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.*

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