The downward propagation of split- and displacement-type SSWs in an idealised model

2020 ◽  
Author(s):  
Ian White ◽  
Chaim Garfinkel ◽  
Edwin Gerber ◽  
Martin Jucker
Keyword(s):  
Polar Vortex ◽  
Momentum Budget ◽  
Ozone Profile ◽  
Tropospheric Circulation ◽  
Downward Influence ◽  
Symmetric Heating ◽  
Free Running ◽  
Downward Propagation ◽  
Idealised Model ◽  
Radiation Scheme

<p>Sudden stratospheric warmings (SSWs) have a significant downward influence on the tropospheric circulation below, although the mechanisms governing this downward impact are not well understood. It is also not known if the type of SSW event – be them splits or displacements – play a role in determining the magnitude of the tropospheric response. We here examine the impacts of split- and displacement-type SSWs on the troposphere.</p><p>To do this, we use the recently developed model of an idealised moist atmosphere to impose zonally-asymmetric warming perturbations to the extratropical stratosphere, extending the work of a recent study by the authors in which a zonally-symmetric heating perturbation was imposed. This model of ‘intermediate complexity’ is particularly suited to this study as it incorporates the radiation scheme that is utilised by operational forecast systems, including both the ECMWF and NCEP. The radiation scheme also allows us to force the model with a realistic ozone profile, and thus to simulate realistic radiative timescales in the stratosphere. From a control run with a realistic climatology, we perform an ensemble of spin-off runs every January 1<sup>st</sup> with imposed high-latitude stratospheric heating perturbations of varying degrees of magnitude. The heating perturbation is switched on for a limited period of time to mimic the sudden nature of a SSW event and the troposphere is allowed to evolve freely. We compare the evolution of the tropospheric response to the forced split and displacement-type SSWs with free-running SSWs of the same type in the control run.</p><p>By modifying only the temperature tendency equation as opposed to the momentum budget, our experiments allow us to isolate the tropospheric response associated with changes in the polar-vortex strength (e.g., a direct or indirect modulation of planetary waves and synoptic waves), rather than due to any planetary-wave momentum torques that initially drive the SSW. Nevertheless, the imposition of wave-1 and wave-2 heating perturbations provide a more realistic post-onset SSW state than that which occurs in response to zonal-mean heating perturbations as performed in our previous study.</p>

Downward Wave Propagation on the Polar Vortex

2005 ◽  
Vol 62 (9) ◽  
pp. 3382-3395 ◽  
Author(s):  
R. K. Scott ◽  
D. G. Dritschel
Keyword(s):  
Wave Propagation ◽  
Differential Rotation ◽  
Potential Vorticity ◽  
Three Dimensional ◽  
Polar Vortex ◽  
Wave Activity ◽  
Stratospheric Polar Vortex ◽  
Downward Influence ◽  
Downward Propagation ◽  
Propagation Of Waves

Abstract This paper considers the propagation of waves on the edge of a stratospheric polar vortex, represented by a three-dimensional patch of uniform potential vorticity in a compressible quasigeostrophic system. Waves are initialized by perturbing the vortex from axisymmetry in the center of the vortex, and their subsequent upward and downward propagation is measured in terms of a nonlinear, pseudomomentum-based wave activity. Under conditions typical of the winter stratosphere, the dominant direction of wave propagation is downward, and wave activity accumulates in the lower vortex levels. The reason for the preferred downward propagation arises from a recent result of Scott and Dritschel, which showed that the three-dimensional Green’s function in the compressible system contains an anisotropy that causes a general differential rotation in a finite volume vortex. The sense of the differential rotation is to stabilize the upper vortex and destabilize the lower vortex. This mechanism is particularly interesting in view of recent interest in the downward influence of the stratosphere on the troposphere and also provides a possible conservative, balanced explanation of the formation of the robust dome plus annulus potential vorticity structure observed in the upper stratosphere.

scholarly journals The Generic Nature of the Tropospheric Response to Sudden Stratospheric Warmings

2020 ◽  
Vol 33 (13) ◽  
pp. 5589-5610 ◽  
Author(s):  
Ian P. White ◽  
Chaim I. Garfinkel ◽  
Edwin P. Gerber ◽  
Martin Jucker ◽  
Peter Hitchcock ◽  
...  
Keyword(s):  
High Latitude ◽  
Planetary Wave ◽  
Polar Vortex ◽  
Stratospheric Polar Vortex ◽  
Near Surface ◽  
Momentum Budget ◽  
Free Running ◽  
Eddy Fluxes ◽  
Surface Jet ◽  
Thermally Triggered

AbstractThe tropospheric response to midwinter sudden stratospheric warmings (SSWs) is examined using an idealized model. SSW events are triggered by imposing high-latitude stratospheric heating perturbations of varying magnitude for only a few days, spun off from a free-running control integration (CTRL). The evolution of the thermally triggered SSWs is then compared with naturally occurring SSWs identified in CTRL. By applying a heating perturbation, with no modification to the momentum budget, it is possible to isolate the tropospheric response directly attributable to a change in the stratospheric polar vortex, independent of any planetary wave momentum torques involved in the initiation of an SSW. Zonal-wind anomalies associated with the thermally triggered SSWs first propagate downward to the high-latitude troposphere after ~2 weeks, before migrating equatorward and stalling at midlatitudes, where they straddle the near-surface jet. After ~3 weeks, the circulation and eddy fluxes associated with thermally triggered SSWs evolve very similarly to SSWs in CTRL, despite the lack of initial planetary wave driving. This suggests that at longer lags, the tropospheric response to SSWs is generic and it is found to be linearly governed by the strength of the lower-stratospheric warming, whereas at shorter lags, the initial formation of the SSW potentially plays a large role in the downward coupling. In agreement with previous studies, synoptic waves are found to play a key role in the persistent tropospheric jet shift at long lags. Synoptic waves appear to respond to the enhanced midlatitude baroclinicity associated with the tropospheric jet shift, and preferentially propagate poleward in an apparent positive feedback with changes in the high-latitude refractive index.

scholarly journals The Downward Influence of Uncertainty in the Northern Hemisphere Stratospheric Polar Vortex Response to Climate Change

2018 ◽  
Vol 31 (16) ◽  
pp. 6371-6391 ◽  
Author(s):  
Isla R Simpson ◽  
Peter Hitchcock ◽  
Richard Seager ◽  
Yutian Wu ◽  
Patrick Callaghan
Keyword(s):  
Northern Hemisphere ◽  
General Circulation ◽  
Polar Vortex ◽  
General Circulation Models ◽  
Cmip5 Models ◽  
Regression Analyses ◽  
Stratospheric Polar Vortex ◽  
Wide Range ◽  
Tropospheric Circulation ◽  
Downward Influence

Abstract General circulation models display a wide range of future predicted changes in the Northern Hemisphere winter stratospheric polar vortex. The downward influence of this stratospheric uncertainty on the troposphere has previously been inferred from regression analyses across models and is thought to contribute to model spread in tropospheric circulation change. Here we complement such regression analyses with idealized experiments using one model where different changes in the zonal-mean stratospheric polar vortex are artificially imposed to mimic the extreme ends of polar vortex change simulated by models from phase 5 of the Coupled Model Intercomparison Project (CMIP5). The influence of the stratospheric vortex change on the tropospheric circulation in these experiments is quantitatively in agreement with the inferred downward influence from across-model regressions, indicating that such regressions depict a true downward influence of stratospheric vortex change on the troposphere below. With a relative weakening of the polar vortex comes a relative increase in Arctic sea level pressure (SLP), a decrease in zonal wind over the North Atlantic, drying over northern Europe, and wetting over southern Europe. The contribution of stratospheric vortex change to intermodel spread in these quantities is assessed in the CMIP5 models. The spread, as given by 4 times the across-model standard deviation, is reduced by roughly 10% on regressing out the contribution from stratospheric vortex change, while the difference between models on extreme ends of the distribution in terms of their stratospheric vortex change can reach up to 50% of the overall model spread for Arctic SLP and 20% of the overall spread in European precipitation.

scholarly journals The Diurnal Variation in Stratospheric Ozone from MACC Reanalysis, ERA-Interim, WACCM, and Earth Observation Data: Characteristics and Intercomparison

Atmosphere ◽  
2021 ◽  
Vol 12 (5) ◽  
pp. 625
Author(s):  
Ansgar Schanz ◽  
Klemens Hocke ◽  
Niklaus Kämpfer ◽  
Simon Chabrillat ◽  
Antje Inness ◽  
...  
Keyword(s):  
Diurnal Variation ◽  
Climate Model ◽  
Stratospheric Ozone ◽  
Polar Vortex ◽  
Model Systems ◽  
Atmospheric Composition ◽  
The Arctic ◽  
Observation Data ◽  
High Latitudes ◽  
Free Running

In this study, we compare the diurnal variation in stratospheric ozone of the MACC (Monitoring Atmospheric Composition and Climate) reanalysis, ECMWF Reanalysis Interim (ERA-Interim), and the free-running WACCM (Whole Atmosphere Community Climate Model). The diurnal variation of stratospheric ozone results from photochemical and dynamical processes depending on altitude, latitude, and season. MACC reanalysis and WACCM use similar chemistry modules and calculate a similar diurnal cycle in ozone when it is caused by a photochemical variation. The results of the two model systems are confirmed by observations of the Superconducting Submillimeter-Wave Limb-Emission Sounder (SMILES) experiment and three selected sites of the Network for Detection of Atmospheric Composition Change (NDACC) at Mauna Loa, Hawaii (tropics), Bern, Switzerland (midlatitudes), and Ny-Ålesund, Svalbard (high latitudes). On the other hand, the ozone product of ERA-Interim shows considerably less diurnal variation due to photochemical variations. The global maxima of diurnal variation occur at high latitudes in summer, e.g., near the Arctic NDACC site at Ny-Ålesund, Svalbard. The local OZORAM radiometer observes this effect in good agreement with MACC reanalysis and WACCM. The sensed diurnal variation at Ny-Ålesund is up to 8% (0.4 ppmv) due to photochemical variations in summer and negligible during the dynamically dominated winter. However, when dynamics play a major role for the diurnal ozone variation as in the lower stratosphere (100–20 hPa), the reanalysis models ERA-Interim and MACC which assimilate data from radiosondes and satellites outperform the free-running WACCM. Such a domain is the Antarctic polar winter where a surprising novel feature of diurnal variation is indicated by MACC reanalysis and ERA-Interim at the edge of the polar vortex. This effect accounts for up to 8% (0.4 ppmv) in both model systems. In summary, MACC reanalysis provides a global description of the diurnal variation of stratospheric ozone caused by dynamics and photochemical variations. This is of high interest for ozone trend analysis and other research which is based on merged satellite data or measurements at different local time.

scholarly journals Evaluation of tropospheric ozone columns derived from assimilated GOME ozone profile observations

2009 ◽  
Vol 9 (20) ◽  
pp. 8105-8120 ◽  
Author(s):  
A. T. J. de Laat ◽  
R. J. van der A ◽  
M. van Weele
Keyword(s):  
Tropospheric Ozone ◽  
Transport Model ◽  
Added Value ◽  
Chemistry Transport Model ◽  
Ozone Profile ◽  
Free Running ◽  
Tropospheric O3 ◽  
Total Column ◽  
Good Agreement

Abstract. Tropospheric O3 column estimates are produced and evaluated from spaceborne O3 observations by the subtraction of assimilated O3 profile observations from total column observations, the so-called Tropospheric O3 ReAnalysis or TORA method. Here we apply the TORA method to six years (1996–2001) of ERS-2 GOME/TOMS total O3 and ERS-2 GOME O3 profile observations using the TM5 global chemistry-transport model with a linearized O3 photochemistry parameterization scheme. Free running TM5 simulations show good agreement with O3 sonde observations in the upper-tropospheric and lower stratospheric region (UTLS), both for short day-to-day variability as well as for monthly means. The assimilation of GOME O3 profile observations counteracts the mid-latitude stratospheric O3 drift caused by the overstrong stratospheric meridional circulation in TM5. Assimilation of GOME O3 profile observations also improves the bias and correlations in the tropical UTLS region but slightly degrades the model-to-sonde correlations and bias of extra-tropical UTLS. We suggest that this degradation is related to the large ground pixel size of the GOME O3 measurements (960×100 km) in combination with retrieval and calibration errors. The added value of the assimilation of GOME O3 profiles compared to stand-alone model simulations lays in the long term variations of stratospheric O3, not in short term synoptic variations. The evaluation of daily and monthly tropospheric O3 columns obtained from total column observations and using the TORA methodology shows that the use of GOME UV-VIS nadir O3 profiles in combination with the spatial resolution of the model does not result in satisfactory residual tropospheric ozone columns.

Stratospheric influence on idealised baroclinic life cycles

2020 ◽  
Author(s):  
Philip Rupp ◽  
Thomas Birner
Keyword(s):  
Life Cycle ◽  
Initial Conditions ◽  
Polar Vortex ◽  
Life Cycles ◽  
Stratospheric Polar Vortex ◽  
Shift Response ◽  
Tropospheric Circulation ◽  
Wave Development ◽  
Final Steady State ◽  
Numerical Model Experiments

<p>The importance of understanding the dynamical coupling of troposphere and stratosphere to make accurate weather and climate predictions is well-known. Over the past years and decades various signatures of such a<br>coupling have been discovered. A very robust result, for example, seems to be an equatorward shift of the tropospheric eddy driven jet following sudden stratospheric warming events, where the westerly winds of the stratospheric polar vortex weaken or even reverse. However, many aspects of this fundamental coupling are still not fully understood and research on how the state of the stratosphere can influence the tropospheric circulation and what dynamical processes are involved is still ongoing.</p><p><br>An important such process arises due to the interaction of a sharp, localised maximum in potential vorticity gradient near the tropopause with baroclinic eddies in the troposphere. Here, we analyse the sensitivity of baroclinic wave development and evolution to changes of various basic state characteristics, by performing a series of idealised baroclinic eddy life cycle experiments. Special attention is paid to sensitivities associated with the dynamical state of the stratosphere. We find that the final (steady) state of the life cycle simulations corresponds to an equatorward shift of the tropospheric jet in cases where the initial conditions do not include a stratospheric polar vortex (such as following sudden warming events) compared to those that do. These results further support the idea that the stratospheric state can strongly influence tropospheric dynamics and, in particular, highlight the robustness of the jet shift response following sudden warmings, that can be seen in a range of observations and numerical model experiments.</p>

Tropospheric Precursors and Stratospheric Warmings

2011 ◽  
Vol 24 (24) ◽  
pp. 6562-6572 ◽  
Author(s):  
Judah Cohen ◽  
Justin Jones
Keyword(s):  
Sea Level ◽  
Energy Flux ◽  
Polar Vortex ◽  
Stratospheric Warming ◽  
Sea Level Pressure ◽  
Winter Climate ◽  
Level Pressure ◽  
The North ◽  
Tropospheric Circulation ◽  
The North Pacific

Abstract Many tropospheric Arctic Oscillation (AO) events are preceded by stratospheric AO events and even earlier in time by anomalous upward energy flux associated with Rossby waves in the troposphere. This study identifies lower-tropospheric circulation anomalies that precede large AO events in both the troposphere and stratosphere and the anomalous upward energy flux. Compositing analysis of stratospheric warming events identifies regional tropospheric precursors, which precede stratospheric warmings. The tropospheric precursor is found to vary when compositing over polar vortex displacements and splits separately. Prior to vortex displacements the main anomaly sea level pressure center of the tropospheric precursor is located across northwest Eurasia and is associated with the Siberian high. Prior to vortex splits a similar anomaly center is identified in the tropospheric precursor but is weaker and appears to be more strongly related to a shift in the storm tracks. Differences in the sea level pressure anomalies in the North Atlantic and the North Pacific are also observed when comparing the precursors prior to vortex displacements and splits. Identification of a unique tropospheric precursor to stratospheric warming and subsequent tropospheric AO events can help to improve understanding troposphere–stratosphere coupling. Furthermore, the observational evidence presented here can be compared with model simulations of winter climate variability and lead to potential model improvements.

Sensitivity of the Tropospheric Circulation to Changes in the Strength of the Stratospheric Polar Vortex

2006 ◽  
Vol 134 (8) ◽  
pp. 2191-2207 ◽  
Author(s):  
Thomas Jung ◽  
Jan Barkmeijer
Keyword(s):  
North Atlantic ◽  
Polar Vortex ◽  
Stratospheric Polar Vortex ◽  
The North ◽  
European Area ◽  
Extended Range ◽  
Tropospheric Circulation ◽  
The North Atlantic Oscillation ◽  
Ecmwf Model ◽  
Strong Vortex

Abstract The sensitivity of the wintertime tropospheric circulation to changes in the strength of the Northern Hemisphere stratospheric polar vortex is studied using one of the latest versions of the ECMWF model. Three sets of experiments were carried out: one control integration and two integrations in which the strength of the stratospheric polar vortex has been gradually reduced and increased, respectively, during the course of the integration. The strength of the polar vortex is changed by applying a forcing to the model tendencies in the stratosphere only. The forcing has been obtained using the adjoint technique. It is shown that, in the ECMWF model, changes in the strength of the polar vortex in the middle and lower stratosphere have a significant and slightly delayed (on the order of days) impact on the tropospheric circulation. The tropospheric response shows some resemblance to the North Atlantic Oscillation (NAO), though the centers of action are slightly shifted toward the east compared to those of the NAO. Furthermore, a separate comparison of the response to a weak and strong vortex forcing suggests that to first order the tropospheric response is linear within a range of realistic stratospheric perturbations. From the results presented, it is argued that extended-range forecasts in the European area particularly benefit from the stratosphere–troposphere link.

scholarly journals CHEM2D-OPP: A new linearized gas-phase ozone photochemistry parameterization for high-altitude NWP and climate models

2006 ◽  
Vol 6 (4) ◽  
pp. 6627-6694
Author(s):  
J. P. McCormack ◽  
S. D. Eckermann ◽  
D. E. Siskind ◽  
T. J. McGee
Keyword(s):  
High Altitude ◽  
Climate Models ◽  
Transport Model ◽  
Stratospheric Ozone ◽  
Weather Prediction ◽  
Forecast Model ◽  
Temperature Bias ◽  
Ozone Profile ◽  
Free Running ◽  
Ozone Photochemistry

Abstract. The new CHEM2D-Ozone Photochemistry Parameterization (CHEM2D-OPP) for high-altitude numerical weather prediction (NWP) systems and climate models specifies the net ozone photochemical tendency and its sensitivity to changes in ozone mixing ratio, temperature and overhead ozone column based on calculations from the CHEM2D interactive middle atmospheric photochemical transport model. We evaluate CHEM2D-OPP performance using both short-term (6-day) and long-term (1-year) stratospheric ozone simulations with the prototype high-altitude NOGAPS-ALPHA forecast model. An inter-comparison of NOGAPS-ALPHA 6-day ozone hindcasts for 7 February 2005 with ozone photochemistry parameterizations currently used in operational NWP systems shows that CHEM2D-OPP yields the best overall agreement with Aura Microwave Limb Sounder ozone profile measurements. A 1-year free-running NOGAPS-ALPHA simulation using CHEM2D-OPP produces a realistic seasonal cycle in zonal mean ozone throughout the stratosphere. We find that the combination of a model cold temperature bias at high latitudes in winter and a warm bias in the CHEM2D-OPP temperature climatology can degrade the performance of the linearized ozone photochemistry parameterization over seasonal time scales despite the fact that the parameterized temperature dependence is weak in these regions.

scholarly journals Origins of Multi-decadal Variability in Sudden Stratospheric Warmings

2021 ◽  
Author(s):  
Oscar Dimdore-Miles ◽  
Lesley Gray ◽  
Scott Osprey
Keyword(s):  
Decadal Variability ◽  
Low Frequency ◽  
Polar Vortex ◽  
Major Influence ◽  
Quasi Biennial Oscillation ◽  
Stratospheric Polar Vortex ◽  
Surface Climate ◽  
Tropospheric Circulation ◽  
Tropical Sea

<p>Sudden Stratospheric Warmings (SSWs) are major disruptions of the Northern Hemisphere (NH) stratospheric polar vortex and occur on average approximately 6 times per decade in observation based records. However, within these records, intervals of significantly higher and lower SSW rates are observed suggesting the possibility of low frequency variations in event occurrence. A better understanding of factors that influence this decadal variability may help to improve predictability of NH mid-latitude surface climate, through stratosphere-troposphere coupling. In this work, multi-decadal variability of SSW events is examined in a 1000-yr pre-industrial simulation of a coupled Atmosphere-Ocean-Land-Sea ice model. Using a wavelet spectral decomposition method, we show that hiatus events (intervals of a decade or more with no SSWs) and consecutive SSW events (extended intervals with at least one SSW in each year) vary on multi-decadal timescales of period between 60 and 90 years. Signals on these timescales are present for approximately 450 years of the simulation. We investigate the possible source of these long-term signals and find that the direct impact of variability in tropical sea surface temperatures, as well as the associated Aleutian Low, can account for only a small portion of the SSW variability. Instead, the major influence on long-term SSW variability is associated with long-term variability in amplitude of the stratospheric quasi biennial oscillation (QBO). The QBO influence is consistent with the well known Holton-Tan relationship, with SSW hiatus intervals associated with extended periods of particularly strong, deep QBO westerly phases. The results support recent studies that have highlighted the role of vertical coherence in the QBO when considering coupling between the QBO, the polar vortex and tropospheric circulation.</p>

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