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| Rain
impacts on the ocean surface damping
the surface waves and generating intense
near-surface mixing. We study the influence
of rainfall of the generation of turbulence
and the subsequent gas flux between
the atmosphere and the ocean. |
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| Small-scale
ocean surface dynamics, including waves and turbulence,
affect global climate through their impact on ocean-atmosphere
exchange. However, the role of rainfall on surface
fluxes, the dynamics of surface waves, and properties
of the marine atmospheric boundary layer have not
been studied in detail. Rough estimates indicate that
a significant percentage of the shear stress at the
ocean surface may be provided, at low wind speed,
by rainfall. In addition, rainfall produces significant
turbulence in the very near surface layers. This turbulence,
in addition to the droplet impacts, disrupts the diffusive
molecular surface layers and therefore has the potential
to greatly influence air-sea gas fluxes. In this work,
laboratory experiments will be performed to directly
measure the turbulence generated by rainfall along
with the air-water gas, momentum, and heat exchange
rates. The role of the dominant parameters such as
rain rate, droplet size, wind speed, shear, and turbulence
will be measured to quantify the mechanisms by which
significant mixing is achieved, and the coupling between
the surface fluxes induced by the wind and that induced
by the rain will be explored. Secondarily, the dynamic
effects of rain-induced stresses on the surface waves
will be investigated, specifically with regard to
the dependence of the droplet impact angle and velocity
(wind speed dependent) on the partition of shear stress
(horizontal) and momentum flux (vertical). These effects
will further be related to the mechanisms responsible
for the surface fluxes. This research is anticipated
to lead to a much-needed, improved understanding of
the transformation of turbulence within the air boundary
layer and fluxes to the upper ocean by rainfall and
the consequent enhanced air-sea gas flux. |
The figure above shows the turbulent Kinetic energy generated
by rainfall on the water surface. One can see both the
KE increase as well as the pnetration rate increase with
higher rain rates.
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