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.

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.

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.

Manifestation of the Pacific Decadal Oscillation in the stationary planetary waves activity

2021 ◽  
Author(s):  
Daria Sobaeva ◽  
Yulia Zyulyaeva ◽  
Sergey Gulev
Keyword(s):  
Pacific Decadal Oscillation ◽  
North American ◽  
Lower Stratosphere ◽  
El Nino ◽  
Planetary Waves ◽  
Positive Phase ◽  
Negative Phase ◽  
Middle Troposphere ◽  
The Pacific ◽  
The Tropics

<p>Strong quasi-decadal oscillations of the stratospheric polar vortex (SPV) intensity are in phase with the Pacific decadal oscillation (PDO). A stronger SPV is observed during the positive phase of the PDO, and during the negative phase, the intensity of the SPV is below the mean climate values. The SPV intensity anomalies, formed by the planetary waves and zonal mean flow interaction, lead to the weakening/intensification of the vortex.</p><p>This research aimed to obtain the differences in the characteristics and the spatial propagation pattern of the planetary waves in the middle troposphere and lower stratosphere during different PDO phases. We analyzed composite periods of years when the PDO index has extremely high and low values. Two periods were constructed for both positive and negative phases, the first consisting of years with El-Nino/La-Nina events and the second without prominent sea surface temperature anomalies in the tropics. </p><p>During the wintertime in the Northern Hemisphere (December-February), wave 2 with two ridges (Siberian and North American Highs) and two troughs (Icelandic and Aleutian Lows) dominates in the middle troposphere, along with wave 1 dominating in the lower stratosphere. In the middle troposphere, at the positive phase ​​of the PDO, the amplitude of wave 2 is higher than in years with negative values of the PDO index. The differences in the Aleutian Low and the North American High intensity between the two phases are significant at the 97.5% level. In the lower stratosphere, the wave amplitude is lower at the negative phase ​​of the PDO, but we can also talk about a slight shift of the wave phase to the east. The regions of the heavy rains in the tropics during El-Nino events are the planetary waves source. They propagate from low to high latitudes, which results in modifying the characteristics and locations of the intensification of the stationary planetary waves in mid-latitudes.</p>

scholarly journals The Climatology of Brewer-Dobson Circulation and the Contribution of Gravity Waves

2018 ◽  
Author(s):  
Kaoru Sato ◽  
Soichiro Hirano
Keyword(s):  
Gravity Waves ◽  
Mass Flux ◽  
Lower Stratosphere ◽  
Reanalysis Data ◽  
Boreal Winter ◽  
Potential Contribution ◽  
Flux Divergence ◽  
Mean Circulation ◽  
Residual Mean Circulation ◽  
Mean State

Abstract. The climatology of residual mean circulation, which is a main component of Brewer-Dobson circulation, and the potential contribution of gravity waves (GWs) are examined for the annual mean state and for each season based on the transformed-Eulerian mean zonal momentum equation using modern four reanalysis data, which allows us to examine the whole stratosphere. First, the potential contribution of Rossby waves (RWs) to residual mean circulation is estimated from Eliassen-Palm flux divergence. The rest of residual-mean circulation, from which the potential RW contribution and zonal mean zonal wind tendency are subtracted, is regarded as the potential GW contribution. These potential wave contributions are exact contributions for the annual mean state and give good approximates for solstitial seasons. The GWs contribute to drive not only the summer hemispheric part of the winter deep branch and low-latitude part of shallow branches, as indicated by previous studies, but also cause a higher-latitude extension of the deep circulation in all seasons except for summer. This GW contribution is essential to determine the location of the turn-around latitude. The autumn circulation is stronger and wider than that of spring in the equinoctial seasons, regardless of almost symmetric RW and GW contributions around the equator. This asymmetry is attributable to the existence of the spring-to-autumn pole circulation corresponding to the angular momentum transport associated with seasonal variation due to the radiative process. The potential GW contribution is larger in September-to-November than in March-to-May in both hemispheres. The upward mass flux is maximized in the boreal winter in the lower stratosphere, while it exhibits semi-annual variation in the upper stratosphere. The GW contribution to the annual mean upward mass flux is in a range of 10–30 %, depending on the reanalysis data. The boreal winter maximum in the lower stratosphere is attributable to stronger RW activity in both hemispheres than in the austral winter.

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 Climatic variability of the mean flow and stationary planetary waves in the NCEP/NCAR reanalysis data

2008 ◽  
Vol 26 (5) ◽  
pp. 1233-1241 ◽  
Author(s):  
A. Yu. Kanukhina ◽  
E. V. Suvorova ◽  
L. A. Nechaeva ◽  
E. K. Skrygina ◽  
A. I. Pogoreltsev
Keyword(s):  
Lower Stratosphere ◽  
Climatic Variability ◽  
Reanalysis Data ◽  
Planetary Waves ◽  
Lower Atmosphere ◽  
Wave Number ◽  
Mean Flow ◽  
The Mean ◽  
The 1960S ◽  
Environmental Prediction

Abstract. NCEP/NCAR (National Center for Environmental Prediction – National Center for Atmospheric Research) data have been used to estimate the long-term variability of the mean flow, temperature, and Stationary Planetary Waves (SPW) in the troposphere and lower stratosphere. The results obtained show noticeable climatic variabilities in the intensity and position of the tropospheric jets that are caused by temperature changes in the lower atmosphere. As a result, we can expect that this variability of the mean flow will cause the changes in the SPW propagation conditions. The simulation of the SPW with zonal wave number m=1 (SPW1), performed with a linearized model using the mean flow distributions typical for the 1960s and for the beginning of 21st century, supports this assumption and shows that during the last 40 years the amplitude of the SPW1 in the stratosphere and mesosphere increased substantially. The analysis of the SPW amplitudes extracted from the geopotential height and zonal wind NCEP/NCAR data supports the results of simulation and shows that during the last years there exists an increase in the SPW1 activity in the lower stratosphere. These changes in the amplitudes are accompanied by increased interannual variability of the SPW1, as well. Analysis of the SPW2 activity shows that changes in its amplitude have a different sign in the northern winter hemisphere and at low latitudes in the southern summer hemisphere. The value of the SPW2 variability differs latitudinally and can be explained by nonlinear interference of the primary wave propagation from below and from secondary SPW2.

Dynamical Forcing of Subseasonal Variability in the Tropical Brewer–Dobson Circulation

2014 ◽  
Vol 71 (9) ◽  
pp. 3439-3453 ◽  
Author(s):  
Marta Abalos ◽  
William J. Randel ◽  
Encarna Serrano
Keyword(s):  
Lower Stratosphere ◽  
Momentum Balance ◽  
Strongly Correlated ◽  
Temperature Changes ◽  
Upper Troposphere ◽  
Weather Forecasts ◽  
Wave Forcing ◽  
Tropical Tropopause ◽  
Subseasonal Variability ◽  
Medium Range

Abstract Upwelling across the tropical tropopause exhibits strong subseasonal variability superimposed on the well-known annual cycle, and these variations directly affect temperature and tracers in the tropical lower stratosphere. In this work, the dynamical forcing of tropical upwelling on subseasonal time scales is investigated using the European Centre for Medium-Range Weather Forecasts (ECMWF) Interim Re-Analysis (ERA-Interim) for 1979–2011. Momentum balance diagnostics reveal that transience in lower-stratospheric upwelling is linked to the effects of extratropical wave forcing, with centers of action in the extratropical winter stratosphere and in the subtropical upper troposphere of both hemispheres. The time-dependent forcing in these regions induces a remote coupled response in the zonal mean wind and the meridional circulation (with associated temperature changes), which drives upwelling variability in the tropical stratosphere. This behavior is observed in the reanalysis, consistent with theory. Dynamical patterns reflect distinctive forcing of the shallow versus deep branches of the Brewer–Dobson circulation; the shallow branch is most strongly correlated with wave forcing in the subtropical upper troposphere and lower stratosphere, while the deep branch is mainly influenced by high-latitude planetary waves.

Equatorial Planetary Waves and Their Signature in Atmospheric Variability

2012 ◽  
Vol 69 (3) ◽  
pp. 857-874 ◽  
Author(s):  
Kevin M. Grise ◽  
David W. J. Thompson
Keyword(s):  
Southern Oscillation ◽  
Function Analysis ◽  
Distinct Pattern ◽  
Planetary Waves ◽  
Momentum Balance ◽  
Tropical Circulation ◽  
Atmospheric Variability ◽  
Tropical Tropopause ◽  
Mean Meridional Circulation ◽  
Mean Circulation

Abstract Equatorial planetary waves are a fundamental component of the tropical climate system. Previous studies have examined their structure in the climatological-mean circulation, their role in the climatological-mean momentum balance of the tropics, and their contribution to the climatological-mean upwelling across the tropical tropopause. In this study, the authors focus on the contribution of the equatorial planetary waves to variability in the tropical circulation about its climatological-mean state. The equatorial planetary waves that dominate the climatological mean exhibit considerable variability on intraseasonal and interannual time scales. Variability in the amplitude of the equatorial planetary waves is associated with a distinct pattern of equatorially symmetric climate variability that also emerges from empirical orthogonal function analysis of various tropical dynamical fields. Variability in the equatorial planetary waves is characterized by variations in 1) convection in the deep tropics, 2) eddy momentum flux convergence and zonal-mean zonal wind in the tropical upper troposphere, 3) the mean meridional circulation of the tropical and subtropical troposphere, 4) temperatures in the tropical lower stratosphere and subtropical troposphere of both hemispheres, and 5) the amplitude of the upper tropospheric anticyclones over the western tropical Pacific Ocean. It is argued that pulsation of the equatorial planetary waves provides an alternative framework for interpreting the response of the tropical circulation to a range of climate phenomena. Pulsation of the equatorial planetary waves is apparent in association with opposing phases of El Niño–Southern Oscillation and select phases of the Madden–Julian oscillation. Pulsation of the equatorial planetary waves also contributes to variability in measures of the width of the tropical belt.

scholarly journals Tropical Wave Driving of the Annual Cycle in Tropical Tropopause Temperatures. Part I: ECMWF Analyses

2006 ◽  
Vol 63 (5) ◽  
pp. 1410-1419 ◽  
Author(s):  
A. M. Kerr-Munslow ◽  
W. A. Norton
Keyword(s):  
Annual Cycle ◽  
Meridional Flow ◽  
Momentum Balance ◽  
Convective Heating ◽  
Stationary Waves ◽  
Flux Divergence ◽  
Wave Dissipation ◽  
Tropical Tropopause ◽  
Adiabatic Cooling ◽  
Mass Divergence

Abstract A quantitative examination of the annual cycle in the tropical tropopause temperatures, tropical ascent, momentum balance, and wave driving is performed using ECMWF analyses to determine how the annual cycle in tropical tropopause temperatures arises. Results show that the annual cycle in tropical tropopause temperatures is driven by the annual variation in ascent and consequent dynamical (adiabatic) cooling at the tropical tropopause. Mass divergence local to the tropical tropopause has the dominant contribution to ascent near the tropical tropopause. The annual cycle in mass divergence, and the associated meridional flow, near the tropical tropopause is driven by Eliassen–Palm (EP) flux divergence, that is, wave dissipation. The EP flux divergence near the tropical tropopause is dominated by stationary waves with both the horizontal and vertical components of the EP flux contributing. However, the largest annual cycle is in the divergence of the vertical EP flux and in particular from the contribution in the vertical flux of zonal momentum. These results do not match the existing theory that the annual cycle is driven by the wave dissipation in the extratropical stratosphere, that is, the stratospheric pump. It is suggested that the annual cycle is linked to equatorial Rossby waves forced by convective heating in the tropical troposphere.

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