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Alphabet Hotel

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DMI Daily Mean Temperatures North of 80 degrees North
« on: April 13, 2022, 06:59:37 AM »
 I was wondering if the lines would cross but so far it appears not.  ;-)


Alphabet Hotel

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Re: DMI Daily Mean Temperatures North of 80 degrees North
« Reply #1 on: April 14, 2022, 09:25:56 AM »

The Walrus

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Re: DMI Daily Mean Temperatures North of 80 degrees North
« Reply #2 on: April 14, 2022, 01:56:25 PM »
It is not uncommon to remain above the mean for the first 100+ days.  In 2106, the temperature did not cross until day 150!

oren

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Re: DMI Daily Mean Temperatures North of 80 degrees North
« Reply #3 on: April 14, 2022, 03:10:51 PM »
The old normal.

ms

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Re: DMI Daily Mean Temperatures North of 80 degrees North
« Reply #4 on: April 14, 2022, 11:10:54 PM »
I like Nico Suns version from
https://cryospherecomputing.com/

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Re: DMI Daily Mean Temperatures North of 80 degrees North
« Reply #5 on: April 15, 2022, 04:07:01 AM »
From the looks of those charts the baseline cold temperature in winter moved up about 7 or 8 degrees.

I’M IN LOVE WITH A RAGER

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Re: DMI Daily Mean Temperatures North of 80 degrees North
« Reply #6 on: April 15, 2022, 07:05:16 AM »
7-8 degrees Celsius is no small amount, that's actually somewhat surprising in magnitude to me, even considering the observed changes in the system

The Walrus

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Re: DMI Daily Mean Temperatures North of 80 degrees North
« Reply #7 on: April 15, 2022, 04:41:03 PM »
When you add up a roughly 8 degrees temperature rise in winter with 1 degree rise in spring and fall, the 10-degree total averaged throughout the year amounts to the 2.5 degree rise measured.

oren

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Re: DMI Daily Mean Temperatures North of 80 degrees North
« Reply #8 on: August 22, 2022, 10:42:22 AM »
For anyone who has DMI's temps North of 80 bookmarked, I recommend to replace with Zack Labe's version which uses the same data but with the correct averaging method.


Niall Dollard

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Re: DMI Daily Mean Temperatures North of 80 degrees North
« Reply #9 on: August 22, 2022, 02:58:10 PM »
For anyone who has DMI's temps North of 80 bookmarked, I recommend to replace with Zack Labe's version which uses the same data but with the correct averaging method.


Zach's charts are great.

However I can see very little difference between his and the dmi version. Is  there really a difference in the averaging, or am I looking at the same chart ?

oren

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Re: DMI Daily Mean Temperatures North of 80 degrees North
« Reply #10 on: August 22, 2022, 03:19:05 PM »
DMI averages weirdly by latitude, Zach averages properly by area. I guess the differences are not that large when the temperatures are nearly uniform between the Pole and the 80 line, but I'm sure there should be a difference somewhere. Or I have misunderstood the weighting methods.

weatherdude88

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Re: DMI Daily Mean Temperatures North of 80 degrees North
« Reply #11 on: August 22, 2022, 03:47:21 PM »
DMI averages weirdly by latitude, Zach averages properly by area. I guess the differences are not that large when the temperatures are nearly uniform between the Pole and the 80 line, but I'm sure there should be a difference somewhere. Or I have misunderstood the weighting methods.

It's the same graph and uses same data. The only difference is the colors.

Quote
Daily 2 m surface air temperature for the Arctic averaged above 80°N. Individual years from 1958-2021 are shown by the sequential blue/purple to yellow lines. 2022 is indicated by the red line. ERA40 has been applied for the 1958-2002 climatology (white line), while the operational ECMWF is used for the current year.

There are other graphs that show 70 N and regional area of temps in the Arctic.

https://zacklabe.com/arctic-temperatures/


oren

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Re: DMI Daily Mean Temperatures North of 80 degrees North
« Reply #12 on: August 22, 2022, 04:56:23 PM »
DMI are quite clear that their averaging method is by latitude, smaller but more northern grid cells
 (e.g. latitude 89) get the same weighting as much larger but more southern cells (e.g. latitude 80), so the result is not physical.

http://ocean.dmi.dk/arctic/documentation/arctic_mean_temp_data_explanation_newest.pdf
Quote
Plus 80N Temperatures - explanation.
The temperature graphs are made from numerical weather prediction (NWP)
"analysis" data. Analyses are the model fields used to start NWP models. They
represent the statistically most likely state of the atmosphere, given the
information available to make the analysis. Since the data are gridded, it is
straight forward to deduce the average temperature North of 80 degree North.
However, since the model is gridded in a regular 0.5 degree grid, the mean
temperature values are strongly biased towards the temperature in the most
northern part of the Arctic! Therefore, do NOT use this measure as an actual
physical mean temperature of the arctic. The 'plus 80 North mean temperature'
graphs can be used for comparing one year to an other.

The proper method to calculate the average is to give each cell its weight according to its area.

This is what I understood Zack Labe is doing. I will pm him to make sure I got it right.

Excellent, thank you Zack.
Just making sure, is temperature averaging N of 70 or 80 weighted by area (as it should be), or by latitude (as DMI does)?
weighted by area

FishOutofWater

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Re: DMI Daily Mean Temperatures North of 80 degrees North
« Reply #13 on: August 22, 2022, 06:22:10 PM »
Zach's temperature graph is a little bit smoother because it does not give one point - the pole - more weight than the points at 80ºN. DMI enhances anomalies at and around 90ºN.

oren

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Re: DMI Daily Mean Temperatures North of 80 degrees North
« Reply #14 on: August 28, 2022, 06:21:45 PM »
Sorry for sowing confusion, I got detailed information from Zack (many thanks!).
Indeed Zack's N of 80 chart data is identical to the DMI chart. Zack does use the correct averaging method in all other charts.

Quote
To clarify, I am simply reproducing the DMI graphic using their same data. Unfortunately, the raw real-time ECMWF model data is behind a paywall, which I do not have access to. So I can't create my own averaging technique.

Otherwise, every other graphic I produce on Twitter and my website uses the area-weighted averaging method.

My personal view is that while it's useful to to get an "approximate" idea of the current temperature at 80°N+ on the DMI graphic, it's a bit overrated (especially during summer) and not as useful from a historical long-term trend perspective. They are concatenating several different datasets together, which I would advise against doing in the scientific literature.

My monthly visualizations on my website are temporally and spatially consistent and are using the most up-to-data (strictly ERA5) - so I would stick with them for getting a better idea of long-term trends, ranks, and monthly mean anomalies.

Blizzard92

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Re: DMI Daily Mean Temperatures North of 80 degrees North
« Reply #15 on: August 29, 2022, 12:28:16 AM »
Hi all,

I just added a spatial view of the monthly mean temperatures and anomalies across the Arctic: https://zacklabe.com/arctic-temperatures/. The 80°N contour line is dashed. Please let me know what other near real-time visuals can be useful for these pages. Thanks!
Currently: Postdoctoral Research Associate - Princeton University and NOAA GFDL - Atmospheric and Oceanic Sciences
UC Irvine - Earth System Science Ph.D.
Cornell University - Atmospheric Sciences B.Sc.

Twitter: @ZLabe
Website: https://sites.uci.edu/zlabe/

kassy

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Re: DMI Daily Mean Temperatures North of 80 degrees North
« Reply #16 on: August 29, 2022, 04:32:22 PM »
It´s nice to have the absolute temperatures and the anomalies side by side. I would love to have this as a standard for anomaly maps (just a general wish, not a suggestion for you).
Þetta minnismerki er til vitnis um að við vitum hvað er að gerast og hvað þarf að gera. Aðeins þú veist hvort við gerðum eitthvað.