Stratospheric variability and trends in IPCC model simulations

Abstract. Atmosphere and Ocean General Circulation Model (AOGCM) experiments for the Intergovernmental Panel on Climate Change Fourth Assessment Report are analyzed using both 20th and 21st century model output to better understand model variability and assess the importance of various forcing mechanisms on stratospheric trends. While models represent the climatology of the stratosphere reasonably well in comparison with NCEP reanalysis, there are biases and large variability among models. In general, AOGCMs are cooler than NCEP throughout the stratosphere, with the largest differences in the tropics. Around half the AOGCMs have a top level beneath ~2 hPa and show a significant cold bias in their upper levels (~10 hPa) compared to NCEP, suggesting that these models may have compromised simulations near 10 hPa due to a low model top or insufficient stratospheric levels. In the lower stratosphere (50 hPa), the temperature variability associated with large volcanic eruptions is either absent (in about half of the models) or the warming is overestimated in the models that do include volcanic aerosols. There is general agreement on the vertical structure of temperature trends over the last few decades, differences between models are explained by the inclusion of different forcing mechanisms, such as stratospheric ozone depletion and volcanic aerosols. However, even when human and natural forcing agents are included in the simulations, significant differences remain between observations and model trends, particularly in the upper tropical troposphere (200 hPa–100 hPa), where, since 1979, models show a warming trend and the observations a cooling trend.

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Stratospheric variability and trends in models used for the IPCC AR4

Atmospheric Chemistry and Physics ◽

10.5194/acp-6-5369-2006 ◽

2006 ◽

Vol 6 (12) ◽

pp. 5369-5380 ◽

Cited By ~ 77

Author(s):

E. C. Cordero ◽

P. M. de F. Forster

Keyword(s):

General Circulation ◽

Stratospheric Ozone ◽

Circulation Model ◽

Volcanic Eruptions ◽

Ocean General Circulation Model ◽

Cold Bias ◽

Intergovernmental Panel ◽

Large Variability ◽

Volcanic Aerosols ◽

Forcing Mechanisms

Abstract. Atmosphere and ocean general circulation model (AOGCM) experiments for the Intergovernmental Panel on Climate Change Fourth Assessment Report (AR4) are analyzed to better understand model variability and assess the importance of various forcing mechanisms on stratospheric trends during the 20th century. While models represent the climatology of the stratosphere reasonably well in comparison with NCEP reanalysis, there are biases and large variability among models. In general, AOGCMs are cooler than NCEP throughout the stratosphere, with the largest differences in the tropics. Around half the AOGCMs have a top level beneath ~2 hPa and show a significant cold bias in their upper levels (~10 hPa) compared to NCEP, suggesting that these models may have compromised simulations near 10 hPa due to a low model top or insufficient stratospheric levels. In the lower stratosphere (50 hPa), the temperature variability associated with large volcanic eruptions is absent in about half of the models, and in the models that do include volcanic aerosols, half of those significantly overestimate the observed warming. There is general agreement on the vertical structure of temperature trends over the last few decades, differences between models are explained by the inclusion of different forcing mechanisms, such as stratospheric ozone depletion and volcanic aerosols. However, even when human and natural forcing agents are included in the simulations, significant differences remain between observations and model trends, particularly in the upper tropical troposphere (200 hPa–100 hPa), where, since 1979, models show a warming trend and the observations a cooling trend.

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Climate variability of the mid- and high-latitudes of the Southern Hemisphere in ensemble simulations from 1500 to 2000 AD

Climate of the Past ◽

10.5194/cp-8-373-2012 ◽

2012 ◽

Vol 8 (1) ◽

pp. 373-390 ◽

Cited By ~ 15

Author(s):

S. B. Wilmes ◽

C. C. Raible ◽

T. F. Stocker

Keyword(s):

Climate Variability ◽

Southern Hemisphere ◽

General Circulation ◽

Circulation Model ◽

Volcanic Eruptions ◽

Ocean General Circulation Model ◽

Southern Annular Mode ◽

Significant Shift ◽

External Forcing ◽

Proxy Records

Abstract. To increase the sparse knowledge of long-term Southern Hemisphere (SH) climate variability, we assess an ensemble of 4 transient simulations over the last 500 yr performed with a state-of-the-art atmosphere ocean general circulation model. The model is forced with reconstructions of solar irradiance, greenhouse gas (GHG) and volcanic aerosol concentrations. A 1990 control simulation shows that the model is able to represent the Southern Annular Mode (SAM), and to some extent the South Pacific Dipole (SPD) and the Zonal Wave 3 (ZW3). During the past 500 yr we find that SPD and ZW3 variability remain stable, whereas SAM shows a significant shift towards its positive state during the 20th century. Regional temperatures over South America are strongly influenced by changing both GHG concentrations and volcanic eruptions, whereas precipitation shows no significant response to the varying external forcing. For temperature this stands in contrast to proxy records, suggesting that SH climate is dominated by internal variability rather than external forcing. The underlying dynamics of the temperature changes generally point to a combination of several modes, thus, hampering the possibilities of regional reconstructing the modes from proxy records. The linear imprint of the external forcing is as expected, i.e. a warming for increase in the combined solar and GHG forcing and a cooling after volcanic eruptions. Dynamically, only the increase in SAM with increased combined forcing is simulated.

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Simulation of the climate impact of Mt. Pinatubo eruption using ECHAM5 – Part 1: Sensitivity to the modes of atmospheric circulation and boundary conditions

Atmospheric Chemistry and Physics ◽

10.5194/acp-9-757-2009 ◽

2009 ◽

Vol 9 (2) ◽

pp. 757-769 ◽

Cited By ~ 29

Author(s):

M. A. Thomas ◽

C. Timmreck ◽

M. A. Giorgetta ◽

H.-F. Graf ◽

G. Stenchikov

Keyword(s):

Boundary Conditions ◽

General Circulation ◽

Circulation Model ◽

Volcanic Eruptions ◽

Climate Impact ◽

The Philippines ◽

Climate Response ◽

Stratospheric Temperature ◽

Pinatubo Eruption ◽

Volcanic Aerosols

Abstract. The eruption of Mt. Pinatubo in the Philippines in June 1991 was one of the strongest volcanic eruptions in the 20th century and this well observed eruption can serve as an important case study to understand the subsequent weather and climate changes. In this paper, the most comprehensive simulations to date of the climate impact of Mt. Pinatubo eruption are carried out with prescribed volcanic aerosols including observed SSTs, QBO and volcanically induced ozone anomalies. This is also the first attempt to include all the known factors for the simulation of such an experiment. Here, the climate response is evaluated under different boundary conditions including one at a time, thereby, investigating the radiative and dynamical responses to individual and combined forcings by observed SSTs, QBO and volcanic effects. Two ensembles of ten members each, for unperturbed and volcanically perturbed conditions were carried out using the middle atmosphere configuration of ECHAM5 general circulation model. Our results show that the simulated climate response that may arise solely from aerosol forcing in lower stratospheric temperature is insensitive to the boundary conditions in the tropics and does not show some observed features such as the temperature signature of the QBO phases. Also, statistically significant positive anomalies in the high latitudes in NH winter of 1991/92 seen in our model simulations with prescribed observed SST and QBO phases as boundary conditions are consistent with the observations. To simulate realistically the lower stratospheric temperature response, one must include all the known factors. The pure QBO and ocean signatures in lower stratospheric temperature are simulated consistently with earlier studies. The indirect effect of the volcanic aerosols manifested as the winter warming pattern is not simulated in the ensemble mean of the experiments. Our analysis also shows that the response to El Niño conditions is very strong in the model and that it partially masks the effects due to volcanic forcing.

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Climate variability of the mid- and high-latitudes of the Southern Hemisphere in ensemble simulations from 1500 to 2000 AD

Climate of the Past Discussions ◽

10.5194/cpd-7-3091-2011 ◽

2011 ◽

Vol 7 (5) ◽

pp. 3091-3129 ◽

Cited By ~ 1

Author(s):

S. B. Wilmes ◽

C. C. Raible ◽

T. F. Stocker

Keyword(s):

Climate Variability ◽

Southern Hemisphere ◽

General Circulation ◽

Circulation Model ◽

Volcanic Eruptions ◽

Ocean General Circulation Model ◽

Southern Annular Mode ◽

Significant Shift ◽

External Forcing ◽

Proxy Records

Abstract. To increase the sparse knowledge of long-term Southern Hemisphere (SH) climate variability we assess an ensemble of 4 transient simulations over the last 500 yr performed with a state-of-the-art atmosphere ocean general circulation model. The model is forced with reconstructions of solar irradiance, greenhouse gas (GHG) and volcanic aerosol concentrations. A 1990 control simulation shows that the model is able to represent the Southern Annular Mode (SAM), and to some extent the South Pacific Dipole (SPD) and the Zonal Wave 3 (ZW3). During the past 500 yr we find that SPD and ZW3 variability remain stable, whereas SAM shows a significant shift towards its positive state during the 20th century. Regional temperatures over South America are strongly influenced by changing both GHG concentrations and volcanic eruptions whereas precipitation shows no significant response to the varying external forcing. For temperature this stands in contrast to proxy records suggesting that SH climate is dominated by internal variability rather than external forcing. The underlying dynamics of the temperature changes generally point to a combination of several modes, thus, hampering the possibilities regional reconstructions of the modes from proxy records. The linear imprint of the external forcing is as expected, i.e. a warming for increase in the combined solar and GHG forcing and a cooling after volcanic eruptions. Dynamically only the increase in SAM with increased combined forcing is simulated.

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Forcing of stratospheric chemistry and dynamics during the Dalton Minimum

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-13-15061-2013 ◽

2013 ◽

Vol 13 (6) ◽

pp. 15061-15104 ◽

Cited By ~ 3

Author(s):

J. G. Anet ◽

S. Muthers ◽

E. Rozanov ◽

C. C. Raible ◽

T. Peter ◽

...

Keyword(s):

General Circulation ◽

Circulation Model ◽

Cosmic Ray ◽

Volcanic Eruptions ◽

Visible Radiation ◽

Linear Superposition ◽

Early 19Th Century ◽

Uv Irradiance ◽

Volcanic Aerosols ◽

Dalton Minimum

Abstract. The response of atmospheric chemistry and climate to volcanic eruptions and a decrease in solar activity during the Dalton Minimum is investigated with the fully coupled atmosphere-ocean-chemistry general circulation model SOCOL-MPIOM covering the time period 1780 to 1840 AD. We carried out several sensitivity ensemble experiments to separate the effects of (i) reduced solar ultra-violet (UV) irradiance, (ii) reduced solar visible and near infrared irradiance, (iii) enhanced galactic cosmic ray intensity as well as less intensive solar energetic proton events and auroral electron precipitation, and (iv) volcanic aerosols. The introduced changes of UV irradiance and volcanic aerosols significantly influence stratospheric climate in the early 19th century, whereas changes in the visible part of the spectrum and energetic particles have smaller effects. A reduction of UV irradiance by 15% causes global ozone decrease below the stratopause reaching 8% in the midlatitudes at 5 hPa and a significant stratospheric cooling of up to 2 °C in the midstratosphere and to 6 °C in the lower mesosphere. Changes in energetic particle precipitation lead only to minor changes in the yearly averaged temperature fields in the stratosphere. Volcanic aerosols heat the tropical lower stratosphere allowing more water vapor to enter the tropical stratosphere, which, via HOx reactions, decreases upper stratospheric and mesospheric ozone by roughly 4%. Conversely, heterogeneous chemistry on aerosols reduces stratospheric NOx leading to a 12% ozone increase in the tropics, whereas a decrease in ozone of up to 5% is found over Antarctica in boreal winter. The linear superposition of the different contributions is not equivalent to the response obtained in a simulation when all forcing factors are applied during the DM – this effect is especially well visible for NOx/NOy. Thus, this study highlights the non-linear behavior of the coupled chemistry-climate system. Finally, we conclude that especially UV and volcanic eruptions dominate the changes in the ozone, temperature and dynamics while the NOx field is dominated by the EPP. Visible radiation changes have only very minor effects on both stratospheric dynamics and chemistry.

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Depth structure of Ningaloo Niño/Niña events and associated drivers

Journal of Climate ◽

10.1175/jcli-d-19-1020.1 ◽

2020 ◽

pp. 1-65 ◽

Cited By ~ 1

Author(s):

Svenja Ryan ◽

Caroline C. Ummenhofer ◽

Glen Gawarkiewicz ◽

Patrick Wagner ◽

Markus Scheinert ◽

...

Keyword(s):

General Circulation ◽

Large Scale ◽

Circulation Model ◽

Recent Decade ◽

Ocean General Circulation Model ◽

Wind Forcing ◽

Global Ocean ◽

Buoyancy Forcing ◽

Leeuwin Current ◽

Forcing Mechanisms

AbstractMarine heatwaves along the coast ofWestern Australia, referred to as Ningaloo Niño, have had dramatic impacts on the ecosystem in the recent decade. A number of local and remote forcing mechanisms have been put forward, however little is known about the depth structure of such temperature extremes. Utilizing an eddy-active global Ocean General Circulation Model, Ningaloo Niño and the corresponding cold Ningaloo Niña events are investigated between 1958-2016, with focus on their depth structure. The relative roles of buoyancy and wind forcing are inferred from sensitivity experiments. Composites reveal a strong symmetry between cold and warm events in their vertical structure and associated large-scale spatial patterns. Temperature anomalies are largest at the surface, where buoyancy forcing is dominant and extend down to 300m depth (or deeper), with wind forcing being the main driver. Large-scale subsurface anomalies arise from a vertical modulation of the thermocline, extending from the western Pacific into the tropical eastern Indian Ocean. The strongest Ningaloo Niños in 2000 and 2011 are unprecedented compound events, where long-lasting high temperatures are accompanied by extreme freshening, which emerges in association with La Niñas, more common and persistent during the negative phase of the Interdecadal Pacific Oscillation. It is shown that Ningaloo Niños during La Nina phases have a distinctively deeper reach and are associated with a strengthening of the Leeuwin Current, while events during El Niño are limited to the surface layer temperatures, likely driven by local atmosphere-ocean feedbacks, without a clear imprint on salinity and velocity.

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Performance evaluation for an ocean general circulation model: vectorization andmultitasking

Proceedings of the 2nd international conference on Supercomputing - ICS '88 ◽

10.1145/55364.55393 ◽

1988 ◽

Cited By ~ 1

Author(s):

P. Andrich ◽

G. Madec

Keyword(s):

Performance Evaluation ◽

General Circulation Model ◽

General Circulation ◽

Circulation Model ◽

Ocean General Circulation Model ◽

Ocean General Circulation

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The South China Sea Throughflow Retrieved from Climatological Data*

Journal of Physical Oceanography ◽

10.1175/2008jpo3955.1 ◽

2009 ◽

Vol 39 (3) ◽

pp. 753-767 ◽

Cited By ~ 40

Author(s):

Max Yaremchuk ◽

Julian McCreary ◽

Zuojun Yu ◽

Ryo Furue

Keyword(s):

South China Sea ◽

General Circulation Model ◽

South China ◽

General Circulation ◽

Circulation Model ◽

Ocean General Circulation Model ◽

Luzon Strait ◽

The South China Sea ◽

China Sea ◽

Ocean General Circulation

Abstract The salinity distribution in the South China Sea (SCS) has a pronounced subsurface maximum from 150–220 m throughout the year. This feature can only be maintained by the existence of a mean flow through the SCS, consisting of a net inflow of salty North Pacific tropical water through the Luzon Strait and outflow through the Mindoro, Karimata, and Taiwan Straits. Using an inverse modeling approach, the authors show that the magnitude and space–time variations of the SCS thermohaline structure, particularly for the salinity maximum, allow a quantitative estimate of the SCS throughflow and its distribution among the three outflow straits. Results from the inversion are compared with available observations and output from a 50-yr simulation of a highly resolved ocean general circulation model. The annual-mean Luzon Strait transport is found to be 2.4 ± 0.6 Sv (Sv ≡ 106 m3 s−1). This inflow is balanced by the outflows from the Karimata (0.3 ± 0.5 Sv), Mindoro (1.5 ± 0.4), and Taiwan (0.6 ± 0.5 Sv) Straits. Results of the inversion suggest that the Karimata transport tends to be overestimated in numerical models. The Mindoro Strait provides the only passage from the SCS deeper than 100 m, and half of the SCS throughflow (1.2 ± 0.3 Sv) exits the basin below 100 m in the Mindoro Strait, a result that is consistent with a climatological run of a 0.1° global ocean general circulation model.

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