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tlcl_td_bolton

Compute the lifting condensation level temperature using dew point temperature.

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_td_bolton (
		t          : numeric,  ; float, double, integer only
		td         : numeric,  
		iounit [2] : integer   
	)

	return_val [dimsizes(t)] :  float or double

Arguments

t

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

td

A scalar or array containing dew point temperatures with the same units as t. If td 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 and td are degrees Celcius (degC)
  • iounit(0)=1 input t and td are degrees Kelvin (degK)
  • iounit(0)=2 input t and td are degrees Farenheit (degF)

  • iounit(1)=0 output tlcl are degrees Celcius (degC)
  • iounit(1)=1 output tlcl are degrees Kelvin (degK)
  • iounit(1)=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 15 in Bolton (1980).

An interactive lifting condensation level calculator is available here. 

References:

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

   Wikipedia: Lifted Condensation Level

See Also

tlcl_rh_bolton, tlcl_evp_bolton, tlcl_mixr_bolton, mixhum_convert

Examples

Example 1: Calculate the temperature at the lifted condensation level (tlcl) using tlcl_td_bolton. The online site: Calculating LCL Temperature gives the following result: tlcl=8.8765C. 


   t    = 20         ; C ==> iounit(0)=0
   td   = 13.5       ; C                    
   tlcl = tlcl_td_bolton(t, td, (/0,0/))  ; tlcl=8.8766 ; C ==> iounit(1)=0
   printVarSummary(tlcl)
The variable output which contains meta data is: 

   Variable: tlcl
   Type: float
   Total Size: 4 bytes
               1 values
   Number of Dimensions: 1
   Dimensions and sizes:	[1]
   Coordinates: 
   Number Of Attributes: 4
     long_name :	temperature: LCL
     units :	degC
     source :	Bolton (1980): Eq. 15: Dew Point Temperature
     NCL :	tlcl_td_bolton

       8.876617 



Example 2: Read temperature (T [degK]) and relative humidity (RELHUM [%]); (a)  compute the dew point temperatures;
(b) calculate the temperatures at the lifted condensation level.


   a  = addfile("cam35.h0.0008-07.nc","r") 
   t  = a->T                  ; K  ==> iounit(0)=1
   rh = a->RELHUM             ; %
   td = dewtemp_trh(t ,rh)  ; dewtemp_trh requires ttlcl_td_bolton(t, td, (/1,1/)) ; K  ==> iounit(1)=1
   printVarSummary(tlcl)
   printMinMax(tlcl,0)


The output is:


   Variable: tlcl
   Type: float
   Total Size: 1437696 bytes
               359424 values
   Number of Dimensions: 4
   Dimensions and sizes:	[time | 1] x [lev | 26] x [lat | 96] x [lon | 144]
   Coordinates: 
               time: [3132..3132]
               lev: [3.54463800000001..992.5560999999998]
               lat: [ -90..89.99999999999999]
               lon: [   0..357.5]
   Number Of Attributes: 4
     long_name :	temperature: LCL
     units :	degK
     source :	Bolton (1980): Eq. 15: Dew Point Temperature
     NCL :	tlcl_td_bolton

     temperature: LCL (degK) : min=164.972   max=298.26