Annual Baroclinic Rossby Waves in the Central North Pacific

We analyze XBT data, collected in the central North Pacific under the NORPAX program (TRANSPAC), by means of inverse methods (cross-spectral fit). We separate the data into two parts: a fluctuation with length scales in the order of the dimensions of the North Pacific basin and a wavelike fluctuation with much shorter scales of a few hundred kilometers. At the annual frequency we find the wavelike fluctuation to consist of a random field of first-order baroclinic Rossby waves traveling basically northwest with wavelengths of ∼300 km and phase speeds of ∼1 cm s−1. The group velocity is directed mainly southwest and is of the order of 1 cm s−1. We describe the fields of temperature, pressure, velocity, sea level elevation, and horizontal and vertical particle displacement associated with the annual baroclinic Rossby waves.