NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT 806 (2016) 279-306
Synchronisation of the equatorial QBO by the annual cycle in tropical upwelling in a warming climate
QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY 142 (2016) 1111-1120
The stratospheric wintertime response to applied extratropical torques and its relationship with the annular mode
CLIMATE DYNAMICS 44 (2015) 2513-2537
Scientific reports 5 (2015) 9068-
The Hurst effect plays an important role in many areas such as physics, climate and finance. It describes the anomalous growth of range and constrains the behavior and predictability of these systems. The Hurst effect is frequently taken to be synonymous with Long-Range Dependence (LRD) and is typically assumed to be produced by a stationary stochastic process which has infinite memory. However, infinite memory appears to be at odds with the Markovian nature of most physical laws while the stationarity assumption lacks robustness. Here we use Lorenz's paradigmatic chaotic model to show that regime behavior can also cause the Hurst effect. By giving an alternative, parsimonious, explanation using nonstationary Markovian dynamics, our results question the common belief that the Hurst effect necessarily implies a stationary infinite memory process. We also demonstrate that our results can explain atmospheric variability without the infinite memory previously thought necessary and are consistent with climate model simulations.
ATMOSPHERIC CHEMISTRY AND PHYSICS 15 (2015) 8459-8477
JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES 120 (2015) 11203-11214
Observation of seasonal variation of atmospheric multiple-muon events in the MINOS Near and Far Detectors
PHYSICAL REVIEW D 91 (2015) ARTN 112006
Atmospheric Chemistry and Physics Discussions 15 (2015) 4333-4382
This thesis advances our understanding of midlatitude storm tracks and how they respond to perturbations in the climate system. The midlatitude storm tracks are regions of maximal turbulent kinetic energy in the atmosphere. Through them, the bulk of the atmospheric transport of energy, water vapor, and angular momentum occurs in midlatitudes. Therefore, they are important regulators of climate, controlling basic features such as the distribution of surface temperatures, precipitation, and winds in midlatitudes. Storm tracks are robustly projected to shift poleward in global-warming simulations with current climate models. Yet the reasons for this shift have remained unclear. Here we show that this shift occurs even in extremely idealized (but still three-dimensional) simulations of dry atmospheres. We use these simulations to develop an understanding of the processes responsible for the shift and develop a conceptual model that accounts for it. We demonstrate that changes in the convective static stability in the deep tropics alone can drive remote shifts in the midlatitude storm tracks. Through simulations with a dry idealized general circulation model (GCM), midlatitude storm tracks are shown to be located where the mean available potential energy (MAPE, a measure of the potential energy available to be converted into kinetic energy) is maximal. As the climate varies, even if only driven by tropical static stability changes, the MAPE maximum shifts primarily because of shifts of the maximum of near-surface meridional temperature gradients. The temperature gradients shift in response to changes in the width of the tropical Hadley circulation, whose width is affected by the tropical static stability. Storm tracks generally shift in tandem with shifts of the subtropical terminus of the Hadley circulation. We develop a one-dimensional diffusive energy-balance model that links changes in the Hadley circulation to midlatitude temperature gradients and so to the storm tracks. It is the first conceptual model to incorporate a dynamical coupling between the tropical Hadley circulation and midlatitude turbulent energy transport. Numerical and analytical solutions of the model elucidate the circumstances of when and how the storm tracks shift in tandem with the terminus of the Hadley circulation. They illustrate how an increase of only the convective static stability in the deep tropics can lead to an expansion of the Hadley circulation and a poleward shift of storm tracks. The simulations with the idealized GCM and the conceptual energy-balance model demonstrate a clear link between Hadley circulation dynamics and midlatitude storm track position. With the help of the hierarchy of models presented in this thesis, we obtain a closed theory of storm track shifts in dry climates. The relevance of this theory for more realistic moist climates is discussed.
Possible impacts of a future grand solar minimum on climate: Stratospheric and global circulation changes.
Journal of geophysical research. Atmospheres : JGR 120 (2015) 9043-9058
A future decline in solar activity would not offset projected global warmingA future decline in solar activity could have larger regional effects in winterTop-down mechanism contributes to Northern Hemisphere regional response.
A comparison of temperature and precipitation responses to different Earth radiation management geoengineering schemes
JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES 120 (2015) 9352-9373
JOURNAL OF CLIMATE 27 (2014) 7462-7474
JOURNAL OF THE ATMOSPHERIC SCIENCES 71 (2014) 391-409
JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES 119 (2014) 2811-2830
Northern winter climate change: Assessment of uncertainty in CMIP5 projections related to stratosphere-troposphere coupling
JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES 119 (2014) ARTN 2013JD021403
PHYSICAL REVIEW D 90 (2014) ARTN 012010
JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES 119 (2014) 2329-2355
Stratospheric variability in 20th Century CMIP5 simulations of the Met Office climate model: High-top versus low-top
J CLIM 26 (2013) 5