Examination of the strenthening of wintertime mid-latitude westerlies over the North Pacific in the 1970s

Strengthening of the wintertime mid-latitude westerlies over the North Pacific since the mid-1970s is examined in wind velocity and sea level pressure (SLP) fields computed from the ship-report data archived in the Comprehensive Ocean-Atmosphere Data Set. Changes in the observed wind fields between 1966-75 and 1976-85 are consistent with geostrophic winds based on the difference of the SLP fields between the two decades. This fact confirms that the strengthening of wintertime mid-latitude westerlies in the latter decade over the North Pacific occurred in the real world. Wind fields of the annual mean and the other three seasons are also examined by the same method, and the ship-report wind velocity fields for these averages also have features consistent with the wind fields estimated from SLP.