WP 4 Assimilation of satellite data in Bulgarian Chemical Weather Forecast System (BgCWFS)
WP 4 leader: Prof. DSc. D. Syrakov

Results from WP 4

Assimilation of satellite data in Bulgarian Chemical Weather Forecast System (BgCWFS)

• New configuration of the BgCWFS  

The BgCWFS was upgraded for offline work and for аssimilating satellite retrived data for the atmospheric composition (AOD, vertical column densities of SO₂ and NO₂).

Fig. 1. Modification of the Bulgarian Chemical Weather Forecast System

• Assimilation technique

Satellite data is directly assimilated in the first three domains of BgCWFS – Europe (resolution 81 km), Balkans (27 km), and Bulgaria (9 km). The method of Optimal Interpolation is chosen for the assimilation of Aerosol Optical Depth (AOD) data by GOME-2 instrument on board of MetOP satellites. Results for the AOD from the modified BgCWFS without use of satellite information (base run) and with assimilated satellite data are presented in Figure 2.

Fig. 2. Maps of AOD, showing the Saharan Dust outbreak towards Bulgaria on 22.03.2018,
captured with assimilation of satellite data

• Calculation of columnar parameters – Vertical columnar densities (VCD) of NO2 and SO2

Fig. 3. Maps of the columnar NO₂ (left) and SO₂ (right) simulated by BgCWFS for 22.03.2018 at 09:00 UTC

• Simulations for two test periods

For studying the performance of the BgCWFS, two past periods of one month each, have been investigated - August 2017 and February 2019. For each month BgCWFS was run in two modes: base run ("mod") and run with assimilation of satellite data ("sat").

Figure 4 shows, as example, the effect of satellite data assimilation on the AOD field in domain Balkans on 22.08.2017 at different hours of the day – before, at , and after the satellite overpass time Hs (Hs = 09:00 UTC).

Fig. 4. Time evolution of the difference AOD "sat-mod" caused by satellite data assimilation
in domain Balkans for 22.08.2017 at h=0:00, 8:00, 9:00(Hs), 10:00, and 14:00 UTC

Figure 5 illustrates the difference in AOD  ("sat" – "mod") over the three nested domains (Europe, Balkans, Bulgaria), at the hour of the satellite overpass time over Bulgaria (Hs=09:00 UTC).

Fig. 5. AODsat - AODmod : fields on 01.08.2017 for the first 3 BgCWFS domains at moment Hs

Figure 6 gives the picture of the mean monthly PM10 concentration in domain Bulgaria for February 2019, simulated by BgCWFS in "mod" and "sat" versions.

Fig. 6. Mean monthly concentrations of PM10 [μgm^-3] for February 2019,
simulated for domain Bulgaria by BgCWFS: "mod" (left), "sat" (right)