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What is SALONEN MODEL of Cloud detection:

Calculation method for liquid water content of clouds:

The required input parameters for the calculations of specific attenuation in clouds are frequency, temperature and liquid water content. However, the liquid water content is not generally an observable quantity. A two-part calculation method has been used in diagnosing the weather forecast model. The first part contains the cloud detection using a critical humidity function and the second part contains the determination of the liquid water content. Based on this idea a new method has been developed, where the two parts as follows:

The critical humidity as a function of the vertical coordinate and used by Geleyn has been tightened for the detection of clouds at each pressure level. According to Geleyn the critical humidity function is

Uc=1-a.s(1-s).[1+b(s-0.5)] (13)

where the parameters

a=1.0

and b=1.732 ;

s is the ratio of the pressure on the considered level and at the surface level.

If the measured humidity (U) is higher than the critical humidity (Uc) at the same pressure level, the measurement level is assumed to be in cloud. The linear interpolation has been used for the calculations of the base and top of the clouds.

The liquid water content w (g/m3) as a function of temperature t (degree Celsius) and height ( h) from cloud base is expressed as

Within cloud layers the water density w (g/m3), is a function of the height, h (m ) and of the air temperature, t [C]:

w =wo {(h-hb) /hr}a (1+c.t); t >=0 [C]

=wo {(h-hb) /hr}a exp(ct); t <0 [C] (14)

where

wo =0.17 [g/m3 ],

c=0.04 [1/C],

hr= 1500 [m],

hb =cloud base height, [m],

a(=1.0) is the parameter for height dependence.

The cloud liquid and solid water density, wl and wi [g/m3 ] are given by:

wl(t,h)=w(t,h) pw(t)

wi(t,h)=w(t,h).[1- pw(t)] (15)

where

pw (t)= liquid water fraction.

The liquid water fraction pw (t) is approximated by the function

pw(t) =1, 00C<t

= 1+ t/20, -200 C< t< 00C , (16)

=0, t< -200C

It is evident from the above liquid water fraction pw(t) and cloud liquid and solid water density, wl and wi [g/m3 ] that for temperature above zero degree Celsius only cloud liquid water exists and below –20 degree Celsius temperature only solid water exists and in the intermediate temperature (i.e. -200 C< t< 00C) both may exist.

After getting the cloud liquid water and solid water profile, the amount of liquid water and solid water can be obtained by integrating the liquid water and solid water density over the corresponding height.

Cloud liquid water = ∫ wl(t,h) dh

= ∫w(t,h) pw(t) dh [g/m2] (17)

Cloud solid water = ∫ wi(t,h) dh

= ∫ w(t,h).[1- pw(t)] dh [g/m2] (18)

where terms being their usual meanings.