I have been plotting a global temperature index based on daily NCEP/NCAR reanalysis. A big spike to unpresedented levels in October has attracted comment. The daily record is characterised by sharp spikes and dips, but bthis was exceptional. I've long been curious about the local temperature changes that might cause such a spike, so I analysed this one.
I calculated trends for each of the 10512 cells of the lat/lon grid over a period of 10 days, from 27 September, to 6 October. In this time, the index rose from 0.271°C to 0.865. The trend of global average was .0634°C/day.
I plotted them with WebGL, with the usual trackball sphere you can see below the fold. You can also click to see the trend at any point.
As people suspected, and I blogged here, Antarctica had been cold in September, and there was a reversal which explains much of the rise. Local trends are very high - up to 3°C per day, which is 30°C over 10 days. But there was also a broad swathe of also very large rises through China and central Asia, continuing through Iran. Further north, there was a cold patch on each side of the Urals, extending to Scandinavia. The US also cooled.
As a sanity check, I note that it says southern Australia also warmed rapidly. Melbourne is in the centre of that, and it shows various trends, as high as 1.264 °C/day. We did indeed have a rapid run-up. Late September was quite cool, which means a daily average of about 13°C, but 5-6 October were very warm, averaging about 27°C, following other warm days. The implied rise of 12.64C in trend is not unreasonable.
Anyway, the WebGL is below the jump. Remember, you can click any shading for a numeric trend to show.
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There are rapid changes in the amount of sunshine over Antarctica around the autumn equinox, but the sun angle is so low so it should hardly make any difference. Also, according to the CCI weather map Antarctica is shrouded in clouds right now. Can I be an intrusion of warm air over the continent that is insulated by the cloud cover?
ReplyDeleteBTW, is it raining in Melbourne right now? Looks so on CCI maps..
Olof,
DeleteThe Melbourne radar is here. We've had thunderstorms about today and yesterday, but just where I am, not a drop. In fact no rain this month. Beautiful spring weather, except when too hot.
In the active polar plot of the NSIDC SH Sea Ice data there is an other spike some weeks ago. I think this could not be real but some sea ice data may wrong.
ReplyDeleteYes, I'm sure it is an error. On 22-24 Sept, the successive raw numbers were 18.316, 20.723 and 18.203. each side, it is about 18.2. I'm sure Sep 23 is wrong. But I just plot the numbers as they are supplied. It's inelegant, but I don't think here it makes any real difference.
DeleteYou say "I calculated trends for each of the 10512 cells of the lat/lon grid over a period of 10 days, from 27 October, to 6 October. "
ReplyDeleteProbably a typo to mean from 27 September to 6 October.
However, the reason could be because when a mouse cursor is placed on any individual day it is pointing to a date one month in future.
WebGL is fantastic work !
Thanks, ugaap. You're right about the typo - I'll fix. I'll check the alignment on the date checker too.
Delete