Brewer-Wilson Seminar Series Past Events 2017 /
08
Dec
2017
Global CO and NOx emission estimates inferred from assimilation of MOPITT and OMI NO2 data, together with observations of O3 , HNO3 , and HCHO.
01
Dec
2017
Bromine release in the high Arctic: what is the role of aerosols?
Exponential build-up of bromine in the polar troposphere is linked to severe multi-day ozone depletion events in springtime. Recent research suggests that saline snowpack and aerosols are the main sources of bromine, but the exact mechanisms of, and conditions required for these ‘bromine explosions’ are not well understood. The two main sources of aerosol in the Arctic spring are transported pollution (Arctic haze), and larger particles produced from the open ocean or potentially through the sublimation of blowing snow. Both types of particles are rich in sea salt and could contribute to bromine release. Eureka, Nunavut (80°N) is an excellent location to monitor springtime bromine explosions and aerosol concentrations. Profiles of bromine monoxide (BrO) retrieved from Multi-AXis Differential Optical Absorption Spectroscopy (MAX-DOAS) measurements show that there is no clear correlation between BrO concentration and haze aerosol. However, larger aerosols correlate well with observed BrO, indicating that these aerosols are likely a source of bromine. This talk investigates the potential direct and indirect links between bromine activation and aerosols in the high Arctic
24
Nov
2017
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
Characterizing atmospheric transport errors in models using GOSAT XCH4 retrievals
10
Nov
2017
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
Evaluating GPP and respiration estimates over northern mid-latitude ecosystems using solar induced fluorescence and atmospheric CO2 measurements
27
Oct
2017
Measuring Wildfire Plumes in the Arctic using a Network of Ground-based FTIR spectrometers
20
Oct
2017
Understanding the variability and sources of moisture for precipitation in mainland southeast Asia from seasonal to interannual time scales
13
Oct
2017
Remote Sensing of NH3 from Satellite and Ground-based Instruments
06
Oct
2017
Seeing the Ocean Through Sea Ice: Signatures of Submesoscale Ocean Flows in Sea Ice patterns in Marginal Ice Zones
07
Apr
2017
Detecting the Transport of Wildfire Emissions to the Arctic using a Network of Ground-based FTIR Spectrometers
07
Apr
2017
Variable-Resolution model: an alternative way to solve the dilemma of high-resolution modeling
31
Mar
2017
High-resolution Seismic Modeling of the Core-mantle Boundary Region Based on Hybrid Methods: Preliminary Results
31
Mar
2017
How well can polar middle atmosphere descent rates be derived from remote sounding measurements?
24
Mar
2017
The influence of curvature extremes on convection in a fluid featuring a temperature dependent viscosity: implications for modelling small spherical bodies
24
Mar
2017
Spectral analysis of large-scale meteorological patterns preceding summer ozone episodes and heat waves in North America
17
Mar
2017
Combining experimental spectra and density functional theory for improved global warming potential calculations
17
Mar
2017
Exploring Lake effects on regional climate using coupled climate model with artificial lake bathymetry
03
Mar
2017
Transport errors in GEOS-Chem model and their impact on methane simulation
24
Feb
2017
Satellite validation of CFCs over the High Arctic
17
Feb
2017
Influence of Midlatitude Thermal Anomalies on the Circulation of an Idealized Moist Model
10
Feb
2017
Modelling urban anthropogenic 12CO2 and 13CO2 in the Greater Toronto Area
Even in urbanized regions, carbon dioxide (CO2) emissions are derived from a variety of biogenic and anthropogenic sources and are influenced by atmospheric transport across borders. As policies are introduced to reduce the emissions of CO2, there is a need for independent verification of emissions reporting. In this work, we use carbon isotope (12CO2 and 13CO2) simulations in combination with atmospheric measurements to distinguish between CO2 sources in the Greater Toronto Area (GTA). This is being done by developing an urban δ13C framework based on CO2 emissions data and forward modelling. We developed the UofT/ECCC inventory, a CO2 inventory for southern Ontario at a very fine spatial and temporal resolution (0.02ox0.02o and hourly, respectively). The inventory is run with the GEM-MACH chemistry transport model and results are used in our framework in combination with region-specific δ13C signatures of the dominant CO2 sources; the product is compared against highly accurate 13CO2 and 12CO2 ambient data made at sites across southern Ontario. The strength of this framework is its potential to estimate contributions of both locally-produced and regionally-transported CO2. Locally, anthropogenic CO2 in urban areas is often derived from natural gas combustion (for heating) and gasoline/diesel combustion (for transportation); the isotopic signatures of these processes were measured to be significantly different (approximately d13CVPDB = -44 ‰ and -28 ‰ respectively) in the GTA and can be used to infer their relative contributions. Utilizing our δ13C framework and differences in sectoral isotopic signatures, we quantify the relative contribution of CO2 sources on the overall measured concentration and assess the ability of this framework as a tool for tracing the evolution of sector-specific emissions.
03
Feb
2017
Global Trends in Water Vapour
Abstract: Stratospheric water vapour is an important greenhouse gas subject to a positive feedback cycle with surface temperature. Work has been done over the last two decades to characterize its behaviour in the stratosphere, and while general consensus shows that stratospheric water vapour is increasing, the majority of studies come to this conclusion using observations from a single area and generalizing over the globe. While this works for well mixed gases, such as carbon dioxide, water vapour displays distinct patterns across the globe. In this talk I will illustrate an alternate approach, using data collected by ACE-FTS and fitting discrete regions across the globe, in an attempt to generate a more comprehensive view of stratospheric water vapour trends.
03
Feb
2017
Characterizing dispersion due to moisture using multi-pole Debye model
Abstract: Ground penetrating radar (GPR) is a nondestructive measurement technique that utilizes electromagnetic waves to locate targets beneath the surface. The speed of EM waves is determined by dielectric permittivity, which is often assumed to be constant within a homogeneous material. However, dielectric permittivities in real materials vary with frequency. This phenomenon, called dispersion, affects the interpretation of GPR signals. Dispersion becomes stronger with increasing moisture content in materials due to the dipolar nature of water molecules. The goal of this work is to isolate the dispersion caused by water from the dispersion inherent to material. We measure the complex permittivities of samples from a massive sulphide mine under both ambient and dry conditions. The measurements are fitted to a 2-pole and a 3-pole Debye model. Results show that dry samples can be fitted well with 2-pole model while the ambient samples require an additional pole. The relaxation time of the additional pole in ambient samples does not match to that of pure water and further experimentation with higher moisture content is needed.
27
Jan
2017
2016: A Stratospheric HCN Oddity
Last year, an unprecedented amount of hydrogen cyanide (HCN) was emitted from Southeast Asia into the upper troposphere and lower stratosphere.