Atmospheric Circulation of Terrestrial Exoplanets

The investigation of planets around other stars began with the study of gas giants, but is now extending to the discovery and characterization of super-Earths and terrestrial planets. Motivated by this observational tide, we survey the basic dynamical principles governing the atmospheric circulation of terrestrial exoplanets, and discuss the interaction of their circulation with the hydrological cycle and global-scale climate feedbacks. Terrestrial exoplanets occupy a wide range of physical and dynamical conditions, only a small fraction of which have yet been explored in detail. Our approach is to lay out the fundamental dynamical principles governing the atmospheric circulation on terrestrial planets--broadly defined--and show how they can provide a foundation for understanding the atmospheric behavior of these worlds. We first survey basic atmospheric dynamics, including the role of geostrophy, baroclinic instabilities, and jets in the strongly rotating regime (the "extratropics") and the role of the Hadley circulation, wave adjustment of the thermal structure, and the tendency toward equatorial superrotation in the slowly rotating regime (the "tropics"). We then survey key elements of the hydrological cycle, including the factors that control precipitation, humidity, and cloudiness. Next, we summarize key mechanisms by which the circulation affects the global-mean climate, and hence planetary habitability. In particular, we discuss the runaway greenhouse, transitions to snowball states, atmospheric collapse, and the links between atmospheric circulation and CO2 weathering rates. We finish by summarizing the key questions and challenges for this emerging field in the future.Comment: Invited review, in press for the Arizona Space Science Series book "Comparative Climatology of Terrestrial Planets" (S. Mackwell, M. Bullock, and J. Harder, editors). 56 pages, 26 figure

Spatiotemporal coding of inputs for a system of globally coupled phase oscillators

Copyright © 2008 The American Physical SocietyWe investigate the spatiotemporal coding of low amplitude inputs to a simple system of globally coupled phase oscillators with coupling function g(ϕ)=−sin(ϕ+α)+rsin(2ϕ+β) that has robust heteroclinic cycles (slow switching between cluster states). The inputs correspond to detuning of the oscillators. It was recently noted that globally coupled phase oscillators can encode their frequencies in the form of spatiotemporal codes of a sequence of cluster states [P. Ashwin, G. Orosz, J. Wordsworth, and S. Townley, SIAM J. Appl. Dyn. Syst. 6, 728 (2007)]. Concentrating on the case of N=5 oscillators we show in detail how the spatiotemporal coding can be used to resolve all of the information that relates the individual inputs to each other, providing that a long enough time series is considered. We investigate robustness to the addition of noise and find a remarkable stability, especially of the temporal coding, to the addition of noise even for noise of a comparable magnitude to the inputs

Eliciting risk preferences that predict risky health behaviour: A comparison of two approaches

Information on attitudes to risk could increase understanding of and explain risky health behaviors. We investigate two approaches to eliciting risk preferences in the health domain, a novel “indirect” lottery elicitation approach with health states as outcomes and a “direct” approach where respondents are asked directly about their willingness to take risks. We compare the ability of the two approaches to predict health-related risky behaviors in a general adult population. We also investigate a potential framing effect in the indirect lottery elicitation approach. We find that risk preferences elicited using the direct approach can better predict health-related risky behavior than those elicited using the indirect approach. Moreover, a seemingly innocuous change to the framing of the lottery question results in significantly different risk preference estimates, and conflicting conclusions about the ability of the indicators to predict risky health behaviors

Systems modelling predicts chronic inflammation and genomic instability prevent effective mitochondrial regulation during biological ageing

The regulation of mitochondrial turnover under conditions of stress occurs partly through the AMPK-NAD+-PGC1α-SIRT1 signalling pathway. This pathway can be affected by both genomic instability and chronic inflammation since these will result in an increased rate of NAD+ degradation through PARP1 and CD38 respectively. In this work we develop a computational model of this signalling pathway, calibrating and validating it against experimental data. The computational model is used to study mitochondrial turnover under conditions of stress and how it is affected by genomic instability, chronic inflammation and biological ageing in general. We report that the AMPK-NAD+-PGC1α-SIRT1 signalling pathway becomes less responsive with age and that this can prime for the accumulation of dysfunctional mitochondria

Advance telephone calls ahead of reminder questionnaires increase response rate in non-responders compared to questionnaire reminders only : The RECORD phone trial

Peer reviewedPublisher PD

Turbulence, waves, and jets in a differentially heated rotating annulus experiment

We report an analog laboratory study of planetary-scale turbulence and jet formation. A rotating annulus was cooled and heated at its inner and outer walls, respectively, causing baroclinic instability to develop in the fluid inside. At high rotation rates and low temperature differences, the flow became chaotic and ultimately fully turbulent. The inclusion of sloping top and bottom boundaries caused turbulenteddies to behave like planetary waves at large scales, and eddy interaction with the zonal flow then led to the formation of several alternating jets at mid-depth. The jets did not scale with the Rhines length, and spectral analysis of the flow indicated a distinct separation between jets and eddies in wavenumber space, with direct energy transfer occurring nonlocally between them. Our results suggest that the traditional “turbulent cascade” picture of zonal jet formation may be an inappropriate one in the geophysically important case of large-scale flows forced by differential solar heating.Engineering and Applied Science

Fermi resonance and the quantum mechanical basis of global warming

Although the scientific principles of anthropogenic climate change are well-established, existing calculations of the warming effect of carbon dioxide rely on spectral absorption databases, which obscures the physical foundations of the climate problem. Here, we show how CO2 radiative forcing can be expressed via a first-principles description of the molecule’s key vibrational-rotational transitions. Our analysis elucidates the dependence of carbon dioxide’s effectiveness as a greenhouse gas on the Fermi resonance between the symmetric stretch mode ν1 and bending mode ν2 . It is remarkable that an apparently accidental quantum resonance in an otherwise ordinary three-atom molecule has had such a large impact on our planet’s climate over geologic time, and will also help determine its future warming due to human activity. In addition to providing a simple explanation of CO2 radiative forcing on Earth, our results may have implications for understanding radiation and climate on other planets

Belonging to a different landscape: repurposing nationalist affects

This is an article about the embodied, sensual experience of rural landscape as a site where racialized feelings of national belonging get produced. Largely impervious to criticism and reformation by 'thin' legal-political versions of multicultural or cosmopolitan citizenship, it is my suggestion that this racialized belonging is best confronted through the recognition and appreciation of precisely what makes it so compelling. Through an engagement with the theorization of affect in the work of Divya Praful Tolia-Kelly, I consider the resources immanent to the perception of landscapes of national belonging that might be repurposed to unravel that belonging from within. I suggest that forms of environmental consciousness can unpick the mutually reinforcing relationships between nature and nation, opening up opportunities for thinking identity and belonging in different ways, and allowing rural landscapes to become more hospitable places

Semi-fortified palatial complexes in Central Asia: new work at the Great Kyz Kala, Merv, Turkmenistan

Within Central Asia there is an unusual group of earthen buildings (köshks), usually constructed on raised platforms, with vertical engaged columns forming iconic ‘corrugations’ on the exterior walls. The complexes are semi-fortified, with a second storey entrance, and often with asymmetrical ranges of rooms around an internal courtyard. Little systematic archaeological work has taken place on these monuments, which have mainly been studied as relatively eroded standing structures. However, recent work at the Great Kyz Kala at Merv, Turkmenistan, the largest surviving monumental köshk in Central Asia, has provided more details of construction and use. The excavations suggest that this complex was constructed in the 8th/9th century CE, with well-appointed rooms on the second storey, including a large hall, and functional rooms and storage spaces around a courtyard on the lower floor. The complex was set within an enclosure, containing gardens and possibly ancillary buildings. This particular köshk may have acted as an elite palatial suburban residence, perhaps for the governor of Merv