Monitoring of ACSAF GOME-2 Total Ozone with data assimilation

The VOD work package is a monitoring activity done by KNMI within the framework of the EUMETSAT ACSAF. In this activity, NRT GOME-2 Total Ozone Column data (Acronym NTO/O3) from DLR is assimilated into the tm3dam assimilation model at KNMI.

The assimilation is done in the following way:

• The tm3dam assimilation model is initialised with a 'save file' that contains the state of the total ozone column of the atmosphere at T-24h.
• Then the assimilation model runs. At each time step the appropriate measured NTO/O3 data is ingested and used in the assimilation. The assimilation uses wind vectors from ECMWF to transport the ozone internally. The data assimilated is from T-24h to T=0h (which is 00:00 UTC). Only the retrievals from the forward scan are assimilated.
• From T=0 the model runs freely and generates ozone column forecasts for the next day. The assimilated ozone fields at 6 hour intervals at +00, +06, +12, +18 and +24 hrs are saved. These fields are called ATO, which stands for Assimilated Total Ozone.
• The ATO fields are given on a 1 by 1.5 degree grid in lat-lon direction respectively.

Using these forecast fields, the actual measured NTO/O3 from T=0 to T+24h can be compared. The comparison can be between each individual NTO/O3 retrieval and the ATO value in the associated grid box, or between 'pre-gridded' NTO/O3 values and the ATO value. Both these comparisons are given.

The colors in the plots are related to the time difference of the NTO measurement with regards to the forecast hour (FC hour). The color scale runs from blue via green to orange. Blue indicates a time difference of -3h with regards to the FC hour, greenish is closest to the FC hour and orange is +3h.

In the plots the numbers at the bottom indicate the number of elements compared (individual or gridded respectively), the mean value in the center of the histogram domain, sometimes the bias is given w.r.t 0.0, and at the bottom the stddev is provided.

The date given in the title of the plot indicates the T=0 day for which the NTO/O3 data is compared. Example: S-O3M_GOME_VOD__M02_20110117Z indicates that the plot is for data from 2011-01-17 00:00 up NTO/O3 files starting at 2011-01-17 23:59 is used.