Publications by Peter Read

Wave number selection in the presence of noise: Experimental results

Chaos 28 (2018)

D Zhilenko, O Krivonosova, M Gritsevich, P Read

© 2018 Author(s). In this study, we consider how the wave number selection in spherical Couette flow, in the transition to azimuthal waves after the first instability, occurs in the presence of noise. The outer sphere was held stationary, while the inner sphere rotational speed was increased linearly from a subcritical flow to a supercritical one. In a supercritical flow, one of two possible flow states, each with different azimuthal wave numbers, can appear depending upon the initial and final Reynolds numbers and the acceleration value. Noise perturbations were added by introducing small disturbances into the rotational speed signal. With an increasing noise amplitude, a change in the dominant wave number from m to m ± 1 was found to occur at the same initial and final Reynolds numbers and acceleration values. The flow velocity measurements were conducted by using laser Doppler anemometry. Using these results, the role of noise as well as the behaviour of the amplitudes of the competing modes in their stages of damping and growth were determined.

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.

A Chorus of the WindsOn Saturn!


PL Read

Atmospheric Dynamics of Terrestrial Planets

in Handbook of Exoplanets, Springer International Publishing (2018) 1-31

PL Read, SR Lewis, GK Vallis

Descent Rate Models of the Synchronization of the Quasi-Biennial Oscillation by the Annual Cycle in Tropical Upwelling


K Rajendran, IM Moroz, SM Osprey, PL Read

Superrotation on Venus, on Titan, and Elsewhere


PL Read, S Lebonnois

Comparative terrestrial atmospheric circulation regimes in simplified global circulation models. Part I: From cyclostrophic super-rotation to geostrophic turbulence

Quarterly Journal of the Royal Meteorological Society (2018)

Y Wang, PL Read, F Tabataba-Vakili, RMB Young

© 2018 The Authors. Quarterly Journal of the Royal Meteorological Society published by John Wiley & Sons Ltd on behalf of the Royal Meteorological Society. The regimes of possible global atmospheric circulation patterns in an Earth-like atmosphere are explored using a simplified Global Circulation Model (GCM) based on the University of Hamburg's Portable University Model for the Atmosphere (PUMA)—with simplified (linear) boundary-layer friction, a Newtonian cooling scheme, and dry convective adjustment (designated here as PUMA-S). A series of controlled experiments is conducted by varying planetary rotation rate and imposed equator-to-pole temperature difference. These defining parameters are combined further with each other into dimensionless forms to establish a parameter space in which the occurrences of different circulation regimes are mapped and classified. Clear, coherent trends are found when varying planetary rotation rate (thermal Rossby number) and frictional and thermal relaxation time-scales. The sequence of circulation regimes as a function of parameters, such as the planetary rotation rate, strongly resembles that obtained in laboratory experiments on rotating, stratified flows, especially if a topographic β-effect is included in those experiments to emulate the planetary vorticity gradients in an atmosphere induced by the spherical curvature of the planet. A regular baroclinic wave regime is also obtained at intermediate values of thermal Rossby number and its characteristics and dominant zonal wavenumber depend strongly on the strength of radiative and frictional damping. These regular waves exhibit some strong similarities to baroclinic storms observed on Mars under some conditions. Multiple jets are found at the highest rotation rates, when the Rossby deformation radius and other eddy-related length-scales are much smaller than the radius of the planet. These exhibit some similarity to the multiple zonal jets observed on gas giant planets. Jets form on a scale comparable to the most energetic eddies and the Rhines scale poleward of the supercritical latitude. The balance of heat transport varies strongly with Ω∗ between eddies and zonally symmetric flows, becoming weak with fast rotation.

Comparative terrestrial atmospheric circulation regimes in simplified global circulation models. Part II: Energy budgets and spectral transfers

Quarterly Journal of the Royal Meteorological Society (2018)

PL Read, F Tabataba-Vakili, Y Wang, P Augier, E Lindborg, A Valeanu, RMB Young

© 2018 The Authors. Quarterly Journal of the Royal Meteorological Society published by John Wiley & Sons Ltd on behalf of the Royal Meteorological Society. The energetics of possible global atmospheric circulation patterns in an Earth-like atmosphere are explored using a simplified global General Circulation Model (GCM) based on the University of Hamburg's Portable University Model for the Atmosphere (designated here as PUMA-S), forced by linear relaxation towards a prescribed temperature field and subject to Rayleigh surface drag and hyperdiffusive dissipation. Results from a series of simulations, obtained by varying planetary rotation rate Ω with an imposed equator-to-pole temperature difference, were analysed to determine the structure and magnitude of the heat transport and other contributions to the energy budget for the time-averaged, equilibrated flow. These show clear trends with rotation rate, with the most intense Lorenz energy cycle for an Earth-sized planet occurring with a rotation rate around half that of the present-day Earth (i.e., Ω∗ = Ω/ΩE = 1/2, where ΩE is the rotation rate of the Earth). Kinetic energy (KE) and available potential energy (APE) spectra, E K(n) and E A(n) (where n is total spherical wavenumber), also show clear trends with rotation rate, with n −3 enstrophy-dominated spectra around Ω∗ = 1 and steeper (∼n −5) slopes in the zonal mean flow with little evidence for the n −5/3 spectrum anticipated for an inverse KE cascade. Instead, both KE and APE spectra become almost flat at scales larger than the internal Rossby radius, L d, and exhibit near-equipartition at high wavenumbers. At Ω∗ < <1, the spectrum becomes dominated by KE with E K(n)∼(2–3)E A(n) at most wavenumbers and a slope that tends towards n −5/3 across most of the spectrum. Spectral flux calculations show that enstrophy and APE are almost always cascaded downscale, regardless of rotation rate. KE cascades are more complicated, however, with downscale transfers across almost all wavenumbers, dominated by horizontally divergent modes, for Ω∗ ≲ 1/4. At higher rotation rates, transfers of KE become increasingly dominated by rotational (horizontally nondivergent) components with strong upscale transfers (dominated by eddy–zonal flow interactions) for scales larger than L d and weaker downscale transfers for scales smaller than L d.

A hexagon in Saturn's northern stratosphere surrounding the emerging summertime polar vortex.

Nature communications 9 (2018) 3564-

LN Fletcher, GS Orton, JA Sinclair, S Guerlet, PL Read, A Antuñano, RK Achterberg, FM Flasar, PGJ Irwin, GL Bjoraker, J Hurley, BE Hesman, M Segura, N Gorius, A Mamoutkine, SB Calcutt

Saturn's polar stratosphere exhibits the seasonal growth and dissipation of broad, warm vortices poleward of ~75° latitude, which are strongest in the summer and absent in winter. The longevity of the exploration of the Saturn system by Cassini allows the use of infrared spectroscopy to trace the formation of the North Polar Stratospheric Vortex (NPSV), a region of enhanced temperatures and elevated hydrocarbon abundances at millibar pressures. We constrain the timescales of stratospheric vortex formation and dissipation in both hemispheres. Although the NPSV formed during late northern spring, by the end of Cassini's reconnaissance (shortly after northern summer solstice), it still did not display the contrasts in temperature and composition that were evident at the south pole during southern summer. The newly formed NPSV was bounded by a strengthening stratospheric thermal gradient near 78°N. The emergent boundary was hexagonal, suggesting that the Rossby wave responsible for Saturn's long-lived polar hexagon-which was previously expected to be trapped in the troposphere-can influence the stratospheric temperatures some 300 km above Saturn's clouds.

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


H Scolan, PL Read

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

Chaos (Woodbury, N.Y.) 27 (2017) 127001-

PL Read, X Morice-Atkinson, EJ Allen, AA Castrejón-Pita

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 δ 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 δ was varied over the range 0.1≤δ≤1. Reducing δ 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, although for the strongest pulse-like forcing profile some degree of synchronization was discernible even at δ=0.1. Complete phase synchronization was obtained within the Arnol'd tongue itself, although 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 on 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 2 (2017) 41-41

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

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

NATURE PHYSICS 13 (2017) 1135-+

RMB Young, PL Read

Ertel potential vorticity versus Bernoulli streamfunction on Mars


TE Dowling, ME Bradley, J Du, SR Lewis, PL Read

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

Spectral analysis of Uranus' 2014 bright storm with VLT/SINFONI

ICARUS 264 (2016) 72-89

PGJ Irwin, LN Fletcher, PL Read, D Tice, I de Pater, GS Orton, NA Teanby, GR Davis

A regime diagram for ocean geostrophic turbulence


A Klocker, DP Marshall, SR Keating, PL Read

Exploring the Venus global super-rotation using a comprehensive general circulation model


JM Mendonca, PL Read