I have glanced at Tsoil and Qsoil values. It seems that after 8 Jan or so the ground started freezing and reported Qsoil values started becoming smaller (since the EC-5 probes don't respond to the dielectric value of ice, only liquid water). At many of the sites, there actually is an interesting large diurnal cycle to Qsoil as water melts and later freezes. In any case, I think gravimetric sampling to compare to the EC-5 Qsoil measurements is hopeless until Tsoil values return to be positive.
It does bring up the interesting question of whether we should continue gravimetric samples to actually measure Qsoil, now that the EC-5 data is hard to interpret. I would ask the PIs. In the past, I've argued that frozen soil moisture isn't going anywhere, i.e. evaporating, so it didn't really matter what Qsoil was. However, in this melt/freeze situation, it is more complicated.
BTW, the values we have been using are volumetric fraction, mislabeled as volumetric %. I've changed the config, but after I started a recalculation of noqc_instrument. noqc_geo should be correctly labeled.
2 Comments
Jacquelyn Witte
I notice CC and PC sites do not exhibit the large diurnal amplitudes the rest of the sites are measuring.
If anything, would it be worthwhile to continue taking soil samples at those two sites, if measurement remain ~stable? Although, now there would be a network of only 2 sampled sites and not 11.
Matt Paulus
From Isabel's site pictures it looks like CC and PC are both covered in a nice layer of snow, while many other sites aren't. I'm guessing this insolation is why we aren't seeing the diurnal freezing-thawing cycles at these two sites. T-soils at PC appear to stay mostly above freezing, while CC T-soils straddle the freezing mark. Every other site is staying consistently below 0C at all depths, albeit with fairly large diurnal cycles in temperature. Based on this I would agree that we should continue taking samples at CC and PC, as Jacquie suggested, as long as this pattern continues.