Coupled Chemistry-Climate Model - UMSLIMCAT

UMSLIMCAT is based on the troposphere-stratosphere-mesosphere version of the Met Office Unified Model (UM v4.5) with a latitude-longitude resolution of 2.5 by 3.75 degrees. The model has 64 vertical levels extending from the surface to 0.01 hPa. The stratospheric chemistry scheme is from the SLIMCAT/TOMCAT chemical transport model (Chipperfield, 1999). The tropospheric chemistry scheme is from the UK Met Office STOCHEM model. A more detailed description of UMSLIMCAT can be found in Tian and Chipperfield (2005).

UMSLIMCAT has a good description of both chemistry and dynamics. It is participating in the Chemistry-Climate Model Validation Activity for SPARC (CCMVAL) and some information on the the performance of the model can be found in Eyring et al. (2006).

The model simulated CH4 field compares well with the SPARC climatology implying that the global stratospheric transport processes in the model are reasonable (see Figure 1). The modelled total column ozone compares well with TOMS observations (Figure 2).

The model (i.e. the UM) can also internally generate a QBO signals which is then also seen in a range of chemical species (see Tian et. al, 2006 for more details) . As an example, the modelled ozone QBO is shown in Figure 3.

Fig 1

Figure 1. The comparison of the modelled CH4 climatology with SPARC data.

Fig 2

Figure 2. The modelled total column ozone compared with a SLIMCAT CTM run (ERA-40 winds) and TOMS observations.

Fig 3

Figure 3. The QBO signals in the modelled and observed (SAGE II) ozone fields.

For more details and comments please email Wenshou Tian and Martyn Chipperfield.