doc/phys_pkgs/land.rst

8679f9097b Jeff*0001 .. _sub_phys_pkg_land:
                0002
                0003 Land package
                0004 ------------
                0005
                0006
                0007 Introduction
                0008 ############
                0009
                0010 This package provides a simple land model based on Rong Zhang
0bad585a21 Navi*0011 [e-mail Rong.Zhang@noaa.gov] two layers model (see documentation below).
8679f9097b Jeff*0012
                0013 It is primarily implemented for AIM (\_v23) atmospheric physics but
                0014 could be adapted to work with a different atmospheric physics. Two
                0015 subroutines (*aim\_aim2land.F* *aim\_land2aim.F* in *pkg/aim\_v23*) are
                0016 used as interface with AIM physics.
                0017
                0018 Number of layers is a parameter (*land\_nLev* in *LAND\_SIZE.h*) and can
                0019 be changed.
                0020
                0021 **Note on Land Model**
                0022 date: June 1999
                0023 author: Rong Zhang
                0024
                0025
                0026 Equations and Key Parameters
                0027 ############################
                0028
                0029 This is a simple 2-layer land model. The top layer depth
0bad585a21 Navi*0030 :math:`z1=0.1` m, the second layer depth :math:`z2=4` m.
8679f9097b Jeff*0031
                0032 Let :math:`T_{g1},T_{g2}` be the temperature of each layer,
                0033 :math:`W_{1,}W_{2}` be the soil moisture of each layer. The field
                0034 capacity :math:`f_{1,}` :math:`f_{2}` are the maximum water amount in
                0035 each layer, so :math:`W_{i}` is the ratio of available water to field
                0036 capacity. :math:`f_{i}=\gamma z_{i},\gamma =0.24` is the field capapcity
0bad585a21 Navi*0037 per meter soil\ :math:`,` so :math:`f_{1}=0.024` m, :math:`f_{2}=0.96` m.
8679f9097b Jeff*0038
                0039 The land temperature is determined by total surface downward heat flux
0bad585a21 Navi*0040 :math:`F`,
8679f9097b Jeff*0041
0bad585a21 Navi*0042 .. math::
                0043     \begin{aligned}
                0044     z_1 C_1 \frac{dT_{g1}}{dt} & = F - \lambda \frac{T_{g1}-T_{g2}}{(z_1 + z_2)/2}, \nonumber\\
                0045     z_2 C_2 \frac{dT_{g2}}{dt} & = \lambda \frac{T_{g1}-T_{g2}}{(z_1 + z_2)/2}, \nonumber
                0046     \end{aligned}
8679f9097b Jeff*0047
0bad585a21 Navi*0048 here :math:`C_{1},C_{2}` are the heat capacity of each layer,
                0049 :math:`\lambda` is the thermal conductivity, :math:`\lambda =0.42` W m\ :sup:`--1` K\ :sup:`--1`.
8679f9097b Jeff*0050
0bad585a21 Navi*0051 .. math::
                0052     \begin{aligned}
                0053     C_{1} & = C_{w}W_{1}\gamma +C_{s}, \nonumber\\
                0054     C_{2} & = C_{w}W_{2}\gamma +C_{s}, \nonumber
                0055     \end{aligned}
8679f9097b Jeff*0056
                0057 :math:`C_{w},C_{s}` are the heat capacity of water and dry soil
0bad585a21 Navi*0058 respectively.
                0059 :math:`C_{w}=4.2\times 10^{6}` J m\ :sup:`--3` K\ :sup:`--1`, :math:`C_{s}=1.13\times 10^{6}` J m\ :sup:`--3` K\ :sup:`--1`.
8679f9097b Jeff*0060
0bad585a21 Navi*0061 The soil moisture is determined by precipitation :math:`P` (m/s), surface
                0062 evaporation :math:`E` (m/s) and runoff :math:`R` (m/s).
8679f9097b Jeff*0063
0bad585a21 Navi*0064 .. math:: \frac{dW_{1}}{dt} = \frac{P-E-R}{f_{1}}+\frac{W_{2}-W_{1}}{\tau},
8679f9097b Jeff*0065
0bad585a21 Navi*0066 :math:`\tau=2` days is the time constant for diffusion of
8679f9097b Jeff*0067 moisture between layers.
                0068
                0069 .. math:: \frac{dW_{2}}{dt}=\frac{f_{1}}{f_{2}}\frac{W_{1}-W_{2}}{\tau }
                0070
                0071 In the code, :math:`R=0` gives better result, :math:`W_{1},W_{2}` are
                0072 set to be within [0, 1]. If :math:`W_{1}` is greater than 1, then let
                0073 :math:`\delta W_{1}=W_{1}-1,W_{1}=1` and
                0074 :math:`W_{2}=W_{2}+p\delta W_{1}\frac{f_{1}}{f_{2}}`, i.e. the runoff of
                0075 top layer is put into second layer. :math:`p=0.5` is the fraction of top
                0076 layer runoff that is put into second layer.
                0077
                0078 The time step is 1 hour, it takes several years to reach equalibrium
                0079 offline.
                0080
9ce7d74115 Jeff*0081 .. _land_diagnostics:
                0082
8679f9097b Jeff*0083 Land diagnostics
                0084 ################
                0085
                0086 ::
                0087
                0088
                0089     ------------------------------------------------------------------------
                0090     <-Name->|Levs|<-parsing code->|<--  Units   -->|<- Tile (max=80c)
                0091     ------------------------------------------------------------------------
                0092     GrdSurfT|  1 |SM      Lg      |degC            |Surface Temperature over land
                0093     GrdTemp |  2 |SM      MG      |degC            |Ground Temperature at each level
                0094     GrdEnth |  2 |SM      MG      |J/m3            |Ground Enthalpy at each level
                0095     GrdWater|  2 |SM P    MG      |0-1             |Ground Water (vs Field Capacity) Fraction at each level
                0096     LdSnowH |  1 |SM P    Lg      |m               |Snow Thickness over land
                0097     LdSnwAge|  1 |SM P    Lg      |s               |Snow Age over land
                0098     RUNOFF  |  1 |SM      L1      |m/s             |Run-Off per surface unit
                0099     EnRunOff|  1 |SM      L1      |W/m^2           |Energy flux associated with run-Off
                0100     landHFlx|  1 |SM      Lg      |W/m^2           |net surface downward Heat flux over land
                0101     landPmE |  1 |SM      Lg      |kg/m^2/s        |Precipitation minus Evaporation over land
                0102     ldEnFxPr|  1 |SM      Lg      |W/m^2           |Energy flux (over land) associated with Precip (snow,rain)
                0103
                0104 References
                0105 ##########
                0106
                0107 Hansen J. et al. Efficient three-dimensional global models for climate
                0108 studies: models I and II. *Monthly Weather Review*, vol.111, no.4, pp.
                0109 609-62, 1983
                0110
                0111 Experiments and tutorials that use land
                0112 #######################################
                0113
                0114 -  Global atmosphere experiment in aim.5l_cs verification directory.
                0115
                0116