Wednesday, November 27, 2013

On the origin of the thunderstorm symbol (R)

This blog post has a special significance to me, as it is the result of wondering about this for years now and finally getting around to digging in and figuring out the story here.  It has to do with the symbol that meteorologists use on weather maps to represent thunderstorms.  You may be familiar with this symbol--a stylized "R" shape with an arrow:
The symbol has acquired quite a following among meteorologists and it is widely used as a "cool" weather emblem.  The University of Oklahoma School of Meteorology even uses it as a part of their logo:
However, I have long wondered---where did this symbol come from?  Who developed it?  What is it actually trying to represent?  The story, as I found it, is as colorful as I had hoped it might be.

The symbol traces its initial origin back to the 1870s.  The late 1800s were a blossoming time for meteorology as a science.  The advent of the telegraph made it possible for weather observations to be rapidly disseminated across countries and continents and made observations of the large-scale structure of the atmosphere (the synoptic scale) possible for the first time.  In 1870, the War Department created a branch of the US Army Signal Corps to collect and publish weather information, and the precursor to our weather service was born.  They started issuing 2-3 times daily weather maps that summarized the temperature, pressure wind direction and sky cover reported in from major telegraph stations across the US.  Our weather mapping was born.  Several other countries also had developed weather services and each country developed their own way of displaying weather information on the maps.  Each country also had different priorities for what sorts of weather they wanted to show on the maps.

It became apparent quickly that given the large scale of synoptic weather features, international cooperation would be needed to get the full picture of the weather.  As such, a series of international conferences were held in Europe to help set international standards for how weather should be observed and recorded. The narrative that follows here is adapted from a report on one of these conferences (the 1973 International Meteoroloical Conference in Vienna) given to the Royal Meteorological Society by Robert H. Scott.  A digital copy is available through Google Books at this link.

Our attention here first turns to the 1872 International Meteorological Conference in Leipzig.  At this conference, a sub-committee was formed to address guidelines for "Hail, Thunderstorm and Cloud".  One of the questions put before this sub-committee was:

"Is it desirable to introduce for Clouds, Hydrometeors and for other extraordinary phenomena, symbols which shall be independent of the language of particular countries and therefore universally intelligible?"

The sub-committee, formed by E. Ebermayer (Bavaria), H. Schoder (German Empire) and C. Sohncke (German Empire) [along with support from H. Wild (Russia), J. Lorenz (Austria) and E. Plantamour (Switzerland)] addressed this question in an interim year and presented their report on the question at the 1873 International Meteorological Conference at Vienna.

 Their procedure for developing symbols was to poll all the nations that had organized weather reporting and mapping and learn how each of them annotated various weather phenomena.  Most nations simply used the first letter of the word that described the phenomenon in their own language.  For instance, in the US we put "R" for rain and "S" for snow (and that was about it).  Since it was expressly noted in the question for the sub-committee that these symbols should be "independent of the language of particular countries and...universally intelligible", the committee sought out more "iconographic" representations of the weather.  In their report, they present the following two tables, which show all of the different nations' weather symbols and the symbols that the sub-committee proposes to be used (click the image to get a bigger view).
There, at the bottom, we see what I believe is the first publication of the thunderstorm "R".  So where did it come from?  Examining each nation's symbols shows us a likely scenario.  If we look at the column for "thunderstorm", most nations don't bother annotating it.  Of those that do, three (Prussia/Saxony, Wurtemburg and Switzerland) all use the letter "G" (or "Gew") which is the first letter of the German word Gewitter, meaning "thunderstorm".  This doesn't match well with the requirement that the symbols be "independent" of the local language.  Austria uses a double-ended arrow for thunderstorm with a single-ended arrow for lightning. But it's the Russian symbol that is the most intriguing.  It is comprised of two components--a zig-zag line for lightning, which makes a lot of intuitive sense, and then the Cyrillic character г on the left.  If you look up the Russian word for "thunderstorm," it's гроза or "groza".  So I believe that again we have a nation just using the first letter of its native word for "thunderstorm" for the symbol.  I'd hypothesize that the sub-committee decided to take the most stylistic of the symbols (the lightning zig-zag is a really nice, intuitive touch) and merge them together to make our thunderstorm symbol  (Even if it included part of a Russian word). The addition of the arrow looks to come from the Austrians who used the arrow to indicate "lightning".  And, voila! Our thunderstorm symbol is born.

While my focus is on the thunderstorm symbol here, you'll note that many of our other symbols we use were also proposed here.  The filled circle for rain was used by France and Russia (and Austria for mist) as was the asterisk/star for snow.  The filled triangle for hail seems to be a hybrid of the open triangle from the Austrians and the filled squares from France and Russia.  Grauple is an extension of that with an open triangle.  But as to mist, hoar frost and dew?  Those aren't so clear...

Regardless, these symbols were proposed at the meeting, but the total number of categories of how many symbols were needed was debated.  The sub-committee later published a more extensive list of proposed symbols for a wide variety of weather categories.
But there was still debate on how many of these symbols to officially adopt, so the conference as a whole postponed the approval to a later meeting.  It wasn't until the 1891 International Meteorological Conference in Munich that the symbols were finally adopted by the committee.

The US seemed to approve of these standards and responded accordingly.  In 1893, amidst a flurry of reports about the climates of a variety of cities and how to observe thunderstorms and whatnot, the US Weather Bureau (having moved to the US Department of Agriculture in 1890) re-published the list of symbols approved by the International Conference, showing that these are the symbols they would start using.

In the meantime, in 1892 the Weather Bureau launched a project to investigate the possibility of forecasting thunderstorms using rapid telegraph messages.  They tried having local telegraph operators telegraph stations to their east if they were experiencing a thunderstorm with the idea that the stations further east could then warn the local population that the thunderstorm was approaching (we're talking thunderstorm warnings in the 1890s here...which I think is amazing...).  They tried it in three regions--the northeast, the upper midwest, and Ohio--and got reports back on the effectiveness.  The findings are summarized in Bulletin 9 of the Weather Bureau (which also is digitalized on Google Books, though you have to scroll way down to get to Bulletin 9 toward the end of the document).  While some of the reporters felt that these warnings were not practical and didn't give enough lead time (things we still work on to this day), the results were generally encouraging.  (As a side note, it probably helped that they focused on June-July-August across the northeastern quadrant of the country, where linear and quasi-linear MCS storms are the dominant mode of convection.  These lines of storms are pretty coherent and can last a long time--even overnight.  This makes them a bit easier to predict in this way.)  The Weather Bureau seems to have realized after this experiment that it could be useful to include thunderstorm information on their weather maps.

Finally, the US Weather Bureau (which was still issuing daily weather maps) upgraded their map printer from a 'milliograph' stencil-duplicator to a faster and more efficient "chalk-plate" process in 1896 (as described in this interesting paper).  All the maps from that time are archived through the NOAA Central Library Data Imaging Project.  There is a clear change in the style of the maps on June 15, 1896.  Here is the title bar and legend before the change:
No mention of thunderstorms--just sky cover, rain or snow, and by "storm track" they mean the path of the low pressure center over the previous few days.  "Storm Signals" indicate if a station reported storm-force winds.  Here's the title bar and legend after the map change:
It appears they hadn't switched over to the new "Rain" and "Snow" symbols (probably because there remained a conflict with the filled dot for "cloudy".  But we see the addition of a "C.W." annotation for "cold wave" (they didn't have the Norwegian cyclone model yet, so the concept of a "cold front" did not exist yet).  And, in the second line from the bottom, we see our R for thunderstorms reported during the previous 12 hours.  Here's a snapshot of the map on June 15, 1896 showing the reports from the central US, including the first thunderstorm symbols on a Weather Bureau map.
Looks like they had thunderstorms in Dodge City, Kansas, Des Moines and Keokuk, IA and Springfield and St. Louis, MO.  Another batch of storms impacted Milwaukee, WI and Grand Rapids, MI.  And so our thunderstorm reporting began.

I had a lot of fun researching this topic.  There's more to come for sure.  A lot of the other symbols we use were defined at a later time.  For instance, when did the extra "kink" in the thunderstorm symbol get added for "heavy thunderstorm"? And what of all the different symbols for each type of cloud?  There's a history there to be sure.

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