Annual mean
In meteorology and climatology, the mean values of measured variables of a certain location that change approximately with the annual period are referred to as annual mean . Such variables are mainly temperature , humidity, cloud cover and precipitation .
Other geo- referenced, often averaged data are e.g. B. the water level of rivers and other bodies of water, or data on traffic density . The sunspot relative number has a similarly important function in astronomy .
Requirements for correct averaging
In order to obtain correct annual mean, a few requirements are necessary:
- Elimination of daily periods. For the air temperature , traditionally the mean values of 7 a.m., 2 p.m. and 9 p.m. are taken as the daily mean ( Mannheim hours ).
- Clear definition of value. The count or measured value must be collected at fixed or characteristic times, depending on its type.
- Only one-dimensional quantities (scalars) can be averaged properly. For vectors such as the wind direction, the procedure is different.
- Clarification of whether fluctuations are also important (e.g. in wind strength ). Instead of daily averages, the maximum or minimum values are often more meaningful, or a measure of dispersion is given for the average .
Annual mean in climate science
While current weather data is a priority for meteorology, climatology primarily requires monthly and annual averages in as many places as possible. In addition to soil and air temperatures, data on air pressure , humidity , cloud cover and wind are also important.
Other typical variables such as precipitation or its water equivalent, the frost days or the duration of sunshine are usually added to annual totals .
The temperature mean, its seasonal course and the amount of precipitation characterize the climatic zone . Reliable, uniformly recorded annual averages (including marine data) are a prerequisite for trend analyzes - for example with regard to climate change . Currently, both the 20 to 50-year trends in temperature and sea level are still being overlaid by other effects.
The annual mean of a location is calculated either from 365 daily or 12 monthly means . The result is largely identical (28–31 days), but the range of variation is very different.
