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satvpr_slope_fao56

Compute the slope of the saturation vapor pressure curve as described in FAO 56. Available in version 6.4.0 and later.

Prototype

```load "\$NCARG_ROOT/lib/ncarg/nclscripts/csm/crop.ncl"  ; This library is automatically loaded
; from NCL V6.5.0 onward.
; No need for user to explicitly load.

function satvpr_slope_fao56 (
temp       : numeric,
iounit  : integer
)
```

Arguments

temp

An array of any dimensionality containing temperatures.

iounit

An integer array of length 2:

• iounit(0)=0 means the input are in degrees C (degC)
• iounit(0)=1 means the input are in degrees K (degK)
• iounit(0)=2 means the input are in degrees F.

If iounit(0)=1 or 2, the temp will be converted to degC internally prior to the computation. The input temp are unaltered.

• iounit(1)=0 means the output are in hPa
• iounit(1)=1 means the output are in Pa
• iounit(1)=2 means the output are in kPa

Return value

An array with the same dimensionality and type as temp containing the slopes of the saturation vapor pressure curve.

Description

Compute the slope of the saturation vapor pressure (kPa/degC) as described in the Food and Agriculture Organization (FAO) Irrigation and Drainage Paper 56 entitled: Crop evapotranspiration - Guidelines for computing crop water requirement. Specifically, see equation 13 of Chapter 3.

Examples

A table which displays slopes of saturation vapor pressure for different temperatures is here.

Example 1: Let t contain a temperature value (degC).

```
t       = 19.75                      ; degC; temperature
; iounit(0)=0 degC
; iounit(1)=2 kPa/C
slpvpr  = satvpr_slope_fao56(t, (/0,2/))   ; 0.142793 kPa/C

printVarSummary(slpvpr)

```
The output for 'slpvpr' is
```
Variable: slpvpr
Type: float
Total Size: 4 bytes
1 values
Number of Dimensions: 1
Dimensions and sizes:	
Coordinates:
Number Of Attributes: 4
long_name :	slope of saturation vapor pressure curve
units :	kPa/degC
url :	http://www.fao.org/docrep/X0490E/x0490e07.htm
info :	FAO 56; EQN 14

```

Example 2: Consider T(time,lat,lon) with sizes (3,73,144) and units of degK. Here iounit=1.

```
slpvpr  = satvpr_slope_fao56(T, (/0,2/))
printVarSummary(slpvpr)

```
The output for 'satvpr' is
```
Variable: slpvpr
Type: float
Total Size: 126144 bytes
31536 values
Number of Dimensions: 3
Dimensions and sizes:	[time | 3] x [lat | 73] x [lon | 144]
Coordinates:
time: [1..3]
lat: [-90..90]
lon: [ 0..357.5]
Number Of Attributes: 4
long_name :	slope saturation vapor pressure curve
units :	kPa/C
url :	http://www.fao.org/docrep/X0490E/x0490e07.htm
info :	FAO 56; EQN 13

```