Morning inversion

This morning there was a pronounced nocturnal inversion visible across the Salt Lake Valley. The below photo was taken from above the Salt Lake City Cemetary at 11th Avenue around 9:30AM. What's interersting about this photo is the very distinct two layers against the East bench. Here we are looking south across the valley at Big and Little Cottonwood canyon in the distance.


Reviewing the 12z SLC sounding, there was a pronounced ground inversion capped at 860mb with a small flattening near 750mb and then a relatively deep layer extending up to 650mb. By mid day the entire valley was likely well mixed to 650mb with surface-driven cumulus across the region. And with a northwest flow aloft, perhaps we will see some of the trapped valley aerosols disperse a bit more before the next Cold Air Pool event settles in for a stay.


The ingredients are right for another Cold Air Pool event, which will give us IOP2 over the next period, but the duration and strength is in question. I'll let Neil or Erik post the details on IOP1 ending and IOP2 starting up.

Glider Test Flight Over Saltair a Success

In anticipation of today's potential mix out, local paraglider pilot Chris Santacroce and a small team from the U of U finally had a good window to test deploying an instrumented Powered Paraglider (PPG) at the edge of the Great Salt Lake over Saltair yesterday (December 2, 2010). The goal was to sample the land / lake interaction in a strong Cold Air Pool and capture the vertical structure in detail. By attaching a GRAW Sonde to the pilot controlling the glider we hoped to create a "new" type of instrumentation that could sample cross sections and vertical profiles of the air.

Paragliders can fly at very low speeds without stalling (around 15 to 20 mph) which allows unique sampling of the air by a human pilot. Imagine being able to ask a balloon to stop at a certain height, sample a cross section, spiral back to the ground, then ascend just above the cold pool and take pictures before returning to the launch location.

A powered paraglider is also unique because of the small space required to take off. This allows us to deploy the glider quickly and with few resources from any number of locations within the Salt Lake Valley. Of course, most first prototypes suffer in the glamor department but this is what we ended up with (sonde mounted on helmet):


The first flight attempt yielded no problems and good quality data. Chris flew for around 40 minutes completing cross sections out to the lake's edge, then back over I-80. Each transect was 100 meters higher than the last until finally the glider was above the Cold Air Pool, where he was met with a 20 knot south wind. We communicated by texting via iPhone and two-way radio. Chris was able to snap a few photos along the way to document the flight in a little more detail.

Photo by Chris Santacroce, Dec 2, 2010.

Looking south over Saltair from 350 meters AGL.

Photo by Chris Santacroce, Dec 2, 2010.
Looking NNW over Saltair from 325 meters AGL.

Yes. Those are feet at the bottom of the photos. Note in the second photo: the lake fog to the west of Lake Point was still quite thick mid day.

Initial analysis of the observations showed that within 150m starting at 250m AGL, temperatures increased just over 9C, which validated well with nearby balloon launches. And where a regular sonde only samples a single vertical profile with few observations in a shallow Cold Air Pool, we were able to maintain flight within the inversion and gather considerably more data.

Our thanks to Chris Santacroce for helping design a working prototype. Chris is a talented pilot and co-creator of the Red Bull Airforce team. We are extremely lucky to have his skills and time donated for PCAPS and we hope to deploy many more glider flights throughout the project.