Fluxes Over Snow Surfaces II
FLOSSII is the second phase of the FLOSS project, studying the surface meteorology of snow-covered rangeland in the North Park region of Colorado, near Walden.
For more information, see also ISFF measurements.
The project used CSAT3 sonic anemometers for all wind sensing. Overall, their performance was excellent, with occasional spikes probably due to precipitation in the path or accumulating on the path.
Krypton hygrometers were used for measuring water vapor fluxes. These were our only sensor for measuring water vapor fluxes, but they did not perform well. The Lake and Sage sensors were connected (using the PMB-version serializers) on 10/10. On 11/18 at sage, 11/19 at lake, and all the time (after about 11/20), all kryptons (but one) were set to a pathlength of 2.6cm, following guidance from Arian van Dyke's paper. Previously, all ISFF kryptons had pathlengths of about 1.2cm.
We deployed our LiCor 6251 (closed-path IRGA) with an inlet at 2m at the main tower to measure CO2 fluxes close to the surface. It was installed 12/16, and valve control (for the gas calibration system) started 12/18. Only a Lo-Cal cylinder was attached initially, since one gas regulator was bad. We installed a new regulator 1/6 and got Hi-Cal working. On 1/7, we swapped Lo-cal cylinders since the pressure was somewhat low. On 1/8, the calibration cycles were shortened to 30 seconds (down from 2 minutes) to extend the life of the calibration gases. Due to an apparent slight leak in the LoCal plumbing, it was necessary to change the LoCal cylinder 3 times during the experiment, whereas only one HiCal cylinder was used throughout
T/RH sensors generally worked, though main tower profiles were often not strictly monotonic. Some of these differences may be real (since fetch changes with height), however at least one swapping test showed a sensor problem.
There were a lot of radiometers, since this experiment tried to repeat (and extend) the longwave-radiative flux divergence study first done during CASES99, in addition to measuring all 4 components to know the surface energy balance at each site.
There were lots of soil measurements for FLOSSII because we wanted to sample the heterogeneous surface. Each of the 3 main sites had 3 subplots with a complete set of sensors. Each subplot had a 3-level temperature profile (2.5, 5, and 10cm), 2-level moisture profile (5 and 10cm), and 1 heat flux measurement (10cm). All of these sites were installed 10/4-5 to give them time to settle in.
There was a weighing precipitation gauge and an ultrasonic snow depth gauge at the main tower site (near grass radiation stand). Both were installed on the 11/21 visit. The weighing gauge did not report values between 11/21 and 12/15 for an unknown reason. It appeared to work later. Its response was tested on 1/7 and it was only one "tip" off (43 reported; 44 expected), so the data should be okay. These tips have been removed from the data.
The October and November data were gathered exclusively through the GOES satellites. Our recent experience with data taken this way is that about 10% of the data have errors. We have eliminated the data when checksums were not correct.