E3 Southern Energy Transportation

Topic

Meridional energy transport is the climate system's response to the latitudinal radiative balance: the tropics absorb more energy than they emit, whereas the poles emit more energy than they absorb. To maintain the climate system's equilibrium in the face of this latitudinal imbalance, meridional energy transport moves energy from the tropics toward the poles via both the atmosphere and the ocean.

Meridional energy transport is calculated at each latitude based on the difference between the energy entering and leaving the atmospheric and oceanic column located at that latitude; the greater this difference, the more energy must be transported across that latitude to maintain the latitudinal radiative balance. When summed across all latitudes, the total meridional energy transport required by the latitudinal radiative balance is on the order of five to six petawatts at mid-latitudes—the point where the accumulated imbalance between the tropics and the poles reaches its peak.

This meridional energy transport is divided between atmospheric and oceanic transport, with the distribution varying by latitude: in the tropics, oceanic transport dominates over atmospheric transport, whereas in mid-latitudes, atmospheric transport dominates—accounting, overall, for nearly eighty percent of all global meridional energy transport.

Within atmospheric transport, there are two distinct mechanisms that move energy toward the poles. The first is mean circulation, comprising the Hadley cell and the Ferrel cell, which transport energy in an organized manner that remains relatively stable over time. The second component consists of extratropical eddies—extratropical cyclones that constantly form and dissipate in mid-latitudes—which transport energy in a much more variable manner (eddy by eddy) rather than through a stable mean circulation like the Hadley or Ferrel cells.

Meridional energy transport does not remain constant as the climate system warms: if the meridional temperature gradient between the tropics and the poles decreases, extratropical eddies—which rely on that very gradient to form—change in intensity; consequently, the efficiency with which atmospheric transport moves energy toward the poles also changes. This shift in the efficiency of meridional energy transport under warming conditions is precisely a key factor in explaining the polar amplification mentioned earlier: the very meridional energy transport that exists to offset the latitudinal imbalance between the tropics and the poles ends up, during warming, responding to a latitudinal imbalance that it itself helps to modify.

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