A Large Annual Cycle in Ozone above the Tropical Tropopause Linked to the Brewer–Dobson Circulation

2007 ◽  
Vol 64 (12) ◽  
pp. 4479-4488 ◽  
Author(s):  
William J. Randel ◽  
Mijeong Park ◽  
Fei Wu ◽  
Nathaniel Livesey
Keyword(s):  
Annual Cycle ◽  
Seasonal Cycle ◽  
Annual Variation ◽  
Lower Stratosphere ◽  
Vertical Gradient ◽  
Relative Amplitude ◽  
Vertical Layer ◽  
Satellite Measurements ◽  
Tropical Tropopause ◽  
Vertical Gradients

Abstract Near-equatorial ozone observations from balloon and satellite measurements reveal a large annual cycle in ozone above the tropical tropopause. The relative amplitude of the annual cycle is large in a narrow vertical layer between ∼16 and 19 km, with approximately a factor of 2 change in ozone between the minimum (during NH winter) and maximum (during NH summer). The annual cycle in ozone occurs over the same altitude region, and is approximately in phase with the well-known annual variation in tropical temperature. This study shows that the large annual variation in ozone occurs primarily because of variations in vertical transport associated with mean upwelling in the lower stratosphere (the Brewer–Dobson circulation); the maximum relative amplitude peak in the lower stratosphere is collocated with the strongest background vertical gradients in ozone. A similar large seasonal cycle is observed in carbon monoxide (CO) above the tropical tropopause, which is approximately out of phase with ozone (associated with an oppositely signed vertical gradient). The observed ozone and CO variations can be used to constrain estimates of the seasonal cycle in tropical upwelling.

scholarly journals Variability in upwelling across the tropical tropopause and correlations with tracers in the lower stratosphere

2012 ◽  
Vol 12 (23) ◽  
pp. 11505-11517 ◽  
Author(s):  
M. Abalos ◽  
W. J. Randel ◽  
E. Serrano
Keyword(s):  
Time Series ◽  
Temporal Variability ◽  
Seasonal Cycle ◽  
Strong Influence ◽  
Lower Stratosphere ◽  
Momentum Balance ◽  
Annual Cycles ◽  
Tropical Tropopause ◽  
Vertical Gradients ◽  
Good Agreement

Abstract. Temporal variability of the upwelling near the tropical tropopause on daily to annual timescales is investigated using three different estimates computed from the ERA-Interim reanalysis. These include upwelling archived by the reanalysis, plus estimates derived from thermodynamic and momentum balance calculations. Substantial variability in upwelling is observed on both seasonal and sub-seasonal timescales, and the three estimates show reasonably good agreement. Tropical upwelling should exert strong influence on temperatures and on tracers with large vertical gradients in the lower stratosphere. We test this behavior by comparing the calculated upwelling estimates with observed temperatures in the tropical lower stratosphere, and with measurements of ozone and carbon monoxide (CO) from the Aura Microwave Limb Sounder (MLS) satellite instrument. Time series of temperature, ozone and CO are well correlated in the tropical lower stratosphere, and we quantify the influence of tropical upwelling on this joint variability. Strong coherent annual cycles observed in each quantity are found to reflect the seasonal cycle in upwelling. Statistically significant correlations between upwelling, temperatures and tracers are also found for sub-seasonal timescales, demonstrating the importance of upwelling in forcing transient variability in the lower tropical stratosphere.

scholarly journals Variability in upwelling across the tropical tropopause and correlations with tracers in the lower stratosphere

2012 ◽  
Vol 12 (7) ◽  
pp. 18817-18851 ◽  
Author(s):  
M. Abalos ◽  
W. J. Randel ◽  
E. Serrano
Keyword(s):  
Time Series ◽  
Temporal Variability ◽  
Seasonal Cycle ◽  
Strong Influence ◽  
Lower Stratosphere ◽  
Momentum Balance ◽  
Annual Cycles ◽  
Tropical Tropopause ◽  
Vertical Gradients ◽  
Good Agreement

Abstract. Temporal variability of the upwelling near the tropical tropopause on daily to annual timescales is investigated using three different estimates computed from the ERA-Interim reanalysis. These include upwelling archived by the reanalysis, plus estimates derived from thermodynamic and momentum balance calculations. Substantial variability in upwelling is observed on both seasonal and sub-seasonal time scales, and the three estimates show reasonably good agreement. Tropical upwelling should exert strong influence on temperatures and on tracers with large vertical gradients in the lower stratosphere. We test this behavior by comparing the calculated upwelling estimates with observed temperatures in the tropical lower stratosphere, and with measurements of ozone and carbon monoxide (CO) from the Aura Microwave Limb Sounder (MLS) satellite instrument. Time series of temperature, ozone and CO are well correlated in the tropical lower stratosphere, and we quantify the influence of tropical upwelling on this joint variability. Strong coherent annual cycles observed in each quantity are found to reflect the seasonal cycle in upwelling. Statistically significant correlations between upwelling, temperatures and tracers are also found for sub-seasonal timescales, demonstrating the importance of upwelling in forcing transient variability in the lower tropical stratosphere.

scholarly journals Tropical Wave Driving of the Annual Cycle in Tropical Tropopause Temperatures. Part II: Model Results

2006 ◽  
Vol 63 (5) ◽  
pp. 1420-1431 ◽  
Author(s):  
W. A. Norton
Keyword(s):  
Annual Cycle ◽  
Rossby Waves ◽  
Lower Stratosphere ◽  
Equation Model ◽  
Stationary Waves ◽  
Mean Flow ◽  
Flux Divergence ◽  
Tropical Tropopause ◽  
Equatorial Rossby Waves ◽  
Tropical Heating

Abstract The atmospheric response to a localized distribution of tropical heating is examined in terms of the stationary waves excited and how these impact the mean flow near the tropical tropopause. This is done by examining nonlinear simulations of the Gill model with a primitive equation model that extends from the surface up into the stratosphere. The model produces strong cooling of zonal mean temperatures near the tropical tropopause when the heating is on the equator but weaker cooling with the heating at 15°N. The model shows that equatorial Rossby waves that penetrate the lower stratosphere and changes in EP flux divergence that correspond to the observed changes between December and August. It is suggested that ascent in the upper tropical troposphere is driven by vorticity advection or equivalently potential vorticity fluxes due to these equatorial Rossby waves, particularly when the heating is close to the equator. The model results provide support to the hypothesis that the annual cycle in tropical tropopause temperatures is a result of the annual variation in latitude of tropical heating and that equatorial Rossby waves are key in producing the response in the upper troposphere and lower stratosphere.

scholarly journals A reassessment of the discrepancies in the annual variation of <i>δ</i>D-H<sub>2</sub>O in the tropical lower stratosphere between the MIPAS and ACE-FTS satellite data sets

2020 ◽  
Vol 13 (1) ◽  
pp. 287-308
Author(s):  
Stefan Lossow ◽  
Charlotta Högberg ◽  
Farahnaz Khosrawi ◽  
Gabriele P. Stiller ◽  
Ralf Bauer ◽  
...  
Keyword(s):  
Atmospheric Chemistry ◽  
Annual Variation ◽  
Lower Stratosphere ◽  
Michelson Interferometer ◽  
Tape Recorder ◽  
Data Sets ◽  
Altitude Effect ◽  
Data Set ◽  
Tropical Tropopause ◽  
Tropopause Region

Abstract. The annual variation of δD in the tropical lower stratosphere is a critical indicator for the relative importance of different processes contributing to the transport of water vapour through the cold tropical tropopause region into the stratosphere. Distinct observational discrepancies of the δD annual variation were visible in the works of Steinwagner et al. (2010) and Randel et al. (2012). Steinwagner et al. (2010) analysed MIPAS (Michelson Interferometer for Passive Atmospheric Sounding) observations retrieved with the IMK/IAA (Institut für Meteorologie und Klimaforschung in Karlsruhe, Germany, in collaboration with the Instituto de Astrofísica de Andalucía in Granada, Spain) processor, while Randel et al. (2012) focused on ACE-FTS (Atmospheric Chemistry Experiment Fourier Transform Spectrometer) observations. Here we reassess the discrepancies based on newer MIPAS (IMK/IAA) and ACE-FTS data sets, also showing for completeness results from SMR (Sub-Millimetre Radiometer) observations and a ECHAM/MESSy (European Centre for Medium-Range Weather Forecasts Hamburg and Modular Earth Submodel System) Atmospheric Chemistry (EMAC) simulation (Eichinger et al., 2015b). Similar to the old analyses, the MIPAS data set yields a pronounced annual variation (maximum about 75 ‰), while that derived from the ACE-FTS data set is rather weak (maximum about 25 ‰). While all data sets exhibit the phase progression typical for the tape recorder, the annual maximum in the ACE-FTS data set precedes that in the MIPAS data set by 2 to 3 months. We critically consider several possible reasons for the observed discrepancies, focusing primarily on the MIPAS data set. We show that the δD annual variation in the MIPAS data up to an altitude of 40 hPa is substantially impacted by a “start altitude effect”, i.e. dependency between the lowermost altitude where MIPAS retrievals are possible and retrieved data at higher altitudes. In itself this effect does not explain the differences with the ACE-FTS data. In addition, there is a mismatch in the vertical resolution of the MIPAS HDO and H2O data (being consistently better for HDO), which actually results in an artificial tape-recorder-like signal in δD. Considering these MIPAS characteristics largely removes any discrepancies between the MIPAS and ACE-FTS data sets and shows that the MIPAS data are consistent with a δD tape recorder signal with an amplitude of about 25 ‰ in the lowermost stratosphere.

scholarly journals Spectrum of Wave Forcing Associated with the Annual Cycle of Upwelling at the Tropical Tropopause

2016 ◽  
Vol 73 (2) ◽  
pp. 855-868 ◽  
Author(s):  
Joowan Kim ◽  
William J. Randel ◽  
Thomas Birner ◽  
Marta Abalos
Keyword(s):  
Annual Cycle ◽  
Lower Stratosphere ◽  
Mass Conservation ◽  
Upper Troposphere ◽  
Wave Forcing ◽  
Planetary Scale ◽  
Tropical Tropopause ◽  
Zonal Wavenumber ◽  
Wavenumber Spectrum ◽  
Transformed Eulerian Mean

Abstract The zonal wavenumber spectrum of atmospheric wave forcing in the lower stratosphere is examined to understand the annual cycle of upwelling at the tropical tropopause. Tropopause upwelling is derived based on the wave forcing computed from ERA-Interim using the momentum and mass conservation equations in the transformed Eulerian-mean framework. The calculated upwelling agrees well with other upwelling estimates and successfully captures the annual cycle, with a maximum during Northern Hemisphere (NH) winter. The spectrum of wave forcing reveals that the zonal wavenumber-3 component drives a large portion of the annual cycle in upwelling. The wave activity flux (Eliassen–Palm flux) shows that the associated waves originate from the NH extratropics and the Southern Hemisphere tropics during December–February, with both regions contributing significant wavenumber-3 fluxes. These wave fluxes are nearly absent during June–August. Wavenumbers 1 and 2 and synoptic-scale waves have a notable contribution to tropopause upwelling but have little influence on the annual cycle, except the wavenumber-4 component. The quasigeostrophic refractive index suggests that the NH extratropical wavenumber-3 component can enhance tropopause upwelling because these planetary-scale waves are largely trapped in the vertical, while being refracted toward the subtropical upper troposphere and lower stratosphere. Regression analysis based on interannual variability suggests that the wavenumber-3 waves are related to tropical convection and wave breaking along the subtropical jet in the NH extratropics.

scholarly journals Transport analysis and source attribution of seasonal and interannual variability of CO in the tropical upper troposphere and lower stratosphere

2013 ◽  
Vol 13 (1) ◽  
pp. 129-146 ◽  
Author(s):  
J. Liu ◽  
J. A. Logan ◽  
L. T. Murray ◽  
H. C. Pumphrey ◽  
M. J. Schwartz ◽  
...  
Keyword(s):  
Annual Cycle ◽  
Annual Variation ◽  
Lower Stratosphere ◽  
Transport Model ◽  
Boreal Summer ◽  
Lower Altitude ◽  
Model Simulations ◽  
Upper Troposphere ◽  
Annual Variations ◽  
Upward Transport

Abstract. We used the GEOS-Chem chemistry-transport model to investigate impacts of surface emissions and dynamical processes on the spatial and temporal patterns of CO observed by the Microwave Limb Sounder (MLS) in the upper troposphere (UT) and lower stratosphere (LS). Model simulations driven by GEOS-4 and GEOS-5 assimilated fields present many features of the seasonal and inter-annual variation of CO in the upper troposphere and lower stratosphere. Both model simulations and the MLS data show a transition from semi-annual variations in the UT to annual variations in the LS. Tagged CO simulations indicate that the semi-annual variation of CO in the UT is determined mainly by the temporal overlapping of surface biomass burning from different continents as well as the north-south shifts of deep convection. Both GEOS-4 and GEOS-5 have maximum upward transport in April and May with a minimum in July to September. The CO peaks from the Northern Hemisphere (NH) fires propagate faster to the LS than do those from the Southern Hemisphere (SH) fires. Thus the transition from a semi-annual to an annual cycle around 80 hPa is induced by a combination of the CO signal at the tropopause and the annual cycle of the Brewer-Dobson circulation. In GEOS-5, the shift to an annual cycle occurs at a lower altitude than in MLS CO, a result of inadequate upward transport. We deduce vertical velocities from MLS CO, and use them to evaluate the velocities derived from the archived GEOS meteorological fields. We find that GEOS-4 velocities are similar to those from MLS CO between 215 hPa and 125 hPa, while the velocities in GEOS-5 are too low in spring and summer. The mean tropical vertical velocities from both models are lower than those inferred from MLS CO above 100 hPa, particularly in GEOS-5, with mean downward, rather than upward motion in boreal summer. Thus the models' CO maxima from SH burning are transported less effectively than those in MLS CO above 147 hPa and almost disappear by 100 hPa. The strongest peaks in the CO tape-recorder are in late 2004, 2006, and 2010, with the first two resulting from major fires in Indonesia and the last from severe burning in South America, all associated with intense droughts.

scholarly journals A reassessment of the discrepancies in the annual variation of δD-H<sub>2</sub>O in the tropical lower stratosphere between the MIPAS and ACE-FTS satellite data sets

2019 ◽  
Author(s):  
Stefan Lossow ◽  
Charlotta Högberg ◽  
Farahnaz Khosrawi ◽  
Gabriele P. Stiller ◽  
Ralf Bauer ◽  
...  
Keyword(s):  
Atmospheric Chemistry ◽  
Annual Variation ◽  
Lower Stratosphere ◽  
Michelson Interferometer ◽  
Tape Recorder ◽  
Data Sets ◽  
Altitude Effect ◽  
Data Set ◽  
Tropical Tropopause ◽  
Spectrometer Data

Abstract. The annual variation of δD in the tropical lower stratosphere is a critical indicator for the relative importance of different processes contributing to the transport of water vapour through the cold tropical tropopause region into the stratosphere. Distinct observational discrepancies of the δD annual variation were visible in the works of Steinwagner et al. (2010) and Randel et al. (2012), focusing on MIPAS (Michelson Interferometer for Passive Atmospheric Sounding) and ACE-FTS (Atmospheric Chemistry Experiment-Fourier Transform Spectrometer) data, respectively. Here we reassess the discrepancies based on newer MIPAS and ACE-FTS data sets, showing for completeness also results from SMR (Sub-Millimetre Radiometer) observations and a ECHAM/MESSy (European Centre for Medium-Range Weather Forecasts Hamburg/Modular Earth Submodel System) Atmospheric Chemistry (EMAC) simulation (Eichinger et al., 2015b). Similar to the old analyses, the MIPAS data sets yield a pronounced annual variation (maximum about 75 ‰) while that derived from the ACE-FTS data sets is rather weak (maximum about 25 ‰). While all data sets exhibit the phase progression typical for the tape recorder the annual maximum in the ACE-FTS data set precedes that in the MIPAS data set by 2 to 3 months. We critically consider several possible reasons for the observed discrepancies, focusing primarily on the MIPAS data set. We show that the δD annual variation in the MIPAS data is up to an altitude of 40 hPa substantially impacted by a start altitude effect, i.e. dependency between the lowermost altitude where MIPAS retrievals are possible and retrieved data at higher altitudes. In addition, there is a mismatch in the vertical resolution of the MIPAS HDO and H2O data (being consistently better for HDO), which actually results in an artificial tape recorder-like signal in δD. Considering these MIPAS characteristics largely removes any discrepancies between the MIPAS and ACE-FTS data sets and confirms a δD tape recorder signal with an amplitude of about 25 ‰ in the lowermost stratosphere.

scholarly journals Transport analysis and source attribution of seasonal and interannual variability of CO in the tropical upper troposphere and lower stratosphere

2012 ◽  
Vol 12 (7) ◽  
pp. 17397-17442 ◽  
Author(s):  
Junhua Liu ◽  
J. A. Logan ◽  
L. T. Murray ◽  
H. C. Pumphrey ◽  
M. J. Schwartz ◽  
...  
Keyword(s):  
Annual Cycle ◽  
Annual Variation ◽  
Lower Stratosphere ◽  
Transport Model ◽  
Boreal Summer ◽  
Lower Altitude ◽  
Model Simulations ◽  
Upper Troposphere ◽  
Annual Variations ◽  
Upward Transport

Abstract. We used the GEOS-Chem chemistry-transport model to investigate impacts of surface emissions and dynamical processes on the spatial and temporal patterns of CO observed by the Microwave Limb Sounder (MLS) in the upper troposphere and lower stratosphere (UTLS). Model simulations driven by GEOS-4 and GEOS-5 assimilated fields present many features of the seasonal and inter-annual variation of CO in the UTLS. Both model simulations and the MLS data show a transition from semi-annual variations in the UT to annual variations in the LS. Tagged CO simulations indicate that the semi-annual variation of CO in the UT is determined mainly by the temporal overlapping of surface biomass burning from different continents as well as the north-south shifts of deep convection. Both GEOS-4 and GEOS-5 have maximum upward transport in April and May with a minimum in July to September. The CO peaks from NH fires propagate faster to the LS than do those from SH fires. Thus the transition from a semi-annual to an annual cycle around 80 hPa is induced by a combination of the CO signal at the tropopause and the annual cycle of the Brewer-Dobson circulation. In GEOS-5, the shift to an annual cycle occurs at a lower altitude than in MLS CO, a result of inadequate upward transport. We deduce vertical velocities from MLS CO, and find that those in GEOS-4 agree well with them between 215 hPa and 125 hPa in boreal summer, fall and winter, while the velocities in GEOS-5 are too low in all seasons. The mean tropical vertical velocities from both models are lower than those inferred from MLS CO above 100 hPa in June to November, particularly in GEOS-5, with mean downward, rather than upward motion in boreal summer. Thus the models' CO maxima from SH burning are transported less effectively than those in MLS CO above 147 hPa and almost disappear by 100 hPa. The strongest peaks in the CO tape-recorder are in late 2004, 2006, and 2010, with the first two resulting from major fires in Indonesia and the last from severe burning in South America, all associated with intense droughts.

Dynamical Balances and Tropical Stratospheric Upwelling

2008 ◽  
Vol 65 (11) ◽  
pp. 3584-3595 ◽  
Author(s):  
William J. Randel ◽  
Rolando Garcia ◽  
Fei Wu
Keyword(s):  
Seasonal Cycle ◽  
Significant Contribution ◽  
Lower Stratosphere ◽  
Reanalysis Data ◽  
Planetary Waves ◽  
Momentum Balance ◽  
Flux Divergence ◽  
Large Component ◽  
Tropical Tropopause ◽  
The Tropics

Abstract The dynamical balances associated with upwelling in the tropical lower stratosphere are investigated based on climatological 40-yr ECMWF Re-Analysis (ERA-40) and NCEP–NCAR reanalysis data. Zonal mean upwelling is calculated from momentum balance and continuity (“downward control”), and these estimates in the deep tropics are found to be in reasonable agreement with stratospheric upwelling calculated from thermodynamic balance (and also with vertical velocity obtained from ERA-40). The detailed momentum balances associated with the dynamical upwelling are investigated, particularly the contributions to climatological Eliassen–Palm (EP) flux divergence in the subtropics. Results show that the equatorward extension of extratropical waves (baroclinic eddies and, in the NH, quasi-stationary planetary waves) contribute a large component of the subtropical wave driving at 100 hPa. Additionally, there is a significant contribution to subtropical forcing from equatorial planetary waves, which exhibit a strong seasonal cycle (a reversal in phase) in response to latitudinal migration of tropical convection. The observed balances suggest that the strong annual cycle in upwelling across the tropical tropopause is forced by subtropical horizontal eddy momentum flux convergence associated with waves originating in both the tropics and extratropics.

Annual, Interannual, and Intraseasonal Variability of Tropical Tropopause Transition Layer Cirrus

2010 ◽  
Vol 67 (10) ◽  
pp. 3097-3112 ◽  
Author(s):  
Katrina S. Virts ◽  
John M. Wallace
Keyword(s):  
Annual Cycle ◽  
El Niño ◽  
Transition Layer ◽  
El Nino ◽  
Southern Oscillation ◽  
Cirrus Clouds ◽  
Boreal Winter ◽  
Central Pacific ◽  
Tropical Tropopause ◽  
The Pacific

Abstract Cloud fields based on the first three years of data from the Cloud–Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) mission are used to investigate the relationship between cirrus within the tropical tropopause transition layer (TTL) and the Madden–Julian oscillation (MJO), the annual cycle, and El Niño–Southern Oscillation (ENSO). The TTL cirrus signature observed in association with the MJO resembles convectively induced, mixed Kelvin–Rossby wave solutions above the Pacific warm pool region. This signature is centered to the east of the peak convection and propagates eastward more rapidly than the convection; it exhibits a pronounced eastward tilt with height, suggestive of downward phase propagation and upward energy dispersion. A cirrus maximum is observed over equatorial Africa and South America when the enhanced MJO-related convection enters the western Pacific. Tropical-mean TTL cirrus is modulated by the MJO, with more than twice as much TTL cirrus fractional coverage equatorward of 10° latitude when the enhanced convection enters the Pacific than a few weeks earlier, when the convection is over the Indian Ocean. The annual cycle in cirrus clouds around the base of the TTL is equatorially asymmetric, with more cirrus observed in the summer hemisphere. Higher in the TTL, the annual cycle in cirrus clouds is more equatorially symmetric, with a maximum in the boreal winter throughout most of the tropics. The ENSO signature in TTL cirrus is marked by a zonal shift of the peak cloudiness toward the central Pacific during El Niño and toward the Maritime Continent during La Niña.

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