Blar i Bergen Open Research Archive på forfatter "Omrani, Nour-Eddine"
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The 11 year solar cycle UV irradiance effect and its dependency on the Pacific Decadal Oscillation
Guttu, Sigmund; Orsolini, Yvan J.; Stordal, Frode; Otterå, Odd Helge; Omrani, Nour-Eddine (Journal article; Peer reviewed, 2021)The stratospheric, tropospheric and surface impacts from the 11 year ultraviolet solar spectral irradiance (SSI) variability have been extensively studied using climate models and observations. Here, we demonstrate using ... -
Assessing the influence of sea surface temperature and arctic sea ice cover on the uncertainty in the boreal winter future climate projections
Cheung, Ho-Nam; Keenlyside, Noel Sebastian; Koenigk, Torben; Yang, Shuting; Tian, Tian; Xu, Zhiqing; Gao, Yongqi; Ogawa, Fumiaki; Omrani, Nour-Eddine; Qiao, Shaobo; Zhou, Wen (Journal article; Peer reviewed, 2022)We investigate the uncertainty (i.e., inter-model spread) in future projections of the boreal winter climate, based on the forced response of ten models from the CMIP5 following the RCP8.5 scenario. The uncertainty in the ... -
Coupled stratosphere-troposphere-Atlantic multidecadal oscillation and its importance for near-future climate projection
Omrani, Nour-Eddine; Keenlyside, Noel Sebastian; Matthes, Katja; Boljka, Lina; Zanchettin, Davide; Jungclaus, Johann H.; Lubis, Sandro W. (Journal article; Peer reviewed, 2022)Northern Hemisphere (NH) climate has experienced various coherent wintertime multidecadal climate trends in stratosphere, troposphere, ocean, and cryosphere. However, the overall mechanistic framework linking these trends ... -
The Dominant Patterns of Intraseasonal Rainfall Variability in May–October and November–April over the Tropical Western Pacific
Pariyar, Sunil Kumar; Keenlyside, Noel; Bhatt, Bhuwan Chandra; Omrani, Nour-Eddine (Journal article, 2019)The space–time structure of intraseasonal (10–90 day) rainfall variability in the western tropical Pacific is studied using daily 3B42 TRMM and ERA-Interim reanalysis data for the period 1998–2014. Empirical orthogonal ... -
Evaluating Impacts of Recent Arctic Sea Ice Loss on the Northern Hemisphere Winter Climate Change
Ogawa, Fumiaki; Keenlyside, Noel; Gao, Yongqi; Koenigk, Torben; Yang, Shuting; Suo, Lingling; Wang, Tao; Gastineau, Guillaume; Nakamura, Tetsu; Cheung, Ho Nam; Omrani, Nour-Eddine; Ukita, Jinro; Semenov, Vladimir (Journal article; Peer reviewed, 2018)Wide disagreement among individual modeling studies has contributed to a debate on the role of recent sea ice loss in the Arctic amplification of global warming and the Siberian wintertime cooling trend. We perform coordinated ... -
Has a warm North Atlantic contributed to recent European cold winters?
Keenlyside, Noel; Omrani, Nour-Eddine (Peer reviewed; Journal article, 2014-06-02)The rise of global surface temperature waned during the last decade, despite increasing greenhouse gas concentrations. The temperature changes were most pronounced over northern hemisphere land masses during winter (Cohen ... -
Identifying quasi-periodic variability using multivariate empirical mode decomposition: a case of the tropical Pacific
Boljka, Lina; Omrani, Nour-Eddine; Keenlyside, Noel Sebastian (Journal article; Peer reviewed, 2023)A variety of statistical tools have been used in climate science to gain a better understanding of the climate system's variability on various temporal and spatial scales. However, these tools are mostly linear, stationary, ... -
Impacts of UV Irradiance and Medium-Energy Electron Precipitation on the North Atlantic Oscillation during the 11-Year Solar Cycle
Guttu, Sigmund; Orsolini, Yvan; Stordal, Frode; Otterå, Odd Helge; Omrani, Nour-Eddine; Tartaglione, Nazario; Verronen, Pekka T.; Rodger, Craig J.; Clilverd, Mark A. (Journal article; Peer reviewed, 2021)Observational studies suggest that part of the North Atlantic Oscillation (NAO) variability may be attributed to the spectral ultra-violet (UV) irradiance variations associated to the 11-year solar cycle. The observed ... -
Inconsistent Wind Speed Trends in Current Twentieth Century Reanalyses
Wohland, Jan; Omrani, Nour-Eddine; Witthaut, Dirk; Keenlyside, Noel (Peer reviewed; Journal article, 2019)Reanalysis data underpin much research in atmospheric and related sciences. While most reanalysis only cover the last couple of decades, National Oceanic and Atmospheric Administration (20CR) and European Centre for ... -
Key Role of the Ocean Western Boundary currents in shaping the Northern Hemisphere climate
Omrani, Nour-Eddine; Ogawa, Fumiaki; Nakamura, Hisashi; Keenlyside, Noel; Lubis, Sandro W.; Matthes, Katja (Peer reviewed; Journal article, 2019)The individual impact of North Atlantic and Pacific Ocean Western Boundary Currents (OWBCs) on the tropospheric circulation has recently been studied in depth. However, their simultaneous role in shaping the hemisphere-scale ... -
Mitigating climate biases in the midlatitude North Atlantic by increasing model resolution: SST gradients and their relation to blocking and the jet
Athanasiadis, Panos J.; Ogawa, Fumiaki; Omrani, Nour-Eddine; Keenlyside, Noel Sebastian; Schiemann, Reinhard; Baker, Alexander J.; Vidale, Pier Luigi; Bellucci, Alessio; Ruggieri, Paolo; Haarsma, Rein; Roberts, Malcolm J.; Roberts, Chris; Novak, Lenka; Gualdi, Silvio (Journal article; Peer reviewed, 2022)Starting to resolve the oceanic mesoscale in climate models is a step change in model fidelity. This study examines how certain obstinate biases in the midlatitude North Atlantic respond to increasing resolution (from 1° ... -
Nonstationarity in the NAO–Gulf Stream SST Front Interaction
Paolini, Luca Famooss; Omrani, Nour-Eddine; Bellucci, Alessio; Athanasiadis, Panos J.; Ruggieri, Paolo; Patrizio, Casey R.; Keenlyside, Noel Sebastian (Journal article; Peer reviewed, 2024)The interaction between the North Atlantic Oscillation (NAO) and the latitudinal shifts of the Gulf Stream sea surface temperature front (GSF) has been the subject of extensive investigations. There are indications of ... -
North Atlantic multi-decadal variability - mechanisms and predictability
Keenlyside, Noel; Ba, Jin; Mecking, Jennifer V.; Omrani, Nour-Eddine; Latif, Mojib; Zhang, Rong; Msadek, Rym (World Scientific Series on Asia-Pacific Weather and Climate, Chapter; Peer reviewed, 2015-10)The North Atlantic Ocean undergoes pronounced basin-wide, multi-decadal variations. The corresponding fluctuations in sea surface temperature (SST) have become known as the Atlantic Multi-decadal Oscillation (AMO) or ... -
Ozone-induced climate change propped up by the Southern Hemisphere oceanic front
Ogawa, Fumiaki; Omrani, Nour-Eddine; Nishii, Kazuaki; Nakamura, Hisashi; Keenlyside, Noel (Peer reviewed; Journal article, 2015-11-23)The late twentieth century was marked by a significant summertime trend in the Southern Annular Mode (SAM), the dominant mode of tropospheric variability in the extratropical Southern Hemisphere (SH). This trend with ... -
Pacific contribution to decadal surface temperature trends in the Arctic during the twentieth century
Svendsen, Lea; Keenlyside, Noel; Muilwijk, Morven; Bethke, Ingo; Omrani, Nour-Eddine; Gao, Yongqi (Journal article; Peer reviewed, 2021)Instrumental records suggest multidecadal variability in Arctic surface temperature throughout the twentieth century. This variability is caused by a combination of external forcing and internal variability, but their ... -
Pacific contribution to the early twentieth-century warming in the Arctic
Svendsen, Lea; Keenlyside, Noel; Bethke, Ingo; Gao, Yongqi; Omrani, Nour-Eddine (Journal article; Peer reviewed, 2018)Arctic surface temperature warmed more than twice as fast as global temperature during the early twentieth century, similar to that during the recent global warming. This Arctic warming has been attributed to both external ... -
Pacific oceanic front amplifies the impact of Atlantic oceanic front on North Atlantic blocking
Cheung, Ho Nam; Omrani, Nour-Eddine; Ogawa, Fumiaki; Keenlyside, Noel Sebastian; Nakamura, Hisashi; Zhou, Wen (Journal article; Peer reviewed, 2023)Atmospheric blocking is a crucial driver of extreme weather events, but its climatological frequency is largely underestimated in state-of-the-art climate models, especially around the North Atlantic. While air-sea interaction ... -
Remarkable link between projected uncertainties of Arctic sea-ice decline and winter Eurasian climate
Cheung, Ho Nam; Keenlyside, Noel; Omrani, Nour-Eddine; Zhou, Wen (Journal article; Peer reviewed, 2018)We identify that the projected uncertainty of the pan-Arctic sea-ice concentration (SIC) is strongly coupled with the Eurasian circulation in the boreal winter (December–March; DJFM), based on a singular value decomposition ... -
Significant multidecadal variability in German wind energy generation
Wohland, Jan; Omrani, Nour-Eddine; Keenlyside, Noel; Witthaut, Dirk (Peer reviewed; Journal article, 2019-09-12)Wind energy has seen large deployment and substantial cost reductions over the last decades. Further ambitious upscaling is urgently needed to keep the goals of the Paris Agreement within reach. While the variability in ... -
Solar forcing synchronizes decadal North Atlantic climate variability
Thiéblemont, Rémi; Matthes, Katja; Omrani, Nour-Eddine; Kodera, Kunihiko; Hansen, Felicitas (Peer reviewed; Journal article, 2015-09-15)Quasi-decadal variability in solar irradiance has been suggested to exert a substantial effect on Earth’s regional climate. In the North Atlantic sector, the 11-year solar signal has been proposed to project onto a pattern ...