  T Bayr and D Dommenget [J. Climate 26 (2013) 1387] proposed a model of
temperature-driven air redistribution to quantify the ratio between changes of
sea level pressure $p_s$ and mean tropospheric temperature $T_a$ in the
tropics. This model assumes that the height of the tropical troposphere is
isobaric. Here problems with this model are identified. A revised relationship
between $p_s$ and $T_a$ is derived governed by two parameters -- the isobaric
and isothermal heights -- rather than just one. Further insight is provided by
the model of R S Lindzen and S Nigam [J. Atmos. Sci. 44 (1987) 2418], which was
the first to use the concept of isobaric height to relate tropical $p_s$ to air
temperature, and did this by assuming that isobaric height is always around 3
km and isothermal height is likewise near constant. Observational data,
presented here, show that neither of these heights is spatially universal nor
do their mean values match previous assumptions. Analyses show that the ratio
of the long-term changes in $p_s$ and $T_a$ associated with land-sea
temperature contrasts in a warming climate -- the focus of Bayr and Dommenget
[2013] -- is in fact determined by the corresponding ratio of spatial
differences in the annual mean $p_s$ and $T_a$. The latter ratio, reflecting
lower pressure at higher temperature in the tropics, is dominated by meridional
pressure and temperature differences rather than by land-sea contrasts.
Considerations of isobaric heights are shown to be unable to predict either
spatial or temporal variation in $p_s$. As noted by Bayr and Dommenget [2013],
the role of moisture dynamics in generating sea level pressure variation
remains in need of further theoretical investigations.
