Estimate of contribution of near-inertial waves to the velocity shear in the Bay of Bengal based on mooring observations from2013 to 2014

Near-inertial motions contribute most of the velocity shear in the upper ocean.In the Bay of Bengal(BoB),the annual-mean energy flux from the wind to near-inertial motions in the mixed layer in 2013 is dominated by tropical cyclone(TC)processes.However,due to the lack of long-term observations of velocity profiles,our knowledge about interior near-inertial waves(NIWs)as well as their shear features is limited.In this study,we quantified the contribution of NIWs to shear by integrating the wavenumber-frequency spectra estimated from velocity profiles in the upper layers(40-440 m)of the southern Bo B from April 2013 to May 2014.It is shown that the annual-mean proportion of near-inertial shear out of the total is approximately 50%,and the high contribution is mainly due to the enhancement of the TC processes during which the near-inertial shear accounts for nearly 80%of the total.In the steady monsoon seasons,the near-inertial shear is dominant to or at least comparable with the subinertial shear.The contribution of NIWs to the total shear is lower during the summer monsoon than during the winter monsoon owing to more active mesoscale eddies and higher subinertial shear during the summer monsoon.The Doppler shifting of the M_(2)internal tide has little effect on the main results since the proportion of shear from the tidal motions is much lower than that from the near-inertial and subinertial motions.

Sea level anomalies in the northwestern Pacific during 2011 associated with La Nina and negative Indian Ocean Dipole

The sea level anomalies(SLAs)pattern in the northwestern Pacific delineated significant differences between La Ni?a events occurring with and without negative Indian Ocean Dipole(IOD)events.During the pure La Ni?a events,positive the sea surface level anomalies(SLAs)appear in the northwestern Pacific,but SLAs are weakened and negative SLAs appear in the northwestern Pacific under the contribution of the negative IOD events in 2010/2011.The negative IOD events can trigger significant westerly wind anomalies in the western tropical Pacific,which lead to the breakdown of the pronounced positive SLAs in the northwestern Pacific.Meanwhile,negative SLAs excited by the positive wind stress curl near the dateline propagated westward in the form of Rossby waves until it approached the western Pacific boundary in mid-2011,which maintained and enhanced the negative phase of SLAs in the northwestern Pacific and eventually,it could significantly influence the bifurcation and transport of the North Equatorial Current(NEC).