The North Equatorial Counter Current (NECC) is an important component of the tropical Pacific upper-ocean circulation. This current flows against easterly trade winds and transports warm water from the Western Pacific warm pool eastward. Its core follows the latitudinal position of the Intertropical Convergence Zone (ITCZ) – a salient feature of tropical atmospheric circulation characterized by convective clouds and intense rainfall. The trade winds converge towards the ITCZ, creating a local minimum in zonal winds and generating a positive wind stress curl that maintains an eastward current despite the westward winds. That the wind curl associated with the ITCZ is a critical driver of the NECC is well established. However, here we show that the relationship between the ITCZ and the NECC is more complex and involves positive feedback: a stronger NECC transports warmer water from the western Pacific to the east thus increasing SST along its path, intensifying convection within the ITCZ and hence strengthening wind stress curl, further strengthening the NECC. We refer to this large-scale feedback as the Wind curl - Advection - SST - Precipitation (WASP) feedback. To confirm the NECC-ITCZ coupling we conduct numerical simulations using a coupled model (CESM) in which we progressively strengthen the surface Ekman component of the NECC and observe the intensification of the ITCZ and the entire NECC. Consequently, a weak NECC leads to a weak ITCZ, which can contribute to the double ITCZ problem in climate models, since weak wind convergence north of the equator enables stronger convergence to the south.

This dataset is the output of the CESM1.2.2.1. We modified the viscosity to 0.1, 0.02, 10 and 50 times of the control run along the NECC over 130E-90W and 4N-10N.

We ran the model for 100 years and only the last 50 years are collected here.

These data are nc files and need to be opened with programs that support NetCDF files.