Abstracts from 2010/2011
17/9/10 Cristen Adams: Fieldwork with two
spectrometers, a sun-tracker, and muskox.
Throughout my PhD, I have spent a total of five months on field
campaigns with two ground-based UV-visible spectrometers and a sun-tracker.
These instruments are usually operated in a challenging high-Arctic
environment: the Polar Environment Atmospheric Research Laboratory (PEARL)
at Eureka, Nunavut (80N, 86W). I will present some of my experiences in the
field and will discuss how small changes to instrumentation can affect data
quality. Furthermore, I will present the resulting ozone, NO2, and BrO
vertical column density time-series and will briefly overview some of the
applications of this dataset.
1/10/10 Yonggang Liu: Hard Snowball Earth Prevention by Dissolved Organic Carbon Remineralization.
"Snowball Earth" refers to a series of global glacial events which were
inferred to have occurred between 800-540 million years ago (Ma). Although
abundant evidence exists to show that most continents could have been
covered by land ice, there are no direct indicators of the extension of sea
ice during these events could be found. Therefore, it is subject to severe
debate whether the oceans were also completely covered by thick sea ice
(Hard snowball) or only the high and mid-latitude oceans were covered (Soft
snowball/Slushball), as they have distinctly different implications on
biological and hydrological evolutions of the Earth. In this talk, I will
describe a negative feedback associated with enhanced dissolved organic
carbon (DOC) remineraliation that might be strong enough to prevent the
Earth from descending into a hard snowball. I will then further discuss the
influence of continental configuration and stochastic perturbations on the
effectiveness of this negative feedback.
8/10/10 Peter Hitchcock: The long and short of stratospheric sudden warmings
About half of the stratospheric sudden warmings in the observed record
are followed by an extended period (of up to several months) during
which wave activity is strongly suppressed in the polar vortex. This
leads to a characteristic evolution of the vortex in which the anomalous
zonal mean winds and temperatures slowly descend.
I will talk about the zonal mean dynamics of these periods, and discuss
some experiments conducted recently while visiting the group of Shigeo
Yoden at Kyoto University. Using a simplified general circulation model,
we were able to control whether or not these periods occurred following
the modeled sudden warmings.
15/10/10 Zen Mariani: Infrared Emission Measurements at Eureka Using the Extended-range
Atmospheric Emitted Radiance Interferometer (E-AERI)
The Extended-range Atmospheric Emitted Radiance Interferometer (E-AERI) is a
moderate resolution (1 cm-1) Fourier transform infrared interferometer for measuring the absolute
downwelling infrared spectral radiance from the atmosphere. Spectra from the E-AERI are being used
to study the radiative balance and budgets of trace gases in the Canadian high Arctic. The instrument
was installed at the Polar Environment Atmospheric Research Laboratory (PEARL) at Eureka, Nunavut,
in October 2008 and has acquired one full year of data. The SFIT2 retrieval code has been modified
so it can be applied to IR emission spectra, such as those recorded by the E-AERI. Total column amounts
of atmospheric constituents above Eureka including O3, CO, CH4, and N2O have been retrieved.
An investigation into the optimal miniwindows used for these retrievals was constructed. Errors on
retrieved total column amounts for these gases are below 10%. A similar instrument, the Polar Atmospheric
Emitted Radiance Interferometer (P-AERI), was installed at the Zero-altitude PEARL Auxiliary Laboratory
(0PAL) at Eureka from 2006-2009. Total columns measured by these two instruments have been compared,
using both the same retrieval code and two independent methods: differences are less than 6% for most
trace gases measured, comparable to the measurement errors, indicating good agreement between the two
instruments and the two algorithms. An overview of the E-AERI's science objectives, capabilities, and
performance relative to the P-AERI will be presented.
29/10/10 Heather Andres: The Role of Natural Forcings in Generating Surface Mass Balance
Variability over the Greenland Ice Sheet
One aspect of climate change that is causing concern worldwide is the effect it will
have on global sea levels. However, constraints on future changes to sea levels have been difficult to ascertain,
because of the large uncertainty in both dynamic and surface effects of climate change on the mass balance of the
world's two ice sheets. My work focuses on the surface mass balance of the Greenland ice sheet. In order to assess
the influence of greenhouse-gas induced warming on the surface mass balance of the Greenland ice sheet, we must first
understand how ice sheet conditions varied without the influence of anthropogenic greenhouse gases. Consequently, I
am performing a suite of global simulations over the past millennium using the Community Climate System Model 3 at
two different resolutions. These simulations use boundary conditions consistent with the Paleoclimate Modelling
Intercomparison Project Phase III, including two different volcanic reconstructions and time-varying orbital forcing.
Currently, the lower-resolution simulations are finished, while the higher-resolution simulations are still running.
On Friday, I will outline the experimental results that are motivating my project, as well as my goals
for my work. I will describe the boundary conditions used to construct my millennium simulations, and initial
validation results. Finally, I will show the results of my analysis of the variability in surface temperatures
and total precipitation on Greenland over the period of my simulations.
5/11/10 Patricia Pernica: Mixing and stratification in the epilimnion of Lake Opeongo
The epilimnion in a lake is considered the layer directly below free
surface that extends downwards to the thermocline, a region of strong
temperature gradient. This layer responds to changes in wind stress and
heat flux and is commonly illustrated as the zone of active mixing.
However, the epilimnion often displays intermittent mixing and a
non-uniform temperature profile. Using field data from May to August
2009 we report observations of persistent micro-stratification in the
epilimnion of Lake Opeongo, Ontario. The epilimnion was isothermal for
only approximately 40% of July and August 2009, while for at least 30%
of July and August there was a temperature stratification in the 5m
layer of deltaT > 2oC. The gradient Richardson number, was determined
using ADCP measurements of velocity and fast-response thermistor
measurements of vertical temperature gradient. The presence of
turbulence in the epilimnion was estimated by measuring the frequency of
temperature inversions, from a fast response thermistor chain. For Rig <
1/4 we saw frequent temperature inversions, while for Rig > 1/4 the
water column was stable with almost no inversions. Measurements of
dissipation were made using a SCAMP profiler and converted into an
estimate of vertical diffusivity. We found that a good relationship
between the vertical diffusivity and the gradient Richardson number, of
the form Kz = Ko(1 + 3.33Rig)-3/2 where Ko is of order 2 x 10-4 m2s-1. For Rig > 1, the estimated
vertical diffusivity in the epilimnion is essentially at molecular
levels with Kz = KT. These observations stress the importance of small but
persistent temperature difference of the order of 1oC over the 5 m depth
of the epilimnion, which can control the mixing in lakes with moderate
winds.
12/11/10 Dave MacKenzie: Sources of Variability in the UTLS Transition Region
Tropospheric ozone plays an important role in determining the oxidative capacity of the troposphere.
It also impacts air quality and is a greenhouse gas. Changes in the abundance of ozone in the upper troposphere and
lower stratosphere (UTLS) are of particular concern as it is in this region of the atmosphere that ozone contributes
most strongly to the radiative forcing of the climate system. We use the GEOS-Chem model together with observations
from the Tropospheric Emission Spectrometer (TES) and the Atmospheric Chemistry Experiment – Fourier Transform
Spectrometer (ACE-FTS) satellite instruments to examine the influence of stratosphere-troposphere exchange (STE) on
the abundance of upper tropospheric ozone. We characterize the regional and seasonal variations in mixing in the UTLS
in GEOS-Chem and assess its impact on upper tropospheric ozone, with a particular focus on quantifying the contribution
of STE to the ozone budget in the subtropics and mid-latitudes of the northern hemisphere in summer.
19/11/10 Sarah Burgess: Mesoscale spectral shallowing in ECMWF IPY analyses
The atmospheric horizontal kinetic energy (KE) spectrum as calculated from aircraft-based wind
measurements near the tropopause shows a -3 slope at large scales and a -5/3 slope at smaller scales, with a fairly
clearly defined spectral break. Power law regimes with these slopes arise in 2D inertial range turbulence. This has
resulted in attempts to explain the atmospheric KE spectrum, dubbed the ‘Nastrom-Gage spectrum’ after its discoverers,
in terms of turbulence.
The Nastrom-Gage spectrum has been reproduced using high resolution GCMs, but has not been seen previously in
meteorological analyses. I will present spectra and other diagnostics computed for new, high-resolution analyses made
available by ECMWF for the International Polar Year (IPY). The horizontal kinetic energy spectra of these analyses show
very clear spectral shallowing into a dual power law Nastrom-Gage-type spectrum at and above the tropopause;
diagnostics indicate that the shallow mesoscale spectrum cannot be explained by 2D turbulence.
26/11/10 Zhe Jiang: Quantifying the impact of model errors on top-down estimates of carbon
monoxide emissions using satellite observations
We conduct inverse analyses of atmospheric CO, using the GEOS-Chem model
and observations from the MOPITT satellite instrument, to quantify the
potential contribution of systematic model errors on top-down source
estimates of CO.
We assess how the specification of the source of CO from the oxidation of
biogenic nonmethane volatile organic compounds (NMVOCs) in the inversion
impacts the top-down estimates. Our results show that when the NMVOC
source of CO is comparable to or larger than the combustion source,
optimizing the CO from NMVOC emissions on larger spatial scales than the
combustion emissions could result in significant
over-adjustment for the a posteriori CO emissions, and could lead to
negative sources of CO. We quantified the impact of aggregation errors on
the source estimates, associated with conducting the inversion at a lower
resolution than the atmospheric model. We also use the GEOS-3 and GEOS-4
meteorological fields in GEOS-Chem to examine the impact of discrepancies
in atmospheric transport and in the atmospheric OH
distribution on the source estimates.
3/12/10 Marie-Ève Gagné: Simulations of selected O_2 airglow emissions in the Venus atmosphere
In the Venus airglow observations, the (0-v') progression of the O_2
Herzberg II band is the most intense feature in the ultra-violet region;
its peak intensity is ~3-6 kR. The Infrared Atmospheric system is also
present in the Venusian nighttime spectra. The latter emission is the
strongest of all O_2 emissions with a maximum vertical intensity of ~5 MR.
In light of the recent measurements from VIRTIS on board Venus Express
and the detailed analysis of the spectra from Garcia Munoz et al.
(2009), we will present new simulations of O_2 emissions from the
Herzberg II and Infrared Atmospheric bands using Venus atmospheric
conditions. The model results are compared to the available observations
to improve our understanding of the oxygen photochemistry and the fate
of the oxygen species during the nighttime in a CO_2 atmosphere. In
particular, we are interested in quantifying the quenching of the
excited states since the chemical process is not well-known in a CO_2
background atmosphere. Our simulations show that the quenching rates by
CO_2 for both the O_2 (c) and O_2 (a) states should be reduced as
compared to the values currently used in the photochemical models.
The goal of our study is to derive an oxygen photochemistry scheme for
CO2 atmospheres that can be applied to both Venus and Mars. The synergy
of both planets atmospheres can then be studied and consistent analysis
of the photochemistry can be deduced.
14/01/11 Thomas Walker: Impacts of midlatitude precursor emissions and local photochemistry on ozone abundances in the Arctic
We assess the impact of transport of pollution from midlatitudes on the
abundance of ozone in the Arctic using the GEOS-Chem global chemical
transport model, together with satellite and in situ observations of
tropospheric ozone and its gaseous precursors. The model reproduces well
the seasonal cycle in the abundances of PAN and ozone as measured at the
surface at Alert and during the summer in the Arctic free troposphere.
Tagged regional tracers are used to construct a budget of ozone
transported from midlatitude source regions, which contribute 25-35% of
the ozone in the middle and upper Arctic troposphere in the summer, and
adjoint sensitivity studies link the summer ozone distribution to specific
sources. An assimilation of tropospheric ozone profiles from the
Tropospheric Emission Spectrometer (TES) satellite instrument at
midlatitudes provides an improved boundary condition for transport from
midlatitudes and reinforces model credibility. Further sensitivity studies
probe the role of reactive nitrogen on Arctic ozone production. Ozone
production in the summer in the Arctic lower troposphere of up to 0.25
ppbv/day is due to the decomposition of peroxyacetyl nitrate near the
surface.
21/01/11 Felicia Kolonjari: Measurements of hydrochlorofluorocarbons from space using the Atmospheric Chemistry Experiment Fourier transform spectrometer and ground-based spectrometers
In the 1980s scientists discovered an annual springtime minimum in stratospheric ozone over the Antarctic. It was determined that the decline in ozone concentration was primarily caused by catalytic reactions of ozone and atomic chlorine and bromine. Chlorofluorocarbons (CFCs) were determined to be the main source of these halogens. The Montreal Protocol on Substances that Deplete the Ozone Layer (with its subsequent amendments) restricts the emissions of ozone depleting substances. To fulfill the need for safe, stable replacements for CFCs, hydrochlorofluorocarbons (HCFCs) and hydrofluorocarbons (HFCs) were developed.
The Atmospheric Chemistry Experiment (ACE) is a mission on-board the Canadian satellite SCISAT. The primary instrument on SCISAT is a high-resolution infrared Fourier Transform Spectrometer (ACE-FTS). With its wide spectral range, the ACE-FTS is capable of measuring a wide range of gases including key CFC and HCFC species. The height information from the ACE-FTS profiles provides information that is complementary to the ground-based sampling that has been used to monitor these species. Validation of the global ACE-FTS dataset is crucial to establishing the reliability of the measurements. To this end, a new collaboration between the University of Toronto and Japan’s National Institute of Information and Communications Technology (NICT) has been established. An overview of the project and initial results of this collaboration will be discussed.
28/01/11 Karen Smith: Why can't climate models capture the observed connection between seasonal snow cover and the Northern Annular Mode?
The suite of general circulation models (GCMs) in the Coupled Model
Intercomparison Project (CMIP3) have been found not to reproduce the
observed relationship between October Eurasian snow cover anomalies and
the wintertime Northern Annular Mode (NAM). This apparent deficiency is
reexamined here based on analysis of observational data and GCM
simulations with prescribed snow forcing. Previous work has shown that in a
comprehensive GCM in which an autumnal Siberian snow forcing is
prescribed, a vertically propagating Rossby wave train is generated that
propagates into the stratosphere, drives dynamical stratospheric warming
and induces a negative NAM response that couples to the troposphere. The
wave response and background climatological stationary wave must interfere
constructively to achieve wave activity amplification into the
stratosphere and the zonal mean stratosphere-troposphere NAM response.
Using observational data, it is shown that constructive interference also
occurs in the observed October Eurasian snow cover-NAM connection. This
constructive interference peaks in December, corresponding to strong wave
activity flux into the stratosphere two months after the snow cover
anomalies in October. By contrast, the CMIP3 GCMs typically show a
negative correlation between October Eurasian snow cover and December wave
activity flux, which is related to destructive interference between the
wave train associated with the snow and the background stationary wave.
This linear interference effect is not only associated with stratospheric
variability related to Eurasian snow cover anomalies but is a general
feature of Northern Hemisphere troposphere-stratosphere interactions, and
in particular dominated the negative NAM events of the fall-winter of
2009-2010.
4/02/11 Ashleigh Ingle: Canopy architecture and leaf distribution: does the atmosphere
care?
Leaves act as the clouds’ hydrological co-conspirators on land: they are
both bodies through which water travels and changes state; and together,
they provide the engine for the water cycle. Much as the shape,
constitution and height of clouds are both responses to and a
precipitating factor in atmospheric conditions: the spatial
distribution, albedo and stomatal resistance of leaves are both
dependent on and a factor in the determination of the state of the soil,
the temperature of the air and the amount of available water. It is
these properties: leaf quantity, distribution, albedo and stomatal
resistance that must be known in order to simulate the contributions of
leaves to the water and energy cycles. The values of stomatal
resistance, albedo and stress responses for a type of leaf are well
known through laboratory experiments. However, the values of the same
parameters for an entire canopy will not generally be equivalent to
these values multiplied by the number of leaves present and so,
empirically and theoretically based algorithms must be created to
determine canopy and forest parameters from reflectance data measured
using both ground and satellite-based optical devices.
The leaf and canopy parameters determined through these methods turn out
to be highly algorithm dependent, which means that the value of
important parameters such as leaf area index can vary a lot between
different devices and research groups. A main contributer to these
differences is the choice of vegetation index and clumping index, which
describes the non-random distribution of leaves. With a focus on the
boreal forests, I will lead you through the description and modelling of
leaf and canopy structures; their representation in GCMs; and the
possible ramifications of these discrepancies on extra-tropical
climate.
11/02/11 Rodica Lindenmaier: Deriving the NOy budget above Eureka using the Bruker 125HR, model and satellite data
Reactive nitrogen species, collectively called NOy, play an important
role in the chemistry of the stratosphere. NOy is responsible for
significant ozone destruction in the mid-stratosphere and influences the
partitioning of the hydrogen, chlorine, and bromine families in the lower
stratosphere.
Four years of measurements have been acquired using the Bruker 125HR
Fourier transform Infrared (FTIR) spectrometer installed at the Polar
Environment Atmospheric Research Laboratory (PEARL) in the High Arctic.
These have been combined with data from three climate models, namely the
Data Assimilation version of the Canadian Middle Atmosphere Model
(CMAM-DAS), the Global Environmental Multiscale stratospheric model, with
the online BIRA Atmospheric Chemistry package (GEM-BACH), and the off-line
3D Chemical Transport Model SLIMCAT. The FTIR data have been also combined
with measurements of the Atmospheric Chemistry
Experiment-Fourier Transform Spectrometer (ACE-FTS), to assess the NOy
budget above Eureka, Nunavut (80.05ºN, 86.42 ºW). The FTIR is able to
measure four of the five primary species that form NOy: NO, NO2, HNO3, and
ClONO2, while the fifth, N2O5, was obtained using the N2O5/(NO+NO2) ratio
derived from the models and ACE-FTS. Combining these results, a four-year
time series of NOy was calculated.
18/02/11 Niall Ryan: Millimetre–wave spectroscopy for mesospheric wind measurements
A variety of techniques exist for measuring wind speeds in the
troposphere and lower stratosphere (mainly balloon- and aircraft-mounted sondes)
as well as above about 80 km (limb sounding, meteor radar, etc.), but as none of
these techniques can measure wind speeds in the range between ~30 and 70 km there
is a major lack in experimental data for the upper stratosphere and lower mesosphere.
Millimetre-wave remote sounding offers a potential to close this gap. Reliable observations
of mesospheric wind speeds would allow improvements of atmospheric circulation models and
direct observation of dynamic processes such as gravity wave breaking. I will talk about
my instrument design and how it can be used to exploit the potential of ground-based
millimetre-wave radiometry by measuring the Doppler shift of emission lines of atmospheric
trace species.
11/03/11 Cynthia Whaley: A Study of Local Atmospheric Composition
Tropospheric trace gases have a significant and direct impact on our
environment and our lives. Pollutants such as carbon monoxide (CO), ozone
(O3) and nitrogen oxides (NOx) are harmful to the ecosystem and human
health and they have many anthropogenic sources. I will be presenting
updated time series of trace gas abundances that are retrieved from
spectra measured at the University of Toronto Atmospheric Observatory
(TAO). I will also present my preliminary comparisons of urban versus
rural observations for ethane, hydrogen chloride, nitrous oxide and
methane (C2H6, HCl, N2O and CH4 respectively).
Modeling of atmospheric composition is also extremely important since it
helps us to understand the chemistry and dynamics hidden within the
observations. GEOS-Chem is a chemical transport model that is driven by
assimilated meteorological fields from the Goddard Earth Observing System
(GEOS). I have compared the model output to TAO measurements for CO, O3
and HCN, and I will discuss the differences between the two. I will
present model simulations that have helped us determine the major sources
of CO and O3 for the Toronto region. And I have started to delve more
deeply into determining the causes for the variability in our time series.
18/03/11 Andre Erler: Objective Identification of the Tropopause
Current definitions of the tropopause are purely empirical, and in the case of the
dynamical tropopause, a wide range of threshold values are used in the literature.
At the same time, accurate identification of the tropopause is important for many
applications ranging from estimation of dynamical stratosphere-troposphere exchange
to the retrieval of atmospheric composition.
Here an objective definition of the tropopause will be proposed, which does not rely
on an empirically chosen parameter.
The basis for the method is the detection of a change in the gradient of a
materially conserved quantity by means of change-point analysis.
Potential temperature or entropy can be used to define an equivalent to the thermal
tropopause, and PV to define the dynamical tropopause.
This method is used to estimate the dynamical tropopause in ERA-40 data. It is shown
that the results obtained with this method provide a better characterization of the
vertical structure than traditional definitions of the dynamical tropopause.
The dynamical tropopause structure is contrasted with a similar estimate of the
thermal tropopause based on entropy.
The change-point method is then applied to high resolution ECMWF analysis data and
data from high resolution baroclinic life-cycles experiments. The thermal tropopause
characteristics and the tropopause evolution during baroclinic wave-breaking will
be discussed.
Furthermore a measure for tropopause sharpness will be introduced, based on the
difference in gradient at the change-point (the tropopause). This measure can be
used to quantitatively determine whether the identification of a tropopause is
meaningful under certain conditions, such as in the centre cyclonic vortices.
Brewer Seminar site maintained by Rodica Lindenmaier. Last updated 22 March 2011.
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