Hydrological cycle changes explain weak Snowball Earth storm track
despite increased surface baroclinicity
Simulations show storm tracks were weaker during past cold, icy climates
relative to the modern climate despite increased surface baroclinicity.
Previous work explained the weak storm track using dry
zonally-asymmetric mechanisms associated with orographic forcing. Here
we show zonally-symmetric changes in the hydrological cycle explain the
weak Snowball Earth storm track. According to the moist static energy
framework, the weak storm track is connected to decreased latent heat
flux (evaporation) and meridional surface moist static energy gradient.
The weak storm track can be predicted using the Clausius-Clapeyron
relation and a surface ice albedo. The weak storm track is also
consistent with decreased latent heat release aloft in the tropics,
which decreases upper-tropospheric baroclinicity and Mean Available
Potential Energy, and is significantly correlated with the meridional
surface moist static energy gradient. Our insights may apply to other
climates such as the Last Glacial Maximum.