scholarly journals The Antarctic Oscillation Structure in an AOGCM with Interactive Stratospheric Ozone

2012 ◽  
Vol 2012 ◽  
pp. 1-12
Author(s):  
S. Brand ◽  
K. Dethloff ◽  
D. Handorf
Keyword(s):  
General Circulation ◽  
Planetary Wave ◽  
Middle Atmosphere ◽  
Stratospheric Ozone ◽  
Circulation Model ◽  
Wave Activity ◽  
Antarctic Oscillation ◽  
Wave Dynamics ◽  
Hemisphere Winter ◽  
The Antarctic

Based on 150-year equilibrium simulations using the atmosphere-ocean-sea ice general circulation model (AOGCM) ECHO-GiSP, the southern hemisphere winter circulation is examined focusing on tropo-stratosphere coupling and wave dynamics. The model covers the troposphere and strato-mesosphere up to 80 km height and includes an interactive stratospheric chemistry. Compared to the reference simulation without interactive chemistry, the interactive simulation shows a weaker polar vortex in the middle atmosphere and is shifted towards the negative phase of the Antarctic Oscillation (AAO) in the troposphere. Differing from the northern hemisphere winter situation, the tropospheric planetary wave activity is weakened. A detailed analysis shows, that the modelled AAO zonal mean signal behaves antisymmetrically between troposphere and strato-mesosphere. This conclusion is supported by reanalysis data and a discussion of planetary wave dynamics in terms of Eliassen-Palm fluxes. Thereby, the tropospheric planetary wave activity appears to be controlled from the middle atmosphere.

scholarly journals Stratospheric temperatures and tracer transport in a nudged 4-year middle atmosphere GCM simulation

2005 ◽  
Vol 5 (1) ◽  
pp. 961-1006 ◽  
Author(s):  
M. K. van Aalst ◽  
J. Lelieveld ◽  
B. Steil ◽  
C. Brühl ◽  
P. Jöckel ◽  
...  
Keyword(s):  
Interannual Variability ◽  
General Circulation ◽  
Middle Atmosphere ◽  
Circulation Model ◽  
Detailed Comparison ◽  
The Arctic ◽  
Cold Bias ◽  
Tracer Transport ◽  
Quasi Biennial Oscillation ◽  
The Antarctic

Abstract. We have performed a 4-year simulation with the Middle Atmosphere General Circulation Model MAECHAM5/MESSy, while slightly nudging the model’s meteorology in the free troposphere (below 113 hPa) towards ECMWF analyses. We show that the nudging 5 technique, which leaves the middle atmosphere almost entirely free, enables comparisons with synoptic observations. The model successfully reproduces many specific features of the interannual variability, including details of the Antarctic vortex structure. In the Arctic, the model captures general features of the interannual variability, but falls short in reproducing the timing of sudden stratospheric warmings. A 10 detailed comparison of the nudged model simulations with ECMWF data shows that the model simulates realistic stratospheric temperature distributions and variabilities, including the temperature minima in the Antarctic vortex. Some small (a few K) model biases were also identified, including a summer cold bias at both poles, and a general cold bias in the lower stratosphere, most pronounced in midlatitudes. A comparison 15 of tracer distributions with HALOE observations shows that the model successfully reproduces specific aspects of the instantaneous circulation. The main tracer transport deficiencies occur in the polar lowermost stratosphere. These are related to the tropopause altitude as well as the tracer advection scheme and model resolution. The additional nudging of equatorial zonal winds, forcing the quasi-biennial oscillation, sig20 nificantly improves stratospheric temperatures and tracer distributions.

scholarly journals Tropospheric Planetary Wave Dynamics and Mixture Modeling: Two Preferred Regimes and a Regime Shift

2007 ◽  
Vol 64 (10) ◽  
pp. 3521-3541 ◽  
Author(s):  
A. Hannachi
Keyword(s):  
General Circulation ◽  
Regime Shift ◽  
Planetary Wave ◽  
Clustering Algorithm ◽  
Spatial Clustering ◽  
Gaussian Mixture Models ◽  
Circulation Model ◽  
Gaussian Mixture ◽  
Stochastic Dynamical Systems ◽  
Wave Dynamics

Abstract Investigation of preferred structures of planetary wave dynamics is addressed using multivariate Gaussian mixture models. The number of components in the mixture is obtained using order statistics of the mixing proportions, hence avoiding previous difficulties related to sample sizes and independence issues. The method is first applied to a few low-order stochastic dynamical systems and data from a general circulation model. The method is next applied to winter daily 500-hPa heights from 1949 to 2003 over the Northern Hemisphere. A spatial clustering algorithm is first applied to the leading two principal components (PCs) and shows significant clustering. The clustering is particularly robust for the first half of the record and less for the second half. The mixture model is then used to identify the clusters. Two highly significant extratropical planetary-scale preferred structures are obtained within the first two to four EOF state space. The first pattern shows a Pacific–North American (PNA) pattern and a negative North Atlantic Oscillation (NAO), and the second pattern is nearly opposite to the first one. It is also observed that some subspaces show multivariate Gaussianity, compatible with linearity, whereas others show multivariate non-Gaussianity. The same analysis is also applied to two subperiods, before and after 1978, and shows a similar regime behavior, with a slight stronger support for the first subperiod. In addition a significant regime shift is also observed between the two periods as well as a change in the shape of the distribution. The patterns associated with the regime shifts reflect essentially a PNA pattern and an NAO pattern consistent with the observed global warming effect on climate and the observed shift in sea surface temperature around the mid-1970s.

scholarly journals Effects of Latitude-Dependent Gravity Wave Source Variations on the Middle and Upper Atmosphere

2021 ◽  
Vol 7 ◽  
Author(s):  
Erdal Yiğit ◽  
Alexander S. Medvedev ◽  
Manfred Ern
Keyword(s):  
General Circulation ◽  
Middle Atmosphere ◽  
Lower Thermosphere ◽  
Three Dimensional ◽  
Circulation Model ◽  
Wave Activity ◽  
Upper Atmosphere ◽  
Lower Atmosphere ◽  
Boreal Summer ◽  
Wave Source

Atmospheric gravity waves (GWs) are generated in the lower atmosphere by various weather phenomena. They propagate upward, carry energy and momentum to higher altitudes, and appreciably influence the general circulation upon depositing them in the middle and upper atmosphere. We use a three-dimensional first-principle general circulation model (GCM) with implemented nonlinear whole atmosphere GW parameterization to study the global climatology of wave activity and produced effects at altitudes up to the upper thermosphere. The numerical experiments were guided by the GW momentum fluxes and temperature variances as measured in 2010 by the SABER (Sounding of the Atmosphere using Broadband Emission Radiometry) instrument onboard NASA’s TIMED (Thermosphere Ionosphere Mesosphere Energetics Dynamics) satellite. This includes the latitudinal dependence and magnitude of GW activity in the lower stratosphere for the boreal summer season. The modeling results were compared to the SABER temperature and total absolute momentum flux and Upper Atmosphere Research Satellite (UARS) data in the mesosphere and lower thermosphere. Simulations suggest that, in order to reproduce the observed circulation and wave activity in the middle atmosphere, GW fluxes that are smaller than observed fluxes have to be used at the source level in the lower atmosphere. This is because observations contain a broader spectrum of GWs, while parameterizations capture only a portion relevant to the middle and upper atmosphere dynamics. Accounting for the latitudinal variations of the source appreciably improves simulations.

scholarly journals Stratospheric warming in Southern Hemisphere high latitudes since 1979

2009 ◽  
Vol 9 (13) ◽  
pp. 4329-4340 ◽  
Author(s):  
Y. Hu ◽  
Q. Fu
Keyword(s):  
Southern Hemisphere ◽  
General Circulation ◽  
Circulation Model ◽  
Warming Trend ◽  
Wave Activity ◽  
Anthropogenic Activity ◽  
High Latitudes ◽  
Stratospheric Warming ◽  
Sst Warming ◽  
The Antarctic

Abstract. In the present study, we show evidence of significant stratospheric warming over Southern Hemisphere high latitudes and large portions of the Antarctic polar region in winter and spring seasons, with a maximum warming of 7–8°C in September and October, using satellite Microwave Sounding Unit observations for 1979–2006. It is found that this warming is associated with increasing wave activity from the troposphere into the stratosphere, suggesting that the warming is caused by enhanced wave-driven adiabatic heating. We show that the stratospheric warming in Southern Hemisphere high latitudes has close correlations with sea surface temperature (SST) increases, and that general circulation model simulations forced with observed time-varying SSTs reproduce similar warming trend patterns in the Antarctic stratosphere. The simulated stratospheric warming is closely related to increasing wave activity in the Southern Hemisphere. These findings suggest that the stratospheric warming is likely induced by SST warming. As SST warming continues as a consequence of greenhouse gas increases due to anthropogenic activity, the stratospheric warming would also continue, which has important implications to the recovery of the Antarctic ozone hole.

scholarly journals Interannual variability and long term changes in planetary wave activity in the middle atmosphere observed by lidar

2006 ◽  
Vol 6 (6) ◽  
pp. 11299-11316 ◽  
Author(s):  
A. Hauchecorne ◽  
P. Keckhut ◽  
M. L. Chanin
Keyword(s):  
Interannual Variability ◽  
Planetary Wave ◽  
Middle Atmosphere ◽  
Stratospheric Ozone ◽  
Wave Activity ◽  
Temperature Data ◽  
Positive Trend ◽  
Stratospheric Temperature ◽  
Rayleigh Lidar

Abstract. The upwelling planetary wave activity (PW) from the troposphere controls the intensity of the equator to pole transport of stratospheric ozone by the Brewer-Dobson circulation and thereby modulates the total ozone content at mid- and high-latitudes. Rayleigh lidar temperature data obtained from 1981 to 2001 at mid-latitude were used to study the interannual variability of PW activity in winter (October to April). The spectrum of stratospheric temperature fluctuations exhibits 2 peaks corresponding to 2 dominant modes of free travelling Rossby waves known as 16 day- and 12 day-waves. The 12 day-wave activity is shown to be anticorrelated with the equatorial QBO wind at 40 hPa. During the period 1981–2000 the global PW activity shows a negative trend for months October to January and a positive trend in March and April.

scholarly journals The Coupled Stratosphere–Troposphere Response to Impulsive Forcing from the Troposphere

2005 ◽  
Vol 62 (9) ◽  
pp. 3337-3352 ◽  
Author(s):  
Thomas Reichler ◽  
Paul J. Kushner ◽  
Lorenzo M. Polvani
Keyword(s):  
General Circulation ◽  
Planetary Wave ◽  
Lower Boundary ◽  
Polar Vortex ◽  
Circulation Model ◽  
Wave Drag ◽  
Wave Activity ◽  
Independent Test ◽  
Mean Circulation

Abstract A simple atmospheric general circulation model (GCM) is used to investigate the transient response of the stratosphere–troposphere system to externally imposed pulses of lower-tropospheric planetary wave activity. The atmospheric GCM is a dry, hydrostatic, global primitive-equations model, whose circulation includes an active polar vortex and a tropospheric jet maintained by baroclinic eddies. Planetary wave activity pulses are generated by a perturbation of the solid lower boundary that grow and decay over a period of 10 days. The planetary wave pulses propagate upward and break in the stratosphere. Subsequently, a zonal-mean circulation anomaly propagates downward, often into the troposphere, at lags of 30–100 days. The evolution of the response is found to be dependent on the state of the stratosphere–troposphere system at the time the pulse is generated. In particular, on the basis of a large ensemble of these simulations, it is found that the length of time the signal takes to propagate downward from the stratosphere is controlled by initial anomalies in the zonal-mean circulation and in the zonal-mean wave drag. Criteria based on these anomaly patterns can be used, therefore, to predict the long-term surface response of the stratosphere–troposphere system to a planetary wave pulse up to 90 days after the pulse is generated. In an independent test, it is verified that the initial states that most strongly satisfy these criteria respond in the expected way to the lower-tropospheric wave activity pulse.

scholarly journals Results of an interactively coupled atmospheric chemistry – general circulation model: Comparison with observations

2001 ◽  
Vol 19 (4) ◽  
pp. 435-457 ◽  
Author(s):  
R. Hein ◽  
M. Dameris ◽  
C. Schnadt ◽  
C. Land ◽  
V. Grewe ◽  
...  
Keyword(s):  
General Circulation Model ◽  
Atmospheric Chemistry ◽  
General Circulation ◽  
Middle Atmosphere ◽  
Stratospheric Ozone ◽  
Circulation Model ◽  
Ozone Layer ◽  
The Arctic ◽  
Time Step ◽  
Stratospheric Dynamics

Abstract. The coupled climate-chemistry model ECHAM4.L39(DLR)/CHEM is presented which enables a simultaneous treatment of meteorology and atmospheric chemistry and their feedbacks. This is the first model which interactively combines a general circulation model with a chemical model, employing most of the important reactions and species necessary to describe the stratospheric and upper tropospheric ozone chemistry, and which is computationally fast enough to allow long-term integrations with currently available computer resources. This is possible as the model time-step used for the chemistry can be chosen as large as the integration time-step for the dynamics. Vertically the atmosphere is discretized by 39 levels from the surface up to the top layer which is centred at 10 hPa, with a relatively high vertical resolution of approximately 700 m near the extra-tropical tropopause. We present the results of a control simulation representing recent conditions (1990) and compare it to available observations. The focus is on investigations of stratospheric dynamics and chemistry relevant to describe the stratospheric ozone layer. ECHAM4.L39(DLR)/CHEM reproduces main features of stratospheric dynamics in the arctic vortex region, including stratospheric warming events. This constitutes a major improvement compared to earlier model versions. However, apparent shortcomings in Antarctic circulation and temperatures persist. The seasonal and interannual variability of the ozone layer is simulated in accordance with observations. Activation and deactivation of chlorine in the polar stratospheric vortices and their inter-hemispheric differences are reproduced. Considering methane oxidation as part of the dynamic-chemistry feedback results in an improved representation of the spatial distribution of stratospheric water vapour concentrations. The current model constitutes a powerful tool to investigate, for instance, the combined direct and indirect effects of anthropogenic trace gas emissions.Key words. Atmospheric composition and structure (middle atmosphere – composition and chemistry) – Meteorology and atmospheric dynamics (general circulation; middle atmosphere dynamics)

How Does Interhemispheric Coupling Contribute to Cool Down the Summer Polar Mesosphere?

2016 ◽  
Vol 29 (24) ◽  
pp. 8807-8821 ◽  
Author(s):  
Bodil Karlsson ◽  
Erich Becker
Keyword(s):  
Gravity Wave ◽  
General Circulation ◽  
Planetary Wave ◽  
Circulation Model ◽  
Internal Variability ◽  
Wave Drag ◽  
Wave Activity ◽  
Current View ◽  
Residual Circulation ◽  
Opposite Hemisphere

Abstract Interhemispheric coupling is commonly associated with events of high planetary wave activity in the winter stratosphere triggering a heating of the polar mesopause region in the opposite hemisphere. Here, a more fundamental role that this mechanism plays in the absence of planetary wave variability is highlighted. This study focuses directly on the mesospheric part of the coupling chain, which is induced by the gravity wave drag in the winter mesosphere. To investigate the effect that the winter residual flow has on the summertime high-latitude upwelling, the Kühlungsborn Mechanistic General Circulation Model (KMCM) is used to compare a control simulation to runs where the parameterized gravity waves are removed from the winter hemisphere. The model response in the summer mesosphere reveals that the winter mesospheric residual circulation fosters a net (and substantial) cooling of the summer polar mesopause. These results offer an extension of the current view of interhemispheric coupling: from a mode of internal variability to a constant, gravity wave–driven phenomenon that is modulated by planetary wave activity.

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