The Role of Wind Forcing in the Interannual Variability of Upper Layer Heat Balance Components in the North Atlantic

Abstract

Large-scale patterns of wind stress and wind stress curl (WSC) over the North Atlantic undergo significant changes at the interannual-to-decadal scales. These changes also manifest in variability of circulation and thermal state of the upper mixed layer (UML). This paper discusses the influence of wind forcing on interannual variability of the UML heat balance in the North Atlantic in January. It is shown that interannual variability of vertical heat advection at the UML base is largely due to the WSC anomalies over the North Atlantic, excepting the vicinity of western boundary currents, Labrador Sea and tropical latitudes (0–15° N). Changes in the intensity of the UML horizontal advective heat transport in the Subtropical gyre are related to the wind field pattern in the mid-Atlantic with a lag of ~2 years. In the years with anomalously high anticyclonic WSC values over the Subtropical Gyre, the vertical heat advection at the base of the UML intensifies. At the same time the anticyclonic WSC area decreases in meridional dimensions, the excessive oceanic heat release and enhanced UML cooling occur in the North Atlantic. Simultaneously the cyclonic WSC areas increase in the tropical and subpolar latitudes. The North Equatorial Current and the Azores Current also noticeably intensify. Alternatively, in years with low anticyclonic WSC values over the Subtropical Gyre, vertical heat advection at the base of the UML weaken, the anticyclonic WSC area increases in meridional dimensions, moderate oceanic heat release and moderate UML cooling occur in the North Atlantic. Simultaneously the cyclonic WSC areas decrease in the tropical and subpolar latitudes. The North Equatorial Current and the Azores Current also noticeably weaken.