Presentation on theme: "Imposed ozone calculations Qualitatively same behaviour in all models (which qualitiatively agrees with the observations). Significant quantitative differences."— Presentation transcript:
Imposed ozone calculations Qualitatively same behaviour in all models (which qualitiatively agrees with the observations). Significant quantitative differences. Radiation schemes? Background ozone climatologies? Care in comparing models with obs
Imposed greenhouse gas calculations Qualitative agreement, but surprising quantitative disagreement in upper stratosphere. Non-CO 2 greenhouse gases cant explain. Gas changes well contrained. Presumably radiation codes? Dont compare models with obs!
SPARC Water Vapour Assessment (2000) Northern midlatitude trends
Imposed water vapour calculations Two classes of calculation Global HALOE and Global Boulder! This dominates the model differences. Note especially the lower stratosphere Dont compare models with obs!
Relevance to understanding forcing mechanisms and attribution Adapted from Shine et al. QJRMS, 2003 Understanding stratospheric temperature trends 32 km 18 km
Coupled model calculations (O 3, ghg, H 2 O?) Spread in trends is no greater in coupled runs than in imposed runs, despite extra degree of freedom. Disagreement with observations in middle and lower stratosphere. Compare models with obs!
An attempt at a synopsis Upper stratosphere OK Mid stratosphere – models overestimate cooling. Why? Error bars? Ozone profile? Temperature data? Linearised view? Missing mechanism? Lower stratosphere – (significant) role for water vapour? Compare models with obs!
Imposed ozone changes Tendency for GCMs to have smaller latitudinal gradient than FDH models. Clear gap between observations and models in Northern Mid-latitudes at 50 hPa
Imposed Greenhouse Gas Changes Most interesting aspect is GISS model response is quite different to all other GCMs in the intercomparison – does it have an extra degree of freedom, e.g. via its gravity wave scheme??
Coupled Models Spread in models and no consensus even in the sign of the temperature change. High southern latitudes is the only consensus region. Hint that coupled models underestimate 50 hpa cooling too.
Zonal-mean conclusions At 100 mbar, agreement between observations and models generally good with ozone change alone.. adding impact of water vapour improves agreement At 50 mbar, ozone incapable of explaining mid- latitude trends – would require considerable water vapour contribution to explain … or does it have a dynamical cause?
Where next? This comparison limited – concentrated on annual means and was to some extent an apples-and-oranges comparison Single model tests of impact of uncertainties in (e.g.) ozone profiles? Transient runs? Multi-model intercomparison of radiative codes (benchmarks are available)?
Annual-mean 11-yr Solar Cycle Signal in Temperature from ECMWF Reanalysis Crooks and Gray, 2005 50 km 20 km S N
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