Hadley Circulation over the Central Equatorial Pacific observed by the Trans-Pacific Profiler Network

The Trans-Pacific Profiler Network (TPPN) spans the Equatorial Pacific from Indonesia to Peru. It is comprised of 50 MHz and 915 MHz wind profilers and is jointly operated by the NOAA Aeronomy Laboratory and the University of Colorado's Cooperative Institute for Research in Environmental Sciences (CIRES). The observations presented in this paper are based mainly on Christmas Island a small atoll located at 2 degrees north in the Line Islands south of Hawaii.

The gross structure of the meridional winds observed at Christmas Island reveals a distinct annual cycle and vertical stucture which can be related to the local mass circulation associated with the ITCZ located to the north of Christmas Island. Strong southward flow is seen in the upper troposphere (10-15 km) from June through October. At the same time another band of southward flow is found at 5-7 km. Northward flow is found at 8-10 km and below 5 km.

Over the central Pacific the northern ITCZ is most pronounced during northern summer and this accounts for the strong meridional flow observed at Christmas Island at this time of the year. The vertical structure of the meridional flow in the northern summer is not so easily explained but it is likely related to the vertical structure of ITCZ convection. The secondary maiximum of southward flow at 5-7 km is quite remarkable and a robust feature suggestive of a mid-tropospheric divergent outflow emanating from the northern ITCZ.