Convective index
The convective index , also known as the KO index , is an important meteorological parameter that describes the stability of the atmospheric air stratification .
meaning
With the help of the KO index, the development of deep convection can be predicted, which is often accompanied by thunderstorms . The KO index is a measure of the vertical change in the pseudopotential temperature . Put simply, the KO index assumes negative values when dry, cold air is above warmer and more humid air, and conversely, higher values when warm and humid air is above dry and cold.
If the index is low and there are also large-scale atmospheric uplifts (the forced rise of air masses), the originally stable thermal stratification is converted into an unstable state. Such a large-scale uplift can, for example, be triggered by a cold front .
If an air mass is now raised with dry-cold air at the top and humid-warm air at the bottom, it first cools down dry adiabatically until the dew point is reached in the moist air layer and the air humidity begins to condense . When the moist air mass is raised further, it now cools damp adiabatically , i.e. H. slower. The increasing temperature difference between the two air masses leads to a rapidly increasing labilization of the air stratification and thus creates the conditions for strong vertical air movements and thus for showers and thunderstorms .
calculation
The KO index is calculated using the following formula:
![{\ displaystyle KO = {\ frac {1} {2}} \ cdot (\ theta _ {e _ {_ {700}}} + \ theta _ {e _ {_ {500}}} - \ theta _ {e_ { _ {1000}}} - \ theta _ {e _ {_ {850}}}) \ qquad [K]}](https://wikimedia.org/api/rest_v1/media/math/render/svg/bf8e7f91427346070097ac8f6185d1c63ac9d0e5)
where θ e represents the pseudopotential temperature in Kelvin at the pressure levels of 1000, 850, 700 and 500 hPa .
If the location for which this index is to be calculated is so high that the ground pressure is below 1000 hPa, the value is determined as follows:
![{\ displaystyle KO = {\ frac {1} {2}} \ cdot (\ theta _ {e _ {_ {700}}} + \ theta _ {e _ {_ {500}}} - 2 \ cdot \ theta _ {e _ {_ {850}}}) \ qquad [K]}](https://wikimedia.org/api/rest_v1/media/math/render/svg/3e52742948b096b1ed3e7f4a74346eb00c288df6)
The index has the unit Kelvin .
Classification of the KO values
The following conclusions regarding atmospheric conditions can be drawn from the KO index:
| KO index | Thermal stratification | Thunderstorm probability |
|---|---|---|
| KO> 10 | potentially very stable | no thunderstorms |
| 6 <KO ≤ 10 | potentially stable | |
| 2 <KO ≤ 6 | potentially indifferent | isolated thunderstorms |
| KO ≤ 2 | potentially unstable | numerous thunderstorms |
supporting documents
- ↑ www.wetter3.de : KO index cards ; Retrieved August 12, 2010
- ↑ a b Institute for Geophysics and Meteorology, University of Cologne : Explanations on the radiosonde diagrams (PDF file; 57 kB); Retrieved October 2, 2009
- ↑ German Weather Service : KO-Index ( Memento of the original from July 10, 2012 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. (PDF; 336 kB); Retrieved October 2, 2009
