| 8 |
\subsubsection{Introduction} |
\subsubsection{Introduction} |
| 9 |
The fizhi (high-end atmospheric physics) package includes a collection of state-of-the-art |
The fizhi (high-end atmospheric physics) package includes a collection of state-of-the-art |
| 10 |
physical parameterizations for atmospheric radiation, cumulus convection, atmospheric |
physical parameterizations for atmospheric radiation, cumulus convection, atmospheric |
| 11 |
boundary layer turbulence, and land surface processes. |
boundary layer turbulence, and land surface processes. The collection of atmospheric |
| 12 |
|
physics parameterizations were originally used together as part of the GEOS-3 |
| 13 |
|
(Goddard Earth Observing System-3) GCM developed at the NASA/Goddard Global Modelling |
| 14 |
|
and Assimilation Office (GMAO). |
| 15 |
|
|
| 16 |
% ************************************************************************* |
% ************************************************************************* |
| 17 |
% ************************************************************************* |
% ************************************************************************* |
| 24 |
\label{sec:fizhi:mc} |
\label{sec:fizhi:mc} |
| 25 |
|
|
| 26 |
Sub-grid scale cumulus convection is parameterized using the Relaxed Arakawa |
Sub-grid scale cumulus convection is parameterized using the Relaxed Arakawa |
| 27 |
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 |
| 28 |
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 |
| 29 |
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. |
| 30 |
|
|
| 46 |
The entrainment parameter, $\lambda$, characterizes a particular subensemble based on its |
The entrainment parameter, $\lambda$, characterizes a particular subensemble based on its |
| 47 |
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 |
| 48 |
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 |
| 49 |
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}, |
| 50 |
$\lambda$ may be written as |
$\lambda$ may be written as |
| 51 |
\[ |
\[ |
| 52 |
\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}}} } , |
| 104 |
towards equillibrium. |
towards equillibrium. |
| 105 |
|
|
| 106 |
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 |
| 107 |
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 |
| 108 |
correspondingly adjusts the temperature assuming $h$ is conserved. RAS in its current |
correspondingly adjusts the temperature assuming $h$ is conserved. RAS in its current |
| 109 |
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. |
| 110 |
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. |
| 224 |
and a $CO_2$ mixing ratio of 330 ppm. |
and a $CO_2$ mixing ratio of 330 ppm. |
| 225 |
For the ozone mixing ratio, monthly mean zonally averaged |
For the ozone mixing ratio, monthly mean zonally averaged |
| 226 |
climatological values specified as a function |
climatological values specified as a function |
| 227 |
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. |
| 228 |
|
|
| 229 |
|
|
| 230 |
\paragraph{Shortwave Radiation} |
\paragraph{Shortwave Radiation} |
| 234 |
clouds, and aerosols and due to the |
clouds, and aerosols and due to the |
| 235 |
scattering by clouds, aerosols, and gases. |
scattering by clouds, aerosols, and gases. |
| 236 |
The shortwave radiative processes are described by |
The shortwave radiative processes are described by |
| 237 |
Chou (1990,1992). This shortwave package |
\cite{chou:90,chou:92}. This shortwave package |
| 238 |
uses the Delta-Eddington approximation to compute the |
uses the Delta-Eddington approximation to compute the |
| 239 |
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). |
| 240 |
The transmittance and reflectance of diffuse radiation |
The transmittance and reflectance of diffuse radiation |
| 241 |
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}. |
| 242 |
|
|
| 243 |
Highly accurate heating rate calculations are obtained through the use |
Highly accurate heating rate calculations are obtained through the use |
| 244 |
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 |
| 324 |
|
|
| 325 |
\paragraph{Longwave Radiation} |
\paragraph{Longwave Radiation} |
| 326 |
|
|
| 327 |
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}. |
| 328 |
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 |
| 329 |
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, |
| 330 |
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}. |
| 360 |
\end{tabular} |
\end{tabular} |
| 361 |
\end{center} |
\end{center} |
| 362 |
\vspace{0.1in} |
\vspace{0.1in} |
| 363 |
\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})} |
| 364 |
\label{tab:fizhi:longwave} |
\label{tab:fizhi:longwave} |
| 365 |
\end{table} |
\end{table} |
| 366 |
|
|
| 462 |
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 |
| 463 |
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. |
| 464 |
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 |
| 465 |
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 |
| 466 |
kinetic energy (TKE), |
kinetic energy (TKE), |
| 467 |
|
|
| 468 |
\[ {\h}{q^2}={\overline{{u^{\prime}}^2}}+{\overline{{v^{\prime}}^2}}+{\overline{{w^{\prime}}^2}}, \] |
\[ {\h}{q^2}={\overline{{u^{\prime}}^2}}+{\overline{{v^{\prime}}^2}}+{\overline{{w^{\prime}}^2}}, \] |
| 496 |
|
|
| 497 |
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 |
| 498 |
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 |
| 499 |
$K_m$, 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 |
| 500 |
and Labraga (1988), these diffusion coefficients are expressed as |
\cite{helflab:88}, these diffusion coefficients are expressed as |
| 501 |
|
|
| 502 |
\[ |
\[ |
| 503 |
K_h |
K_h |
| 572 |
\] |
\] |
| 573 |
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 |
| 574 |
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 |
| 575 |
layers according to Helfand and Schubert, 1995. |
layers according to \cite{helfschu:95}. |
| 576 |
|
|
| 577 |
$\psi_g$ 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, |
| 578 |
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 |
| 579 |
elements, in which temperature and moisture gradients can be quite large. |
elements, in which temperature and moisture gradients can be quite large. |
| 580 |
Based on Yaglom and Kader (1974): |
Based on \cite{yagkad:74}: |
| 581 |
\[ |
\[ |
| 582 |
\psi_{g} = { 0.55 (Pr^{2/3} - 0.2) \over \nu^{1/2} } |
\psi_{g} = { 0.55 (Pr^{2/3} - 0.2) \over \nu^{1/2} } |
| 583 |
(h_{0}u_{*} - h_{0_{ref}}u_{*_{ref}})^{1/2} |
(h_{0}u_{*} - h_{0_{ref}}u_{*_{ref}})^{1/2} |
| 591 |
{z_0} = c_1u^3_* + c_2u^2_* + c_3u_* + c_4 + {c_5 \over {u_*}} |
{z_0} = c_1u^3_* + c_2u^2_* + c_3u_* + c_4 + {c_5 \over {u_*}} |
| 592 |
\] |
\] |
| 593 |
where the constants are chosen to interpolate between the reciprocal relation of |
where the constants are chosen to interpolate between the reciprocal relation of |
| 594 |
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} |
| 595 |
for moderate to large winds. Roughness lengths over land are specified |
for moderate to large winds. Roughness lengths over land are specified |
| 596 |
from the climatology of Dorman and Sellers (1989). |
from the climatology of \cite{dorsell:89}. |
| 597 |
|
|
| 598 |
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 |
| 599 |
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 |
| 600 |
(Panofsky, 1973) for momentum, and its generalization for heat and moisture: |
(\cite{pano:73}) for momentum, and its generalization for heat and moisture: |
| 601 |
\[ |
\[ |
| 602 |
{\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} |
| 603 |
{\phi_h}^2 - 18 \zeta {\phi_h}^3 = 1 \hspace{1cm} . |
{\phi_h}^2 - 18 \zeta {\phi_h}^3 = 1 \hspace{1cm} . |
| 606 |
speed approaches zero. |
speed approaches zero. |
| 607 |
|
|
| 608 |
For a stable surface layer, the stability functions are the observationally |
For a stable surface layer, the stability functions are the observationally |
| 609 |
based functions of Clarke (1970), slightly modified for |
based functions of \cite{clarke:70}, slightly modified for |
| 610 |
the momemtum flux: |
the momemtum flux: |
| 611 |
\[ |
\[ |
| 612 |
{\phi_m} = { { 1 + 5 {{\zeta}_1} } \over { 1 + 0.00794 {{\zeta}_1} |
{\phi_m} = { { 1 + 5 {{\zeta}_1} } \over { 1 + 0.00794 {{\zeta}_1} |
| 664 |
surface temperature of the ice. |
surface temperature of the ice. |
| 665 |
|
|
| 666 |
$C_g$ 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 |
| 667 |
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: |
| 668 |
\[ |
\[ |
| 669 |
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} |
| 670 |
{86400 \over 2 \pi} } \, \, . |
{86400 \over 2 \pi} } \, \, . |
| 679 |
Land Surface Processes: |
Land Surface Processes: |
| 680 |
|
|
| 681 |
\paragraph{Surface Type} |
\paragraph{Surface Type} |
| 682 |
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}) |
| 683 |
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 |
| 684 |
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 |
| 685 |
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 |
| 686 |
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 |
| 687 |
Defries and Townshend (1994), and information about the location of permanent |
\cite{deftow:94}, and information about the location of permanent |
| 688 |
ice was obtained from the classifications of Dorman and Sellers (1989). |
ice was obtained from the classifications of \cite{dorsell:89}. |
| 689 |
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}. |
| 690 |
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 |
| 691 |
10 minute by 10 minute Navy topography |
10 minute by 10 minute Navy topography |
| 739 |
|
|
| 740 |
\paragraph{Surface Roughness} |
\paragraph{Surface Roughness} |
| 741 |
The surface roughness length over oceans is computed iteratively with the wind |
The surface roughness length over oceans is computed iteratively with the wind |
| 742 |
stress by the surface layer parameterization (Helfand and Schubert, 1991). |
stress by the surface layer parameterization (\cite{helfschu:95}). |
| 743 |
It employs an interpolation between the functions of Large and Pond (1981) |
It employs an interpolation between the functions of \cite{larpond:81} |
| 744 |
for high winds and of Kondo (1975) for weak winds. |
for high winds and of \cite{kondo:75} for weak winds. |
| 745 |
|
|
| 746 |
|
|
| 747 |
\paragraph{Albedo} |
\paragraph{Albedo} |
| 748 |
The surface albedo computation, described in Koster and Suarez (1991), |
The surface albedo computation, described in \cite{ks:91}, |
| 749 |
employs the ``two stream'' approximation used in Sellers' (1987) Simple Biosphere (SiB) |
employs the ``two stream'' approximation used in Sellers' (1987) Simple Biosphere (SiB) |
| 750 |
Model which distinguishes between the direct and diffuse albedos in the visible |
Model which distinguishes between the direct and diffuse albedos in the visible |
| 751 |
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 |
| 756 |
|
|
| 757 |
Gravity Wave Drag: |
Gravity Wave Drag: |
| 758 |
|
|
| 759 |
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}). |
| 760 |
This scheme is a modified version of Vernekar et al. (1992), |
This scheme is a modified version of Vernekar et al. (1992), |
| 761 |
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). |
| 762 |
In this version, the gravity wave stress at the surface is |
In this version, the gravity wave stress at the surface is |
| 773 |
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. |
| 774 |
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. |
| 775 |
|
|
| 776 |
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}. |
| 777 |
Experiments using the gravity wave drag parameterization yielded significant and |
Experiments using the gravity wave drag parameterization yielded significant and |
| 778 |
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 |
| 779 |
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 |
| 830 |
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 |
| 831 |
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 |
| 832 |
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 |
| 833 |
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*} |
|
| 834 |
|
|
| 835 |
The standard deviation of the subgrid-scale topography |
The standard deviation of the subgrid-scale topography is computed by interpolating the 10 minute |
| 836 |
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. |
|
| 837 |
The sub-grid scale variance is constructed based on this smoothed dataset. |
The sub-grid scale variance is constructed based on this smoothed dataset. |
| 838 |
|
|
| 839 |
|
|
| 1539 |
\noindent |
\noindent |
| 1540 |
$\phi_h$ 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 |
| 1541 |
the temperature and moisture gradients, specified differently for stable and unstable |
the temperature and moisture gradients, specified differently for stable and unstable |
| 1542 |
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 |
| 1543 |
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 |
| 1544 |
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 |
| 1545 |
(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. |
| 1561 |
\noindent |
\noindent |
| 1562 |
$\phi_m$ 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 |
| 1563 |
the temperature and moisture gradients, specified differently for stable and unstable layers |
the temperature and moisture gradients, specified differently for stable and unstable layers |
| 1564 |
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 |
| 1565 |
non-dimensional stability parameter, $u_*$ is the surface stress velocity |
non-dimensional stability parameter, $u_*$ is the surface stress velocity |
| 1566 |
(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. |
| 1567 |
\\ |
\\ |
| 1573 |
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 |
| 1574 |
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 |
| 1575 |
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 |
| 1576 |
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, $K_h$ |
| 1577 |
takes the form: |
takes the form: |
| 1578 |
\[ |
\[ |
| 1579 |
{\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}} } |
| 1592 |
|
|
| 1593 |
\noindent |
\noindent |
| 1594 |
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, |
| 1595 |
see Helfand and Labraga, 1988. |
see \cite{helflab:88}. |
| 1596 |
|
|
| 1597 |
\noindent |
\noindent |
| 1598 |
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, |
| 1614 |
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 |
| 1615 |
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 |
| 1616 |
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. |
| 1617 |
In the Helfand and Labraga (1988) adaptation of this closure, $K_m$ |
In the \cite{helflab:88} adaptation of this closure, $K_m$ |
| 1618 |
takes the form: |
takes the form: |
| 1619 |
\[ |
\[ |
| 1620 |
{\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}} } |
| 1634 |
|
|
| 1635 |
\noindent |
\noindent |
| 1636 |
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, |
| 1637 |
see Helfand and Labraga, 1988. |
see \cite{helflab:88}. |
| 1638 |
|
|
| 1639 |
\noindent |
\noindent |
| 1640 |
In the surface layer, ${\bf {EU}}$ is the exchange coefficient for momentum, |
In the surface layer, ${\bf {EU}}$ is the exchange coefficient for momentum, |
| 2024 |
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 |
| 2025 |
flux, and $C_g$ is the total heat capacity of the ground. |
flux, and $C_g$ is the total heat capacity of the ground. |
| 2026 |
$C_g$ is obtained by solving a heat diffusion equation |
$C_g$ is obtained by solving a heat diffusion equation |
| 2027 |
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: |
| 2028 |
\[ |
\[ |
| 2029 |
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} |
| 2030 |
{ 86400. \over {2 \pi} } } \, \, . |
{ 86400. \over {2 \pi} } } \, \, . |
| 2379 |
|
|
| 2380 |
\noindent |
\noindent |
| 2381 |
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 |
| 2382 |
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, |
| 2383 |
the roughness length is a function of the surface-stress velocity, $u_*$. |
the roughness length is a function of the surface-stress velocity, $u_*$. |
| 2384 |
\[ |
\[ |
| 2385 |
{\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_*}} |
| 2387 |
|
|
| 2388 |
\noindent |
\noindent |
| 2389 |
where the constants are chosen to interpolate between the reciprocal relation of |
where the constants are chosen to interpolate between the reciprocal relation of |
| 2390 |
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} |
| 2391 |
for moderate to large winds. |
for moderate to large winds. |
| 2392 |
\\ |
\\ |
| 2393 |
|
|