Geoscience Reference
In-Depth Information
An important concept behind climate observations is representativeness, which
is the degree to which the observation accurately describes the value of the variable
needed for a specific purpose. Therefore, it is not a fixed quality of any observation,
but results from joint appraisal of instrumentation, measurement interval and
exposure against the requirements of some particular application [WMO 08]. An
estimate of spatiotemporal representativeness of air temperature and precipitation is
shown in Figure 1.2, with much higher spatial correlation for air temperature
compared with precipitation. It can be concluded from this results that station
density has to be much higher for precipitation compared with air temperature and
that station density has to be increased for investigations with increasing temporal
resolution.
Figure 1.2.
Average decorrelation distances (r² decreasing below 0.5) for air temperature
and precipitation in four time resolutions. Samples: daily values for all of Europe; monthly,
seasonal and annual for the Greater Alpine Region (from [AUE 05])
Various meteorological applications have their own preferred timescale and
space scale for averaging, station density, and resolution of phenomena. From there,
for example, weather forecast requires more frequent observations compared to
climate monitoring. The spatio-temporal dependency of meteorological phenomena
results in simple scaling convention (see Table 1.1).
Type of motion
Spatial scale
Temporal scale
(m)
Eddy 0.001 0.001
Micro turbulence 10 10
Tornado 100 60
Cumulus convection 1,000 20 min
Cumulunimbus 100,000 1 h
Front 100,000 3 h
Hurrican 100,000 3 h
Cyclone 1,000,000 1 d
Planetaric waves 10,000,000 10 d
Table 1.1.
Spatial and temporal scales of meteorological phenomena
