Distribution of the humidity characteristics with height in the surface layer

Let’s find S=S(z) in the surface layer integrate (20.5) from 0 to Z

z	s dz k s / z ( k s / z)
	t
			0
0
		negligibly small comparing to				(20.6)
With the accuracy 10 % :			k s	( k		s )0 0	(20.7)
			z			z

Is the w.v.flux at z=0, i.e. the rate of evaporation from the

Earth’s surface:

( k	s )0 Q'0
	z	12

k	s	Q'0 0	or Q'0 k	s	(20.8)
	z			z

(20.8) shows that the w.v. eddy flux in the surface layer can be regarded as approximately unchangeable

with height ( as well as a heat flux).

Similarly to the heat flux :

S(z) S2	Q'0	ln	z z0	(20.9)
			z2 z0
	a 0

“S” decreases at Q’0 < 0 with height proportionally to ln z

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Humidity distribution above the surface layer

e		p		exp(	g z			)	(20.10)
e					R T
		p	0
0							m

Comparision of calculated and observed w.v. pressure values shows that the observed values decrease with height much more rapidly than calculated ones.

			z			z 2
	S S0 *10		g		120		(20.11)

Suring’s formula

Z in km

( empirical)

True within the boundary layer above the surface layer

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Diurnal variation of the humidity characteristics

w.v.pressure

Absolute humidity

Near	7 a.m. 3-5 p.m. 7-10 p.m.
sunrise

Diurnal variation is better pronounced over land in the warm season

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Diurnal variation of the humidity characteristics

relative humidity

In winter/over water surfaces:

One min, usually before sunrise.

	Weak max, supposed before noon.
	Reasons:
	1.	Eddy exchange is weak
3 p.m. In the night	2.	Eddy transfer of the w.v. is
when T air drops		compensated by evaporation

RH=100% *e/E

e decreases near noon (summer)

E sharply increases (account for T rise)

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