Where and when

Seminars are held in room 408 or 606 of the McLennan Laboratories at 4:10pm on Mondays unless otherwise noted. Coffee and cookies are provided at 3:45pm. A short abstract for the forthcoming talk will be circulated at the beginning of each week. Each seminar is 45-50 minutes, with 5 to 10 minutes for questions.

Upcoming seminars

When: December 14, 2009, 11:00 am
Where: MP 505 (note the special time and room)
Presenter: Gerard Thuillier
Title: The PICARD Mission: an investigation based on measurements dedicated to solar and climate modeling
Abstract:

PICARD is a satellite mission dedicated to the understanding of the solar activity origin and its consequences for the Earth's climate. The measurements are the total and spectral solar irradiance, solar diameter, limb shape, solar asphericity, and helioseismic waves, which are all critical inputs for solar physics modeling. To carry out this program, the PICARD team develops models of the solar convective zone and of Earth's climate, which are especially tailored to allow for variable solar irradiance. The measurements will be carried out by two absolute radiometers, sunphotometers, and a metrological imaging telescope onboard a microsatellite built by the French Space Agency CNES, with launch foreseen for February 2010. The radiometers are similar to the ones on board SOHO. The imaging telescope contains an angular reference allowing a permanent control of the instrument metrological characteristics, which are ultimately referred to angular stars distances. Optical distortion and flatfield of the imaging telescope are regularly measured. The measurements carried out by the sunphotometers and the imaging telescope use the same wavelengths, and are synchronized with the radiometric measurements. Furthermore, with the space measurements, several other measurements will be carried out: i) solar diameter measured on the ground revealing inconsistent variations with solar activity, to understand the role of the Earth'atmosphere, ground-based instruments will be also run during the mission allowing PICARD to extent its domain of interest toward atmospheric physics. ii) for extending the observations after the space mission, measurements from a stratospheric balloon have been initiated by a successful flight on 17 October 2009. iii) the technique of measuring the limb shape using sun eclipse by the moon, is foreseen as well as by using the transit method. The design of the instruments will be presented as well as the state of development of the mission, and the expected performances.

Seminar Schedule for 2009/2010

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Previous Seminars

When: October 5, 2009
Presenter: Frédéric Laliberté
Title: Identifying eddies in the moist Isentropic Circulation
Abstract:

I will discuss fundamentals of the meridional overturning circulation in moist coordinates as described in Pauluis et al. (2008) and show how one can use it to identify moist baroclinic eddies. These moist eddies can be quantified and their thermodynamical properties retrieved, allowing one to investigate how the strength and energy transport ability of these eddies change across seasons and under climate change.

When: October 22, 2009
Presenter: Carl Wunsch
Title: Ocean variability from days to decades. The challenges
Abstract:

A quantitative description in frequency and wavenumber of oceanic variability has many applications, ranging from designing sampling schemes, determining the significance of apparent trends, and the test of numerical models. Surprisingly little is known about variability at periods beyond a few months. This talk will sketch a first attempt at describing the complete spectrum of variability and outline the challenges of rendering it complete and useful.

When: October 26, 2009
Presenter: Matthias Schneider
Title: The ground-based FTIR network's potential for investigating water transport patterns
Abstract:

Water is a key player in climate change since upper tropospheric water vapour amounts widely control the Earth's radiative balance. However, the dynamic and microphysical processes determining upper tropospheric water vapor amounts are not well understood. The existence of different stable water isotopologues (most importantly H₂¹⁶O, H₂¹⁸O, H₂¹⁷O, and HD¹⁶O) offers a unique opportunity for investigating these processes.
The first part of the talk will briefly review the development of a ground-based FTIR water vapour profile analysis algorithm. The most important features of the algorithm are: a fit of a variety of different water vapour lines with different strength, a logarithmic scale inversion, a speed dependent Voigt line shape model, and a joint temperature profile inversion. The logarithmic scale inversion allows for introducing an interspecies constraint between HD¹⁶O and H₂¹⁶O and consequently for an optimal estimation of HD¹⁶O/H₂¹⁶OH profiles.
The second part will document the potential of the H₂¹⁶O and HD¹⁶O/H₂¹⁶O profile data for investigating water transport patterns. Therefore the FTIR measurements of a northern hemispheric high and low latitude site are compared with an isotope incorporated atmospheric general circulation model (AGCM). For an AGCM with reasonable dynamics (achieved by nudging towards reanalysis wind and temperature fields) the agreement is very satisfactory on time scales ranging from daily to inter-annual, which documents the good quality of the ground-based FTIR data. For the low latitude site the Hadley circulation is very important. The measurements reveal a strong connection between the subtropical middle/upper troposphere and the tropical upper troposphere, but also that the transport pathways are affected by the Northern Atlantic Oscillation (NAO). At the high latitude site the FTIR data demonstrate that the water transport to the lower troposphere is correlated with the Arctic Oscillation (AO) and that the transport to the middle/upper troposphere is correlated with the northern Atlantic sea surface temperature.

When: November 2, 2009
Presenter: Dargan Frierson
Title: Latent Heating and the General Circulation in a Hierarchy of GCMs
Abstract:

Latent heating is a dominant term in the energy budget of the atmosphere in the tropics and extratropics alike: for instance, approximately half of the poleward heat transport by the climate system in midlatitudes is accomplished by moisture fluxes. Since we expect the moisture content of the atmosphere to increase rapidly with global warming, understanding of moisture effects on the general circulation can be useful for interpreting simulations of global warming. We describe a hierarchy of GCMs that we have used to study this problem, ranging from models with highly simplified physical parameterizations, to fully coupled climate models. We present some recent results using these models on the effect of moisture on the midlatitude static stability, the poleward transport of energy, the response of the tropics to extratropical forcing, and the position of the jet streams.

When: November 30, 2009
Presenter: Alan Plumb
Title: Annular modes and the dynamical response of the extratropical atmosphere to climate perturbations.
Abstract:

The so-called “annular modes” are the leading modes of variability of the extratropical atmosphere. Aside from their importance in this “natural” variability, they have attracted attention because of evidence from observations and models that, like true modes, they also represent the preferred response of the atmosphere to perturbations such as those associated with greenhouse warming and ozone depletion. This property can be understood from the fluctuation-dissipation theorem, which can give quantitative predictions of the response to a given forcing. I will describe our attempts to understand results of model experiments from this perspective.

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