Wind power forecasting - Wind Power Integration: Connection and System Operational Aspects - page 220

1.0E+008

1 m/s

Earth's mean radius

Climate
change

1.0E+006

Season

1.0E+004

1.0E+002

1.0E+000

1.0E-002

Week

Hour

Year

Minute

Second Day

1.0E-004

1E+000 1E+002 1E+004 1E+006 1E+008 1E+010

Time scale (s)

Figure 6.1 Spatial and temporal scales of disturbance phenomena in the

atmosphere

is governed by seven physical equations, three arising from thermodynamic con-
siderations and four arising from hydrodynamic considerations (Atkinson, 1981).
The thermodynamic equations are the gas law, also known as the equation of state,
the first law of thermodynamics and an equation representing the conservation of
moisture. The hydrodynamic equations are the equation of continuity and the three
equations of motion corresponding to the components of Newton's second law in
three directions. The seven governing equations involve the atmospheric variables
and their spatial and time derivatives. In order for the atmospheric model to provide
a usable description of the behaviour of the atmosphere, a solution must be found to
the equations. In general, no analytical solution is possible and numerical methods
must be adopted. The task involved is to calculate how each of the meteorological
variables will change as the simulation runs forward in time.
NWP is an objective forecast in which the future state of the atmosphere is
determined by the numerical solution of a set of equations describing the evolution
of meteorological variables which together define the state of the atmosphere
(Meteorological Office, 1991). In the excellent review of the developments in NWP
to be found in Kalnay et al. (1998) it is pointed out that, while there has been huge
progress in the last two decades, with a doubling of forecast skill, there are three
major requirements for improved NWP: (1) better atmospheric models, (2) better
observational data and (3) better methods for data assimilation. Data assimilation
involves the quality check run on the weather observations received via the Global