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

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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Phase-speed Spectra of Eddy Tracer Fluxes Linked to Isentropic Stirring and Mixing in the Upper Troposphere and Lower Stratosphere

Journal of the Atmospheric Sciences ◽

10.1175/jas-d-16-0167.1 ◽

2016 ◽

Vol 73 (12) ◽

pp. 4711-4730 ◽

Cited By ~ 7

Author(s):

Marta Abalos ◽

William J. Randel ◽

Thomas Birner

Keyword(s):

Rossby Waves ◽

Lower Stratosphere ◽

Southern Oscillation ◽

Phase Speed ◽

Transient Eddy ◽

Tracer Transport ◽

Quasi Biennial Oscillation ◽

Upper Troposphere ◽

Eddy Fluxes ◽

Subtropical Jets

Abstract The regions around the subtropical jets in the upper troposphere and lower stratosphere (UTLS) are characterized by strong isentropic stirring and mixing. In this work, the wave spectrum of the associated eddy tracer fluxes is examined using an artificial passive tracer advected on isentropes by the two-dimensional flow. The eddy diffusivity computed from the flux–gradient relation captures the main features of the mixing structure. Eddy transport in the UTLS is strongest in the summer hemisphere, and weak eddy fluxes are found at the core and poleward of the subtropical jets, especially in the winter hemisphere. There is an important contribution of stationary planetary equatorial Rossby waves in the tropical upper troposphere. The transient eddy tracer transport is primarily linked to medium-scale waves (wavenumbers ~4–7) breaking in the regions of weak westerlies around the subtropical jets and to planetary-scale waves at high latitudes. Phase-speed spectra for transient eddy fluxes show a close relationship of waves to the background zonal wind. In the deep tropics, traveling equatorial and Rossby waves of extratropical origin lead to cross-equatorial tracer transport throughout the upper troposphere. Interannual changes show that eddy tracer fluxes closely follow the shifts in the zonal winds associated with El Niño–Southern Oscillation and the quasi-biennial oscillation.

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

10.5194/acp-2020-881 ◽

2020 ◽

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

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

<p>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.<br>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.</p>

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Validation of COSMIC water vapor data in the upper troposphere and lower stratosphere using MLS, MERRA and ERA-Interim

10.5194/amt-2016-248 ◽

2016 ◽

Cited By ~ 4

Author(s):

Ming Shangguan ◽

Katja Matthes ◽

Wuke Wang ◽

Tae-Kwon Wee

Keyword(s):

Water Vapor ◽

Seasonal Cycle ◽

Lower Stratosphere ◽

Southern Oscillation ◽

Weather Forecast ◽

Cosmic Radio ◽

Quasi Biennial Oscillation ◽

Medium Range Weather Forecast ◽

Upper Troposphere ◽

The Antarctic

Abstract. Water vapor is the most important greenhouse gas in the atmosphere with important implications not only for the Earth’s radiation and energy budget but also for various chemical, physical and dynamical processes in the stratosphere. The Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC) Radio Occultation (RO) dataset from 2007 through 2013 is used for the first time to study the distribution and variability water vapor in the upper troposphere and lower stratosphere (UTLS). The COSMIC data are compared to the Microwave Limb Sounder (MLS) data, and to two global reanalyses: The Modern-Era Retrospective analysis for Research and Application (MERRA) of the National Aeronautics and Space Administration (NASA); and, the latest reanalysis of the European Center for Medium-range Weather Forecast (ECMWF), the ERA-Interim. The MLS data have been assimilated into the MERRA, whereas the COSMIC data are used for the ERA-Interim. As a result, the MERRA agrees well with the MLS data and so does the ERA-Interim with the COSMIC data. While the monthly zonal mean distributions of water vapor from the four datasets show good agreements in northern mid-latitudes, large discrepancies exist in high southern latitudes and tropics. The MERRA shows overall a consistent seasonal cycle with MLS, but has too strong winter dehydration over the Antarctic, and is very weak in the interannual variations. The ERA-Interim fails to properly represent the winter dehydration over the Antarctic, and shows an unrealistic seasonal cycle in the tropical upper troposphere. The COSMIC data shows a good agreement with the MLS data except for the tropical "taper recorder" signal, where the COSMIC data suggest a faster upward motion than the MLS data. The COSMIC data are able to represent the moisture variabilities associated with the Quasi-Biennial Oscillation and the El Niño-Southern Oscillation.

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Variability of temperature and ozone in the upper troposphere and lower stratosphere from multi-satellite observations and reanalysis data

Atmospheric Chemistry and Physics ◽

10.5194/acp-19-6659-2019 ◽

2019 ◽

Vol 19 (10) ◽

pp. 6659-6679 ◽

Cited By ~ 16

Author(s):

Ming Shangguan ◽

Wuke Wang ◽

Shuanggen Jin

Keyword(s):

Lower Stratosphere ◽

Climate Model ◽

Southern Oscillation ◽

Satellite System ◽

Reanalysis Data ◽

Data Sets ◽

Positive Temperature ◽

Quasi Biennial Oscillation ◽

Model Simulations ◽

Upper Troposphere

Abstract. Temperature and ozone changes in the upper troposphere and lower stratosphere (UTLS) are important components of climate change. In this paper, variability and trends of temperature and ozone in the UTLS are investigated for the period 2002–2017 using high-quality, high vertical resolution Global Navigation Satellite System radio occultation (GNSS RO) data and improved merged satellite data sets. As part of the Stratosphere-troposphere Processes And their Role in Climate (SPARC) Reanalysis Intercomparison Project (S-RIP), three reanalysis data sets, including the ERA-I, MERRA2 and the recently released ERA5, are evaluated for their representation of temperature and ozone in the UTLS. The recent temperature and ozone trends are updated with a multiple linear regression (MLR) method and related to sea surface temperature (SST) changes based on model simulations made with NCAR's Whole Atmosphere Community Climate Model (WACCM). All reanalysis temperatures show good agreement with the GNSS RO measurements in both absolute value and annual cycle. Interannual variations in temperature related to Quasi-Biennial Oscillation (QBO) and the El Niño–Southern Oscillation (ENSO) processes are well represented by all reanalyses. However, evident biases can be seen in reanalyses for the linear trends of temperature since they are affected by discontinuities in assimilated observations and methods. Such biases can be corrected and the estimated trends can be significantly improved. ERA5 is significantly improved compared to ERA-I and shows the best agreement with the GNSS RO temperature. The MLR results indicate a significant warming of 0.2–0.3 K per decade in most areas of the troposphere, with a stronger increase of 0.4–0.5 K per decade at midlatitudes of both hemispheres. In contrast, the stratospheric temperature decreases at a rate of 0.1–0.3 K per decade, which is most significant in the Southern Hemisphere (SH). Positive temperature trends of 0.1–0.3 K per decade are seen in the tropical lower stratosphere (100–50 hPa). Negative trends of ozone are found in the Northern Hemisphere (NH) at 150–50 hPa, while positive trends are evident in the tropical lower stratosphere. Asymmetric trends of ozone can be found in the midlatitudes of two hemispheres in the middle stratosphere, with significant ozone decrease in the NH and increase in ozone in the SH. Large biases exist in reanalyses, and it is still challenging to do trend analysis based on reanalysis ozone data. According to single-factor-controlled model simulations with WACCM, the temperature increase in the troposphere and the ozone decrease in the NH stratosphere are mainly connected to the increase in SST and subsequent changes of atmospheric circulations. Both the increase in SSTs and the decrease in ozone in the NH contribute to the temperature decrease in the NH stratosphere. The increase in temperature in the lower stratospheric tropics may be related to an increase in ozone in that region, while warming SSTs contribute to a cooling in that area.

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Variability of Zonal Mean Tropical Temperatures Derived from a Decade of GPS Radio Occultation Data

Journal of the Atmospheric Sciences ◽

10.1175/jas-d-14-0216.1 ◽

2015 ◽

Vol 72 (3) ◽

pp. 1261-1275 ◽

Cited By ~ 28

Author(s):

William J. Randel ◽

Fei Wu

Keyword(s):

Time Scales ◽

Seasonal Cycle ◽

Lower Stratosphere ◽

Southern Oscillation ◽

Low Frequency ◽

Quasi Biennial Oscillation ◽

Radiative Relaxation ◽

Upper Troposphere ◽

Stratospheric Water Vapor ◽

Cold Point

Abstract Variability in tropical zonal mean temperatures over 10–30 km is analyzed based on high-quality, high-vertical-resolution GPS temperature measurements covering 2001–13. The observations are used to quantify variability spanning time scales of weeks to over a decade, with focus on behavior of the tropopause region and coupling with the upper troposphere and stratosphere. Large variations associated with the seasonal cycle, quasi-biennial oscillation (QBO), and El Niño–Southern Oscillation (ENSO) are isolated and removed, and residual time series are analyzed using principal components and spectrum analysis. The residual temperature exhibits maximum variance in the lower stratosphere, with a vertical structure similar to the seasonal cycle. Residual temperatures exhibit two dominant modes of variability: a “deep stratosphere mode” tied to high-latitude planetary wave forcing and a shallow “near-tropopause mode” linked to dynamically forced upwelling near the tropopause. Variations in the cold point tropopause (and by inference in global stratospheric water vapor) are closely tied to the near-tropopause mode. These coherent temperature patterns provide further evidence of distinct upper and lower branches of the tropical Brewer–Dobson circulation. Zonal mean temperatures in the lower stratosphere and near the cold point are most strongly coupled to the upper troposphere on time scales of ~(30–60) days, probably linked to the Madden–Julian oscillation (MJO). Enhanced temperature variance near the tropopause is consistent with the long radiative relaxation time scales in the lower stratosphere, which makes this region especially sensitive to low-frequency dynamical forcing.

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On interpreting studies of tracer transport by deep cumulus convection and its effects on atmospheric chemistry

Atmospheric Chemistry and Physics ◽

10.5194/acp-8-6037-2008 ◽

2008 ◽

Vol 8 (20) ◽

pp. 6037-6050 ◽

Cited By ~ 28

Author(s):

M. G. Lawrence ◽

M. Salzmann

Keyword(s):

Atmospheric Chemistry ◽

Large Scale ◽

Deep Convection ◽

Convective Transport ◽

Advective Transport ◽

Tracer Transport ◽

Transport Models ◽

Mass Fluxes ◽

Split Treatment ◽

The Mean

Abstract. Global chemistry-transport models (CTMs) and chemistry-GCMs (CGCMs) generally simulate vertical tracer transport by deep convection separately from the advective transport by the mean winds, even though a component of the mean transport, for instance in the Hadley and Walker cells, occurs in deep convective updrafts. This split treatment of vertical transport has various implications for CTM simulations. In particular, it has led to a misinterpretation of several sensitivity simulations in previous studies in which the parameterized convective transport of one or more tracers is neglected. We describe this issue in terms of simulated fluxes and fractions of these fluxes representing various physical and non-physical processes. We then show that there is a significant overlap between the convective and large-scale mean advective vertical air mass fluxes in the CTM MATCH, and discuss the implications which this has for interpreting previous and future sensitivity simulations, as well as briefly noting other related implications such as numerical diffusion.

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Structural changes in the shallow and transition branch of the Brewer–Dobson circulation induced by El Niño

10.5194/acp-2018-688 ◽

2018 ◽

Author(s):

Mohamadou Diallo ◽

Paul Konopka ◽

Michelle L. Santee ◽

Rolf Müller ◽

Mengchu Tao ◽

...

Keyword(s):

El Niño ◽

Structural Changes ◽

Lower Stratosphere ◽

Transport Model ◽

El Nino ◽

Southern Oscillation ◽

Satellite Observations ◽

Trace Gas ◽

Residual Circulation ◽

Mixing Ratios

Abstract. The stratospheric Brewer–Dobson circulation (BD-circulation) determines the transport and lifetime of key radiatively active trace gases and further impacts surface climate through downward coupling. Here, we quantify the variability in the lower stratospheric BD-circulation induced by the El Nino Southern Oscillation (ENSO), using satellite trace gas measurements and simulations with the Lagrangian chemistry transport model, CLaMS, driven by ERA-Interim and JRA-55 reanalyses. We show that despite discrepancies in the deseasonalised ozone (O3) mixing ratios between CLaMS simulations and satellite observations, the patterns of changes in the lower stratospheric O3 anomalies induced by ENSO agree remarkably well over the 2005–2016 period. Particularly during the most recent El Niño in 2015–2016, both satellite observations and CLaMS simulations show the largest negative tropical O3 anomaly in the record. Regression analysis of different metrics of the BD-circulation strength, including mean age of air, vertical velocity, residual circulation and age spectrum, shows clear evidence for structural changes of the BD-circulation in the lower stratosphere induced by El Niño, consistent with observed O3 anomalies. These structural changes during El Niño include a weakening of the transition branch of the BD-circulation between about 370–420 K (∼ 100–70 hPa) and equatorward of about 60° and, a strengthening of the shallow branch at the same latitudes and between about 420–500 K (∼ 70–30 hPa). The strengthening of the shallow branch induces negative tropical O3 anomalies due to enhanced tropical upwelling, while the weakening of the transition branch combined with enhanced downwelling due to the strengthening shallow branch leads to positive O3 anomalies in the extratropical upper troposphere-lower stratosphere (UTLS). Our results suggest that a shift of the ENSO basic state toward more frequent El Niño-like conditions in a warming future climate will substantially alter UTLS trace gas distributions due to these changes in the vertical structure of the stratospheric circulation.

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Modeling the transport of very short-lived substances into the tropical upper troposphere and lower stratosphere

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-9-18511-2009 ◽

2009 ◽

Vol 9 (5) ◽

pp. 18511-18543 ◽

Cited By ~ 2

Author(s):

J. Aschmann ◽

B. M. Sinnhuber ◽

E. L. Atlas ◽

S. M. Schauffler

Keyword(s):

Large Scale ◽

Lower Stratosphere ◽

Transport Model ◽

Three Dimensional ◽

Chemical Transport Model ◽

Heating Rates ◽

Model Calculations ◽

Upper Troposphere ◽

Mass Fluxes ◽

Tropical Upper Troposphere

Abstract. The transport of very short-lived substances into the tropical upper troposphere and lower stratosphere is investigated by a three-dimensional chemical transport model using archived convective updraft mass fluxes (or detrainment rates) from the European Centre for Medium-Range Weather Forecast's ERA-Interim reanalysis. Large-scale vertical velocities are calculated from diabatic heating rates. With this approach we explicitly model the large scale subsidence in the tropical troposphere with convection taking place in fast and isolated updraft events. The model calculations agree generally well with observations of bromoform and methyl iodide from aircraft campaigns and with ozone and water vapor from sonde and satellite observations. Using a simplified treatment of dehydration and bromine product gas washout we give a range of 1.6 to 3 ppt for the contribution of bromoform to stratospheric bromine, assuming a uniform source in the boundary layer of 1 ppt. We show that the most effective region for VSLS transport into the stratosphere is the West Pacific, accounting for about 55% of the bromine from bromoform transported into the stratosphere under the supposition of a uniformly distributed source.

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High-resolution large-eddy simulations of sub-kilometer-scale turbulence in the upper troposphere lower stratosphere

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-13-31891-2013 ◽

2013 ◽

Vol 13 (12) ◽

pp. 31891-31932 ◽

Cited By ~ 4

Author(s):

R. Paoli ◽

O. Thouron ◽

J. Escobar ◽

J. Picot ◽

D. Cariolle

Keyword(s):

Large Scale ◽

Lower Stratosphere ◽

Atmospheric Model ◽

Large Eddy Simulations ◽

Stratified Flows ◽

Flow Topology ◽

Upper Troposphere ◽

Large Eddy ◽

Scale Turbulence ◽

The Impact

Abstract. Large-eddy simulations of sub-kilometer-scale turbulence in the upper troposphere lower stratosphere (UTLS) are carried out and analyzed using the mesoscale atmospheric model Méso-NH. Different levels of turbulence are generated using a large-scale stochastic forcing technique that was especially devised to treat atmospheric stratified flows. The study focuses on the analysis of turbulence statistics, including mean quantities and energy spectra, as well as on a detailed description of flow topology. The impact of resolution is also discussed by decreasing the grid spacing to 2 m and increasing the number of grid points to 8×109. Because of atmospheric stratification, turbulence is substantially anisotropic, and large elongated structures form in the horizontal directions, in accordance with theoretical analysis and spectral direct numerical simulations of stably stratified flows. It is also found that the inertial range of horizontal kinetic energy spectrum, generally observed at scales larger than a few kilometers, is prolonged into the sub-kilometric range, down to the Ozmidov scales that obey isotropic Kolmorogov turbulence. The results are in line with observational analysis based on in situ measurements from existing campaigns.

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