# Publications

## ASPECTS OF STRATOSPHERIC SUDDEN WARMINGS STUDIED FROM A TRANSFORMED EULERIAN-MEAN VIEWPOINT

JOURNAL OF GEOPHYSICAL RESEARCH-OCEANS **86** (1981) 9679-9687

## DIAGNOSTIC STUDY OF A WAVENUMBER-2 STRATOSPHERIC SUDDEN WARMING IN A TRANSFORMED EULERIAN-MEAN FORMALISM

JOURNAL OF THE ATMOSPHERIC SCIENCES **38** (1981) 844-855

## Gravitational energy-momentum: The Einstein pseudotensor reexamined

General Relativity and Gravitation **12** (1980) 149-154

By using a suitable two-point scalar field, a covariant formulation of the Einstein pseudotensor is given. A unique choice of scalar field is made possible by examining the role of linear and angular momentum in their correct geometric context. It is shown that, contrary to many text-book statements, linear momentum is not generated by infinitesimal coordinate transformations on space-time. Use is made of the nonintersecting lifted geodesies on the tangent bundle, TM, to space-time, to define a globally regular three-dimensional Lagrangian submanifold of TM, relative to an observer at some point z in space-time. By integrating over this submanifold rather than a necessarily singular spacelike hypersurface, gravitational linear and angular momentum, relative to z, are defined, and shown to have sensible physical properties. © 1980 Plenum Publishing Corporation.

## OBSERVATION AND SIMULATION OF A STRATOSPHERIC SUDDEN WARMING

GEOPHYSICAL JOURNAL OF THE ROYAL ASTRONOMICAL SOCIETY **61** (1980) 222-222

## Incorporation of climatology into a Backus‐Gilbert variational scheme for atmospheric temperature retrieval

Quarterly Journal of the Royal Meteorological Society **105** (1979) 803-809

A method is proposed for explicitly incorporating climatological information into a Backus‐Gilbert variational scheme for atmospheric temperature retrieval by a remote sounding radiometer. The method is applied to a study of the retrieval ability of a ground‐based microwave radiometer. Copyright © 1979 Royal Meteorological Society

## MOMENTUM-TRANSFER IN GRAVITATION THEORY

GENERAL RELATIVITY AND GRAVITATION **10** (1979) 623-629

## DERRICKS THEOREM IN CURVED SPACE

JOURNAL OF PHYSICS A-MATHEMATICAL AND GENERAL **12** (1979) L17-L19

## COVARIANT CONSERVATION EQUATIONS AND THEIR RELATION TO THE ENERGY-MOMENTUM CONCEPT IN GENERAL RELATIVITY

PHYSICAL REVIEW D **18** (1978) 4399-4407

## COVARIANT CONSERVATION EQUATIONS AND THEIR RELATION TO THE ENERGY-MOMENTUM CONCEPT IN GENERAL RELATIVITY

PHYSICAL REVIEW C (1978) 4399-4407

## CONSERVATION EQUATIONS AND GRAVITATIONAL SYMPLECTIC FORM

JOURNAL OF MATHEMATICAL PHYSICS **19** (1978) 2324-2331

## Recovering Valuations on Demushkin Fields

ArXiv (0)

Let $K$ be a field with $G_K(2) \simeq G_{\mathbb{Q}_2}(2)$, where $G_F(2)$ denotes the maximal pro-2 quotient of the absolute Galois group of a field $F$. We prove that then $K$ admits a (non-trivial) valuation $v$ which is 2-henselian and has residue field $\mathbb{F}_2$. Furthermore, $v(2)$ is a minimal positive element in the value group $\Gamma_v$ and $[\Gamma_v:2\Gamma_v]=2$. This forms the first positive result on a more general conjecture about the structure of pro-$p$ Galois groups which we formulate precisely (cf. Conjecture 1). As an application, we prove a strong version of the birational section conjecture for smooth, complete curves $X$ over $\mathbb{Q}_2$, as well as an analogue for varieties.

## Climate SPHINX: evaluating the impact of resolution and stochastic physics parameterisations in climate simulations

Copernicus GmbH (0)

<jats:p>&lt;p&gt;&lt;strong&gt;Abstract.&lt;/strong&gt; The Climate SPHINX (Stochastic Physics HIgh resolutioN eXperiments) project is a comprehensive set of ensemble simulations aimed at evaluating the sensitivity of present and future climate to model resolution and stochastic parameterisation. The EC-Earth Earth-System Model is used to explore the impact of stochastic physics in a large ensemble of 30-year climate integrations at five different atmospheric horizontal resolutions (from 125&amp;#8201;km up to 16&amp;#8201;km). The project includes more than 120 simulations in both a historical scenario (1979&amp;#8211;2008) and a climate change projection (2039&amp;#8211;2068), together with coupled transient runs (1850&amp;#8211;2100). A total of 20.4&amp;#8201;million core hours have been used, made available from a single year grant from PRACE (the Partnership for Advanced Computing in Europe), and close to 1.5&amp;#8201;PBytes of output data have been produced on SuperMUC IBM Petascale System at the Leibniz Supercomputing Center (LRZ) in Garching, Germany. About 140&amp;#8201;TBytes of post-processed data are stored on the CINECA supercomputing center archives and are freely accessible to the community thanks to an EUDAT Data Pilot project. This paper presents the technical and scientific setup of the experiments, including the details on the forcing used for the simulations performed, defining the SPHINX v1.0 protocol. In addition, an overview of preliminary results is given: an improvement in the simulation of Euro-Atlantic atmospheric blocking following resolution increases is observed. It is also shown that including stochastic parameterisation in the low resolution runs helps to improve some aspects of the tropical climate &amp;#8211; specifically the Madden-Julian Oscillation and the tropical rainfall variability. These findings show the importance of representing the impact of small scale processes on the large scale climate variability either explicitly (with high resolution simulations) or stochastically (in low resolution simulations).&lt;/p&gt; </jats:p>

## Canonical Valuations and the Birational Section Conjecture

ArXiv (0)

We develop a notion of a `canonical $\mathcal{C}$-henselian valuation' for a class $\mathcal{C}$ of field extensions, generalizing the construction of the canonical henselian valuation of a field. We use this to show that the $p$-adic valuation on a finite extension $F$ of $\mathbb{Q}_p$ can be recovered entirely (or up to some indeterminacy of the residue field) from various small quotients of $G_F$, the absolute Galois group of $F$. In particular, it can be recovered fully from the maximal solvable quotient. We use this to prove several versions of the birational section conjecture for varieties over $p$-adic fields.

## Introducing the Probabilistic Earth-System Model: Examining The Impact of Stochasticity in EC-Earth v3.2

Geoscientific Model Development Discussions Copernicus GmbH (0) 1-33

<jats:p><p><strong>Abstract.</strong> We introduce and study the impact of three stochastic schemes in the EC-Earth climate model, two atmospheric schemes and one stochastic land scheme. These form the basis for a probabilistic earth-system model in atmosphere-only mode. Stochastic parametrisations have become standard in several operational weather-forecasting models, in particular due to their beneficial impact on model spread. In recent years, stochastic schemes in the atmospheric component of a model have been shown to improve aspects important for the models long-term climate, such as ENSO, North Atlantic weather regimes and the Indian monsoon. Stochasticity in the land-component has been shown to improve variability of soil processes and improve the representation of heatwaves over Europe. However, the raw impact of such schemes on the model mean is less well studied, It is shown that the inclusion all three schemes notably change the model mean state. While many of the impacts are beneficial, some are too large in amplitude, leading to large changes in the model's energy budget. This implies that in order to keep the benefits of stochastic physics without shifting the mean state too far from observations, a full re-tuning of the model will typically be required.</p> </jats:p>

## Jet Latitude Regimes and the Predictability of the North Atlantic Oscillation

ArXiv (0)

In recent years, numerical weather prediction models have begun to show notable levels of skill at predicting the average winter North Atlantic Oscillation (NAO) when initialised one month ahead. At the same time, these model predictions exhibit unusually low signal-to-noise ratios, in what has been dubbed a `signal-to-noise paradox'. We analyse both the skill and signal-to-noise ratio of the Integrated Forecast System (IFS), the European Center for Medium-range Weather Forecasts (ECMWF) model, in an ensemble hindcast experiment. Specifically, we examine the contribution to both from the regime dynamics of the North Atlantic eddy-driven jet. This is done by constructing a statistical model which captures the predictability inherent to to the trimodal jet latitude system, and fitting its parameters to reanalysis and IFS data. Predictability in this regime system is driven by interannual variations in the persistence of the jet latitude regimes, which determine the preferred state of the jet. We show that the IFS has skill at predicting such variations in persistence: because the position of the jet strongly influences the NAO, this automatically generates skill at predicting the NAO. We show that all of the skill the IFS has at predicting the winter NAO over the period 1980-2010 can be attributed to its skill at predicting regime persistence in this way. Similarly, the tendency of the IFS to underestimate regime persistence can account for the low signal-to-noise ratio, giving a possible explanation for the signal-to-noise paradox. Finally, we examine how external forcing drives variability in jet persistence, as well as highlight the role played by transient baroclinic eddy feedbacks to modulate regime persistence.

## On the shallow atmosphere approximation in finite element dynamical cores

ArXiv (0)

We provide an approach to implementing the shallow atmosphere approximation in three dimensional finite element discretisations for dynamical cores. The approach makes use of the fact that the shallow atmosphere approximation metric can be obtained by writing equations on a three-dimensional manifold embedded in $\mathbb{R}^4$ with a restriction of the Euclidean metric. We show that finite element discretisations constructed this way are equivalent to the use of a modified three dimensional mesh for the construction of metric terms. We demonstrate our approach via a convergence test for a prototypical elliptic problem.

## Compatible finite element methods for numerical weather prediction

ArXiv (0)

This article takes the form of a tutorial on the use of a particular class of mixed finite element methods, which can be thought of as the finite element extension of the C-grid staggered finite difference method. The class is often referred to as compatible finite elements, mimetic finite elements, discrete differential forms or finite element exterior calculus. We provide an elementary introduction in the case of the one-dimensional wave equation, before summarising recent results in applications to the rotating shallow water equations on the sphere, before taking an outlook towards applications in three-dimensional compressible dynamical cores.

## The impact of stochastic physics on climate sensitivity in EC-Earth

ArXiv (0)

Stochastic schemes, designed to represent unresolved sub-grid scale variability, are frequently used in short and medium-range weather forecasts, where they are found to improve several aspects of the model. In recent years, the impact of stochastic physics has also been found to be beneficial for the model's long term climate. In this paper, we demonstrate for the first time that the inclusion of a stochastic physics scheme can notably affect a model's projection of global warming, as well as its historical climatological global temperature. Specifically, we find that when including the 'stochastically perturbed parametrisation tendencies' scheme (SPPT) in the fully coupled climate model EC-Earth v3.1, the predicted level of global warming between 1850 and 2100 is reduced by 10% under an RCP8.5 forcing scenario. We link this reduction in climate sensitivity to a change in the cloud feedbacks with SPPT. In particular, the scheme appears to reduce the positive low cloud cover feedback, and increase the negative cloud optical feedback. A key role is played by a robust, rapid increase in cloud liquid water with SPPT, which we speculate is due to the scheme's non-linear interaction with condensation.

## An interdecadal shift of the extratropical teleconnection from the tropical Pacific during boreal summer

Geophysical Research Letters American Geophysical Union (0)

## The moderate impact of the 2015 El Niño over East Africa and its representation in seasonal reforecasts

Journal of Climate American Meteorological Society (0) JCLI-D-19-0201.1