Open topic with navigation

EddyPro Help > Data Processing Reference > Preliminary Processing > Calculating Micrometeorological Variables

Calculating MicrometeorologicalVariables

Before calculating fluxes, EddyPro calculates anadditional set of micrometeorological parameters,which are used to calculate corrected fluxes or forfuture analysis of calculated fluxes. These are listedand briefly described here.

Molecularweightofwetair(Ma,kgmol1)Calculated as the sum of molecular weights of dry air and water vapor, weighted by the watervapor mole fraction:

Ma=Mh2oh2o+Md(1-h2o)

where the subscript d is used for quantities referring to dry air, and where Md=0.02897 kg mol-1 and Mh2o=0.01802 kg mol-1.

Ambientwatervapormassdensity(h2o,kgm3)Calculated form water vapor mole fraction as:

Watervaporpartialpressure(e,Pa)Calculated from the ideal gas law:

e=h2oRh2oTa

where , is the water vapor gas constant.

Watervaporpartialpressureatsaturation(es,Pa)Calculated after Campbell and Norman (1998) as:

(e=2.7182, the base of the exponential function, not the water vapor partial pressure)

Relativehumidity(RH,%)RH is computed according to its definition as:

Watervaporpressuredeficit(VPD,Pa)It is given by the difference between actual water vapor pressure and its saturation value:

Resources:

Video Tutorials

Overview of EddyPro Work-flows

Printable PDF Manual

EddyPro Forum

VPD = e-es

Dewpointtemperature(Tdew,K)It is calculated after Campbell and Norman (1998) as:

where e is intended to be in kPa.

Dryairpartialpressure(Pd,Pa)This is given simply by the difference between total (ambient) pressure and water vapor partialpressure.

Pd = Pa - e

Dryairmolarvolume(vd,m3mol1)It is calculated after Ibrom et al. (2007b) as:

,

this formula has the same result as the direct application of the ideal gas law.

Dryairmassdensity(d,kgm3)From the ideal gas law:

,

where is the dry air gas constant.

Moistairmassdensity(a,kgm3)It is given by the sum of dry air and water vapor mass densities:

.

Dryairheatcapacityatconstantpressure(cp,d,Jkg1K1)It is calculated as a function of temperature as:

,

where Ta is expressed in degrees Celsius.

Watervaporheatcapacityatconstantpressure(cp,h2o,Jkg1K1)It is calculated as a function of temperature and relative humidity as:

,

where Ta is expressed in degrees Celsius.

Specifichumidity(Q,kgkg1)It is calculated according to its definition as:

.

Refiningambienttemperature(Ta,K)If ambient air temperature was calculated from sonic temperature, it is now corrected for theeffect of ambient moisture content (van Dijk, 2004, eq. 3.49):

.

Otherwise, if ambient air temperature was calculated by averaging raw data of ambient airtemperature, Ta does not need a correction. In this case, a temperature mapping factor (Tmap) iscalculated to rescale covariances that involve sonic temperature fluctuations arising frompossible errors in the estimation of the acoustic path length of the anemometer (van Dijk,2004):

where x is any other variable, notably w.

Refinementofcelltemperature(Tc,K)(closedpathsystemsonly)Cell temperature is now updated to account for the effect of ambient moisture content if, in theprevious calculation, it was set equal to ambient air temperature. Recall that this happens onlywhen no temperature reading from inside the cell is available.

Moistairheatcapacityatconstantpressure(Cp,Jkg1K1)It is calculated as a function of ambient moisture content as:

Specificevaporationheat(,Jkg1)It is calculated as a function of ambient air temperature:

=103(3147.5-2.37Ta)

Watertodryairdensityratio(,nondimensional)It is given by:

Product Information:

EddyPro 4 Eddy Covariance SoftwareHelp updated on: 2/13/2013

Copyright 2012 LI-COR, Inc.

Contact Us:

envsupport@licor.comwww.licor.com/envInternational: 1-402-467-3576US: 800-447-3576