Global tropospheric ozone column
Description
The global tropospheric ozone column product provides information about vertical column densities of ozone in the troposphere, from the surface to the tropopause and from the surface to 500 hPa (∼5 km).
The height of the tropopause varies, depending on the latitude, season and regional effects of large scale meteorological systems. Usually the tropopause height is near 13 km in the tropics, comes down to about 10 km in mid-latitudes and can go as low as 7 km in polar areas with sustained subsidence.
For latitudes <19 °N/S the thermal tropopause is used (where valid). Between 19° and 36° latitude (both in N and S direction), there is a linear transition between the thermal tropopause pressure and the PV based tropopause. From 36° latitude to the poles the PV based tropopause pressure is used.
From the validation of the ozone profiles, it is known that the UTLS region of the profiles has a larger uncertainty, which often translates into an unintended increase in ozone below the tropopause in the profile. This counts towards the tropospheric vertical column.
If the user wants to avoid the risk of stratospheric ozone being counted towards the tropospheric column, we recommend to use the column from the surface to 500 hPa.
Type
Level 2. The product is available in NRT (<3 hrs after sensing) and offline (usually within a few days, but <2 weeks).
Theoretical basis
The product is calculated by vertically integrating the GOME-2 vertical ozone profile products, in combination with temperature and potential vorticity information from the ECMWF NWP model to determine the tropopause.
Processing
KNMI generates the tropospheric ozone produts based on the Opera ozone profile retrieval algorithm. The profiles are based on optimal estimation and produce 40 sub-columns from the surface to 0.001 hPa.
Units and spatial resolution
Ozone columns are given in Dobson Units (DU). The spatial resolution is the native footprint of the GOME-2 instrument (80 km x 40 km during nominal operation).
Validation
This product is validated by KMI. The validation is based on detailed comparisons of satellite data with ozone soundings at several stations across the globe. Refer to the tropospheric ozone column validation report for further information.
Archiving and dissemination
This product is part of the NRT and offline vertical ozone profile products (NHP/OHP) and archived at the FMI. For dissemination options, see NRT access and offline access pages.
File format
The NRT product is delivered in BUFR format and the offline product in HDF5 format.
Algorithm version information
| Satellite | Time period | Algorithm version |
|---|---|---|
| Metop-A | Sep 2015 - current | 1.37 |
| Metop-B | Sep 2015 - current | 1.37 |
Important changes in the latest algorithm version (2.00)
- Degradation correction