Publications


A water budget dichotomy of rocky protoplanets from 26Al-heating

Nature Astronomy Springer Nature 3 (2018) 307–313-

T Lichtenberg, GJ Golabek, Y Alibert, R Burn, C Mordasini, TV Gerya


An experimental investigation of blocking by partial barriers in a rotating baroclinic annulus

Geophysical and Astrophysical Fluid Dynamics (2017) 1-33

SD Marshall, PL Read

© 2017 Informa UK Limited, trading as Taylor & Francis Group We present a series of experimental investigations in which a differentially-heated annulus was used to investigate the effects of topography on rotating, stratified flows with similarities to the Earth’s atmospheric or oceanic circulation. In particular, we compare and investigate blocking effects via partial mechanical barriers to previous experiments by the authors utilising azimuthally-periodic topography. The mechanical obstacle used was an isolated ridge, forming a partial barrier, employed to study the difference between partially blocked and fully unblocked flow. The topography was found to lead to the formation of bottom-trapped waves, as well as impacting the circulation at a level much higher than the top of the ridge. This produced a unique flow structure when the drifting flow and the topography interacted in the form of an “interference” regime at low Taylor number, but forming an erratic “irregular” regime at higher Taylor number. The results also showed evidence of resonant wave-triads, similar to those noted with periodic wavenumber-3 topography by Marshall and Read (Geophys. Astrophys. Fluid Dyn., 2015, 109), though the component wavenumbers of the wave-triads and their impact on the flow were found to depend on the topography in question. With periodic topography, wave-triads were found to occur between both the baroclinic and barotropic components of the zonal wavenumber-3 mode and the wavenumber-6 baroclinic component, whereas with the partial barrier two nonlinear resonant wave-triads were noted, each sharing a common wavenumber-1 mode.


Impact splash chondrule formation during planetesimal recycling

Icarus Elsevier BV 302 (2018) 27-43

T Lichtenberg, GJ Golabek, CP Dullemond, M Schönbächler, TV Gerya, MR Meyer


Late metal–silicate separation on the IAB parent asteroid: Constraints from combined W and Pt isotopes and thermal modelling

Earth and Planetary Science Letters Elsevier BV 482 (2018) 490-500

AC Hunt, DL Cook, T Lichtenberg, PM Reger, M Ek, GJ Golabek, M Schönbächler


Atmospheric Dynamics of Terrestrial Planets

in Handbook of Exoplanets, Springer (2018)

P Read, GK Vallis

<p style="text-align:justify;">The solar system presents us with a number of planetary bodies with shallow atmospheres that are sufficiently Earth-like in their form and structure to be termed “terrestrial.” These atmospheres have much in common, in having circulations that are driven primarily by heating from the Sun and radiative cooling to space, which vary markedly with latitude. The principal response to this forcing is typically in the form of a (roughly zonally symmetric) meridional overturning that transports heat vertically upward and in latitude. But even within the solar system, these planets exhibit many differences in the types of large-scale waves and instabilities that also contribute substantially to determining their respective climates. Here we argue that the study of simplified models (either numerical simulations or laboratory experiments) provides considerable insights into the likely roles of planetary size, rotation, thermal stratification, and other factors in determining the styles of global circulation and dominant waves and instability processes. We discuss the importance of a number of key dimensionless parameters, for example, the thermal Rossby and the Burger numbers as well as nondimensional measures of the frictional or radiative timescales, in defining the type of circulation regime to be expected in a prototypical planetary atmosphere subject to axisymmetric driving. These considerations help to place each of the solar system terrestrial planets into an appropriate dynamical context and also lay the foundations for predicting and understanding the climate and circulation regimes of (as yet undiscovered) Earth-like extrasolar planets. However, as recent discoveries of “super-Earth” planets around some nearby stars are beginning to reveal, this parameter space is likely to be incomplete, and other factors, such as the possibility of tidally locked rotation and tidal forcing, may also need to be taken into account for some classes of extrasolar planet.</p>


The Influence of a Substellar Continent on the Climate of a Tidally Locked Exoplanet

The Astrophysical Journal 854 (2018) 171-171

NT Lewis, FH Lambert, IA Boutle, NJ Mayne, J Manners, DM Acreman


Descent rate models of the synchronization of the Quasi-Biennial Oscillation by the annual cycle in tropical upwelling

Journal of the Atmospheric Sciences American Meteorological Society 75 (2018) 2281–2297-

K Rajendran, I Moroz, S Osprey, PL Read

The response of the Quasi-Biennial Oscillation (QBO) to an imposed mean upwelling with a periodic modulation is studied, by modelling the dynamics of the zero wind line at the equator using a class of equations known as ‘descent rate’ models. These are simple mathematical models that capture the essence of QBO synchronization by focusing on the dynamics of the height of the zero wind line. A heuristic descent rate model for the zero wind line is described, and is shown to capture many of the synchronization features seen in previous studies of the QBO. Using a simple transformation, it is then demonstrated that the standard Holton-Lindzen model of the QBO can itself be put into the form of a descent rate model if a quadratic velocity profile is assumed below the zero wind line. The resulting non-autonomous ordinary differential equation captures much of the synchronization behaviour observed in the full Holton-Lindzen partial differential equation. The new class of models provides a novel framework within which to understand synchronization of the QBO, and we demonstrate a close relationship between these models and the circle map well-known in the mathematics literature. Finally, we analyse reanalysis datasets to validate some of the predictions of our descent rate models, and find statistically significant evidence for synchronization of the QBO that is consistent with model behaviour.


Isca, v1.0: a framework for the global modelling of the atmospheres of Earth and other planets at varying levels of complexity

GEOSCIENTIFIC MODEL DEVELOPMENT 11 (2018) 843-859

GK Vallis, G Colyer, R Geen, E Gerber, M Jucker, P Maher, A Paterson, M Pietschnig, J Penn, SI Thomson


Exploring the atmosphere of Neoproterozoic Earth: The effect of O2 on haze formation and composition

Astrophysical Journal American Astronomical Society 858 (2018) 119

S Hörst, AM Jellinek, C He, R Pierrehumbert, MA Tolbert

Previous studies of haze formation in the atmosphere of the early Earth have focused on N2/CO2/CH4 atmospheres. Here, we experimentally investigate the effect of O2 on the formation and composition of aerosols to improve our understanding of haze formation on the Neoproterozoic Earth. We obtained in situ size, particle density, and composition measurements of aerosol particles produced from N2/CO2/CH4/O2 gas mixtures subjected to FUV radiation (115–400 nm) for a range of initial CO2/CH4/O2 mixing ratios (O2 ranging from 2 ppm to 0.2%). At the lowest O2 concentration (2 ppm), the addition increased particle production for all but one gas mixture. At higher oxygen concentrations (20 ppm and greater), particles are still produced, but the addition of O2 decreases the production rate. Both the particle size and number density decrease with increasing O2, indicating that O2 affects particle nucleation and growth. The particle density increases with increasing O2. The addition of CO2 and O2 not only increases the amount of oxygen in the aerosol, but it also increases the degree of nitrogen incorporation. In particular, the addition of O2 results in the formation of nitrate-bearing molecules. The fact that the presence of oxygen-bearing molecules increases the efficiency of nitrogen fixation has implications for the role of haze as a source of molecules required for the origin and evolution of life. The composition changes also likely affect the absorption and scattering behavior of these particles but optical property measurements are required to fully understand the implications for the effect on the planetary radiative energy balance and climate.


Superrotation on Venus, on Titan, and elsewhere

Annual Review of Earth and Planetary Sciences Annual Reviews 46 (2018) 175-202

P Read, S Lebonnois

The superrotation of the atmospheres of Venus and Titan has puzzled dynamicists for many years and seems to put these planets in a very different dynamical regime from most other planets. In this review, we consider how to define superrotation objectively and explore the constraints that determine its occurrence. Atmospheric superrotation also occurs elsewhere in the Solar System and beyond, and we compare Venus and Titan with Earth and other planets for which wind estimates are available. The extreme superrotation on Venus and Titan poses some difficult challenges for numerical models of atmospheric circulation, much more difficult than for more rapidly rotating planets such as Earth or Mars. We consider mechanisms for generating and maintaining a superrotating state, all of which involve a global meridional overturning circulation. The role of nonaxisymmetric eddies is crucial, however, but the detailed mechanisms may differ between Venus, Titan, and other planets.


Ice-shelf damming in the glacial Arctic Ocean: dynamical regimes of a basin-covering kilometre-thick ice shelf

Cryosphere European Geosciences Union 11 (2017) 1745-1765

J Nilsson, M Jakobsson, N Kirchner, C Borstad, G Björk, R Pierrehumbert, C Stranne

Recent geological and geophysical data suggest that a 1km thick ice shelf extended over the glacial Arctic Ocean during Marine Isotope Stage 6, about 140000 years ago. Here, we theoretically analyse the development and equilibrium features of such an ice shelf, using scaling analyses and a one-dimensional ice-sheet–ice-shelf model. We find that the dynamically most consistent scenario is an ice shelf with a nearly uniform thickness that covers the entire Arctic Ocean. Further, the ice shelf has two regions with distinctly different dynamics: a vast interior region covering the central Arctic Ocean and an exit region towards the Fram Strait. In the interior region, which is effectively dammed by the Fram Strait constriction, there are strong back stresses and the mean ice-shelf thickness is controlled primarily by the horizontally integrated mass balance. A narrow transition zone is found near the continental grounding line, in which the ice-shelf thickness decreases offshore and approaches the mean basin thickness. If the surface accumulation and mass flow from the continental ice masses are sufficiently large, the ice-shelf thickness grows to the point where the ice shelf grounds on the Lomonosov Ridge. As this occurs, the back stress increases in the Amerasian Basin and the ice-shelf thickness becomes larger there than in the Eurasian Basin towards the Fram Strait. Using a one-dimensional ice-dynamic model, the stability of equilibrium ice-shelf configurations without and with grounding on the Lomonosov Ridge are examined. We find that the grounded ice-shelf configuration should be stable if the two Lomonosov Ridge grounding lines are located on the opposites sides of the ridge crest, implying that the downstream grounding line is located on a downward sloping bed. This result shares similarities with the classical result on marine ice-sheet stability of Weertman, but due to interactions between the Amerasian and Eurasian ice-shelf segments the mass flux at the downstream grounding line decreases rather than increases with ice thickness.


A rotating annulus driven by localized convective forcing: a new atmosphere-like experiment

Experiments in Fluids Springer Berlin Heidelberg 2017 (2017) 75

H Scolan, PL Read

We present an experimental study of flows in a cylindrical rotating annulus convectively forced by local heating in an annular ring at the bottom near the external wall and via a cooled circular disk near the axis at the top surface of the annulus. This new configuration is distinct from the classical thermally-driven annulus analogue of the atmosphere circulation, in which thermal forcing is applied uniformly on the sidewalls, but with a similar aim to investigate the baroclinic instability of a rotating, stratified flow subject to zonally symmetric forcing. Two vertically and horizontally displaced heat sources/sinks are arranged so that, in the absence of background rotation, statically unstable Rayleigh-Bénard convection would be induced above the source and beneath the sink, thereby relaxing strong constraints placed on background temperature gradients in previous experimental configurations based on the conventional rotating annulus. This better emulates local vigorous convection in the tropics and polar regions of the atmosphere whilst also allowing stably-stratified baroclinic motion in the central zone of the annulus, as in midlatitude regions in the Earth’s atmosphere. Regimes of flow are identified, depending mainly upon control parameters that in turn depend on rotation rate and the strength of differential heating. Several regimes exhibit baroclinically unstable flows which are qualitatively similar to those previously observed in the classical thermally-driven annulus, However, in contrast to the classical configuration, they typically exhibit more spatiotemporal complexity. Thus, several regimes of flow demonstrate the equilibrated co-existence of, and interaction between, free convection and baroclinic wave modes. These new features were not previously observed in the classical annulus and validate the new setup as a tool for exploring fundamental atmosphere-like dynamics in a more realistic framework. Thermal structure in the fluid is investigated and found to be qualitatively consistent with previous numerical results, with nearly isothermal conditions respectively above and below the heat source and sink, and stably-stratified, sloping isotherms in the near-adiabatic interior.


Was Planet 9 captured in the Sun’s natal star-forming region?

Monthly Notices of the Royal Astronomical Society: Letters Oxford University Press (OUP) 472 (2017) L75-L79

RJ Parker, T Lichtenberg, SP Quanz


Phase synchronization of baroclinic waves in a differentially heated rotating annulus experiment subject to periodic forcing with a variable duty cycle

Chaos AIP Publishing 27 (2017) 127001

A Castrejon Pita, X Morice-Atkinson, EJ Allen, PL Read

A series of laboratory experiments in a thermally driven, rotating fluid annulus are presented that investigate the onset and characteristics of phase synchronization and frequency entrainment between the intrinsic, chaotic, oscillatory amplitude modulation of travelling baroclinic waves and a periodic modulation of the (axisymmetric) thermal boundary conditions, subject to time-dependent coupling. The time-dependence is in the form of a prescribed duty cycle in which the periodic forcing of the boundary conditions is applied for only a fraction ߜ of each oscillation. For the rest of the oscillation, the boundary conditions are held fixed. Two profiles of forcing were investigated that capture different parts of the sinusoidal variation and ߜ was varied over the range 0.1 ൑ ߜ ൑ 1. Reducing ߜ was found to act in a similar way to a reduction in a constant coupling coefficient in reducing the width of the interval in forcing frequency or period over which complete synchronization was observed (the “Arnol’d tongue”) with respect to the detuning, though for the strongest pulselike forcing profile some degree of synchronization was discernible even at ߜ ൌ 0.1. Complete phase synchronization was obtained within the Arnol’d tongue itself, though the strength of the amplitude modulation of the baroclinic wave was not significantly affected. These experiments demonstrate a possible mechanism for intraseasonal and/or interannual “teleconnections” within the climate system of the Earth and other planets that does not rely upon Rossby wave propagation across the planet along great circles.


Regimes of axisymmetric flow and scaling laws in a rotating annulus with local convective forcing

Fluids MDPI 2 (2017) 41

S Wright, S Su, R Young, H Scolan, PL Read

We present a numerical study of axisymmetric flow in a rotating annulus in which local thermal forcing, via a heated annular ring on the outside of the base and a cooled circular disk in the centre of the top surface, drives convection. This new configuration is a variant of the classical thermally-driven annulus, where uniform heating and cooling are applied through the outer and inner sidewalls respectively. The annulus provides an analogue to a planetary circulation and the new configuration, with its more relaxed vertical thermal boundary conditions, is expected to better emulate vigorous convection in the tropics and polar regions as well as baroclinic instability in the mid-latitude baroclinic zone. Using the Met Office/Oxford Rotating Annulus Laboratory (MORALS) code, we have investigated a series of equilibrated, two dimensional axisymmetric flows across a large region of parameter space. These are characterized in terms of their velocity and temperature fields. When rotation is applied several distinct flow regimes may be identified for different rotation rates and strengths of differential heating. These regimes are defined as a function of the ratio of the horizontal Ekman layer thickness to the non-rotating thermal boundary layer thickness and are found to be similar to those identified in previous annulus experiments. Convection without rotation is also considered and the scaling of the heat transport with Rayleigh number is calculated. This is then compared with existing work on the classical annulus as well as horizontal and Rayleigh-Bénard convection. As with previous studies on both rotating and non-rotating convection the system’s behaviour is found to be aspect ratio dependent. This dependence is seen in the scaling of the non-rotating Nusselt number and in transitions between regimes in the rotating case although further investigation is required to fully explain these observations.


Forward and inverse kinetic energy cascades in Jupiter’s turbulent weather layer

Nature Physics Nature Publishing Group 13 (2017) 1135–1140-

RMB Young, PL Read

Jupiter’s turbulent weather layer contains phenomena of many different sizes, from local storms up to the Great Red Spot and banded jets. The global circulation is driven by complex interactions with (as yet uncertain) small scale processes. We have calculated structure functions and kinetic energy spectral fluxes from Cassini observations over a wide range of length scales in Jupiter’s atmosphere. We found evidence for an inverse cascade of kinetic energy from length scales comparable with the first baroclinic Rossby deformation radius to the global jet scale, but also a forward cascade of kinetic energy from the deformation radius to smaller scales. The latter disagrees with the traditional picture of Jupiter’s atmospheric dynamics, but has some similarities with mesoscale phenomena in the Earth’s atmosphere and oceans. We conclude that the inverse cascade driving Jupiter’s jets may have a dominant energy source at scales close to the deformation radius, such as baroclinic instability.


The Atmospheric Dynamics of Venus

Space Science Reviews 212 (2017) 1541-1616

A Sánchez-Lavega, S Lebonnois, T Imamura, P Read, D Luz

© 2017, Springer Science+Business Media B.V. We review our current knowledge of the atmospheric dynamics of Venus prior to the Akatsuki mission, in the altitude range from the surface to approximately the cloud tops located at about 100 km altitude. The three-dimensional structure of the wind field in this region has been determined with a variety of techniques over a broad range of spatial and temporal scales (from the mesoscale to planetary, from days to years, in daytime and nighttime), spanning a period of about 50 years (from the 1960s to the present). The global panorama is that the mean atmospheric motions are essentially zonal, dominated by the so-called super-rotation (an atmospheric rotation that is 60 to 80 times faster than that of the planetary body). The zonal winds blow westward (in the same direction as the planet rotation) with a nearly constant speed of ∼100ms−1 at the cloud tops (65–70 km altitude) from latitude 50°N to 50°S, then decreasing their speeds monotonically from these latitudes toward the poles. Vertically, the zonal winds decrease with decreasing altitude towards velocities ∼1–3ms−1 in a layer of thickness ∼10km close to the surface. Meridional motions with peak speeds of ∼15ms−1 occur within the upper cloud at 65 km altitude and are related to a Hadley cell circulation and to the solar thermal tide. Vertical motions with speeds ∼1–3ms−1 occur in the statically unstable layer between altitudes of ∼50–55km. All these motions are permanent with speed variations of the order of ∼ 10 %. Various types of wave, from mesoscale gravity waves to Rossby-Kelvin planetary scale waves, have been detected at and above cloud heights, and are considered to be candidates as agents for carrying momentum that drives the super-rotation, although numerical models do not fully reproduce all the observed features. Momentum transport by atmospheric waves and the solar tide is thought to be an indispensable component of the general circulation of the Venus atmosphere. Another conspicuous feature of the atmospheric circulation is the presence of polar vortices. These are present in both hemispheres and are regions of warmer and lower clouds, seen prominently at infrared wavelengths, showing a highly variable morphology and motions. The vortices spin with a period of 2–3 days. The South polar vortex rotates around a geographical point which is itself displaced from the true pole of rotation by ∼ 3 degrees. The polar vortex is surrounded and constrained by the cold collar, an infrared-dark region of lower temperatures. We still lack detailed models of the mechanisms underlying the dynamics of these features and how they couple (or not) to the super-rotation. The nature of the super-rotation relates to the angular momentum stored in the atmosphere and how it is transported between the tropics and higher latitudes, and between the deep atmosphere and upper levels. The role of eddy processes is crucial, but likely involves the complex interaction of a variety of different types of eddy, either forced directly by radiative heating and mechanical interactions with the surface or through various forms of instability. Numerical models have achieved some significant recent success in capturing some aspects of the observed super-rotation, consistent with the scenario discussed by Gierasch (J. Atmos. Sci. 32:1038–1044, 1975) and Rossow and Williams (J. Atmos. Sci. 36:377–389, 1979), but many uncertainties remain, especially in the deep atmosphere. The theoretical framework developed to explain the circulation in Venus’s atmosphere is reviewed, as well as the numerical models that have been built to elucidate the super-rotation mechanism. These tools are used to analyze the respective roles of the different waves in the processes driving the observed motions. Their limitations and suggested directions for improvements are discussed.


The martian planetary boundary layer

in The Atmosphere and Climate of Mars, (2017) 172-202

PL Read, B Galperin, SE Larsen, SR Lewis, A Määttänen, A Petrosyan, N Rennó, H Savijärvi, T Siili, A Spiga, A Toigo, L Vázquez


The global circulation

in The Atmosphere and Climate of Mars, (2017) 229-294

JR Barnes, RM Haberle, RJ Wilson, SR Lewis, JR Murphy, PL Read


Mountain glaciers as paleoclimate proxies

Annual Review of Earth and Planetary Sciences Annual Reviews 49 (2017) 649-680

AN Mackintosh, BM Anderson, R Pierrehumbert

Glaciers offer the potential to reconstruct past climate over timescales from decades to millennia. They are found on nearly every continent, and at the Last Glacial Maximum, glaciers were larger in all regions on Earth. The physics of glacier-climate interaction is relatively well understood, and glacier models can be used to reconstruct past climate from geological evidence of past glacier extent. This can lead to significant insights regarding past, present and future climate. For example, glacier modelling has demonstrated that the near ubiquitous global pattern of glacier retreat during the last few centuries resulted from a global-scale climate warming of ~1°C, consistent with instrumental data and climate proxy records. Climate reconstructions from glaciers also demonstrated that the tropics were colder at the Last Glacial Maximum than was originally inferred from sea surface temperature reconstructions. Future efforts to reconstruct climate from glaciers may provide new constraints on climate sensitivity to CO2 forcing, polar amplification of climate change, and more.

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