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Abstracts from 2009/2010

25/9/09    Daniel Abreu:   Lightning detection via ground wave and sky wave propagation

Current methods of ground-based lightning detection involve an analysis of the ground wave or sky wave produced by a single lightning discharge. The Canadian Lightning Detection Network (CLDN) and the World Wide Lightning Location Network (WWLLN) employ such techniques. The performance of these networks is characterized by their location accuracy and detection efficiency. In this talk, I will be introducing the basics of lightning processes, then investigate the structure and performance of these networks.


02/10/09    Jahanshah Davoudi:   Stochastic aspects of deep convection

Recently some theoretical ideas motivated by statistical mechanics have been suggested for describing deep convection in the context of radiative convective equilibrium. I shortly review the theoretical ideas. The predictions based on the theory will be tested by means of diagnosing a cloud resolving simulation with diurnal forcing.


16/10/09    Lei Wang:   Stationary waves in CCMVal-2 models

Stationary waves, the zonally asymmetric component of the time mean or seasonal mean atmospheric circulation, originate from the zonal asymmetries in the lower boundary. The observed stationary waves have great influences on regional climate and contribute significantly to large scale circulation such as Brewer-Dobson Circulation (BDC). Therefore, predicting stationary wave changes is an important task in future climate projections. In this talk I will show some diagnoses of stationary waves, with a focus on stratosphere, in CCMVal(Chemistry-Climate Model Validation Activity for SPARC)-2 models, including seasonal cycle, vertical structure, the shape and position of the polar vortex, and long-term trends. Usually the stationary wave field is not heavily tuned in such models and thus may be considered as a fairly independent dynamic quantity to evaluate the model performance in certain aspects.


30/10/09    Chris Fletcher:   What controls the extratropical teleconnection response to tropical SST forcing?

Seasonal climate predictions for the extratropics depend mainly on linking day-to-day atmospheric variability there with persistent sea- surface temperature (SST) anomalies in the Tropics. These links, known as teleconnection patterns, can be maintained for weeks, months or even years by, for example, El Nino/Southern Oscillation (ENSO) episodes or secular warming trends in the tropical Indian Ocean. In this talk I will show results from atmospheric GCM experiments where the model was forced with prescribed (a) warm ENSO and (b) warm Indian Ocean SST perturbations. The resulting extratropical teleconnections have opposite sign: Indian Ocean warming produces a positive NAO response, while ENSO warming produces a negative NAO response. I will use recently developed linear interference arguments to explain this difference, and also discuss the importance of topographic forcing of planetary waves.


06/11/09    Cristen Adams:   Measurements of atmospheric bromine monoxide at 80N

Despite its low concentrations in the atmosphere, bromine monoxide (BrO) accounts for up to half of springtime catalytic ozone depletion in the stratosphere. In the troposphere, large quantities of BrO can appear suddenly and linger for several days. These bromine explosions have been linked to mercury deposition in the Arctic.

Retrieval of BrO is difficult and measurements of bromine species at high latitudes are scarce. Therefore, there are large uncertainties in our knowledge of the amount of bromine in the atmosphere. In order to improve this situation, we measure BrO columns with two ground-based UV-visible spectrometers at the Polar Environment Atmospheric Research Laboratory (PEARL) in Eureka, Nunavut, Canada (80N, 86W). I will discuss the techniques and challenges for ground-based BrO measurements. Furthermore, I will compare ground-based measurements of BrO above Eureka and those made by the OMI satellite instrument.


13/11/09    Andre Erler:   Tropopause Dynamics and Implications for Stratosphere-Troposphere Exchange in the extra-tropics

Abstract: Mixing processes in the extra-tropical tropopause region are usually thought of as isentropic dynamical mixing (following the chaotic advection paradigm); breaking of planetary waves is one of the major driving force.

In baroclinic life-cycle experiments a net rise of the (thermal) tropopause can be observed, implying a significant mass flux from the stratosphere into the troposphere. In this sense there are two ways of Stratosphere-Troposphere Exchange due to baroclinic wave-breaking: isentropic stirring and mixing at a material surface (e.g. the 2-PVU-iso-surface), and migration of the tropopause itself (which is not a material layer).

In the simulations presented here, the rise of the tropopause is much stronger in LC1 than in LC2. However, a previous study found more efficient Stratosphere-Troposphere Exchange in LC2 (Esler&Polvani 2007). I will address this apparent contradiction, and discuss the relevance of the tropopause definition in the context of Stratosphere-Troposphere Exchange and implications for chemical trace correlations.

In a climatological equilibrium state the tendency of wave-breaking to raise the tropopause must be balanced by a different effect, presumably radiation. I propose the hypothesis that the tropopause height undergoes intermittent, but strong fluctuations which involve both isentropic mixing and significant cross-isentropic transport.

I will present supporting evidence from simple radiative transfer calculations, and briefly discuss implications for the nature of mixing in the extra-tropical tropopause region.


20/11/09    Ray Nassar:   Using Tropospheric Emission Spectrometer (TES) CO2 observations to improve inverse modeling estimates of carbon fluxes

Abstract: The strength of CO2 sources and sinks can be determined from a set of atmospheric measurements and a model simulation of CO2 using a Bayesian inversion approach. This approach has traditionally been used with ground-based measurements; however, the capability to retrieve CO2 from observations by the Tropospheric Emission Spectrometer (TES) on the Aura satellite, has recently been developed. Although the sensitivity of TES CO2 peaks in the mid-troposphere (511 hPa) and TES CO2 accuracy and precision are lower than those of ground-based in situ measurements, the coverage provided by TES provides an important benefit for flux inversions. This talk will discuss the new TES CO2 data product, recent and ongoing improvements to the GEOS-Chem global CO2 simulation, and compare inverse modeling estimates of CO2 sources/sinks from TES and the in situ surface network.


27/11/09    Jane Liu:   Interannual Variability of Tropospheric Ozone in the Middle East

Abstract: Recent satellite observations have shown that ozone abundances over the Middle East and North Africa are enhanced in the middle troposphere in summer. Understanding the processes responsible for this buildup of ozone and its year-to-year variations is important because ozone in the middle and upper troposphere is a significant greenhouse gas. In this talk, I will present results from our analysis with the GEOS-Chem global chemical transport model to understand the variations in ozone over the Middle East between 1987 - 2006. Our results show that the summertime enhancement of ozone in the middle troposphere is a robust feature over the 20-year period and that long-range transport of pollution from Asia and local production of ozone are the dominant sources of ozone in the region. We find that the magnitude of the ozone contribution from Asia and local production fluctuated by about ±30% and ±20%, respectively, during the 20-year period. Although these two sources are always the major contributors to the elevated ozone abundances, we found that in years when the Asian influence was weaker, transport from other areas, such as North American, was more dominant. This trade off between transport from Asia and the other regions is related to the subtropical westerly jet over Central Asia, which is associated with the intensity of the high-pressure region in the upper troposphere over the Tibetan Plateau. Earlier studies have suggested that the atmospheric general circulation will possibly respond to climate change with a poleward and upward shift of the subtropical jet and an enlarged Tibetan High. Our study suggests that climate-related changes in the subtropical jet and the Tibetan High will have implications for the transport of pollution into the region. Such changes in pollution in the region could feedback on the climate system through changes in the radiative forcing associated with ozone.


04/12/09    Yonggang Liu:   A Carbon Cycle Coupled Climate Model of Neoproterozoic Glaciation

Abstract: It has been suggested that a negative climate feedback may have operated during the Neoproterozoic Era as a consequence of the existence of a massive oceanic pool of dissolved organic carbon (DOC). As climate conditions cooled so as to induce intense glaciation, the drawdown of oxygen into the Neoproterozoic ocean would have been enhanced because of the temperature dependence of the solubility of oxygen in sea water. Such increasing ventilation would have enhanced DOC respiration, thus increasing the content of dissolved carbon dioxide. In an oceanic environment saturated with respect to carbonate, a fraction of this increase would have been exhausted into the atmosphere, thereby enhancing the greenhouse effect and inhibiting further climate cooling. The model employed to illustrate the resulting climate dynamical behavior was one for which it was assumed that the additional source of atmospheric carbon dioxide due to volcanic outgassing was precisely balanced by the sink due to calcium-magnesium silicate weathering. Furthermore the paleogeography assumed for the purpose of the published analyses was one more appropriate to the Marinoan glaciation than to the earlier Sturtian event. Here we relax both of these assumptions and thereby demonstrate that the tendency of the model to support cyclic glaciation on timescales compatible with inferences based upon Neoproterozoic carbon isotopic variability is rather robust in the presence of such additional complexity.


11/12/09    Peter Hitchcock:   Downward Propagating Temperature Anomalies in the Arctic Polar Vortex

Abstract: The Arctic polar vortex exhibits strong dynamical variability on intra-seasonal and inter-annual time scales. This variability has important consequences for polar ozone chemistry, dynamical coupling between the mesosphere, stratosphere, and troposphere, and creates challenges for detection and attribution of long term changes in the polar middle atmosphere. It is also dynamically interesting of its own accord, for those who enjoy such things.

I will describe a diagnostic tool for visualizing the temporal evolution of the zonal mean component of this variability. From this I will argue that one particular feature--namely the coherent descent of large amplitude temperature anomalies on seasonal time scales--occurs with sufficient frequency and regularity as to warrant more detailed study. Moreover, the representation of these episodes in CMAM appears to match observations reasonably well.

I will then describe some common features of these episodes in CMAM simulations, and suggest for future work that a zonal mean quasi-geostrophic model would shed useful light on questions regarding their dynamical evolution.


08/01/10    Felicia Kolonjari:   PARIS-IR: Highlights from the Canadian Arctic ACE Validation Campaigns, recent developments and plans for the future

Abstract: The Portable Atmospheric Research Interferometric Spectrometer for the Infrared (PARIS-IR) has been deployed annually in Eureka, Nunavut during the Canadian Arctic Atmospheric Chemistry Experiment (ACE) Validation Campaigns since 2004. The campaigns, which begin at polar sunrise in late February, are conducted for the purpose of studying the chemical composition of the Earth's atmosphere and validating the ACE satellite data products. PARIS-IR is a portable Fourier transform spectrometer (FTS) which measures in the mid-infrared region of the spectrum, allowing it to record the absorption features of dozens of atmospheric trace gases to determine total column densities.

Since July 2009, PARIS-IR has been operating at the Toronto Atmospheric Observatory (TAO). A retrieval of CH4 from the PARIS-IR Eureka spectra has been developed recently, which has been applied to the Eureka spring campaign data set and will additionally be applied to spectra recorded at TAO. Measurements trace gas species obtained during the 2007, 2008 and 2009 campaigns will be presented. Plans for validation of other satellite instruments will also be discussed.


15/01/10    Heather Andres:   Analysing surface climate effects from century-scale and 11-year solar variability

Abstract: Resolving the different roles that natural and anthropogenic forcings have played in the climate system over the past few centuries has been the central effort of many coupled, atmosphere-ocean modelling studies. In particular, the effects of total solar irradiance (TSI) variability on the climate system have been emphasised in these studies, due to the perceived strength of century-scale, solar variability in TSI models. However, direct measurements of total and spectral solar irradiance via radiometers and spectrometers on board spacecraft and satellites have only been available since 1978 [Frohlich 2004] and suffer from calibration issues between instruments [Jones 2008]. Consequently, there is little observational data that can be used to verify solar variability models on century timescales, and thereby the effects of century-scale solar variability on surface climate. Thus, one approach has been to compare responses to the 11-year solar cycle between models and observations, in order to understand how well the models replicate the key processes involved on that timescale. This knowledge can then be used to interpret the longer-term effects obtained from model simulations.

I will present the results of my study of two models with different estimates of century-scale solar variability. I have produced four sets of eight global warming simulations spanning 1870 to 2000 using the National Center for Atmospheric Research Community Climate System Model 3.0 (CCSM3). These simulations include both anthropogenic and natural forcings, consistent with those used in the CCSM3 analyses performed in support of the 4th IPCC Assessment Report. Firstly, I will present analyses of direct climate responses to the 11-year solar cycle within these simulations. I will compare the climate responses to previous analyses performed using both reanalysis data and other models, in order to establish how robust these features are and how well CCSM3 replicates the important processes. Secondly, I will present the results of my analysis of the effects of century-scale variability in these simulations. I will interpret these results using the conclusions from my examination of the 11-year solar cycle.


29/01/10    Sarah Burgess:   Schramm Loewner Evolutions in Two Dimensional Turbulence

Abstract: In this talk, I give basic introductions to α-turbulence models and Schramm (a.k.a. stochastic) Loewner evolutions (SLEs). SLEs are conformally invariant growth processes that describe interfaces between different phases in 2D critical statistical mechanical systems. I will review the recent discovery of SLE curves in numerical simulations of α-turbulence. The presence of SLE curves allows certain turbulent statistics to be calculated analytically, using existing results from the mathematical literature. Despite this exciting development, the appearance of SLE in turbulence is puzzling, as the models in question seem not to be described by the conformal field theories normally associated with SLEs.


05/02/10    Ashley Jones:   Analysis of HCl and ClO time series in the upper stratosphere using satellite data sets


12/02/10    Zhe Jiang:   Model errors in carbon monoxide inversion analysis and application for improving the model simulation in China

Abstract: Inverse modeling is used to improve the estimation of the surface emissions of trace gases. Understanding the model errors in this process is important. We showed the influence of three model errors (aggregation, linearizing in chemistry and model transport error) on the CO inversion analysis. Their effect is significant and should be fully considered in future work.

The MOPITT instrument, which is usually believed as low sensitivity to low altitude, observed strong CO signals at 850hPa over China. These signals are highly consistent with our a priori knowledge about the surface CO emission is this region. Our result also shows that the MOPITT has enough sensitivity at regions with high surface-atmosphere thermal comparison. However, the model simulation has large difference with the observation data. It may be caused by the missing of CO source. An inversion analysis for this region will be done in next step to improve the model simulation.


26/02/10    Isla Simpson:   Sea surface temperature variability and the Antarctic stratosphere.

Abstract: An ensemble of chemistry climate model (CCM) simulations has been examined for evidence of an influence of sea surface temperature (SST) variability on Antarctic stratospheric dynamics and ozone concentrations.

In the Canadian middle atmosphere model (CMAM) it is found that pre-1980's ozone trends differ significantly between simulations that use observed SSTs and those that use modelled SSTs. There is a lack of ozone depletion in the mid-1970's in the simulations with observed SSTs at the lower boundary as in the observations. Furthermore, in the CMAM there is evidence that during La Nina years there is a tendency for an anomalously warmer polar stratosphere with higher ozone concentrations. Thus, this lack of ozone depletion in the mid-1970's in simulations forced with observed SSTs could be associated with the prevalence of La Nina conditions at that time.

The statistical robustness of this signal, and the extent to which it is present in other CCMs, is examined.


05/03/10    Marie-Ève Gagné:   Are O2 nightglow emissions present in the Martian atmosphere?

Abstract: The SPICAM instrument on board Mars Express confirmed the nightglow as a feature of the Martian atmosphere through a clear detection of the H Lyman-alpha and the NO delta and gamma bands. The measurements also suggest the presence of the O2 Herzberg II emission, but a more rigorous analysis of the data is required for a clear confirmation. Although not yet detected, the presence of O2 emissions in the Martian atmosphere is expected since they are observed on Venus, which has similar atmospheric composition at the airglow altitude. One major difficulty in simulating the expected level of O2 nightglow in an atmosphere dominated by CO2 is the lack of knowledge on the photochemical parameters associated with those emissions. In this presentation, I will show simulations of the Herzberg II airglow feature using the new photochemical parameters recently derived from measurements with the VIRTIS instrument on the Venus Express mission along with the Mars-LMD atmospheric model to estimate the expected O2 (c-X) and O2 (A-X) band emissions in the Martian atmosphere, and to evaluate the possibility that SPICAM has indeed detected the presence of the O2 Herzberg II emission in the Martian atmosphere.


19/03/10    Niall Ryan:   A new radiometer (no acronym yet...) to make the first measurement of ClO in the Canadian Arctic

Abstract: In this talk I will discuss the development of a new ground-based radiometer to measure ozone related trace gases in the Arctic stratosphere. The main species of interest are ozone (O3), chlorine monoxide (ClO) and nitric acid (HNO3). ClO is involved in all of the chlorine radical, ozone destroying catalytic cycles and can be challenging to measure in the atmosphere, while studies of HNO3 will help in understanding denitrification processes in the Arctic stratosphere. Upon completion, the radiometer will make the first measurement of ClO from Canada and can perform measurements year round, day and night.

The presentation will discuss the instrument, the motivation behind the project and the development of a retrieval scheme for the trace species of interest.


09/04/10    Gordan Stuhne:   A Global Unstructured Grid Modeling Framework, with Land-Ice and Ocean Applications

Abstract: I am developing a numerical framework for global climate modeling using unstructured grids. The current focus is on the implementation of a new version of the University of Toronto Glacial Systems Model (GSM), beginning from a code base that was originally developed for ocean and tidal modeling applications. The initial aim in land-ice simulation is to enhance simulations of Greenland paleoclimate, as previously performed according to the EISMINT protocols. In any context, unstructured grids allow for resolution to be concentrated in regions that are of interest because of high-resolution data availability or important local small-scale physics (e.g., ice margins and ice streams in glaciers, or eddies and small-scale currents in the oceans). The numerical scheme was originally based on conservative finite-volume spatial discretizations, but accuracy issues have motivated a recent generalization to higher-order, state-of-the-art discontinuous Galerkin methods. Physical and numerical issues related to the key applications will be discussed, along with some results.


16/04/10    Karen Smith:   The role of linear interference in the Annular Mode response to extratropical surface forcing: models versus observations

Abstract: The classical problem of predicting the atmospheric circulation response to extratropical surface forcing is revisited in the context of the observed connection between autumnal snow cover anomalies over Siberia and wintertime anomalies of the Northern Annular Mode (NAM). Previous work has shown that in GCM simulations in which 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. Important questions remain regarding the dynamics of the response to this surface cooling. We show that previously unexplained aspects of the evolution of the response in a comprehensive GCM can be explained by examining the time evolution of the phasing, and hence the linear interference, between the Rossby wave response and the background stationary wave. The effects of linear interference are probed further in a simplified GCM, where an imposed lower tropospheric cooling is varied in position, strength, and sign. As in the comprehensive GCM, linear interference strongly influences the response over a realistic range of forcing strengths. The transition from linear to nonlinear behavior is shown to be a simple function of forcing strength.

One of the outstanding questions regarding the observed relationship between October Eurasian snow cover anomalies and NAM is what causes the significant lag between the Eurasian snow cover anomalies in October and the associated peak wave activity flux in December. I will show that the lag in peak wave activity flux is related to unfavourable linear interference conditions between the Rossby wave train associated with the snow cover anomalies and the background stationary wave from October to mid-November. Beginning in mid-November the associated wave train migrates to a position that constructively interferes with the background stationary wave until mid-January.


30/04/10    Lawrence Mudryk:   Sources of Annular Mode Time Scales

Abstract: Time scales derived from annular mode (AM) variability are useful diagnostics to compare the ability of General Circulation Models to capture temporal details of intraseasonal and climate variability. In this talk I present a methodology for examining contributions to AM variability from variations in the surface pressure and temperature fields. I demonstrate that the contributions from these two fields are decomposed by atmospheric region: surface pressure variations are the dominant source of annular mode variability in the troposphere, while temperature variations are the dominant source in the stratosphere.

I compare results of the decomposition for AM timescales as well as winter-time vortex event composites using four data sets: the National Centers for Environmental Prediction and ERA40 reanalysis data sets, as well as two Canadian Middle Atmosphere Model (CMAM) integrations. I also discuss preliminary results which suggest that the decomposition of these temporal signatures by region is related to the influence of differing eddy fluxes contributing to the polar cap potential vorticity budget, evolving on different timescales, in each region: surface pressure (and hence surface wind) contributions reflect upper tropospheric eddy momentum fluxes (which are related to vorticity fluxes), and stratospheric temperature variations reflect eddy heat fluxes (which are related to fluxes of isentropic thickness).


07/05/10    Cynthia Whaley:   Atmospheric Composition Measured at the Toronto Atmospheric Observatory

Abstract: Tropospheric trace gases have a significant and direct impact on our environment and our lives. I will be talking about how these trace gases are measured at the University of Toronto Atmospheric Observatory (TAO) through remote sensing. I will show results from recent changes in retrieval parameters, such as microwindows and a priori profiles. I will also show time series of total and partial columns of O3, CO, CH4, C2H6, N2O, and HCN and discuss the possibility of determining long term trends.

I will also talk about the Greenhouse Gas Observing Satellite (GOSAT) and recent comparisons to TAO measurements of CH4. Finally I will talk about the Goddard Earth Observing System-Chemistry (GEOS-Chem) model and show a preliminary comparison with TAO data.


14/05/10    Robert Field:   The effects of post-condensation exchange on the isotopic composition of water in the atmosphere

Abstract: We conducted experiments with an atmospheric general circulation model to determine the effects of non-Rayleigh, post-condensation exchange (PCE) on the isotopic composition of water in the atmosphere. PCE was found to universally deplete vapor isotopes, but had differential effects on precipitation. At low latitudes, local PCE with fresh vapor at the surface enriches precipitation, particularly during light rainfall. When rainfall is heavy, PCE tends to deplete precipitation via vapor recycling, supporting recent interpretations of vapor isotope measurements from satellites. In the extratropics, local PCE enrichment of precipitation can be offset by upstream PCE depletion of the vapor reservoir, and result in a net depletion. The transition from net enrichment to net depletion is controlled by the transition from rain to snow-dominated precipitation. Surprisingly, this transition was also found to influence the temperature effect, the positive correlation between temperature and isotopic composition. In regions with a strong seasonal mix of rain and snow, such as Europe, the temperature effect appears to be controlled by PCE rather than Rayleigh depletion.


21/05/10    Rodica Lindenmaier:   Optimization of trace gas retrievals at Eureka, NU

Abstract: The Bruker 125HR Fourier transform spectrometer was installed at the Polar Environment Atmospheric Research Laboratory (PEARL) at Eureka, Nunavut, Canada in the summer of 2006 to study atmospheric composition. Using the Optimal Estimation Method, typically over a limited spectral region called a microwindow, information about the vertical distribution of trace gas species that have absorption bands in the mid-infrared spectral range can be retrieved.

My past year’s research proved that for O3, the 1000-1005cm-1 microwindow is the best for retrievals at Eureka. Since improving our retrieval technique for each gas is one of our main goals, we intensely collaborate with the Network for the Detection of Atmospheric Composition Change (NDACC) to find the best parameters for retrievals of ten important stratospheric and tropospheric species. In the first stage I tested the microwindows that would give us the highest number of degrees of freedom for signal and a good fit. The second step involves the best choice of a priori profiles, Sa covariance matrix, signal to noise ratio, and interlayer correlation. In my talk I will focus on preliminary results obtained for O3, HCL, HNO3, CLONO2, CH4, CO, N2O, C2H6.


Brewer Seminar site maintained by Rodica Lindenmaier. Last updated 21 May 2010.