Temperature Comparison at Utqiaġvik

Way back in 2014, I posted some analysis of temperature differences between the airport and CRN sites in Alaska's northernmost town, Utqiaġvik (formerly Barrow).  With more than 20 years of climate data now in the books from the CRN site, I thought it would be interesting to revisit this - and in particular, to take another look at the apparent warming trend in the town's temperature relative to the outlying CRN site.

Here are the previous posts:

https://ak-wx.blogspot.com/2014/08/barrow-area-temperatures.html

https://ak-wx.blogspot.com/2014/08/barrow-area-temperatures-part-2.html

The locations of the two thermometers are indicated here:

 

First, let's confirm the close correspondence between the instruments at the two sites on a monthly mean basis:

No concerns there.  As noted and discussed in the previous posts, daily maximum temperatures tend to be most different between the two sites in summer, and for daily minimum temperatures the greatest differences are found in winter.  In both cases, the airport is usually warmer than the CRN site.  Systematic differences are least in autumn, when there's relatively little land-sea contrast in temperature.

 

The following charts provide another perspective on the overall relationship between temperature and temperature difference.

Now for the trend over time - see below.  Interestingly, there does seem to be a small but statistically significant increase in the temperature difference between the two sites, with the airport ASOS becoming progressively warmer than the CRN site.

How does the trend vary over the course of the year?

Interestingly, the trend in temperature difference is not confined to one season, but appears throughout the year, although with some variability.  This seems to suggest it is indeed a systematic trend at the local level rather than a trend caused by changing weather patterns at a certain time of year.

The largest trend has occurred for minimum temperatures in summer, and the charts below provide another perspective.  For the minimum temperatures (blue lines), there's a slight but perceptible tendency for relatively cooler CRN temperatures in recent years.  The maximum temperatures are less affected, except in June.

What do we make of this?  Occam's Razor suggests that the growth of the town is producing a gradually increased urban heat island effect.  In my 2014 post, I speculated that urban warming was unlikely to be the cause, because the Utqiaġvik population had decreased in the 2010 census; but the 2020 census reversed that trend, taking the population to an all-time high of about 4900.  This is a modest but perhaps significant increase of 8% in 20 years.

How significant is the divergence in temperatures compared to the overall long-term warming trend?  Well, two decades is not a long time in climate terms, but based on this limited history, the linear trends in annual mean temperature differ by about 15%.

This difference isn't remotely enough to alter the picture of rapid Arctic warming, but nevertheless it does illustrate the value of having a long-term climate monitoring program that's designed to avoid problems of instrument and site changes.  In other words, I'm a big fan of the CRN program.

CRN Data Visualization

Here's a follow-up to a post from a few weeks ago, where I mentioned that I was working on a web interface to visualize the high-quality climate data coming out of the Alaska CRN network.  Here's a first draft:

http://worldagweather.com/crn/

Note that the page is not designed for mobile viewing - sorry if that's an inconvenience.  And various refinements are needed; this is just a first attempt that provides static, pre-generated images for fixed intervals.  I'd like to move to a more interactive charting capability at some point, but that will depend on how much time I have.

Also note that I haven't included the two newest sites in southwestern Alaska, one in the Yukon-Kuskokwim Delta, and one at Aleknagik (near Dillingham).  This is because I prefer to have at least a couple of years of data to calculate a seasonal "normal" for each of the weather variables.

The page should update every day by around 7am AKST, but let me know if you see any problems.

CRN Data Visualization

Spare time for new blog posts has been in short supply lately, but I'll mention a little project I've been working on that may be of some interest.  As many readers know, NOAA's Climate Reference Network of top-quality climate observing instruments has been gradually adding sites in Alaska over the past several years, and the state's network is now up to 22 sites.  Here's a map (click to enlarge):

All of the data is readily available from NCEI, but options to visualize the data appear to be very limited.  I'm aiming, therefore, to put together a simple interface that provides some charting and perhaps mapping capabilities to summarize the wealth of climate monitoring data that's flowing from the CRN instruments.

Here are a few prototype charts showing departures from normal of climate variables observed at the CRN site near Fairbanks over the past several months.  The seasonal normals are calculated from the full period of record, which is already nearly 18 years long for temperature, precipitation, and solar radiation, but only 10 years for wind speed and humidity.  Click to enlarge the images.

Here's precipitation since the beginning of the year.

Look for more posts on the CRN data in (hopefully) the not-too-distant future.

Radiation Normals

In the past week I've been digging deeper into the CERES radiation data for Alaska (see the previous post) and making some interesting discoveries along the way.  It really is quite fascinating - at least to me - to explore a new data set that deals with aspects of the climate that most of us don't often think about.

There's too much to discuss in one post, so here I'll focus on a few monthly averages over the period of record for just a couple of locations.  The chart below, for the Fairbanks area, shows the monthly average downward shortwave radiation at the surface, or simply the incoming "solar radiation" at the surface.  The CERES data set provides one set of numbers for a grid point near Fairbanks, and we can compare these to data from the high-quality Climate Reference Network (CRN) site just to the northeast of the city.

Interestingly the CERES numbers are consistently a bit higher, and especially so in March and April.  Some of the difference could arise from shading of the CRN site by nearby hills, but more investigation would be needed to find out how much solar energy is lost this way.  The larger difference in March and April looks more like a systematic bias that could be related to reflection and scattering of solar radiation from the snow-covered ground; perhaps there is locally more reflection and then downward scattering of the sun's rays at the CRN site than the CERES model estimates for the broad area contained in the (1x1 degree) grid box.

Here's the same chart for Utqiaġvik, formerly Barrow.  As expected the summer peak is narrower, but it's also higher than in Fairbanks; despite more abundant cloud cover on the Arctic coast, longer daylight hours allow Utqiaġvik to see more direct solar energy than Fairbanks in May and June (and July according to CERES).  The same positive bias is observed in the CERES data relative to the CRN site just a few miles outside Utqiaġvik.

As discussed in the previous post, longwave (infrared) radiation is just as important for the climate as direct solar radiation.  I'll illustrate this in more detail in the next post, but for now the chart below shows the overall surface radiation budget (longwave and shortwave combined) for the same two locations.

The most striking difference between Fairbanks and Utqiaġvik is seen in spring, as Fairbanks quickly sees a building surplus of energy in April and May, while Utqiaġvik really struggles to gain any ground in terms of radiative transfer until high summer - at least according to the CERES data.  The main reason is quite obvious: the universal snow and ice cover around Utqiaġvik create a high albedo in April and May, so the spring sunshine is largely reflected in the north, whereas the generally wooded environment and earlier snowmelt near Fairbanks allow for much more efficient absorption at this time of year.

The time series of CERES and CRN data also reveal some very interesting results over the ~15 year history, but I'll document these in another post.

Sunshine at CRN Sites

After reviewing the status of Alaska's CRN data last week, curiosity led me to take a look at the solar radiation measurements from these sites.  For example, it's interesting to find out what these instruments have to say about how solar radiation varies across the state - at least for the last few years.

The chart below shows a summary of April-October total solar energy for the 11 sites that have been in operation since at least 2013 and have essentially complete data for these months.  The horizontal black lines show the 5-year mean for each site, and the blue bars indicate the minimum and maximum values within this brief 5-year period.

The sites near Fairbanks and Tok are the only interior sites represented here, and as we would expect they are at the top for solar energy.  Interestingly Metlakatla, on Annette Island in Alaska's far southeast, is in 3rd place and close behind Fairbanks.  It's not surprising to find that rainy Sitka is easily in last place; but note that the difference in solar energy between the cloudiest site and the sunniest site is less than 50%.

The range between minimum and maximum seasonal totals is remarkably high at the Red Dog site, but this is mostly because of a very low total from 2013; this looks suspicious and might be incorrect.  (If we exclude 2013, Red Dog actually comes in above Fairbanks for mean solar energy, and the Red Dog instrument also reported the highest seasonal total of any site in any year.)  More robust, perhaps, is the very low variance of solar radiation at the sites near Barrow (Utqiaġvik) and Tok; it's quite extraordinary, actually, how consistent the solar energy has been at these locations in the past 5 years.  But in the case of Barrow, data from earlier years showed higher values - see below.

The decrease of solar energy at the Barrow CRN site, evident in the chart below, is highly statistically significant even over such a short period.  Presumably this is related to the increase in open water area in the Arctic Ocean and therefore higher evaporation and increased cloudiness in recent years.

Improvement in CRN Data

I've mentioned the US Climate Reference Network program on previous occasions - it's a national effort to install high-quality climate monitoring instruments throughout the nation in locations that are unlikely to be affected significantly by urbanization in the coming decades.  So far 21 such sites have been installed in Alaska, with the most recent being near Toolik Lake and Cordova last summer.  Several more are planned:

Read more about the program here:

https://www.ncdc.noaa.gov/crn/

https://www.ncdc.noaa.gov/news/new-climate-observing-stations-alaska

In previous years it has been very disappointing to see that several of the sites had serious and persistent problems with missing temperature data in the winter months.   This is apparently caused by the fuel systems being unable to produce sufficient electrical power to operate the instruments and other electronics during cold weather.  It's a little surprising that the system engineering wasn't up to the challenge of Alaska's climate, but one must concede that it's no small task to run a complex array of instruments without external power throughout the deep cold and dark of the high-latitude winter.

But happily there is now some good news: some modifications were made in last summer's maintenance visits, and the past winter saw a significant reduction in the amount of missing data from a number of sites.  The chart below shows (in green) the statewide percentage of all November-March days for which daily high and low temperature data are available in GHCN, and the black columns show the number of sites.  The network was in a rather sorry state in winter 2015-2016, with more than 20% of days missing from the 18 sites around the state, but in the past winter only 7% of days were missing statewide.  If the improving trend continues, we'll soon be in good shape.

Here's the percent complete over the lifetime of each site.  Notice that the really bad locations are some of the coldest and most remote locations, whereas the instruments in southeast Alaska are performing just fine.

The sites that improved dramatically this winter were Deadhorse, Nowitna (Ruby 44 ESE), and the sites near Selawik and King Salmon: whatever tweaks were made at these locations worked nicely.  On the other hand, there are still significant problems at Ivotuk and Denali 27 N.  Let's hope that one more year does the trick to get the network running as intended.