1 |
jmc |
1.13 |
% $Header: /u/gcmpack/manual/part2/mom_fluxform.tex,v 1.12 2008/01/18 21:26:45 jmc Exp $ |
2 |
adcroft |
1.2 |
% $Name: $ |
3 |
adcroft |
1.1 |
|
4 |
|
|
\section{Flux-form momentum equations} |
5 |
jmc |
1.9 |
\label{sect:flux-form_momentum_equations} |
6 |
edhill |
1.8 |
\begin{rawhtml} |
7 |
|
|
<!-- CMIREDIR:flux-form_momentum_eqautions: --> |
8 |
|
|
\end{rawhtml} |
9 |
adcroft |
1.1 |
|
10 |
|
|
The original finite volume model was based on the Eulerian flux form |
11 |
|
|
momentum equations. This is the default though the vector invariant |
12 |
|
|
form is optionally available (and recommended in some cases). |
13 |
|
|
|
14 |
|
|
The ``G's'' (our colloquial name for all terms on rhs!) are broken |
15 |
|
|
into the various advective, Coriolis, horizontal dissipation, vertical |
16 |
|
|
dissipation and metric forces: |
17 |
|
|
\marginpar{$G_u$: {\bf Gu} } |
18 |
|
|
\marginpar{$G_v$: {\bf Gv} } |
19 |
|
|
\marginpar{$G_w$: {\bf Gw} } |
20 |
|
|
\begin{eqnarray} |
21 |
|
|
G_u & = & G_u^{adv} + G_u^{cor} + G_u^{h-diss} + G_u^{v-diss} + |
22 |
adcroft |
1.2 |
G_u^{metric} + G_u^{nh-metric} \label{eq:gsplit_momu} \\ |
23 |
adcroft |
1.1 |
G_v & = & G_v^{adv} + G_v^{cor} + G_v^{h-diss} + G_v^{v-diss} + |
24 |
adcroft |
1.2 |
G_v^{metric} + G_v^{nh-metric} \label{eq:gsplit_momv} \\ |
25 |
adcroft |
1.1 |
G_w & = & G_w^{adv} + G_w^{cor} + G_w^{h-diss} + G_w^{v-diss} + |
26 |
adcroft |
1.2 |
G_w^{metric} + G_w^{nh-metric} \label{eq:gsplit_momw} |
27 |
adcroft |
1.1 |
\end{eqnarray} |
28 |
|
|
In the hydrostatic limit, $G_w=0$ and $\epsilon_{nh}=0$, reducing the |
29 |
|
|
vertical momentum to hydrostatic balance. |
30 |
|
|
|
31 |
|
|
These terms are calculated in routines called from subroutine {\em |
32 |
jmc |
1.11 |
MOM\_FLUXFORM} a collected into the global arrays {\bf Gu}, {\bf Gv}, |
33 |
adcroft |
1.1 |
and {\bf Gw}. |
34 |
|
|
|
35 |
|
|
\fbox{ \begin{minipage}{4.75in} |
36 |
jmc |
1.11 |
{\em S/R MOM\_FLUXFORM} ({\em pkg/mom\_fluxform/mom\_fluxform.F}) |
37 |
adcroft |
1.1 |
|
38 |
|
|
$G_u$: {\bf Gu} ({\em DYNVARS.h}) |
39 |
|
|
|
40 |
|
|
$G_v$: {\bf Gv} ({\em DYNVARS.h}) |
41 |
|
|
|
42 |
|
|
$G_w$: {\bf Gw} ({\em DYNVARS.h}) |
43 |
|
|
\end{minipage} } |
44 |
|
|
|
45 |
|
|
|
46 |
|
|
\subsection{Advection of momentum} |
47 |
|
|
|
48 |
|
|
The advective operator is second order accurate in space: |
49 |
|
|
\begin{eqnarray} |
50 |
|
|
{\cal A}_w \Delta r_f h_w G_u^{adv} & = & |
51 |
|
|
\delta_i \overline{ U }^i \overline{ u }^i |
52 |
|
|
+ \delta_j \overline{ V }^i \overline{ u }^j |
53 |
adcroft |
1.2 |
+ \delta_k \overline{ W }^i \overline{ u }^k \label{eq:discrete-momadvu} \\ |
54 |
adcroft |
1.1 |
{\cal A}_s \Delta r_f h_s G_v^{adv} & = & |
55 |
|
|
\delta_i \overline{ U }^j \overline{ v }^i |
56 |
|
|
+ \delta_j \overline{ V }^j \overline{ v }^j |
57 |
adcroft |
1.2 |
+ \delta_k \overline{ W }^j \overline{ v }^k \label{eq:discrete-momadvv} \\ |
58 |
adcroft |
1.1 |
{\cal A}_c \Delta r_c G_w^{adv} & = & |
59 |
|
|
\delta_i \overline{ U }^k \overline{ w }^i |
60 |
|
|
+ \delta_j \overline{ V }^k \overline{ w }^j |
61 |
adcroft |
1.2 |
+ \delta_k \overline{ W }^k \overline{ w }^k \label{eq:discrete-momadvw} |
62 |
adcroft |
1.1 |
\end{eqnarray} |
63 |
|
|
and because of the flux form does not contribute to the global budget |
64 |
|
|
of linear momentum. The quantities $U$, $V$ and $W$ are volume fluxes |
65 |
|
|
defined: |
66 |
|
|
\marginpar{$U$: {\bf uTrans} } |
67 |
|
|
\marginpar{$V$: {\bf vTrans} } |
68 |
|
|
\marginpar{$W$: {\bf rTrans} } |
69 |
|
|
\begin{eqnarray} |
70 |
adcroft |
1.2 |
U & = & \Delta y_g \Delta r_f h_w u \label{eq:utrans} \\ |
71 |
|
|
V & = & \Delta x_g \Delta r_f h_s v \label{eq:vtrans} \\ |
72 |
|
|
W & = & {\cal A}_c w \label{eq:rtrans} |
73 |
adcroft |
1.1 |
\end{eqnarray} |
74 |
|
|
The advection of momentum takes the same form as the advection of |
75 |
|
|
tracers but by a translated advective flow. Consequently, the |
76 |
|
|
conservation of second moments, derived for tracers later, applies to |
77 |
|
|
$u^2$ and $v^2$ and $w^2$ so that advection of momentum correctly |
78 |
|
|
conserves kinetic energy. |
79 |
|
|
|
80 |
|
|
\fbox{ \begin{minipage}{4.75in} |
81 |
|
|
{\em S/R MOM\_U\_ADV\_UU} ({\em mom\_u\_adv\_uu.F}) |
82 |
|
|
|
83 |
|
|
{\em S/R MOM\_U\_ADV\_VU} ({\em mom\_u\_adv\_vu.F}) |
84 |
|
|
|
85 |
|
|
{\em S/R MOM\_U\_ADV\_WU} ({\em mom\_u\_adv\_wu.F}) |
86 |
|
|
|
87 |
|
|
{\em S/R MOM\_U\_ADV\_UV} ({\em mom\_u\_adv\_uv.F}) |
88 |
|
|
|
89 |
|
|
{\em S/R MOM\_U\_ADV\_VV} ({\em mom\_u\_adv\_vv.F}) |
90 |
|
|
|
91 |
|
|
{\em S/R MOM\_U\_ADV\_WV} ({\em mom\_u\_adv\_wv.F}) |
92 |
|
|
|
93 |
jmc |
1.11 |
$uu$, $uv$, $vu$, $vv$: {\bf aF} (local to {\em mom\_fluxform.F}) |
94 |
adcroft |
1.1 |
\end{minipage} } |
95 |
|
|
|
96 |
|
|
|
97 |
|
|
|
98 |
|
|
\subsection{Coriolis terms} |
99 |
|
|
|
100 |
|
|
The ``pure C grid'' Coriolis terms (i.e. in absence of C-D scheme) are |
101 |
|
|
discretized: |
102 |
|
|
\begin{eqnarray} |
103 |
|
|
{\cal A}_w \Delta r_f h_w G_u^{Cor} & = & |
104 |
|
|
\overline{ f {\cal A}_c \Delta r_f h_c \overline{ v }^j }^i |
105 |
|
|
- \epsilon_{nh} \overline{ f' {\cal A}_c \Delta r_f h_c \overline{ w }^k }^i \\ |
106 |
|
|
{\cal A}_s \Delta r_f h_s G_v^{Cor} & = & |
107 |
|
|
- \overline{ f {\cal A}_c \Delta r_f h_c \overline{ u }^i }^j \\ |
108 |
|
|
{\cal A}_c \Delta r_c G_w^{Cor} & = & |
109 |
|
|
\epsilon_{nh} \overline{ f' {\cal A}_c \Delta r_f h_c \overline{ u }^i }^k |
110 |
|
|
\end{eqnarray} |
111 |
|
|
where the Coriolis parameters $f$ and $f'$ are defined: |
112 |
|
|
\begin{eqnarray} |
113 |
cnh |
1.4 |
f & = & 2 \Omega \sin{\varphi} \\ |
114 |
|
|
f' & = & 2 \Omega \cos{\varphi} |
115 |
adcroft |
1.1 |
\end{eqnarray} |
116 |
cnh |
1.4 |
where $\varphi$ is geographic latitude when using spherical geometry, |
117 |
adcroft |
1.2 |
otherwise the $\beta$-plane definition is used: |
118 |
adcroft |
1.1 |
\begin{eqnarray} |
119 |
|
|
f & = & f_o + \beta y \\ |
120 |
|
|
f' & = & 0 |
121 |
|
|
\end{eqnarray} |
122 |
|
|
|
123 |
|
|
This discretization globally conserves kinetic energy. It should be |
124 |
|
|
noted that despite the use of this discretization in former |
125 |
|
|
publications, all calculations to date have used the following |
126 |
|
|
different discretization: |
127 |
|
|
\begin{eqnarray} |
128 |
|
|
G_u^{Cor} & = & |
129 |
|
|
f_u \overline{ v }^{ji} |
130 |
|
|
- \epsilon_{nh} f_u' \overline{ w }^{ik} \\ |
131 |
|
|
G_v^{Cor} & = & |
132 |
|
|
- f_v \overline{ u }^{ij} \\ |
133 |
|
|
G_w^{Cor} & = & |
134 |
|
|
\epsilon_{nh} f_w' \overline{ u }^{ik} |
135 |
|
|
\end{eqnarray} |
136 |
|
|
\marginpar{Need to change the default in code to match this} |
137 |
|
|
where the subscripts on $f$ and $f'$ indicate evaluation of the |
138 |
|
|
Coriolis parameters at the appropriate points in space. The above |
139 |
adcroft |
1.3 |
discretization does {\em not} conserve anything, especially energy and |
140 |
|
|
for historical reasons is the default for the code. A |
141 |
|
|
flag controls this discretization: set run-time logical {\bf |
142 |
|
|
useEnergyConservingCoriolis} to {\em true} which otherwise defaults to |
143 |
|
|
{\em false}. |
144 |
adcroft |
1.1 |
|
145 |
|
|
\fbox{ \begin{minipage}{4.75in} |
146 |
|
|
{\em S/R MOM\_CDSCHEME} ({\em mom\_cdscheme.F}) |
147 |
|
|
|
148 |
|
|
{\em S/R MOM\_U\_CORIOLIS} ({\em mom\_u\_coriolis.F}) |
149 |
|
|
|
150 |
|
|
{\em S/R MOM\_V\_CORIOLIS} ({\em mom\_v\_coriolis.F}) |
151 |
|
|
|
152 |
jmc |
1.11 |
$G_u^{Cor}$, $G_v^{Cor}$: {\bf cF} (local to {\em mom\_fluxform.F}) |
153 |
adcroft |
1.1 |
\end{minipage} } |
154 |
|
|
|
155 |
|
|
|
156 |
|
|
\subsection{Curvature metric terms} |
157 |
|
|
|
158 |
|
|
The most commonly used coordinate system on the sphere is the |
159 |
cnh |
1.4 |
geographic system $(\lambda,\varphi)$. The curvilinear nature of these |
160 |
adcroft |
1.1 |
coordinates on the sphere lead to some ``metric'' terms in the |
161 |
|
|
component momentum equations. Under the thin-atmosphere and |
162 |
|
|
hydrostatic approximations these terms are discretized: |
163 |
|
|
\begin{eqnarray} |
164 |
|
|
{\cal A}_w \Delta r_f h_w G_u^{metric} & = & |
165 |
cnh |
1.4 |
\overline{ \frac{ \overline{u}^i }{a} \tan{\varphi} {\cal A}_c \Delta r_f h_c \overline{ v }^j }^i \\ |
166 |
adcroft |
1.1 |
{\cal A}_s \Delta r_f h_s G_v^{metric} & = & |
167 |
cnh |
1.4 |
- \overline{ \frac{ \overline{u}^i }{a} \tan{\varphi} {\cal A}_c \Delta r_f h_c \overline{ u }^i }^j \\ |
168 |
adcroft |
1.1 |
G_w^{metric} & = & 0 |
169 |
|
|
\end{eqnarray} |
170 |
|
|
where $a$ is the radius of the planet (sphericity is assumed) or the |
171 |
|
|
radial distance of the particle (i.e. a function of height). It is |
172 |
|
|
easy to see that this discretization satisfies all the properties of |
173 |
|
|
the discrete Coriolis terms since the metric factor $\frac{u}{a} |
174 |
cnh |
1.4 |
\tan{\varphi}$ can be viewed as a modification of the vertical Coriolis |
175 |
|
|
parameter: $f \rightarrow f+\frac{u}{a} \tan{\varphi}$. |
176 |
adcroft |
1.1 |
|
177 |
|
|
However, as for the Coriolis terms, a non-energy conserving form has |
178 |
|
|
exclusively been used to date: |
179 |
|
|
\begin{eqnarray} |
180 |
cnh |
1.4 |
G_u^{metric} & = & \frac{u \overline{v}^{ij} }{a} \tan{\varphi} \\ |
181 |
|
|
G_v^{metric} & = & \frac{ \overline{u}^{ij} \overline{u}^{ij}}{a} \tan{\varphi} |
182 |
adcroft |
1.1 |
\end{eqnarray} |
183 |
cnh |
1.4 |
where $\tan{\varphi}$ is evaluated at the $u$ and $v$ points |
184 |
adcroft |
1.1 |
respectively. |
185 |
|
|
|
186 |
|
|
\fbox{ \begin{minipage}{4.75in} |
187 |
|
|
{\em S/R MOM\_U\_METRIC\_SPHERE} ({\em mom\_u\_metric\_sphere.F}) |
188 |
|
|
|
189 |
|
|
{\em S/R MOM\_V\_METRIC\_SPHERE} ({\em mom\_v\_metric\_sphere.F}) |
190 |
|
|
|
191 |
jmc |
1.11 |
$G_u^{metric}$, $G_v^{metric}$: {\bf mT} (local to {\em mom\_fluxform.F}) |
192 |
adcroft |
1.1 |
\end{minipage} } |
193 |
|
|
|
194 |
|
|
|
195 |
|
|
|
196 |
|
|
\subsection{Non-hydrostatic metric terms} |
197 |
|
|
|
198 |
|
|
For the non-hydrostatic equations, dropping the thin-atmosphere |
199 |
|
|
approximation re-introduces metric terms involving $w$ and are |
200 |
cnh |
1.6 |
required to conserve angular momentum: |
201 |
adcroft |
1.1 |
\begin{eqnarray} |
202 |
|
|
{\cal A}_w \Delta r_f h_w G_u^{metric} & = & |
203 |
|
|
- \overline{ \frac{ \overline{u}^i \overline{w}^k }{a} {\cal A}_c \Delta r_f h_c }^i \\ |
204 |
|
|
{\cal A}_s \Delta r_f h_s G_v^{metric} & = & |
205 |
|
|
- \overline{ \frac{ \overline{v}^j \overline{w}^k }{a} {\cal A}_c \Delta r_f h_c}^j \\ |
206 |
|
|
{\cal A}_c \Delta r_c G_w^{metric} & = & |
207 |
|
|
\overline{ \frac{ {\overline{u}^i}^2 + {\overline{v}^j}^2}{a} {\cal A}_c \Delta r_f h_c }^k |
208 |
|
|
\end{eqnarray} |
209 |
|
|
|
210 |
|
|
Because we are always consistent, even if consistently wrong, we have, |
211 |
|
|
in the past, used a different discretization in the model which is: |
212 |
|
|
\begin{eqnarray} |
213 |
|
|
G_u^{metric} & = & |
214 |
|
|
- \frac{u}{a} \overline{w}^{ik} \\ |
215 |
|
|
G_v^{metric} & = & |
216 |
|
|
- \frac{v}{a} \overline{w}^{jk} \\ |
217 |
|
|
G_w^{metric} & = & |
218 |
|
|
\frac{1}{a} ( {\overline{u}^{ik}}^2 + {\overline{v}^{jk}}^2 ) |
219 |
|
|
\end{eqnarray} |
220 |
|
|
|
221 |
|
|
\fbox{ \begin{minipage}{4.75in} |
222 |
|
|
{\em S/R MOM\_U\_METRIC\_NH} ({\em mom\_u\_metric\_nh.F}) |
223 |
|
|
|
224 |
|
|
{\em S/R MOM\_V\_METRIC\_NH} ({\em mom\_v\_metric\_nh.F}) |
225 |
|
|
|
226 |
jmc |
1.11 |
$G_u^{metric}$, $G_v^{metric}$: {\bf mT} (local to {\em mom\_fluxform.F}) |
227 |
adcroft |
1.1 |
\end{minipage} } |
228 |
|
|
|
229 |
|
|
|
230 |
|
|
\subsection{Lateral dissipation} |
231 |
|
|
|
232 |
|
|
Historically, we have represented the SGS Reynolds stresses as simply |
233 |
|
|
down gradient momentum fluxes, ignoring constraints on the stress |
234 |
|
|
tensor such as symmetry. |
235 |
|
|
\begin{eqnarray} |
236 |
|
|
{\cal A}_w \Delta r_f h_w G_u^{h-diss} & = & |
237 |
|
|
\delta_i \Delta y_f \Delta r_f h_c \tau_{11} |
238 |
|
|
+ \delta_j \Delta x_v \Delta r_f h_\zeta \tau_{12} \\ |
239 |
|
|
{\cal A}_s \Delta r_f h_s G_v^{h-diss} & = & |
240 |
|
|
\delta_i \Delta y_u \Delta r_f h_\zeta \tau_{21} |
241 |
|
|
+ \delta_j \Delta x_f \Delta r_f h_c \tau_{22} |
242 |
|
|
\end{eqnarray} |
243 |
|
|
\marginpar{Check signs of stress definitions} |
244 |
|
|
|
245 |
|
|
The lateral viscous stresses are discretized: |
246 |
|
|
\begin{eqnarray} |
247 |
cnh |
1.4 |
\tau_{11} & = & A_h c_{11\Delta}(\varphi) \frac{1}{\Delta x_f} \delta_i u |
248 |
|
|
-A_4 c_{11\Delta^2}(\varphi) \frac{1}{\Delta x_f} \delta_i \nabla^2 u \\ |
249 |
|
|
\tau_{12} & = & A_h c_{12\Delta}(\varphi) \frac{1}{\Delta y_u} \delta_j u |
250 |
|
|
-A_4 c_{12\Delta^2}(\varphi)\frac{1}{\Delta y_u} \delta_j \nabla^2 u \\ |
251 |
|
|
\tau_{21} & = & A_h c_{21\Delta}(\varphi) \frac{1}{\Delta x_v} \delta_i v |
252 |
|
|
-A_4 c_{21\Delta^2}(\varphi) \frac{1}{\Delta x_v} \delta_i \nabla^2 v \\ |
253 |
|
|
\tau_{22} & = & A_h c_{22\Delta}(\varphi) \frac{1}{\Delta y_f} \delta_j v |
254 |
|
|
-A_4 c_{22\Delta^2}(\varphi) \frac{1}{\Delta y_f} \delta_j \nabla^2 v |
255 |
adcroft |
1.1 |
\end{eqnarray} |
256 |
cnh |
1.4 |
where the non-dimensional factors $c_{lm\Delta^n}(\varphi), \{l,m,n\} \in |
257 |
adcroft |
1.1 |
\{1,2\}$ define the ``cosine'' scaling with latitude which can be |
258 |
|
|
applied in various ad-hoc ways. For instance, $c_{11\Delta} = |
259 |
jmc |
1.13 |
c_{21\Delta} = (\cos{\varphi})^{3/2}$, $c_{12\Delta}=c_{22\Delta}=1$ would |
260 |
adcroft |
1.1 |
represent the an-isotropic cosine scaling typically used on the |
261 |
|
|
``lat-lon'' grid for Laplacian viscosity. |
262 |
|
|
\marginpar{Need to tidy up method for controlling this in code} |
263 |
|
|
|
264 |
cnh |
1.6 |
It should be noted that despite the ad-hoc nature of the scaling, some |
265 |
adcroft |
1.1 |
scaling must be done since on a lat-lon grid the converging meridians |
266 |
|
|
make it very unlikely that a stable viscosity parameter exists across |
267 |
|
|
the entire model domain. |
268 |
|
|
|
269 |
|
|
The Laplacian viscosity coefficient, $A_h$ ({\bf viscAh}), has units |
270 |
|
|
of $m^2 s^{-1}$. The bi-harmonic viscosity coefficient, $A_4$ ({\bf |
271 |
|
|
viscA4}), has units of $m^4 s^{-1}$. |
272 |
|
|
|
273 |
|
|
\fbox{ \begin{minipage}{4.75in} |
274 |
|
|
{\em S/R MOM\_U\_XVISCFLUX} ({\em mom\_u\_xviscflux.F}) |
275 |
|
|
|
276 |
|
|
{\em S/R MOM\_U\_YVISCFLUX} ({\em mom\_u\_yviscflux.F}) |
277 |
|
|
|
278 |
|
|
{\em S/R MOM\_V\_XVISCFLUX} ({\em mom\_v\_xviscflux.F}) |
279 |
|
|
|
280 |
|
|
{\em S/R MOM\_V\_YVISCFLUX} ({\em mom\_v\_yviscflux.F}) |
281 |
|
|
|
282 |
jmc |
1.13 |
$\tau_{11}$, $\tau_{12}$, $\tau_{21}$, $\tau_{22}$: {\bf vF}, {\bf |
283 |
jmc |
1.11 |
v4F} (local to {\em mom\_fluxform.F}) |
284 |
adcroft |
1.1 |
\end{minipage} } |
285 |
|
|
|
286 |
|
|
Two types of lateral boundary condition exist for the lateral viscous |
287 |
|
|
terms, no-slip and free-slip. |
288 |
|
|
|
289 |
|
|
The free-slip condition is most convenient to code since it is |
290 |
|
|
equivalent to zero-stress on boundaries. Simple masking of the stress |
291 |
|
|
components sets them to zero. The fractional open stress is properly |
292 |
|
|
handled using the lopped cells. |
293 |
|
|
|
294 |
|
|
The no-slip condition defines the normal gradient of a tangential flow |
295 |
|
|
such that the flow is zero on the boundary. Rather than modify the |
296 |
|
|
stresses by using complicated functions of the masks and ``ghost'' |
297 |
adcroft |
1.7 |
points (see \cite{adcroft:98}) we add the boundary stresses as |
298 |
adcroft |
1.1 |
an additional source term in cells next to solid boundaries. This has |
299 |
|
|
the advantage of being able to cope with ``thin walls'' and also makes |
300 |
|
|
the interior stress calculation (code) independent of the boundary |
301 |
|
|
conditions. The ``body'' force takes the form: |
302 |
|
|
\begin{eqnarray} |
303 |
|
|
G_u^{side-drag} & = & |
304 |
|
|
\frac{4}{\Delta z_f} \overline{ (1-h_\zeta) \frac{\Delta x_v}{\Delta y_u} }^j |
305 |
cnh |
1.4 |
\left( A_h c_{12\Delta}(\varphi) u - A_4 c_{12\Delta^2}(\varphi) \nabla^2 u \right) |
306 |
adcroft |
1.1 |
\\ |
307 |
|
|
G_v^{side-drag} & = & |
308 |
|
|
\frac{4}{\Delta z_f} \overline{ (1-h_\zeta) \frac{\Delta y_u}{\Delta x_v} }^i |
309 |
cnh |
1.4 |
\left( A_h c_{21\Delta}(\varphi) v - A_4 c_{21\Delta^2}(\varphi) \nabla^2 v \right) |
310 |
adcroft |
1.1 |
\end{eqnarray} |
311 |
|
|
|
312 |
|
|
In fact, the above discretization is not quite complete because it |
313 |
|
|
assumes that the bathymetry at velocity points is deeper than at |
314 |
cnh |
1.6 |
neighboring vorticity points, e.g. $1-h_w < 1-h_\zeta$ |
315 |
adcroft |
1.1 |
|
316 |
|
|
\fbox{ \begin{minipage}{4.75in} |
317 |
|
|
{\em S/R MOM\_U\_SIDEDRAG} ({\em mom\_u\_sidedrag.F}) |
318 |
|
|
|
319 |
|
|
{\em S/R MOM\_V\_SIDEDRAG} ({\em mom\_v\_sidedrag.F}) |
320 |
|
|
|
321 |
jmc |
1.11 |
$G_u^{side-drag}$, $G_v^{side-drag}$: {\bf vF} (local to {\em mom\_fluxform.F}) |
322 |
adcroft |
1.1 |
\end{minipage} } |
323 |
|
|
|
324 |
|
|
|
325 |
|
|
\subsection{Vertical dissipation} |
326 |
|
|
|
327 |
|
|
Vertical viscosity terms are discretized with only partial adherence |
328 |
|
|
to the variable grid lengths introduced by the finite volume |
329 |
|
|
formulation. This reduces the formal accuracy of these terms to just |
330 |
|
|
first order but only next to boundaries; exactly where other terms |
331 |
cnh |
1.6 |
appear such as linear and quadratic bottom drag. |
332 |
adcroft |
1.1 |
\begin{eqnarray} |
333 |
|
|
G_u^{v-diss} & = & |
334 |
|
|
\frac{1}{\Delta r_f h_w} \delta_k \tau_{13} \\ |
335 |
|
|
G_v^{v-diss} & = & |
336 |
|
|
\frac{1}{\Delta r_f h_s} \delta_k \tau_{23} \\ |
337 |
|
|
G_w^{v-diss} & = & \epsilon_{nh} |
338 |
|
|
\frac{1}{\Delta r_f h_d} \delta_k \tau_{33} |
339 |
|
|
\end{eqnarray} |
340 |
|
|
represents the general discrete form of the vertical dissipation terms. |
341 |
|
|
|
342 |
|
|
In the interior the vertical stresses are discretized: |
343 |
|
|
\begin{eqnarray} |
344 |
|
|
\tau_{13} & = & A_v \frac{1}{\Delta r_c} \delta_k u \\ |
345 |
|
|
\tau_{23} & = & A_v \frac{1}{\Delta r_c} \delta_k v \\ |
346 |
|
|
\tau_{33} & = & A_v \frac{1}{\Delta r_f} \delta_k w |
347 |
|
|
\end{eqnarray} |
348 |
|
|
It should be noted that in the non-hydrostatic form, the stress tensor |
349 |
adcroft |
1.7 |
is even less consistent than for the hydrostatic (see |
350 |
|
|
\cite{wajsowicz:93}). It is well known how to do this properly (see |
351 |
|
|
\cite{griffies:00}) and is on the list of to-do's. |
352 |
adcroft |
1.1 |
|
353 |
|
|
\fbox{ \begin{minipage}{4.75in} |
354 |
|
|
{\em S/R MOM\_U\_RVISCLFUX} ({\em mom\_u\_rviscflux.F}) |
355 |
|
|
|
356 |
|
|
{\em S/R MOM\_V\_RVISCLFUX} ({\em mom\_v\_rviscflux.F}) |
357 |
|
|
|
358 |
jmc |
1.11 |
$\tau_{13}$: {\bf urf} (local to {\em mom\_fluxform.F}) |
359 |
adcroft |
1.1 |
|
360 |
jmc |
1.11 |
$\tau_{23}$: {\bf vrf} (local to {\em mom\_fluxform.F}) |
361 |
adcroft |
1.1 |
\end{minipage} } |
362 |
|
|
|
363 |
|
|
|
364 |
|
|
As for the lateral viscous terms, the free-slip condition is |
365 |
|
|
equivalent to simply setting the stress to zero on boundaries. The |
366 |
|
|
no-slip condition is implemented as an additional term acting on top |
367 |
|
|
of the interior and free-slip stresses. Bottom drag represents |
368 |
|
|
additional friction, in addition to that imposed by the no-slip |
369 |
|
|
condition at the bottom. The drag is cast as a stress expressed as a |
370 |
|
|
linear or quadratic function of the mean flow in the layer above the |
371 |
|
|
topography: |
372 |
|
|
\begin{eqnarray} |
373 |
|
|
\tau_{13}^{bottom-drag} & = & |
374 |
|
|
\left( |
375 |
|
|
2 A_v \frac{1}{\Delta r_c} |
376 |
|
|
+ r_b |
377 |
|
|
+ C_d \sqrt{ \overline{2 KE}^i } |
378 |
|
|
\right) u \\ |
379 |
|
|
\tau_{23}^{bottom-drag} & = & |
380 |
|
|
\left( |
381 |
|
|
2 A_v \frac{1}{\Delta r_c} |
382 |
|
|
+ r_b |
383 |
|
|
+ C_d \sqrt{ \overline{2 KE}^j } |
384 |
|
|
\right) v |
385 |
|
|
\end{eqnarray} |
386 |
|
|
where these terms are only evaluated immediately above topography. |
387 |
|
|
$r_b$ ({\bf bottomDragLinear}) has units of $m s^{-1}$ and a typical value |
388 |
|
|
of the order 0.0002 $m s^{-1}$. $C_d$ ({\bf bottomDragQuadratic}) is |
389 |
|
|
dimensionless with typical values in the range 0.001--0.003. |
390 |
|
|
|
391 |
|
|
\fbox{ \begin{minipage}{4.75in} |
392 |
|
|
{\em S/R MOM\_U\_BOTTOMDRAG} ({\em mom\_u\_bottomdrag.F}) |
393 |
|
|
|
394 |
|
|
{\em S/R MOM\_V\_BOTTOMDRAG} ({\em mom\_v\_bottomdrag.F}) |
395 |
|
|
|
396 |
jmc |
1.12 |
$\tau_{13}^{bottom-drag}/\Delta r_f$, $\tau_{23}^{bottom-drag}/\Delta r_f$: |
397 |
|
|
{\bf vf} (local to {\em mom\_fluxform.F}) |
398 |
adcroft |
1.1 |
\end{minipage} } |
399 |
|
|
|
400 |
|
|
\subsection{Derivation of discrete energy conservation} |
401 |
|
|
|
402 |
|
|
These discrete equations conserve kinetic plus potential energy using the |
403 |
|
|
following definitions: |
404 |
|
|
\begin{equation} |
405 |
|
|
KE = \frac{1}{2} \left( \overline{ u^2 }^i + \overline{ v^2 }^j + |
406 |
|
|
\epsilon_{nh} \overline{ w^2 }^k \right) |
407 |
|
|
\end{equation} |
408 |
|
|
|
409 |
molod |
1.10 |
\subsection{Mom Diagnostics} |
410 |
|
|
\label{sec:pkg:mom_common:diagnostics} |
411 |
|
|
|
412 |
|
|
\begin{verbatim} |
413 |
|
|
|
414 |
|
|
------------------------------------------------------------------------ |
415 |
|
|
<-Name->|Levs|<-parsing code->|<-- Units -->|<- Tile (max=80c) |
416 |
|
|
------------------------------------------------------------------------ |
417 |
|
|
VISCAHZ | 15 |SZ MR |m^2/s |Harmonic Visc Coefficient (m2/s) (Zeta Pt) |
418 |
|
|
VISCA4Z | 15 |SZ MR |m^4/s |Biharmonic Visc Coefficient (m4/s) (Zeta Pt) |
419 |
|
|
VISCAHD | 15 |SM MR |m^2/s |Harmonic Viscosity Coefficient (m2/s) (Div Pt) |
420 |
|
|
VISCA4D | 15 |SM MR |m^4/s |Biharmonic Viscosity Coefficient (m4/s) (Div Pt) |
421 |
|
|
VAHZMAX | 15 |SZ MR |m^2/s |CFL-MAX Harm Visc Coefficient (m2/s) (Zeta Pt) |
422 |
|
|
VA4ZMAX | 15 |SZ MR |m^4/s |CFL-MAX Biharm Visc Coefficient (m4/s) (Zeta Pt) |
423 |
|
|
VAHDMAX | 15 |SM MR |m^2/s |CFL-MAX Harm Visc Coefficient (m2/s) (Div Pt) |
424 |
|
|
VA4DMAX | 15 |SM MR |m^4/s |CFL-MAX Biharm Visc Coefficient (m4/s) (Div Pt) |
425 |
|
|
VAHZMIN | 15 |SZ MR |m^2/s |RE-MIN Harm Visc Coefficient (m2/s) (Zeta Pt) |
426 |
|
|
VA4ZMIN | 15 |SZ MR |m^4/s |RE-MIN Biharm Visc Coefficient (m4/s) (Zeta Pt) |
427 |
|
|
VAHDMIN | 15 |SM MR |m^2/s |RE-MIN Harm Visc Coefficient (m2/s) (Div Pt) |
428 |
|
|
VA4DMIN | 15 |SM MR |m^4/s |RE-MIN Biharm Visc Coefficient (m4/s) (Div Pt) |
429 |
|
|
VAHZLTH | 15 |SZ MR |m^2/s |Leith Harm Visc Coefficient (m2/s) (Zeta Pt) |
430 |
|
|
VA4ZLTH | 15 |SZ MR |m^4/s |Leith Biharm Visc Coefficient (m4/s) (Zeta Pt) |
431 |
|
|
VAHDLTH | 15 |SM MR |m^2/s |Leith Harm Visc Coefficient (m2/s) (Div Pt) |
432 |
|
|
VA4DLTH | 15 |SM MR |m^4/s |Leith Biharm Visc Coefficient (m4/s) (Div Pt) |
433 |
|
|
VAHZLTHD| 15 |SZ MR |m^2/s |LeithD Harm Visc Coefficient (m2/s) (Zeta Pt) |
434 |
|
|
VA4ZLTHD| 15 |SZ MR |m^4/s |LeithD Biharm Visc Coefficient (m4/s) (Zeta Pt) |
435 |
|
|
VAHDLTHD| 15 |SM MR |m^2/s |LeithD Harm Visc Coefficient (m2/s) (Div Pt) |
436 |
|
|
VA4DLTHD| 15 |SM MR |m^4/s |LeithD Biharm Visc Coefficient (m4/s) (Div Pt) |
437 |
|
|
VAHZSMAG| 15 |SZ MR |m^2/s |Smagorinsky Harm Visc Coefficient (m2/s) (Zeta Pt) |
438 |
|
|
VA4ZSMAG| 15 |SZ MR |m^4/s |Smagorinsky Biharm Visc Coeff. (m4/s) (Zeta Pt) |
439 |
|
|
VAHDSMAG| 15 |SM MR |m^2/s |Smagorinsky Harm Visc Coefficient (m2/s) (Div Pt) |
440 |
|
|
VA4DSMAG| 15 |SM MR |m^4/s |Smagorinsky Biharm Visc Coeff. (m4/s) (Div Pt) |
441 |
|
|
momKE | 15 |SM MR |m^2/s^2 |Kinetic Energy (in momentum Eq.) |
442 |
|
|
momHDiv | 15 |SM MR |s^-1 |Horizontal Divergence (in momentum Eq.) |
443 |
|
|
momVort3| 15 |SZ MR |s^-1 |3rd component (vertical) of Vorticity |
444 |
|
|
Strain | 15 |SZ MR |s^-1 |Horizontal Strain of Horizontal Velocities |
445 |
|
|
Tension | 15 |SM MR |s^-1 |Horizontal Tension of Horizontal Velocities |
446 |
|
|
UBotDrag| 15 |UU 129MR |m/s^2 |U momentum tendency from Bottom Drag |
447 |
|
|
VBotDrag| 15 |VV 128MR |m/s^2 |V momentum tendency from Bottom Drag |
448 |
|
|
USidDrag| 15 |UU 131MR |m/s^2 |U momentum tendency from Side Drag |
449 |
|
|
VSidDrag| 15 |VV 130MR |m/s^2 |V momentum tendency from Side Drag |
450 |
|
|
Um_Diss | 15 |UU 133MR |m/s^2 |U momentum tendency from Dissipation |
451 |
|
|
Vm_Diss | 15 |VV 132MR |m/s^2 |V momentum tendency from Dissipation |
452 |
|
|
Um_Advec| 15 |UU 135MR |m/s^2 |U momentum tendency from Advection terms |
453 |
|
|
Vm_Advec| 15 |VV 134MR |m/s^2 |V momentum tendency from Advection terms |
454 |
|
|
Um_Cori | 15 |UU 137MR |m/s^2 |U momentum tendency from Coriolis term |
455 |
|
|
Vm_Cori | 15 |VV 136MR |m/s^2 |V momentum tendency from Coriolis term |
456 |
|
|
Um_Ext | 15 |UU 137MR |m/s^2 |U momentum tendency from external forcing |
457 |
|
|
Vm_Ext | 15 |VV 138MR |m/s^2 |V momentum tendency from external forcing |
458 |
|
|
Um_AdvZ3| 15 |UU 141MR |m/s^2 |U momentum tendency from Vorticity Advection |
459 |
|
|
Vm_AdvZ3| 15 |VV 140MR |m/s^2 |V momentum tendency from Vorticity Advection |
460 |
|
|
Um_AdvRe| 15 |UU 143MR |m/s^2 |U momentum tendency from vertical Advection (Explicit part) |
461 |
|
|
Vm_AdvRe| 15 |VV 142MR |m/s^2 |V momentum tendency from vertical Advection (Explicit part) |
462 |
|
|
ADVx_Um | 15 |UM 145MR |m^4/s^2 |Zonal Advective Flux of U momentum |
463 |
|
|
ADVy_Um | 15 |VZ 144MR |m^4/s^2 |Meridional Advective Flux of U momentum |
464 |
|
|
ADVrE_Um| 15 |WU LR |m^4/s^2 |Vertical Advective Flux of U momentum (Explicit part) |
465 |
|
|
ADVx_Vm | 15 |UZ 148MR |m^4/s^2 |Zonal Advective Flux of V momentum |
466 |
|
|
ADVy_Vm | 15 |VM 147MR |m^4/s^2 |Meridional Advective Flux of V momentum |
467 |
|
|
ADVrE_Vm| 15 |WV LR |m^4/s^2 |Vertical Advective Flux of V momentum (Explicit part) |
468 |
|
|
VISCx_Um| 15 |UM 151MR |m^4/s^2 |Zonal Viscous Flux of U momentum |
469 |
|
|
VISCy_Um| 15 |VZ 150MR |m^4/s^2 |Meridional Viscous Flux of U momentum |
470 |
|
|
VISrE_Um| 15 |WU LR |m^4/s^2 |Vertical Viscous Flux of U momentum (Explicit part) |
471 |
|
|
VISrI_Um| 15 |WU LR |m^4/s^2 |Vertical Viscous Flux of U momentum (Implicit part) |
472 |
|
|
VISCx_Vm| 15 |UZ 155MR |m^4/s^2 |Zonal Viscous Flux of V momentum |
473 |
|
|
VISCy_Vm| 15 |VM 154MR |m^4/s^2 |Meridional Viscous Flux of V momentum |
474 |
|
|
VISrE_Vm| 15 |WV LR |m^4/s^2 |Vertical Viscous Flux of V momentum (Explicit part) |
475 |
|
|
VISrI_Vm| 15 |WV LR |m^4/s^2 |Vertical Viscous Flux of V momentum (Implicit part) |
476 |
|
|
\end{verbatim} |