scholarly journals The influence of the stratosphere on the tropospheric zonal wind response to CO<sub>2</sub> doubling

2010 ◽  
Vol 10 (10) ◽  
pp. 23895-23925
Author(s):  
Y. B. L. Hinssen ◽  
C. J. Bell ◽  
P. C. Siegmund
Keyword(s):  
Northern Hemisphere ◽  
Zonal Wind ◽  
High Latitude ◽  
Climate Models ◽  
Polar Vortex ◽  
Late Winter ◽  
Wave Forcing ◽  
Eddy Heat Flux ◽  
Wind Response ◽  
Hemisphere Winter

Abstract. The influence of a CO2 doubling on the stratospheric potential vorticity (PV) is examined in two climate models. Subsequently, the influence of changes in the stratosphere on the tropospheric zonal wind response is investigated, by inverting the stratospheric PV. Radiative effects dominate the stratospheric response to CO2 doubling in the Southern Hemisphere. These lead to a stratospheric PV increase at the edge of the polar vortex, resulting in an increased westerly influence of the stratosphere on the tropospheric midlatitude winds in late winter. In the Northern Hemisphere, dynamical effects are also important. Both models show a reduced polar PV and an enhanced midlatitude PV in the Northern Hemisphere winter stratosphere. These PV changes are related to an enhanced wave forcing of the winter stratosphere, as measured by an increase in the 100 hPa eddy heat flux, and result in a reduced westerly influence of the stratosphere on the high latitude tropospheric winds. In one model, the high latitude PV decreases are, however, restricted to higher altitudes, and the tropospheric response due to the stratospheric changes is dominated by an increased westerly influence in the midlatitudes, related to the increase in midlatitude PV in the lower stratosphere. The tropospheric response in zonal wind due to the stratospheric PV changes is of the order of 0.5 to 1 m s−1. The total tropospheric response has a somewhat different spatial structure, but is of similar magnitude. This indicates that the stratospheric influence is of importance in modifying the tropospheric zonal wind response to CO2 doubling.

scholarly journals The influence of the stratosphere on the tropospheric zonal wind response to CO<sub>2</sub> doubling

2011 ◽  
Vol 11 (10) ◽  
pp. 4915-4927 ◽  
Author(s):  
Y. B. L. Hinssen ◽  
C. J. Bell ◽  
P. C. Siegmund
Keyword(s):  
Northern Hemisphere ◽  
Zonal Wind ◽  
High Latitude ◽  
Climate Models ◽  
Polar Vortex ◽  
Late Winter ◽  
Wave Forcing ◽  
Eddy Heat Flux ◽  
Wind Response ◽  
Hemisphere Winter

Abstract. The influence of a CO2 doubling on the stratospheric potential vorticity (PV) is examined in two climate models. Subsequently, the influence of changes in the stratosphere on the tropospheric zonal wind response is investigated, by inverting the stratospheric PV. Radiative effects seem to dominate the stratospheric response to CO2 doubling in the Southern Hemisphere. These lead to a stratospheric PV increase at the edge of the polar vortex, resulting in an increased westerly influence of the stratosphere on the troposphere, increasing the midlatitude tropospheric westerlies in late winter. In the Northern Hemisphere, dynamical effects are also important. Both models show a reduced polar PV and an enhanced midlatitude PV in the Northern Hemisphere winter stratosphere. These PV changes are likely related to an enhanced wave forcing of the winter stratosphere, as measured by an increase in the 100 hPa eddy heat flux, and result in a reduced westerly influence of the stratosphere on the high latitude tropospheric winds. In one model, the high latitude PV decreases are, however, restricted to higher altitudes, and the tropospheric response due to the stratospheric changes is dominated by an increased westerly influence in the midlatitudes, related to the increase in midlatitude PV in the lower stratosphere. The tropospheric response in zonal wind due to the stratospheric PV changes is of the order of 0.5 to 1 m s−1. The total tropospheric response has a somewhat different spatial structure, but is of similar magnitude. This indicates that the stratospheric influence is of importance in modifying the tropospheric zonal wind response to CO2 doubling.

scholarly journals Solar and QBO Influences on the Timing of Stratospheric Sudden Warmings

2004 ◽  
Vol 61 (23) ◽  
pp. 2777-2796 ◽  
Author(s):  
Lesley J. Gray ◽  
Simon Crooks ◽  
Charlotte Pascoe ◽  
Sarah Sparrow ◽  
Michael Palmer
Keyword(s):  
Northern Hemisphere ◽  
Zonal Wind ◽  
Polar Vortex ◽  
Quasi Biennial Oscillation ◽  
Model Experiments ◽  
Zonal Winds ◽  
Stratospheric Sudden Warmings ◽  
Hemisphere Winter ◽  
Biennial Oscillation ◽  
Northern Hemisphere Winter

Abstract The interaction of the 11-yr solar cycle (SC) and the quasi-biennial oscillation (QBO) and their influence on the Northern Hemisphere (NH) polar vortex are studied using idealized model experiments and ECMWF Re-Analysis (ERA-40). In the model experiments, the sensitivity of the NH polar vortex to imposed easterlies at equatorial/subtropical latitudes over various height ranges is tested to explore the possible influence from zonal wind anomalies associated with the QBO and the 11-yr SC in those regions. The experiments show that the timing of the modeled stratospheric sudden warmings (SSWs) is sensitive to the imposed easterlies at the equator/subtropics. When easterlies are imposed in the equatorial or subtropical upper stratosphere, the onset of the SSWs is earlier. A mechanism is proposed in which zonal wind anomalies in the equatorial/subtropical upper stratosphere associated with the QBO and 11-yr SC either reinforce each other or cancel each other out. When they reinforce, as in Smin–QBO-east (Smin/E) and Smax–QBO-west (Smax/W), it is suggested that the resulting anomaly is large enough to influence the development of the Aleutian high and hence the time of onset of the SSWs. Although highly speculative, this mechanism may help to understand the puzzling observations that major warmings often occur in Smax/W years even though there is no strong waveguide provided by the QBO winds in the lower equatorial stratosphere. The ERA-40 data are used to investigate the QBO and solar signals and to determine whether the observations support the proposed mechanism. Composites of ERA-40 zonally averaged zonal winds based on the QBO (E/W), the SC (min/max), and both (Smin/E, Smin/W, Smax/E, Smax/W) are examined, with emphasis on the Northern Hemisphere winter vortex evolution. The major findings are that QBO/E years are more disturbed than QBO/W years, primarily during early winter. Sudden warmings in Smax years tend to occur later than in Smin years. Midwinter warmings are more likely during Smin/E and Smax/W years, although the latter result is only barely statistically significant at the 75% level. The data show some support for the proposed mechanism, but many more years are required before it can be fully tested.

The Dynamics of Northern Hemisphere Stratospheric Final Warming Events

2007 ◽  
Vol 64 (8) ◽  
pp. 2932-2946 ◽  
Author(s):  
Robert X. Black ◽  
Brent A. McDaniel
Keyword(s):  
Northern Hemisphere ◽  
Zonal Wind ◽  
Potential Vorticity ◽  
High Latitude ◽  
Dynamical Behavior ◽  
Polar Vortex ◽  
Stratospheric Polar Vortex ◽  
Stratospheric Final Warming ◽  
Concomitant Reduction ◽  
Indirect Consequence

A lag composite analysis is performed of the zonal-mean structure and dynamics of Northern Hemisphere stratospheric final warming (SFW) events. SFW events are linked to distinct zonal wind deceleration signatures in the stratosphere and troposphere. The period of strongest stratospheric decelerations (SD) is marked by a concomitant reduction in the high-latitude tropospheric westerlies. However, a subsequent period of tropospheric decelerations (TD) occurs while the stratospheric circulation relaxes toward climatological conditions. During SFW onset, a wavenumber-1 disturbance at stratospheric altitudes evolves into a circumpolar anticyclonic circulation anomaly. Transformed Eulerian-mean dynamical diagnoses reveal that the SD period is characterized by an anomalous upward Eliassen–Palm (EP) signature at high latitudes extending from the surface to the middle stratosphere. The associated wave-driving pattern consists of zonal decelerations extending from the upper troposphere to the midstratosphere. Piecewise potential vorticity tendency analyses further indicate that zonal wind decelerations in the lower and middle troposphere result, at least in part, from the direct response to latitudinal redistributions of potential vorticity occurring in the lower stratosphere. The TD period exhibits a distinct dynamical behavior with anomalous downward EP fluxes in the high-latitude stratosphere as the zero zonal wind line descends toward the tropopause. This simultaneously allows the stratospheric polar vortex to radiatively recover while providing anomalous upper-tropospheric zonal decelerations (as tropospheric Rossby wave activity is vertically trapped in the high-latitude troposphere). The tropospheric decelerations that occur during the TD period are regarded as a subsequent indirect consequence of SFW events.

Final Sudden Stratospheric Warmings and the memory of the stratosphere

2021 ◽  
Author(s):  
Alain Hauchecorne ◽  
Chantal Claud ◽  
Philippe Keckhut
Keyword(s):  
Zonal Wind ◽  
Planetary Wave ◽  
Middle Atmosphere ◽  
Temperature Anomaly ◽  
Polar Vortex ◽  
Wave Activity ◽  
Late Winter ◽  
Easterly Wind ◽  
Weather Forecasts ◽  
Stratospheric Circulation

&lt;p&gt;Sudden Stratospheric Warming (SSW) is the most spectacular dynamic event occurring in the middle atmosphere. It can lead to a warming of the winter polar stratosphere by a few tens of K in one to two weeks and a reversal of the stratospheric circulation from wintertime prevailing westerly winds to easterly winds similar to summer conditions. This strong modification of the stratospheric circulation has consequences for several applications, including the modification of the stratospheric infrasound guide. Depending on the date of the SSW, the westerly circulation can be re-established if the SSW occurs in mid-winter or the summer easterly circulation can be definitively established if the SSW occurs in late winter. In the latter case it is called Final Warming (FW). Each year, it is possible to define the date of the FW as the date of the final inversion of the zonal wind at 60&amp;#176;N - 10 hPa . If the FW is associated with a strong peak of planetary wave activity and a rapid increase in polar temperature, it is classified as dynamic FW. If the transition to the easterly wind is smooth without planetary wave activity, the FW is classified as radiative.&lt;/p&gt;&lt;p&gt;The analysis of the ERA5 database, which has recently been extended to 1950 (71 years of data), allowed a statistical analysis of the evolution of the stratosphere in winter. The main conclusions of this study will be presented :&lt;/p&gt;&lt;p&gt;- the state of the polar vortex in a given month is anticorrelated with its state 2 to 3 months earlier. The beginning of winter is anticorrelated with mid-winter and mid-winter is anticorrelated with the end of winter;&lt;/p&gt;&lt;p&gt;- dynamic FWs occur early in the season (March - early April) and are associated with a strong positive polar temperature anomaly, while radiative FWs occur later (late April - early May) without a polar temperature anomaly;&lt;/p&gt;&lt;p&gt;- the summer stratosphere (polar temperature and zonal wind) keeps the memory of its state in April-May at the time of FW at least until July .&lt;/p&gt;&lt;p&gt;These results could help to improve medium-range weather forecasts in the Northern Hemisphere due to the strong dynamic coupling between the troposphere and stratosphere during SSW events.&lt;/p&gt;

scholarly journals Assessing stratospheric transport in the CMAM30 simulations using ACE-FTS measurements

2017 ◽  
Author(s):  
Felicia Kolonjari ◽  
David A. Plummer ◽  
Kaley A. Walker ◽  
Chris D. Boone ◽  
James W. Elkins ◽  
...  
Keyword(s):  
Atmospheric Chemistry ◽  
Climate Models ◽  
Middle Atmosphere ◽  
Polar Vortex ◽  
Sampling Technique ◽  
Dynamics Simulation ◽  
Global Circulation Models ◽  
Extratropical Tropopause ◽  
Hemisphere Winter ◽  
June July

Abstract. Stratospheric transport in global circulation models and chemistry-climate models is an important component in simulating the recovery of the ozone layer as well as changes in the climate system. The Brewer-Dobson circulation is not well constrained by observations and further investigation is required to resolve uncertainties related to the mechanisms driving the circulation. This study has assessed the specified dynamics mode of the Canadian Middle Atmosphere Model (CMAM30) by comparing to the Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS) profile measurements of CFC-11 (CCl3F), CFC-12 (CCl2F2), and N2O. In the CMAM30 specified dynamics simulation, the meteorological fields are nudged using the ERA-Interim Reanalysis and a specified tracer was used for each species, with hemispherically-defined surface measurements used as the boundary condition. A comprehensive sampling technique along the line-of-sight of the ACE-FTS measurements has been employed to allow for direct comparisons between the simulated and measured tracer concentrations. The model consistently overpredicts tracer concentrations in the lower stratosphere, particularly in the Northern Hemisphere winter and spring seasons. The three mixing barriers investigated, including the polar vortex, the extratropical tropopause, and the tropical pipe, show that there are significant inconsistencies between the measurements and the simulations. In particular, the CMAM30 simulation exhibits too little isentropic mixing in the June-July-August season.

Decadal Fluctuations in Planetary Wave Forcing Modulate Global Warming in Late Boreal Winter

2009 ◽  
Vol 22 (16) ◽  
pp. 4418-4426 ◽  
Author(s):  
Judah Cohen ◽  
Mathew Barlow ◽  
Kazuyuki Saito
Keyword(s):  
Northern Hemisphere ◽  
Land Surface ◽  
Warming Trend ◽  
Late Winter ◽  
Boreal Winter ◽  
Wave Forcing ◽  
Scale Temperature ◽  
Decadal Scale ◽  
Seasonal Time Scale ◽  
Global Surface

Abstract The warming trend in global surface temperatures over the last 40 yr is clear and consistent with anthropogenic increases in greenhouse gases. Over the last 2 decades, this trend appears to have accelerated. In contrast to this general behavior, however, here it is shown that trends during the boreal cold months in the recent period have developed a marked asymmetry between early winter and late winter for the Northern Hemisphere, with vigorous warming in October–December followed by a reversal to a neutral/cold trend in January–March. This observed asymmetry in the cold half of the boreal year is linked to a two-way stratosphere–troposphere interaction, which is strongest in the Northern Hemisphere during late winter and is related to variability in Eurasian land surface conditions during autumn. This link has been demonstrated for year-to-year variability and used to improve seasonal time-scale winter forecasts; here, this coupling is shown to strongly modulate the warming trend, with implications for decadal-scale temperature projections.

scholarly journals Modeling Seasonal Sudden Stratospheric Warming Climatology Based on Polar Vortex Statistics

2017 ◽  
Vol 30 (24) ◽  
pp. 10101-10116 ◽  
Author(s):  
Matthew F. Horan ◽  
Thomas Reichler
Keyword(s):  
Statistical Model ◽  
Seasonal Cycle ◽  
General Circulation ◽  
Climate Models ◽  
Polar Vortex ◽  
General Circulation Models ◽  
Late Winter ◽  
Sudden Stratospheric Warming ◽  
Main Factors ◽  
Observational Record

This study investigates the climatological frequency distribution of sudden stratospheric warmings (SSWs). General circulation models (GCMs) tend to produce SSW maxima later in winter than observations, which has been considered as a model deficiency. However, the observed record is short, calling into question the representativeness of the observational record. To study the seasonality of SSWs and the factors behind it, the authors use observations, a long control simulation with a stratosphere resolving GCM, and also a simple statistical model that is based on the climatological seasonal cycle of the polar vortex winds. From the combined analysis, the authors conclude that the late-winter SSW maximum seen in most climate models is realistic and that observations would also have a late-winter SSW maximum if more data were available. The authors identify the seasonally varying strengths of the polar vortex and stratospheric wave driving as the two main factors behind the seasonal SSW distribution. The statistical model also indicates that there exists a continuum of weak polar vortex states and that SSWs simply form the tail of normally distributed stratospheric winds.

scholarly journals The effect of interactive ozone chemistry on weak and strong stratospheric polar vortex events

2020 ◽  
Author(s):  
Jessica Oehrlein ◽  
Gabriel Chiodo ◽  
Lorenzo M. Polvani
Keyword(s):  
Climate Variability ◽  
Northern Hemisphere ◽  
North Atlantic ◽  
Climate Model ◽  
Stratospheric Ozone ◽  
Polar Vortex ◽  
Late Winter ◽  
Stratospheric Polar Vortex ◽  
Winter Climate ◽  
The Impact

Abstract. Modeling and observational studies have reported effects of stratospheric ozone extremes on Northern Hemisphere spring climate. Recent work has further suggested that the coupling of ozone chemistry and dynamics amplifies the surface response to midwinter sudden stratospheric warmings (SSWs). Here, we study the importance of interactive ozone chemistry in representing the stratospheric polar vortex and Northern Hemisphere winter surface climate variability. We contrast two simulations from the interactive and specified chemistry (and thus ozone) versions of the Whole Atmosphere Community Climate Model, designed to isolate the impact of interactive ozone on polar vortex variability. In particular, we analyze the response with and without interactive chemistry to midwinter SSWs, March SSWs, and strong polar vortex events (SPVs). With interactive chemistry, the stratospheric polar vortex is stronger, and more SPVs occur, but we find little effect on the frequency of midwinter SSWs. At the surface, interactive chemistry results in a pattern resembling a more negative North Atlantic Oscillation following midwinter SSWs, but with little impact on the surface signatures of late winter SSWs and SPVs. These results suggest that including interactive ozone chemistry is important for representing North Atlantic and European winter climate variability.

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