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Author Topic: DMI 80N+ graph, large increase at start of year 2000  (Read 1962 times)

Niall Dollard

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DMI 80N+ graph, large increase at start of year 2000
« on: February 07, 2017, 01:12:28 AM »
Recent posts in the 2016/2017 freezing thread about centring the DMI 80N+ temp graph at winter time (rather than summer) prompted me to look back over the previous years.

Assuming the graphs display the full 365/366 days (and no days have been truncated) I noticed a large jump in the order of +16 K when you compare the last day of 1999 (~246 K) with the first day on the 2000 year graph (~262 K). Graph attached.

http://ocean.dmi.dk/arctic/meant80n.uk.php

I wonder is it possible to have such a large increase in one day ? By my eye the daily increases are never more than about 5 K.

So is this some sort of bug in the data ? The infamous Y2K bug?   

CognitiveBias

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Re: DMI 80N+ graph, large increase at start of year 2000
« Reply #1 on: February 07, 2017, 03:06:49 AM »
Niall,
  I would be very suspect of such a discontinuity.  FWIW, here is a proxy set of data derived from ECMWF data. 


80N Approximation using ECMWF data set
DegreeC           sdate
244.592055   1999-12-25
245.004763   1999-12-26
246.090541   1999-12-27
248.024847   1999-12-28
253.065222   1999-12-29
256.955333   1999-12-30
256.590708   1999-12-31
256.928041   2000-01-01
260.009305   2000-01-02
257.683527   2000-01-03
256.973972   2000-01-04
255.931277   2000-01-05

Neven

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Re: DMI 80N+ graph, large increase at start of year 2000
« Reply #2 on: February 07, 2017, 10:01:12 AM »
I'm sure there is a better thread to discuss this. Either way, this is the wrong category.
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ktonine

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Re: DMI 80N+ graph, large increase at start of year 2000
« Reply #3 on: February 07, 2017, 02:11:11 PM »
Recent posts in the 2016/2017 freezing thread about centring the DMI 80N+ temp graph at winter time (rather than summer) prompted me to look back over the previous years.

Assuming the graphs display the full 365/366 days (and no days have been truncated) I noticed a large jump in the order of +16 K when you compare the last day of 1999 (~246 K) with the first day on the 2000 year graph (~262 K). Graph attached.

Niall, I can't speak to the graphs, but the raw data files don't show that jump.  Here's what I have from the data files:

1999   360   246.118582   243.869741
1999   361   249.668921   243.743231
1999   362   256.79156   243.774908
1999   363   260.427556   244.006179
1999   364   258.812742   243.900104
1999   365   260.085622   243.804996
2000   1   261.983298   243.894301
2000   2   260.105925   244.023126
2000   3   258.758819   243.664103
2000   4   258.181293   243.20243

CognitiveBias

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Re: DMI 80N+ graph, large increase at start of year 2000
« Reply #4 on: February 07, 2017, 02:19:23 PM »
ktonine,
  I'm not familiar with the DMI data set.  Can you explain what column 3 and 4 represent?  I would have expected a single quantity per day.

Thanks!

Seumas

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Re: DMI 80N+ graph, large increase at start of year 2000
« Reply #5 on: February 07, 2017, 03:20:51 PM »
Can you explain what column 3 and 4 represent?
Thanks!

The third column is the temperature. The fourth is "daily mean temperatures for the period from 1958 to 2002" (from the website).

In other words, the third column is the red line on the graph, and the fourth is the green line.
« Last Edit: February 07, 2017, 03:26:35 PM by Seumas »

CognitiveBias

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Re: DMI 80N+ graph, large increase at start of year 2000
« Reply #6 on: February 07, 2017, 04:10:32 PM »
Sorry, I guess that was a bit obvious...

Seumas

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Re: DMI 80N+ graph, large increase at start of year 2000
« Reply #7 on: February 07, 2017, 04:15:12 PM »
As with most things in life, it's only obvious when you already know it :)

Niall Dollard

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Re: DMI 80N+ graph, large increase at start of year 2000
« Reply #8 on: February 07, 2017, 04:17:13 PM »
Thanks for the daily data ktonine & CognitiveBias.

It looks to me now that the last 5 days of 1999 are not included on the 1999 year graph. The red line hitting the y axis at Day 360 (ie last value being 246.1 at Dec 26th). The line graph being truncated at that point for some reason.

Well that solves that mystery.  :)

 Incidently the first day of 2000 (261.9) seems to be one of the highest January values in the series (excepting another peak above 260 in 2006, which looks like it maybe just inside the month of January).

ktonine

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Re: DMI 80N+ graph, large increase at start of year 2000
« Reply #9 on: February 07, 2017, 04:47:24 PM »
Sorry, I guess that was a bit obvious...
No, it isn't obvious. I made a mistake when copying from my spreadsheet. I didn't intend to post the climatological mean.  I actually have it hidden on my spreadsheet, but hidden cells are still copied and appear when pasted.  I didn't even notice it when I posted it here. 

So consider it my mistake for not checking before posting or including an explanation.

Cate

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Re: DMI 80N+ graph, large increase at start of year 2000
« Reply #10 on: March 19, 2017, 03:38:20 PM »
I'm getting 404 Not Found for the DMI website today. 'Sup? Maintenance, perhaps?

Jim Williams

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Re: DMI 80N+ graph, large increase at start of year 2000
« Reply #11 on: March 19, 2017, 04:08:58 PM »
I'm getting 404 Not Found for the DMI website today. 'Sup? Maintenance, perhaps?
The directory appears to be empty.  I'd guess a machine crashed -- and it is Sunday.

Cate

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Re: DMI 80N+ graph, large increase at start of year 2000
« Reply #12 on: March 19, 2017, 07:36:43 PM »
Thanks, Jim. It's back online now.