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Abstracts from 2004/2005 10/9/04 Dr. Rada O. Manuilova The self-consistent model of daytime emissions of electronic-vibrationally excited products of O3 and O2 photolysis: Retrieval of vertical ozone profile from measured intensity of these emissions Traditional kinetics of electronically excited products of O3 and O2 photolysis is supplemented with the processes of energy exchange between electronic-vibrationally excited molecules of singlet oxygen, excited atomic oxygen, and molecules of oxygen in the ground electronic state. The model of the photochemical source of vibrationally excited O2 molecules suggested by the two authors of this study in (Yankovsky and Manuilova, 2002) is based both on the analysis of the processes of direct forming of vibrationally excited oxygen in the fundamental electronic state in O3 photolysis and on the analysis of relaxation processes of the other products of O3 photolysis. The model proposed allows calculating not only the vertical profiles of the O2(a1Dg,v=0) and O2(b1,S+g,v=0) concentrations, but also the profiles of O2(a1Dg,v=1-5) and O2(b1S+g,v=1,2). The example of the ozone concentration profiles retrieved separately from simultaneously measured intensities of emissions at 762 nm and 1.27 um is presented. Taking into account electronic-vibrational kinetics of excited products of ozone, the ozone concentration profiles retrieved from the observations of these emissions turn out to be in good agreement. 17/9/04 Prof. Dylan Jones Characterizing forward model errors for the inverse modeling of atmospheric CO Inverse modelling is now widely used in atmospheric science to better constrain estimates of surface fluxes of environmentally important trace gases such as CO, CO2, and CH4. However, the flux estimates derived from this technique depend critically on properly characterizing forward model error. I will discuss the work we have been conducting to better quantify forward model error. Our specific focus in this case is the inverse modeling of atmospheric CO. We have adapted the NMC method, which was used previously for numerical weather prediction. In this approach, the model error for the GEOS-CHEM simulation of CO is estimated using the differences between successive chemical forecasts of CO (48-hours vs. 24-hours). I will examine the error structure in the model and the regional dependence of the error correlation length scales. To validate this approach, we will compare the error statistics from the NMC method with those calculated by comparison of the CO simulation from GEOS-CHEM with that from the FRSGC/UCI model, and those based on the differences between GEOS-CHEM and observations of CO from MOPITT. 24/9/04 Matt Reszka "Things to do with CMAM" Or "A Funny Thing Happened on my Way to Balanced Tropical Dynamics" Global wind-field analyses are often found to exhibit significant errors in the tropics, particularly in the middle atmosphere. In 3DVar data assimilation, background error covariance patterns are typically modelled using physically meaningful diagnostic relationships between the assimilated variables. Here, a dynamical balance is sought that could be used to improve zonal winds in the stratosphere based on the temperature field, which is better constrained due to the availability of satellite observations. The implementation of 3DVar currently used in CMAM data assimilation (CMAM-DA) and, operationally, at the Canadian Meteorological Centre, is briefly introduced. Variants of the traditional Linear Balance are motivated through a scaling analysis, in particular, semigeostrophic arguments, and are investigated numerically in the context of output from the CMAM as well as CMAM-DA analyses. Although these balances are advantageous in the vicinity of the equator, where geostrophic balance breaks down, recovery of the zonal velocity from the mass variable is still problematic in some regions of the tropical stratosphere. The reasons appear to be that the assumptions of semigeostrophy and an advective timescale do not hold in a robust way, as well as the fact that the fields of interest consistently vanish at certain tropical latitudes. Some peripheral findings are also presented. 1/10/04 Denis Dufour The Sun in a Lab: Building a Solar Simulator for Scisat-1 Spectral Measurements This talk will give a flavor of some of the challenges faced by experimentalists in testing atmospheric remote sensing instruments. In this case, the challenge was constructing a high power, wide wavelength range, temporally and spatially stable solar simulator for testing the Scisat-1 spectrometers prior to launch. Scisat-1 is a Canadian satellite, launched in August 2003, which has as a primary focus the study of ozone related chemistry and dynamics in the high-latitude stratosphere. It has two spectrometers, ACE-FTS (Atmospheric Chemistry Experiment - Fourier Transform Spectrometer) and MAESTRO (Measurement of Aerosol Extinction in the Stratosphere and Troposphere Retrieved by Occultation) which are designed to measure spectra in the infrared and near-UV to visible, respectively. Since they are designed to measure direct sunlight filtered by stratospheric absorbers, it was necessary to build a solar-like light source in the lab in order to test the instruments properly prior to launch. Such a simulator was built and used to take high-resolution absorption spectra of NO2 and O3 with both instruments simultaneously, with the objective of assessing the continuity of their published cross-sectional values from the visible to the infrared. A description of the experimental apparatus, tests performed, and the performance of the sun simulator obtained from analysis of the NO2 and O3 laboratory spectra will be presented. 8/10/04 Lei Wang Southern Hemisphere Annular Mode Trends: An aspect of the extratropical atmospheric circulation response to global warming and ozone depletion This talk will be a review of Southern Hemisphere Annular Mode (SAM), also known as Antarctic Oscillation (AAO), and its trends during recent decades. The Annular Mode is the dominant pattern of extratropical atmospheric circulation variability and has shown significant positive trends during last several decades, which are characterized by a strengthening of the circumpolar westerly flow that extends from the surface to the stratosphere and a poleward shift in the zonal mean flow. The SAM trends are regarded as the consequence of the greenhouse gases increasing and the ozone depletion in the Southern polar regions. However, I found that the stratospheric water vapor changes might also play an important role in the SAM trends. In this talk, I will present evidences which associate the stratospheric water vapor trends with the SAM trends. 15/10/04 Thomas Birner The tropopause puzzle The tropopause is a distinct feature of the atmosphere (with some notable exceptions, mostly in the polar regions during winter). More than 100 years after its discovery, some characteristics of the tropopause remain mysterious. In particular, there is still no satisfying theory that explains its position and sharpness. Even the fundamental question of why the tropopause exists at all might be considered as a challenge. This talk will give an historical survey of advancements in our understanding of the tropopause. Observations, theory, and modeling will be discussed. 29/10/04 Flávio Justino Quantifying Climate Feedbacks During the Last Glacial Maximum A growing number of studies reveal that changes in surface albedo, orbital parameters, atmospheric CO2 concetration and atmospheric topography can significantly influence the climate. This seminar aims to discuss these influences with a three dimensional coupled atmosphere-ocean-sea-ice model (ECBilt-Clio), mimicking the Last Glacial Maximum (LGM) in terms of albedo, orbital forcing, ice sheet topography and reduced atmospheric CO2 concentration. As compared to a present day climate simulatiom, the "LGM Simulation" exhibits lower SST over most parts of the ocean except for the Pacific. The origin of this peculiar SST pattern will be explained in terms of changes of the atmospheric and oceanic circulation. In addition to studying changes in the climate mean state our presentation will focus on the changes in stationary waves and transient addy activity induced by the modified atmospheric boundary conditions. The results will be compared with recontructed temperature changes and other proxies data. 5/11/04 Constantine Nenkov Thermal Convection in a Rapidly Rotating Spherical Shell: the Emergence of Zonal Jets The observation of zonal jets on the disks of the gas giant planets of Jupiter and Saturn provide a realization of planetary scale hydrodynamic circulation that differ radically from that of our own planet. Two of the main characteristics of the atmospheres of these planets: rapid rotation and large radial extent suggest that not only Coriolis forces but also deep convection must play major roles in shaping the evolution of their atmospheres. In addressing this issue I will present initial results involving a test case for the atmospheres of Jupiter and Saturn, using a fully 3D non-hydrostatic anelastic primitive equations GCM, which I have been developing for the past 2+1/2 years. This new model is based on the use of an icosahedral grid structure and explicitly treats the non-hydrostatic vertical motions associated with the convection processes. I will show that the model is able to explain the existence of prograde equatorial jets on both Jupiter and Saturn, but also that the detailed structure and amplitude of these jets is sensitive to the mechanical boundary condition applied at the base of the convection zone. 12/11/04 James Anstey The Stratosphere Is Red During winter in the Northern Hemisphere, stratospheric circulation anomalies are often observed to move downwards into the troposphere. The exact reason for this behaviour is unknown, but we speculate that one contribution to the effect may be given by the stratospheric signature of wave-induced torques occuring in the troposphere. Such a mechanism would not require any information to be transmitted from stratosphere to troposphere; essentially the stratosphere would be acting as a redshifter of tropospheric variability. This question is related to the issue of whether or not stratospheric dynamics can be considered as "slaved" to tropospheric dynamics. 19/11/04 Amit Ghosh Baroclinic Wave Growth and Evolution in a Primitive Equations Model on the Sphere Baroclinic Instability is cited as the main cause of midlatitude cyclones and other features we associate with weather maps. In this talk I will discuss the simulation of baroclinic waves employing a spherical primitive equations model. I will discuss both the theory behind the inital growth of a baroclinically unstable state and the process by which a realistic atmospheric state is established, and how these simulations are employed as a basis for testing the integrity of an atmospheric model. I will also discuss the formation of regions of high baroclinic wave activity; `storm tracks', and their character under the influence of a varying background of topographically generated stationary long waves. 26/11/04 Rebekah Martin Numerical Simulations of Cyclone Interaction with the Topography of Greenland The topography of Greenland is very striking in that as a plateau that is over 3 km high at some points, it presents a very significant barrier to atmospheric flow in the North Atlantic. Not coincidentally, the Icelandic Low sits off of the eastern side of the island, and provides a steering mechanism for storms moving off the coast of Newfoundland and Labrador across the North Atlantic. Often, deep synoptic scale cyclones can be seen to actually impinge on the southern tip of Greenland, known as Cape Farewell. Subsequently, high wind speed events downstream of Cape Farewell known as tip jets can be seen to occur in satellite imagery and simulation output over the Labrador or Irminger Seas. Some of these events have been simulated with the Penn State/NCAR Mesoscale Model version 5 (MM5) and the mesoscale structure of the high wind speed events has been examined. These simulations will be presented along with an investigation of the air-sea interaction associated with the tip jet. 3/12/04 Andreas Dörnbrack Fine structures of extratropical cyclones Differential absorption lidar (DIAL) observations and dropsonde data are investigated to characterize the mesoscale fine structure of extratropical cyclones. The tropospheric water vapor DIAL data are obtained during transfer flights from central Europe to North America in May and June 2002. A great variety of different and often surprising water vapor features were found. I will try to explain them in the context of synoptic-scale analyses and mesoscale numerical modelling. Another fine-scale pattern frequently observed near fronts are gravity waves. We report about observations of such waves excited in the vicinity of an intense cyclone during NORPEX98 north of the islands of Hawaii. Dropsonde data of potential temperature and wind resemble mountain-wave induced gravity wave characteristics. High-resolution numerical modelling is applied to resolve the likely source of the observed features. 10/12/04 Jeff Taylor Measuring Ozone Concentrations at the Toronto Atmospheric Observatory The Toronto Atmospheric Observatory (TAO) was commissioned in 2001, and a newly redesigned Bomem DA8 high resolution Fourier Transform Infrared Spectrometer (FTIR) was installed as its principal instrument. Since 2002, spectra have been recorded routinely with both an InSb and an MCT detector, over a spectral range of 720 to 4300 cm-1 with a nominal resolution of 0.004 cm-1. To date, total and partial column concentrations of O3, N20, CH4, HF, HCl, NO2, NO, CO, HCN, OCS and C2H6 over Toronto have been determined. In March 2004, the TAO FTIR was formally designated as a complementary site of the Network for the Detection of Stratospheric Change (NDSC). This presentation will focus on the measurement and retrieval techniques currently employed at TAO, highlighting the formalism of the optimal estimation method and utility of information content analysis. Preliminary results of ozone total and partial column concentrations above Toronto will be shown and comparisons with like measurements from both satellite and ground based observation systems will be discussed. 7/1/05 Mark Fruman Linear and Nonlinear Symmetric Stability in the Equatorial Middle Atmosphere Steady zonal flows over the equator can be unstable with respect to axially symmetric perturbations depending on the distributions of potential temperature and absolute angular momentum. This so-called "symmetric instability" plays a role in the circulation in the equatorial middle atmosphere during the solstice seasons, when the maximum heating from the sun is off the equator. Using an anelastic equations system on the equatorial beta-plane, I will discuss conditions for symmetric stability, considering the cases of small and finite amplitude disturbances separately. 14/1/05 Dmitry Vyushin A new statistical model for total ozone variability International agreements for the limitation of ozone-depleting substances have already resulted in decreases in concentrations of some of these chemicals in the troposphere. Full compliance and understanding of all factors contributing to ozone depletion are still uncertain; however, reasonable expectations are for a gradual recovery of the ozone layer over the next 50 years. Because of the complexity of the processes involved in ozone depletion, it is crucial to detect not just a decrease in ozone-depleting substances but also a recovery in the ozone layer. Statistical models containing several components such as annual cycle, QBO, solar variability, trend and serially correlated noise may be fitted to observed total ozone data. When such a model is fitted, the estimated character of the noise determines the precision of the estimated trend. How different statistical models (AR1, FAR1) affect the the precision of the estimated trend and what is the prediction according to these models for the number of years required to detect a fixed trend in total ozone is a subject of my Brewer talk. 21/1/05 Lisa Neef The Joy of Simple Models, Part II: Breaking of the Internal Tide via Resonant Triad Interactions Or: This one time, at Math Camp.... Mixing in the deep ocean is driven by the breaking of internal waves, that is, the nonlinear transfer of energy from internal waves to turbulence. It is estimated that roughly half of internal wave energy in the ocean is produced by the movement of the tide around topography, which generates internal waves with the same frequency as the tide. The mechanisms that cause this internal tide to cascade to mixing scales, however, are not yet well understood. MacKinnon and Winters (2003) used an idealized model to show that the 6-hour internal tide seems to break very efficiently into waves of about half that frequency, near the latitude where the inertial frequency (f) is half the tidal frequency. Their result suggests that Parametric Subharmonic Instability (PSI) is an important mechanism for energy transfer out of the internal tide, and could be at least in part responsible for mixing "hotspots" at certain latitudes. Not one to model systems with more than 5 variables, in this talk I will discuss a simple investigation of MacKinnon and Winters' hypothesis which uses a well-known (yet consistently confusing) "simple" triad resonance argument. By distilling the governing equations down to a single triad of interacting waves, we can examine how PSI depends intrinsically on latitude, without any other complicating factors. The triad equations can also give us a first-guess estimate of the magnitude of energy that might be dissipated out of the diurnal tide via PSI. This work-in-progress was begun as my project for the Woods Hole GFD Summer School, 2003. 28/1/05 Caroline Nowlan Temperature and Pressure Retrievals from the MAESTRO Space Instrument MAESTRO (Measurement of Aerosol Extinction in the Stratosphere and Troposphere Retrieved by Occultation) is a photodiode array spectrometer making solar occultation measurements from the SCISAT-1 satellite. The instrument produces vertical profiles of various constituents involved in ozone distribution in the middle atmosphere. Atmospheric temperature and pressure profiles are necessary for accurate retrievals of aerosols and molecular species from MAESTRO. This talk will summarize a method to retrieve temperature and pressure profiles from on-orbit using the A and B absorption bands of molecular oxygen, including the radiative transfer model, instrument characterization model, and global-fitting retrieval code developed for this work. 4/2/05 Sorin Codoban Available Potential Energy and its Applications The concept of APE has been developed in order to quantify the processes which drive and maintain the atmospheric circulations, from meso- to planetary scales. Several approaches may be considered with respect to the definition of the APE. A key issue is the choice of the reference state, relative to which the APE is determined. In the classic theory (Lorenz, 1955) the reference state is completely defined by its mass distribution. Applied in this form, the APE diagnostic may lead to an incorrect assessment of the causality of mechanically driven flows (e.g. of the middle atmosphere circulation). Other constraints, for example using angular momentum, may be added to the definition of the reference state. Their inclusion may be achieved by taking into account the Hamiltonian structure of the conservative dynamics. I will present a review of the concept of APE in this new setup, with application to the energetic budget of cross-stream circulations. 11/2/05 Anthony Liu The Effect of the Sea-ice Zone on the Development of Boundary Layer Roll Clouds during Cold Air Outbreaks High latitude air-sea interaction is an important component of the earth's climate system and the exchanges of mass and energy over the sea-ice zone are complicated processes that, at present, are not well understood. In this study, we perform a series of experiments to examine the effect of sea-ice concentration on the development of high latitude boundary-layer roll clouds. The experiments are performed at sufficiently high spatial resolution to resolve the individual convective roll clouds, and over a large enough domain to be able to examine the rolls' downstream development, thus allowing for a more realistic representation of the dynamic and thermodynamic processes that are important. Furthermore the high spatial resolution of the experiments allows for an explicit representation of heterogeneity within the sea-ice zone. The results show that the sea-ice zone has a significant impact on the atmospheric boundary layer development, which can be seen in both the evolution of the atmospheric structure and the development of heat and moisture transfer patterns. In particular, we find the air-sea exchanges of momentum, moisture and heat fluxes are modified by the presence of the roll vortices (typically a 10% difference in surface heat fluxes between updrafts and downdrafts) and by the concentration and spatial distribution of the sea-ice. This suggests that a more realistic representation of processes over the sea-ice zone is needed to properly calculate the air-sea energy and mass exchange budgets. I will also present some recent results of high-resolution numerical simulations of lake-effect cloud bands, which have been performed on the Earth Simulator, the fastest supercomputer in the world, two weeks ago. 25/2/05 Rick Wehr Speed-Dependent Dicke-Narrowed Line Shapes in CO-Ar Although there is much published research on the absorption spectra of atmospheric gases, including many studies of complicated polyatomic molecules, much of the research is descriptive rather than explanatory. That is, it lacks theoretical models that can reproduce the measured spectra without relying on empirical, phenomenological parameters. It may be surprising to hear that at present, no truly theoretical calculation can reproduce modern, high-resolution measurements of any gaseous absorption spectrum -- not even that of a single isolated infrared line in a diatomic gas, which is probably the simplest of all such spectra. In this seminar, I will present the final results of my Ph.D. work on the detailed shapes of isolated IR lines in carbon monoxide. The primary goal of the work has been to bring us closer to a proper calculation of these elementary spectral features. Along the way, I have also obtained novel measurements of several interesting line shape effects in the CO-Ar system, including collisional (pressure) broadening, collisional shifting, and Dicke narrowing. I will begin the seminar with a (re-)introduction to infrared line shapes, before describing what is involved in a proper line shape calculation. Finally I will present my work and its results. 4/3/05 Mohammad Hamidian The Importance of Being ENSO (From CCSM Results and the ICE AGE to Toy Models) While some believe that a good understanding of the El Nino Southern Oscillation (ENSO) mechanism now exists, there are still some important issues that are not completely resolved. I will begin by presenting early CCSM results of ENSO for modern and LGM conditions and draw comparisons with recent findings. The discrepancy raises a global issue of how the mean state of the planet affects climate variability. The talk proceeds with presenting the delayed oscillator theory for ENSO and its ability to answer some of the key questions regarding ENSO's initiation, demise, and quasi-periodic timescale, while arguably failing to capture the true equatorial ocean dynamics. Finally, I will close with a brief overview of my own research in the field. 11/3/05 Ted Shepherd Self-similarity of decaying two-dimensional turbulence Similarity theory is a powerful tool for analyzing complex problems such as turbulence. Batchelor (1969) proposed a similarity theory for decaying two-dimensional turbulence, but subsequent numerical simulations showed his theory to be incorrect. In collaborative work with Prof. Takahiro Iwayama of Kobe University, I have revisited this problem and derived a new self-similarity theory. We assess the validity of this new self-similarity theory against direct numerical simulations. 1/4/05 Theophilus Ola RETRIEVING ABUNDANCES OF ATMOSPHERIC SO2 FROM THE GOME AND SCIAMACHY SATELLITE INSTRUMENTS SO2 and sulphate aerosols play a significant role in global warming. I discuss our current work on retrieving SO2 slant column abundances in the troposphere. Contributions of SO2 to the troposphere arise mainly from the burning of fossil fuels, with secondary contributions coming from volcanoes and the oxidation of certain organic materials. The purpose of the retrieval is to produce reliable SO2 data over major anthropogenic source regions. The retrieval is implemented using data acquired from the GOME and SCIAMACHY instruments. The two satellites measure backscattered solar radiation in the UV and the visible region of the spectrum. Specifically, the spectral window we are looking at is [300nm,330nm], where ozone absorption is dominant. As well, the slit-widths for GOME and SCIAMACHY are non-constant over this spectral region. These two factors contribute to a more complicated retrieval process, which I shall present a discussion of and show some of its preliminary results. 8/4/05 Debra Wunch The MSC FTS and MANTRA 2004 A balloon-borne Fourier transform spectrometer (historically called the MSC FTS) was flown for the second and third times during the MANTRA 2004 campaign. An enormous amount of work went into the redesign of the MSC FTS, and the instrument is now fairly reliable and robust. I will describe the work that went into the redesign of the MSC FTS, and the ground-based data that resulted. I will also discuss the MANTRA 2004 campaign and present the data derived from the first flight. 22/4/05 Elham Farahani My Arctic Stratospheric Adventure: Four Years of Measurements and Models Comparison In the Arctic, the ozone column shows high inter-annual variability, with low values during cold winters, where stratospheric temperatures are low and the vortex breakup occurs late in spring, and high ozone values during warmer winters with higher stratospheric temperatures and disturbed vortex. Although the fundamental mechanism for polar ozone depletion is generally understood, the Arctic ozone depletion process is complicated by the strong coupling between transport, heterogeneous chemistry, and halogen activation. Also atmospheric models differ in their ability to reproduce the observed Arctic ozone loss, which points out unresolved questions regarding the coupling between transport, temperature, and chemistry. In this talk, I will present the final results of my Ph.D. project on Arctic ozone depletion. I will start by introducing the chemical processes in the Arctic and their influence on Arctic ozone. Then I will present comparison of the solar/lunar measurements at Eureka with the chemical fields from the Canadian Middle Atmosphere Model (CMAM), a chemistry-climate model and SLIMCAT, a chemical-transport model to assess these fields, and to determine the day-to-day as well as the inter-annual variability of ozone, NO2 and HNO3, N2O, and CH4 during the chemically perturbed conditions of winter/spring. Along the way also OClO column measurements during cold year of 2000 will be presented! 29/4/05 Matt Toohey Middle Atmosphere Nitrogen TRend Assessment - A story from multiple perspectives One of the many aims of the MANTRA balloon mission is to quantify any possible changes in the reactive nitrogen budget of the stratosphere, and tie such changes to ozone chemistry. To this end, the MANTRA instrument complement has included two seasoned veterans of atmospheric observation: the emission radiometers. The central goal of my work is to develop a retrieval technique to be applied to modern flights as well as past, and look for possible trends in the nitric acid profiles the retrieval process produces. Trend detection is a difficult business in the best of times, and is made even more difficult when working with a limited data set from a limited instrument. Thus, I will also talk about ongoing work that aims to pin down the natural variability of nitric acid and other stratospheric trace species in the stratosphere by looking at output from the CMAM and very new results from the ACE-FTS satellite instrument. Throughout the short survey of nitric acid observations past and present, I will try to make a case for the emission radiometers being a potentially key supporting character in the ongoing saga of stratospheric observation. 6/5/05 Clarck Zhao The linkage between the North Atlantic Oscillation (NAO) And the North Pacific Climate My talk will be composed of two topics: 1. A non-linear expression of the NAO in the North Pacific The NAO is one of the most important modes of variability in the climate system but our knowledge of its impacts is based largely on linear analysis techniques. Non-linearities associated with it are largely unknown. In this study, we use recently proposed non-linear compositing and one-sided regression techniques as well as a new rectified regression technique to show that the non-linear expression of the NAO is fundamentally different from its linear expression. 2. A seasonally lagged response to the NAO in the North Pacific In this study, I will discuss the existence of a seasonally lagged response to the NAO in the North Pacific region. In particular, we show that the spring sea-level pressures and surface temperatures in the region are positively correlated with the sign of the NAO during the preceding winter. This response is identified in a number of long-term climate datasets including a Japanese tree ring time series that has been shown to be a proxy for spring temperatures in the northeast Asia. We identify two distinct mechanisms responsible for this lagged signal: one involving sea surface temperature anomalies in the North Pacific and the other involving Eurasian snow anomalies. We show that both of these anomalies develop during the winter and persist into the spring resulting in the observed lagged response. 13/5/05 Christina Pencarski A Review of Parameterizations of Mixing in Geophysical Models and Primary Instabilities in Stratified Shear Layers This talk will be composed of two interconnected topics. In the first part, I will provide a review of some of the parameterizations of mixing that have been proposed, with special focus on turbulent mixing in tropical oceanic regions. Mixing in geophysical fluid problems is a sub-grid process that requires parameterization in general circulation models. The need for more realistic parameterizations is frequently cited; in most cases the turbulent eddy coefficients are chosen arbitrarily or are adjusted to force agreement with observed density and velocity fields. Presently, combined efforts from loosely coupled analytical models, numerical simulations, laboratory experiments and fragmentary field observations lead the way to understanding mixing processes. I will give a brief review of the parameterizations of mixing in geophysical models in which focus will be directed towards turbulent fluxes that are generated by shear instabilities in a thermocline. In addition, a discussion of the parameterization of mixing in the Equatorial Pacific Ocean will be provided, including motivation for its study. In the second part of my talk, I will discuss the normal-mode stability analysis for a symmetric, stably stratified, inviscid parallel flow in the Boussinesq limit. Such a flow may deliver one of two types of primary instability: the Kelvin-Helmholtz instability, and the Holmboe instability. I will elucidate to the audience some of the interesting characteristics of these instabilities and conclude with my future studies. 20/5/05 Shuang Liang Atmospheric Predictability This talk will be a review of atmospheric predictability followed by some preliminary results. The prediction of the evolution of a system from an initial condition with some uncertainties can be intrinsically limited by its dynamics. Following the turbulence closure approach of Thompson (1957), Lorenz (1969) and Leith (1971) explored the predictability of 2D turbulence models and respectively claimed finite and infinite predictability. Their results are essentially ascribed to their different assumptions about the slopes of the energy spectrum in the inertial range. Dimensional arguments relate the predictability to the error growth rate as a function of scale. It is widely accepted that the error growth rates on small scales are much faster than those on large scales, and therefore the error growth rate on the smallest scale, characterized by the leading Lyapunov exponent, is irrelevant to the predictability. The Finite Size Lyapunov Exponent (FSLE) was proposed to formulate the dependence of error growth rate on the magnitude. Its successful application in simple systems such as the coupled Lorenz (1963) and Lorenz (1996) models motivate my attempt to introduce it into a 1D turbulence model. Some very preliminary results will be briefly presented at the end of the talk. 27/5/05 Aldona Wiącek Retrievals of Atmospheric Trace Gas Profiles from Ground-Based Solar Absorption InfraRed Spectra 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. TAO has been a Complementary Observation Station of the Network for the Detection of Stratospheric Change (NDSC, http://www.ndsc.ncep.noaa.gov/) since March, 2004. This talk will give an update on the progress of » measurements of ground-based spectra (720-4300 cm-1 or 13.9-2.3 m) at TAO, » retrievals of partial and total columns of atmospheric constituents such as O3, NO2, NO, N2O, CH4, HCl, HF, and ClONO2 from the above spectra, » and characterization of the vertical resolution and information content of the above optimal estimation retrievals. 3/6/05 Annemarie Fraser Rainbows at Sunset: Adventures in UV-Vis Spectroscopy The UofT ground-based spectrometer and I have had quite an exciting year, traveling to both Saskatchewan for the MANTRA 2004 campaign and Nunavut for the second ACE Arctic Validation Campaign in Eureka. Not one to be the same instrument twice, the spectrometer has also had two detector changes in this year of travel. In this talk I'll fill you in on some of the adventures we've shared. I'll present some results (some more preliminary than others) from both campaigns, focusing mainly on ozone and NO2 comparisons with the spectrometer's new best friend: SAOZ. SAOZ (Système d'Analyse par Observations Zénithales) is a French instrument very similar to our own. With a global network operating (almost) from pole-to-pole, it is the main UV-Visible instrument of the NDSC (Network for the Detection of Stratospheric Change). A ground-based SAOZ took part in both the MANTRA and Eureka campaigns. These campaigns were the first opportunity for our two instruments to take measurements side-by-side. 10/6/05 Tiffany Shaw The Importance of Momentum and Energy Conservation in the Parameterization of Subgrid-scale Processes in Atmospheric Models ... Gravity Wave Drag and Beyond The partial differential equations governing geophysical fluid dynamics represent all physical processes relevant to climate. When calculating numerical solutions to such equations over a discretized spatial grid covering the Earth, subgrid-scale processes are necessarily parameterized. The process of parameterization is one of the most difficult problems in climate modelling. Fundamentally, the governing equations are conservative, conserving both momentum (Newton's second law) and energy (first law of thermodynamics). These conservation laws necessarily apply to subgrid-scale processes such as the transfer of energy and momentum by boundary layer turbulence, convection, and gravity wave propagation. However, these fundamental constraints are typically only partially acknowledged in the parameterization of subgrid-scale processes. In this talk I will review some of the inherent difficulties associated with subgrid-scale parameterization drawing examples from the parameterization of gravity wave drag. I will illustrate the importance of momentum conservation in the parameterization of gravity wave drag, referring to idealized calculations from a zonal mean model. Those calculations show that a violation of momentum conservation leads to unphysical behaviour which could be falsely interpreted as stratospheric effects on climate. Finally, I will discuss how the dual constraints of momentum and energy conservation can be treated self-consistently using Hamiltonian geophysical fluid dynamics. 17/6/05 Jennifer Walker UV-Visible Spectroscopy with the MSC SunPhotoSpectrometer The SunPhotoSpectrometer (SPS) is a photodiode array spectrometer from the Meteorological Service of Canada, which has enjoyed a long and illustrious history in the field of stratospheric composition measurement. This instrument measures direct sun and zenith sky scattered ultra-violet and visible sunlight, and is used to retrieve abundances of stratospheric constituents such as ozone and nitrogen dioxide. It has been a part of a wide variety of field projects relating to ozone budget studies, and has been used for aircraft-borne, balloon-borne, and ground-based measurements. Most recently it has traveled to Eureka, Nunavut, as part of the second ACE satellite validation campaign, and to Saskatchewan for the 2004 MANTRA campaign. In this seminar I will review the instrumentation and data processing techniques for the SPS and discuss its role in the Eureka and MANTRA campaigns. I will present preliminary results for ozone and NO2 from SPS measurements in Eureka, and will compare these with the results from the other two UV-visible spectrometers: the U of T grating spectrometer and the French instrument SAOZ (Systeme d'Analyse par Observations Zenithales). |