Condensation mass sink and intensification of tropical storms
arxiv(2024)
摘要
Intensification of tropical storms measured as the central pressure tendency
represents a subtle imbalance, of the order of 10^-3, between the inflow
and outflow of air in the storm core. Factors driving this imbalance,
especially in cases of rapid intensification, remain elusive. Here, using an
analysis of intensification rates and precipitation in North Atlantic cyclones,
it is shown that the storms on average deepen at a rate with which maximum
local precipitation removes mass from the atmospheric column. Means for
lifetime maximum intensification rate and maximum concurrent precipitation
(multiplied by the acceleration of gravity) are, respectively, 23 and 17
hPa day^-1. This equivalence is not limited to average values: both
intensification rates and precipitation have the same dependence on the inverse
radius of maximum wind. It is further shown using a numerical model that with
the mass sink switched off, storms driven by sensible and latent heat alone
either do not develop at all or develop significantly more slowly reaching
lower maximum intensities. It is discussed that the conclusions of previous
studies about the relative insignificance of the mass sink arose from a
long-standing misinterpretation of mass nonconservation assessments for
assesments of the actual impact of the mass sink on storm dynamics.
Condensation mass sink provides for a fundamental positive feedback between
surface pressure and vertical velocity that was earlier shown to be
instrumental in analytical descriptions of storm intensification. This feedback
allows the storm circulation to get more compact during intensification in
contrast to modeled heat-driven storms that increase their radius of maximum
wind as they intensify. These findings indicate that the condensation mass sink
is a dominant process governing the dynamics of tropical storms.
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