Jonny is a scientist at European Centre for Medium-Range Weather Forecasts (ECMWF) working on weather and climate processes and prediction. He is a member of the Long-range (seasonal) forecasting team at ECMWF, focusing on coupled land-atmosphere and ice-ocean-atmosphere processes.
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Coupled weather and climate processes
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Predictability and prediction
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Process-oriented forecast evaluation
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Climate variability and change
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Land-atmosphere feedbacks
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Sea ice prediction
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Polar Meteorology
Before joining ECMWF in 2017 Jonny was an AXA Post-Doctoral Research Fellow at the University of Reading. His research focussed on Arctic cyclones, sea ice prediction and polar climate processes. Before this he was a Post-Doc at the Japan Agency for Marine Earth Science and Technology (JAMSTEC). He received his PhD from the University of Bristol in 2011.
Jonny was a steering group member of the World Weather Research Program – Polar Prediction Project (from 2013-2022), a 10 year WMO initiative designed to improve the provision of polar weather forecasting in the polar regions.
- 2025
- Jonathan Day, Frederic Vitart, Tim Stockdale, Patricia de Rosnay, Constantin Ardilouze, Daniele Peano, Antonella Sanna, Kristina Fröhlich, Martin Andrews (January 2025) Soil-moisture-atmosphere coupling hotspots and their representation in seasonal forecasts of boreal summer. DOI: 10.21203/rs.3.rs-5483979/v1
- Luise Schulte, Linus Magnusson, Richard Forbes, Jonathan Day, Vera Schemann, Susanne Crewell (January 2025) Representation of Arctic mixed-phase clouds in the ECMWF Integrated Forecasting System during MOSAiC. DOI: 10.5194/egusphere-egu24-20507
- 2024
- Taneil Uttal, Leslie M. Hartten, Siri Jodha Khalsa, Barbara Casati, Gunilla Svensson, Jonathan Day, Jareth Holt, Elena Akish, Sara Morris, Ewan O'Connor, Roberta Pirazzini, Laura X. Huang, Robert Crawford, Zen Mariani, Øystein Godøy, Johanna A. K. Tjernström, Giri Prakash, Nicki Hickmon, Marion Maturilli, Christopher J. Cox (July 2024) Merged Observatory Data Files (MODFs): an integrated observational data product supporting process-oriented investigations and diagnostics, Geoscientific Model Development. DOI: 10.5194/gmd-17-5225-2024
- Alexander Frank Vessey, Kevin I. Hodges, Len C. Shaffrey, Jonathan J. Day (June 2024) The risk of synoptic-scale Arctic cyclones to shipping, Natural Hazards and Earth System Sciences. DOI: 10.5194/nhess-24-2115-2024
- Jonathan Day, Tim Stockdale, Frederic Vitart (August 2024) How well do dynamical seasonal forecasts capture soil-moisture atmosphere coupling?. DOI: 10.5194/ems2024-738
- Johanna Tjernström, Michael Gallagher, Jareth Holt, Gunilla Svensson, Matthew D. Shupe, Jonathan J. Day, Lara Ferrighi, Siri Jodha Khalsa, Leslie M. Hartten, Ewan O'Connor, Zen Mariani, Øystein Godøy (October 2024) Accelerating research through community open source software for a standardized file format to improve process representation in numerical weather prediction models. DOI: 10.5194/egusphere-2024-2088
- Zen Mariani, Sara Morris, Taneil Uttal, Elena Akish, Robert Crawford, Laura Huang, Jonathan Day, Johanna Tjernström, Øystein Godøy, Lara Ferrighi, Leslie Hartten, Jareth Holt, Christopher Cox, Ewan O'Connor, Roberta Pirazzini, Marion Maturilli, Giri Prakash, James Mather, Kimberly Strong, Pierre Fogal, Vasily Kustov, Gunilla Svensson, Michael Gallagher, Brian Vasel (January 2024) Special Observing Period (SOP) Data for the Year of Polar Prediction site Model Intercomparison Project (YOPPsiteMIP). DOI: 10.5194/essd-2023-497
- Alistair Duffey, Robbie Mallett, Victoria R. Dutch, Julia Steckling, Antoine Hermant, Jonathan James Day, Felix Pithan (April 2024) Stability of the Arctic Winter Atmospheric Boundary Layer over Sea Ice in CMIP6 Models. DOI: 10.22541/essoar.171405347.78397213/v1
- Zen Mariani, Sara M. Morris, Taneil Uttal, Elena Akish, Robert Crawford, Laura Huang, Jonathan Day, Johanna Tjernström, Øystein Godøy, Lara Ferrighi, Leslie M. Hartten, Jareth Holt, Christopher J. Cox, Ewan O'Connor, Roberta Pirazzini, Marion Maturilli, Giri Prakash, James Mather, Kimberly Strong, Pierre Fogal, Vasily Kustov, Gunilla Svensson, Michael Gallagher, Brian Vasel (July 2024) Special Observing Period (SOP) data for the Year of Polar Prediction site Model Intercomparison Project (YOPPsiteMIP), Earth System Science Data. DOI: 10.5194/essd-16-3083-2024
- Jonathan J. Day, Gunilla Svensson, Barbara Casati, Taneil Uttal, Siri-Jodha Khalsa, Eric Bazile, Elena Akish, Niramson Azouz, Lara Ferrighi, Helmut Frank, Michael Gallagher, Øystein Godøy, Leslie M. Hartten, Laura X. Huang, Jareth Holt, Massimo Di Stefano, Irene Suomi, Zen Mariani, Sara Morris, Ewan O'Connor, Roberta Pirazzini, Teresa Remes, Rostislav Fadeev, Amy Solomon, Johanna Tjernström, Mikhail Tolstykh (July 2024) The Year of Polar Prediction site Model Intercomparison Project (YOPPsiteMIP) phase 1: project overview and Arctic winter forecast evaluation, Geoscientific Model Development. DOI: 10.5194/gmd-17-5511-2024
- 2023
- Alexander Frank Vessey, Kevin I. Hodges, Len C. Shaffrey, Jonathan J. Day (November 2023) The Risk of Synoptic-Scale Arctic Cyclones to Shipping. DOI: 10.5194/egusphere-2023-2222
- Alexander Frank Vessey, Kevin I. Hodges, Len C. Shaffrey, Jonathan J. Day (November 2023) Supplementary material to "The Risk of Synoptic-Scale Arctic Cyclones to Shipping". DOI: 10.5194/egusphere-2023-2222-supplement
- Taneil Uttal, Leslie M. Hartten, Siri Jodha Khalsa, Barbara Casati, Gunilla Svensson, Jonathan Day, Jareth Holt, Elena Akish, Sara Morris, Ewan O'Connor, Roberta Pirazzini, Laura X. Huang, Robert Crawford, Zen Mariani, Øystein Godøy, Johanna A. K. Tjernström, Giri Prakash, Nicki Hickmon, Marion Maturilli, Christopher J. Cox (December 2023) Merged Observatory Data Files (MODFs): An Integrated Observational Data Product Supporting Process-Oriented Investigations and Diagnostics. DOI: 10.5194/egusphere-2023-2413
- Jonathan Day, Gunilla Svensson, Barbara Casati, Taniel Uttal, Siri-Jodha Khalsa, Eric Bazile, Elena Akish, Niramson Azouz, Lara Ferrighi, Helmut Frank, Michael Gallagher, Øystein Godøy, Leslie Hartten, Laura X. Huang, Jareth Holt, Massimo Di Stefano, Irene Suomi, Zen Mariani, Sara Morris, Ewan O'Connor, Roberta Pirazzini, Teresa Remes, Rostislav Fadeev, Amy Solomon, Johanna Tjernström, Mikhail Tolstykh (December 2023) The YOPP site Model Intercomparison Project (YOPPsiteMIP) phase 1: project overview and Arctic winter forecast evaluation. DOI: 10.5194/egusphere-2023-1951
- Gillian Young McCusker, Jutta Vüllers, Peggy Achtert, Paul Field, Jonathan J. Day, Richard Forbes, Ruth Price, Ewan O'Connor, Michael Tjernström, John Prytherch, Ryan Neely III, Ian M. Brooks (April 2023) Evaluating Arctic clouds modelled with the Unified Model and Integrated Forecasting System, Atmospheric Chemistry and Physics. DOI: 10.5194/acp-23-4819-2023
- 2022
- Yongwu Xiu, Hao Luo, Qinghua Yang, Steffen Tietsche, Jonathan Day, Dake Chen (April 2022) The Challenge of Arctic Sea Ice Thickness Prediction by ECMWF on Subseasonal Time Scales, Geophysical Research Letters n. 8. DOI: 10.1029/2021GL097476
- Gabriele Arduini, Sarah Keeley, Jonathan J. Day, Irina Sandu, Lorenzo Zampieri, Gianpaolo Balsamo (July 2022) On the Importance of Representing Snow Over Sea‐Ice for Simulating the Arctic Boundary Layer, Journal of Advances in Modeling Earth Systems n. 7. DOI: 10.1029/2021MS002777
- Jonathan Day, Sarah Keeley, Gabriele Arduini, Linus Magnusson, Kristian Mogensen, Mark Rodwell, Irina Sandu, Steffen Tietsche (January 2022) Supplementary material to "Benefits and challenges of dynamic sea-ice for weather forecasts". DOI: 10.5194/wcd-2022-5-supplement
- Jonathan J. Day, Sarah Keeley, Gabriele Arduini, Linus Magnusson, Kristian Mogensen, Mark Rodwell, Irina Sandu, Steffen Tietsche (July 2022) Benefits and challenges of dynamic sea ice for weather forecasts, Weather and Climate Dynamics. DOI: 10.5194/wcd-3-713-2022
- Jonathan Day, Sarah Keeley, Gabriele Arduini, Linus Magnusson, Kristian Mogensen, Mark Rodwell, Irina Sandu, Steffen Tietsche (January 2022) Benefits and challenges of dynamic sea-ice for weather forecasts. DOI: 10.5194/wcd-2022-5
- 2021
- irina sandu, Gabriele Arduini, Jonathan Day, Linus Magnusson, Heather Lawrence, Niels Bormann, Peter Bauer, Sarah Keeley, Gianpaolo Balsamo, Thomas Haiden (July 2021) How APPLICATE contributed to ECMWF core activities, ECMWF Newsletter, issue 168, pp. 24-31. DOI: 10.21957/ir5fk44das
- Gillian Young, Jutta Vüllers, Peggy Achtert, Paul Field, Jonathan J. Day, Richard Forbes, Ruth Price, Ewan O'Connor, Michael Tjernström, John Prytherch, Ryan Neely III, Ian M. Brooks (September 2021) Supplementary material to "Evaluating Arctic clouds modelled with the Unified Model and Integrated Forecasting System". DOI: 10.5194/acp-2021-662-supplement
- Gillian Young, Jutta Vüllers, Peggy Achtert, Paul Field, Jonathan J. Day, Richard Forbes, Ruth Price, Ewan O'Connor, Michael Tjernström, John Prytherch, Ryan Neely III, Ian M. Brooks (September 2021) Evaluating Arctic clouds modelled with the Unified Model and Integrated Forecasting System. DOI: 10.5194/acp-2021-662
- 2020
- Jonathan Day, Gabriele Arduini, Irina Sandu, Linus Magnusson, Anton Beljaars, Gianpaolo Balsamo, Mark Rodwell, David Richardson (May 2020) Measuring the impact of a new snow model using surface energy budget process relationships. DOI: 10.1002/essoar.10502951.1
- Jonathan J. Day, Gabriele Arduini, Irina Sandu, Linus Magnusson, Anton Beljaars, Gianpaolo Balsamo, Mark Rodwell, David Richardson (December 2020) Measuring the Impact of a New Snow Model Using Surface Energy Budget Process Relationships, Journal of Advances in Modeling Earth Systems n. 12. DOI: 10.1029/2020MS002144
- irina sandu, Thomas Haiden, Gianpaolo Balsamo, Polly Schmederer, Gabriele Arduini, Jonathan Day, Anton Beljaars, Zied Ben Bouallègue, Souhail Boussetta, Martin Leutbecher, Linus Magnusson, Patricia de Rosnay (November 2020) Addressing near-surface forecast biases: outcomes of the ECMWF project 'Understanding uncertainties in surface atmosphere exchange' (USURF), ECMWF Technical Memoranda n. 875. DOI: 10.21957/wxjwsojvf
- 2019
- Jonathan J. Day, Irina Sandu, Linus Magnusson, Mark J. Rodwell, Heather Lawrence, Niels Bormann, Thomas Jung (October 2019) Increased Arctic influence on the midlatitude flow during Scandinavian Blocking episodes, Quarterly Journal of the Royal Meteorological Society. DOI: 10.1002/qj.3673
- Gabriele Arduini, Gianpaolo Balsamo, Emanuel Dutra, Jonathan J. Day, Irina Sandu, Souhail Boussetta, Thomas Haiden (December 2019) Impact of a Multi‐Layer Snow Scheme on Near‐Surface Weather Forecasts, Journal of Advances in Modeling Earth Systems. DOI: 10.1029/2019MS001725
- 2018
- Jonathan J. Day, Marika M. Holland, Kevin I. Hodges (May 2018) Seasonal differences in the response of Arctic cyclones to climate change in CESM1, Climate Dynamics n. 9-10, pp. 3885-3903. DOI: 10.1007/s00382-017-3767-x
- Jonathan J. Day, Marika M. Holland, Kevin I. Hodges (May 2018) Correction to: Seasonal differences in the response of Arctic cyclones to climate change in CESM1, Climate Dynamics n. 9-10, pp. 3905-3907. DOI: 10.1007/s00382-018-4112-8
- Jonathan J. Day, Kevin I. Hodges (April 2018) Growing Land‐Sea Temperature Contrast and the Intensification of Arctic Cyclones, Geophysical Research Letters n. 8, pp. 3673-3681. DOI: 10.1029/2018GL077587
- 2017
- Paul J. Valdes, Edward Armstrong, Marcus P. S. Badger, Catherine D. Bradshaw, Fran Bragg, Michel Crucifix, Taraka Davies-Barnard, Jonathan J. Day, Alex Farnsworth, Chris Gordon, Peter O. Hopcroft, Alan T. Kennedy, Natalie S. Lord, Dan J. Lunt, Alice Marzocchi, Louise M. Parry, Vicky Pope, William H. G. Roberts, Emma J. Stone, Gregory J. L. Tourte, Jonny H. T. Williams (October 2017) The BRIDGE HadCM3 family of climate models: HadCM3@Bristol v1.0, Geoscientific Model Development n. 10, pp. 3715-3743. DOI: 10.5194/gmd-10-3715-2017
- Paul J. Valdes, Edward Armstrong, Marcus P. S. Badger, Catherine D. Bradshaw, Fran Bragg, Taraka Davies-Barnard, Jonathan J. Day, Alex Farnsworth, Peter O. Hopcroft, Alan T. Kennedy, Natalie S. Lord, Dan J. Lunt, Alice Marzocchi, Louise M. Parry, William H. G. Roberts, Emma J. Stone, Gregory J. L. Tourte, Jonny H. T. Williams (February 2017) The BRIDGE HadCM3 family of climate models: HadCM3@Bristol v1.0. DOI: 10.5194/gmd-2017-16
- Paul J. Valdes, Edward Armstrong, Marcus P. S. Badger, Catherine D. Bradshaw, Fran Bragg, Taraka Davies-Barnard, Jonathan J. Day, Alex Farnsworth, Peter O. Hopcroft, Alan T. Kennedy, Natalie S. Lord, Dan J. Lunt, Alice Marzocchi, Louise M. Parry, William H. G. Roberts, Emma J. Stone, Gregory J. L. Tourte, Jonny H. T. Williams (February 2017) Supplementary material to "The BRIDGE HadCM3 family of climate models: HadCM3@Bristol v1.0". DOI: 10.5194/gmd-2017-16-supplement
- 2016
- Goessling H.F., Tietsche S., Day J.J., Hawkins E., Jung T. (February 2016) Predictability of the Arctic sea ice edge, Geophysical Research Letters. DOI: 10.1002/2015GL067232
- Guemas V., Blanchard-Wrigglesworth E., Chevallier M., Day J.J., Déqué M., Doblas-Reyes F.J., Fučkar N.S., Germe A., Hawkins E., Keeley S., Koenigk T., Salas y Mélia D., Tietsche S. (February 2016) A review on Arctic sea-ice predictability and prediction on seasonal to decadal time-scales, Quarterly Journal of the Royal Meteorological Society. DOI: 10.1002/qj.2401
- Hawkins E., Tietsche S., Day J.J., Melia N., Haines K., Keeley S. (February 2016) Aspects of designing and evaluating seasonal-to-interannual Arctic sea-ice prediction systems, Quarterly Journal of the Royal Meteorological Society. DOI: 10.1002/qj.2643
- Tietsche S., Hawkins E., Day J.J. (February 2016) Atmospheric and oceanic contributions to irreducible forecast uncertainty of Arctic surface climate, Journal of Climate. DOI: 10.1175/JCLI-D-15-0421.1
- Tom Edinburgh, Jonathan J. Day (November 2016) Estimating the extent of Antarctic summer sea ice during the Heroic Age of Antarctic Exploration, The Cryosphere n. 6, pp. 2721-2730. DOI: 10.5194/tc-10-2721-2016
- Jonathan J. Day, Steffen Tietsche, Mat Collins, Helge F. Goessling, Virginie Guemas, Anabelle Guillory, William J. Hurlin, Masayoshi Ishii, Sarah P. E. Keeley, Daniela Matei, Rym Msadek, Michael Sigmond, Hiroaki Tatebe, Ed Hawkins (June 2016) The Arctic Predictability and Prediction on Seasonal-to-Interannual TimEscales (APPOSITE) data set version 1, Geoscientific Model Development n. 6, pp. 2255-2270. DOI: 10.5194/gmd-9-2255-2016
- Jonathan Day (September 2016) response. DOI: 10.5194/tc-2016-90-AC1
- Jonathan Day (September 2016) response. DOI: 10.5194/tc-2016-90-AC2
- Tom Edinburgh, Jonathan J. Day (April 2016) Estimating the extent of Antarctic summer sea ice during the Heroic Age of Exploration. DOI: 10.5194/tc-2016-90
- Tom Edinburgh, Jonathan J. Day (April 2016) Supplementary material to "Estimating the extent of Antarctic summer sea ice during the Heroic Age of Exploration". DOI: 10.5194/tc-2016-90-supplement
- 2015
- Stephens E., Day J.J., Pappenberger F., Cloke H. (February 2015) Precipitation and floodiness, Geophysical Research Letters. DOI: 10.1002/2015GL066779
- J. J. Day, S. Tietsche, M. Collins, H. F. Goessling, V. Guemas, A. Guillory, W. J. Hurlin, M. Ishii, S. P. E. Keeley, D. Matei, R. Msadek, M. Sigmond, H. Tatebe, E. Hawkins (October 2015) The Arctic Predictability and Prediction on Seasonal-to-Interannual TimEscales (APPOSITE) data set. DOI: 10.5194/gmdd-8-8809-2015
- 2014
- Tietsche S., Day J.J., Guemas V., Hurlin W.J., Keeley S.P.E., Matei D., Msadek R., Collins M., Hawkins E. (February 2014) Seasonal to interannual Arctic sea ice predictability in current global climate models, Geophysical Research Letters. DOI: 10.1002/2013GL058755
- Day J.J., Tietsche S., Hawkins E. (February 2014) Pan-arctic and regional sea ice predictability: Initialization month dependence, Journal of Climate. DOI: 10.1175/JCLI-D-13-00614.1
- Day J.J., Hawkins E., Tietsche S. (February 2014) Will Arctic sea ice thickness initialization improve seasonal forecast skill?, Geophysical Research Letters. DOI: 10.1002/2014GL061694
- 2013
- Day J.J., Bamber J.L., Valdes P.J. (February 2013) The Greenland Ice Sheet's surface mass balance in a seasonally sea ice-free Arctic, Journal of Geophysical Research: Earth Surface. DOI: 10.1002/jgrf.20112
- 2012
- Day J.J., Bamber J.L., Valdes P.J., Kohler J. (February 2012) Erratum: The impact of a seasonally ice free Arctic Ocean on the temperature, precipitation and surface mass balance of Svalbard (Cryosphere (2012) 6 (35-50)), Cryosphere. DOI: 10.5194/tc-6-141-2012
- Day J.J., Bamber J.L., Valdes P.J., Kohler J. (February 2012) The impact of a seasonally ice free Arctic Ocean on the temperature, precipitation and surface mass balance of Svalbard, Cryosphere. DOI: 10.5194/tc-6-35-2012
- Day J.J., Hargreaves J.C., Annan J.D., Abe-Ouchi A. (February 2012) Sources of multi-decadal variability in Arctic sea ice extent, Environmental Research Letters. DOI: 10.1088/1748-9326/7/3/034011