21 |
\label{sec:fizhi:mc} |
\label{sec:fizhi:mc} |
22 |
|
|
23 |
Sub-grid scale cumulus convection is parameterized using the Relaxed Arakawa |
Sub-grid scale cumulus convection is parameterized using the Relaxed Arakawa |
24 |
Schubert (RAS) scheme of Moorthi and Suarez (1992), which is a linearized Arakawa Schubert |
Schubert (RAS) scheme of \cite{moorsz:92}, which is a linearized Arakawa Schubert |
25 |
type scheme. RAS predicts the mass flux from an ensemble of clouds. Each subensemble is identified |
type scheme. RAS predicts the mass flux from an ensemble of clouds. Each subensemble is identified |
26 |
by its entrainment rate and level of neutral bouyancy which are determined by the grid-scale properties. |
by its entrainment rate and level of neutral bouyancy which are determined by the grid-scale properties. |
27 |
|
|
43 |
The entrainment parameter, $\lambda$, characterizes a particular subensemble based on its |
The entrainment parameter, $\lambda$, characterizes a particular subensemble based on its |
44 |
detrainment level, and is obtained by assuming that the level of detrainment is the level of neutral |
detrainment level, and is obtained by assuming that the level of detrainment is the level of neutral |
45 |
buoyancy, ie., the level at which the moist static energy of the cloud, $h_c$, is equal |
buoyancy, ie., the level at which the moist static energy of the cloud, $h_c$, is equal |
46 |
to the saturation moist static energy of the environment, $h^*$. Following Moorthi and Suarez (1992), |
to the saturation moist static energy of the environment, $h^*$. Following \cite{moorsz:92}, |
47 |
$\lambda$ may be written as |
$\lambda$ may be written as |
48 |
\[ |
\[ |
49 |
\lambda = { {h_B - h^*_D} \over { {c_p \over g} {\int_{P_D}^{P_B}\theta(h^*_D-h)dP^{\kappa}}} } , |
\lambda = { {h_B - h^*_D} \over { {c_p \over g} {\int_{P_D}^{P_B}\theta(h^*_D-h)dP^{\kappa}}} } , |
101 |
towards equillibrium. |
towards equillibrium. |
102 |
|
|
103 |
In addition to the RAS cumulus convection scheme, the fizhi package employs a |
In addition to the RAS cumulus convection scheme, the fizhi package employs a |
104 |
Kessler-type scheme for the re-evaporation of falling rain (Sud and Molod, 1988), which |
Kessler-type scheme for the re-evaporation of falling rain (\cite{sudm:88}), which |
105 |
correspondingly adjusts the temperature assuming $h$ is conserved. RAS in its current |
correspondingly adjusts the temperature assuming $h$ is conserved. RAS in its current |
106 |
formulation assumes that all cloud water is deposited into the detrainment level as rain. |
formulation assumes that all cloud water is deposited into the detrainment level as rain. |
107 |
All of the rain is available for re-evaporation, which begins in the level below detrainment. |
All of the rain is available for re-evaporation, which begins in the level below detrainment. |
221 |
and a $CO_2$ mixing ratio of 330 ppm. |
and a $CO_2$ mixing ratio of 330 ppm. |
222 |
For the ozone mixing ratio, monthly mean zonally averaged |
For the ozone mixing ratio, monthly mean zonally averaged |
223 |
climatological values specified as a function |
climatological values specified as a function |
224 |
of latitude and height (Rosenfield, et al., 1987) are linearly interpolated to the current time. |
of latitude and height (\cite{rosen:87}) are linearly interpolated to the current time. |
225 |
|
|
226 |
|
|
227 |
\paragraph{Shortwave Radiation} |
\paragraph{Shortwave Radiation} |
231 |
clouds, and aerosols and due to the |
clouds, and aerosols and due to the |
232 |
scattering by clouds, aerosols, and gases. |
scattering by clouds, aerosols, and gases. |
233 |
The shortwave radiative processes are described by |
The shortwave radiative processes are described by |
234 |
Chou (1990,1992). This shortwave package |
\cite{chou:90,chou:92}. This shortwave package |
235 |
uses the Delta-Eddington approximation to compute the |
uses the Delta-Eddington approximation to compute the |
236 |
bulk scattering properties of a single layer following King and Harshvardhan (JAS, 1986). |
bulk scattering properties of a single layer following King and Harshvardhan (JAS, 1986). |
237 |
The transmittance and reflectance of diffuse radiation |
The transmittance and reflectance of diffuse radiation |
238 |
follow the procedures of Sagan and Pollock (JGR, 1967) and Lacis and Hansen (JAS, 1974). |
follow the procedures of Sagan and Pollock (JGR, 1967) and \cite{lhans:74}. |
239 |
|
|
240 |
Highly accurate heating rate calculations are obtained through the use |
Highly accurate heating rate calculations are obtained through the use |
241 |
of an optimal grouping strategy of spectral bands. By grouping the UV and visible regions |
of an optimal grouping strategy of spectral bands. By grouping the UV and visible regions |
321 |
|
|
322 |
\paragraph{Longwave Radiation} |
\paragraph{Longwave Radiation} |
323 |
|
|
324 |
The longwave radiation package used in the fizhi package is thoroughly described by Chou and Suarez (1994). |
The longwave radiation package used in the fizhi package is thoroughly described by \cite{chsz:94}. |
325 |
As described in that document, IR fluxes are computed due to absorption by water vapor, carbon |
As described in that document, IR fluxes are computed due to absorption by water vapor, carbon |
326 |
dioxide, and ozone. The spectral bands together with their absorbers and parameterization methods, |
dioxide, and ozone. The spectral bands together with their absorbers and parameterization methods, |
327 |
configured for the fizhi package, are shown in Table \ref{tab:fizhi:longwave}. |
configured for the fizhi package, are shown in Table \ref{tab:fizhi:longwave}. |
357 |
\end{tabular} |
\end{tabular} |
358 |
\end{center} |
\end{center} |
359 |
\vspace{0.1in} |
\vspace{0.1in} |
360 |
\caption{IR Spectral Bands, Absorbers, and Parameterization Method (from Chou and Suarez, 1994)} |
\caption{IR Spectral Bands, Absorbers, and Parameterization Method (from \cite{chzs:94})} |
361 |
\label{tab:fizhi:longwave} |
\label{tab:fizhi:longwave} |
362 |
\end{table} |
\end{table} |
363 |
|
|
459 |
of second turbulent moments is explicitly modeled by representing the third moments in terms of |
of second turbulent moments is explicitly modeled by representing the third moments in terms of |
460 |
the first and second moments. This approach is known as a second-order closure modeling. |
the first and second moments. This approach is known as a second-order closure modeling. |
461 |
To simplify and streamline the computation of the second moments, the level 2.5 assumption |
To simplify and streamline the computation of the second moments, the level 2.5 assumption |
462 |
of Mellor and Yamada (1974) and Yamada (1977) is employed, in which only the turbulent |
of Mellor and Yamada (1974) and \cite{yam:77} is employed, in which only the turbulent |
463 |
kinetic energy (TKE), |
kinetic energy (TKE), |
464 |
|
|
465 |
\[ {\h}{q^2}={\overline{{u^{\prime}}^2}}+{\overline{{v^{\prime}}^2}}+{\overline{{w^{\prime}}^2}}, \] |
\[ {\h}{q^2}={\overline{{u^{\prime}}^2}}+{\overline{{v^{\prime}}^2}}+{\overline{{w^{\prime}}^2}}, \] |
493 |
|
|
494 |
In the level 2.5 approach, the vertical fluxes of the scalars $\theta_v$ and $q$ and the |
In the level 2.5 approach, the vertical fluxes of the scalars $\theta_v$ and $q$ and the |
495 |
wind components $u$ and $v$ are expressed in terms of the diffusion coefficients $K_h$ and |
wind components $u$ and $v$ are expressed in terms of the diffusion coefficients $K_h$ and |
496 |
$K_m$, respectively. In the statisically realizable level 2.5 turbulence scheme of Helfand |
$K_m$, respectively. In the statisically realizable level 2.5 turbulence scheme of |
497 |
and Labraga (1988), these diffusion coefficients are expressed as |
\cite{helflab:88}, these diffusion coefficients are expressed as |
498 |
|
|
499 |
\[ |
\[ |
500 |
K_h |
K_h |
569 |
\] |
\] |
570 |
Here $\phi_h$ is the similarity function of $\zeta$, which expresses the stability dependance of |
Here $\phi_h$ is the similarity function of $\zeta$, which expresses the stability dependance of |
571 |
the temperature and moisture gradients, and is specified differently for stable and unstable |
the temperature and moisture gradients, and is specified differently for stable and unstable |
572 |
layers according to Helfand and Schubert, 1995. |
layers according to \cite{helfschu:95}. |
573 |
|
|
574 |
$\psi_g$ is the non-dimensional temperature or moisture gradient in the viscous sublayer, |
$\psi_g$ is the non-dimensional temperature or moisture gradient in the viscous sublayer, |
575 |
which is the mosstly laminar region between the surface and the tops of the roughness |
which is the mosstly laminar region between the surface and the tops of the roughness |
576 |
elements, in which temperature and moisture gradients can be quite large. |
elements, in which temperature and moisture gradients can be quite large. |
577 |
Based on Yaglom and Kader (1974): |
Based on \cite{yagkad:74}: |
578 |
\[ |
\[ |
579 |
\psi_{g} = { 0.55 (Pr^{2/3} - 0.2) \over \nu^{1/2} } |
\psi_{g} = { 0.55 (Pr^{2/3} - 0.2) \over \nu^{1/2} } |
580 |
(h_{0}u_{*} - h_{0_{ref}}u_{*_{ref}})^{1/2} |
(h_{0}u_{*} - h_{0_{ref}}u_{*_{ref}})^{1/2} |
588 |
{z_0} = c_1u^3_* + c_2u^2_* + c_3u_* + c_4 + {c_5 \over {u_*}} |
{z_0} = c_1u^3_* + c_2u^2_* + c_3u_* + c_4 + {c_5 \over {u_*}} |
589 |
\] |
\] |
590 |
where the constants are chosen to interpolate between the reciprocal relation of |
where the constants are chosen to interpolate between the reciprocal relation of |
591 |
Kondo(1975) for weak winds, and the piecewise linear relation of Large and Pond(1981) |
\cite{kondo:75} for weak winds, and the piecewise linear relation of \cite{larpond:81} |
592 |
for moderate to large winds. Roughness lengths over land are specified |
for moderate to large winds. Roughness lengths over land are specified |
593 |
from the climatology of Dorman and Sellers (1989). |
from the climatology of \cite{dorsell:89}. |
594 |
|
|
595 |
For an unstable surface layer, the stability functions, chosen to interpolate between the |
For an unstable surface layer, the stability functions, chosen to interpolate between the |
596 |
condition of small values of $\beta$ and the convective limit, are the KEYPS function |
condition of small values of $\beta$ and the convective limit, are the KEYPS function |
597 |
(Panofsky, 1973) for momentum, and its generalization for heat and moisture: |
(\cite{pano:73}) for momentum, and its generalization for heat and moisture: |
598 |
\[ |
\[ |
599 |
{\phi_m}^4 - 18 \zeta {\phi_m}^3 = 1 \hspace{1cm} ; \hspace{1cm} |
{\phi_m}^4 - 18 \zeta {\phi_m}^3 = 1 \hspace{1cm} ; \hspace{1cm} |
600 |
{\phi_h}^2 - 18 \zeta {\phi_h}^3 = 1 \hspace{1cm} . |
{\phi_h}^2 - 18 \zeta {\phi_h}^3 = 1 \hspace{1cm} . |
603 |
speed approaches zero. |
speed approaches zero. |
604 |
|
|
605 |
For a stable surface layer, the stability functions are the observationally |
For a stable surface layer, the stability functions are the observationally |
606 |
based functions of Clarke (1970), slightly modified for |
based functions of \cite{clarke:70}, slightly modified for |
607 |
the momemtum flux: |
the momemtum flux: |
608 |
\[ |
\[ |
609 |
{\phi_m} = { { 1 + 5 {{\zeta}_1} } \over { 1 + 0.00794 {{\zeta}_1} |
{\phi_m} = { { 1 + 5 {{\zeta}_1} } \over { 1 + 0.00794 {{\zeta}_1} |
661 |
surface temperature of the ice. |
surface temperature of the ice. |
662 |
|
|
663 |
$C_g$ is the total heat capacity of the ground, obtained by solving a heat diffusion equation |
$C_g$ is the total heat capacity of the ground, obtained by solving a heat diffusion equation |
664 |
for the penetration of the diurnal cycle into the ground (Blackadar, 1977), and is given by: |
for the penetration of the diurnal cycle into the ground (\cite{black:77}), and is given by: |
665 |
\[ |
\[ |
666 |
C_g = \sqrt{ {\lambda C_s \over 2\omega} } = \sqrt{(0.386 + 0.536W + 0.15W^2)2\times10^{-3} |
C_g = \sqrt{ {\lambda C_s \over 2\omega} } = \sqrt{(0.386 + 0.536W + 0.15W^2)2\times10^{-3} |
667 |
{86400 \over 2 \pi} } \, \, . |
{86400 \over 2 \pi} } \, \, . |
676 |
Land Surface Processes: |
Land Surface Processes: |
677 |
|
|
678 |
\paragraph{Surface Type} |
\paragraph{Surface Type} |
679 |
The fizhi package surface Types are designated using the Koster-Suarez (1992) mosaic |
The fizhi package surface Types are designated using the Koster-Suarez (\cite{ks:91,ks:92}) |
680 |
philosophy which allows multiple ``tiles'', or multiple surface types, in any one |
Land Surface Model (LSM) mosaic philosophy which allows multiple ``tiles'', or multiple surface |
681 |
grid cell. The Koster-Suarez Land Surface Model (LSM) surface type classifications |
types, in any one grid cell. The Koster-Suarez LSM surface type classifications |
682 |
are shown in Table \ref{tab:fizhi:surftype}. The surface types and the percent of the grid |
are shown in Table \ref{tab:fizhi:surftype}. The surface types and the percent of the grid |
683 |
cell occupied by any surface type were derived from the surface classification of |
cell occupied by any surface type were derived from the surface classification of |
684 |
Defries and Townshend (1994), and information about the location of permanent |
\cite{deftow:94}, and information about the location of permanent |
685 |
ice was obtained from the classifications of Dorman and Sellers (1989). |
ice was obtained from the classifications of \cite{dorsell:89}. |
686 |
The surface type for the \txt GCM grid is shown in Figure \ref{fig:fizhi:surftype}. |
The surface type for the \txt GCM grid is shown in Figure \ref{fig:fizhi:surftype}. |
687 |
The determination of the land or sea category of surface type was made from NCAR's |
The determination of the land or sea category of surface type was made from NCAR's |
688 |
10 minute by 10 minute Navy topography |
10 minute by 10 minute Navy topography |
736 |
|
|
737 |
\paragraph{Surface Roughness} |
\paragraph{Surface Roughness} |
738 |
The surface roughness length over oceans is computed iteratively with the wind |
The surface roughness length over oceans is computed iteratively with the wind |
739 |
stress by the surface layer parameterization (Helfand and Schubert, 1991). |
stress by the surface layer parameterization (\cite{helfschu:95}). |
740 |
It employs an interpolation between the functions of Large and Pond (1981) |
It employs an interpolation between the functions of \cite{larpond:81} |
741 |
for high winds and of Kondo (1975) for weak winds. |
for high winds and of \cite{kondo:75} for weak winds. |
742 |
|
|
743 |
|
|
744 |
\paragraph{Albedo} |
\paragraph{Albedo} |
745 |
The surface albedo computation, described in Koster and Suarez (1991), |
The surface albedo computation, described in \cite{ks:91}, |
746 |
employs the ``two stream'' approximation used in Sellers' (1987) Simple Biosphere (SiB) |
employs the ``two stream'' approximation used in Sellers' (1987) Simple Biosphere (SiB) |
747 |
Model which distinguishes between the direct and diffuse albedos in the visible |
Model which distinguishes between the direct and diffuse albedos in the visible |
748 |
and in the near infra-red spectral ranges. The albedos are functions of the observed |
and in the near infra-red spectral ranges. The albedos are functions of the observed |
753 |
|
|
754 |
Gravity Wave Drag: |
Gravity Wave Drag: |
755 |
|
|
756 |
The fizhi package employs the gravity wave drag scheme of Zhou et al. (1996). |
The fizhi package employs the gravity wave drag scheme of \cite{zhouetal:96}). |
757 |
This scheme is a modified version of Vernekar et al. (1992), |
This scheme is a modified version of Vernekar et al. (1992), |
758 |
which was based on Alpert et al. (1988) and Helfand et al. (1987). |
which was based on Alpert et al. (1988) and Helfand et al. (1987). |
759 |
In this version, the gravity wave stress at the surface is |
In this version, the gravity wave stress at the surface is |
770 |
escape through the top of the model, although this effect is small for the current 70-level model. |
escape through the top of the model, although this effect is small for the current 70-level model. |
771 |
The subgrid scale standard deviation is defined by $h$, and is not allowed to exceed 400 m. |
The subgrid scale standard deviation is defined by $h$, and is not allowed to exceed 400 m. |
772 |
|
|
773 |
The effects of using this scheme within a GCM are shown in Takacs and Suarez (1996). |
The effects of using this scheme within a GCM are shown in \cite{taksz:96}. |
774 |
Experiments using the gravity wave drag parameterization yielded significant and |
Experiments using the gravity wave drag parameterization yielded significant and |
775 |
beneficial impacts on both the time-mean flow and the transient statistics of the |
beneficial impacts on both the time-mean flow and the transient statistics of the |
776 |
a GCM climatology, and have eliminated most of the worst dynamically driven biases |
a GCM climatology, and have eliminated most of the worst dynamically driven biases |
827 |
Surface geopotential heights are provided from an averaging of the Navy 10 minute |
Surface geopotential heights are provided from an averaging of the Navy 10 minute |
828 |
by 10 minute dataset supplied by the National Center for Atmospheric Research (NCAR) to the |
by 10 minute dataset supplied by the National Center for Atmospheric Research (NCAR) to the |
829 |
model's grid resolution. The original topography is first rotated to the proper grid-orientation |
model's grid resolution. The original topography is first rotated to the proper grid-orientation |
830 |
which is being run, and then |
which is being run, and then averages the data to the model resolution. |
|
averages the data to the model resolution. |
|
|
The averaged topography is then passed through a Lanczos (1966) filter in both dimensions |
|
|
which removes the smallest |
|
|
scales while inhibiting Gibbs phenomena. |
|
|
|
|
|
In one dimension, we may define a cyclic function in $x$ as: |
|
|
\begin{equation} |
|
|
f(x) = {a_0 \over 2} + \sum_{k=1}^N \left( a_k \cos(kx) + b_k \sin(kx) \right) |
|
|
\label{eq:fizhi:filt} |
|
|
\end{equation} |
|
|
where $N = { {\rm IM} \over 2 }$ and ${\rm IM}$ is the total number of points in the $x$ direction. |
|
|
Defining $\Delta x = { 2 \pi \over {\rm IM}}$, we may define the average of $f(x)$ over a |
|
|
$2 \Delta x$ region as: |
|
|
|
|
|
\begin{equation} |
|
|
\overline {f(x)} = {1 \over {2 \Delta x}} \int_{x-\Delta x}^{x+\Delta x} f(x^{\prime}) dx^{\prime} |
|
|
\label{eq:fizhi:fave1} |
|
|
\end{equation} |
|
|
|
|
|
Using equation (\ref{eq:fizhi:filt}) in equation (\ref{eq:fizhi:fave1}) and integrating, we may write: |
|
|
|
|
|
\begin{equation} |
|
|
\overline {f(x)} = {a_0 \over 2} + {1 \over {2 \Delta x}} |
|
|
\sum_{k=1}^N \left [ |
|
|
\left. a_k { \sin(kx^{\prime}) \over k } \right /_{x-\Delta x}^{x+\Delta x} - |
|
|
\left. b_k { \cos(kx^{\prime}) \over k } \right /_{x-\Delta x}^{x+\Delta x} |
|
|
\right] |
|
|
\end{equation} |
|
|
or |
|
|
|
|
|
\begin{equation} |
|
|
\overline {f(x)} = {a_0 \over 2} + \sum_{k=1}^N {\sin(k \Delta x) \over {k \Delta x}} |
|
|
\left( a_k \cos(kx) + b_k \sin(kx) \right) |
|
|
\label{eq:fizhi:fave2} |
|
|
\end{equation} |
|
|
|
|
|
Thus, the Fourier wave amplitudes are simply modified by the Lanczos filter response |
|
|
function ${\sin(k\Delta x) \over {k \Delta x}}$. This may be compared with an $mth$-order |
|
|
Shapiro (1970) filter response function, defined as $1-\sin^m({k \Delta x \over 2})$, |
|
|
shown in Figure \ref{fig:fizhi:lanczos}. |
|
|
It should be noted that negative values in the topography resulting from |
|
|
the filtering procedure are {\em not} filled. |
|
|
|
|
|
\begin{figure*}[htbp] |
|
|
\centerline{ \epsfysize=7.0in \epsfbox{part6/lanczos.ps}} |
|
|
\caption{ \label{fig:fizhi:lanczos} Comparison between the Lanczos and $mth$-order Shapiro filter |
|
|
response functions for $m$ = 2, 4, and 8. } |
|
|
\end{figure*} |
|
831 |
|
|
832 |
The standard deviation of the subgrid-scale topography |
The standard deviation of the subgrid-scale topography is computed by interpolating the 10 minute |
833 |
is computed from a modified version of the the Navy 10 minute by 10 minute dataset. |
data to the model's resolution and re-interpolating back to the 10 minute by 10 minute resolution. |
|
The 10 minute by 10 minute topography is passed through a wavelet |
|
|
filter in both dimensions which removes the scale smaller than 20 minutes. |
|
|
The topography is then averaged to $1^\circ x 1^\circ$ grid resolution, and then |
|
|
re-interpolated back to the 10 minute by 10 minute resolution. |
|
834 |
The sub-grid scale variance is constructed based on this smoothed dataset. |
The sub-grid scale variance is constructed based on this smoothed dataset. |
835 |
|
|
836 |
|
|
1536 |
\noindent |
\noindent |
1537 |
$\phi_h$ is the similarity function of $\zeta$, which expresses the stability dependance of |
$\phi_h$ is the similarity function of $\zeta$, which expresses the stability dependance of |
1538 |
the temperature and moisture gradients, specified differently for stable and unstable |
the temperature and moisture gradients, specified differently for stable and unstable |
1539 |
layers according to Helfand and Schubert, 1993. k is the Von Karman constant, $\zeta$ is the |
layers according to \cite{helfschu:95}. k is the Von Karman constant, $\zeta$ is the |
1540 |
non-dimensional stability parameter, Pr is the Prandtl number for air, $\nu$ is the molecular |
non-dimensional stability parameter, Pr is the Prandtl number for air, $\nu$ is the molecular |
1541 |
viscosity, $z_{0}$ is the surface roughness length, $u_*$ is the surface stress velocity |
viscosity, $z_{0}$ is the surface roughness length, $u_*$ is the surface stress velocity |
1542 |
(see diagnostic number 67), and the subscript ref refers to a reference value. |
(see diagnostic number 67), and the subscript ref refers to a reference value. |
1558 |
\noindent |
\noindent |
1559 |
$\phi_m$ is the similarity function of $\zeta$, which expresses the stability dependance of |
$\phi_m$ is the similarity function of $\zeta$, which expresses the stability dependance of |
1560 |
the temperature and moisture gradients, specified differently for stable and unstable layers |
the temperature and moisture gradients, specified differently for stable and unstable layers |
1561 |
according to Helfand and Schubert, 1993. k is the Von Karman constant, $\zeta$ is the |
according to \cite{helfschu:95}. k is the Von Karman constant, $\zeta$ is the |
1562 |
non-dimensional stability parameter, $u_*$ is the surface stress velocity |
non-dimensional stability parameter, $u_*$ is the surface stress velocity |
1563 |
(see diagnostic number 67), and $W_s$ is the magnitude of the surface layer wind. |
(see diagnostic number 67), and $W_s$ is the magnitude of the surface layer wind. |
1564 |
\\ |
\\ |
1570 |
In the level 2.5 version of the Mellor-Yamada (1974) hierarchy, the turbulent heat or |
In the level 2.5 version of the Mellor-Yamada (1974) hierarchy, the turbulent heat or |
1571 |
moisture flux for the atmosphere above the surface layer can be expressed as a turbulent |
moisture flux for the atmosphere above the surface layer can be expressed as a turbulent |
1572 |
diffusion coefficient $K_h$ times the negative of the gradient of potential temperature |
diffusion coefficient $K_h$ times the negative of the gradient of potential temperature |
1573 |
or moisture. In the Helfand and Labraga (1988) adaptation of this closure, $K_h$ |
or moisture. In the \cite{helflab:88} adaptation of this closure, $K_h$ |
1574 |
takes the form: |
takes the form: |
1575 |
\[ |
\[ |
1576 |
{\bf ET} = K_h = -{( {\overline{w^{\prime}\theta_v^{\prime}}}) \over {\pp{\theta_v}{z}} } |
{\bf ET} = K_h = -{( {\overline{w^{\prime}\theta_v^{\prime}}}) \over {\pp{\theta_v}{z}} } |
1589 |
|
|
1590 |
\noindent |
\noindent |
1591 |
For the detailed equations and derivations of the modified level 2.5 closure scheme, |
For the detailed equations and derivations of the modified level 2.5 closure scheme, |
1592 |
see Helfand and Labraga, 1988. |
see \cite{helflab:88}. |
1593 |
|
|
1594 |
\noindent |
\noindent |
1595 |
In the surface layer, ${\bf {ET}}$ is the exchange coefficient for heat and moisture, |
In the surface layer, ${\bf {ET}}$ is the exchange coefficient for heat and moisture, |
1611 |
In the level 2.5 version of the Mellor-Yamada (1974) hierarchy, the turbulent heat |
In the level 2.5 version of the Mellor-Yamada (1974) hierarchy, the turbulent heat |
1612 |
momentum flux for the atmosphere above the surface layer can be expressed as a turbulent |
momentum flux for the atmosphere above the surface layer can be expressed as a turbulent |
1613 |
diffusion coefficient $K_m$ times the negative of the gradient of the u-wind. |
diffusion coefficient $K_m$ times the negative of the gradient of the u-wind. |
1614 |
In the Helfand and Labraga (1988) adaptation of this closure, $K_m$ |
In the \cite{helflab:88} adaptation of this closure, $K_m$ |
1615 |
takes the form: |
takes the form: |
1616 |
\[ |
\[ |
1617 |
{\bf EU} = K_m = -{( {\overline{u^{\prime}w^{\prime}}}) \over {\pp{U}{z}} } |
{\bf EU} = K_m = -{( {\overline{u^{\prime}w^{\prime}}}) \over {\pp{U}{z}} } |
1631 |
|
|
1632 |
\noindent |
\noindent |
1633 |
For the detailed equations and derivations of the modified level 2.5 closure scheme, |
For the detailed equations and derivations of the modified level 2.5 closure scheme, |
1634 |
see Helfand and Labraga, 1988. |
see \cite{helflab:88}. |
1635 |
|
|
1636 |
\noindent |
\noindent |
1637 |
In the surface layer, ${\bf {EU}}$ is the exchange coefficient for momentum, |
In the surface layer, ${\bf {EU}}$ is the exchange coefficient for momentum, |
2021 |
sea ice, $H$ is the upward sensible heat flux, $LE$ is the upward latent heat |
sea ice, $H$ is the upward sensible heat flux, $LE$ is the upward latent heat |
2022 |
flux, and $C_g$ is the total heat capacity of the ground. |
flux, and $C_g$ is the total heat capacity of the ground. |
2023 |
$C_g$ is obtained by solving a heat diffusion equation |
$C_g$ is obtained by solving a heat diffusion equation |
2024 |
for the penetration of the diurnal cycle into the ground (Blackadar, 1977), and is given by: |
for the penetration of the diurnal cycle into the ground (\cite{black:77}), and is given by: |
2025 |
\[ |
\[ |
2026 |
C_g = \sqrt{ {\lambda C_s \over {2 \omega} } } = \sqrt{(0.386 + 0.536W + 0.15W^2)2x10^{-3} |
C_g = \sqrt{ {\lambda C_s \over {2 \omega} } } = \sqrt{(0.386 + 0.536W + 0.15W^2)2x10^{-3} |
2027 |
{ 86400. \over {2 \pi} } } \, \, . |
{ 86400. \over {2 \pi} } } \, \, . |
2376 |
|
|
2377 |
\noindent |
\noindent |
2378 |
Over the land surface, the surface roughness length is interpolated to the local |
Over the land surface, the surface roughness length is interpolated to the local |
2379 |
time from the monthly mean data of Dorman and Sellers (1989). Over the ocean, |
time from the monthly mean data of \cite{dorsell:89}. Over the ocean, |
2380 |
the roughness length is a function of the surface-stress velocity, $u_*$. |
the roughness length is a function of the surface-stress velocity, $u_*$. |
2381 |
\[ |
\[ |
2382 |
{\bf Z0} = c_1u^3_* + c_2u^2_* + c_3u_* + c_4 + {c_5 \over {u_*}} |
{\bf Z0} = c_1u^3_* + c_2u^2_* + c_3u_* + c_4 + {c_5 \over {u_*}} |
2384 |
|
|
2385 |
\noindent |
\noindent |
2386 |
where the constants are chosen to interpolate between the reciprocal relation of |
where the constants are chosen to interpolate between the reciprocal relation of |
2387 |
Kondo(1975) for weak winds, and the piecewise linear relation of Large and Pond(1981) |
\cite{kondo:75} for weak winds, and the piecewise linear relation of \cite{larpond:81} |
2388 |
for moderate to large winds. |
for moderate to large winds. |
2389 |
\\ |
\\ |
2390 |
|
|