# Atmospheric Profiles

`ClearSky`

contains functions for common atmospheric profiles and quantities.

## Temperature Profiles

Many radiative transfer calculations require an atmospheric temperature profile. `ClearSky`

is designed to work with any arbitrary temperature profile if it can be defined as a function of pressure, `T(P)`

.

For convenience, dry and moist adiabatic profiles are available through the `DryAdiabat`

and `MoistAdiabat`

types, which are function-like types. There is also a `tropopause`

function.

`ClearSky.DryAdiabat`

— TypeFunction-like type for initializing and evaluating a dry adiabatic temperature profile. Optional uniform upper atmospheric temperature below a specified temperature or pressure.

**Constructor**

`DryAdiabat(Tₛ, Pₛ, cₚ, μ, Pₜ=1.0e-9; Tstrat=0.0, Ptropo=0.0)`

`Tₛ`

: surface temperature [K]`Pₛ`

: surface pressure [K]`Pₜ`

: highest allowable pressure (can be small but not zero) [Pa]`cₚ`

: specific heat of the atmosphere [J/kg/K]`μ`

: molar mass of the atmosphere [kg/mole]`Pₜ`

: highest pressure in the temperature profile (should generally be small to avoid evaluating out of range) [Pa]

If `Tstrat`

is greater than zero, the temperature profile will not drop below that temperature. If `Ptropo`

is greater than zero, the temperature profile at pressures lower than `Ptropo`

will be equal to the temperature at exactly `Ptropo`

. `Tstrat`

and `Ptropo`

cannot be greater than zero simultaneously.

**Example**

Once constructed, use a `DryAdiabat`

like a function to compute temperature at a given pressure.

```
Tₛ = 288; #surface temperature [K]
Pₛ = 1e5; #surface pressure [Pa]
cₚ = 1040; #specific heat of air [J/kg/K]
μ = 0.029; #molar mass of air [kg/mole]
#construct the dry adiabat with an upper atmosphere temperature of 190 K
D = DryAdiabat(Tₛ, Pₛ, cₚ, μ, Tstrat=190);
#temperatures at 40-10 kPa
D.([4e4, 3e4, 2e4, 1e4])
```

`ClearSky.MoistAdiabat`

— TypeFunction-like type for initializing and evaluating a moist adiabatic temperature profile. Optional uniform upper atmospheric temperature below a specified temperature or pressure.

**Constructor**

`MoistAdiabat(Tₛ, Pₛ, cₚₙ, cₚᵥ, μₙ, μᵥ, L, psat, Pₜ=1.0e-9; Tstrat=0, Ptropo=0, N=1000)`

`Tₛ`

: surface temperature [K]`Pₛ`

: surface pressure [K]`cₚₙ`

: specific heat of the non-condensible atmospheric component (air) [J/kg/K]`cₚᵥ`

: specific heat of the condensible atmospheric component [J/kg/K]`μₙ`

: molar mass of the non-condensible atmospheric component (air) [kg/mole]`μᵥ`

: molar mass of the condensible atmospheric component [kg/mole]`L`

: condsible component's latent heat of vaporization [J/kg]`psat`

: function defining the saturation vapor pressure for a given temperature,`psat(T)`

`Pₜ`

: highest pressure in the temperature profile (should generally be small to avoid evaluating pressures out of range) [Pa]

If `Tstrat`

is greater than zero, the temperature profile will not drop below that temperature. If `Ptropo`

is greater than zero, the temperature profile at pressures lower than `Ptropo`

will be equal to the temperature at exactly `Ptropo`

. `Tstrat`

and `Ptropo`

cannot be greater than zero simultaneously.

The profile is evaluated along a number of pressure values in the atmosphere set by `N`

. Those points are then used to construct a cubic spline interpolator for efficient and accurate temperature calculation. Experience indicates that 1000 points is very accurate and also fast.

**Example**

Once constructed, use a `MoistAdiabat`

like a function to compute temperature at a given pressure.

```
Tₛ = 288; #surface temperature [K]
Pₛ = 1e5; #surface pressure [Pa]
cₚₙ = 1040; #specific heat of air [J/kg/K]
cₚᵥ = 1996; #specific heat of H2O [J/kg/K]
μₙ = 0.029; #molar mass of air [kg/mole]
μᵥ = 0.018; #molar mass of H2O [kg/mole]
L = 2.3e6; #H2O latent heat of vaporization [J/kg]
#a saturation vapor pressure function for H2O is built in
psat = psatH2O;
#construct the moist adiabat with a tropopause pressure of 1e4 Pa
M = MoistAdiabat(Tₛ, Pₛ, cₚₙ, cₚᵥ, μₙ, μᵥ, L, psat, Ptropo=1e4);
#temperatures at 30-5 kPa
M.([3e4, 2e4, 1e4, 5e3])
```

`ClearSky.tropopause`

— Function`tropopause(Γ::AbstractAdiabat)`

Compute the temperature [K] and pressure [Pa] at which the tropopause occurs in an adiabatic temperature profile. This function can be called on a `DryAdiabat`

or a `MoistAdiabat`

if it was constructed with nonzero `Tstrat`

or `Ptropo`

. Returns a tuple, `(T,P)`

.

## Pressure Profiles

In case a pressure profile with constant scale height isn't sufficient, hydrostatic profiles with arbitrary temperature and mean molar mass functions are available through the `Hydrostatic`

type and related functions.

`ClearSky.Hydrostatic`

— TypeFunction-like type for initializing and evaluating a hydrostatic pressure profile with arbitrary temperature and mean molar mass profiles. A `Hydrostatic`

object maps altitude to pressure.

**Constructor**

`Hydrostatic(Pₛ, Pₜ, g, fT, fμ, N=1000)`

`Pₛ`

: surface pressure [Pa]`Pₜ`

: top of profile pressure [Pa]`g`

: gravitational acceleration [m/s$^2$]`fT`

: temperature [K] as a function of presssure,`fT(P)`

`fμ`

: mean molar mass [kg/mole] as a function of temperature and pressure,`fμ(T,P)`

`N`

: optional, number of interpolation nodes

For a constant molar mass or temperature, you can use anonymous functions directly. For example, to construct a hydrostatic pressure profile for a crude Earth-like atmosphere:

```
#moist adiabatic temperature profile
M = MoistAdiabat(288, 1e5, 1040, 1996, 0.029, 0.018, 2.3e6, psatH2O, Ptropo=1e4);
#hydrostatic pressure profile with constant mean molar mass
H = Hydrostatic(1e5, 1, 9.8, M, (T,P)->0.029);
#evaluate pressures at a few different altitudes
H.([0, 1e3, 1e4])
```

`ClearSky.hydrostatic`

— Function`hydrostatic(z, Pₛ, g, fT, fμ)`

Compute the hydrostatic pressure [Pa] at a specific altitude using arbitrary atmospheric profiles of temperature and mean molar mass

**Arguments**

`z`

: altitude [m] to compute pressure at`Pₛ`

: surface pressure [Pa]`g`

: gravitational acceleration [m/s$^2$]`fT`

: temperature [K] as a function of pressure,`fT(P)`

`fμ`

: mean molar mass [kg/mole] as a function of pressure and temperature`fμ(T,P)`

`ClearSky.scaleheight`

— Function`scaleheight(g, μ, T)`

Evaluate the atmospheric scale height,

$\frac{RT}{μg}$

where $R$ is the universial gas constant.

**Arguments**

`g`

: gravitational acceleration [m/s$^s$]`μ`

: mean molar mass [kg/mole]`T`

: temperature [K]

`ClearSky.altitude`

— Function`altitude(P, Pₛ, g, fT, fμ)`

Compute the altitude [m] at which a specific hydrostatic pressure occurs using arbitrary atmospheric profiles of temperature and mean molar mass

**Arguments**

`P`

: pressure [Pa] to compute altitude at`Pₛ`

: surface pressure [Pa]`g`

: gravitational acceleration [m/s$^2$]`fT`

: temperature [K] as a function of pressure,`fT(P)`

`fμ`

: mean molar mass [kg/mole] as a function of pressure and temperature`fμ(T,P)`

`altitude(H::Hydrostatic, P)`

Compute the altitude at which a specific pressure occurs in a `Hydrostatic`

pressure profile.

## Other Functions

`ClearSky.psatH2O`

— Function`psatH2O(T)`

Compute the saturation partial pressure of water vapor at a certain temperature using expressions from

`ClearSky.tsatCO2`

— Function`tsatCO2(P)`

Compute the saturation pressure of carbon dioxide at a certain pressure using an expression from Fanale et al. (1982)

`ClearSky.ozonelayer`

— Function`ozonelayer(P, Cmax=8e-6)`

Approximate the molar concentration of ozone in Earth's ozone layer using an 8 ppm peak at 1600 Pa which falls to zero at 100 Pa and 25500 Pa. Peak concentration is defined by `Cmax`

.