The advective Brewer-Dobson circulation in the ERA5 reanalysis: variability and trends

Abstract. The stratospheric Brewer-Dobson circulation (BDC) is an important element of climate as it determines the transport and distributions of key radiatively active atmospheric trace gases, which affect the Earth’s radiation budget and surface climate. Here, we evaluate the inter-annual variability and trends of the BDC in the ERA5 reanalysis and inter-compare with the ERA-Interim reanalysis for the 1979–2018 period. We also assess the modulation of the circulation by the Quasi-Biennial Oscillation (QBO) and the El Niño-Southern Oscillation (ENSO), and the forcings of the circulation by the planetary and gravity wave drag. A comparison of ERA5 and ERA-Interim reanalyses shows a very good agreement in the morphology of the BDC and in its structural modulations by the natural variability related to QBO and ENSO. Despite the good agreement in the spatial structure, there are substantial differences in the strength of the BDC and of the natural variability impacts on the BDC between the two reanalyses, particularly in the upper troposphere and lower stratosphere (UTLS), and in the upper stratosphere. Throughout most regions of the stratosphere, the variability and trends of the advective BDC are stronger in the ERA5 reanalysis due to stronger planetary and gravity wave forcings, except in the UTLS below 20 km where the tropical upwelling is about 40 % weaker due to a weaker gravity wave forcings at the equatorial flank of the subtropical jet. In the extra-tropics, the large-scale downwelling is stronger in ERA5 than in ERA-Interim linked to significant differences in planetary and gravity wave forcings. Analysis of the BDC trend shows a global acceleration of the annual mean residual circulation with an acceleration rate of about 1.5 % per decade at 70 hPa due to the long-term intensification in gravity and planetary wave breaking, consistent with observed and future climate model predicted BDC changes.

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The advective Brewer-Dobson circulation in the ERA5 reanalysis: climatology, variability, and trends

10.5194/egusphere-egu21-11920 ◽

2021 ◽

Author(s):

Mohamadou Diallo ◽

Manfred Ern ◽

Felix Ploeger

Keyword(s):

Gravity Wave ◽

Large Scale ◽

Climate Model ◽

Southern Oscillation ◽

Natural Variability ◽

Radiation Budget ◽

Residual Circulation ◽

Quasi Biennial Oscillation ◽

Acceleration Rate ◽

Good Agreement

The stratospheric Brewer-Dobson circulation (BDC) is an important element of climate as it determines the transport and distributions of key radiatively active atmospheric trace gases, which affect the Earth&#8217;s radiation budget and surface climate. Here, we evaluate the inter-annual variability and trends of the BDC in the ERA5 reanalysis and inter-compare with the ERA-Interim reanalysis for the 1979&#8211;2018 period. We also assess the modulation of the circulation by the Quasi-Biennial Oscillation (QBO) and the El Ni&#241;o-Southern Oscillation (ENSO), and the forcings of the circulation by the planetary and gravity wave drag. A comparison of ERA5 and ERA-Interim reanalyses shows a very good agreement in the morphology of the BDC and in its structural modulations by the natural variability related to QBO and ENSO. Despite the good agreement in the spatial structure, there are substantial differences in the strength of the BDC and of the natural variability impacts on the BDC between the two reanalyses, particularly in the upper troposphere and lower stratosphere (UTLS), and in the upper stratosphere. Throughout most regions of the stratosphere, the variability and trends of the advective BDC are stronger in the ERA5 reanalysis due to stronger planetary and gravity wave forcings, except in the UTLS below 20 km where the tropical upwelling is about 40 % weaker due to a weaker gravity wave forcings at the equatorial flank of the subtropical jet. In the extra-tropics, the large-scale downwelling is stronger in ERA5 than in ERA-Interim linked to significant differences in planetary and gravity wave forcings. Analysis of the BDC trend shows a global acceleration of the annual mean residual circulation with an acceleration rate of about 1.5 % per decade at 70 hPa due to the long-term intensification in gravity and planetary wave breaking, consistent with observed and future climate model predicted BDC changes.

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The advective Brewer–Dobson circulation in the ERA5 reanalysis: climatology, variability, and trends

Atmospheric Chemistry and Physics ◽

10.5194/acp-21-7515-2021 ◽

2021 ◽

Vol 21 (10) ◽

pp. 7515-7544

Author(s):

Mohamadou Diallo ◽

Manfred Ern ◽

Felix Ploeger

Keyword(s):

Gravity Wave ◽

Large Scale ◽

Climate Model ◽

Southern Oscillation ◽

Natural Variability ◽

Radiation Budget ◽

Quasi Biennial Oscillation ◽

Acceleration Rate ◽

The Impact ◽

Good Agreement

Abstract. The stratospheric Brewer–Dobson circulation (BDC) is an important element of climate as it determines the transport and distributions of key radiatively active atmospheric trace gases, which affect the Earth's radiation budget and surface climate. Here, we evaluate the interannual variability, climatology, and trends of the BDC in the ERA5 reanalysis and intercompare them with its predecessor, the ERA-Interim reanalysis, for the 1979–2018 period. We also assess the modulation of the circulation by the Quasi-Biennial Oscillation (QBO) and the El Niño–Southern Oscillation (ENSO), as well as the forcings of the circulation by the planetary and gravity wave drag. The comparison of ERA5 and ERA-Interim reanalyses shows a very good agreement in the morphology of the BDC and in its structural modulations by the natural variability related to QBO and ENSO. Despite the good agreement in the spatial structure, there are substantial and significant differences in the strength of the BDC and natural variability impacts on the BDC between the two reanalyses, particularly in the upper troposphere and lower stratosphere (UTLS) and in the upper stratosphere. Throughout most regions of the stratosphere, the variability and trends of the advective BDC are stronger in the ERA5 reanalysis due to stronger planetary and gravity wave forcings, except in the UTLS below 20 km where the tropical upwelling is up to 40 % weaker mainly due to a significantly weaker gravity wave forcing at the equatorial-ward upper flank of the subtropical jet. In the extratropics, the large-scale downwelling is stronger in ERA5 than in ERA-Interim that is linked to significant differences in planetary and gravity wave forcings in the upper stratosphere. Analysis of the BDC trend shows a global insignificant acceleration of the annual mean residual circulation with an acceleration rate of about 1.5 % decade−1 at 70 hPa due to the long-term intensification in gravity and planetary wave breaking, consistent with observed and modelled BDC changes. Our findings suggest that the advective BDC from the kinematic ERA5 reanalysis is well suited for climate model validation in the UTLS and mid-stratosphere when using the standard formula of zonally averaged zonal momentum equation. The reported differences between the two reanalyses may also affect the nudged climate model simulations. Therefore, additional studies are needed to investigate whether or not nudging climate models toward ERA5 reanalysis will reproduce the upwelling trends from free-running simulations and from ERA5. Finally, further studies are also needed to better understand the impact of the new non-orographic gravity wave parameterization scheme, higher model top, and the representation of the sponge layer in ERA5 on the differences in the upper stratosphere and polar regions.

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Using the Artificial Tracer e90 to Examine Present and Future UTLS Tracer Transport in WACCM

Journal of the Atmospheric Sciences ◽

10.1175/jas-d-17-0135.1 ◽

2017 ◽

Vol 74 (10) ◽

pp. 3383-3403 ◽

Cited By ~ 17

Author(s):

Marta Abalos ◽

William J. Randel ◽

Douglas E. Kinnison ◽

Rolando R. Garcia

Keyword(s):

Large Scale ◽

Lower Stratosphere ◽

Southern Oscillation ◽

Convective Transport ◽

Strong Impact ◽

Tracer Transport ◽

Residual Circulation ◽

Quasi Biennial Oscillation ◽

Upper Troposphere ◽

The Future

Abstract Large-scale tracer transport in the upper troposphere and lower stratosphere (UTLS) is investigated using simulations of the Whole Atmosphere Community Climate Model (WACCM) over the period 1955–2099. The analyses are based on e90, an artificial passive tracer with constant emissions and atmospheric loss rates. The separate contributions of advection by the residual circulation, eddy mixing, and subgrid convection to total transport are explicitly evaluated. The results highlight distinct large-scale transport regimes in the tropics, characterized by efficient vertical tracer transport, and the extratropics, dominated by isentropic mixing. One novel result is the important role of vertical eddy mixing in the tropical upper troposphere. It is shown that interannual variability in e90 is largely driven by El Niño–Southern Oscillation and the quasi-biennial oscillation. The long-term trends emphasize a strong impact of a rising tropopause with climate change on UTLS dynamics and tracer transport. The analyses directly attribute the e90 trends to changes in the different transport components. Stronger residual circulation in the future leads to increased tracer concentrations in the tropical lower stratosphere. Enhanced eddy mixing increases e90 in the extratropical lowermost stratosphere, linked to an upward shift of wave dissipation tied to the tropopause rise. In the troposphere, reduced concentrations in the future are due to weaker convective transport out of the boundary layer and weaker extratropical isentropic eddy mixing.

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Tropical troposphere to stratosphere transport of carbon monoxide and long-lived trace species in the Chemical Lagrangian Model of the Stratosphere (CLaMS)

Geoscientific Model Development Discussions ◽

10.5194/gmdd-7-5087-2014 ◽

2014 ◽

Vol 7 (4) ◽

pp. 5087-5139 ◽

Cited By ~ 6

Author(s):

R. Pommrich ◽

R. Müller ◽

J.-U. Grooß ◽

P. Konopka ◽

F. Ploeger ◽

...

Keyword(s):

Carbon Monoxide ◽

Large Scale ◽

Lower Stratosphere ◽

Lagrangian Model ◽

Quasi Biennial Oscillation ◽

Data Set ◽

Model Version ◽

The Tropics ◽

The Impact ◽

Good Agreement

Abstract. Variations in the mixing ratio of trace gases of tropospheric origin entering the stratosphere in the tropics are of interest for assessing both troposphere to stratosphere transport fluxes in the tropics and the impact of these transport fluxes on the composition of the tropical lower stratosphere. Anomaly patterns of carbon monoxide (CO) and long-lived tracers in the lower tropical stratosphere allow conclusions about the rate and the variability of tropical upwelling to be drawn. Here, we present a simplified chemistry scheme for the Chemical Lagrangian Model of the Stratosphere (CLaMS) for the simulation, at comparatively low numerical cost, of CO, ozone, and long-lived trace substances (CH4, N2O, CCl3F (CFC-11), CCl2F2 (CFC-12), and CO2) in the lower tropical stratosphere. For the long-lived trace substances, the boundary conditions at the surface are prescribed based on ground-based measurements in the lowest model level. The boundary condition for CO in the free troposphere is deduced from MOPITT measurements (at &approx; 700–200 hPa). Due to the lack of a specific representation of mixing and convective uplift in the troposphere in this model version, enhanced CO values, in particular those resulting from convective outflow are underestimated. However, in the tropical tropopause layer and the lower tropical stratosphere, there is relatively good agreement of simulated CO with in-situ measurements (with the exception of the TROCCINOX campaign, where CO in the simulation is biased low &approx; 10–20 ppbv). Further, the model results are of sufficient quality to describe large scale anomaly patterns of CO in the lower stratosphere. In particular, the zonally averaged tropical CO anomaly patterns (the so called "tape recorder" patterns) simulated by this model version of CLaMS are in good agreement with observations. The simulations show a too rapid upwelling compared to observations as a consequence of the overestimated vertical velocities in the ERA-interim reanalysis data set. Moreover, the simulated tropical anomaly patterns of N2O are in good agreement with observations. In the simulations, anomaly patterns for CH4 and CFC-11 were found to be consistent with those of N2O; for all long-lived tracers, positive anomalies are simulated because of the enhanced tropical upwelling in the easterly phase of the quasi-biennial oscillation.

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In-cloud scavenging scheme for sectional aerosol modules – implementation in the framework of the Sectional Aerosol module for Large Scale Applications version 2.0 (SALSA2.0) global aerosol module

10.5194/egusphere-egu21-15018 ◽

2021 ◽

Author(s):

Eemeli Holopainen ◽

Harri Kokkola ◽

Anton Laakso ◽

Thomas Kühn

Keyword(s):

Wet Deposition ◽

Large Scale ◽

Climate Model ◽

Radiation Budget ◽

Cloud Formation ◽

The Arctic ◽

Vertical Profiles ◽

Size Classes ◽

Aerosol Emission ◽

Aerosol Module

Black carbon (BC) affects the radiation budget of the Earth by absorbing solar radiation, darkening snow and ice covers, and influencing cloud formation and life cycle. Modelling BC in remote regions, such as the Arctic, has large inter-model variability which causes variation in the modelled aerosol effect over the Arctic. This variability can be due to differences in the transport of aerosol species which is affected by how wet deposition is modelled. In this study we developed an aerosol size-resolved in-cloud wet deposition scheme for liquid and ice clouds for models which use a size-segregated aerosol description. This scheme was tested in the ECHAM-HAMMOZ global aerosol-climate model. The scheme was compared to the original wet deposition scheme which uses fixed scavenging coefficients for different sized particles. The comparison included vertical profiles and mass and number wet deposition fluxes, and it showed that the current scheme produced spuriously long BC lifetimes when compared to the estimates made in other studies. Thus, to find a better setup for simulating aerosol lifetimes and vertical profiles we conducted simulations where we altered the aerosol emission distribution and hygroscopicity. We compared the modelled BC vertical profiles to the ATom aircraft campaign measurements. In addition, we compared the aerosol lifetimes against those from AEROCOM model means. We found that, without further tuning, the current scheme overestimates the BC concentrations and lifetimes more than the fixed scavenging scheme when compared to the measurements. Sensitivity studies showed that the model skill of reproducing the measured vertical BC mass concentrations improved when BC emissions were directed to larger size classes, they were mixed with soluble compounds during emission, or BC-containing particles were transferred to soluble size classes after aging. These changes also produced atmospheric BC lifetimes which were closer to AEROCOM model means. The best comparison with the measured vertical profiles and estimated BC lifetimes was when BC was mixed with soluble aerosol compounds during emission.

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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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Global climate simulations at 2.8 km on GPU with the ICON model

10.5194/egusphere-egu2020-10306 ◽

2020 ◽

Author(s):

Xavier Lapillonne ◽

William Sawyer ◽

Philippe Marti ◽

Valentin Clement ◽

Remo Dietlicher ◽

...

Keyword(s):

High Resolution ◽

Large Scale ◽

Climate Model ◽

Global Climate ◽

Weather Prediction ◽

Time Integration ◽

Horizontal Resolution ◽

Performance Comparison ◽

Quasi Biennial Oscillation ◽

Numerical Weather

The ICON modelling framework is a unified numerical weather and climate model used for applications ranging from operational numerical weather prediction to low and high resolution climate projection. In view of further pushing the frontier of possible applications and to make use of the latest evolution in hardware technologies, parts of the model were recently adapted to run on heterogeneous GPU system. This initial GPU port focus on components required for high-resolution climate application, and allow considering multi-years simulations at 2.8 km on the Piz Daint heterogeneous supercomputer. These simulations are planned as part of the QUIBICC project &#8220;The Quasi-Biennial Oscillation (QBO) in a changing climate&#8221;, which propose to investigate effects of climate change on the dynamics of the QBO.Because of the low compute intensity of atmospheric model the cost of data transfer between CPU and GPU at every step of the time integration would be prohibitive if only some components would be ported to the accelerator. We therefore present a full port strategy where all components required for the simulations are running on the GPU. For the dynamics, most of the physical parameterizations and infrastructure code the OpenACC compiler directives are used. For the soil parameterization, a Fortran based domain specific language (DSL) the CLAW-DSL has been considered. We discuss the challenges associated to port a large community code, about 1 million lines of code, as well as to run simulations on large-scale system at 2.8 km horizontal resolution in terms of run time and I/O constraints. We show performance comparison of the full model on CPU and GPU, achieving a speed up factor of approximately 5x, as well as scaling results on up to 2000 GPU nodes. Finally we discuss challenges and planned development regarding performance portability and high level DSL which will be used with the ICON model in the near future.

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Potential state shifts in terrestrial ecosystems related to changes in El Niño-Southern Oscillation dynamics

10.5194/egusphere-egu2020-12346 ◽

2020 ◽

Author(s):

Mateo Duque-Villegas ◽

Juan Fernando Salazar ◽

Angela Maria Rendón

Keyword(s):

Large Scale ◽

Climate Model ◽

Extreme Values ◽

Southern Oscillation ◽

Climatic Variability ◽

Terrestrial Ecosystems ◽

Eastern Africa ◽

State Transitions ◽

Climate Change Scenarios ◽

Earth’S Climate

The El Ni&#241;o-Southern Oscillation (ENSO) phenomenon is regarded as a policy-relevant tipping element of the Earth's climate system. It has a prominent planetary-scale influence on climatic variability and it is susceptible to anthropogenic forcing, which could alter irreversibly its dynamics. Changes in frequency and/or amplitude of ENSO would have major implications for terrestrial hydrology and ecosystems. The amount of extreme events such as droughts and floods could vary regionally, as well as their intensities. Here, we use an intermediate complexity climate model, namely the Planet Simulator (PlaSim), to study the potential impact on Earth's climate and its terrestrial ecosystems of changing ENSO dynamics in a couple of experiments. Initially we investigate the global effects of a permanent El Ni&#241;o, and then we analyse changes in the amplitude of the fluctuation. We found that PlaSim model yields a sensible representation of current large-scale climatological patterns, including ENSO-related variability, as well as realistic estimates of global energy and water budgets. For the permanent El Ni&#241;o state, there were significant differences in the global distribution of water and energy fluxes that led to asymmetrical effects on vegetation production, which increased in the tropics and decreased in temperate regions. In terrestrial ecosystems of regions such as western North America, the Amazon rainforest, south-eastern Africa and Australia, we found that these El Ni&#241;o-induced changes could be associated with biome state transitions. Particularly for Australia, we found country-wide aridification as a result of sustained El Ni&#241;o conditions, which is a potential state in which recent wildfires would be even more dramatic. When the amplitude of the ENSO fluctuation changes, we found that although mean climatological values do not change significantly, extreme values of variables such as temperature and precipitation become more extreme. Our approach aims at recognizing potential threats for terrestrial ecosystems in climate change scenarios in which there are more frequent El Ni&#241;o phenomena or the intensities of the ENSO phases change. Although it is not enough to prove such effects will be observed, we show a consistent picture and it should raise awareness about conservation of global ecosystems.

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Large-Scale Atmospheric Drivers of Snowfall on Thwaites Glacier

10.5194/egusphere-egu2020-12441 ◽

2020 ◽

Author(s):

Michelle Maclennan ◽

Jan Lenaerts

Keyword(s):

Temporal Variability ◽

Large Scale ◽

Climate Model ◽

Southern Oscillation ◽

Regional Climate ◽

Southern Annular Mode ◽

Spatial And Temporal Variability ◽

Atmospheric Conditions ◽

Amundsen Sea ◽

Weather Patterns

High snowfall events on Thwaites Glacier are a key influencer of its ice mass change. In this study, we diagnose the mechanisms for orographic precipitation on Thwaites Glacier by analyzing the atmospheric conditions that lead to high snowfall events. A high-resolution regional climate model, RACMO2, is used in conjunction with MERRA-2 and ERA5 reanalysis to map snowfall and associated atmospheric conditions over the Amundsen Sea Embayment. We examine these conditions during high snowfall events over Thwaites Glacier to characterize the drivers of the precipitation and their spatial and temporal variability. Then we examine the seasonal differences in the associated weather patterns and their correlations with El Nino Southern Oscillation and the Southern Annular Mode. Understanding the large-scale atmospheric drivers of snowfall events allows us to recognize how these atmospheric drivers and consequent snowfall climatology will change in the future, which will ultimately improve predictions of accumulation on Thwaites Glacier.

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A multi-year short-range hindcast experiment with CESM1 for evaluating climate model moist processes from diurnal to interannual timescales

Geoscientific Model Development ◽

10.5194/gmd-14-73-2021 ◽

2021 ◽

Vol 14 (1) ◽

pp. 73-90

Author(s):

Hsi-Yen Ma ◽

Chen Zhou ◽

Yunyan Zhang ◽

Stephen A. Klein ◽

Mark D. Zelinka ◽

...

Keyword(s):

Short Range ◽

Large Scale ◽

Climate Models ◽

Climate Model ◽

Southern Oscillation ◽

Heat Fluxes ◽

Model Errors ◽

Moist Processes ◽

The Mean ◽

Mean State

Abstract. We present a multi-year short-range hindcast experiment and its experimental design for better evaluation of both the mean state and variability of atmospheric moist processes in climate models from diurnal to interannual timescales and facilitate model development. We used the Community Earth System Model version 1 as the base model and performed a suite of 3 d hindcasts initialized every day starting at 00:00 Z from 1997 to 2012. Three processes – the diurnal cycle of clouds during different cloud regimes over the central US, precipitation and diabatic heating associated with the Madden–Julian Oscillation (MJO), and the response of precipitation, surface radiative and heat fluxes, as well as zonal wind stress to sea surface temperature anomalies associated with the El Niño–Southern Oscillation – are evaluated as examples to demonstrate how one can better utilize simulations from this experiment to gain insights into model errors and their connection to physical parameterizations or large-scale state. This is achieved by comparing the hindcasts with corresponding long-term observations for periods based on different phenomena. These analyses can only be done through this multi-year hindcast approach to establish robust statistics of the processes under well-controlled large-scale environment because these phenomena are either a result of interannual climate variability or only happen a few times in a given year (e.g., MJO, or cloud regime types). Furthermore, comparison of hindcasts to the typical simulations in climate mode with the same model allows one to infer what portion of a model's climate error directly comes from fast errors in the parameterizations of moist processes. As demonstrated here, model biases in the mean state and variability associated with parameterized moist processes usually develop within a few days and manifest within weeks to affect the simulations of large-scale circulation and ultimately the climate mean state and variability. Therefore, model developers can achieve additional useful understanding of the underlying problems in model physics by conducting a multi-year hindcast experiment.

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