Publications


A dynamical systems explanation of the Hurst effect and atmospheric low-frequency variability.

Scientific reports 5 (2015) 9068-

CL Franzke, SM Osprey, P Davini, NW Watkins

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.


The stratospheric wintertime response to applied extratropical torques and its relationship with the annular mode

CLIMATE DYNAMICS 44 (2015) 2513-2537

PAG Watson, LJ Gray


Possible impacts of a future Grand Solar Minimum on climate: Stratospheric and global circulation changes

Journal of Geophysical Research: Atmospheres (2015) n/a-n/a

AC Maycock, S Ineson, LJ Gray, AA Scaife, JA Anstey, M Lockwood, N Butchart, SC Hardiman, DM Mitchell, SM Osprey


Global distributions of overlapping gravity waves in HIRDLS data

Atmospheric Chemistry and Physics Discussions 15 (2015) 4333-4382

CJ Wright, SM Osprey, JC Gille


Does the ECMWF IFS Convection Parameterization with Stochastic Physics Correctly Reproduce Relationships between Convection and the Large-Scale State?

JOURNAL OF THE ATMOSPHERIC SCIENCES 72 (2015) 236-242

PAG Watson, HM Christensen, TN Palmer


Observation of seasonal variation of atmospheric multiple-muon events in the MINOS Near and Far Detectors

PHYSICAL REVIEW D 91 (2015) ARTN 112006

P Adamson, I Anghel, A Aurisano, G Barr, M Bishai, A Blake, GJ Bock, D Bogert, SV Cao, CM Castromonte, S Childress, JAB Coelho, L Corwin, D Cronin-Hennessy, JK de Jong, AV Devan, NE Devenish, MV Diwan, CO Escobar, JJ Evans, E Falk, GJ Feldman, MV Frohne, HR Gallagher, RA Gomes, MC Goodman, P Gouffon, N Graf, R Gran, K Grzelak, A Habig, SR Hahn, J Hartnell, R Hatcher, A Holin, J Huang, J Hylen, GM Irwin, Z Isvan, C James, D Jensen, T Kafka, SMS Kasahara, G Koizumi, M Kordosky, A Kreymer, K Lang, J Ling, PJ Litchfield, P Lucas, WA Mann, ML Marshak, N Mayer, C McGivern, MM Medeiros, R Mehdiyev, JR Meier, MD Messier, WH Miller, SR Mishra, SM Sher, CD Moore, L Mualem, J Musser, D Naples, JK Nelson, HB Newman, RJ Nichol, JA Nowak, J O'Connor, M Orchanian, S Osprey, RB Pahlka, J Paley, RB Patterson, G Pawloski, A Perch, S Phan-Budd, RK Plunkett, N Poonthottathil, X Qiu, A Radovic, B Rebel, C Rosenfeld, HA Rubin, MC Sanchez, J Schneps, A Schreckenberger, P Schreiner, R Sharma, A Sousa, N Tagg, RL Talaga, J Thomas, MA Thomson, X Tian, A Timmons, SC Tognini, R Toner, D Torretta, J Urheim, P Vahle, B Viren, A Weber, RC Webb, C White, L Whitehead, LH Whitehead, SG Wojcicki, R Zwaska, MINOS Collaboration


The stratospheric wintertime response to applied extratropical torques and its relationship with the annular mode

Climate Dynamics 44 (2015) 2513-2537

PAG Watson, LJ Gray, LJ Gray

© 2014, The Author(s). The response of the wintertime Northern Hemisphere (NH) stratosphere to applied extratropical zonally symmetric zonal torques, simulated by a primitive equation model of the middle atmosphere, is presented. This is relevant to understanding the effect of gravity wave drag (GWD) in models and the influence of natural forcings such as the quasi-biennial oscillation (QBO), El Ninõ-Southern Oscillation (ENSO), solar cycle and volcanic eruptions on the polar vortex. There is a strong feedback due to planetary waves, which approximately cancels the direct effect of the torque on the zonal acceleration in the steady state and leads to an EP flux convergence response above the torque’s location. The residual circulation response is very different to that predicted assuming wave feedbacks are negligible. The results are consistent with the predictions of ray theory, with applied westerly torques increasing the meridional potential vorticity gradient, thus encouraging greater upward planetary wave propagation into the stratosphere. The steady state circulation response to torques applied at high latitudes closely resembles the Northern annular mode (NAM) in perpetual January simulations. This behaviour is analogous to that shown by the Lorenz system and tropospheric models. Imposed westerly high-latitude torques lead counter-intuitively to an easterly zonal mean zonal wind (Formula Presented.) response at high latitudes, due to the wave feedbacks. However, in simulations with a seasonal cycle, the feedbacks are qualitatively similar but weaker, and the long-term response is less NAM-like and no longer easterly at high latitudes. This is consistent with ray theory and differences in climatological (Formula Presented.) between the two types of simulations. The response to a tropospheric wave forcing perturbation is also NAM-like. These results suggest that dynamical feedbacks tend to make the long-term NH extratropical stratospheric response to arbitrary external forcings NAM-like, but only if the feedbacks are sufficiently strong. This may explain why the observed polar vortex responses to natural forcings such as the QBO and ENSO are NAM-like. The results imply that wave feedbacks must be understood and accurately modelled in order to understand and predict the influence of GWD and other external forcings on the polar vortex, and that biases in a model’s climatology will cause biases in these feedbacks.


Mechanisms for the Holton-Tan relationship and its decadal variation

JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES 119 (2014) 2811-2830

H Lu, TJ Bracegirdle, T Phillips, A Bushell, L Gray


Northern winter climate change: Assessment of uncertainty in CMIP5 projections related to stratosphere-troposphere coupling

JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES 119 (2014) ARTN 2013JD021403

E Manzini, AY Karpechko, J Anstey, MP Baldwin, RX Black, C Cagnazzo, N Calvo, A Charlton-Perez, B Christiansen, P Davini, E Gerber, M Giorgetta, L Gray, SC Hardiman, Y-Y Lee, DR Marsh, BA McDaniel, A Purich, AA Scaife, D Shindell, S-W Son, S Watanabe, G Zappa


Interaction of gravity waves with the QBO: A satellite perspective

JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES 119 (2014) 2329-2355

M Ern, F Ploeger, P Preusse, JC Gille, LJ Gray, S Kalisch, MG Mlynczak, RJM III, M Riese


Observation of muon intensity variations by season with the MINOS far detector

Physical Review D - Particles, Fields, Gravitation and Cosmology 81 (2010)

P Adamson, C Andreopoulos, KE Arms, R Armstrong, DJ Auty, DS Ayres, C Backhouse, J Barnett, G Barr, WL Barrett, BR Becker, M Bishai, A Blake, B Bock, GJ Bock, DJ Boehnlein, D Bogert, C Bower, S Cavanaugh, JD Chapman, D Cherdack, S Childress, BC Choudhary, BC Choudhary, JH Cobb, SJ Coleman, D Cronin-Hennessy, AJ Culling, IZ Danko, JK De Jong, JK De Jong, NE Devenish, MV Diwan, M Dorman, CO Escobar, JJ Evans, JJ Evans, E Falk, GJ Feldman, TH Fields, MV Frohne, MV Frohne, HR Gallagher, A Godley, MC Goodman, P Gouffon, R Gran, EW Grashorn, EW Grashorn, EW Grashorn, K Grzelak, K Grzelak, A Habig, D Harris, PG Harris, J Hartnell, J Hartnell, R Hatcher, K Heller, A Himmel, A Holin, J Hylen, GM Irwin, Z Isvan, DE Jaffe, C James, D Jensen, T Kafka, SMS Kasahara, G Koizumi, S Kopp, M Kordosky, M Kordosky, K Korman, DJ Koskinen, DJ Koskinen, DJ Koskinen, Z Krahn, A Kreymer, K Lang, J Ling, PJ Litchfield, L Loiacono, P Lucas, J Ma, WA Mann, ML Marshak, JS Marshall, N Mayer, AM McGowan, AM McGowan, AM McGowan, R Mehdiyev, JR Meier, MD Messier, CJ Metelko, DG Michael, WH Miller, SR Mishra, J Mitchell

The temperature of the upper atmosphere affects the height of primary cosmic ray interactions and the production of high-energy cosmic ray muons which can be detected deep underground. The MINOS far detector at Soudan, MN, has collected over 67×106 cosmic ray induced muons. The underground muon rate measured over a period of five years exhibits a 4% peak-to-peak seasonal variation which is highly correlated with the temperature in the upper atmosphere. The coefficient, αT, relating changes in the muon rate to changes in atmospheric temperature was found to be αT=0.873±0. 009(stat)±0.010(syst). Pions and kaons in the primary hadronic interactions of cosmic rays in the atmosphere contribute differently to αT due to the different masses and lifetimes. This allows the measured value of αT to be interpreted as a measurement of the K/π ratio for Ep 7TeV of 0.12-0.05+0.07, consistent with the expectation from collider experiments. © 2010 The American Physical Society.


Observation of muon intensity variations by season with the MINOS near detector

PHYSICAL REVIEW D 90 (2014) ARTN 012010

P Adamson, I Anghel, A Aurisano, G Barr, M Bishai, A Blake, GJ Bock, D Bogert, SV Cao, CM Castromonte, S Childress, JAB Coelho, L Corwin, D Cronin-Hennessy, JK de Jong, AV Devan, NE Devenish, MV Diwan, CO Escobar, JJ Evans, E Falk, GJ Feldman, TH Fields, MV Frohne, HR Gallagher, RA Gomes, MC Goodman, P Gouffon, N Graf, R Gran, K Grzelak, A Habig, SR Hahn, J Hartnell, R Hatcher, A Holin, J Huang, J Hylen, GM Irwin, Z Isvan, C James, D Jensen, T Kafka, SMS Kasahara, G Koizumi, M Kordosky, A Kreymer, K Lang, J Ling, PJ Litchfield, P Lucas, WA Mann, ML Marshak, M Mathis, N Mayer, C McGivern, MM Medeiros, R Mehdiyev, JR Meier, MD Messier, WH Miller, SR Mishra, SM Sher, CD Moore, L Mualem, J Musser, D Naples, JK Nelson, HB Newman, RJ Nichol, JA Nowak, J O'Connor, M Orchanian, S Osprey, RB Pahlka, J Paley, RB Patterson, G Pawloski, A Perch, S Phan-Budd, RK Plunkett, N Poonthottathil, X Qiu, A Radovic, B Rebel, C Rosenfeld, HA Rubin, MC Sanchez, J Schneps, A Schreckenberger, P Schreiner, R Sharma, A Sousa, N Tagg, RL Talaga, J Thomas, MA Thomson, X Tian, A Timmons, SC Tognini, R Toner, D Torretta, J Urheim, P Vahle, B Viren, A Weber, RC Webb, C White, L Whitehead, LH Whitehead, SG Wojcicki, R Zwaska, MINOS Collaboration


How Does the Quasi-Biennial Oscillation Affect the Stratospheric Polar Vortex?

JOURNAL OF THE ATMOSPHERIC SCIENCES 71 (2014) 391-409

PAG Watson, LJ Gray


Skillful Seasonal Prediction of the Southern Annular Mode and Antarctic Ozone

JOURNAL OF CLIMATE 27 (2014) 7462-7474

WJM Seviour, SC Hardiman, LJ Gray, N Butchart, C MacLachlan, AA Scaife


The Influence of Stratospheric Vortex Displacements and Splits on Surface Climate

JOURNAL OF CLIMATE 26 (2013) 2668-2682

DM Mitchell, LJ Gray, J Anstey, MP Baldwin, AJ Charlton-Perez


Recent variability of the solar spectral irradiance and its impact on climate modelling

ATMOSPHERIC CHEMISTRY AND PHYSICS 13 (2013) 3945-3977

I Ermolli, K Matthes, TD de Wit, NA Krivova, K Tourpali, M Weber, YC Unruh, L Gray, U Langematz, P Pilewskie, E Rozanov, W Schmutz, A Shapiro, SK Solanki, TN Woods


Multi-model analysis of Northern Hemisphere winter blocking: Model biases and the role of resolution

Journal of Geophysical Research: Atmospheres 118 (2013) 3956-3971

JA Anstey, P Davini, P Davini, LJ Gray, TJ Woollings, N Butchart, C Cagnazzo, C Cagnazzo, B Christiansen, SC Hardiman, SM Osprey, S Yang

Blocking of the tropospheric jet stream during Northern Hemisphere winter (December-January-February) is examined in a multi-model ensemble of coupled atmosphere-ocean general circulation models (GCMs) obtained from the Coupled Model Intercomparison Project Phase 5 (CMIP5). The CMIP5 models exhibit large biases in blocking frequency and related biases in tropospheric jet latitude, similar to earlier generations of GCMs. Underestimated blocking at high latitudes, especially over Europe, is common. In general, model biases decrease as model resolution increases. Increased blocking frequency at high latitudes in both the Atlantic and Pacific basins, as well as more realistic variability of Atlantic jet latitude, are associated with increased vertical resolution in the mid-troposphere to lowermost stratosphere. Finer horizontal resolution is associated with higher blocking frequency at all latitudes in the Atlantic basin but appears to have no systematic impact on blocking near Greenland or in the Pacific basin. Results from the CMIP5 analysis are corroborated by additional controlled experiments using selected GCMs. Key PointsCMIP5 models have large blocking biases and associated jet biasesIncreased spatial resolution is associated with reduced blocking and jet biasesVertical and horizontal resolution give blocking changes in different regions ©2013. American Geophysical Union. All Rights Reserved.


The impact of stratospheric resolution on the detectability of climate change signals in the free atmosphere

GEOPHYSICAL RESEARCH LETTERS 40 (2013) 937-942

DM Mitchell, PA Stott, LJ Gray, MR Allen, FC Lott, N Butchart, SC Hardiman, SM Osprey


Revisiting the controversial issue of tropical tropospheric temperature trends

Geophysical Research Letters 40 (2013) 2801-2806

DM Mitchell, PW Thorne, PA Stott, LJ Gray, LJ Gray

Controversy remains over a discrepancy between modeled and observed tropical upper tropospheric temperature trends. This discrepancy is reassessed using simulations from the Coupled Climate Model Inter-comparison Project phase 5 (CMIP 5) together with radiosonde and surface observations that provide multiple realizations of possible "observed" temperatures given various methods of homogenizing the data. Over the 1979-2008 period, tropical temperature trends are not consistent with observations throughout the depth of the troposphere, and this primarily stems from a poor simulation of the surface temperature trends. This discrepancy is substantially reduced when (1) atmosphere-only simulations are examined or (2) the trends are considered as an amplification of the surface temperature trend with height. Using these approaches, it is shown that within observational uncertainty, the 5-95 percentile range of temperature trends from both coupled-ocean and atmosphere-only models are consistent with the analyzed observations at all but the upper most tropospheric level (150 hPa), and models with ultra-high horizontal resolution (≤ 0.5° × 0.5°) perform particularly well. Other than model resolution, it is hypothesized that this remaining discrepancy could be due to a poor representation of stratospheric ozone or remaining observational uncertainty. © 2013 American Geophysical Union. All Rights Reserved.


A practical method to identify displaced and split stratospheric polar vortex events

Geophysical Research Letters 40 (2013) 5268-5273

WJM Seviour, DM Mitchell, DM Mitchell, LJ Gray, LJ Gray

Extreme variability of the stratospheric polar vortex during winter can manifest as a displaced vortex event or a split vortex event. The influence of this vortex disruption can extend downwards and affect surface weather patterns. In particular, vortex splitting events have been associated with a negative Arctic Oscillation pattern. An assessment of the impacts of climate change on the polar vortex is therefore important, and more climate models now include a wella-resolved stratosphere. To aid this analysis, we introduce a practical thresholda-based method to distinguish between displaced and split vortex events. It requires only geopotential height at 10 hPa to measure the geometry of the vortex using twoa-dimensional moment diagnostics. It captures extremes of vortex variability at least, as well as previous methods when applied to reanalysis data, and has the advantage of being easily employed to analyze climate model simulations. Key Points It is important to distinguish split and displaced vortex events Current methods to do so are not easily-applicable to climate models A new method is easily-applicable and can accurately identify these events ©2013. American Geophysical Union. All Rights Reserved.