<s>
An	O
atmospheric	B-Application
model	I-Application
is	O
a	O
mathematical	O
model	O
constructed	O
around	O
the	O
full	O
set	O
of	O
primitive	O
dynamical	O
equations	O
which	O
govern	O
atmospheric	O
motions	O
.	O
</s>
<s>
It	O
can	O
supplement	O
these	O
equations	O
with	O
parameterizations	B-Application
for	O
turbulent	O
diffusion	O
,	O
radiation	O
,	O
moist	O
processes	O
(	O
clouds	O
and	O
precipitation	O
)	O
,	O
heat	O
exchange	O
,	O
soil	O
,	O
vegetation	O
,	O
surface	O
water	O
,	O
the	O
kinematic	O
effects	O
of	O
terrain	O
,	O
and	O
convection	O
.	O
</s>
<s>
Most	O
atmospheric	B-Application
models	I-Application
are	O
numerical	O
,	O
i.e.	O
</s>
<s>
They	O
can	O
predict	O
microscale	O
phenomena	O
such	O
as	O
tornadoes	B-Language
and	O
boundary	O
layer	O
eddies	O
,	O
sub-microscale	O
turbulent	O
flow	O
over	O
buildings	O
,	O
as	O
well	O
as	O
synoptic	O
and	O
global	O
flows	O
.	O
</s>
<s>
Global	O
models	O
often	O
use	O
spectral	B-Algorithm
methods	I-Algorithm
for	O
the	O
horizontal	O
dimensions	O
and	O
finite-difference	B-Algorithm
methods	I-Algorithm
for	O
the	O
vertical	O
dimension	O
,	O
while	O
regional	O
models	O
usually	O
use	O
finite-difference	B-Algorithm
methods	I-Algorithm
in	O
all	O
three	O
dimensions	O
.	O
</s>
<s>
For	O
specific	O
locations	O
,	O
model	O
output	O
statistics	O
use	O
climate	O
information	O
,	O
output	O
from	O
numerical	B-General_Concept
weather	I-General_Concept
prediction	I-General_Concept
,	O
and	O
current	O
surface	O
weather	O
observations	O
to	O
develop	O
statistical	O
relationships	O
which	O
account	O
for	O
model	O
bias	O
and	O
resolution	O
issues	O
.	O
</s>
<s>
The	O
history	B-Application
of	I-Application
numerical	I-Application
weather	I-Application
prediction	I-Application
began	O
in	O
the	O
1920s	O
through	O
the	O
efforts	O
of	O
Lewis	O
Fry	O
Richardson	O
who	O
utilized	O
procedures	O
developed	O
by	O
Vilhelm	O
Bjerknes	O
.	O
</s>
<s>
It	O
was	O
not	O
until	O
the	O
advent	O
of	O
the	O
computer	O
and	O
computer	B-Application
simulation	I-Application
that	O
computation	O
time	O
was	O
reduced	O
to	O
less	O
than	O
the	O
forecast	O
period	O
itself	O
.	O
</s>
<s>
ENIAC	B-Device
created	O
the	O
first	O
computer	O
forecasts	O
in	O
1950	O
,	O
and	O
more	O
powerful	O
computers	O
later	O
increased	O
the	O
size	O
of	O
initial	O
datasets	O
and	O
included	O
more	O
complicated	O
versions	O
of	O
the	O
equations	O
of	O
motion	O
.	O
</s>
<s>
The	O
development	O
of	O
global	O
forecasting	O
models	O
led	O
to	O
the	O
first	O
climate	B-Application
models	I-Application
.	O
</s>
<s>
Even	O
with	O
the	O
increasing	O
power	O
of	O
supercomputers	O
,	O
the	O
forecast	O
skill	O
of	O
numerical	B-General_Concept
weather	I-General_Concept
models	I-General_Concept
only	O
extends	O
to	O
about	O
two	O
weeks	O
into	O
the	O
future	O
,	O
since	O
the	O
density	O
and	O
quality	O
of	O
observations	O
—	O
together	O
with	O
the	O
chaotic	O
nature	O
of	O
the	O
partial	O
differential	O
equations	O
used	O
to	O
calculate	O
the	O
forecast	O
—	O
introduce	O
errors	O
which	O
double	O
every	O
five	O
days	O
.	O
</s>
<s>
The	O
length	O
of	O
the	O
time	O
step	O
chosen	O
within	O
the	O
model	O
is	O
related	O
to	O
the	O
distance	O
between	O
the	O
points	O
on	O
the	O
computational	O
grid	O
,	O
and	O
is	O
chosen	O
to	O
maintain	O
numerical	B-Algorithm
stability	I-Algorithm
.	O
</s>
<s>
The	O
UKMET	O
Unified	B-Application
model	I-Application
is	O
run	O
six	O
days	O
into	O
the	O
future	O
,	O
the	O
European	O
Centre	O
for	O
Medium-Range	O
Weather	O
Forecasts	O
model	O
is	O
run	O
out	O
to	O
10days	O
into	O
the	O
future	O
,	O
while	O
the	O
Global	O
Forecast	O
System	O
model	O
run	O
by	O
the	O
Environmental	B-Application
Modeling	I-Application
Center	I-Application
is	O
run	O
16days	O
into	O
the	O
future	O
.	O
</s>
<s>
Different	O
models	O
use	O
different	O
solution	O
methods	O
:	O
some	O
global	O
models	O
use	O
spectral	B-Algorithm
methods	I-Algorithm
for	O
the	O
horizontal	O
dimensions	O
and	O
finite	B-Algorithm
difference	I-Algorithm
methods	I-Algorithm
for	O
the	O
vertical	O
dimension	O
,	O
while	O
regional	O
models	O
and	O
other	O
global	O
models	O
usually	O
use	O
finite-difference	B-Algorithm
methods	I-Algorithm
in	O
all	O
three	O
dimensions	O
.	O
</s>
<s>
Weather	O
and	O
climate	B-Application
model	I-Application
gridboxes	O
have	O
sides	O
of	O
between	O
and	O
.	O
</s>
<s>
Therefore	O
,	O
the	O
processes	O
that	O
such	O
clouds	O
represent	O
are	O
parameterized	B-Application
,	O
by	O
processes	O
of	O
various	O
sophistication	O
.	O
</s>
<s>
Weather	B-General_Concept
models	I-General_Concept
that	O
have	O
gridboxes	O
with	O
sides	O
between	O
and	O
can	O
explicitly	O
represent	O
convective	O
clouds	O
,	O
although	O
they	O
still	O
need	O
to	O
parameterize	O
cloud	O
microphysics	O
.	O
</s>
<s>
Rather	O
than	O
assuming	O
that	O
clouds	O
form	O
at	O
100%	O
relative	O
humidity	O
,	O
the	O
cloud	B-Application
fraction	I-Application
can	O
be	O
related	O
to	O
a	O
critical	O
relative	O
humidity	O
of	O
70%	O
for	O
stratus-type	O
clouds	O
,	O
and	O
at	O
or	O
above	O
80%	O
for	O
cumuliform	O
clouds	O
,	O
reflecting	O
the	O
sub	O
grid	O
scale	O
variation	O
that	O
would	O
occur	O
in	O
the	O
real	O
world	O
.	O
</s>
<s>
The	O
amount	O
of	O
solar	O
radiation	O
reaching	O
ground	O
level	O
in	O
rugged	O
terrain	O
,	O
or	O
due	O
to	O
variable	O
cloudiness	O
,	O
is	O
parameterized	B-Application
as	O
this	O
process	O
occurs	O
on	O
the	O
molecular	O
scale	O
.	O
</s>
<s>
High-resolution	O
models	O
—	O
also	O
called	O
mesoscale	O
models	O
—	O
such	O
as	O
the	O
Weather	B-Application
Research	I-Application
and	I-Application
Forecasting	I-Application
model	I-Application
tend	O
to	O
use	O
normalized	O
pressure	O
coordinates	O
referred	O
to	O
as	O
sigma	O
coordinates	O
.	O
</s>
<s>
Some	O
of	O
the	O
better	O
known	O
global	O
numerical	B-Application
models	I-Application
are	O
:	O
</s>
<s>
Some	O
of	O
the	O
better	O
known	O
regional	O
numerical	B-Application
models	I-Application
are	O
:	O
</s>
<s>
WRF	O
The	O
Weather	B-Application
Research	I-Application
and	I-Application
Forecasting	I-Application
model	I-Application
was	O
developed	O
cooperatively	O
by	O
NCEP	O
,	O
NCAR	O
,	O
and	O
the	O
meteorological	O
research	O
community	O
.	O
</s>
<s>
WRF-NMM	B-Application
The	O
WRF	O
Nonhydrostatic	O
Mesoscale	O
Model	O
is	O
the	O
primary	O
short-term	O
weather	O
forecast	O
model	O
for	O
the	O
U.S.	O
,	O
replacing	O
the	O
Eta	O
model	O
.	O
</s>
<s>
HARMONIE-Climate	O
(	O
HCLIM	O
)	O
is	O
a	O
limited	O
area	O
climate	B-Application
model	I-Application
based	O
on	O
the	O
model	O
developed	O
by	O
a	O
large	O
consortium	O
of	O
European	O
weather	O
forecastign	O
and	O
research	O
institutes	O
.	O
</s>
<s>
MAR	O
(	O
Modele	O
Atmospherique	O
Regionale	O
)	O
is	O
a	O
regional	B-Application
climate	I-Application
model	I-Application
developed	O
at	O
the	O
University	O
of	O
Grenoble	O
in	O
France	O
and	O
the	O
University	O
of	O
Liege	O
in	O
Belgium	O
.	O
</s>
<s>
HIRHAM5	O
is	O
a	O
regional	B-Application
climate	I-Application
model	I-Application
developed	O
at	O
the	O
Danish	O
Meteorological	O
Institute	O
and	O
the	O
Alfred	O
Wegener	O
Intitute	O
in	O
Potsdam	O
.	O
</s>
<s>
It	O
is	O
also	O
based	O
on	O
the	O
HIRLAM	B-Application
dynamics	O
with	O
physical	O
schemes	O
based	O
on	O
those	O
in	O
the	O
ECHAM	O
model	O
.	O
</s>
<s>
NAM	B-Application
The	O
term	O
North	B-Application
American	I-Application
Mesoscale	I-Application
model	I-Application
refers	O
to	O
whatever	O
regional	O
model	O
NCEP	O
operates	O
over	O
the	O
North	O
American	O
domain	O
.	O
</s>
<s>
Beginning	O
in	O
May	O
2006	O
,	O
NCEP	O
began	O
to	O
use	O
the	O
WRF-NMM	B-Application
as	O
the	O
operational	O
NAM	B-Application
.	O
</s>
<s>
ARPS	O
the	O
Advanced	O
Region	O
Prediction	O
System	O
developed	O
at	O
the	O
University	O
of	O
Oklahoma	O
is	O
a	O
comprehensive	O
multi-scale	O
nonhydrostatic	O
simulation	O
and	O
prediction	O
system	O
that	O
can	O
be	O
used	O
for	O
regional-scale	O
weather	O
prediction	O
up	O
to	O
the	O
tornado-scale	O
simulation	O
and	O
prediction	O
.	O
</s>
<s>
HIRLAM	B-Application
High	O
Resolution	O
Limited	O
Area	O
Model	O
,	O
is	O
developed	O
by	O
the	O
European	O
NWP	O
research	O
consortia	O
co-funded	O
by	O
10	O
European	O
weather	O
services	O
.	O
</s>
<s>
The	O
meso-scale	O
HIRLAM	B-Application
model	O
is	O
known	O
as	O
HARMONIE	O
and	O
developed	O
in	O
collaboration	O
with	O
Meteo	O
France	O
and	O
ALADIN	O
consortia	O
.	O
</s>
<s>
Its	O
application	O
is	O
from	O
mesoscale	O
to	O
centimetric	O
scales	O
weather	B-General_Concept
simulations	I-General_Concept
.	O
</s>
<s>
Statistical	O
models	O
were	O
created	O
based	O
upon	O
the	O
three-dimensional	O
fields	O
produced	O
by	O
numerical	B-General_Concept
weather	I-General_Concept
models	I-General_Concept
,	O
surface	O
observations	O
,	O
and	O
the	O
climatological	O
conditions	O
for	O
specific	O
locations	O
.	O
</s>
<s>
These	O
statistical	O
models	O
are	O
collectively	O
referred	O
to	O
as	O
model	O
output	O
statistics	O
(	O
MOS	O
)	O
,	O
and	O
were	O
developed	O
by	O
the	O
National	O
Weather	O
Service	O
for	O
their	O
suite	O
of	O
weather	B-Application
forecasting	I-Application
models	I-Application
.	O
</s>
<s>
The	O
United	O
States	O
Air	O
Force	O
developed	O
its	O
own	O
set	O
of	O
MOS	O
based	O
upon	O
their	O
dynamical	O
weather	B-General_Concept
model	I-General_Concept
by	O
1983	O
.	O
</s>
<s>
Model	O
output	O
statistics	O
differ	O
from	O
the	O
perfect	O
prog	O
technique	O
,	O
which	O
assumes	O
that	O
the	O
output	O
of	O
numerical	B-General_Concept
weather	I-General_Concept
prediction	I-General_Concept
guidance	O
is	O
perfect	O
.	O
</s>
<s>
This	O
was	O
the	O
first	O
successful	O
climate	B-Application
model	I-Application
.	O
</s>
<s>
Several	O
groups	O
then	O
began	O
working	O
to	O
create	O
general	B-Application
circulation	I-Application
models	I-Application
.	O
</s>
<s>
The	O
first	O
general	O
circulation	O
climate	B-Application
model	I-Application
combined	O
oceanic	O
and	O
atmospheric	O
processes	O
and	O
was	O
developed	O
in	O
the	O
late	O
1960s	O
at	O
the	O
Geophysical	O
Fluid	O
Dynamics	O
Laboratory	O
,	O
a	O
component	O
of	O
the	O
U.S.	O
National	O
Oceanic	O
and	O
Atmospheric	O
Administration	O
.	O
</s>
<s>
By	O
the	O
early	O
1980s	O
,	O
the	O
U.S.	O
National	O
Center	O
for	O
Atmospheric	O
Research	O
had	O
developed	O
the	O
Community	O
Atmosphere	O
Model	O
(	O
CAM	O
)	O
,	O
which	O
can	O
be	O
run	O
by	O
itself	O
or	O
as	O
the	O
atmospheric	O
component	O
of	O
the	O
Community	B-Application
Climate	I-Application
System	I-Application
Model	I-Application
.	O
</s>
<s>
Coupled	O
ocean-atmosphere	O
climate	B-Application
models	I-Application
,	O
such	O
as	O
the	O
Hadley	O
Centre	O
for	O
Climate	O
Prediction	O
and	O
Research	O
's	O
HadCM3	B-Application
model	O
,	O
are	O
being	O
used	O
as	O
inputs	O
for	O
climate	O
change	O
studies	O
.	O
</s>
<s>
Air	O
pollution	O
forecasts	O
depend	O
on	O
atmospheric	B-Application
models	I-Application
to	O
provide	O
fluid	O
flow	O
information	O
for	O
tracking	O
the	O
movement	O
of	O
pollutants	O
.	O
</s>
<s>
The	O
Movable	O
Fine-Mesh	O
model	O
,	O
which	O
began	O
operating	O
in	O
1978	O
,	O
was	O
the	O
first	O
tropical	B-Application
cyclone	I-Application
forecast	I-Application
model	I-Application
to	O
be	O
based	O
on	O
atmospheric	O
dynamics	O
.	O
</s>
<s>
Despite	O
the	O
constantly	O
improving	O
dynamical	O
model	O
guidance	O
made	O
possible	O
by	O
increasing	O
computational	O
power	O
,	O
it	O
was	O
not	O
until	O
the	O
1980s	O
that	O
numerical	B-General_Concept
weather	I-General_Concept
prediction	I-General_Concept
(	O
NWP	O
)	O
showed	O
skill	O
in	O
forecasting	O
the	O
track	O
of	O
tropical	O
cyclones	O
.	O
</s>
