cc: , , Jay Lawrimore , Byron Gleason , david.easterling@noaa.gov date: Fri Jul 15 11:40:55 2005 from: Phil Jones subject: Fwd: RE: [Fwd: Re: [Fwd: Re: Some more thoughts on DTR map for to: Lisa et al, Thanks. Forwarding to the others at NCDC involved in all the discussions. I think the main conclusion to draw from all this is that 1979-2004 is too short a period. If Russ produces a map for 1951-2004 then hopefully they will all look much more similar. We should likely go with one of these plots. We probably need to consider if we want a trend map. I would say yes, as if we get the right one, it will show that DTR is decreasing as an average, but definitely not in many locations. There are certainly lots of potential problem areas as Lisa alludes to, as does the detail from Aiguo. Cheers Phil Reply-To: From: "Lisa Alexander" To: "'Kevin Trenberth'" , "'Phil Jones'" , "'Klein Tank, Albert'" Subject: RE: [Fwd: Re: [Fwd: Re: Some more thoughts on DTR map for 1979-2004]] Date: Fri, 15 Jul 2005 20:07:11 +1000 Organization: BMRC, Bureau of Meteorology - Australia X-Mailer: Microsoft Outlook, Build 10.0.2627 Hi all, I have plotted up the 1979-2003 DTR trends using the global extremes data. Ive tried to use a similar colour scheme and range to Aiguo since he also has trends for the longer period. Things to note:- 1. I have only used quality controlled stations which have at least 40 years of data between 1951-2003. This is because otherwise I would have had to regrid all of the data which would take some more time to complete. The spatial coverage would be better if I say regridded using stations that had at least 20 years of data between 1979 and 2003 and this might be something worth considering. 2. Figure caption:- Observed trends per decade for 1979-2003 for the diurnal temperature range index. Trends were calculated for grid boxes which had at least 20 years of data during this period and ended no later than 1999. Black lines enclose regions where trends are significant at the 5% level using the method of Wang and Swail, [2001]. 3. I have used the HadCM3 grid size (2.5 x 3.75). 4. There are very few areas showing significant change. We can safely say that there is not general agreement between the 3 results! I agree well with Aiguo in some regions and with Russ in others. For comparison I asked Dean Collins to plot DTR trends for Australia for the two periods (attached). I would say that Russ and I agree better over Australia than Aiguo. Since Dean and I source the same daily data our results should be similar but there are some differences in detail which would need to be checked out. Aiguo and I agree better in terms of the sign of the trend over South America but not in magnitude. I have not read Russs or Aiguos papers so I cant comment on their methods. Potential areas of discrepancy are: 1. Are we all using exactly the same definition of DTR? 2. Data sources. 3. Different gridding methodologies. 4. Different trend calculation methodologies and missing data tolerance. One might suggest that the sample size is too small to accurately calculate trends over 25 years. However it is quite worrying that the sign of the trend can be so different between the methods. When I calculated the correlation decay distances for the paper, DTR was one of the less coherent indices which may be a factor. For some reason Im having trouble getting the percentile maps and timeseries diagram exactly how you want them. Perhaps its because its Friday. Im attaching what I have so far. Y-axis now represents the anomalies in days. Perhaps Ill have better luck on Monday. Regards. Lisa. - Prof. Phil Jones Climatic Research Unit Telephone +44 (0) 1603 592090 School of Environmental Sciences Fax +44 (0) 1603 507784 University of East Anglia Norwich Email p.jones@uea.ac.uk NR4 7TJ UK ----------------------------------------------------------------------------