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Start Over Author "Nicholas, M. J." Topic environmental science
11 results on '"Nicholas, M. J."'

1. The extratropical response to a developing MJO: forecast and climate simulations with the DREAM model

Author

Stéphanie Leroux, Nicholas M. J. Hall, and Hong Hanh Le

Subjects
Atmospheric Science, 010504 meteorology & atmospheric sciences, Convective heat transfer, Wave propagation, Phase (waves), Madden–Julian oscillation, Atmospheric model, 010502 geochemistry & geophysics, 01 natural sciences, Atmosphere, Climatology, Extratropical cyclone, Environmental science, Physics::Atmospheric and Oceanic Physics, 0105 earth and related environmental sciences, Teleconnection
Abstract

The Madden Julian oscillation (MJO) has a systematic influence on the state of the extratropical atmosphere. The physical mechanism involves teleconnections from tropical deep convective heat sources through wave propagation. MJO heating resembles a propagating dipole that cycles through phases on a timescale similar to the response timescale. This complicates the attribution of the response to a well identified phase in the tropical heat source. In this paper the Dynamical Research Empirical Atmospheric Model (DREAM) is used to examine the extratropical response to a moving cyclic MJO-like tropical heat source based on outgoing long-wave radiation data. A set of ensemble forecast experiments and consistent stationary wave solutions are analysed, together with longer equilibrium integrations, to investigate how the extratropical response relates to the phase of the MJO heating. We find that the response is modified by the propagation of the source in a way that depends on the initial phase. It also displays both stationary and transient nonlinearity which can account for an asymmetric response to opposite-phase dipole heat sources. The solution for Indian Ocean heating/West Pacific cooling is more zonally oriented and weaker than the solution for the opposite phase. If the MJO heat source is specified as a continuous cycle, it modifies the time-mean extratropical circulation and generates remote teleconnections. The timing and starting phase of MJO events can greatly modify the relationship between MJO phase and extratropical response, especially when an unforced “resting” period is inserted between simulated MJO cycles.

Published
2020
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2. Transient contributions to the forcing of the atmospheric annual cycle

Author

Stéphanie Leroux, Tércio Ambrizzi, and Nicholas M. J. Hall

Subjects
Atmospheric Science, Momentum (technical analysis), 010504 meteorology & atmospheric sciences, Atmospheric circulation, Flow (psychology), Forcing (mathematics), Atmospheric model, 010502 geochemistry & geophysics, Annual cycle, 01 natural sciences, Term (time), Climatology, Environmental science, Southern Hemisphere, Physics::Atmospheric and Oceanic Physics, 0105 earth and related environmental sciences
Abstract

The forcing of the global circulation is examined using a primitive equation model and a 38-year reanalysis dataset. One-timestep integrations are initialised with selected sets of initial conditions, and the forcing budget for the mean annual cycle is deduced. This budget consists of sources and sinks of momentum, temperature and humidity which are balanced by dynamical terms. The associated timescale interactions are examined in detail. The time-mean forcing is balanced by time-mean fluxes, annual cycle interactions and transient fluxes. The annual cycle of the forcing is balanced by the interaction of annual cycle anomalies with the time-mean flow and with themselves (this latter cycle-cycle interaction term is found to be important for the moisture supply over West Africa). Transient interactions on other timescales also contribute to the forcing of the annual cycle, but the interaction term between the annual cycle and other timescales is small, as is the storage term associated with seasonal tendencies. This objectively derived empirical forcing is then used to drive the dynamical model. The resulting simple GCM is called DREAM (Dynamical Research Empirical Atmospheric Model). This is the first time this approach has been used with an annual cycle. The systematic errors of DREAM compared to the reanalysis chiefly concern the momentum balance in the southern hemisphere jet. Perpetual season simulations are similar to individual seasons from the annual cycle run, consistent with the small seasonal tendency term in the forcing.

Published
2018
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3. Impact of the observed extratropics on climatological simulations of the MJO in a tropical channel model

Author

Séverin Thibaut, Nicholas M. J. Hall, and Patrick Marchesiello

Subjects
Atmospheric Science, 010504 meteorology & atmospheric sciences, WRF, Mode (statistics), Regional model, Boundary (topology), Madden–Julian oscillation, Intraseasonal variability, 010502 geochemistry & geophysics, Atmospheric sciences, 01 natural sciences, MJO, Tropical-extratropical interactions, Climatology, Weather Research and Forecasting Model, Extratropical cyclone, Hindcast, Environmental science, Coherence (signal processing), Boundary value problem, 0105 earth and related environmental sciences
Abstract

A regional model is used to quantify the influence of the extratropics on simulated tropical intraseasonal variability. The Weather Research and Forecasting (WRF) model is run in tropical channel mode with the boundaries at 30 $$^{\circ }$$ N and S constrained to 6-hourly reanalysis data. Experiments with modified boundary conditions are carried out in which intraseasonal (20–100 days) timescales are removed, or in which only the annual and diurnal cycles are retained. Twin runs are used to give an objective measure of the boundary-independant component of the variance in each case. The model captures MJO-like propagating structures and shows greater zonal-wind variance in runs with full boundary conditions. Comparison between experiments indicates that about half the intraseasonal variance can be attributed to boundary influence, and specifically to the presence of an intraseasonal extratropical signal. This signal is associated with stronger correlations between low-level zonal wind precursors in the Pacific sector and Indian Ocean convective events. Temporal coherence between MJO events in the model and the observations is analysed by defining four phases based on convectively coupled signals in the low-level zonal wind. The model can only match observed events above the level of chance when intraseasonal boundary information is provided. Results are analysed in terms of ‘primary’ and ‘successive’ events. Although the model hindcast skill is generally poor, it is better for successive events.

Published
2017

4. The Extratropical Signal Generated by a Midlatitude SST Anomaly. Part II: Influence on Seasonal Forecasts

Author

Nicholas M. J. Hall, Jacques Derome, and Hai Lin

Subjects
Atmospheric Science, Sea surface temperature, Climatology, Middle latitudes, Anomaly (natural sciences), Extratropical cyclone, Initial value problem, Environmental science, Perturbation (astronomy), Forcing (mathematics), Teleconnection
Abstract

A simple GCM based on a primitive equation model with empirically derived time-independent forcing is used to make forecasts in the extended to seasonal range. The results are analyzed in terms of the response to a midlatitude Pacific sea surface temperature anomaly (SSTA), represented here by a heating perturbation. A set of 90-day, 30-member ensemble forecasts is made with 54 widely differing initial conditions, both with and without the SSTA. The development of the response, defined as the difference between ensemble means, is split into three 30-day averages: month 1, month 2, and month 3. During month 1, ensemble members separate, and the local response and remote teleconnections are established. The local response is not very sensitive to the initial condition. In month 2, the extended range, the responses are relatively strong and vary greatly from one initial condition to another. However, a linear analysis reveals that large variations in the response do not correlate strongly with large...

Published
2001
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5. Extratropical Summertime Response to Tropical Interannual Variability in an Idealized GCM

Author

Laurent Li, Nicholas M. J. Hall, Hervé Douville, Océan du Large et Variabilité Climatique (OLVAC), Laboratoire d'études en Géophysique et océanographie spatiales (LEGOS), Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire Midi-Pyrénées (OMP), Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Centre National de la Recherche Scientifique (CNRS), Centre d'Etudes de la Neige (CEN), Centre national de recherches météorologiques (CNRM), Institut national des sciences de l'Univers (INSU - CNRS)-Météo France-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Météo France-Centre National de la Recherche Scientifique (CNRS), Laboratoire de Météorologie Dynamique (UMR 8539) (LMD), Département des Géosciences - ENS Paris, École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Centre National de la Recherche Scientifique (CNRS)-École des Ponts ParisTech (ENPC)-École polytechnique (X)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Pierre et Marie Curie - Paris 6 (UPMC), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire Midi-Pyrénées (OMP), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Centre National de la Recherche Scientifique (CNRS), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire Midi-Pyrénées (OMP), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire Midi-Pyrénées (OMP), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Centre National de la Recherche Scientifique (CNRS)-Observatoire des Sciences de l'Univers de Grenoble (OSUG ), Institut national des sciences de l'Univers (INSU - CNRS)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE)-Université Grenoble Alpes (UGA)-Météo-France -Institut national des sciences de l'Univers (INSU - CNRS)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE)-Université Grenoble Alpes (UGA), Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut national des sciences de l'Univers (INSU - CNRS)-École polytechnique (X)-École des Ponts ParisTech (ENPC)-Centre National de la Recherche Scientifique (CNRS)-Département des Géosciences - ENS Paris, École normale supérieure - Paris (ENS-PSL), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-École normale supérieure - Paris (ENS-PSL), and Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)

Subjects
DYNAMICS, Atmospheric Science, 010504 meteorology & atmospheric sciences, FLOW, General circulation models, Monsoons, Intraseasonal variability, 010502 geochemistry & geophysics, Monsoon, Atmospheric sciences, 01 natural sciences, Latitude, Atmosphere, Interannual variability, ROSSBY-WAVE PROPAGATION, Extratropical cyclone, 0105 earth and related environmental sciences, OSCILLATION, Monsoon of South Asia, [SDU.OCEAN]Sciences of the Universe [physics]/Ocean, Atmosphere, Anomaly (natural sciences), Tropics, TELECONNECTION, NORTH-AMERICA, ATMOSPHERE, INDIAN MONSOON, MODEL, 1988 DROUGHT, 13. Climate action, Climatology, Teleconnections, Environmental science, Teleconnection
Abstract

ISI Document Delivery No.: 213LB Times Cited: 0 Cited Reference Count: 44 Cited References: AMBRIZZI T, 1995, J ATMOS SCI, V52, P3661, DOI 10.1175/1520-0469(1995)0522.0.CO;2 Bielli S, 2010, CLIM DYNAM, V35, P159, DOI 10.1007/s00382-009-0667-8 Blackburn M, 2008, WEATHER, V63, P280, DOI 10.1002/wea.322 Blade I, 1995, J ATMOS SCI, V52, P4448, DOI 10.1175/1520-0469(1995)0522.0.CO;2 Branstator G, 2002, J CLIMATE, V15, P1893, DOI 10.1175/1520-0442(2002)0152.0.CO;2 Cassou C, 2005, J CLIMATE, V18, P2805, DOI 10.1175/JCLI3506.1 Ding QH, 2011, J CLIMATE, V24, P1878, DOI 10.1175/2011JCLI3621.1 Ding QH, 2007, J CLIMATE, V20, P3751, DOI 10.1175/JCLI4221.1 Ding QH, 2005, J CLIMATE, V18, P3483, DOI 10.1175/JCLI3473.1 Douville H, 2011, CLIM DYNAM, V37, P1783, DOI 10.1007/s00382-011-0997-1 Enomoto T, 2003, Q J ROY METEOR SOC, V129, P157, DOI 10.1256/gj.01.211 FERRANTI L, 1990, J ATMOS SCI, V47, P2177, DOI 10.1175/1520-0469(1990)0472.0.CO;2 Hall NMJ, 2000, J ATMOS SCI, V57, P1557, DOI 10.1175/1520-0469(2000)0572.0.CO;2 Hall NMJ, 2001, J CLIMATE, V14, P2035, DOI 10.1175/1520-0442(2001)0142.0.CO;2 Hall NMJ, 2000, J ATMOS SCI, V57, P3992, DOI 10.1175/1520-0469(2001)0582.0.CO;2 Hoskins B, 2012, Q J ROY METEOR SOC, V138, P1618, DOI 10.1002/qj.1881 HOSKINS BJ, 1993, J ATMOS SCI, V50, P1661, DOI 10.1175/1520-0469(1993)0502.0.CO;2 HOSKINS BJ, 1981, J ATMOS SCI, V38, P1179, DOI 10.1175/1520-0469(1981)0382.0.CO;2 HOSKINS BJ, 1975, Q J ROY METEOR SOC, V101, P637, DOI 10.1002/qj.49710142918 Hourdin F, 2006, CLIM DYNAM, V27, P787, DOI 10.1007/s00382-006-0158-0 Janicot S, 2009, J CLIMATE, V22, P1541, DOI 10.1175/2008JCLI2314.1 JIN FF, 1995, J ATMOS SCI, V52, P307, DOI 10.1175/1520-0469(1995)0522.0.CO;2 Jung T, 2010, MON WEATHER REV, V138, P2434, DOI 10.1175/2010MWR3255.1 Jung T, 2010, MON WEATHER REV, V138, P3157, DOI 10.1175/2010MWR3258.1 Kanamitsu M, 2002, B AM METEOROL SOC, V83, P1631, DOI [10.1175/Bams-83-11-1631, 10.1175/BAMS-83-11-1631] Lau K. -M, 2004, E ASIAN MONSOON LAU KM, 1992, J CLIMATE, V5, P140, DOI 10.1175/1520-0442(1992)0052.0.CO;2 Lau NC, 2005, J CLIMATE, V18, P2922, DOI 10.1175/JCLI3445.1 Leroux S, 2011, J CLIMATE, V24, P5378, DOI 10.1175/JCLI-D-11-00049.1 Lin H, 2007, J CLIMATE, V20, P5642, DOI 10.1175/2007JCLI1383.1 Lin H, 2009, J ATMOS SCI, V66, P2697, DOI 10.1175/2009JAS3008.1 Salas-Melia D., 2005, 103 CNRM, V103 Sardeshmukh PD, 2007, J CLIMATE, V20, P5677, DOI 10.1175/2007JCLI1411.1 SARDESHMUKH PD, 1988, J ATMOS SCI, V45, P1228, DOI 10.1175/1520-0469(1988)0452.0.CO;2 SIMMONS AJ, 1978, J ATMOS SCI, V35, P414, DOI 10.1175/1520-0469(1978)0352.0.CO;2 TING MF, 1990, J ATMOS SCI, V47, P2546, DOI 10.1175/1520-0469(1990)0472.0.CO;2 Ting MF, 2001, J ATMOS SCI, V58, P2331, DOI 10.1175/1520-0469(2001)0582.0.CO;2 TING MF, 1993, J ATMOS SCI, V50, P907, DOI 10.1175/1520-0469(1993)0502.0.CO;2 Trenberth K. E., 1998, J GEOPHYS RES, V103 Trenberth KE, 1996, J CLIMATE, V9, P1288, DOI 10.1175/1520-0442(1996)0092.0.CO;2 TRENBERTH KE, 1992, J CLIMATE, V5, P159, DOI 10.1175/1520-0442(1992)0052.0.CO;2 Uppala SM, 2005, Q J ROY METEOR SOC, V131, P2961, DOI 10.1256/qj.04.176 VALDES PJ, 1989, J ATMOS SCI, V46, P2509, DOI 10.1175/1520-0469(1989)0462.0.CO;2 Yasui S, 2010, J CLIMATE, V23, P2093, DOI 10.1175/2009JCLI3323.1 Hall, Nicholas M. J. Douville, Herve Li, Laurent ANR (French National Research Agency); VMC (Vulnerabilite Milieux et Climat) program We wish to thank Daniel J. Vimont for his editorial contribution and Mike Blackburn and the two anonymous reviewers for comments on the manuscript that lead to great improvements in clarity, focus, and relevance. This study was supported by the ANR (French National Research Agency) VMC (Vulnerabilite Milieux et Climat) program. 0 AMER METEOROLOGICAL SOC BOSTON J CLIMATE; A primitive equation model is used to investigate the role of the tropics in generating seasonal-mean anomalies in the extratropics. A nudging technique is applied to guide selected tropical regions toward 40-yr European Centre for Medium-Range Weather Forecasts (ECMWF) Re-Analysis (ERA-40) and the National Centers for Environmental Prediction (NCEP)/Department of Energy Reanalysis (NCEP-2). The time-independent linear response to these tropical anomalies is calculated for extratropical basic states taken from reanalysis climatologies and also from the climatological states of Action de Recherche Petite Echelle Grande Echelle (ARPEGE) and Laboratoire de Meteorologie Dynamique (LMDZ) general circulation model simulations. For summer case studies, time-independent linear solutions show that some seasonal anomalies can be attributed to linear wave propagation from the tropics, especially for lower extratropical latitudes. If nudging is applied to the anomaly part of the tropical flow, the linear response shows little dependence on the basic state. Regional tropical nudging experiments display a global extratropical response. The persistent European summer anomaly in 2003 is partly attributable to a linear response to both Central American and West African monsoon circulations. The African region also triggers a wave train along the Asian subtropical jet. The model is then used in "simple GCM" mode to obtain extratropical responses that include a contribution from transient eddies. Tropical nudging improves the simple GCM's stationary wave climatology, and transient eddy forcing can produce substantial seasonal anomalies at high latitudes with better correspondence to some observed cases, especially in the Western Hemisphere, with stronger communication between the Asian monsoon and North America.

Published
2013
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6. The Maintenance of the Last Great Ice Sheets: A UGAMP GCM Study

Author

Paul J. Valdes, Buwen Dong, and Nicholas M. J. Hall

Subjects
Ice-sheet model, Atmospheric Science, geography, geography.geographical_feature_category, Climatology, Sea ice thickness, Sea ice, Environmental science, Cryosphere, Ice-albedo feedback, Ice sheet, Arctic ice pack, Sea ice concentration
Abstract

A 5-yr simulation of the last glacial maximum using the UGAMP GCM is presented. It has a full seasonal cycle, T42 resolution, and interactive land surface and sea ice. Boundary conditions of SST, sea ice extent and land ice elevation are taken from the CLIMAP dataset and orbital parameters and carbon dioxide concentration are adjusted. It is compared with a 10-yr simulation of present-day climate using the same model. The results are analyzed in terms of processes leading to the maintenance of the atmospheric circulation and temperature structure, midlatitude transient behavior, precipitation, and eventually accumulation of ice over the glaciers. The model responds in a similar manner to previous studies in global mean statistics but differs in its treatment of regional climates. Changes in sea ice and orography are equally important in determining the positions of the upper-level jets. The Atlantic jet and storm track in particular are much stronger than in the present-day simulation, and the as...

Published
1996
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7. Atmospheric equilibrium, instability and energy transport at the last glacial maximum

Author

Nicholas M. J. Hall, Buwen Doug, and Paul J. Valdes

Subjects
Atmospheric Science, Heat flux, Climatology, Baroclinity, Northern Hemisphere, Flux, Environmental science, Last Glacial Maximum, Storm track, Eddy diffusion, Latitude
Abstract

A range of diagnostics from two GCM simulations, one of the present-day climate and one of the last glacial maximum (LGM) is used to gain insight into their different temperature structures and eddy dynamics. There are large local increases in baroclinicity at the LGM, especially in the Atlantic storm track, with large accompanying increases in the low level transient eddy heat flux. However, the differences in the zonal mean are much smaller, and the increases in both baroclinicity and heat flux are confined to low levels. Supplementary experiments with baroclinic wave lifecycles confirm the marked contrast between local and zonal mean behaviour, but do not adequately explain the differences between the zonal mean climates. The total flux of energy across latitude circles in the Northern Hemisphere does not change much during DJF, although its transient component is actually reduced at the LGM (during JJA the transient component is increased). Calculations of total linear eddy diffusivity reveal that changes in the time mean stationary waves are chiefly responsible for the seasonal range of this quantity at the LGM, while they only account for half the seasonal range at the present-day.

Published
1996
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8. Storm tracks in a high-resolution GCM with doubled carbon dioxide

Author

Nicholas M. J. Hall, Paul J. Valdes, Brian J. Hoskins, and Catherine A. Senior

Subjects
Atmospheric Science, Energy flux, Storm, Forcing (mathematics), Sensible heat, Atmospheric sciences, Atmosphere, chemistry.chemical_compound, chemistry, Eddy, Climatology, Carbon dioxide, Environmental science, Storm track
Abstract

Transient eddy activity has been diagnosed for the winter season of two ten-year equilibrium GCM integrations carried out at the UK Meteorological Office, one with present-day levels of carbon dioxide concentration (control) and one with doubled carbon dioxide (2CO2). On synoptic timescales, indicators of storm-track activity such as eddy kinetic energy are shifted northwards and intensified downstream in the 2CO2 experiment relative to the control. This effect is particularly marked for the Atlantic storm track. These patterns correspond closely to changes in relevant diagnostics of the time mean, such as the Eady growth rate and the diabatic heating. In the latter, the downstream intensification is effected by a decrease in the sensible heating and an increase in the latent heating in a warmer, moister atmosphere. Changes in the jet structure are consistent with changes in baroclinicity and eddy forcing. The total zonal-mean poleward energy transport is only slightly different between the two experiments. However, the component of this transport due to transient eddies has a different character when the carbon dioxide is doubled. In particular, the moist contribution to the transient energy flux is enhanced.

Published
1994
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9. Tropical influence on boreal summer mid-latitude stationary waves

Author

Nicholas M. J. Hall, Christophe Cassou, Hervé Douville, Soline Bielli, S. Tyteca, Michel Déqué, Aurore Voldoire, Groupe d'étude de l'atmosphère météorologique (CNRM-GAME), Institut national des sciences de l'Univers (INSU - CNRS)-Météo France-Centre National de la Recherche Scientifique (CNRS), Centre Européen de Recherche et de Formation Avancée en Calcul Scientifique (CERFACS), CERFACS, Océan du Large et Variabilité Climatique (OLVAC), Laboratoire d'études en Géophysique et océanographie spatiales (LEGOS), Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire Midi-Pyrénées (OMP), Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), and Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Centre National de la Recherche Scientifique (CNRS)

Subjects
[SDU.OCEAN]Sciences of the Universe [physics]/Ocean, Atmosphere, Atmospheric Science, 010504 meteorology & atmospheric sciences, Atmospheric circulation, 010502 geochemistry & geophysics, Atmospheric sciences, 01 natural sciences, African easterly jet, Sea surface temperature, 13. Climate action, Anticyclone, Climatology, Middle latitudes, Extratropical cyclone, Environmental science, Climate model, 0105 earth and related environmental sciences, Teleconnection
Abstract

International audience; While organized tropical convection is a well-known source of extratropical planetary waves, state-of-the-art climate models still show serious deficiencies in simulating accurately the atmospheric response to tropical sea surface temperature (SST) anomalies and the associated teleconnections. In the present study, the remote influence of the tropical atmospheric circulation is evaluated in ensembles of global boreal summer simulations in which the Arpege-Climat atmospheric General Circulation Model (GCM) is nudged towards 6-h reanalyses. The nudging is applied either in the whole tropical band or in a regional summer monsoon domain. Sensitivity tests to the experimental design are first conducted using prescribed climatological SST. They show that the tropical relaxation does not improve the zonal mean extratropical climatology but does lead to a significantly improved representation of the mid-latitude stationary waves in both hemispheres. Low-pass filtering of the relaxation fields has no major effect on the model response, suggesting that high-frequency tropical variability is not responsible for extratropical biases. Dividing the nudging strength by a factor 10 only decreases the magnitude of the response. Model errors in each monsoon domain contribute to deficiencies in the model's mid-latitude climatology, although an exaggerated large-scale subsidence in the central equatorial Pacific appears as the main source of errors for the representation of stationary waves in the Arpege-Climat model. Case studies are then conducted using either climatological or observed SST. The focus is first on summer 2003 characterized by a strong and persistent anticyclonic anomaly over western Europe. This pattern is more realistic in nudging experiments than in simulations only driven by observed SST, especially when the nudging domain is centred over Central America. Other case studies also show a significant tropical forcing of the summer mid-latitude stationary waves and suggest a weak influence of prescribed observed SST in the northern extratropics. Results therefore indicate that improving the tropical divergent circulation and its response to tropical SST anomalies remains a key issue for increasing the skill of extratropical seasonal predictions, not only in the winter hemisphere but also in the boreal summer hemisphere where the prediction of heatwave and drought likelihood is expected to become an important challenge with increasing concentrations of greenhouse gases.

Published
2011
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10. Monsoon Multidisciplinary Analysis (AMMA) : an integrated project for understanding of the West African climate system and its human dimension

Author

G. de Coëtlogon, Romain Roehrig, Sally L. Lavender, Bernard Fontaine, Flore Mounier, Romain Marteau, Christopher M. Taylor, Christophe Lavaysse, Serge Janicot, Guy Caniaux, Fabrice Chauvin, George N. Kiladis, Stéphanie Leroux, Jean-Philippe Lafore, Benjamin Sultan, Nathalie Philippon, Nicholas M. J. Hall, Laboratoire d'Océanographie et du Climat : Expérimentations et Approches Numériques ( LOCEAN ), Muséum National d'Histoire Naturelle ( MNHN ) -Université Pierre et Marie Curie - Paris 6 ( UPMC ) -Institut national des sciences de l'Univers ( INSU - CNRS ) -Centre National de la Recherche Scientifique ( CNRS ), Groupe d'étude de l'atmosphère météorologique ( CNRM-GAME ), Institut national des sciences de l'Univers ( INSU - CNRS ) -Météo France-Centre National de la Recherche Scientifique ( CNRS ), ESTER - LATMOS, Laboratoire Atmosphères, Milieux, Observations Spatiales ( LATMOS ), Université de Versailles Saint-Quentin-en-Yvelines ( UVSQ ) -Université Pierre et Marie Curie - Paris 6 ( UPMC ) -Institut national des sciences de l'Univers ( INSU - CNRS ) -Centre National de la Recherche Scientifique ( CNRS ) -Université de Versailles Saint-Quentin-en-Yvelines ( UVSQ ) -Université Pierre et Marie Curie - Paris 6 ( UPMC ) -Institut national des sciences de l'Univers ( INSU - CNRS ) -Centre National de la Recherche Scientifique ( CNRS ), Centre de Recherches de Climatologie ( CRC ), Université de Bourgogne ( UB ) -Centre National de la Recherche Scientifique ( CNRS ), Laboratoire d'études en Géophysique et océanographie spatiales ( LEGOS ), Université Paul Sabatier - Toulouse 3 ( UPS ) -Centre National d'Etudes Spatiales ( CNES ) -Institut national des sciences de l'Univers ( INSU - CNRS ) -Observatoire Midi-Pyrénées ( OMP ) -Centre National de la Recherche Scientifique ( CNRS ), NOAA Earth System Research Laboratory ( ESRL ), National Oceanic and Atmospheric Administration ( NOAA ), Department of Atmospheric and Oceanic Sciences [Montreal], McGill University, School of Environmental Sciences [Norwich], University of East Anglia [Norwich] ( UEA ), Centre for Ecology and Hydrology [Wallingford] ( CEH ), Natural Environment Research Council ( NERC ), Laboratoire d'Océanographie et du Climat : Expérimentations et Approches Numériques (LOCEAN), 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)), 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)-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), Centre national de recherches météorologiques (CNRM), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire Midi-Pyrénées (OMP), Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Centre National de la Recherche Scientifique (CNRS), Laboratoire Atmosphères, Milieux, Observations Spatiales (LATMOS), Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Centre de Recherches de Climatologie (CRC), Université de Bourgogne (UB)-Centre National de la Recherche Scientifique (CNRS), Laboratoire d'études en Géophysique et océanographie spatiales (LEGOS), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire Midi-Pyrénées (OMP), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Centre National de la Recherche Scientifique (CNRS), NOAA Earth System Research Laboratory (ESRL), National Oceanic and Atmospheric Administration (NOAA), Department of Atmospheric and Oceanic Sciences [Montréal], McGill University = Université McGill [Montréal, Canada], University of East Anglia [Norwich] (UEA), Centre for Ecology and Hydrology [Wallingford] (CEH), Natural Environment Research Council (NERC), 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)), 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)-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), Groupe d'étude de l'atmosphère météorologique (CNRM-GAME), Institut national des sciences de l'Univers (INSU - CNRS)-Météo France-Centre National de la Recherche Scientifique (CNRS), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire Midi-Pyrénées (OMP), and Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Centre National de la Recherche Scientifique (CNRS)

Subjects
Atmospheric Science, 010504 meteorology & atmospheric sciences, 0207 environmental engineering, 02 engineering and technology, [SDU.STU.ME]Sciences of the Universe [physics]/Earth Sciences/Meteorology, Intraseasonal variability, Monsoon, Atmospheric sciences, 01 natural sciences, West africa, West African monsoon, predictability, Monsoon onset, monsoon onset, Crop yield, Precipitation, Predictability, 020701 environmental engineering, 0105 earth and related environmental sciences, intraseasonal variability, [ SDU.STU.ME ] Sciences of the Universe [physics]/Earth Sciences/Meteorology, crop yield, Scale (music), West african, 13. Climate action, Climatology, Environmental science, Atmospheric dynamics
Abstract

International audience; The intraseasonal time scale is critical in West Africa where resources are highly rainfall dependent. Three main modes of variability have been identified, two with a mean periodicity of 15 days and one with a mean periodicity around 40 days. These modes have a regional scale and can strongly influence precipitation and convective activity. They are mainly controlled by atmospheric dynamics and land-surface interactions. They can also modulate the very specific phase of the African summer monsoon onset. A better knowledge of the mechanisms controlling this scale is necessary to improve its predictability.

Published
2011
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11. Internal variability in a regional climate model over West Africa

Author

Stéphanie Leroux, Christophe Messager, Emilie Vanvyve, Jean-Pascal van Ypersele, Nicholas M. J. Hall, Institut d'Astronomie et de Géophysique Georges Lemaître (UCL-ASTR), Université Catholique de Louvain = Catholic University of Louvain (UCL), Laboratoire d'études en Géophysique et océanographie spatiales (LEGOS), Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire Midi-Pyrénées (OMP), Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Centre National de la Recherche Scientifique (CNRS), Institute for Climate and Atmospheric Science [Leeds] (ICAS), School of Earth and Environment [Leeds] (SEE), University of Leeds-University of Leeds, Laboratoire de physique des océans (LPO), Institut de Recherche pour le Développement (IRD)-Institut Français de Recherche pour l'Exploitation de la Mer (IFREMER)-Université de Brest (UBO)-Centre National de la Recherche Scientifique (CNRS), Laboratoire d'étude des transferts en hydrologie et environnement (LTHE), Institut National Polytechnique de Grenoble (INPG)-Centre National de la Recherche Scientifique (CNRS)-Observatoire des Sciences de l'Univers de Grenoble (OSUG), Université Joseph Fourier - Grenoble 1 (UJF)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Institut national des sciences de l'Univers (INSU - CNRS)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS)-Université Joseph Fourier - Grenoble 1 (UJF)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Institut national des sciences de l'Univers (INSU - CNRS)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS), Université Catholique de Louvain (UCL), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Centre National d'Études Spatiales [Toulouse] (CNES)-Observatoire Midi-Pyrénées (OMP), Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS), Centre National de la Recherche Scientifique (CNRS)-Institut National Polytechnique de Grenoble (INPG)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Joseph Fourier - Grenoble 1 (UJF)-Observatoire des Sciences de l'Univers de Grenoble (OSUG), and Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Joseph Fourier - Grenoble 1 (UJF)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes (UGA)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes (UGA)

Subjects
Atmospheric Science, 010504 meteorology & atmospheric sciences, 0207 environmental engineering, 02 engineering and technology, Atmospheric model, 01 natural sciences, Confidence interval, West africa, 13. Climate action, Internal variability, Climatology, Range (statistics), Spatial ecology, Environmental science, Climate model, Precipitation, 020701 environmental engineering, [SDU.STU.OC]Sciences of the Universe [physics]/Earth Sciences/Oceanography, 0105 earth and related environmental sciences
Abstract

International audience; Sensitivity studies with regional climate models are often performed on the basis of a few simulations for which the difference is analysed and the statistical significance is often taken for granted. In this study we present some simple measures of the confidence limits for these types of experiments by analysing the internal variability of a regional climate model run over West Africa. Two 1-year long simulations, differing only in their initial conditions, are compared. The difference between the two runs gives a measure of the internal variability of the model and an indication of which timescales are reliable for analysis. The results are analysed for a range of timescales and spatial scales, and quantitative measures of the confidence limits for regional model simulations are diagnosed for a selection of study areas for rainfall, low level temperature and wind. As the averaging period or spatial scale is increased, the signal due to internal variability gets smaller and confidence in the simulations increases. This occurs more rapidly for variations in precipitation, which appear essentially random, than for dynamical variables, which show some organisation on larger scales.

Published
2008
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