as follow:Near the second Island chain region, the correlation of SSH between HYCOMdata and AVISO data is higher than0.8, highly larger than the99%significant level.Furthermore, as for the higher resolution of HYCOM data, this paper is mainly basedon HYCOM data, with AVISO data for proof. In the studied STCC region,3171anticyclonic eddies and3214cyclonic ones are detected. Anticyclonic eddies are moreeasy to maintain their features while cyclonic eddies are more easy to dissipate. Theaverage radius of anticyclones in each latitude band is greater than cyclones, bothwith a maximum near22°N. The second Island chain in this paper is from12°N to28°N, which lies beside the maximum zone of eddy activities. The pattern ofclimatology mean eddy kinetic energy (EKE) in the STCC region presentswestward enhancement. However, the EKE west of the Islands chain is30%lowerthan the EKE on the eastern side, indicating the blocking and dissipation effect of theIslands on eddies.Eddies migrate through the Second Island Chain through various paths. About88%of anticyclonic eddies and77%of cyclonic eddies could travel through theislands. Most anticyclones could pass through the Islands as a whole while cyclonestend to split into smaller one during their interaction with Islands. Weak and largeeddies with smaller Rossby number are easier to pass the Islands. Eddies with smaller nonlinear coefficient are more likely to maintain their integrity. Almost allthe eddies lost energy and amplitude after the passing process. Stronger eddies getlarger percent of energy and amplitude loss after traveling through the Islands. If thecenter of a weak and small eddy collides into the island, it is easy to dissipate andlost its shape. If only part of a large eddy encountered an Island, it may stretch andsplit into two smaller eddies, either go through the Islands or get disintegrated.