Changes between Version 1 and Version 2 of doc/tec/coupled

Timestamp:

May 10, 2016 3:42:45 PM (9 years ago)

Author:

Giersch

Comment:

--

doc/tec/coupled

@@ -1 +1 @@
 [[NoteBox(warn,This site is currently under construction!)]]
+
+= Coupled atmosphere-ocean simulations =
+A coupled mode for the atmospheric and oceanic versions of PALM has been developed in order to allow for studying the interaction between
+turbulent processes in the ABL and OML. The coupling is realized by the online exchange of information at the sea surface (boundary
+conditions) between two PALM runs (one atmosphere and one ocean). The atmospheric model uses a constant flux layer and transfers the
+kinematic surface fluxes of heat and moisture as well as the momentum fluxes to the oceanic model. Flux conservation between the ocean and
+the atmosphere requires an adjustment of the fluxes for the density of water ''ρ'',,l,0,,:
+{{{
+#!Latex
+\begin{align*}
+  &                    \overline{w^{\prime\prime}u^{\prime\prime}}_0\big\vert_{\text{ocean}} = \frac{\rho_0}{\rho_{\mathrm{l},0}} \overline{w^{\prime\prime}u^{\prime\prime}}_0\;,\nonumber\\
+  &
+  \overline{w^{\prime\prime}v^{\prime\prime}}_0\big\vert_{\text{ocean}}
+  = \frac{\rho_0}{\rho_{\mathrm{l},0}}
+  \overline{w^{\prime\prime}v^{\prime\prime}}_0\;.
+\end{align*}
+}}}
+Since evaporation leads to cooling of the surface water, the kinematic flux of heat in the ocean depends on both the atmospheric kinematic surface fluxes of heat and moisture and is calculated by
+{{{
+#!Latex
+\begin{align*}
+  &
+  \overline{w^{\prime\prime}\theta^{\prime\prime}}_0\big\vert_{\text{ocean}}
+  = \frac{\rho_0}{\rho_{\mathrm{l},0}} \frac{c_p}{c_{p, \mathrm{l}}}
+  \left(\overline{w^{\prime\prime}\theta^{\prime\prime}}_0 +
+    \frac{L_\mathrm{V}}{c_p}
+    \overline{w^{\prime\prime}q^{\prime\prime}}_0 \right)\;.
+\end{align*}
+}}}
+Here, ''c'',,p,l,, is the specific heat of water at constant pressure. Since salt does not evaporate, evaporation of water also leads to an increase in salinity in the ocean subsurface. This process is modeled after [#steinhorn1991 Steinhorn (1991)] by a negative (downward) salinity flux at the sea surface:
+{{{
+#!Latex
+\begin{align*}
+  \overline{w^{\prime\prime}S^{\prime\prime}}_0\big\vert_{\text{ocean}} = - \frac{\rho_0}{\rho_{\mathrm{l},0}} \frac{S}{1000\, \mathrm{PSU} - S} \overline{w^{\prime\prime}q^{\prime\prime}}_0\;.
+\end{align*}
+}}}
+Sea surface values of potential temperature and the horizontal velocity components are transferred as surface boundary conditions to
+the atmosphere:
+{{{
+#!Latex
+\begin{align*}
+  & \theta_0 = \theta_0\big\vert_{\text{ocean}}\;,\,u_0 =
+  u_0\big\vert_{\text{ocean}}\;,\,v_0 = v_0\big\vert_{\text{ocean}}.
+\end{align*}
+}}}
+The time steps for atmosphere and ocean are set individually and are not required to be equal. The coupling is then executed at
+a user-prescribed frequency. At the moment, the coupling requires equal extents of the horizontal model domains in both atmosphere and
+ocean. In order to account for the fact that eddies in the ocean are generally smaller but usually have lower velocities than in the
+atmosphere, it is beneficial to use different grid spacings in both models (i.e., finer grid spacing in the ocean model). In this case,
+the coupling is realized by a two-way bi-linear interpolation of the data fields at the sea surface. Furthermore, it is possible to perform
+uncoupled precursor runs for both atmosphere and ocean, followed by a coupled restart run. In this way it is possible to reduce the
+computational load due to different spin-up times in atmosphere and ocean.
+
+As mentioned above, this coupling has been successfully applied for the first time in the recent study of [#esau2014 Esau (2014)]. Furthermore, we would encourage the atmospheric and oceanic scientific community to consider the coupled atmosphere-ocean LES technique for further applications in the future.
+
+== References ==
+
+* [=#steinhorn1991]''' Steinhorn, I.''' 1991. Salt flux and evaporation. J. Phys. Oceanogr. 21: 1681–1683.
+
+* [=#esau2014]''' Esau, I.''' 2014. Indirect air-sea interactions simulated with a coupled turbulence-resolving model. Ocean Dynam. 64: 689–705. [http://dx.doi.org/10.1007/s10236-014-0712-y doi]