cc: "Mitchell, John FB" , "Senior, Cath" , "Jenkins, Geoff" , "Jones, Richard" , j.turnpenny@uea.ac.uk date: Tue, 29 Jan 2002 09:27:05 +0000 from: Catherine Senior subject: Re: UKCIP confidences to: Mike Hulme Mike, Here are my comments on your statements > Temperature > 1. ?SE>NW gradient?: could we retain the ?H? confidence if we > restricted this just to summer? There is certainly better model > agreement for this gradient in summer, and the physical basis should > be better continentality, the winter role of the ice-albedo f/b at > higher latitudes counter-acting this gradient is absent, the weakening > of the THC leads to reduced NW warming We wern't sure we understood the physical arguments, although I agree that there is better model consistency in summer. John had stronger views on this. > 2. ?Night>day in winter, Day>night in summer?: I had ?M? and you > suggest ?L?. I would have thought the physical basis for this is > reasonable greater cloud in winter but higher humidity, and less > cloud in summer allowing greater insolation. Not sure about other > models, but I would have thought ?M? is reasonable. My concern here was the assumptions about cloud cover. Whilst I agree with the links between cloud and soil moisture locally, the changes in the storm track are very uncertain and this could affect cloud over the UK in both seasons. We have found no consistency in changes in the position of the storm track between models. I think there is more model consistency for N>D in winter (e.g. Kharin and Zwiers, 2000) than D>N in summer, so perhaps one could split the two statements if you wanted M for the former? > Cloud cover: > 3. ?Reduction in summer cloud, esp. in south?: you had only ?L?, I > had ?M?. I would have thought a consistent picture is being told > here reduced cloud, reduced precip. (which we give ?M? for), reduced > soil moisture (which we give ?M? for), and increased in summer DTR > (see above). Hard to argue that with these other changes we would > actually get increased summer cloud. Yes, but see above. I am not really happy about assigning anything above L for local cloud changes. > Wind > 4. ?Average windspeeds increase more over south than north? I had > ?L?, but you would rather omit. If we exclude this one then we will > have no headline statements about wind. I agree that model > consistency will be low, but the physical reasoning I would have > thought is due to the circulation changes and storm tracks pushing > further south if Had3AMH model is worth anything then isn?t it giving > us greater confidence about storm tracks. I would prefer to retain an > ?L? here. But again, HadMA3H is only one model, and the local wind changes are complex and very inconsistent across the UK. Whilst this model has an improved storm track in the contol, I think we need to understand the dominating processes forcing the changes in the storm track to really increase our confidence. Hence to say we have 'confidence in the physical representation within the model' is premature. All of this points to a L confidence, which you had of course!. The problem, of course is that just by puuting it in the table assigns it a certain 'level of confidence' which we felt this statement didn't warrant. However, If you feel we *must have* a statement about wind then I guess this is OK, but John might disagree! > Soil moisture: > 5. ?Decreases in summer, esp. in SE?: you had ?M? and I had ?H?. This > is part of the story above, reduced cloud, reduced precip, increased > DTR, and therefore reduced soil moisture. Even though precip. change > in summer may only be ?M?, surely there is greater physical basis to > think that soil moisture levels will decrease with large summer > warming? I would prefer to retain ?H?. Again, see above re cloud. I think John argued for this to be M because we are not sure about the physical arguments. > One statement that seemed to get lost was this one. It should be > accorded a ?H? status. > > 6. ?Although the strength of the Gulf Stream may weaken in future, it > is very unlikely that this would lead to a cooling of UK climate over > the next century?. > > Or if you don?t like this one, some other equivalent that makes some > clear statement about THC and that we are not going to ?freeze? in the > foreseeable future!! I think this just got lost. We were happy to give this a H Best Wishes Cath Catherine A. Senior, Manager of Climate Model Sensitivity Room H214, Hadley Centre for Climate Prediction and Research, Met Office, London Road, Bracknell, Berkshire, RG12 2SY, U.K Tel +44 (0)1344 856895; Fax. +44 (0) 1344 854898 email: casenior@metoffice.com http://www.metoffice.com/research/hadleycentre