Publications


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

Icarus Elsevier 264 (2015) 72-89

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

An extremely bright storm system observed in Uranus' atmosphere by amateur observers in September 2014 triggered an international campaign to observe this feature with many telescopes across the world. Observations of the storm system in the near infrared were acquired in October and November 2014 with SINFONI on ESO's Very Large Telescope (VLT) in Chile. SINFONI is an Integral Field Unit spectrometer returning 64. ×. 64 pixel images with 2048 wavelengths and uses adaptive optics. Image cubes in the H-band (1.43-1.87. μm) were obtained at spatial resolutions of ~0.1″ per pixel. The observations show that the centre of the storm feature shifts markedly with increasing altitude, moving in the retrograde direction and slightly poleward with increasing altitude. We also see a faint 'tail' of more reflective material to the immediate south of the storm, which again trails in the retrograde direction. The observed spectra were analysed with the radiative transfer and retrieval code, NEMESIS (Irwin et al. [2008]. J. Quant. Spec. Radiat. Transfer, 109, 1136-1150). We find that the storm is well-modelled using either two main cloud layers of a 5-layer aerosol model based on Sromovsky et al. (Sromovsky et al. [2011]. Icarus, 215, 292-312) or by the simpler two-cloud-layer model of Tice et al. (Tice et al. [2013]. Icarus, 223, 684-698). The deep component appears to be due to a brightening (i.e. an increase in reflectivity) and increase in altitude of the main tropospheric cloud deck at 2-3. bars for both models, while the upper component of the feature was modelled as being due to either a thickening of the tropospheric haze of the 2-layer model or a vertical extension of the upper tropospheric cloud of the 5-layer model, assumed to be composed of methane ice and based at the methane condensation level of our assumed vertical temperature and abundance profile at 1.23. bar. We also found this methane ice cloud to be responsible for the faint 'tail' seen to the feature's south and the brighter polar 'hood' seen in all observations polewards of ~45°N for the 5-layer model. During the twelve days between our sets of observations the higher-altitude component of the feature was observed to have brightened significantly and extended to even higher altitudes, while the deeper component faded.


The solsticial pause on Mars: 2 modelling and investigation of causes

Icarus Elsevier 264 (2015) 465-477

DP Mulholland, SR Lewis, P Read, J-B Madeleine, F Forget

The martian solsticial pause, presented in a companion paper (Lewis et al., 2016), was investigated further through a series of model runs using the UK version of the LMD/UK Mars Global Climate Model. It was found that the pause could not be adequately reproduced if radiatively active water ice clouds were omitted from the model. When clouds were used, along with a realistic time-dependent dust opacity distribution, a substantial minimum in near-surface transient eddy activity formed around solstice in both hemispheres. The net effect of the clouds in the model is, by altering the thermal structure of the atmosphere, to decrease the vertical shear of the westerly jet near the surface around solstice, and thus reduce baroclinic growth rates. A similar effect was seen under conditions of large dust loading, implying that northern midlatitude eddy activity will tend to become suppressed after a period of intense flushing storm formation around the northern cap edge. Suppression of baroclinic eddy generation by the barotropic component of the flow and via diabatic eddy dissipation were also investigated as possible mechanisms leading to the formation of the solsticial pause but were found not to make major contributions. Zonal variations in topography were found to be important, as their presence results in weakened transient eddies around winter solstice in both hemispheres, through modification of the near-surface flow. The zonal topographic asymmetry appears to be the primary reason for the weakness of eddy activity in the southern hemisphere relative to the northern hemisphere, and the ultimate cause of the solsticial pause in both hemispheres. The meridional topographic gradient was found to exert a much weaker influence on near-surface transient eddies.


Predictability of the thermally-driven laboratory rotating annulus

Quarterly Journal of the Royal Meteorological Society John Wiley and Sons (2015) n/a-n/a

RMB Young, PL Read

We investigate the predictability of the thermally driven rotating annulus, a laboratory experiment used to study the dynamics of planetary atmospheres under controlled and reproducible conditions. Our approach is to apply the same principles used to predict the atmosphere in operational weather forecasting. We build a forecasting system for the annulus using the analysis correction method for data assimilation, the breeding method for ensemble generation, and the Met Office/Oxford Rotating Annulus Laboratory Simulation as the forecast model. The system forecasts the annulus in steady (2S), amplitude vacillating (3AV), and structurally vacillating (3SV) flow regimes, verifying the forecasts against laboratory data. The results show that a range of flow regimes from this experiment can be accurately predicted. Forecasts in the steady wave flow regime perform well, and are predictable until the end of the available data. Forecasts in the amplitude and structural vacillation flow regimes lose quality and skill by a combination of wave drift and wavenumber transition. Amplitude vacillation is predictable up to several hundred seconds ahead, and structural vacillation is predictable for a few hundred seconds. The wavenumber transitions are partly explained by hysteresis in the rotating annulus experiment and model.


General Circulation of Planetary Atmospheres: Insights from Rotating Annulus and Related Experiments

Modeling Atmospheric and Oceanic Flows: Insights from Laboratory Experiments and Numerical Simulations John Wiley & Sons Ltd. (2015) 9-44

PL Read, EP Perez, IM Moroz, RMB Young


A new, fast and flexible radiative transfer method for Venus general circulation models

PLANETARY AND SPACE SCIENCE 105 (2015) 80-93

JM Mendonca, PL Read, CF Wilson, C Lee


The thermally-driven rotating annulus: horizontal velocities in regular and weakly chaotic flow regimes

(2015)

RMB Young, PL Read, W-G Früh, D Smith, SH Risch


Overview of MAST results

NUCLEAR FUSION 55 (2015) ARTN 104008

IT Chapman, J Adamek, RJ Akers, S Allan, L Appel, O Asunta, M Barnes, N Ben Ayed, T Bigelow, W Boeglin, J Bradley, J Bruenner, P Cahyna, M Carr, J Caughman, M Cecconello, C Challis, S Chapman, J Chorley, G Colyer, N Conway, WA Cooper, M Cox, N Crocker, B Crowley, G Cunningham, A Danilov, D Darrow, R Dendy, A Diallo, D Dickinson, S Diem, W Dorland, B Dudson, D Dunai, L Easy, S Elmore, A Field, G Fishpool, M Fox, E Fredrickson, S Freethy, L Garzotti, YC Ghim, K Gibson, J Graves, C Gurl, W Guttenfelder, C Ham, J Harrison, D Harting, E Havlickova, J Hawke, N Hawkes, T Hender, S Henderson, E Highcock, J Hillesheim, B Hnat, J Holgate, J Horacek, J Howard, B Huang, K Imada, O Jones, S Kaye, D Keeling, A Kirk, I Klimek, M Kocan, H Leggate, M Lilley, B Lipschultz, S Lisgo, YQ Liu, B Lloyd, B Lomanowski, I Lupelli, G Maddison, J Mailloux, R Martin, G McArdle, K McClements, B McMillan, A Meakins, H Meyer, C Michael, F Militello, J Milnes, AW Morris, G Motojima, D Muir, E Nardon, V Naulin, G Naylor, A Nielsen, M O'Brien, T O'Gorman, Y Ono, H Oliver, S Pamela, L Pangione, F Parra, A Patel, W Peebles, M Peng, R Perez, S Pinches, L Piron, M Podesta, M Price, M Reinke, Y Ren, C Roach, J Robinson, M Romanelli, V Rozhansky, S Saarelma, S Sangaroon, A Saveliev, R Scannell, A Schekochihin, S Sharapov, R Sharples, V Shevchenko, S Silburn, J Simpson, J Storrs, Y Takase, H Tanabe, H Tanaka, D Taylor, G Taylor, D Thomas, N Thomas-Davies, A Thornton, M Turnyanskiy, M Valovic, R Vann, N Walkden, H Wilson, LV Wyk, T Yamada, S Zoletnik, MAST Team, MASTU Team


Comparison of "warm and wet" and "cold and icy" scenarios for early Mars in a 3-D climate model

JOURNAL OF GEOPHYSICAL RESEARCH-PLANETS 120 (2015) 1201-1219

RD Wordsworth, L Kerber, RT Pierrehumbert, F Forget, JW Head


Feedback temperature dependence determines the risk of high warming

GEOPHYSICAL RESEARCH LETTERS 42 (2015) 4973-4980

J Bloch-Johnson, RT Pierrehumbert, DS Abbot


Non-axisymmetric flows in a differential-disk rotating system

JOURNAL OF FLUID MECHANICS 775 (2015) 349-386

T Vo, L Montabone, PL Read, GJ Sheard


Modeling gravitational instabilities in self-gravitating protoplanetary disks with adaptive mesh refinement techniques

Astronomy & Astrophysics EDP Sciences 579 (2015) A32-A32

T Lichtenberg, DRG Schleicher


Climate Intervention: Reflecting Sunlight to Cool Earth

National Academies Press, 2015

Committee on Geoengineering Climate, RT Pierrehumbert

Weather modification, which could also be called “weather intervention,” is the intentional alteration of the composition, behavior, or dynamics of the atmosphere occurring over a specified area and time period to accomplish a particular goal ...


Climate Intervention Carbon Dioxide Removal and Reliable Sequestration

National Academies Press, 2015

Committee on Geoengineering Climate, RT Pierrehumbert

Carbon Dioxide Removal and Reliable Sequestration Committee on Geoengineering Climate: Technical Evaluation and Discussion of Impacts, Board on Atmospheric Sciences and Climate, Ocean Studies Board, Division on Earth and Life ...


A laboratory study of global-scale wave interactions in baroclinic flow with topography II: vacillations and low-frequency variability

Geophysical and Astrophysical Fluid Dynamics Taylor and Francis 109 (2015) 359-390

S Risch, P Read

A laboratory investigation is presented with the aim of studying systematically the occurrence and characteristics of low-frequency variability of flows resulting from the interaction of a baroclinic flow with periodic bottom topography. Low-frequency variability within the baroclinic wave regime occurred in two distinct forms in separate regions of parameter space. One corresponded to the transition region between the baroclinic travelling and stationary wave regimes. It involved primarily an interaction between the drifting baroclinic waves and stationary components of the topographically forced wave. The resulting flow had characteristics similar to amplitude vacillation and had a time-scale of 30–60 annulus revolutions (days), which also corresponded to the wave drift period. A new regime of low-frequency amplitude vacillation was discovered in the transition region with the axisymmetric flow regime. As the complexity of the flow increased the period of the vacillation cycles grew to ∼100–180 “days”. This slower vacillation seemed to involve a cyclic enabling and disabling of nonlinear interactions between the forced stationary wave and the growing and azimuthally drifting wave, which in turn was linked to a decrease in mean flow shear. Subsequent chains of wave-wave interactions characterised the complex but robust oscillation phenomenon. The resulting behaviour has several features in common with some recent models of intraseasonal oscillations in the mid-latitude troposphere and with sudden stratospheric warmings.


An experimental investigation into topographic resonance in a baroclinic rotating annulus

GEOPHYSICAL AND ASTROPHYSICAL FLUID DYNAMICS 109 (2015) 391-421

SD Marshall, PL Read


An assessment of the impact of local processes on dust lifting in martian climate models

ICARUS 252 (2015) 212-227

DP Mulholland, A Spiga, C Listowski, PL Read


Climate impact of beef: an analysis considering multiple time scales and production methods without use of global warming potentials

Environmental Research Letters Institute of Physics Publishing 10 (2015) 085002-085002

G Eshel, R Pierrehumbert

An analysis of the climate impact of various forms of beef production is carried out, with a particular eye to the comparison between systems relying primarily on grasses grown in pasture (‘grass-fed’ or ‘pastured’beef) and systems involving substantial use of manufactured feed requiring significant external inputs in the form of synthetic fertilizer and mechanized agriculture (‘feedlot’beef). The climate impact is evaluated without employing metrics such asCO e 2 or global warming potentials. The analysis evaluates the impact at all time scales out to 1000 years. It is concluded that certain forms of pastured beef production have substantially lower climate impact than feedlot systems. However, pastured systems that require significant synthetic fertilization, inputs from supplemental feed, or deforestation to create pasture, have substantially greater climate impact at all time scales than the feedlot and dairy-associated systems analyzed. Even the best pastured system analyzed has enough climate impact to justify efforts to limit future growth of beef production, which in any event would be necessary if climate and other ecological concerns were met by a transition to primarily pasture-based systems. Alternate mitigation options are discussed, but barring unforseen technological breakthroughs worldwide consumption at current North American per capita rates appears incompatible with a 2 °C warming target.


The solsticial pause on Mars: 2 modelling and investigation of causes

Icarus 264 (2015) 465-477

DP Mulholland, SR Lewis, PL Read, JB Madeleine, F Forget

© 2015 Elsevier Inc. The martian solsticial pause, presented in a companion paper (. Lewis et al., 2016), was investigated further through a series of model runs using the UK version of the LMD/UK Mars Global Climate Model. It was found that the pause could not be adequately reproduced if radiatively active water ice clouds were omitted from the model. When clouds were used, along with a realistic time-dependent dust opacity distribution, a substantial minimum in near-surface transient eddy activity formed around solstice in both hemispheres. The net effect of the clouds in the model is, by altering the thermal structure of the atmosphere, to decrease the vertical shear of the westerly jet near the surface around solstice, and thus reduce baroclinic growth rates. A similar effect was seen under conditions of large dust loading, implying that northern midlatitude eddy activity will tend to become suppressed after a period of intense flushing storm formation around the northern cap edge. Suppression of baroclinic eddy generation by the barotropic component of the flow and via diabatic eddy dissipation were also investigated as possible mechanisms leading to the formation of the solsticial pause but were found not to make major contributions. Zonal variations in topography were found to be important, as their presence results in weakened transient eddies around winter solstice in both hemispheres, through modification of the near-surface flow. The zonal topographic asymmetry appears to be the primary reason for the weakness of eddy activity in the southern hemisphere relative to the northern hemisphere, and the ultimate cause of the solsticial pause in both hemispheres. The meridional topographic gradient was found to exert a much weaker influence on near-surface transient eddies.


Constraints on southern hemisphere tropical climate change during the Little Ice Age and Younger Dryas based on glacier modeling of the Quelccaya Ice Cap, Peru

Quaternary Science Reviews Elsevier 125 (2015) 106-116

TV Lowell, MA Kelly, AGO Malone, R Pierrehumbert, JS Stroup

© 2015 The Authors. Improving the late Quaternary paleoclimate record through climate interpretations of low-latitude glacier length changes advances our understanding of past climate change events and the mechanisms for past, present, and future climate change. Paleotemperature reconstructions at low-latitude glaciers are uniquely fruitful because they can provide both site-specific information and enhanced understanding of regional-scale variations due to the structure of the tropical atmosphere. We produce Little Ice Age (LIA) and Younger Dryas (YD) paleoclimate reconstructions for the Huancané outlet glacier of the Quelccaya Ice Cap (QIC) and low-latitude southern hemisphere regional sea surface temperatures (SSTs) using a coupled ice-flow and energy balance model. We also model the effects of long-term changes in the summit temperature and precipitiation rate and the effects of interannual climate variability on the Huancané glacier length. We find temperature to be the dominant climate driver of glacier length change. Also, we find that interannual climate variability cannot adequately explain glacier advances inferred from the geomorphic record, necessitating that these features were formed during past colder climates. To constrain our LIA reconstruction, we incorporate the QIC ice core record, finding a LIA air temperature cooling at the ice cap of between ~0.7 °C and ~1.1 °C and ~0.4 °C and regional SSTs cooling of ~0.6 °C. For the YD paleoclimate reconstructions, we propose two limits on the precipitation rate, since the ice core record does not extend into the Pleistocene: 1) the precipitation rate scales with the Clausius-Clapeyron relationship (upper limit on cooling) and 2) the precipitation rate increases by 40% (lower limit on cooling), which is an increase about twice as great as the regional increases realized in GCM simulations for the period. The first limit requires ~1.6 °C cooling in ice cap air temperatures and ~0.9 °C cooling in SSTs, and the second limit requires ~1.0 °C cooling in ice cap air temperatures and ~0.5 °C cooling in SSTs. Our temperature reconstructions are in good agreement with the magnitude and trend of GCM simulations that incorporate the forcing mechanisms hypothesized to have caused these climate change events.


Polar vortices on Earth and Mars: A comparative study of the climatology and variability from reanalyses.

Quarterly journal of the Royal Meteorological Society. Royal Meteorological Society (Great Britain) 141 (2015) 550-562

DM Mitchell, L Montabone, S Thomson, PL Read

Polar vortices on Mars provide case-studies to aid understanding of geophysical vortex dynamics and may help to resolve long-standing issues regarding polar vortices on Earth. Due to the recent development of the first publicly available Martian reanalysis dataset (MACDA), for the first time we are able to characterise thoroughly the structure and evolution of the Martian polar vortices, and hence perform a systematic comparison with the polar vortices on Earth. The winter atmospheric circulations of the two planets are compared, with a specific focus on the structure and evolution of the polar vortices. The Martian residual meridional overturning circulation is found to be very similar to the stratospheric residual circulation on Earth during winter. While on Earth this residual circulation is very different from the Eulerian circulation, on Mars it is found to be very similar. Unlike on Earth, it is found that the Martian polar vortices are annular, and that the Northern Hemisphere vortex is far stronger than its southern counterpart. While winter hemisphere differences in vortex strength are also reported on Earth, the contrast is not as large. Distinctions between the two planets are also apparent in terms of the climatological vertical structure of the vortices, in that the Martian polar vortices are observed to decrease in size at higher altitudes, whereas on Earth the opposite is observed. Finally, it is found that the Martian vortices are less variable through the winter than on Earth, especially in terms of the vortex geometry. During one particular major regional dust storm on Mars (Martian year 26), an equatorward displacement of the vortex is observed, sharing some qualitative characteristics of sudden stratospheric warmings on Earth.

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