Modulation of hydroxyl variability by ENSO in the absence of external forcing

The hydroxyl radical (OH) is the primary oxidant in the troposphere, and the impact of its fluctuations on the methane budget has been disputed in recent years, however measurements of OH are insufficient to characterize global interannual fluctuations relevant for methane. Here, we use a 6,000-y control simulation of preindustrial conditions with a chemistry-climate model to quantify the natural variability in OH and internal feedbacks governing that variability. We find that, even in the absence of external forcing, maximum OH changes are 3.8 ± 0.8% over a decade, which is large in the context of the recent methane growth from 2007–2017. We show that the OH variability is not a white-noise process. A wavelet analysis indicates that OH variability exhibits significant feedbacks with the same periodicity as the El Niño–Southern Oscillation (ENSO). We find intrinsically generated modulation of the OH variability, suggesting that OH may show periods of rapid or no change in future decades that are solely due to the internal climate dynamics (as opposed to external forcings). An empirical orthogonal function analysis further indicates that ENSO is the dominant mode of OH variability, with the modulation of OH occurring primarily through lightningNOx. La Niña is associated with an increase in convection in the Tropical Pacific, which increases the simulated occurrence of lightning and allows for more OH production. Understanding this link between OH and ENSO may improve the predictability of the oxidative capacity of the troposphere and assist in elucidating the causes of current and historical trends in methane.

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The Effect of a Well-Resolved Stratosphere on Surface Climate: Differences between CMIP5 Simulations with High and Low Top Versions of the Met Office Climate Model

Journal of Climate ◽

10.1175/jcli-d-11-00579.1 ◽

2012 ◽

Vol 25 (20) ◽

pp. 7083-7099 ◽

Cited By ~ 44

Author(s):

S. C. Hardiman ◽

N. Butchart ◽

T. J. Hinton ◽

S. M. Osprey ◽

L. J. Gray

Keyword(s):

General Circulation ◽

Climate Model ◽

Southern Oscillation ◽

Coupled Model ◽

Circulation Model ◽

Climate Simulation ◽

Reanalysis Dataset ◽

Quasi Biennial Oscillation ◽

Surface Climate ◽

The Impact

Abstract The importance of using a general circulation model that includes a well-resolved stratosphere for climate simulations, and particularly the influence this has on surface climate, is investigated. High top model simulations are run with the Met Office Unified Model for the Coupled Model Intercomparison Project Phase 5 (CMIP5). These simulations are compared to equivalent simulations run using a low top model differing only in vertical extent and vertical resolution above 15 km. The period 1960–2002 is analyzed and compared to observations and the European Centre for Medium-Range Weather Forecasts (ECMWF) reanalysis dataset. Long-term climatology, variability, and trends in surface temperature and sea ice, along with the variability of the annular mode index, are found to be insensitive to the addition of a well-resolved stratosphere. The inclusion of a well-resolved stratosphere, however, does improve the impact of atmospheric teleconnections on surface climate, in particular the response to El Niño–Southern Oscillation, the quasi-biennial oscillation, and midwinter stratospheric sudden warmings (i.e., zonal mean wind reversals in the middle stratosphere). Thus, including a well-represented stratosphere could improve climate simulation on intraseasonal to interannual time scales.

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Progress towards a probabilistic Earth system model: examining the impact of stochasticity in the atmosphere and land component of EC-Earth v3.2

Geoscientific Model Development ◽

10.5194/gmd-12-3099-2019 ◽

2019 ◽

Vol 12 (7) ◽

pp. 3099-3118 ◽

Cited By ~ 2

Author(s):

Kristian Strommen ◽

Hannah M. Christensen ◽

Dave MacLeod ◽

Stephan Juricke ◽

Tim N. Palmer

Keyword(s):

Climate Model ◽

Weather Forecasting ◽

Southern Oscillation ◽

Earth System Model ◽

System Model ◽

Earth System ◽

Beneficial Impact ◽

The Impact ◽

Mean State

Abstract. We introduce and study the impact of three stochastic schemes in the EC-Earth climate model: two atmospheric schemes and one stochastic land scheme. These form the basis for a probabilistic Earth system model in atmosphere-only mode. Stochastic parametrization have become standard in several operational weather-forecasting models, in particular due to their beneficial impact on model spread. In recent years, stochastic schemes in the atmospheric component of a model have been shown to improve aspects important for the models long-term climate, such as El Niño–Southern Oscillation (ENSO), North Atlantic weather regimes, and the Indian monsoon. Stochasticity in the land component has been shown to improve the variability of soil processes and improve the representation of heatwaves over Europe. However, the raw impact of such schemes on the model mean is less well studied. It is shown that the inclusion of all three schemes notably changes the model mean state. While many of the impacts are beneficial, some are too large in amplitude, leading to significant changes in the model's energy budget and atmospheric circulation. This implies that in order to maintain the benefits of stochastic physics without shifting the mean state too far from observations, a full re-tuning of the model will typically be required.

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Impact of Indo-Pacific Feedback Interactions on ENSO Dynamics Diagnosed Using Ensemble Climate Simulations

Journal of Climate ◽

10.1175/jcli-d-11-00287.1 ◽

2012 ◽

Vol 25 (21) ◽

pp. 7743-7763 ◽

Cited By ~ 49

Author(s):

A. Santoso ◽

M. H. England ◽

W. Cai

Keyword(s):

Indian Ocean ◽

Climate Model ◽

Southern Oscillation ◽

Ocean Basin ◽

Climate Feedback ◽

Enso Events ◽

Thermocline Feedback ◽

Enso Dynamics ◽

The Indian Ocean ◽

The Impact

The impact of Indo-Pacific climate feedback on the dynamics of El Niño–Southern Oscillation (ENSO) is investigated using an ensemble set of Indian Ocean decoupling experiments (DCPL), utilizing a millennial integration of a coupled climate model. It is found that eliminating air–sea interactions over the Indian Ocean results in various degrees of ENSO amplification across DCPL simulations, with a shift in the underlying dynamics toward a more prominent thermocline mode. The DCPL experiments reveal that the net effect of the Indian Ocean in the control runs (CTRL) is a damping of ENSO. The extent of this damping appears to be negatively correlated to the coherence between ENSO and the Indian Ocean dipole (IOD). This type of relationship can arise from the long-lasting ENSO events that the model simulates, such that developing ENSO often coincides with Indian Ocean basin-wide mode (IOBM) anomalies during non-IOD years. As demonstrated via AGCM experiments, the IOBM enhances western Pacific wind anomalies that counteract the ENSO-enhancing winds farther east. In the recharge oscillator framework, this weakens the equatorial Pacific air–sea coupling that governs the ENSO thermocline feedback. Relative to the IOBM, the IOD is more conducive for ENSO growth. The net damping by the Indian Ocean in CTRL is thus dominated by the IOBM effect which is weaker with stronger ENSO–IOD coherence. The stronger ENSO thermocline mode in DCPL is consistent with the absence of any IOBM anomalies. This study supports the notion that the Indian Ocean should be viewed as an integral part of ENSO dynamics.

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Global fire activity patterns (1996–2006) and climatic influence: an analysis using the World Fire Atlas

Atmospheric Chemistry and Physics ◽

10.5194/acp-8-1911-2008 ◽

2008 ◽

Vol 8 (7) ◽

pp. 1911-1924 ◽

Cited By ~ 68

Author(s):

Y. Le Page ◽

J. M. C. Pereira ◽

R. Trigo ◽

C. da Camara ◽

D. Oom ◽

...

Keyword(s):

El Niño ◽

El Nino ◽

Southern Oscillation ◽

Function Analysis ◽

European Space Agency ◽

Global Scale ◽

Fire Dynamics ◽

Fire Activity ◽

Fire Atlas ◽

The Impact

Abstract. Vegetation fires have been acknowledged as an environmental process of global scale, which affects the chemical composition of the troposphere, and has profound ecological and climatic impacts. However, considerable uncertainty remains, especially concerning intra and inter-annual variability of fire incidence. The main goals of our global-scale study were to characterise spatial-temporal patterns of fire activity, to identify broad geographical areas with similar vegetation fire dynamics, and to analyse the relationship between fire activity and the El Niño-Southern Oscillation. This study relies on 10 years (mid 1996–mid 2006) of screened European Space Agency World Fire Atlas (WFA) data, obtained from Along Track Scanning Radiometer (ATSR) and Advanced ATSR (AATSR) imagery. Empirical Orthogonal Function analysis was used to reduce the dimensionality of the dataset. Regions of homogeneous fire dynamics were identified with cluster analysis, and interpreted based on their eco-climatic characteristics. The impact of 1997–1998 El Niño is clearly dominant over the study period, causing increased fire activity in a variety of regions and ecosystems, with variable timing. Overall, this study provides the first global decadal assessment of spatial-temporal fire variability and confirms the usefulness of the screened WFA for global fire ecoclimatology research.

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Indo-Pacific warm pool expansion modulates MJO lifecycle

10.5194/egusphere-egu2020-1039 ◽

2020 ◽

Author(s):

Panini Dasgupta ◽

Roxy Mathew Koll ◽

Michael J. McPhaden ◽

Tamaki Suematsu ◽

Chidong Zhang ◽

...

Keyword(s):

Life Cycle ◽

Indian Ocean ◽

Southern Oscillation ◽

Average Rate ◽

Warm Pool ◽

Dominant Mode ◽

Maritime Continent ◽

Pacific Warm Pool ◽

The Indian Ocean ◽

The Impact

The Madden&#8211;Julian Oscillation (MJO) is the most dominant mode of intraseasonal variability in the tropics, characterized by an eastward propagating zonal circulation pattern and rain bands. MJO is very crucial phenomenon due to its interactions with other timescales of ocean-atmosphere like El Ni&#241;o Southern Oscillation, tropical cyclones, monsoons, and the extreme rainfall events all across the globe. MJO events travel almost half of the globe along the tropical oceans, majorly over the Indo-Pacific Warm Pool (IPWP) region. This IPWP region has been warming during the twentieth and early twenty- first centuries in response to increased anthropogenic emissions of greenhouse gases and is projected to warm further. However, the impact of the warming of the IPWP region on the MJO life cycle is largely unknown. Here we show that rapid warming over the IPWP region during 1981&#8211;2018 has significantly changed the MJO life cycle, with its residence time decreasing over the Indian Ocean by 3&#8211;4 days, and increasing over the Indo-Pacific Maritime Continent by 5&#8211;6 days. We find that these changes in the MJO life cycle are associated with a twofold expansion of the Indo-Pacific warm pool. The warm pool has been expanding on average by 2.3 &#215; 105 km2 per year during 1900&#8211;2018 and at an accelerated average rate of 4 &#215; 105 km2 per year during 1981&#8211;2018. The accelerated warm pool expansion has increased moisture in the lower and middle troposphere over IPWP and thereby increased the gradient of lower-middle tropospheric moisture between the Indian Ocean and western Pacific. This zonal gradient of moisture between the Indian Ocean and west Pacific and the increased subsidence over the Indian ocean due to increased convective duration of MJO over maritime continent are likely the reasons behind the changing lifecycle of MJO.

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Reproducibility of South American Precipitation due to Subtropical South Atlantic SSTs

Journal of Climate ◽

10.1175/2007jcli1865.1 ◽

2008 ◽

Vol 21 (12) ◽

pp. 2835-2851 ◽

Cited By ~ 9

Author(s):

Andréa S. Taschetto ◽

Ilana Wainer

Keyword(s):

General Circulation ◽

Climate Model ◽

Function Analysis ◽

Regional Climate ◽

Circulation Model ◽

Internal Variability ◽

South Atlantic ◽

The South ◽

Potential Predictability ◽

The Impact

Abstract This work investigates the reproducibility of precipitation simulated with an atmospheric general circulation model (AGCM) forced by subtropical South Atlantic sea surface temperature (SST) anomalies. This represents an important test of the model prior to investigating the impact of SSTs on regional climate. A five-member ensemble run was performed using the National Center for Atmospheric Research (NCAR) Community Climate Model, version 3 (CCM3). The CCM3 was forced by observed monthly SST over the South Atlantic from 20° to 60°S. The SST dataset used is from the Hadley Centre covering the period of September 1949–October 2001; this covers more than 50 yr of simulation. A statistical technique is used to determine the reproducibility in the CCM3 runs and to assess potential predictability in precipitation. Empirical orthogonal function analysis is used to reconstruct the ensemble using the most reproducible forced modes in order to separate the atmospheric response to local SST forcing from its internal variability. Results for reproducibility show a seasonal dependence, with higher values during austral autumn and spring. The spatial distribution of reproducibility shows that the tropical atmosphere is dominated by the underlying SSTs while variations in the subtropical–extratropical regions are primarily driven by internal variability. As such, changes in the South Atlantic convergence zone (SACZ) region are mainly dominated by internal atmospheric variability while the ITCZ has greater external dependence, making it more predictable. The reproducibility distribution reveals increased values after the reconstruction of the ensemble.

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The Southern Oscillation Regulates the Annual Numbers of Green Turtles (Chelonia-Mydas) Breeding Around Northern Australia

Wildlife Research ◽

10.1071/wr9880157 ◽

1988 ◽

Vol 15 (2) ◽

pp. 157 ◽

Cited By ~ 54

Author(s):

CJ Limpus ◽

N Nicholls

Keyword(s):

Southern Oscillation ◽

Chelonia Mydas ◽

Northern Australia ◽

Biological Impact ◽

Turtle Species ◽

Green Turtles ◽

Interannual Fluctuations ◽

The Impact ◽

The Relationship ◽

The Tropical Pacific

The green turtle (Chelonia mydas) is one of six turtle species which breeds around northern Australia and Indonesia. The number of green turtles observed nesting varies substantially from year to year. The interannual fluctuations in the number of nesting turtles are in phase at widely separated rookeries. They are also correlated with an index of the Southern Oscillation, a coherent pattern of atmospheric pressure, temperature and rainfall fluctuations which dominates the interannual variability of the climate of the tropical Pacific. Major fluctuations in the numbers of turtles breeding occur two years after major fluctuations in the Southern Oscillation. The relationship is strong enough to be useful in predicting, two years in advance, the numbers of green turtles breeding in Great Barrier Reef rookeries. This is the first study to report a biological impact of the Southern Oscillation that allows such a long-range prediction of the impact.

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Description of the resolution hierarchy of the global coupled HadGEM3-GC3.1 model as used in CMIP6 HighResMIP experiments

Geoscientific Model Development ◽

10.5194/gmd-12-4999-2019 ◽

2019 ◽

Vol 12 (12) ◽

pp. 4999-5028 ◽

Cited By ~ 25

Author(s):

Malcolm J. Roberts ◽

Alex Baker ◽

Ed W. Blockley ◽

Daley Calvert ◽

Andrew Coward ◽

...

Keyword(s):

Experimental Design ◽

Ocean Circulation ◽

Climate Model ◽

Initial Conditions ◽

Southern Oscillation ◽

Global Climate Model ◽

Coupled Model ◽

Climate Simulation ◽

Model Biases ◽

The Impact

Abstract. The Coupled Model Intercomparison Project phase 6 (CMIP6) HighResMIP is a new experimental design for global climate model simulations that aims to assess the impact of model horizontal resolution on climate simulation fidelity. We describe a hierarchy of global coupled model resolutions based on the Hadley Centre Global Environment Model 3 – Global Coupled vn 3.1 (HadGEM3-GC3.1) model that ranges from an atmosphere–ocean resolution of 130 km–1∘ to 25 km–1∕12∘, all using the same forcings and initial conditions. In order to make such high-resolution simulations possible, the experiments have a short 30-year spinup, followed by at least century-long simulations with constant forcing to assess drift. We assess the change in model biases as a function of both atmosphere and ocean resolution, together with the effectiveness and robustness of this new experimental design. We find reductions in the biases in top-of-atmosphere radiation components and cloud forcing. There are significant reductions in some common surface climate model biases as resolution is increased, particularly in the Atlantic for sea surface temperature and precipitation, primarily driven by increased ocean resolution. There is also a reduction in drift from the initial conditions both at the surface and in the deeper ocean at higher resolution. Using an eddy-present and eddy-rich ocean resolution enhances the strength of the North Atlantic ocean circulation (boundary currents, overturning circulation and heat transport), while an eddy-present ocean resolution has a considerably reduced Antarctic Circumpolar Current strength. All models have a reasonable representation of El Niño–Southern Oscillation. In general, the biases present after 30 years of simulations do not change character markedly over longer timescales, justifying the experimental design.

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Regional and Global Impacts of Land Cover Change and Sea Surface Temperature Anomalies

Journal of Climate ◽

10.1175/2008jcli2580.1 ◽

2009 ◽

Vol 22 (12) ◽

pp. 3248-3269 ◽

Cited By ~ 58

Author(s):

Kirsten L. Findell ◽

Andrew J. Pitman ◽

Matthew H. England ◽

Philip J. Pegion

Keyword(s):

Land Cover ◽

Land Cover Change ◽

Land Surface ◽

Climate Model ◽

Southern Oscillation ◽

Regional Scale ◽

Sea Surface ◽

Sst Forcing ◽

The Impact ◽

Sst Anomalies

Abstract The atmospheric and land components of the Geophysical Fluid Dynamics Laboratory’s (GFDL’s) Climate Model version 2.1 (CM2.1) is used with climatological sea surface temperatures (SSTs) to investigate the relative climatic impacts of historical anthropogenic land cover change (LCC) and realistic SST anomalies. The SST forcing anomalies used are analogous to signals induced by El Niño–Southern Oscillation (ENSO), the North Atlantic Oscillation (NAO), and the background global warming trend. Coherent areas of LCC are represented throughout much of central and eastern Europe, northern India, southeastern China, and on either side of the ridge of the Appalachian Mountains in North America. Smaller areas of change are present in various tropical regions. The land cover changes in the model are almost exclusively a conversion of forests to grasslands. Model results show that, at the global scale, the physical impacts of LCC on temperature and rainfall are less important than large-scale SST anomalies, particularly those due to ENSO. However, in the regions where the land surface has been altered, the impact of LCC can be equally or more important than the SST forcing patterns in determining the seasonal cycle of the surface water and energy balance. Thus, this work provides a context for the impacts of LCC on climate: namely, strong regional-scale impacts that can significantly change globally averaged fields but that rarely propagate beyond the disturbed regions. This suggests that proper representation of land cover conditions is essential in the design of climate model experiments, particularly if results are to be used for regional-scale assessments of climate change impacts.

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The role of halogens in the regulation of the oxidative capacity of the Earth’s troposphere in low-polluted environments

10.5194/egusphere-egu2020-15450 ◽

2020 ◽

Author(s):

Cyril Karam ◽

Sophie Szopa

Keyword(s):

Climate Model ◽

Anthropogenic Activities ◽

Self Regulation ◽

Oxidative Capacity ◽

Active Species ◽

Oh Radicals ◽

Transport Models ◽

The Earth ◽

The Impact

The oxidative capacity, usually represented by the concentration of OH radicals in the troposphere, regulates the lifetime of reactive compounds injected into the atmosphere by the biosphere and by anthropogenic activities. Recently, naturally emitted halogenated species (I, Br, Cl) have been showed to play a significant role in the consumption of global tropospheric ozone, a primary precursor of the hydroxyl radical. So far, the state-of-the-art chemistry of iodine, bromine, and chlorine has been implemented in a few global chemistry-transport models (GEOS-CHEM, CAM-Chem, TOMCAT, WRF-Chem). The 3D global chemistry-climate model (LMDz-INCA) has been recently updated to consider the chemistry of halogens. We present here the impact of this chemistry on the global oxidant budgets as well as the lifetime of chemically active species. We discuss how this chemistry affects the self-regulation of radicals in present low-polluted atmospheres as well as pre-industrial and future climate scenarios.

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