Wind power forecasting - Wind Power Integration: Connection and System Operational Aspects - page 218

As the development of wind power forecasting techniques has progressed over the
last decade there has been significant cross fertilisation between the physical and
statistical approaches, with the result that most modern advanced wind power fore-
casting systems use a combination of both physical and statistical modelling.
In this chapter, some relevant meteorological background is first outlined,
leading to a brief description of the very complex field of NWP. The most basic
forecasting model, that is, persistence forecasting, is then explored, and the oppor-
tunity is taken to introduce the various error measures that are used to quantify the
performance of wind power forecasting systems. The more advanced wind power
forecasting systems are then considered. In the discussion of the different systems
results from particular applications are provided to illustrate important features.

6.2 Meteorological background

6.2.1 Meteorology, weather and climate
Meteorology is the science of the atmosphere of planets. As applied to the earth, it is
concerned with the physical, dynamical and chemical state of the atmosphere and the
interactions between the atmosphere and the underlying surface including the bio-
sphere (Meteorological Office, 1991). The methods employed are both qualitative and
quantitative, based on observation but also on analysis and the use of complex math-
ematical models. Understanding and predicting the internal motion of the atmosphere,
which is caused by solar radiative heating, lies at the heart of meteorology.
Meteorology includes the study of weather and climate. Weather is the changing
atmospheric conditions at a particular location and time as they affect the planet. The
elements of the weather are temperature, atmospheric pressure, wind, humidity,
cloudiness, rain, sunshine and visibility. Climate is a summary of the weather
experienced at a location in the course of the year and over the years. Climate is
usually described not only by average values but also extreme values and frequency of
occurrence of the weather elements. As the average condition of the weather elements
change from year-to-year, climate can only be defined in terms of some period of time.
Climate data are usually expressed for individual calendar months and are calculated
over a period long enough (e.g. 30 years) to ensure that representative values for
the month are obtained. The climate at a particular location is affected by its latitude,
by its proximity to oceans and continental land masses and large-scale atmospheric
circulation patterns, its altitude and local geographical features.
Wind power meteorology is a new term used by Petersen et al. (1997) to
describe the theories and practice of both meteorology and climatology as they
apply specifically to wind power. This field has developed in the last few decades
and includes three main areas: (1) regional wind resource assessment, (2) micro-
siting of wind turbines and (3) wind farms and short-term wind power forecasting.

6.2.2 Atmospheric structure and scales
The atmosphere is a thin film of gas clinging to the earth's surface under gravita-
tional attraction. The horizontal and vertical spatial scales in the atmosphere