Abstracts from 2002/2003

The attribution of the Antarctic ozone hole to anthropogenic emissions of halogen species is well established. The same chemistry is operative in the Arctic, although is strongly modulated by year-to-year dynamical variability. In midlatitudes, stratospheric ozone has also been observed to have decreased over the past 20 or so years, but the attribution of these midlatitude ozone changes is far less clear than is that of the polar late-winter/spring depletion. Because of concurrent changes in Northern Hemisphere dynamical quantities such as stratospheric planetary-wave drag, tropopause height, and the Northern Annular Mode (NAM) index, some argue that it is the dynamical changes that have caused the ozone changes. (The dynamical changes are not sufficiently well known in the Southern Hemisphere to be discussed at this point.)

This talk will describe some of the fundamental issues involved, and the available evidence, for understanding the observed midlatitude ozone changes, including the key question of how to separate natural variability from anthropogenic influences.

4/10/02    Adrian Vitcu    Laughing (gas) spectroscopy

Contrary to what one may think, there’s nothing funny about doing spectroscopy in N₂O (at least not while you’re trying to get a degree out of it). In my talk I will present the concepts of difference frequency spectroscopy that allow us to do high resolution and high signal-to-noise spectral measurements in atmospheric gases. In particular, I will be presenting the results obtained for the 03¹0 ← 01¹0 Q-branch of N₂O, near 1160 cm^-1 or 8.6 mm (don’t worry, I will make a point of explaining what’s with the fancy notation). If you’re interested, I’ll try – I’m not a theorist though – and explain why we even have a Q branch to look at (poor Rick, he’s only looking at CO). I will also try to convince you that my results qualify for a shot at a Ph. D., by presenting a theoretical model and comparing it to the experimental results. Now that’s the tricky part…  

11/10/02    Simal Saujani     Towards a General Theory of Balanced Dynamics

I will outline the idea of balance.  The concept is not difficult and can be nicely applied to simple systems. The shallow water equations reveal these ideas nicely.  Generalizing to the sphere is not straightforward and I will outline the difficulties involved.   

18/10/02    Loic Jounot     MOPITT-A

MOPITT (Measurements of Pollution In The Troposphere) is a carbon monoxide and methane remote sounder launched in 1999 with the Terra spacecraft. An aircraft replica of MOPITT (MOPITT-A) has been developed to perform validation of MOPITT radiances as well as small scale pollution studies. MOPITT-A is based on the engineering model of MOPITT, modified for flight in NASA's ER-2 research aircraft. The instrument was first tested over California from the NASA Dryden Flight Research Center in July 2000 and flown over Southern Africa in August and September of the same year. This talk will describe some aspects of the data analysis peformed so far. MOPITT-A is financed by the Canadian Space Agency and the Natural Sciences and Engineering Research Council.

25/10/02    Lisa Neef    Data Assimilation and Balance Dynamic

An inherent problem of predicatbility is that the governing dynamical equations of the atmosphere admit flows with a wide range of frequencies, from sound-waves to inertia-gravity waves, to "slow" vortical motions. Somewhat mysteriously, the real atmosphere tends to prefer the large-scale vortical flows. However, small errors in our calculations can easily excite spurious high-frequency oscillations that are supported by the dynamics, but not physical.

Four-dimensional data assimilation schemes try to estimate the most probable atmospheric state in time, given a model's forecast and observations -- both of which are imperfect. Ideally, an assimilation scheme should therefore return a state that reflects the "near balance" found in the real atmosphere. But does it? There is surprisingly little consideration of the idea of balance in the data assimilation literature.

This study reviews some possible problems of Data Assimilation from a Balance Dynamics perspective, via simulations of the Extended Kalman Filter algorithm using a low-order chaotic model.    

1/11/02    James Drummond    To Kyoto or Not?

It is a bit surreal to have one of the major political debates of this year surrounding a piece of scientific research which is practically at the heart of our discipline. On the one hand we should participate, on the other hand the debate often seems far from our own research program or even our own scientific language.

This talk is going to be about the context of the Kyoto protocol and the various controversies surrounding it. I am not an expert in this area, indeed it is changing so fast, that I doubt that anyone is fully aware of all that is happening. My motivation for giving this talk is as much to force me to think about the issues and the debate, as it is to communicate this to others. I hope to use what little scientific understanding and ability that I have to see if we can discern some sense in the debate and what some of these esoteric terms such as "$15billion" and "450,000 jobs" actually mean.

8/11/02    Constantine Nenkov    Comparative Study with the Icosahedral Vector Shallow Water Model on the Sphere

In recent years the icosahedral grid structure and the associated with it numerical technology received considerable interest in the modeling community.
This is because this technology offers important potential advantages over the more traditional spectral methodology when modeling global hydrodynamical flows on the sphere.

In this talk I will present the current status in the development of a vector shallow water model defined on the sphere which utilizes the icosahedral technology. Two key advantages of this model as compared to a spectral one are the absence of a pole problem inherent to the global spherical polar coordinates and the reduced complexity in operation count per time step of integration. To support the usefulness of this new numerical technology I will present a comparative study of our icosahedral vector shallow water model and a well established NCAR spectral transform Global Circulation Model (GCM) based on results from a suite of standard test cases. The results from the standard test cases show very clearly that the icosahedral approach is a viable alternative to the traditional spectral methods for modeling global flows in spherical geometry.    

22/11/02   Jay Kar    Some studies of Stratospheric and Tropospheric ozone using SAGE II version 6 data

Stratospheric Aerosol and Gas Experiment (SAGE) II has been measuring O3, NO2, H2O, and aerosols since 1984. Recently the retrieval algorithm for these data products was significantly modified (version 6). With an improved vertical resolution it becomes possible to study the structures in the vertical profiles. I will present the results of a study of  global climatology of layer like structures seen in stratospheric ozone mixing ratio profiles in the subtropics and high latitudes. The similarities and differences between this and ozonesonde climatology of thinner structures called laminae will be discussed.

Unlike the stratosphere, the troposphere has not so far been directly studied using satellite data, the tropospheric column ozone having only been estimated by subtracting the stratospheric column from the total column. Many of the SAGE II retrievals extend to middle and upper troposphere during cloudfree conditions. I will show that the retrieved profiles (seasonally averaged) in the upper troposphere are consistent with ozonesonde profiles and that the global upper tropospheric climatology in the tropics confirms the zonal wave 1 pattern inferred from the residual techniques. These results indicate that the solar occultation technique may be utilized for studying tropospheric ozone in future.
 

6/12/2002    Michael Carleer    Water, water, water...

Water is the most abundant of the greenhouse gases present in the atmosphere. Due to its spectrum extending well into the visible up to the UV, it also plays an important role in the modelling of the radiative transfer properties of the atmosphere. It is therefore very important to accurately know the water vapor spectroscopic properties.

The Laboratoire de Chimie Physique Moléculaire of the Université Libre de Bruxelles, in collaboration with the Belgian Institute of Space Aeronomy and the Université de Reims, has recorded water vapor spectra from 2500 up to 26000 cm^-1 using a very long multiple pass absorption cell (path lengths up to several km). The analysis of these spectra has lead to more than doubling the number of absorption lines reported into the existing spectroscopic databases.

More importantly, the analysis of the spectra showed the existence of a very broad continuum extending from the IR to the UV. This continuum is tentatively attributed to an extinction coefficient due to the presence of very small water droplets (r ~ 0.8 mm) in suspension, even at very low water vapor pressures. The existence of water droplets at pressures well below saturation is still unexplained. However, it could explain the rather large discrepancy observed between the observed and predicted radiative transfer of the atmosphere under clear sky conditions.    

The experiment in which a fluid is confined to the gap between two cylinders with different radii arranged around a common axis in such a way that they can rotate independently has been studied in many contexts during its history, which dates back at least to Isaac Newton. The experiment is now named after Maurice Couette, who built a version of the experiment in 1888 in order to test Navier's theory of fluid viscosity, and after G. I. Taylor, who repeated the experiment in 1923 and confirmed his own predictions about the instability of laminar Couette flow. The pattern that emerges due to the instability is known today as Taylor vortex flow. 

The experiment is normally linked with the study of viscous fluids, but the instability threshold of laminar Couette flow in the case of the cylinders rotating in the same sense is described approximately by Rayleigh's centrifugal theorem for inviscid fluids, and the steady state Couette velocity profile is the same for any viscous fluid, no matter how small its viscosity. It is therefore not unreasonable to apply the methods of Hamiltonian (inviscid) dynamics to the problem. In this talk, I will show that if the gradient of angular momentum in the fluid is positive (Rayleigh's criterion) and less than a certain upper limit (the James Taylor limit), the flow is nonlinearly stable and then use this result to estimate the amplitude of Taylor vortex flow that can develop from a given unstable steady state.    

Bomem DA8 high resolution (0.0026 cm^-1) ground-based Fourier Transform Infrared Spectrometer (covering 650 - 7140 cm^-1) is in operation at the Toronto Atmospheric Observatory (TAO). The solar absorption measurements were started routinely in October 2001. The measured spectra allow the retrievals of vertical profiles and column amounts (total or partial) for a number of atmospheric tracers (currently up to 20). The retrieval algorithm is based on the OEM method and therefore, the caracterization of the retrievals can be applied according to Rodgers formalism. The results of such characterization performed to FTIR Toronto retrievals will be discussed. Data retrieved from summer 2002 measurements will be presented.

Scisat-1 is a Canadian satellite scheduled for launch in 2003. The mission objective is to study stratospheric ozone trends, with a particular focus on the polar regions where significant ozone loss has been observed in the past two decades. Measurements of solar attenuation by ozone and other stratospheric constituents are to be taken during occultation events (sunrises and sunsets) as viewed by the satellite. The two spectrometer instruments on board Scisat-1, ACE-MAESTRO (Atmospheric Chemistry Experiment - Measurement of Aerosol Extinction in The Stratosphere and Troposphere Retrieved by Occultation) and the ACE-FTS (ACE - Fourier Transform Spectrometer), are designed to measure absorption spectra in the visible/near-ultraviolet and infrared regions, respectively. One of the principal scientific objectives for both instruments being the retrieval of vertical ozone profiles, an important question to ask when characterizing the instruments prior to launch is Do we measure the same amount from both instruments? In order to answer this question, an experimental apparatus that allows simultaneous instrument characterization, consisting of a simulated solar source and gas cells, has been assembled. The experimental apparatus will be described and preliminary results from the Scisat-1 test program at the University of Toronto will be presented.

A brief review of the concept of available potential energy (APE) will be presented. The classical approach to APE definition (Lorenz, 1955) has some limitations. One of them is that it doesn't take into account the (possible) momentum constraints on the basic state flow. This may cause problems when one tries to apply the APE diagnosis to the middle atmosphere circulation.

An improved APE definition which includes momentum constraints is proposed. The theory is based on the Hamiltonian structure of the underlying dynamics. Some results and possible applications of this APE are presented.

Polar lows are short-lived, intense mesoscale storm systems that develop over oceans in Polar Regions. The interaction of the very cold atmosphere with the relatively warm ocean below is what provides these storm systems with their intense energies. As a result of their small spatial and temporal scales, and their development in regions where observational coverage is minimal, models and observations can easily miss the genesis and lifetime of a polar low. It is for this reason that satellite imagery, and in particular Synthetic Aperture Radar (SAR) imagery, is a very important tool in the furthering of our understanding of these systems. SAR is an excellent way to image marine weather systems specifically because it can penetrate the dense cloud cover that accompanies these systems, and it can provide information to within a 100 m resolution about surface winds.

31/01/03    Caroline Nowlan    First Results from a MAESTRO Instrument:: Field-Testing MAESTRO-B During the MANTRA 2002 Balloon Campaign

The MAESTRO (Measurement of Aerosol Extinction in the Stratosphere and Troposphere Retrieved by Occultation) satellite instrument will accompany the Atmospheric Chemistry Experiment Fourier Transform Spectrometer on the Canadian satellite SciSat-1. MAESTRO is a UV-visible photodiode array spectrometer that will make solar occultation and nadir measurements of the atmosphere to investigate the dynamical and chemical processes affecting ozone in the middle atmosphere. The primary measurement mode of solar occultation will provide vertical profiles of ozone, several trace gases involved in ozone chemistry, aerosols, and pressure and temperature at a vertical resolution of approximately 1 km. In addition to the MAESTRO satellite flight model, two other nearly identical spectrometers have been assembled. One of these spectrometers was launched on the MANTRA (Middle Atmosphere Nitrogen TRend Assessment) high-altitude balloon on September 3, 2002 from Vanscoy, Saskatchewan. During the flight MAESTRO-B collected solar occultation and atmospheric limb spectra from a float altitude in the middle stratosphere.

07/02/03    Jane Liu    Distributions of Carbon Monoxide in the Atmosphere: An Analysis from MOPITT Data

Lake-effect snowstorms are an important source of severe winter weather over the Great Lakes region that are often triggered by the passage of a synoptic-scale cyclone. In this talk, I will present a climatology of lake-effect snowstorms and associated cyclone characteristics over southern Ontario for the period 1992-1999. As we shall show, the passage of a synoptic-scale cyclone is a necessary but not sufficient condition for the development of an intense lake-effect snowstorm. In particular, we show that intense lake-effect snowstorms are usually associated with cyclones with anomalous northeasterly tracks towards the northern Quebec and the Labrador Sea. Cyclones that track towards the east, the most common trajectory in the winter months, typically do not result in the development of intense lake-effect snowstorms. The synoptic environment associated with these two classes of cyclone trajectory will be investigated to understand the reasons for the difference in outcome vis-à-vis lake-effect snowstorms.

Turbulent flows are ubiquitous in the natural environment, encompassing a wide range of temporal and spatial scales. Several laboratory experiments, as well as oceanic observations, exhibit the formation of "fine structure" evolving from the action of turbulent mixing in a stably stratified environment. This fine structure is often characterized by a series of layers of well-mixed fluid separated by high-gradient interfaces. It has been conjectured (Phillips 1972, Posmentier 1977) that this phenomenon is due to the existence of a non-monotonic relationship between the mixing efficiency and the initial Richardson number characteristic of the stratification. These earliest suggestions of the plausibility of such effects were based upon heuristic arguments formulated in terms of a nonlinear anti-diffusion process. More recently, several phenomenological models (Barenblatt et al. 1993, Balmforth et at. 1998) have been proposed which predict the evolution of this layering phenomenon. Most recently, a detailed analysis of turbulent mixing has been performed by Peltier & Caulfield (2003). Their work focussed upon a stratified shear flow undergoing turbulent collapse and suggests that a numerical value of mixing efficiency of approximately 0.2 follows directly from the Direct Numerical Simulation (DNS) results, which is in full accord with experimental observations. Furthermore, their analysis of turbulent mixing directly delivers a non-monotonic dependence of this efficiency upon the Richardson number. The goal of my continuing research is to address the way in which the extent of the range of non-monotonicity depends upon the Reynolds number. The impact of the anti-diffusion phenomenon on the large scale structure of the oceanic general circulations may be of fundamental importance if it is found that the range over which anti-diffusion operates is significantly increased as the Reynolds number is increased.

Downstairs in the difference-frequency spectroscopy laboratory, we study the absorption of infrared light by atmospheric gases on the molecular level. Usually, we do so by measuring the spectral line shapes of a gas sample at a known temperature and pressure with our spectrometer. Recently, however, we decided to try turning our experiment around.

I will describe how we were able to use what we know about spectral line shapes to measure the temperature and pressure of a gas sample remotely, non-invasively, and at a time resolution of 200 microseconds. Our technique allowed us to clearly resolve temperature oscillations with a magnitude of 40 Kelvin and period of only 20 milliseconds in a pressure modulator gas cell like those found in MOPITT. I will also describe how we were (and weren't) able to model the observed temperature and pressure cycles in the MOPITT cell with a simple numerical model.

The University of Toronto Atmospheric Observatory (TAO) has been operational since October 2001, with a high-resolution (ABB Bomem Inc., Québec) Fourier Transform infrared Spectrometer (FTS) serving as the primary instrument. Solar absorption infrared spectra are recorded during clear-sky conditions from 720 to 4300 cm-1 (13.9 to 2.3 mm) with a maximum spectral resolution of 0.0026 cm-1. A new heliostat (Aim Controls Inc., California) provides active solar tracking, collecting the incoming solar radiation and directing it into the FTS.

The geographic position of TAO (43.66oN, 79.40oW) makes it well suited for long-term measurements of mid-latitude stratospheric ozone, ozone-related species, and dynamical tracers. TAO’s urban setting will enable measurements of important tropospheric species and pollutants. Studies are also under way to investigate the feasibility of detecting the size and composition of tropospheric and stratospheric aerosols. Finally, TAO is to participate in validation efforts for the MOPITT, Odin/OSIRIS, ACE-FTS, and MAESTRO satellite instruments.

This talk will explain how we carry out our data analysis and present results obtained from spectra recorded between May and September of 2002. In particular, work-in-progress results for CO, CH4, C2H6, OCS, HCl, HF, NO2 and N2O will be presented. Some outstanding issues pertaining to our data analysis will be highlighted. Finally, CO total columns from August and September will be compared with MOPITT CO measurements.

21/3/03    David Sankey    Correlations of long-lived chemical species in a middle atmosphere general circulation model

My Brewer seminar will consist of two distinct sections: one describing the outcome of the MANTRA 2002 campaign and the other discussing some attempts at characterizing and predicting turnaround events.

The MANTRA (Middle Atmosphere Nitrogen TRend Assessment) 2002 balloon was launched on September 3, 2002 and carried a variety of instruments. The one that I was responsible for is a Fourier Transform Spectrometer. I will discuss the preparations for and the results from the launch and future work towards the MANTRA 2004 campaign.

Second, I shall discuss the atmospheric conditions necessary for launch. Turnaround, which occurs when the extra-tropical stratospheric zonal winds change direction, happens twice per year (once in the spring and once in late August) and is the ideal time for a balloon launch. An accurate prediction of turnaround is important for high-altitude balloon-based measurements, since low stratospheric wind speed is a desirable launch andrecovery condition. It turns out that this event is very difficult to predict due to dynamic variability that seems, as yet, to be poorly understood. I will discuss our attempts to improve our predictive capabilities using three unique sources of stratospheric wind data: NCEP, CMAM and UKMO.