[FRIAM] Metaphors and Meteorology

[thompnickson2 at gmail.com]

Dear Phellow Phriamers, 

 

After an ox-stunning spate of hot weather, we are now back in the 59 degree
fog bank here in sunny Massachusetts.  I cannot go out in the garden, so you
all are the "beneficiaries" of my being at loose ends. 

 

As one might expect, when Meteorology developed between the wars, it took on
a military metaphor.  There were armies of warm and cold air that fought for
control of the landscape.  Between them were "fronts" where warm air would
liberate  the land only to be reconquered by the cold air.  The fronts were
ideally thought of as sharp changes in temperature, dewpoint and wind
direction accompanied by a fall and then a rise in pressure.  I used to draw
weather maps as a kid from the station reports on SW radio, and I found it
much harder to locate fronts than the metaphor allowed.  It seemed more like
a contest between guerilla units than the advance and retreat of disciplined
armies along a front.  In fact, when I wrote the weather book, I couldn't
find an archetypal weather map that demonstrated fronts cleanly, and so had
to draw the fronts and then make up the observations to illustrate the
concept.   

 

I read forecast discussions obsessively, partly for the science and partly
because their language is so rich and tortured.  Talk about metaphors!  In
any case, these discussions are becoming harder and harder to read purely in
terms of military incursions at the surface and more and more a matter of
upper=air fluid dynamics.   I thought perhaps that was because I have been
living at 7000 for a year-and-a-half with more than the quarter of the
atmosphere already below me.  

 

But now I am back in MA and the forecast discussions are still talking about
upper air features as much as they are about surface ones. Below is a
current discussion, marked up by me to translate some of the Jargon.  It is
full of references to upper level events.  

 

Now here is my quandary.  Given Critchlow's Law [LAYERS IN THE ATMOSPHERE DO
NOT MIX [ but they can be STiRRED -NST]], how on earth do events in the
upper atmosphere affect events in the lower atmosphere.   Think of those jet
streams roaring along a 100 mph up at 30,000 feet.  They contain only 10
percent of the mass of the atmosphere.  How are we to thinking of them as
affecting anything below them.   What metaphor is at work when we think of
the ridges and troughs aloft as causing the highs, lows and front's at the
surface.  

 

Also, do jet's use more fuel or less fuel when flying with a jet stream; on
the one hand you would expect less because they are getting help from the
wind; on the other you would expect less because the plane has to fly faster
to stay aloft.  Or perhaps the same because the two factors compensate for
one another? 

 

Anyway, here's the forecast discussion, as annotated  .

 

 

Tuesday Night through Friday:
 
Rain from the daytime Tuesday period come to an end early Tues night. The
vast majority of the mid to latter part of the workweek features really
pleasant weather, under cyclonic flow
<https://forecast.weather.gov/glossary.php?word=flow>  aloft (associated
with an anomalously [= unusually]strong upper trough
<https://forecast.weather.gov/glossary.php?word=trough>  over eastern CONUS
<https://forecast.weather.gov/glossary.php?word=CONUS> ) and a surface ridge
<https://forecast.weather.gov/glossary.php?word=ridge>  of high pressure.
Cool pocket [= a layer of air over head that its unsually cool for its
altitude]of air aloft and below-normal
<https://forecast.weather.gov/glossary.php?word=normal>  850 mb
<https://forecast.weather.gov/glossary.php?word=mb>  temps with strong
insolation <https://forecast.weather.gov/glossary.php?word=insolation>  [=
sunlight]support deep mixing [= when air is cool aloft and heated at the
surface it tends to convect, and therefore to be stirred to the next layer
of warmer air.]; fairly small thing but opted to lower dewpoints toward the
10th percentile NBM values each afternoon given the envisioned strong
mixing. Expect mostly sunny skies with clear nights and fairly strong
diurnal <https://forecast.weather.gov/glossary.php?word=diurnal>  ranges in
temps.
 
By Friday, mid-level trough
<https://forecast.weather.gov/glossary.php?word=trough>  [= a trough is a
dip in the upper air flow, like the dip between two waves; the tops of the
waves are called ridges]axis shifts offshore as geopotential heights [= a
"height" is the altitude at which a particular pressure is reached. It is
the weight of the atmosphere below that point. Think low pressure,
roughly]transition to shortwave
<https://forecast.weather.gov/glossary.php?word=shortwave>  ridging[= i.e.,
a teensy ridge]. Warming trend to temperatures then set to commence as well
with 925 mb <https://forecast.weather.gov/glossary.php?word=mb>  temps upper
teens to around 20C/850 mb
<https://forecast.weather.gov/glossary.php?word=mb>   [= i.e. in the 3-5,000
foot range. This is very generally the top of the layer which interacts with
the surface, but of course, for mother church members, it's two to four
thousand feet below the bottoms of their shoes. ] temps around the mid teens
C <https://forecast.weather.gov/glossary.php?word=C> . Dewpoints [= the
dewpoint is the temperature at which water vapor condenses. Low dewpoint air
is dry air, and, therefore, heavier than wetter air around it. Since the
body's cooling mechanisms depend on evaporation, it is also "more
comfortable to be in warm dry air than to be in warm wet air.  Think swamp
coolers.]still look comfortable (mid to upper 50s) but will see highs in the
interior push into the low-mid 80s.

 

 

 

Nick Thompson

ThompNickSon2 at gmail.com <mailto:ThompNickSon2 at gmail.com> 

https://wordpress.clarku.edu/nthompson/

 

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