scholarly journals Tropical atmospheric circulation response to the G1 sunshade geoengineering radiative forcing experiment

2018 ◽  
Vol 18 (12) ◽  
pp. 8689-8706 ◽  
Author(s):  
Anboyu Guo ◽  
John C. Moore ◽  
Duoying Ji
Keyword(s):  
Radiative Forcing ◽  
Hadley Circulation ◽  
Walker Circulation ◽  
Static Stability ◽  
Solar Radiation Management ◽  
Management Scenario ◽  
The Difference ◽  
Radiation Management ◽  
Different Response ◽  
The Walker Circulation

Abstract. We investigate the multi-Earth system model response of the Walker circulation and Hadley circulations under the idealized solar radiation management scenario (G1) and under abrupt4xCO2. The Walker circulation multi-model ensemble mean shows changes in some regions but no significant change in intensity under G1, while it shows a 4∘ eastward movement and 1.9 × 109 kg s−1 intensity decrease in abrupt4xCO2. Variation in the Walker circulation intensity has the same high correlation with sea surface temperature gradient between the eastern and western Pacific under both G1 and abrupt4xCO2. The Hadley circulation shows significant differences in behavior between G1 and abrupt4xCO2, with intensity reductions in the seasonal maximum northern and southern cells under G1 correlated with equatorward motion of the Intertropical Convergence Zone (ITCZ). Southern and northern cells have a significantly different response, especially under abrupt4xCO2 when impacts on the southern Ferrel cell are particularly clear. The southern cell is about 3 % stronger under abrupt4xCO2 in July, August and September than under piControl, while the northern is reduced by 2 % in January, February and March. Both circulations are reduced under G1. There are significant relationships between northern cell intensity and land temperatures, but not for the southern cell. Changes in the meridional temperature gradients account for changes in Hadley intensity better than changes in static stability in G1 and especially in abrupt4xCO2. The difference in the response of the zonal Walker circulation and the meridional Hadley circulations under the idealized forcings may be driven by the zonal symmetric relative cooling of the tropics under G1.

scholarly journals Tropical atmospheric circulation response to the G1 sunshade geoengineering radiative forcing experiment

2018 ◽  
Author(s):  
Anboyu Guo ◽  
John C. Moore ◽  
Duoying Ji
Keyword(s):  
Radiative Forcing ◽  
Hadley Circulation ◽  
Walker Circulation ◽  
Static Stability ◽  
Solar Radiation Management ◽  
Inter Tropical Convergence Zone ◽  
Management Scenario ◽  
Radiation Management ◽  
Different Response ◽  
The Walker Circulation

Abstract. We investigate the multi-earth system model response of the Walker circulation and Hadley circulations under the idealized solar radiation management scenario (G1) and under abrupt4 × CO2. The Walker circulation multi-model ensemble mean shows changes in some regions but no significant change in intensity under G1, while it shows 4° eastward movement and 1.9 × 109 kg s−1 intensity decrease in abrupt4 × CO2. Variation of the Walker circulation intensity has the same high correlation with sea surface temperature gradient between eastern and western Pacific under both G1 and abrupt4 × CO2. The Hadley circulation shows significant differences in behavior between G1 and abrupt4 × CO2 with intensity reductions in the seasonal maximum northern and southern cells under G1 correlated with equator-ward motion of the Inter Tropical Convergence Zone (ITCZ). Southern and northern cells have significantly different response, especially under abrupt4 × CO2 when impacts on the southern Ferrel cell are particular clear. The southern cell is about 3 % stronger under abrupt4 × CO2 in July, August and September than under piControl, while the northern is reduced by 2 % in January, February and March. Both circulations are reduced under G1. There are good correlations between northern cell intensity and land temperatures, but not for the southern cell. Changes in the meridional temperature gradients account for changes in Hadley intensity better than changes in static stability both in G1 and especially in abrupt4 × CO2. The difference in response to the zonal Walker circulation and the meridional Hadley circulations under the idealized forcings may be driven by the zonal symmetric relative cooling of the tropics under G1.

scholarly journals The Key Role of Ozone-Depleting Substances in Weakening the Walker Circulation in the Second Half of the Twentieth Century

2019 ◽  
Vol 32 (5) ◽  
pp. 1411-1418 ◽  
Author(s):  
Lorenzo M. Polvani ◽  
Katinka Bellomo
Keyword(s):  
Twentieth Century ◽  
Pacific Ocean ◽  
Greenhouse Gases ◽  
Radiative Forcing ◽  
Climate Model ◽  
Walker Circulation ◽  
Surface Warming ◽  
Ozone Depleting Substances ◽  
The Antarctic ◽  
The Walker Circulation

It is widely appreciated that ozone-depleting substances (ODS), which have led to the formation of the Antarctic ozone hole, are also powerful greenhouse gases. In this study, we explore the consequence of the surface warming caused by ODS in the second half of the twentieth century over the Indo-Pacific Ocean, using the Whole Atmosphere Chemistry Climate Model (version 4). By contrasting two ensembles of chemistry–climate model integrations (with and without ODS forcing) over the period 1955–2005, we show that the additional greenhouse effect of ODS is crucial to producing a statistically significant weakening of the Walker circulation in our model over that period. When ODS concentrations are held fixed at 1955 levels, the forcing of the other well-mixed greenhouse gases alone leads to a strengthening—rather than weakening—of the Walker circulation because their warming effect is not sufficiently strong. Without increasing ODS, a surface warming delay in the eastern tropical Pacific Ocean leads to an increase in the sea surface temperature gradient between the eastern and western Pacific, with an associated strengthening of the Walker circulation. When increasing ODS are added, the considerably larger total radiative forcing produces a much faster warming in the eastern Pacific, causing the sign of the trend to reverse and the Walker circulation to weaken. Our modeling result suggests that ODS may have been key players in the observed weakening of the Walker circulation over the second half of the twentieth century.

scholarly journals Changes of the Boreal Winter Hadley Circulation in the NCEP–NCAR and ECMWF Reanalyses: A Comparative Study

2007 ◽  
Vol 20 (20) ◽  
pp. 5191-5200 ◽  
Author(s):  
Hua Song ◽  
Minghua Zhang
Keyword(s):  
Radiative Forcing ◽  
Atmospheric Transport ◽  
Vertical Motion ◽  
Hadley Circulation ◽  
Western Pacific ◽  
Boreal Winter ◽  
Tropical Western Pacific ◽  
The Difference ◽  
Upper Level ◽  
Static Energy

Abstract Both the ECMWF and the NCEP–NCAR reanalyses show a strengthening of the atmospheric Hadley circulation in boreal winter over the last 50 years, but the intensification is much stronger in the ECMWF than in the NCEP–NCAR reanalysis. This study focuses on the difference of these trends in the two reanalyses. It is shown that trends in the Hadley circulation in the two reanalyses differ mainly over the tropical western Pacific. This difference is found to be consistent with respective trends of the atmospheric transport of moist static energy, longwave cloud radiative forcing, and upper-level clouds in the two reanalyses. Two independent datasets of upper-level cloud cover and sea level pressure from ship-based measurements are then used to evaluate the reanalyses over the tropical western Pacific. They are found to be more consistent with the trends in the NCEP–NCAR reanalysis than those in the ECMWF reanalysis. The results suggest a weakening of the vertical motion associated with the Hadley circulation in the tropical western Pacific.

scholarly journals Tropical Clouds and Circulation Changes during the 2006/07 and 2009/10 El Niños

2013 ◽  
Vol 26 (2) ◽  
pp. 399-413 ◽  
Author(s):  
Hui Su ◽  
Jonathan H. Jiang
Keyword(s):  
El Niño ◽  
Radiative Forcing ◽  
El Nino ◽  
Dominant Role ◽  
Hadley Circulation ◽  
Walker Circulation ◽  
Reanalysis Data ◽  
Tropical Circulation ◽  
Different Characteristics ◽  
Tropical Clouds

Abstract Changes in tropical cloud vertical structure, cloud radiative forcing (CRF), and circulation exhibit distinctly different characteristics during the 2006/07 and 2009/10 El Niños, revealed by CloudSat and Cloud–Aerosol Lidar and Infrared Pathfinder Satellite (CALIPSO) observations and reanalysis data. On the tropical average, the 2009/10 has a decrease of clouds from 2 to 14 km, an increase of clouds in the boundary layer, and an increase of cirrus clouds above 14 km. The tropical-mean cloud anomalies in the middle to upper troposphere (6–14 km) for the 2006/07 El Niño are nearly opposite to those in 2009/10 El Niño. The tropical averaged net CRF anomaly at the top of the atmosphere (TOA) is 0.6–0.7 W m−2 cooling (0.02–0.5 W m−2 warming) for the 2009/10 (2006/07) El Niño. The 2009/10 El Niño is associated with a strengthening of tropical circulation, increased high (low) clouds in extremely strong ascending (descending) regimes, and decreased clouds in the middle and high altitudes in a broad range of moderate circulation regimes. The strengthening of tropical circulation is primarily caused by the enhancement of the Hadley circulation. The 2006/07 El Niño is associated with a weakening of the tropical circulation, primarily caused by the reduction of the Walker circulation. The cloud anomalies in each circulation regime are approximately opposite for these two El Niños. The analysis herein suggests that both the magnitude and pattern of sea surface temperature anomalies in the two events contribute to the differences in clouds and circulation anomalies, with magnitude playing a dominant role. The contrasting behaviors of the two El Niños highlight the nonlinear response of tropical clouds and circulation to El Niño SST forcing.

scholarly journals Walker circulation response to extratropical radiative forcing

2020 ◽  
Vol 6 (47) ◽  
pp. eabd3021
Author(s):  
Sarah M. Kang ◽  
Shang-Ping Xie ◽  
Yechul Shin ◽  
Hanjun Kim ◽  
Yen-Ting Hwang ◽  
...  
Keyword(s):  
Ocean Circulation ◽  
Radiative Forcing ◽  
Climate Model ◽  
Walker Circulation ◽  
Coupled System ◽  
Subsurface Water ◽  
Eastern Equatorial Pacific ◽  
Global Impacts ◽  
Climate Model Simulations ◽  
The Walker Circulation

Walker circulation variability and associated zonal shifts in the heating of the tropical atmosphere have far-reaching global impacts well into high latitudes. Yet the reversed high latitude–to–Walker circulation teleconnection is not fully understood. Here, we reveal the dynamical pathways of this teleconnection across different components of the climate system using a hierarchy of climate model simulations. In the fully coupled system with ocean circulation adjustments, the Walker circulation strengthens in response to extratropical radiative cooling of either hemisphere, associated with the upwelling of colder subsurface water in the eastern equatorial Pacific. By contrast, in the absence of ocean circulation adjustments, the Walker circulation response is sensitive to the forcing hemisphere, due to the blocking effect of the northward-displaced climatological intertropical convergence zone and shortwave cloud radiative effects. Our study implies that energy biases in the extratropics can cause pronounced changes of tropical climate patterns.

scholarly journals Interactions between reducing CO 2 emissions, CO 2 removal and solar radiation management

2012 ◽  
Vol 370 (1974) ◽  
pp. 4343-4364 ◽  
Author(s):  
Naomi E. Vaughan ◽  
Timothy M. Lenton
Keyword(s):  
Carbon Dioxide ◽  
Solar Radiation ◽  
Carbon Dioxide Emissions ◽  
Radiative Forcing ◽  
Carbon Capture ◽  
Climate Model ◽  
Carbon Capture And Storage ◽  
Solar Radiation Management ◽  
Radiation Management ◽  
And Storage

We use a simple carbon cycle–climate model to investigate the interactions between a selection of idealized scenarios of mitigated carbon dioxide emissions, carbon dioxide removal (CDR) and solar radiation management (SRM). Two CO 2 emissions trajectories differ by a 15-year delay in the start of mitigation activity. SRM is modelled as a reduction in incoming solar radiation that fully compensates the radiative forcing due to changes in atmospheric CO 2 concentration. Two CDR scenarios remove 300 PgC by afforestation (added to vegetation and soil) or 1000 PgC by bioenergy with carbon capture and storage (removed from system). Our results show that delaying the start of mitigation activity could be very costly in terms of the CDR activity needed later to limit atmospheric CO 2 concentration (and corresponding global warming) to a given level. Avoiding a 15-year delay in the start of mitigation activity is more effective at reducing atmospheric CO 2 concentrations than all but the maximum type of CDR interventions. The effects of applying SRM and CDR together are additive, and this shows most clearly for atmospheric CO 2 concentration. SRM causes a significant reduction in atmospheric CO 2 concentration due to increased carbon storage by the terrestrial biosphere, especially soils. However, SRM has to be maintained for many centuries to avoid rapid increases in temperature and corresponding increases in atmospheric CO 2 concentration due to loss of carbon from the land.

scholarly journals Field experiments on solar geoengineering: report of a workshop exploring a representative research portfolio

2014 ◽  
Vol 372 (2031) ◽  
pp. 20140175 ◽  
Author(s):  
David W. Keith ◽  
Riley Duren ◽  
Douglas G. MacMartin
Keyword(s):  
Solar Radiation ◽  
Radiative Forcing ◽  
Field Experiments ◽  
Field Research ◽  
Research Programme ◽  
Solar Radiation Management ◽  
Systematic Research ◽  
Cirrus Cloud ◽  
Solar Geoengineering ◽  
Radiation Management

We summarize a portfolio of possible field experiments on solar radiation management (SRM) and related technologies. The portfolio is intended to support analysis of potential field research related to SRM including discussions about the overall merit and risk of such research as well as mechanisms for governing such research and assessments of observational needs. The proposals were generated with contributions from leading researchers at a workshop held in March 2014 at which the proposals were critically reviewed. The proposed research dealt with three major classes of SRM proposals: marine cloud brightening, stratospheric aerosols and cirrus cloud manipulation. The proposals are summarized here along with an analysis exploring variables such as space and time scale, risk and radiative forcing. Possible gaps, biases and cross-cutting considerations are discussed. Finally, suggestions for plausible next steps in the development of a systematic research programme are presented.

scholarly journals Impact of Mountains on Tropical Circulation in Two Earth System Models

2017 ◽  
Vol 30 (11) ◽  
pp. 4149-4163 ◽  
Author(s):  
Zachary Naiman ◽  
Paul J. Goodman ◽  
John P. Krasting ◽  
Sergey L. Malyshev ◽  
Joellen L. Russell ◽  
...  
Keyword(s):  
Time Scales ◽  
Hadley Circulation ◽  
Walker Circulation ◽  
Pacific Basin ◽  
Earth System ◽  
Tropical Circulation ◽  
System Models ◽  
The Mean ◽  
Earth System Models ◽  
The Walker Circulation

Abstract Two state-of-the-art Earth system models (ESMs) were used in an idealized experiment to explore the role of mountains in shaping Earth’s climate system. Similar to previous studies, removing mountains from both ESMs results in the winds becoming more zonal and weaker Indian and Asian monsoon circulations. However, there are also broad changes to the Walker circulation and El Niño–Southern Oscillation (ENSO). Without orography, convection moves across the entire equatorial Indo-Pacific basin on interannual time scales. ENSO has a stronger amplitude, lower frequency, and increased regularity. A wider equatorial wind zone and changes to equatorial wind stress curl result in a colder cold tongue and a steeper equatorial thermocline across the Pacific basin during La Niña years. Anomalies associated with ENSO warm events are larger without mountains and have greater impact on the mean tropical climate than when mountains are present. Without mountains, the centennial-mean Pacific Walker circulation weakens in both models by approximately 45%, but the strength of the mean Hadley circulation changes by less than 2%. Changes in the Walker circulation in these experiments can be explained by the large spatial excursions of atmospheric deep convection on interannual time scales. These results suggest that mountains are an important control on the large-scale tropical circulation, impacting ENSO dynamics and the Walker circulation, but have little impact on the strength of the Hadley circulation.

scholarly journals Sensitivity of simulated climate to latitudinal distribution of solar insolation reduction in solar radiation management

2014 ◽  
Vol 14 (15) ◽  
pp. 7769-7779 ◽  
Author(s):  
A. Modak ◽  
G. Bala
Keyword(s):  
Climate Change ◽  
Radiative Forcing ◽  
Solar Radiation Management ◽  
Sulfate Aerosols ◽  
Latitudinal Distribution ◽  
Solar Insolation ◽  
Global Mean Temperature ◽  
Mean Climate ◽  
Radiation Management ◽  
Global Mean

Abstract. Solar radiation management (SRM) geoengineering has been proposed as a potential option to counteract climate change. We perform a set of idealized geoengineering simulations using Community Atmosphere Model version 3.1 developed at the National Center for Atmospheric Research to investigate the global hydrological implications of varying the latitudinal distribution of solar insolation reduction in SRM methods. To reduce the solar insolation we have prescribed sulfate aerosols in the stratosphere. The radiative forcing in the geoengineering simulations is the net forcing from a doubling of CO2 and the prescribed stratospheric aerosols. We find that for a fixed total mass of sulfate aerosols (12.6 Mt of SO4), relative to a uniform distribution which nearly offsets changes in global mean temperature from a doubling of CO2, global mean radiative forcing is larger when aerosol concentration is maximum at the poles leading to a warmer global mean climate and consequently an intensified hydrological cycle. Opposite changes are simulated when aerosol concentration is maximized in the tropics. We obtain a range of 1 K in global mean temperature and 3% in precipitation changes by varying the distribution pattern in our simulations: this range is about 50% of the climate change from a doubling of CO2. Hence, our study demonstrates that a range of global mean climate states, determined by the global mean radiative forcing, are possible for a fixed total amount of aerosols but with differing latitudinal distribution. However, it is important to note that this is an idealized study and thus not all important realistic climate processes are modeled.

scholarly journals Local Energetic Constraints on Walker Circulation Strength

2017 ◽  
Vol 74 (6) ◽  
pp. 1907-1922 ◽  
Author(s):  
Robert C. Wills ◽  
Xavier J. Levine ◽  
Tapio Schneider
Keyword(s):  
Global Warming ◽  
Energy Input ◽  
Climate Models ◽  
Walker Circulation ◽  
Static Stability ◽  
Net Energy ◽  
Open Questions ◽  
Wide Range ◽  
Gross Moist Stability ◽  
The Walker Circulation

Abstract The weakening of tropical overturning circulations is a robust response to global warming in climate models and observations. However, there remain open questions on the causes of this change and the extent to which this weakening affects individual circulation features such as the Walker circulation. The study presents idealized GCM simulations of a Walker circulation forced by prescribed ocean heat flux convergence in a slab ocean, where the longwave opacity of the atmosphere is varied to simulate a wide range of climates. The weakening of the Walker circulation with warming results from an increase in gross moist stability (GMS), a measure of the tropospheric moist static energy (MSE) stratification, which provides an effective static stability for tropical circulations. Baroclinic mode theory is used to determine changes in GMS in terms of the tropical-mean profiles of temperature and MSE. The GMS increases with warming, owing primarily to the rise in tropopause height, decreasing the sensitivity of the Walker circulation to zonally anomalous net energy input. In the absence of large changes in net energy input, this results in a rapid weakening of the Walker circulation with global warming.

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