<s>
In	O
models	O
of	O
radiative	O
transfer	O
,	O
the	O
two-stream	B-Algorithm
approximation	I-Algorithm
is	O
a	O
discrete	O
ordinate	O
approximation	O
in	O
which	O
radiation	O
propagating	O
along	O
only	O
two	O
discrete	O
directions	O
is	O
considered	O
.	O
</s>
<s>
The	O
two-stream	B-Algorithm
approximation	I-Algorithm
is	O
commonly	O
used	O
in	O
parameterizations	O
of	O
radiative	O
transport	O
in	O
global	B-Application
circulation	I-Application
models	I-Application
and	O
in	O
weather	B-General_Concept
forecasting	I-General_Concept
models	I-General_Concept
,	O
such	O
as	O
the	O
WRF	B-Application
.	O
</s>
<s>
There	O
is	O
a	O
large	O
number	O
of	O
applications	O
of	O
the	O
two-stream	B-Algorithm
approximation	I-Algorithm
,	O
including	O
variants	O
such	O
as	O
the	O
Kubelka-Munk	O
approximation	O
.	O
</s>
<s>
The	O
two-stream	B-Algorithm
approximation	I-Algorithm
comes	O
in	O
many	O
variants	O
,	O
including	O
the	O
Eddington	O
approximation	O
,	O
as	O
well	O
as	O
the	O
modified	O
Eddington	O
,	O
Quadrature	O
,	O
and	O
Hemispheric	O
constant	O
models	O
.	O
</s>
<s>
Mathematical	O
descriptions	O
of	O
the	O
two-stream	B-Algorithm
approximation	I-Algorithm
are	O
given	O
in	O
several	O
books	O
.	O
</s>
