Three‐dimensional ozone analyses and their use for short‐term ozone forecasts

A statistical interpolation method is evaluated for routine production of ozone three‐dimensional fields over western Europe. These fields are used for initializing short‐term ozone forecasts issued from a chemistry‐transport model. We mainly address two questions: (1) To what extent can the use of surface ozone observation data improve the description of ozone fields relative to raw simulations? (2) Does the use of ozone analysis improve short‐term forecasts of the troposphere's chemical composition? The method consists of combining ozone simulations with surface ozone measurements. The resulting analyses are compared with independent observations in a statistical way over a long period of time (four consecutive summers). The improvement of the root‐mean‐square (RMS) error of the analyses relative to the raw simulations is ∼30%. The short‐term (1–2 days in advance) ozone forecasts are improved on average (by ∼1 ppb of RMS error) if ozone analyses are used for initialization. The improvement is almost lost after a lead time of 36 hours. However, in cases where a model error propagates throughout the model domain, the improvement can be much larger (∼10 ppb). We analyze one such case.