Basin Cold Pools of the Peter Sinks

The high-amplitude ridge is settling in over Utah and we are in for several days of clear, dry weather with large daily temperature ranges.

Large diurnal temperature ranges will be observed during this period, especially in basins, closed topographic depressions with no drainage outlet.  Such basins include the Rush Valley south of Tooele (which is misleadingly named and is really a basin) and the meteorological king of the diurnal temperature range, the Peter Sinks of the Bear River Mountains east of Logan.

We'll have a look at the Rush Valley tomorrow, but let's talk about the Peter Sinks today.  The Peter Sinks are a series of limestone sinkholes known for remarkably cold temperatures.  As described by wikipedia, the lowest temperature ever recorded in Utah -69.3F, was measured in the Peter Sinks on 1 Feb 1985.

The Peter Sinks aren't much to look at.  They aren't even very deep.  They are modest depressions, but do feature a pronounced vegetation inversion with trees growing only on the upper slopes and rim.  This may be due to the extreme temperatures that occur within the sinks.

A view of the Peter Sinks.  Photo: John Horel

Craig Clements, Dave Whiteman, and John Horel ran a field program examining the cold pools that form in the Peter Sinks during September 1999 (Clements et al. 2003).  They instrumented the northern portion of the Sinks with a series of meteorological instruments and ran a few tethersondes (i.e., tethered balloons that can be lowered and raised) near the bottom and along the sidewall of the Sinks.

Peter Sinks field experiment design
(Clements et al. 2003)

The remarkable cold pool that forms in the valley floor is well described by data from the meteorological stations (T1–T5, with T1 the lowest) during EXP1, a clear, calm night.  The meteorological stations have similar temperatures at sunset (SS), but the diurnal temperature range is more than 10C larger on the floor of the Sink (T1) than on the rim (T5).  Considerable variability in the temperature at T5 during the night reflects the occasionally sloshing of cold air from the sink across the rim.  Temperatures quickly become similar again shortly after sunrise (SR).

Temperature traces from meteorological stations T1–T5
(Clements et al. 2003)

Basins become extremely cold at night for two major reasons.  First, they are more protected from the large-scale flow and see less turbulence, which tends to mix the atmosphere and prevent such intense cold pools from forming.  Second, the cold air that forms has no place to go.  It sits there and continues to cool via radiative and sensible heat fluxes during the night.  Typically the cold pool in a basin grows to a depth of the lowest gap on the rim, which serves as a conduit for the cold air.

Tomorrow we'll have a look at another great cold pool basin, the Rush Valley.