# pvl_calcPwat

Calculates precipitable water (cm) from ambient air temperature (C) and relatively humidity (%).

## Contents

- Syntax
- Description
- Inputs
- Output
- Example
- Reference:

## Syntax

- `Pwat = pvl_calcPwat(T,RH)`

## Description

Calculates precipitable water (cm) from ambient air temperature (C) and relatively humidity (%) using an empirical model [1]. The model was developed by expanding Eq. 1 in [2]:

using Eq. 2 in [2]

is the apparant water vapor scale height (km). The expression for is Eq. 4 in [2]:

is the surface water vapor density (g/m^3). In the expression , is the saturation water vapor pressure (millibar). The expression for is Eq. 1 in [3]

## Inputs

- `T` - ambient air temperature at the surface (C)
- `RH` - relative humidity at the surface (%)

## Output

- `Pwat` - precipitable water (cm)

## Example

     [Pwat] = pvl_calcPwat(25,70) %Pressure at STC temperature and RH of 70%

    Pwat =

        3.5090

## Reference:

[1] W. M. Keogh and A. W. Blakers, Accurate Measurement, Using Natural Sunlight, of Silicon Solar Cells, Prog. in Photovoltaics: Res. and Appl. 2004, vol 12, pp. 1-19 (doi: 10.1002/pip.517).

    % [2]   C. Gueymard, Analysis of Monthly Average Atmospheric Precipitable
    %           Water and Turbidity in Canada and Northern United States,
    %           Solar Energy vol 53(1), pp. 57-71, 1994.
    %           (doi:10.1016/S0038-092X(94)90606-8).

    % [3]   C. Gueymard, Assessment of the Accuracy and Computing Speed of
    %           simplified saturation vapor equations using a new reference
    %           dataset, J. of Applied Meteorology 1993, vol. 32(7), pp.
    %           1294-1300 (doi:
    %           10.1175/1520-0450(1993)032<1294:AOTAAC>2.0.CO;2).

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