Monday, November 23, 2015

Interesting Data from Russ Scott

First, the gusty winds forecast over the weekend were very sporadic, especially on Saturday - there were some gusts in the 20 to 25 mph range but these were not strong enough to have much impact on the bicycle races. Winds were stronger on Sunday morning, with gusts from the east up to 32 mph at TUS. Morning lows here were in 30s F but above freezing.

Russ Scott has sent along some interesting data from his flux towers over near Tombstone. The sites of interest are those in green, and Charleston (CM), along the San Pedro is at 1200 m, Lucky Hills (LH) at 1370, and Kendall (KN) is at 1531 m. The sites are about 12 km apart.

He notes:

"Your Madweather post this morning got me wondering again about why some mornings have the valley bottomlands that are so much colder than the higher locations in the valleys.  Is it local radiational cooling, cold air drainage, or even evaporative cooling (from moisture riparian-esque vegetation)?

Here are some plots from the last seven days in the San Pedro Valley from my three metflux towers."

The temperature plots above from the 12th through the 14th of November indicate that the site near the San Pedro was dramatically colder than the other two sites to the east. - the morning lows being 10 C or more colder. 

However, the radiative flux data (above) show that the nighttime, long-wave cooling was was similar, and also smallest at the CM (coldest) site.

The wind speeds, however, (below) show that the CM site is less windy than the other two sites, especially during the night.

My guess concerning what's going on:

First - low-level radiational cooling at night is probably more effective in producing a cold and stable and very shallow layer just above the surface at CM, particularly because of the nearly calm winds and less vertical mixing than at the other two sites. 

Second - there is probably cold drainage occurring within the very shallow, cold and stable layer from the nearby, slightly higher and more barren (lower heat capacity surfaces) areas, both to the east and west of the San Pedro.

Other thoughts and/or comments most welcome.

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