SCMS95: BPH Messages: 2 Entries..

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Entry Date Title Site Author
36Wed 19-Jul-1995Scaling for bandpass parametersnoneHorst, Tom
129Sun 13-Aug-1995Moved BPH sensors to height of hygros at all sitesnoneSemmer, Steve


36: BPH/none Wed 19-Jul-1995 22:27:12 GMT Scaling for bandpass parameters
I have calculated the required scaling for bandpass quantities:

w:rh2o (wq in EVE) in units of m/s gm/kg
----------------------------------------

Latent heat flux (W) = LE = rho*L*w:rh2o

w:rh2o = LE/(rho*L) = (J/m^2-s)/(1 kg/m^3 * 2.5e6 J/kg)
                    = LE*4e-7 m/s * 1e3 gm/kg
                    = LE*4e-4 m/s gm/kg

Thus a range of +- 1000 W/m^2 for LE requires a range
of +- 0.4 m/s gm/kg for w:rh20; 
a resolution of 0.1 W/m^2 for LE requires a resolution
of   4e-5 m/s gm/kg for w:rh2o

Similar requirements would apply to "a" in wq = a + b*wt

w:t (wt in EVE) in units of m/s degC
------------------------------------

Sensible heat flux (W) = S = rho*Cp*w:t

w:t = S/(rho*Cp) = (J/m^2-s)/(1 kg/m^3 * 1e3 J/kg-degC)
                 = S*1e-3 m/s degC

Thus a range of +- 1000 W/m^2 for S requires a range
of +- 1 m/s degC for w:t;
a resolution of 0.1 W/m^2 for S requires a resolution
of 1e-3 m/s degC for w:t

b = w:rh2o/w:t in units of gm/kg-degC
-------------------------------------

Bowen ratio = B = S/LE = rho*Cp*w:t/(rho*L*w:rh2o)

b = Cp/(L*B)*1e3 gm/kg = (1e3 J/kg-degC)/(2.5e6 J/kg)*(1e3 gm/kg)
                   = 0.4/B gm/kg-degC 

We might want a resolution of +- 0.01 for B and a range of +- 100
to cover circumstances where either heat flux is more than 1% of 
their sum.  Thus a similar range and resolution is required for b,
since 0.4 ~ 1.

129: BPH/none Sun 13-Aug-1995 17:59:10 GMT Moved BPH sensors to height of hygros at all sites