Brewer-Wilson Seminar Series Past Events 2017 / 11
24
Nov
2017
12:10 p.m.
- 1 p.m.
MP606
Bernard Yang
High-frequency observations of temperature and dissolved oxygen reveal under-ice convection in a large lake
Detailed observations of thermal structure over two winters in a large lake reveal the presence of large (10-20 m) overturns under the ice, driven by diurnal solar heating. Convection can occur in the early winter, but the most vigorous convection occurred near the end of winter. Both periods are when our lake ice model suggest thinner ice that would have been transparent. This under-ice convection led to a deepening of the mixed layer over time, consistent with previous short-term studies. During periods of vigorous convection under the ice at the end of winter, the dissolved oxygen had become super-saturated from the surface to 23 m below the surface, suggesting abundant algal growth. Analysis of our high-frequency observations over the entire winter of 2015 using the Thorpe scale method quantified the scale of mixing. Furthermore, it revealed that changes in oxygen concentrations are closely related to the intensity of mixing that could be influenced by climate change or the increased input of salt into the lake. I will briefly present an overview of some of the basics of physical limnology before presenting our results.
17
Nov
2017
12:10 p.m.
- 1 p.m.
MP606
Ilya Stanevich
Characterizing atmospheric transport errors in models using GOSAT XCH4 retrievals
10
Nov
2017
12:10 p.m.
- 1 p.m.
MP606
Stephanie Hay
Comparing the robustness of the coupled circulation response to high and low latitude forcing
Four fully coupled climate models, CESM1, CanESM2, CNRM-CM5 and GFDL-CM3Z are used to isolate the impact of Arctic sea ice loss on the atmosphere. In all models, Arctic sea ice is melted in isolation from the effects of external radiative forcing. However the method through which this melting is achieved, as well as the radiative forcing protocol, differs between the sets of experiments. Nonetheless, several aspects of the wintertime response are remarkably robust. Arctic sea ice loss in coupled models produces warming that is strongest over the Arctic Ocean and high latitude land masses alongside a weak cooling over eastern Eurasia, a dipole pattern in sea level pressure with lower pressure over North America and higher pressure over Eurasia, a strengthening of 850 hPa zonal winds in mid-latitudes along with a weakening on the poleward side, and an increase in precipitation over northern high latitudes. Because there are different amounts of warming at lower latitudes between the models, a pattern scaling approach is used to separate out the part of the pattern that scales with low-latitude warming and the part that scales with sea ice loss. The similarity in the part that scales with sea ice loss remains after applying pattern scaling, but the part of the pattern that scales with low-latitude warming is model-dependent.
03
Nov
2017
12:10 p.m.
- 1 p.m.
MP606
Brendan Byrne
Evaluating GPP and respiration estimates over northern mid-latitude ecosystems using solar induced fluorescence and atmospheric CO2 measurements