Search

Your search keyword '"Oscar Dimdore‐Miles"' showing total 9 results
Start Over Author "Oscar Dimdore‐Miles"
9 results on '"Oscar Dimdore‐Miles"'

1. The Evaluation of the North Atlantic Climate System in UKESM1 Historical Simulations for CMIP6

Author

Jon Robson, Yevgeny Aksenov, Thomas J. Bracegirdle, Oscar Dimdore‐Miles, Paul T. Griffiths, Daniel P. Grosvenor, Daniel L. R. Hodson, James Keeble, Claire MacIntosh, Alex Megann, Scott Osprey, Adam C. Povey, David Schröder, Mingxi Yang, Alexander T. Archibald, Ken S. Carslaw, Lesley Gray, Colin Jones, Brian Kerridge, Diane Knappett, Till Kuhlbrodt, Maria Russo, Alistair Sellar, Richard Siddans, Bablu Sinha, Rowan Sutton, Jeremy Walton, and Laura J. Wilcox

Subjects
North Atlantic, Earth system model, CMIP6, model evaluation, Physical geography, GB3-5030, Oceanography, GC1-1581
Abstract

Abstract Earth system models enable a broad range of climate interactions that physical climate models are unable to simulate. However, the extent to which adding Earth system components changes or improves the simulation of the physical climate is not well understood. Here we present a broad multivariate evaluation of the North Atlantic climate system in historical simulations of the UK Earth System Model (UKESM1) performed for CMIP6. In particular, we focus on the mean state and the decadal time scale evolution of important variables that span the North Atlantic climate system. In general, UKESM1 performs well and realistically simulates many aspects of the North Atlantic climate system. Like the physical version of the model, we find that changes in external forcing, and particularly aerosol forcing, are an important driver of multidecadal change in UKESM1, especially for Atlantic Multidecadal Variability and the Atlantic Meridional Overturning Circulation. However, many of the shortcomings identified are similar to common biases found in physical climate models, including the physical climate model that underpins UKESM1. For example, the summer jet is too weak and too far poleward; decadal variability in the winter jet is underestimated; intraseasonal stratospheric polar vortex variability is poorly represented; and Arctic sea ice is too thick. Forced shortwave changes may be also too strong in UKESM1, which, given the important role of historical aerosol forcing in shaping the evolution of the North Atlantic in UKESM1, motivates further investigation. Therefore, physical model development, alongside Earth system development, remains crucial in order to improve climate simulations.

Published
2020
Full Text
View/download PDF

2. Interactions between the stratospheric polar vortex and Atlantic circulation on seasonal to multi-decadal timescales

Author

Scott Osprey, Jon Robson, Rowan Sutton, Lesley J. Gray, Bablu Sinha, and Oscar Dimdore-Miles

Subjects
Atmospheric Science, North Atlantic oscillation, Polar vortex, Climatology, Ocean current, Northern Hemisphere, Polar, Jet stream, Hiatus, Geology, Physics::Atmospheric and Oceanic Physics, Vortex, Physics::Geophysics
Abstract

Variations in the strength of the Northern Hemisphere winter polar stratospheric vortex can influence surface variability in the Atlantic sector. Disruptions of the vortex, known as sudden stratospheric warmings (SSW), are associated with an equatorward shift and deceleration of the North Atlantic jet stream, negative phases of the North Atlantic Oscillation as well as cold snaps over Eurasia and North America. Despite clear influences at the surface on sub-seasonal timescales, how stratospheric vortex variability interacts with ocean circulation on decadal to multi-decadal timescales is less well understood. In this study, we use a 1000-year pre-industrial control simulation of the UK Earth System Model to study such interactions using a wavelet analysis technique to examine non-stationary periodic signals in the vortex and ocean. We find that intervals which exhibit persistent anomalous vortex behaviour lead to oscillatory responses in the Atlantic Meridional Overturning Circulation (AMOC). The origin of these responses appears to be highly non-stationary with spectral power in vortex variability and the AMOC at periods of 30 and 50 years. In contrast, AMOC variations on longer timescales (near 90-year periods) are found to lead to a vortex response, through a pathway involving the equatorial Pacific and Quasi-biennial Oscillation. Using the relationship between persistent vortex behaviour and the AMOC response established in the model, we use a regression analysis to estimate the potential contribution of the 8 year SSW hiatus interval in the 1990s to the recent negative trend in AMOC observations. The result suggests that approximately 30 % of the trend may have been caused by the SSW hiatus.

Published
2022

5. Assessing the spread of the novel coronavirus in the absence of mass testing

Author

Oscar Dimdore-Miles and David Miles

Subjects
2019-20 coronavirus outbreak, Coronavirus disease 2019 (COVID-19), viruses, Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), Transmission rate, Population, 030204 cardiovascular system & hematology, medicine.disease_cause, Asymptomatic, Virus, 1117 Public Health and Health Services, Indirect evidence, 03 medical and health sciences, 0302 clinical medicine, medicine, Humans, 030212 general & internal medicine, education, General Clinical Medicine, Coronavirus, Original Paper, education.field_of_study, SARS-CoV-2, business.industry, COVID-19, 1103 Clinical Sciences, General Medicine, Original Papers, Virology, Geography, 1701 Psychology, Communicable Disease Control, medicine.symptom, business, Epidemic model, Demography
Abstract

Background Assessing why the spread of the COVID 19 virus slowed down in many countries in March through to May of 2020 is of great significance. The relative role of restrictions on behaviour (”lockdowns”) and of a natural slowing for other reasons is difficult to asses when mass testing was not widely done. This paper assesses the evolution of the spread of the COVID 19 virus over this period when there was not data on test results for a large, random sample of the population. Method We estimate a version of the SIR model applied to data on the numbers who were tested positive in several countries over the period when the virus spread very fast and then its spread slowed sharply. Up to the end of April 2020 test data came from non random samples of populations who were overwhelmingly those who displayed symptoms. Using data from a period when the criteria used for testing (which was that people had clear symptoms) was relatively consistent is important in drawing out the message from test results. We use this data to assess two things: how large might be the group of those infected who were not recorded; how effective were lockdown measures in slowing the spread of the infection. Results We find that to match data on daily new cases of the virus, the estimated model favours high values for the number of people infected but not recorded. Conclusions Our findings suggest that the infection may have spread far enough in many countries by April 2020 to have been a significant factor behind the fall in measured new cases. Government restrictions on behavior ‐ lockdowns ‐ were only one factor behind slowing in the spread of the virus.

Published
2020
Full Text
View/download PDF

6. The Evaluation of the North Atlantic Climate System in UKESM1 Historical Simulations for CMIP6

Author

Till Kuhlbrodt, Thomas J. Bracegirdle, Alistair Sellar, James Keeble, David Schröder, Adam C. Povey, Daniel P. Grosvenor, Richard Siddans, Daniel L. R. Hodson, Bablu Sinha, Jeremy Walton, Brian Kerridge, Alexander T. Archibald, Scott Osprey, Kenneth S. Carslaw, Mingxi Yang, M. R. Russo, Jon Robson, Claire Macintosh, Laura Wilcox, Yevgeny Aksenov, Alex Megann, Lesley J. Gray, Diane Knappett, Paul T. Griffiths, Oscar Dimdore-Miles, Rowan Sutton, and C. Jones

Subjects
model evaluation, Physical geography, 010504 meteorology & atmospheric sciences, Climate system, Forcing (mathematics), GC1-1581, 010502 geochemistry & geophysics, Oceanography, 01 natural sciences, Polar vortex, Environmental Chemistry, Earth system model, CMIP6, 0105 earth and related environmental sciences, Global and Planetary Change, geography, geography.geographical_feature_category, North Atlantic, Arctic ice pack, GB3-5030, Earth system science, 13. Climate action, Climatology, General Earth and Planetary Sciences, Environmental science, Climate model, Shortwave
Abstract

Earth system models enable a broad range of climate interactions that physical climate models are unable to simulate. However, the extent to which adding Earth system components changes or improves the simulation of the physical climate is not well understood. Here we present a broad multivariate evaluation of the North Atlantic climate system in historical simulations of the UK Earth System Model (UKESM1) performed for CMIP6. In particular, we focus on the mean state and the decadal time scale evolution of important variables that span the North Atlantic climate system. In general, UKESM1 performs well and realistically simulates many aspects of the North Atlantic climate system. Like the physical version of the model, we find that changes in external forcing, and particularly aerosol forcing, are an important driver of multidecadal change in UKESM1, especially for Atlantic Multidecadal Variability and the Atlantic Meridional Overturning Circulation. However, many of the shortcomings identified are similar to common biases found in physical climate models, including the physical climate model that underpins UKESM1. For example, the summer jet is too weak and too far poleward; decadal variability in the winter jet is underestimated; intraseasonal stratospheric polar vortex variability is poorly represented; and Arctic sea ice is too thick. Forced shortwave changes may be also too strong in UKESM1, which, given the important role of historical aerosol forcing in shaping the evolution of the North Atlantic in UKESM1, motivates further investigation. Therefore, physical model development, alongside Earth system development, remains crucial in order to improve climate simulations.

Published
2020

7. Dynamical-Chemical Feedbacks in General Circulation Models and Their Influence on Sudden Stratospheric Warming Events

Author

Oscar Dimdore-Miles, Scott Osprey, and Lesley J. Gray

Subjects
General Circulation Model, Climatology, Environmental science, Sudden stratospheric warming
Abstract

Sudden Stratospheric Warming events (SSWs) are rapid disruptions of the Northern Hemisphere (NH) winter stratospheric polar vortex and represent the largest source of inter-annual variability in the NH winter stratosphere. They have been linked to winter surface climate anomalies such as cold snaps over North America and Eurasia. Representing these events accurately in large scale GCMs as well as developing a greater understanding of them is key to improving predictability of winter surface climate. A key component of a GCM is its representation of atmospheric chemistry. Chemical distributions are either prescribed or calculated interactively by coupling an atmospheric chemistry model to radiation and dynamical components, thus capturing any chemical dynamical feedback mechanisms but incurring significant running cost.This work evaluates the impact of interactive chemistry when modelling SSW events and explores the feedback mechanisms between chemical distributions and stratospheric dynamical variability. Pre-industrial control runs from the MetOffice HadGEMGC3.1 model which prescribes chemical fields and UKESM1 which calculates trace gas concentration interactively are utilised. Over the whole season - The Earth System Model appears to suppress warmings while the model with prescribed physics overestimates their occurrence compared to reanalysis. The differing representation of the equatorial stratosphere appears to be partially responsible for this difference. Additionally we find that middle stratosphere equatorial ozone concentration in late NH summer is closely associated with SSW probability in the ensuing winter in UKESM1. Anomalously low ozone is generally associated with an elevated SSW rate. This implies a chemical-dynamical coupling between the equator and the vortex in this model which preliminary results suggest could be driven by chemical feedbacks influencing the state of the early winter Quasi Biennial Oscillation (QBO) and Semi-Annual Oscillation (SAO) in zonal winds which can alter the distribution of planetary wave propagation and breaking (the primary cause of SSWs). Further work will assess whether this phenomenon is observed in other GCMs and further explore the physical mechanisms responsible.

Published
2020

8. Anthropogenic Forcings and Associated Changes in Fire Risk in Western North America and Australia During 2015/16

Author

Nicolas Freychet, Sam Knight, Caroline E. R. Lehmann, Megan Rogers, Michael J. Mineter, Fiona Spuler, Joshua Wainwright, Calum Turner, Alexander Falk, Oscar Dimdore-Miles, and Simon F. B. Tett

Subjects
03 medical and health sciences, Atmospheric Science, 0302 clinical medicine, Geography, Oceanography, 010504 meteorology & atmospheric sciences, Climatology, 030212 general & internal medicine, 01 natural sciences, Fire risk, 0105 earth and related environmental sciences
Published
2018

9. Preindustrial Control Simulations With HadGEM3‐GC3.1 for CMIP6

Author

Prince K. Xavier, Christopher D. Roberts, Oscar Dimdore-Miles, Rosie Eade, Julie Deshayes, Jon Robson, Lesley J. Gray, Sarah Ineson, Richard Wood, Juliette Mignot, Jeff Ridley, Martin B. Andrews, Till Kuhlbrodt, Matthew Menary, Océan et variabilité du climat (VARCLIM), Laboratoire d'Océanographie et du Climat : Expérimentations et Approches Numériques (LOCEAN), Muséum national d'Histoire naturelle (MNHN)-Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Institut Pierre-Simon-Laplace (IPSL (FR_636)), École normale supérieure - Paris (ENS-PSL), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-École polytechnique (X)-Centre National d'Études Spatiales [Toulouse] (CNES)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université Paris Cité (UPCité)-École normale supérieure - Paris (ENS-PSL), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-École polytechnique (X)-Centre National d'Études Spatiales [Toulouse] (CNES)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université Paris Cité (UPCité)-Muséum national d'Histoire naturelle (MNHN)-Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Institut Pierre-Simon-Laplace (IPSL (FR_636)), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-École polytechnique (X)-Centre National d'Études Spatiales [Toulouse] (CNES)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université Paris Cité (UPCité), Met Office Hadley Centre for Climate Change (MOHC), United Kingdom Met Office [Exeter], NCAS-Climate [Reading], Department of Meteorology [Reading], University of Reading (UOR)-University of Reading (UOR), European Centre for Medium-Range Weather Forecasts (ECMWF), Nucleus for European Modeling of the Ocean (NEMO R&D ), Muséum national d'Histoire naturelle (MNHN)-Institut de Recherche pour le Développement (IRD)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Institut Pierre-Simon-Laplace (IPSL (FR_636)), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris Diderot - Paris 7 (UPD7)-École polytechnique (X)-Centre National d'Études Spatiales [Toulouse] (CNES)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-École normale supérieure - Paris (ENS-PSL), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université Paris Diderot - Paris 7 (UPD7)-École polytechnique (X)-Centre National d'Études Spatiales [Toulouse] (CNES)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Muséum national d'Histoire naturelle (MNHN)-Institut de Recherche pour le Développement (IRD)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Institut Pierre-Simon-Laplace (IPSL (FR_636)), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université Paris Diderot - Paris 7 (UPD7)-École polytechnique (X)-Centre National d'Études Spatiales [Toulouse] (CNES)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS), LEFE/INSU DECLIC project, European Project: 641816,H2020,H2020-SC5-2014-two-stage,CRESCENDO(2015), Institut Pierre-Simon-Laplace (IPSL (FR_636)), École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-École polytechnique (X)-Centre National d'Études Spatiales [Toulouse] (CNES)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université de Paris (UP)-École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-École polytechnique (X)-Centre National d'Études Spatiales [Toulouse] (CNES)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université de Paris (UP)-Institut de Recherche pour le Développement (IRD)-Muséum national d'Histoire naturelle (MNHN)-Centre National de la Recherche Scientifique (CNRS)-Sorbonne Université (SU)-Institut Pierre-Simon-Laplace (IPSL (FR_636)), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-École polytechnique (X)-Centre National d'Études Spatiales [Toulouse] (CNES)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université de Paris (UP)-Institut de Recherche pour le Développement (IRD)-Muséum national d'Histoire naturelle (MNHN)-Centre National de la Recherche Scientifique (CNRS)-Sorbonne Université (SU), Institut de Recherche pour le Développement (IRD)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Muséum national d'Histoire naturelle (MNHN)-Institut Pierre-Simon-Laplace (IPSL (FR_636)), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris Diderot - Paris 7 (UPD7)-École polytechnique (X)-Centre National d'Études Spatiales [Toulouse] (CNES)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université Paris Diderot - Paris 7 (UPD7)-École polytechnique (X)-Centre National d'Études Spatiales [Toulouse] (CNES)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Muséum national d'Histoire naturelle (MNHN)-Institut Pierre-Simon-Laplace (IPSL (FR_636)), Muséum national d'Histoire naturelle (MNHN)-Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Muséum national d'Histoire naturelle (MNHN)-Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS), Met Office Hadley Centre (MOHC), and Institut de Recherche pour le Développement (IRD)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Muséum national d'Histoire naturelle (MNHN)-Institut de Recherche pour le Développement (IRD)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Muséum national d'Histoire naturelle (MNHN)

Subjects
preindustrial, 010504 meteorology & atmospheric sciences, Temperature salinity diagrams, [PHYS.PHYS.PHYS-GEO-PH]Physics [physics]/Physics [physics]/Geophysics [physics.geo-ph], Forcing (mathematics), 010502 geochemistry & geophysics, 01 natural sciences, Atmosphere, Ocean gyre, Environmental Chemistry, 14. Life underwater, climate, climate modeling, CMIP6, 0105 earth and related environmental sciences, Global and Planetary Change, Coupled model intercomparison project, geography, geography.geographical_feature_category, IPCC, Baseline (sea), resolution, Unified Model, 13. Climate action, [SDU]Sciences of the Universe [physics], Climatology, General Earth and Planetary Sciences, Environmental science, Climate model
Abstract

International audience; Preindustrial control simulations with the third Hadley Centre Global Environmental Model,run in the Global Coupled configuration 3.1 of the Met Office Unified Model (HadGEM3-GC3.1) are presented at two resolutions. These are N216ORCA025, which has a horizontal resolution of 60 km in the atmosphere and 0.25° in the ocean, and N96ORCA1, which has a horizontal resolution of 130 km in the atmosphere and 1∘in the ocean. The aim of this study is to document the climate variability in these simulations, make comparisons against present-day observations (albeit under different forcing), and discuss differences arising due to resolution. In terms of interannual variability in the leading modes of climate variability the two resolutions behave generally very similarly. Notable differences are in the westward extent of El Niñ oand the pattern of Atlantic multidecadal variability, in which N216ORCA025 compares more favorably to observations, and in the Antarctic Circumpolar Current, which is far too weak in N216ORCA025. In the North Atlantic region, N216ORCA025 has a stronger and deeper Atlantic Meridional Overturning Circulation, which compares well against observations, and reduced biases in temperature and salinity in the North Atlantic subpolar gyre. These simulations are being provided to the sixth Coupled Model Intercomparison Project(CMIP6) and provide a baseline against which further forced experiments may be assessed.

Full Text
View/download PDF

Catalog

Books, media, physical & digital resources
See catalog results