Seminar Schedule for 2008/2009






15 Sep. 2008

Richard Dowden

University of Otago

Kim Strong

Global Lightning Location by VLF TOGA

17 Sep. 2008

Meiyun Lin

University Wisconsin- Madison

Dylan Jones

Regional Atmospheric Chemistry in Asia

22 Sep. 2008

Edwin Schneider


Dmitry Vyushin

The role of weather noise in climate variability

29 Sep. 2008

Gloria Manney


Ted Shepherd

Trace Gas Evolution in Recent Satellite Datasets: Relationships to the Stratospheric Polar Night Jet, Upper Tropospheric Jets and the Tropopause

20 Oct. 2008

Qinbin Li


Jane Liu

What can we learn about upper tropospheric CO2?

22 Oct. 2008

Tim Palmer


Ted Shepherd

Seamless prediction of weather and climate

23 Oct. 2008

Michael Gausa

Andoya Rocket Range

Mareile Wolff

ALOMAR Observatory, Atmosphere Reasearch from Ground to Space in the vicinity of the Andoya Rocket Range

27 Oct. 2008

Prashant Sardeshmukh


Jahanshah Davoudi

An interpretation of non-Gaussian Statistics in Geophysical Data

13 Nov. 2008

Anne Thompson

Penn. State

Dylan Jones

Insights into the Tropical Troposphere and Tropopause Layer from Ten Years of SHADOZ (Southern Hemisphere Additional Ozonesondes) - 1998-2007

6 Jan. 2009

Laura Pan


Michaela Hegglin

Concept of the Tropopause Revisited

12 Jan. 2009

Isla Simpson

Imperial College

Ted Shepherd

Solar influence on tropospheric circulation via the stratosphere

28 Jan. 2009

Phil Austin

Univ. British Columbia

Jahanshah Davoudi

Aerosol indirect effects: Hot or Cold?

2 Feb. 2009

John Worden


Robert Field

Insights into the water cycle using satellite measurements of water vapor isotopes from Aura TES

23 Feb. 2009

Tianjun Zhou

Chinese Academy of Sciences

Jane Liu

Understanding and Attributing East Asian Climate Change

16 Mar. 2009

Gang Chen


Paul Kushner

Quantifying the Eddy Feedback and the Persistence of Zonal Index in an Idealized Atmospheric Model

30 Mar. 2009

Ron Stewart

University of Manitoba

Marie-Eve Gagne

Precipitation In Our Canadian Winter

1 Apr. 2009

Beatriz Monge-Sanz

University of Leeds

Ted Shepherd

Data assimilation winds in the SLIMCAT chemistry-transport model: Stratospheric transport evaluation

13 Apr. 2009

Adam Sobel

Columbia University

Paul Kushner

Atmospheric Water Vapor: Some Studies of Mechanisms that Control It

15 Apr. 2009

Isaac Held


Ted Shepherd

Some variations on the theme of climate sensitivity

20 Apr. 2009

Seok-Woo Son

McGill University

Michael Sigmond

Southern Hemisphere Westerly Jets in the Future Climate: Interpretation with a Simple AGCM and Results of Chemistry-Climate Models

30 July 2009

3:30 pm

Stephen Griffiths

University of Leeds

Dick Peltier

Global Modeling of Ocean Tides

31 July 2009,

12:00 pm

Ralph Lehmann

Alfred Wegener Institute for Polar and Marine


Mareile Wolff

Two applications of chemical modelling: Calculation of ascent rates in the

tropical lower stratosphere and the automatic determination of catalytic

ozone production and destruction cycles

31 July 2009,

3:30 pm

Hiro Yamazaki

University of Oxford

Dick Peltier

Paleo-Data Constraints on Ensemble Climate Predictions

4 Aug. 2009,

12:00 pm

Colin Price

Tel Aviv University

Florian Nichitiu

Will a Drier Climate Result in More Lightning Activity



Speaker: Richard Dowden, Emeritus Professor of Physics

Institution: University of Otago, New Zealand

Title:  Global Lightning Location by VLF TOGA

When: Monday, September 15 2008 at 4pm.

Where: MP 408


Radio location of lightning, and lightning hazard prediction, over some developed countries is obtained by a high density of ground stations. Thus the US National Lightning Detection Network (NLDN) uses 100 ground stations to cover the 48 contiguous states (or about 10 million square km), with a corresponding ground station spacing of about 300 km. Cloud-to-ground lightning strokes are located by both the time of arrival (TOA) of the radio impulse and direction of its arrival using crossed loops (magnetic direction finding, or MDF). Both methods require line-of-sight (ground wave) propagation at light speed, avoiding all ionospheric reflections (sky waves). This is achieved by ignoring all but the first few microseconds of the radio impulse; thus excluding the sky wave which arrives later.


Such a system provides high accuracy (~1km), but to be commercial it needs wealthy customers to meet the costs of setup and operation. In our case we were initially engaged in lightning research in a sparsely populated area not covered by any location network, so we set up our own based on VLF propagation in the Earth-Ionosphere Wave Guide (EIWG).


Our system is similar in many ways to the global Omega Navigation System, now superseded by GPS. The essential difference being that the lightning strokes are the transmitters to be located, while the receiving stations are already known. The Omega system consisted of eight transmitters optimally placed around the world, each transmitting a set of eight frequencies in turn. To get your location the receiver measured the phases of all the VLF transmissions. The lightning impulse (officially named sferic by the International Union of Radio Science) is already very wide-band (ULF to optical), so we measure the rate of change of phase with respect to frequency: returning the time of arrival of the sferic in seconds. The pulse (sferic) propagates at the waveguide group velocity, so we call this the Time Of Group Arrival (TOGA).


Our system works (as did Omega) because VLF propagation in the EIWG is very stable and long range. It is also cheap to set up and run. In fact (once fully established) we intend to make it free for non-commercial use. The location accuracy is never worse than 10 km RMS.



Speaker: Meiyun Lin

Institution: University Wisconsin-Madison

Title:  Regional Atmospheric Chemistry in Asia

When: Wednesday, September 17 2008 at 4pm.

Where: MP 408


Atmospheric chemistry in Asia is strongly affected by local emissions, monsoon circulation, regional transport, and global pollution inflow. This work employs global and regional models, satellite observations, and ground-based data to distinguish the mechanisms controlling acid deposition, nitrate and sulfate aerosols, and tropospheric ozone (O3) throughout Asia. In evaluating tropospheric NO2 column, we found a more than 50% discrepancy between the Community Multiscale Air Quality (CMAQ) model calculated values and the GOME (Global Ozone Monitoring Experiment) satellite retrieval over industrial area of eastern China in March and December. The pronounced discrepancy is not only due to the uncertainty in the bottom-up emission inventory used in the model but also to the reliability of the GOME retrieval scheme. By using boundary conditions from the global Model for Ozone and Related Tracers (MOZART), the full chemistry CMAQ regional model estimated surprisingly high levels (10-40%) of sulfur imported to Asia from other parts of the world. Our most recent work examines the seasonal and diurnal variability of O3 in the boundary layer over Asia using the regional CMAQ model and recently available observational data including six sites in China and nine sites in Japan. We find that the seasonal cycle of simulated O3 in the boundary layer does not exhibit the observed sharp low-O3 drop in July and August that is evident in Beijing and at two mountain sites in central east China. In addition to model inability in simulating cloud activities and convective mixing as suggested by previous studies, our analysis suggest that the systematic overprediction of summertime O3 over central east China and central Japan are also attributed to the uncertainties in photochemical production of O3, inter-annual variability of monsoonal intrusion of low-O3 marine air masses during East Asian summer monsoon, and overprediction of nighttime O3 in urban and rural areas. Building on these past studies, we are now working with the Weather Research and Forecasting Model with Chemistry (WRF-Chem) and the Community Atmosphere Model with Chemistry (CAM-Chem) to examine how the regional processes such as surface driven convection, frontal activity, and land-sea breezes can affect the intercontinental transport of O3, carbon monoxide, aerosols, and other climate- and heath-relevant pollutants.



Speaker: Edwin Schneider

Institution: COLA / George Mason University

Title:  The role of weather noise in climate variability

When: Monday, September 22 2008 at 4pm.

Where: MP 408


A method has been developed to test the null hypothesis that low frequency surface climate variability in a coupled GCM is the response to weather noise forcing. The method also provides opportunities to better understand the mechanisms of simulated and observed climate variability. The method has two parts:

1) "Weather noise" surface fluxes are defined as the residual, after the feedbacks from the boundary evolution are removed from the total surface fluxes by AMIP-like AGCM ensemble simulations.

2) An interactive ensemble (IE) CGCM, in which a single OGCM is coupled to the mean of an ensemble of the AGCMs is then forced by this weather noise.

The IE CGCM will reproduce the observed SST evolution and the null hypothesis will be satisfied, except for errors in the model, the surface fluxes, and the ocean initial state, as long as there is no internal ocean “weather noise” or coupled instabilities. External forcing must also be taken into account. The method is applied both to understanding low frequency variability in CGCM simulations and to diagnosing the mechanisms of observed low frequency variability. Using the NCEP reanalysis surface fluxes and a state of the art coupled GCM, the observed North Atlantic low frequency SST evolution for the latter half of the 20th century can be simulated reasonably well, indicating that it is weather noise forced. Local heat flux weather noise forcing plays a major role. Ocean dynamics also has important effects on the SST evolution.


Speaker: Gloria Manney

Institution: Jet Propulsion Laboratory, California Institute of Technology

Title:  Trace Gas Evolution in Recent Satellite Datasets: Relationships to the Stratospheric Polar Night Jet, Upper Tropospheric Jets and the Tropopause

When: Monday, September 29 2008 at 4pm.

Where: MP 408


A method has been developed for categorizing the location and characteristics of upper tropospheric jets and of the lower reaches of the stratospheric polar night jet that extends into the upper troposphere/ lower stratosphere (UTLS). This method is applied to define the position, width and dynamical characteristics (e.g., windspeed/direction, potential vorticity, temperature, static stability, etc) of the primary subtropical jet (STJ) core, as well as similar information on multiple jets in the extratropical (ET) UTLS. The polar night jet in the UTLS is characterized at each level by its position, width, and dynamical characteristics. Jet characteristics during quasi-isentropic stratosphere-troposphere exchange (STE) events and seasonal evolution of jet structure are investigated in Goddard Earth Observing System Version 5 (GEOS-5) and other meteorological analyses. Satellite trace gas measurements from several current instruments, including the Aura Microwave Limb Sounder (MLS), Atmospheric Chemistry Experiment-Fourier Transform Spectrometer (ACE-FTS) and the Aura High Resolution Dynamics Limb Sounder (HIRDLS), are studied to further our understanding of the seasonal evolution ET-STE events in relation to the STJ and the tropopause.


Speaker: Qinbin Li

Institution: University of California, Los Angeles

Title:  What can we learn about upper tropospheric CO2?

When: Monday, October 20 2008 at 4pm.

Where: MP 408


It is generally assumed that upper tropospheric CO2 exhibits little variability. We present clear evidence to the contrary. Our analysis centers on CO2 mixing ratios from Atmospheric Infrared Sounder (AIRS) retrievals. The AIRS middle to upper tropospheric (~500-300 hPa) CO2 data show unequivocally large spatial and temporal variability in the northern mid-latitudes in summer. For example, there is a 2-3 ppmv longitudinal gradient in the CO2 concentrations across North America in July. Aircraft in situ observations from the COBRA and ICARTT campaigns support such large variability. In addition to the surface sources/uptakes, the distributions of AIRS CO2 are modulated by large-scale circulation such as the mid-latitude jet streams in both hemispheres and by synoptic weather systems including the warm conveyor belt. How well can chemistry and transport models(CTMs) simulate upper tropospheric CO2 including its seasonal cycle and trend? Is there a semi-annual cycle in upper tropospheric CO2, and if so, what are the controlling processes? These questions and the impact of stratospheric sudden warming on polar upper tropospheric CO2 will also be addressed in this talk.


Speaker: Tim Palmer

Institution: European Centre for Medium-Range Weather Forecasts

Title:  Seamless prediction of weather and climate

When: Wednesday, October 22 2008 at 4pm.

Where: MP 408


"Seamless Prediction" has become a bit of a buzz-phrase in the last year or so, and it probably means different things to different people. Here I use the phrase to invoke the objective of bringing insights and constraints from numerical weather prediction into the climate-change arena. I will offer three examples of the potential of seamless prediction. The first is where 6-hour weather forecasts have been used to constrain significantly the probability distributions of climate sensitivity (to doubling of CO2). The second is the use of diagnostics on the reliability of seasonal forecast multi-model ensembles to calibrate regional predictions of precipitation climate change. The third is the use of stochastic parametrisations in numerical weather prediction models as the basis of next-generation Probabilistic Earth Systems Models.


Speaker: Michael Gausa and Kolbjorn Dahle

Institution: Andoya Rocket Range, Norway

Title:  The ALOMAR Observatory and Andoya Rocket Range

When: Thursday, October 23 2008 at 11am.

Where: MP 606


ALOMAR, the Arctic Lidar Observatory for Middle Atmosphere Research is a research facility initiated for a special height region. Since the introduction one and a half decade ago, ALOMAR has developed into a modern and international recognized research facility. ALOMAR is part of the Andøya Rocket Range, the northernmost launch site for scientific sounding rockets and balloons. ALOMAR hosts a variety of remote sensing instruments operated by groups from the US, Canada, Japan and five European countries, and has several times received funding from the EU commission’s excellence programmes for infrastructures. ALOMAR’s location at high latitude (69N) gives rise to topical scientific questions in all atmospheric layers. The present talk will introduce some of these topics and show how the participating international scientists gain through the synergy generated by the set of instruments located at ALOMAR. Synergy is not only gained through co-location of different instruments, investigating in the same height region; co-operation across the atmospheric layers can achieve snap shots of physical atmosphere properties from ground to the ionosphere. The proximity to the Rocket Range and the local airport (3.2km runway) offers unique opportunities for large scale ground based, air- and rocket-borne atmosphere studies.


Speaker: Prashant D. Sardeshmukh

Institution: CIRES, University of Colorado

Title:  An interpretation of non-Gaussian Statistics in Geophysical Data

When: Monday, October 27 2008 at 2pm.

Where: MP 408


The statistics of climate variables are often found to be non-Gaussian, and this fact is often attributed to non-linear dynamics. Nonetheless, we find that many features of the non-Gaussian statistics can also be reconciled with linear dynamics that are stochastically perturbed. A mixture of stochastic noises whose amplitudes are either system state-independent ("additive noise") or linearly state-dependent ("multiplicative noise") can produce not only systematic but also skewed non-Gaussian probability distributions if the additive and multiplicative noises are correlated. Furthermore, one expects such correlations from first principles. A generic stochastically generated skewed (SGS) distribution can be analytically derived from the Fokker-Planck equation for a single-component system. In addition to skewness, all such SGS distributions have power-law tails, and a striking property that the kurtosis K is always greater than 1.5 times the square of the skew S. Remarkably, this K-S inequality is found to be satisfied by circulation variables even in the observed multi-component climate system. This can be understood in terms of a principle of "Diagonal Dominance" in the equations for the higher statistical moments of mutli-component linear systems.


To clarify the nature of the stochastic noises (turbulent adiabatic versus diabatic fluctuations) responsible for the observed non-Gaussian statistics of atmospheric flows at the jet stream level, a long 1200-winter simulation of the northern winter climate is generated using an adiabatic atmospheric general circulation model forced only with the observed long-term mean diabatic forcing as a constant forcing. Despite the complete neglect of diabatic variation, the model reproduces the observed K-S relationships, and also the spatial patterns of the skewness and kurtosis of the daily vorticity variations at the jet stream level. This suggests that the stochastic generators of these higher moments of vorticity are mostly associated with local adiabatic turbulent fluxes. The model also simulates fifth moments that are approximately 10 times the skewness, and probability densities with power-law tails, as predicted by the remarkably simple linear theory.


Speaker: Anne Thompson

Institution: Penn. State

Title:  Insights into the Tropical Troposphere and Tropopause Layer from Ten Years of SHADOZ (Southern Hemisphere Additional Ozonesondes) - 1998-2007

When: Thursday, November 13 2008 at 2pm.

Where: MP 408


Speaker: Laura Pan

Institution: NCAR

Title:  Concept of the tropopause revisited

When: Monday, January 6 2009 at 4pm.

Where: MP 606

The tropopause is an important physical boundary in the atmosphere and a

much watched climate change indicator. The behavior of the tropopause as a

transport boundary between the stratosphere and the troposphere has been an

ongoing research topic. This talk will focus on the extratropical

tropopause.  The history and the concept of the 3 existing models of the

extratropical tropopause, i.e., the thermal, the dynamical tropopause and

the extratropical transition layer, ExTL, will be reviewed. These models

are examined, using new aircraft and satellite observations, for how well

they represent the discontinuities, or the lack of, in the air mass. The

investigations reveal the relationship of the tropopause definitions and the

transport pathways between the stratosphere and troposphere. In particular,

these issues will be discussed using recent observations on NCAR research

aircraft HIAPER during the Stratosphere-Troposphere Analyses of Regional

Transport experiment in 2008 (START08).


Speaker: Isla Simpson

Institution: Imperial College

Title:  Solar influence on tropospheric circulation via the stratosphere

When: Monday, January 12 2009 at 4pm.

Where: MP 606


There is increasing evidence that changing solar activity over the 11-year

solar cycle influences the Earth's climate. However, as yet the mechanisms

involved remain uncertain. With the now widely accepted view that there is

a two way dynamical coupling between the stratosphere and troposphere, a

possible explanation for the tropospheric response to solar activity is

through a dynamical response to the larger heating that occurs in the



A weakening and poleward shift of the mid-latitude jets along with a

weakening and expansion of the Hadley cells and a poleward shift of the

Ferrell cells is found at solar maximum compared to solar minimum in the

observations. This is accompanied by a banded increase in temperature in

the mid-latitudes. Previous results using a simplified general circulation

model (GCM) have demonstrated that a similar response to that seen over the

solar cycle can be produced by simply heating the lower stratosphere in the

equatorial region.


Spin-up ensemble experiments using this simplified GCM have now been used to

further investigate the mechanisms by which altered stratospheric heating

can produce tropospheric circulation changes. Results suggest that changes

in eddy momentum flux are important in producing the response.

Investigations using the quasi-geostrophic index of refraction have shown

that the change in vertical temperature gradient around the tropopause is

primarily what influences eddy propagation to initially trigger the

response. Furthermore, there is a feedback with zonal wind changes in the

troposphere influencing eddy propagation there.


Speaker: Phil Austin

Institution: University of British Columbia

Title:  Aerosol indirect effects: Hot or Cold?

When: Wednesday, January 28, 2009 at 3pm.

Where: MP 606


The impact of aerosols on clouds and climate is often represented by two pathways that assume: i) increasing aerosol concentrations reduce cloud droplet size and increase cloud reflectivity (the Twomey effect) while ii) reducing collision-coalescence and decreasing precipitation (the lifetime effect). Both of these effects are presumed to exert a negative radiative forcing on the atmosphere, with an average impact in global climate models of more than -1 W/m^2.


Modelling and observational work by many investigators has added a wide variety of additional cloud-aerosol interactions to this pair, including aerosol-induced changes to boundary layer stability and large-scale boundary layer circulations that in turn effect cloud liquid water path and rain rate, introducing significant new uncertainties to the calculation of aerosol indirect forcing. I will present a new technique to retrieve cloud droplet size, cloud thickness and their uncertainties from nighttime satellite imagery, and show how it might be used to constrain some of these cloud/aerosol interactions.


Speaker: John Worden

Institution: Jet Propulsion Laboratory

Title:  Insights into the water cycle using satellite measurements of water vapor isotopes from Aura TES

When: Monday, February 2, 2009 at 4pm.

Where: MP 606


Water Isotopes are useful measurements for estimating the sources and processes controlling the hydrological balance in the atmosphere and on or in the earth because lighter isotopes preferentially evaporate, heavier isotopes preferentially condense, and the isotopic composition of the primary water source, the ocean, is well known. In this talk I discuss the remote sensing of tropospheric concentrations of water vapor and its isotopes using new space based infrared measurements from the Tropospheric Emission Spectrometer. I will then discuss some recent applications of these measurements such as estimating the balance of moist processes controlling hydrology over tropical regions and estimating evaporation and condensation strengths.


Speaker: Tianjun Zhou

Institution: Chinese Academy of Sciences

Title:  Understanding and Attributing East Asian Climate Change

When: Monday, February 23, 2009 at 4pm.

Where: MP 606


Associated with the regime shift of global climate system around the late 1970s, East Asian climate has experienced an inter-decadal transition. Summer precipitation has increased in central eastern China along the middle and lower reaches of Yangtze River valley, whereas it has decreased in North China. In the mean time, against the surface warming elsewhere, a surface cooling has been observed over central eastern China. There are controversies in the mechanisms responsible for the observed change. Recent work of the authors' group demonstrates the dominance of large scale circulation change on the regional scale East Asian climate change. This presentation will summarize the authors’ progresses in understanding and attributing East Asian climate change. A significant interdecadal cooling with vivid seasonality and three-dimensional structure is revealed in the upper troposphere and lower stratosphere over East Asia. The seasonally-dependent upper tropospheric cooling leads to a clear seasonality of interdecadal changes in the atmospheric general circulation and precipitation against their normal seasonal cycle over East Asia. Possible causes for the robust interdecadal change are discussed. Some model results supporting the proposed mechanism will be presented, including a set of Indo - Pacific Ocean forcing experiments, global and tropical sea surface temperature forcing experiment, CLIVAR C20C experiments and WCRP CMIP3 experiments.


Speaker: Gang Chen

Institution: Massachusetts Institute of Technology

Title:  Quantifying the Eddy Feedback and the Persistence of Zonal Index in an Idealized Atmospheric Model

When: Monday, March 16, 2009 at 11am.

Where: MP 408


An idealized atmospheric model is used to examine what determines the strength of the eddy feedback and the persistence of zonal index. The strength of the surface frictional damping on the zonal index is varied, and an external zonal momentum forcing is included to compensate for the momentum change associated with the friction change so as to keep the climatological jet latitude and shape.


The model can generate a nearly identical climatology and leading mode of the zonal mean zonal wind for different frictional damping rates, except when the jet undergoes a regime transition. As the surface friction is increased, the strength of eddy feedback is enhanced, but the zonal index becomes less persistent. A simple feedback model suggests that the e-folding decorrelation time scale of zonal index can be determined by the frictional damping rate and the strength of eddy feedback. The strength of eddy feedback is found to be related to the instantaneous vertical wind shears near the surface controlled by the frictional damping. Accordingly, the lagged regression with respect to the zonal index shows that the eddy heat flux responds roughly linearly to the magnitude of surface meridional temperature gradient. Furthermore, the climate response to an external zonal torque is found to be proportional to the decorrelation time scale, although our simple prediction overestimates the climate response by a factor of two.



Speaker: Ron Stewart

Institution: University of Manitoba

Title:  Precipitation in our Canadian winter

When: Monday, March 30, 2009 at 11am.

Where: MP 606


The issue of precipitation continues to be one of the key issues for both weather and climate. A great deal of progress has been made in understanding its formation although the emphasis has been on rain and hail and, to a lesser extent, snow. What about the other types of precipitation that we experience in Canada such as wet snow, freezing rain and ice pellets? These precipitation types bring misery each year to all parts of the country but little research has actually focussed on them.  This presentation will discuss some of the fundamental aspects of this precipitation including its occurrence, morphology, formation and organization within winter storms. Even though progress is being made, we are still a long way from understanding all the features of this fascinating precipitation.


Speaker: Beatriz Monge-Sanz

Institution: University of Leeds

Title:  Data assimilation winds in the SLIMCAT chemistry-transport model: Stratospheric transport evaluation

When: Wednesday, April 1, 2009 at 4pm.

Where: MP 606


The accuracy of the stratospheric transport provided by meteorological analyses is crucial for off-line chemistry transport models (CTMs) to produce realistic distributionsof tracers. However, stratospheric CTMs driven by most existing (re)analyses are known to produce too young age-of-air distributions, i.e. they overestimate the stratospheric circulation,and produce excessive subtropical mixing.


In this study the TOMCAT/SLIMCAT CTM has been used to evaluate different stratospheric (re)analyses from the European Centre for Medium-Range Weather Forecasts (ECMWF), including experimental datasets from the ERA-Interim preparatory phase, to assess how the newer analyses compare with previous ones (e.g. ERA-40 or U.K. Met Office). This work has revealed CTMs as powerful tools for evaluating meteorological datasets, and information from our investigations fed into the final set-up for the ERA-Interim reanalysis production.


Various transport diagnostics have been calculated to assess the Brewer-Dobson circulation and mixing processes in the different datasets. Problems detected in the past for ERA-40 have been greatly overcome in the recent ECMWF reanalysis tests and ERA-Interim, which provide realistic age-of-air in the lower stratosphere, and better overall agreement with observations. The use of there more realistic stratospheric (re)analyses result into more accurate tracers distributions and trends being obtained by the CTM.


Causes for the improvements in the (re)analyses have also been explored, revealing theroles that some aspects of the assimilation technique play in the description of stratospheric transport. The effect of different frequencies for the winds update in the CTM is also discussed. Results show there is a threshold to the analysis frequency CTMs can use to correctly simulate stratospheric transport. In particular, the use of 12 hourly winds results in very unrealistic transport in the stratosphere. Some transport deficiencies attributed in the past to the use of ECMWF DAS winds in CTMs appear to be due to the use of unsuitable too long update frequencies. The effect of different (re)analysis read-in frequencies is further explored with reanalysis data from the Canadian Middle Atmosphere Model (CMAM), which enable a clean comparison of trajectories obtained with 3-hourly and 6-hourly atmospheric data.


Speaker: Adam Sobel

Institution: Columbia University

Title: Atmospheric Water Vapor: Some Studies of Mechanisms that Control It

When: Monday, April 13, 2009 at 4:10pm.

Where: MP 606


I will present two studies with numerical models which address two different aspects of the physics controlling atmospheric water vapor. In the first, we disable all evaporation of condensate in an atmospheric GCM while holding the circulation fixed to that of a control simulation. The difference between the resulting humidity distribution and that of the control case can be viewed as giving us an upper bound (according to this model) on the importance of cloud and precipitation microphysics for atmospheric water vapor. In the second, we focus on the role of large-scale advection and condensation, using "tracers of last saturation" in an offline transport model driven by reanalysis data. These tracers allow us to diagnose the pathways by which air with low relative humidity is produced by tracing it back to the locations at which it was last saturated. We find that the dry air at lower and midlevels in the subtropics was to a large extent last saturated in the regions of the midlatitude jets, rather than in the outflow of the tropical deep convective regions, indicating that baroclinic eddies rather than the Hadley circulation are most directly responsible for the dryness of the subtropics.


Speaker: Isaac Held

Institution: NOAA Geophysical Fluid Dynamics Laboratory, Princeton, USA

Title:  Some variations on the theme of climate sensitivity

When: Wednesday, April 15, 2009 at 11:10am.

Where: MP 606


Several aspects of climate feedback analysis and the use of simple models to analyze observational constraints on climate sensitivity will be discussed.


Speaker: Seok-Woo Son

Institution: McGill University

Title:  Southern Hemisphere Westerly Jets in the Future Climate: Interpretation with a Simple AGCM and Results of Chemistry-Climate Models.

When: Monday, April 20, 2009 at 4:10pm.

Where: MP 606


The spatial structure of the Southern Annular Mode (SAM) shows a remarkable resemblance to that of the recent and future circulation changes in the southern extratropics. By integrating a series of simple dry AGCM, we examine to what extent the annular-mode-like internal variability projects onto the climate change. A wide range of parameter study shows that climate change is not necessarily projected onto the annular mode. It suggests that the projection of Southern Hemisphere climate change onto the SAM could be a coincidence.


The future trend in Southern Hemisphere westerlies are further examined with SPARC/Chemistry-Climate Model Validation (CCMVal) and IPCC/AR4 model output. It is found that, owing to the disappearance of the ozone hole in the 21st century, the CCMVal models predict deceleration of westerlies in southern high latitudes, or negative trend of the SAM index, in stark contrast to the IPCC/AR4 models. This result suggests that stratospheric ozone should be more carefully taken into account in the climate model integrations.



Speaker: Stephen Griffiths

Institution: University of Leeds

Title:  Global Modeling of Ocean Tides

When: Thursday, July 30, 2009 at 3:30 pm.

Where: MP 606

Abstract: A longstanding challenge in oceanography is the production of accurate global maps of the amplitude and phase of the ocean tides, from simple hydrodynamical equations with appropriate astronomical forcing and global topography. Over the last forty years, such prognostic models have improved in accuracy, partly due to increases in computing power, but also as the role of supposedly secondary physical processes have been recognised. Here, the development of a new prognostic global tidal model is described. Special emphasis is placed upon accounting for an internal-tide drag in a physically consistent way, which is achieved via explicit modeling of small-scale internal waves. Having demonstrated the integrity of this model by comparison with data-constrained tidal models, we use it to predict the form of the tides during the last Ice Age, when the ocean depth and coastal configuration were quite different to those of today.


Speaker: Ralph Lehmann

Institution: Alfred Wegener Institute for Polar and Marine Research

Title:  Two applications of chemical modelling: Calculation of ascent rates in the tropical lower stratosphere and the automatic determination of catalytic ozone production and destruction cycles

When: Friday, July 31, 2009 at 12:00 pm.

Where: MP 606

Abstract: The presentation gives examples for the gain of information arising from the combination of observations and a chemical model (A) and the application of an additional algorithm to better understand the complex interactions in the chemical model (and also in the atmosphere) (B):


A) Mean ascent rates of air in the tropical lower stratosphere are

calculated from the combined information on vertical gradients and temporalvariations of ozone mixing ratios, supplied by ozonesondes, and the rate ofchemical ozone production, calculated by a chemical model. This providesestimates independent from conventional methods, that are based on thecalculation of radiative heating rates or the analysis of the verticaltransport of chemically inert tracers (e.g., the water vapour "taperecorder"). The dependence of the ascent rates on the phase of theQuasi-Biennial Oscillation (QBO) is investigated in more detail.


B) An algorithm for the automatic determination of reaction pathways, e.g.catalytic cycles, in complex chemical reaction systems is presented.The algorithm was applied to analyse output from a chemical box model thathad been initialised by a three-dimensional chemistry-climate model. It wasused to determine catalytic production and destruction cycles of ozone inthe stratosphere and mesosphere. The dominant ozone destruction cycles atdifferent altitudes in the atmosphere belong to the following families: HOx(lower stratosphere: tropics, mid latitudes), ClOx and BrOx (lowerstratosphere: polar spring), NOx and ClOx (upper stratosphere), HOx(mesosphere).



Speaker: Hiro Yamazaki

Institution: University of Oxford

Title:  Paleo-Data Constraints on Ensemble Climate Predictions

When: Friday, July 31, 2009 at 3:30 pm.

Where: MP 606

Abstract: We use a simple energy balance model and discuss a way to improve probabilistic climate predictions by employing paleoclimate data for the last millennium. We will also discuss, an internet-wide distributed computing framework that allows large-ensemble GCM experiments to be performed.


Speaker: Colin Price

Institution: Tel Aviv University

Title:  Will a Drier Climate Result in More Lightning Activity?

When: Tuesday, August 4, 2009 at 12:00 pm.

Where: MP 606

Abstract: With recent projections of a warmer climate in the future, one of the key questions is related to the impact of global warming on thunderstorms, and severe weather. Will lightning activity increase in a warmer world? Since the majority of global lightning activity occurs in the tropics, changes in future global lightning activity will depend on changes in the tropical climate. The latest IPCC (2007) projections show a partial drying out of the tropical landmasses as the global climate gets warmer. This is caused by both changes in rainfall patterns, but also due to increases in evapo-transpiration. We would expect a drier climate to produce fewer thunderstorms, and less lightning. However, experimental and modeling studies have shown that as tropical regions dry in the present climate, they experience greater lightning activity. This paradox may be explained by noting that while drier climate conditions result in fewer thunderstorms and less rainfall, the thunderstorms that do occur are more explosive, resulting in more lightning activity.