Meridional Heat Transport Variability Inferred from Top-of-Atmosphere Radiation and Ocean Heat Content Observations

Zonally averaged meridional heat transport (MHT) is comprised of atmosphere and ocean
heat transports, which can further be decomposed into moist and dry atmospheric heat transports
and individual ocean basin heat transports. While the detailed decomposition shows significant
sensitivity to the state of the climate, the decomposed changes compensate each other, called
Bjerknes compensation, rendering the total planetary MHT relatively stable. The direct
calculation of MHT components requires detailed information about the climate fields. However,
a simple one-dimensional energy balance model allows one to use energy conservation to infer
the MHT from just the top-of-atmosphere (TOA) energy budget and the planetary heat content.
Here we apply this one-dimensional energy balance model to infer monthly planetary MHT
profiles from observational and model datasets of TOA radiation and approximate the planetary
heat content by ocean heat content. Our results show that this method can successfully reproduce
a strong climatological seasonal cycle in MHT. MHT anomalies (MHTa) composited over El-
Niño/La-Niña/Neutral conditions show that ENSO signals are not averaged out by the zonal
average inherent in calculating MHTa. Composite El-Niño/La-Niña events show
northward/southward MHTa concentrated in the northern Tropics with peak MHTa of
approximately 1 PW, which is notable when compared to the peak annual average MHT of 5.8
PW. We also find that monthly MHTa have extreme events with non-Gaussian tails, and we
explore the relationship between large-scale climate variability and extreme MHTa events.