Ticker for January 30, 2002

                
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January 30, 2002   January 30, 2002   January 30, 2002   January 30, 2002


Calm Winds, Gusting to Seventy Miles an Hour?

Yesterday's Ticker talked about the ability to "observe" freezing
precipitation by looking for the otherwise out-of-place low-to-calm
wind speeds on the Mesonet maps.  The freezing belt certainly showed
up today in northern, central and southwestern Oklahoma:




But, wait a second ... what's the deal with the wind gusts at
Breckinridge (north-central Oklahoma)?  59 mph?  72 mph?  What?

That's a related quirky effect that yesterday's Ticker didn't get to
address.  Remember from yesterday's Ticker that the prop part of a
propvane measures windspeed.  It does this by counting the number of
turns of the prop in a given time period.  How?  With magnets!

When the prop makes a revolution, magnets pass each other and
revolutions are counted.  This action is demonstrated simply and
crudely in this graphic from the Ticker Art Dept, whose talent is
always on vacation:


(by the way, there are more magnets than shown in this graphic)

When the propvanes are frozen stiff (and they are), vibrations from the
wind can cause these magnets to dance radiply near each other,
registering a huge number of "rotations".  This is interpreted as a
large wind speed.

It's yet another headache for the Mesonet's QA Manager, who makes sure
data like this is flagged in the final archives.  But it's a lot of fun
for people who like to know how things work.