Events

CliMathNet seminar: Dew Droplets and Cloud Droplets - Droplet Growth, Size Distributions, and Corrections to Scaling

Oct
25
Fri 2013

16:00 - 17:00

CliMathNet seminar: A Simple Conceptual Framework for Stratosphere Troposphere Coupling

Oct
22
Tue 2013

16:00 - 17:00

Hosted by University of Exeter.

At mid-to-high latitudes, the stratosphere contains >25 percent of the column of atmospheric mass. Large-scale vertically-propagating waves alter the strength of the stratospheric polar vortex and drive a synchronised meridional circulation. These stratospheric changes are associated with substantial effects on surface weather and climate, especially on the Northern and Southern Annular Modes (NAM, SAM) and associated long-lasting shifts in the jet streams, storm tracks, pre- cipitation, and likelihood of blocking events. Despite unambiguous observations of this phenomenon, as well as numerical simulations, the primary dynamics of this downward coupling are not understood. I will show that the meridional circulation extends below the tropopause, modulating the day-to-day thickness of the troposphere, especially at high northern latitudes. The vertical displacement of the polar air column acts like a plunger controlling the movement of water in a pipe. The return flow in the troposphere is also synchronised to the strength of the polar vortex. I will make the case that the altered meridional circulation acts as a trigger for tropospheric eddy feedbacks. This conceptual framework predicts surface pressure variations similar to the NAM, and linear variation of tropospheric phenomena with the strength of the polar vortex. The results point to the importance of the Arctic tropopause layer for assessing the fidelity of stratosphere– troposphere coupling in climate and weather forecast models.

Quantum Mechanics and Topology

Oct
8
Tue 2013

15:00 - 16:00

Organised by Prof Jitesh Gajjar.

Hosted by University of Manchester.

Abstract: I will give a gentle introduction to some deep and important quantum phenomena associated with topology. The first is the Aharonov-Bohm effect, and the second is quantum statistics for identical particles. No prior knowledge of quantum mechanics will be assumed. I will go on to discuss some new work on quantum statistics in discrete spaces associated with recent developments in characterizing their topology.

CliMathNet seminar: Multiscale Methods for the Multiscale Environment of Climate Simulation

Jul
16
Tue 2013

16:00 - 17:00

Hosted by University of Exeter.

To combine high resolution atmospheric flow models with state-of-the-art data assimilation and statistical analyses is one of the biggest current challenges for numerical weather and climate prediction. In this talk we will show how hierarchical multiscale or multilevel methods can be designed to tackle this challenge. They are essential as scalable PDE solvers for individual simulations, but their biggest potential lies in accelerating standard Monte Carlo (or ensemble-type) methods for statistical analyses and for data assimilation, including Markov chain Monte Carlo methods which are of great interest also in the atmospheric sciences. Monte Carlo methods are notorious for their slow convergence and high computational cost. In this talk we will present revolutionary recent developments to mitigate and overcome this serious problem using novel multilevel strategies that can lead to a more than 100-fold acceleration of existing ensemble-type methods. The talk will focus on methodology. Most of the applications are so far mainly coming from subsurface flow.

CliMathNet e-seminar: Inclusion of Linearized Moist Physics in NASA's Goddard Earth Observing System Data Assimilation Tools

Jul
12
Fri 2013

14:00 - 15:00

Hosted by University of Exeter.

Variational data assimilation techniques in numerical weather prediction make use of the tangent linear and adjoint versions of the weather forecast model. Inclusion of the moist atmospheric processes, such as convection and precipitation, in the linear model is highly beneficial. Doing so allows the sensitivity to moisture to be effectively measured and enables the assimilation of observations of clouds and precipitation. However, the schemes developed to model the so called `moist physics' do not generally behave in a linear way. Many of the processes being represented are inherently nonlinear and artificial switches in the numerics are commonplace. Here we show a how the Jacobian, with various perturbation structures, can be used for analysing the linearity and stability for a given scheme. Using this method, linearised versions of the in situ moist physics schemes are developed and implemented in NASA's GEOS-5 data assimilation tools. The benefits of including moist physics are shown through observation impact experiments and in sensitivity studies.

AG Dynamics Seminar: Symbolic Toolkit for Exploration of Deterministic Chaos

Jun
4
Tue 2013

16:00 - 17:00

Hosted by University of Exeter.

Computational technique based on the symbolic description utilizing kneading invariants is proposed for exploration of parametric chaos in three exemplary systems with the Lorenz attractor: the canonical model itself, a normal model from mathematics, and a laser model from nonlinear optics. The technique allows for uncovering the stunning complexity and universality of the patterns discovered in the bi-parametric scans of the given models and detects their organizing centers: codimension-two T-points and separating saddles. This work is joint with Tingli Xing and Roberto Barrio.

CliMathNet Seminar: Data assimilation and modelling the carbon cycle

May
28
Tue 2013

16:00 - 17:00

Hosted by University of Exeter.

In the first part of this talk (Aston), we describe the qualitative behaviour of one of the simplest car- bon cycle models, the Data Assimilation Linked Ecosystem Carbon (DALEC) model, which is a simple vegetation model of processes involved in the carbon cycle of forests. We review the dynamical structure of the model. Our analysis shows that the dynamics of both evergreen and deciduous forests in DALEC are dependent on a few key parameters and it is possible to find a limit point where there is stable sustainable behaviour on one side but unsustainable conditions on the other side. The fact that typical parameter values reside close to this limit point highlights the difficulty of predicting even the correct trend without sufficient data and has implications for the use of data assimilation methods.
In the second part of the talk (Delahaies), will review techniques from four-dimensional variational data assimilation applied to DALEC. Using synthetic flux tower measurements together with a linearization of DALEC model, we show that the assimilation problem is highly ill-posed, and that parameters related to slow processes are not observable. We study the impact of regularization methods (TSVD, Tikhonov, and random Gaussian matrices) on the quality of the analysis and on the reduction of the uncertainty.

AG Dynamics seminar: Stick-Slip Transition in a Model with Dry Friction

May
14
Tue 2013

16:00 - 17:00

Organised by Professor Alastair Rucklidge.

Hosted by University of Leeds.

A consistent theoretical description of friction is certainly one of the most challenging topics nature has still in stock. While talk won't contribute to this fundamental issue, we rather analyse a simple phenomenological model. In particular, we will focus on the impact of stochastic forcing on dry friction and the associated stick-slip transition. Analytical solutions of the Fokker-Planck equation and of the corresponding eigenvalue problem will be presented, uncovering the dynamical phenomena in this piecewise smooth stochastic model.

CliMathNet Seminar: Sensing the natural world

Apr
30
Tue 2013

16:00 - 17:00

Hosted by University of Exeter.

Grand environmental challenges are spread across a host of different environmental media and issues including climate change, carbon in soils, water and air, water quality and quantity, air pollution, transport and the urban environment, radioactivity, biodiversity and landscape fragmentation. Grand technology issues include: development of sensors able to measure pollutants such as pm2.5, nitrates, novel organic compounds (e.g. pharmaceuticals) at environmental levels (such as ppb), integration and synthesis of observations from a variety of sensor networks, development of statistical models to handle large data sets and visualisation and communication challenges. Improvements in monitoring impact will significantly enhance our ability to detect and attribute change (in the presence of considerable natural variability). In this presentation, I will consider a variety of environmental change situations and think about the distinguishing statistical techniques that are needed.

MAGIC058: Theory of partial differential equations.

Apr
19
Fri 2013

12:05 - 12:55

Organised by Dr David Harris.

Hosted by University of Manchester.

MAGIC course lecture to replace cancelled lecture.

MAGIC058: Theory of partial differential equations.

Apr
15
Mon 2013

09:05 - 09:55

Organised by Dr David Harris.

Hosted by University of Manchester.

MAGIC course lecture to replace cancelled lecture.

MAGIC062: Introductory Functional Analysis

Apr
12
Fri 2013

14:05 - 14:55

Organised by Prof John Pryce.

Hosted by Cardiff University.

MAGIC course lecture to replace cancelled lecture.

MAGIC062: Introductory Functional Analysis

Apr
12
Fri 2013

11:05 - 11:55

Organised by Prof John Pryce.

Hosted by Cardiff University.

MAGIC course lecture to replace cancelled lecture.

MAGIC062: Introductory Functional Analysis

Apr
11
Thu 2013

14:05 - 14:55

Organised by Prof John Pryce.

Hosted by Cardiff University.

MAGIC course lecture to replace cancelled lecture.

MAGIC062: Introductory Functional Analysis

Apr
11
Thu 2013

11:05 - 11:55

Organised by Prof John Pryce.

Hosted by Cardiff University.

MAGIC course lecture to replace cancelled lecture.