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# tlcl_evp_bolton

Compute the lifting condensation level temperature using water vapor pressure. Available in version 6.5.0 and later.

## Prototype

```load "\$NCARG_ROOT/lib/ncarg/nclscripts/csm/contributed.ncl"  ; This library is automatically loaded
; from NCL V6.2.0 onward.
; No need for user to explicitly load.

function tlcl_evp_bolton (
t          : numeric,  ; float, double, integer only
evp        : numeric,
iounit  : integer
)

return_val [dimsizes(t)] :  float or double
```

## Arguments

t

A scalar or array containing temperature (units: degC, degK, degF). If t and rh are arrays they must be the same size and shape.

evp

A scalar or array containing water vapor pressure. If evp and t are arrays they must be the same size and shape.

iounit

An integer array of length 2 which specifies the units of the input t and the units of the returned variable.

• iounit(0)=0 input t in degrees Celcius (degC)
• iounit(0)=1 input t in degrees Kelvin (degK)
• iounit(0)=2 input t in degrees Farenheit (degF)

• iounit(1)=0 input t in hecto-Pascals (hPa)
• iounit(1)=1 input t in Pascals (Pa)
• iounit(1)=2 input t in kilo-Pascals (kPa)

• iounit(2)=0 output tlcl are degrees Celcius (degC)
• iounit(2)=1 output tlcl are degrees Kelvin (degK)
• iounit(2)=2 output tlcl are degrees Farenheit (degF)

## Return value

A variable of the same size and shape as t.

## Description

The lifted condensation level or lifting condensation level (LCL) is formally defined as the height or pressure at which the relative humidity (RH) of an air parcel will reach 100% with respect to liquid water when it is cooled by dry adiabatic lifting. The temperature at the LCL is denoted as the 'lifted condensation level temperature' (tlcl). In theory, the lifting condensation level (LCL) is for a parcel of air lifted from the surface.

This function is based on Equation 21 in Bolton (1980).

An interactive lifting condensation level calculator is available here.kjkj

```References:

Bolton, D. (1980): The Computation of Equivalent Potential Temperature
Monthly Weather Review, vol. 108, no. 7 (july),  p. 1047

Wikipedia: Lifted Condensation Level
```

## Examples

Example 1: Calculate the temperature at the lifted condensation level (tlcl) using tlcl_evp_bolton.

```
t    = 20         ; C     ==>  iounit(0)=0
evp  = 17.39      ; hPa   ==>  iounit(1)=0
tlcl = tlcl_evp_bolton(t, evp, (/0,0,0/))  ; C  ==> iounit(2)=0;
printVarSummary(tlcl)

```
The edited output is:
```   Variable: tlcl
Type: float
Total Size: 4 bytes
1 values
Number of Dimensions: 1
Dimensions and sizes:	
Coordinates:
Number Of Attributes: 4
long_name :	temperature: LCL
units :	degC
source :	Bolton (1980): Eq. 21: Water Vapor Pressure
NCL :	tlcl_evp_bolton_21

14.22739
```