Chapter 7: APPLICATIONS
b) Rain-mediated fluxes
Section 1.5 discussed the heat, freshwater and momentum fluxes
associated with rainfall. These effects are generally ignored in ocean and
coupled models, even though they can have substantial impacts in some
regions and at some times. Even on climate time scales, the net effects can
be significant. For example, for the four months of the TOGA COARE
intensive observing period there was a net sensible heat flux of 6 W m
-2 due
to rainfall (Weller and Anderson, 1996). This may seem insignificant, but
the net heat flux for the same period was only about 20 W m
-2 .
Parameterization of rainfall contributions to air-sea fluxes is moot at this
time because obtaining accurate estimates of rainrates, which vary strongly
in time and space, is so problematic. Even in atmospheric analyses and
coupled models, where rainrates are known for grid-scale averages, the
errors are large. Because of the small spatial scales and large temporal
variability, and the nonlinearity of the rainfall-mediated processes,
parameterization using grid-scale rainrates is not likely to be successful.
c) Spray-mediated fluxes
Under the very high winds in tropical and midlatitude cyclones,
momentum, heat, and moisture fluxes are significantly altered from those
estimated from Monin-Oboukhov similarity profiles, due to the presence of
spray. Spray redistributes air-sea energy fluxes from sensible to latent heat,
and it enhances the momentum flux from the atmosphere to the ocean
(Section 6.2). Both positive and negative feedbacks are involved with spray
modification of heat and momentum fluxes (Zhang and Perrie, 2001).
Because the effects of spray are not completely understood and well
modeled, it remains undecided whether tropical cyclones may become more
intense due to spray (Andreas and Emmanuel, 2001; Wang et al., 2001).
Air-sea fluxes within extratropical cyclones are apparently altered by
spray effects, leading to changes in surface winds and rainfall within the
storms. Meirink (2002) compared latent and sensible heat fluxes in modeled
North Sea storms with and without spray effects using a parameterization
based on Makin (1998) and Andreas (1998). Maximum differences of latent
fluxes were over 100 W m
-2 , while sensible heat flux differences were
reduced by comparable amounts. The net heat flux difference was as large as
50 W m
-2 . Because of enhanced evaporation, the inclusion of spray effects
resulted in an increase in rainfall by as much as 7 mm d
-1 .
499
b) Rain-mediated fluxes
Section 1.5 discussed the heat, freshwater and momentum fluxes
associated with rainfall. These effects are generally ignored in ocean and
coupled models, even though they can have substantial impacts in some
regions and at some times. Even on climate time scales, the net effects can
be significant. For example, for the four months of the TOGA COARE
intensive observing period there was a net sensible heat flux of 6 W m
-2 due
to rainfall (Weller and Anderson, 1996). This may seem insignificant, but
the net heat flux for the same period was only about 20 W m
-2 .
Parameterization of rainfall contributions to air-sea fluxes is moot at this
time because obtaining accurate estimates of rainrates, which vary strongly
in time and space, is so problematic. Even in atmospheric analyses and
coupled models, where rainrates are known for grid-scale averages, the
errors are large. Because of the small spatial scales and large temporal
variability, and the nonlinearity of the rainfall-mediated processes,
parameterization using grid-scale rainrates is not likely to be successful.
c) Spray-mediated fluxes
Under the very high winds in tropical and midlatitude cyclones,
momentum, heat, and moisture fluxes are significantly altered from those
estimated from Monin-Oboukhov similarity profiles, due to the presence of
spray. Spray redistributes air-sea energy fluxes from sensible to latent heat,
and it enhances the momentum flux from the atmosphere to the ocean
(Section 6.2). Both positive and negative feedbacks are involved with spray
modification of heat and momentum fluxes (Zhang and Perrie, 2001).
Because the effects of spray are not completely understood and well
modeled, it remains undecided whether tropical cyclones may become more
intense due to spray (Andreas and Emmanuel, 2001; Wang et al., 2001).
Air-sea fluxes within extratropical cyclones are apparently altered by
spray effects, leading to changes in surface winds and rainfall within the
storms. Meirink (2002) compared latent and sensible heat fluxes in modeled
North Sea storms with and without spray effects using a parameterization
based on Makin (1998) and Andreas (1998). Maximum differences of latent
fluxes were over 100 W m
-2 , while sensible heat flux differences were
reduced by comparable amounts. The net heat flux difference was as large as
50 W m
-2 . Because of enhanced evaporation, the inclusion of spray effects
resulted in an increase in rainfall by as much as 7 mm d
-1 .
499