One way to test our understanding of the impact of convective processes
on the isotopic composition of water vapor and precipitation is to
analyze the isotopic mesoscale variations during organized convective
systems such as tropical cyclones or squall lines. The goal of this
study is to understand these isotopic mesoscale variations with particular
attention to isotopic signals in near-surface vapor and precipitation
that may be present in observations and in paleoclimate proxies. With
this aim, we run cloud resolving model simulations in radiative-convective
equilibrium in which rotation or wind shear is added, allowing us
to simulate tropical cyclones or squall lines. The simulations capture
the robust aspects of mesoscale isotopic variations in observed cyclones
and squall lines. We interpret these variations using a simple water
budget model for the sub-cloud layer of different parts of the domain.
We find that rain evaporation and rain-vapor diffusive exchanges are
the main drivers of isotopic depletion within cyclones and squall
lines. Horizontal advection spreads isotopic anomalies, thus reshaping
the mesoscale isotopic pattern. Variations in near-surface relative
humidity and wind speed have a significant impact on d-excess variations
within tropical cyclones, but the evaporation of sea spray is not
necessary to explain the observed enrichment in the eye. This study
strengthens our understanding of mesoscale isotopic variability and
provides physical arguments supporting the interpretation of paleoclimate
isotopic archives in tropical regions in terms of past cyclonic activity.