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Abstracts from 2003/2004 19/9/03 Dr. Matt Reszka Dynamical Balances in the Tropical Middle Atmosphere Balance relations in the tropical stratosphere are investigated in the context of numerical simulations using the Canadian Middle Atmosphere Model (CMAM) and daily wind field analyses from the United Kingdom Meteorological Office (UKMO). The degree of geostrophic and gradient-wind imbalance in the zonal velocity is computed at individual pressure levels and also as zonal means. Balance seems to be maintained over wide areas of the tropics in both CMAM output and UKMO data, although the latter exhibits a greater amount of departure. While significantly unbalanced motion does occur, it tends to be associated with mesoscale variability of the fields themselves, rather than a vanishing Coriolis parameter. Balance improves for fields that have been spectrally filtered, and contain only low zonal wavenumbers. As part of a scaling analysis, autocorrelation lengthscales of the zonal wind field and the sizes of the relevant nondimensional parameters are estimated from available data. The results suggest that semi-geostrophic balance at the equator deserves further investigation. Finally, possible sources of error in the computation of imbalance, as well as potential improvements, are discussed.26/9/03 Amit Ghosh Baroclinic Waves in a New Primitive Equations Model on the Sphere In this talk I will discuss the generation and lifecycle of baroclinically generated waves in a new primitive equations model. This is the first step towards the abilty to simulate the long-term dynamics of the dry atmosphere.The ultimate goal of this project is to understand the influence that topographically generated stationary long waves have on the evolution of continental ice-sheets during the Last Glacial Maximum. 3/10/03 Prof. G.W.K. Moore Climate Change in the North Pacific Region since 1700 The relatively short length of most instrumental climate datasets restricts the study of variability and trends that exists in the climate system. This is particularly true regarding the atmosphere where high quality spatially dense data exists only since the late 1940s.In this talk,I will describe the climate signal contained in a 301-year ice core record from a high elevation site on Mount Logan. This record contains an expression of the Pacific North America (PNA) teleconnection as well as the regional Hadley and Walker circulations in the Pacific. It also contains a signal that appears to be related to variability in solar irradiance that occurs on the decadal to centennial time scale. 10/10/03 Loic Jounot Measurements of tropospheric CO with MOPITT-A MOPITT (Measurements of Pollution In The Troposphere) is a CO remote sounder launched in 1999 with the Terra spacecraft. An aircraft version of MOPITT, called MOPITT-A, was built one year later to perform smaller scale pollution studies. MOPITT-A participated in the SAFARI 2000 field campaign in South Africa, monitoring CO emissions from biomass burning. This talk will describe the CO retreival method and present some data collected during SAFARI 2000. MOPITT-A is financed by the Canadian Space Agency and the Natural Sciences and Engineering Research Council.17/10/03 Dr. Guido Vettoretti The Science of Climate Change: A Paleoclimate Perspective I will discuss some of the climate modelling research being conducted in theatmospheric physics group and the type of models used to perform these numerically intensive simulations. Confidence in predicting future anthropogenic induced climate change will require a detailed understanding of the complex response of the coupled atmosphere-ocean system to radically different climate forcing (e.g. conditions during the inception and the peak of the last glacial cycle). I will illustrate some examples of how these complex models lack the proper representation of climate feedbacks that may be necessary in replicating past climate conditions derived from geologically inferred changes of past climate state. The apparent lack of model sensitivity required to reproduce the large and dramatic climate changes that have occurred in the past will likely have a direct impact on the prediction of the magnitude of future climate change. 24/10/03 Rebekah Martin A Look at Mesoscale After-Effects
of Cyclone Interaction with the 31/10/03 James Anstey Stratospheric influence on the troposphere How can the stratosphere influence the troposphere? Upward-propagating waves from the troposphere control the stratospheric winds, but it is unclear if a stratospheric feedback exerts a control on the troposphere. Results such as Baldwin and Dunkerton's (2001) finding that knowledge of stratospheric vortex anomalies can increase the predictability of tropospheric NAM (Northern Annular Mode) events suggests that influence could go in both directions, but the mechanisms by which this might happen are unknown. It is possible that the stratospheric signal simply reflects the effect of a tropospheric event without exerting any independent influence. We attempt to explore this question using a simple quasigeostropic model forced by a torque designed to model the effects of breaking waves.7/11/03 Denis Dufour Simultaneous Characterization of the MAESTRO and ACE FTS Space Instruments Scisat-1 is a Canadian scientific satellite launched by NASA in August 2003. It's mission objective is to study stratospheric ozone trends, with a particular focus on the polar regions. Measurements of solar attenuation by ozone and other stratospheric constituents are taken during occultation events (sunrises and sunsets) as viewed by the satellite. The two spectrometer instruments on board Scisat-1, MAESTRO (Measurement of Aerosol Extinction in The Stratosphere and Troposphere Retrieved by Occultation) and the ACE-FTS (Atmospheric Chemistry Experiment - 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, was assembled. An intense and successful series of characterization tests took place here during February and March 2003, during which absorption spectra of Ozone and NO2were taken with both instruments. In this talk I will briefly describe Scisat-1, the experimental apparatus, results from the pre-flight characterization tests, as well as show the first MAESTRO solar spectra from space, taken just two weeks ago.14/11/03 Simal Saujani Balanced Dynamics at the Equator?!?? Balance is a common and useful theme in geophysical fluid dynamics. Our understanding of balance away from the equator is quite good. Unfortunately, we have no similar results for the tropics. There is a good reason to expect a general balanced theory at the equator. We discuss the problem. 21/11/03 Jeff Taylor Instrument Characterization of a Fourier Transform Spectrometer at the Toronto Atmospheric Observatory A Bomem DA8 high-resolution Fourier-Transform Infrared (FTIR) spectrometer is the primary instrument at the University of Toronto Atmospheric Observatory (TAO). Continuous measurements of solar absorption spectra were started in October 2001. Spectra are recorded in six filter bands from 750 to 4300 cm-1 at a resolution of 0.0026 cm-1, which allows the absorption lines of a broad range of atmospheric trace gases to be distinguished. A blackbody source has recently been optically coupled to the FTIR to enable accurate calibration of the solar measurements with an N2O gas cell. Characterization of the instrumental line shape with the LINEFIT algorithm (developed at the Institut für Meteorologie und Klimaforschung, Karlsruhe, Germany) was carried out in the Summer of 2003. The capabilities of the FTIR spectrometer and results from these blackbody measurements will be presented. The effects of incorporating the instrumental line shape into trace gas profile retrievals with SFIT-2 will also be shown. 28/11/03 Mark Fruman Conditions for the symmetric stability of the equatorial middle atmosphere Steady solutions to the equations of atmospheric dynamics which are independent of longitude can be subject to "symmetric" instability depending on the distributions in height and latitude of potential temperature and angular momentum. Symmetric instability is thus a combination of convective instability, which depends on the vertical profile of potential temperature, and inertial instability, which depends on the distribution of absolute angular momentum relative to the axis of rotation of the coordinate system. The equatorial middle atmosphere is prone to symmetric instability during the solstice periods. Since the middle atmosphere is stably stratified, the instability is predominantly inertial rather than convective. In this talk, the concept of inertial instability will be introduced through analogy with convective instability, and the role of the instability in the dynamics of the equatorial middle atmosphere during the solstices will be discussed. Finally, a derivation of conditions for symmetric stability in an adiabatic anelastic beta plane model will be sketched. The result is novel in that it incorporates the effects of Coriolis force terms related to the northward component of the earth's rotation vector which are neglected in traditional hydrostatic models. 5/12/03 Prof. Ulrike Lohmann Global simulations of the indirect aerosol effect on water and mixed-phase clouds Hygroscopic aerosol particles, such as sulfates, sea salt and some organics, exert an influence on warm clouds by acting as cloud condensation nuclei. A subset of aerosols act as ice nuclei and thus control cold cloud formation in addition to or in competition with homogeneous freezing of supercooled aqueous phase aerosols. By changing the microphysical structure of clouds, aerosols are one of the factors that determine whether or not the cloud will precipitate. In this talk, I'll show global climate model simulations of different aerosol effects. I'll discuss aerosol induced changes of liquid water clouds, and put this into perspective of estimates from satellites, ground based observations and inferred from inverse simulations. I'll also discuss the effect aerosol may have on changes of the snowfall rate due to pollution induced decreases in the riming rate of snow flakes with cloud droplets. 12/12/03 Dr. Marek Stastna THC Transport Without the Jail Time In this talk I will discuss aspects of the Thermohaline Circulation (THC) of the ocean. After some initial definitions I will show some proxy records for climate variability during the last glacial epoch and discuss in general terms some of the theories that exist for explaining this variability. Using the results of the NCAR coupled climate model I will illustrate several differences between today's North Atlantic and that found at the Last Glacial Maximum (LGM), both at "equilibrium". I will subsequently discuss two competing dynamical explanations for millenial timescale climate variability in the late glacial epoch. This will be done using simplified box-models. Throughout, I hope to keep the jargon to a minimum and the mathematics largely out of view. 9/1/04 Dmitry Vyushin Scaling in Temperature Time Series In the first part of my talk I'll describe the universal persistence law and the test of the scaling performance of seven leading global climate models by using detrended fluctuation analysis (DFA) for three different scenarios: (i) control run, (ii) greenhouse gas forcing only, and (iii) greenhouse gas plus aerosol forcing. The simulated records for these scenarios fail to reproduce the universal scaling behaviour of the observed records, and display wide performance differences. In the second part of my talk I'll consider ensemble experiments performed with the NCAR PCM for 10 different historical scenarios, including "no forcings", "greenhouse gas", "sulphate aerosol", "ozone", "solar", "volcanic forcing" and various combinations, such as "natural", "anthropogenic" and "all forcings". I'll compare the scaling exponents characterizing the long-term correlations of the observed and simulated model data for 16 representative land stations and 16 sites in the Atlantic Ocean for these scenarios. I'll show that the inclusion of a certain forcing improves the NCAR PCM scaling behaviour. 16/1/04 Lisa Neef * The Joy of Simple Models * In this talk I will discuss how low-order mathematical models can be used to understand the dynamics of complex, chaotic systems, such as, but not limited to, the earth's atmosphere. One example is the "swinging spring" - a seemingly simple system that can actually be used to model several complex dynamical properties, particularly balance between motions on different timescales. A similar simple model is the 5-component model of Lorenz (which actually has 4 components), and its extension by Wirosoetisno and Shepherd (2000), which is a bit more directly related to the flow of the atmosphere. Because of its simplicity, this model lends itself well to all kinds of studies about balance in the atmosphere - particularly, as is the case of my thesis, experiments in data assimilation. I will also (if there's time) talk about a third, more complex Lorenz model, which also contains two timescales, as well as a spatial parameter. 23/1/04 Constantine Nenkov The Development of a 3D Anelastic GCM on an Icosahedral Grid 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 in modeling global hydrodynamical flows on the sphere. In this talk I will discuss the development of a 3-D non-hydrostatic anelastic primitive equations GCM which utilizes the icosahedral grid-point technology. This new model is the outgrowth of a vector shallow water model which I presented in previous seminars and tries to improve considerably over the canonical hydrostatic three-dimensional atmospheric GCM's. One of the greater potential advantages of this model is the explicit treatment of the vertical convective motions as compared to the multitude of parameterization schemes applied in the hydrostatic approach. To support the usefulness of the anelastic approach in combination with the new icosahedral technology I will present first results from convective instability test cases in the linear and non-linear regime with the Boussinesq approximation. I will also discuss some problems and approaches to solve them. The long term goal of this research is the development of dynamical core for a fully 3-D GCM which should achieve high resolution and computational efficiency at low computational cost. We hope that this anelastic model will prove useful in the study of Jupiter-like planetary atmospheres where convection is the dominant factor in structure formation. 30/1/04 Caroline Nowlan Pressure-Temperature and Trace Gas Measurements from the MAESTRO Space and Balloon Instruments The MAESTRO (Measurement of Aerosol Extinction in the Stratosphere and Troposphere Retrieved by Occultation) space instrument was launched on Canada's SciSat-1 satellite on August 12, 2003 as part of the Atmospheric Chemistry Experiment (ACE) payload. MAESTRO is a UV-Visible-NIR dual spectrometer taking solar occultation and nadir backscatter spectra of the atmosphere. The occultation spectra can be used to determine high vertical resolution profiles of ozone and several other trace gases involved in ozone chemistry. While SciSat-1 is still undergoing commissioning activities, MAESTRO has already recorded many high sun extraterrestrial spectra and some early atmospheric occultation spectra. A prototype version of the instrument was flown during the MANTRA 2002 campaign on a high altitude balloon and provided the first MAESTRO atmospheric spectra. These measurements are being used for the development of the MAESTRO analysis code for trace gas retrievals. Of particular interest are the molecular oxygen A and B bands in the near-infrared, whose use is being assessed for making measurements of atmospheric temperature and pressure profiles from orbit. 6/2/04 Sorin Codoban Available potential energy - an overview For almost a century now people have tried to understand and quantify what drives the observed circulation in the atmosphere. It is known, for example, that the middle atmosphere circulation is driven by momentum deposition by breaking waves (i.e. is "mechanically driven"). Starting with the classical work of Lorenz (1955) we think of this problem in terms of available potential energy (APE). I will review this concept as it appears in the physics of the atmosphere. Issues related to the definition of APE and its usage for the diagnosis of large-scale circulations will be discussed. A theory of APE can be developed based on the Hamiltonian structure of the underlying fluid dynamics. I will show how this approach enables one to obtain a meaningful diagnostic of the middle atmospheric circulation. 13/2/04 Anthony Liu A Numerical Study of Convective Roll Clouds Associated with High Latitude Cold Air Outbreaks A ubiquitous feature of the high latitude ocean is the occurrence of convective clouds that are organized into two-dimensional structures known as roll clouds or cloud streets. In my talk, I will present a simulation of these structures that was performed in a domain large enough to simulate numerous roll clouds and their downstream evolution at a resolution sufficient to resolve the individual convective clouds. The simulations were initialized and validated using observations of roll clouds over the Labrador Sea. The existence of sea ice makes the above process even more complicated. In the talk I will also present some preliminary results from the experiment with sea ice imbedded. 27/2/04 Prof. W. R. Peltier Past Climate Tests of a Model of Future Climate Evolution Existing models of the climate warming expected as a consequence of the increasing (anthropogenically derived) load of greenhouse gases differ significantly in the degree of warming predicted for a given scenario of trace gas increase. The magnitude of these differences, which are usually attributed to differences in the "parameterization schemes" employed in the models to represent processes not explicitly resolved, is such as to undermine confidence in the models themselves. One method that can be employed to test model "robustness" is to compare the predictions that the model makes for climates of the distant past for epochs from which high quality data exists that may be employed to confirm or to deny model validity. The ocean thermohaline circulation is an especially important target for model validation as it exists as an integrated consequence of atmospheric physical and dynamical processes. I will describe recent work that has been designed to investigate the extent to which existing models "pass the paleoclimate test", using NCAR CCSM integrations of Last Glacial Maximum climate performed on SNOWBALL as the basis for discussion. 5/3/04 Aldona Wiacek Ground-Based Solar Absorption FTIR Measurements at TAO: Comparisons with Models and Other Measurements The University of Toronto Atmospheric Observatory (TAO) has been operational since October 2001, with a high-resolution 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 heliostat 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. Also, TAO's urban setting has enabled measurements of important tropospheric pollutants. I will present some total and partial column results retrieved from spectra recorded between May 2002 and September of 2003. Climatological comparisons with two different versions of the Canadian Middle Atmosphere Model (CMAM) will be presented, focusing on CH4, N2O and HCl. CMAM is a comprehensive 3-D chemistry-climate model incorporating radiation, interactive chemistry, gravity-wave drag, moisture, and momentum. Finally, comparisons of CO total columns with results from the MOPITT experiment will also be presented. MOPITT measures CO from space in nadir-viewing geometry. Lastly, I will show the results of a recent retrieval intercomparison that was performed in order to qualify TAO as a complementary observation station of the Network for the Detection of Stratospheric Change (NDSC). In this simple, yet revealing exercise, different operators (including myself) retrieved O3, N2O and HCl total columns from the same spectra. Find out on Friday if the total column amounts were the same! 12/3/04 Dr. Stella Melo Mid-latitude stratospheric nitrogen partitioning during summer time using MANTRA measurements and the Canadian Middle Atmosphere Model Although ozone depletion itself is not the principal cause of climate change, ozone changes and climate changes are linked in important ways. At mid-latitudes, ozone columns have decreased by about 6% in the last 20 years. Although the basic mechanisms for mid-latitude ozone loss are generally understood, there are still discrepancies between models and observations. The quantification of the processes contributing to mid-latitude ozone depletion, and the response of the climate system to those changes requires measurements of not only ozone but also of related trace gases, specially the nitrogen and chlorine species. This work reports on measurements taken during three Middle Atmospheric Nitrogen TRend Assessment (MANTRA) balloon campaigns which involved the launch of large balloons from Vanscoy, Saskatchewan, Canada (52N, 107W) on August 24 1998, August 29 2000, and September 3 2002. The objective here is to compare MANTRA measurements with the Canadian Middle Atmosphere Model (CMAM) and then use the model to complement the measurements to study the nitrogen partitioning at mid-latitudes during summer time. Late summer is an ideal time for such approach because of low dynamical variability in the stratosphere. We show that overall all the NO2 profiles measured during the three MANTRA campaigns with different instruments and from different platforms are generally consistent among themselves and that they compare very well with a climatology based on observations from satellites, other balloons, and a set of NDSC sites. This gives us confidence in MANTRA measurements and in the adopted retrieval techniques. Following, we show that CMAM reproduces well the MANTRA scenario. CMAM output for temperature, ozone, and the long-lived species agree very well with measurements. An exception is HCl which we found to be overestimated in CMAM. As for NO2, our results suggests that CMAM forecasts larger concentrations for sunset while reproducing well the measurements made during sunrise. This follows when comparing CMAM measurements from OSIRIS, a satellite instrument. We then follow discussing the nitrogen partitioning in CMAM, compared with MANTRA. 19/3/04 Dr. Vicky Hipkin Mars exploration by disequilibrium chemistry In this talk I will give a brief overview of the Mars Exploration Program and discuss our efforts to identify atmospheric objectives of such key importance that we will secure a place on a competed future mission. Mars has a very dynamic atmosphere with strong seasonal effects: a condensation cycle based around CO2 with trace amounts of water vapour, giant dust storms and thermal tides. There is no question that Mars weather and climate are extremely interesting to atmospheric scientists and especially those interested in comparative atmospheres. A big problem for the Mars atmospheric community is making an atmospheric mission higher priority than sampling the surface for signs of life! One proposal that we have helped develop is the idea of using the atmosphere to search for life through detecting disequilibrium chemistry. This is a powerful idea that in theory can put an upper limit on the near surface habitibility of Mars, going beyond what can be achieved by any single lander mission. We have shown that detection limits are feasible using current technology that effectively rule out the existence of surface based microbial communities. Detection of disequilibrium requires deep understanding of the Mars atmospheric system and surface-atmospheric interaction: from the dynamic evolution of plumes from surface sources, to atmospheric trace chemistry and atmospheric escape. An important aspect of this idea is that within the scope of this mission many other atmospheric questions could be addressed. 26/3/04 Rick Wehr Collisional Narrowing of Spectral Line Shapes in CO-Ar The individual spectral line is the basic building block of discrete spectra. Accordingly, some understanding of spectral line shapes underlies nearly all research in experimental atmospheric physics, and most of us have dealt with line shapes (probably Lorentz or Voigt) at some level in the course of our research. What is startling then, is that while work continues on very complicated spectra involving multiple complex molecules, no one has ever been able to accurately model the shape of a single isolated spectral line. One of the last stumbling blocks in such modelling is a line shape effect called collisional narrowing, which is not included in simple models like the Lorentz or Voigt. I will be talking about my efforts to combine experimental evidence with theoretical calculations to show that collisional narrowing may be suppressed in certain systems of atmospheric interest, such as CO-Ar. This information will become important as the resolution and retrieval capabilities of remote sounders increases. I will begin the talk by explaining the necessary concepts in spectral line shapes so that everyone is on the same footing. Then I will outline the experiment that I performed and describe the exciting results that I am currently obtaining. 2/4/04 Elham Farahani Comparison of Stratospheric Measurements in the Canadian High Arctic with Atmospheric Models In order to investigate the influence of chemical processes on Arctic ozone loss, a ground-based UV-visible spectrometer has been deployed five times at Environment Canada's Arctic STRatospheric Ozone Observatory (ASTRO) in Eureka, Nunavut (80N, 86W) during winter/spring of 1999 2004. This instrument is used to record UV-visible absorption spectra from which vertical column amounts of ozone, NO2, BrO, OClO, and NO3 can be retrieved. Operation in zenith-sky mode is fully automated so that twilight spectra of scattered sunlight are recorded daily. In first part of my talk, I will review chemical processes in the Arctic and their influence on Arctic ozone, and then I will take you to Eureka for a lab tour of our UV-visible spectrometer and two other instruments there, their viewing geometries as well as their retrieval methods. Particularly, I will focus on Differential Optical Absorption Spectroscopy (DOAS) retrieval technique applied to data from UV-visible spectrometer, the resulting slant columns, air mass factor calculations and vertical columns. In second part, in order to see how atmospheric models do, I will compare total columns of different atmospheric gases such as ozone, NO2, HNO3, N2O, and CH4 obtained from the UV-visible DOAS measurements and coincident Fourier transform infrared solar/lunar absorption measurements with chemical fields from the Canadian Middle Atmosphere Model (CMAM), a chemistry-climate model and SLIMCAT, a chemical-transport model. 16/4/04 Loic Jounot MOPITT-A Retrievals: A Case Study Guess what... I volunteered to give a second Brewer seminar this year. I know... you're thinking it's going to be the same old story: the one you've already heard six times. Well, no. This time I promise it's going to be fresh and different. I'll talk about the case study that's in my thesis. On September 7th 2000, MOPITT-A flew a high altitude mission onboard the ER-2 research aircraft. MOPITT-A is a correlation radiometer that measures carbon monoxide. The flight was part of SAFARI 2000, a regional study of biomass burning in southern Africa. One of the highlights of the flight was a large fire in the Timbivati Game reserve in the South African bush. Based on this case study, I'll discuss the strengths and weaknesses of MOPITT-A retrievals. You don't think this really sounds fresh and different? You don't have a choice anyways. Ha! Brewer seminars are mandatory. 23/4/04 Debra Wunch The MSC FTS and MANTRA A Fourier Transform Spectrometer (FTS) from the Meteorological Service of Canada (MSC) will fly aboard the Middle Atmosphere Nitrogen TRend Assessment (MANTRA) high-altitude balloon payload in August 2004. This will be it's second high-altitude flight. Many of you know of the problems encountered during the MANTRA 2002 flight of the MSC FTS, and I will describe them and how we have addressed these issues and are preparing for flight this summer. I will discuss the basics of Fourier transform spectroscopy and the concepts behind the ideal Fourier transform spectrometer (FTS). Of course, no instrument is ideal, and so I will also discuss the practical constraints of these instruments, with a focus on the highly restrictive requirements for FTS instruments designed for high-altitude balloon platforms. Hope to see you there! 30/4/04 Clarck Zhao What do ice-core data from the Himalayas tell us? To understand climate change and to predict the future climate requires the study of both modern and past climates. Ice core records provide a longer (than instrumental records), more direct and more complete measure of past climate change in comparison with other recorders such as tree rings and deep-sea and continental sediments. The ice core from Dasuopu Glacier in the Himalayas is invaluable because it originates at the lowest latitude and highest elevation (~7200m) of all cores from the monsoon region. One of our findings is that, despite the glacier's proximity to the Indian subcontinent, the snowfall recorded in the core does not exhibit any statistically significant relationship with the Indian monsoon rainfall for the period 1956-1993, for which we have data. We attribute these differences to the extreme height of the ice core site, which effectively decoupled snow accumulation at the site from the surface-confined moisture transport that is associated with the Indian summer monsoon. Furthermore, we found a statistically significant decreasing trend in the ice-core snow record, which is consistent with other regional droughts, for example, in western Africa and northern China, during the latter half of the 20th century. This implies that there may exist a common mechanism that explains such trends in geographically separated locations. We explored the hypothesis that these trends are related to changes in the regional Hadley and Walker circulations. We concluded that the decreasing trends in the three precipitation time series during the latter half of the 20th century are the result of large-scale changes in the global tropical overturning circulation. In addition to the above work, we also note the difference between the effects of snowfall on the Tibetan plateau, which is at a mean elevation of ~4000m, and that which occurs on the Dasuopu Glacier, at an elevation of ~7000m. If time permits, I will present our recent research on the relationship between Tibetan snow cover, the Indian summer monsoon and the Tibetan plateau monsoon. 7/5/04 Annemarie Fraser The Tale of the ACE 2004 Arctic Validation Campaign In February 2004, an intrepid group of scientists set out from southern Ontario on their way to Eureka, Nunavut. They went not to tame polar bears, but to selflessly give three weeks of their lives to the pursuit of science. The recently launched SCISAT-1 Satellite needed to be validated from the ground in its primary region of interest: the Canadian Arctic. This week's Brewer will tell the tale of these brave souls and their instruments, and, where possible, their data. I will of course focus on the UofT ground-based spectrometer, the instrument I have been working with the past few years. It measures zenith-scattered spectra of UV-Visible light, enabling the retrieval of total columns of ozone, NO2, BrO, and NO3 at sunrise. I'll show you some of my preliminary results and compare with preliminary results from some of the other seven instruments taking part in the campaign. Along the way, I'll try to take you on a virtual (sorry, no air miles) journey from this hopefully warm spring day to the decidedly not warm Eureka weather station and environs. 14/5/04 Dr. Florian Nichitiu MAESTRO Sun Scan analysis The ACE payload (Atmospheric Chemistry Experiment launched on August 12, 2003 on board the Canadian scientific satellite SciSat-1) consists of two instruments: ACE-FTS (a high resolution Fourier transform infrared spectrometer) and MAESTRO (Measurement of Aerosol Extinction in the Stratosphere and Troposphere Retrieved by Occultation), a dual UV-visible spectrograph. Both instruments use solar occultation to retrieve abundances of trace gases, especially ozone, and temperature and pressure profiles. After on-orbit commissioning
of the spacecraft and instruments, a series of on-orbit science-oriented
activities have been undertaken. The purpose of these activities is to extend
and verify the results obtained during the pre-launch lab-tests and to find
the appropriate parameters for operational measurements. In this respect,
two important activities were done: the Sun Scanning measurements, performed
on 21 Feb. 2004 and High Sun Scanning measurements performed on 14-17 Apr.
2004. Here, I will try to describe the analysis of these two types of measurements
and the results obtained. 21/5/04 Shuang Liang Atmospheric Predictability This talk will be a review of atmospheric predictability. The prediction of the evolution of a system from its initial conditions is a fundamental problem with wide applications in geophysical flows. The predictability can be severely limited by the dynamics or the practical approachability. Atmospheric predictability, in particular the intrinsic limit associated with weather forecasting, was addressed first by Thompson (1957). Lorenz (1969) and Leith (1971) studied atmospheric predictability using two-dimensional numerical models and respectively claimed finite and infinite predictability. Their results are related, in an essential way, to differences in their turbulence approximations, as well as the slopes of the energy spectrum in the inertial range. This talk will focus on the history and various discussions of these issues. In recent years, people have used a number of different approaches to address the problem of predictability. The main advances will be introduced briefly. 28/5/04 Christina Pencarski A Funny Thing Happened on the Way Towards My DNS Studies (or Instability of Continuously Stratified Parallel Inviscid Flows: Solving the Taylor-Goldstein Equation) The topic of my research is the study of turbulent mixing in stratified flows. Of particular interest is the formation of "fine-structure" evolving from the action of turbulent mixing in a stably stratified environment. This research will be conducted through the Direct Numerical Simulation (DNS) of the full Navier-Stokes equations of motion of a stratified shear flow undergoing turbulent collapse. The detailed analysis of turbulent mixing performed by Peltier & Caulfield (2003) of such a flow delivered a non-monotonic dependence between the mixing efficiency and the initial Richardson number characteristic of the stratification; a dependence which had been conjectured by Phillips (1972) and Posmentier (1977). Moreover, the analysis suggests a numerical value of mixing efficiency of approximately 0.2, which has been observed experimentally, in addition to evidence of the development of an intermediate layer of well-mixed fluid. To perform the DNS studies, an understanding of the stability of continuously stratified parallel flow is required. After a brief introduction for the motivation of the study of turbulent mixing, and of the observed formation of fine structure in the laboratory and in the atmosphere, I will review some of the basic theory of the instability of continuously stratified parallel flows, including the relevant stability equation in the Boussinesq limit for an inviscid flow, namely the Taylor-Goldstein equation. Following this, I will present the various methods I have employed in order to solve this stability equation, discuss my results, and conclude with an account of my current efforts and future goals. 4/6/04 Prof. Paul Kushner Lessons learned from GFDL's new land/atmosphere general circulation model, "AM2/LM2" In this talk, I will present an overview of NOAA/GFDL's new atmosphere/land general circulation model, which is known as "AM2/LM2". This model, which represents a considerable increase in sophistication and realism over the previous generation of atmospheric GCMs at the lab, has been the result of an intensive team-based development effort over the past several years. Along the way, we have been exposed to a wide variety of scientific issues related to interesting sensitivities displayed by the model. We have also learned much about the practicalities of model development in a team setting, including the need to balance scientific goals over the short term with good software-development practice over the long term. 11/6/04 Matt Toohey Long-term stratospheric nitrogen trend assessment based on low-spectral-resolution emission radiometer observations As any hockey fan can tell you, a great team requires the intangibles provided by proven veteran leaders. And as an athlete ages, and their competition becomes quicker and stronger, they must rely on "smarts" in order to maintain relevance. At this Friday's Brewer, I will introduce two emission radiometers: two humble instruments of the many on-board the MANTRA balloon payload making observations of the chemical state of the atmosphere. I will discuss the evolving and improving data analysis techniques used to produce vertical profiles of chemical mixing ratios from the instruments' radiance observations, and discuss the unique scientific opportunities afforded by the instruments' illustrious heritage which dates back to the 1970's. In order to motivate this work, I will spend some time on the relevant stratospheric chemistry, especially that concerning active nitrogen species and their role in ozone chemistry. I hope to do all this and more in the time allotted to me on Friday, thereby avoiding (sudden-death) overtime. 18/6/04 Gerald Chang Hawaiian Cloud Bands: Flow Around a Gigantic Obstacle With the troposphere being around 12km in the tropics, one could imagine that a 4km mountain would create quite a stir in the atmosphere. It just so happens that there are two summits on the Island of Hawaii reaching such a height. This generates a very interesting cloud pattern on the windward side of the island called the Hawaiian Cloud Bands. Most introductory meteorology textbooks will have you believe that clouds form on the windward side of mountains because air is forced up along the slope, expands, cools, condenses and lo and behold, we have clouds! However, it is actually the air going downslope, back towards where it came from, that results in the cloud bands. In this talk, I will review a very basic concept of flow over topography (i.e. the Froude number), discuss the Hawaiian Cloud bands from the perspective of other scientists (Smolarkiewicz et al, 1988) and present some of my results. 25/6/04 Dr. Wataru Yanase Effects of baroclinicity on the cloud pattern and structure of polar lows: High-resolution numerical experiments Polar lows (PL) are meso-scale cyclones that often develop over high-latitude oceans on the polar side of the polar front in cold seasons. Some PLs resemble tropical cyclones having a cloud-free eye and spiral cloud bands, some look like miniature extratropical cyclones having a comma-shaped cloud pattern, and the others have complex cloud patterns which are different from the above two types. It is not easy to observe their detailed structures because they are small short-lived cyclones which form over data-sparse high-latitude oceans in winter. In order to clarify what determines the cloud pattern and structure of polar lows, I performed high-resolution numerical experiments using a three-dimensional non-hydrostatic model with horizontal grid size of 5 or 2 km. An axisymmetric initial vortex is imposed in a baroclinic basic state in which the uniform vertical shear of the zonal wind and the meridional temperature gradient are in thermal wind balance. It is found that when the baroclinicity is absent, a hurricane-like vortex with spiral cloud bands, a cloud-free eye, and a warm core develops. When the baroclinicity is strong, on the other hand, a vortex with a comma-shaped cloud and slightly larger horizontal scale develops. The former appears to develop due to CISK/WISHE mechanism like a tropical cyclone, while the latter due to baroclinic instability modified by latent heating. |