scholarly journals A quantitative measure of polar vortex strength using the functionM

2014 ◽  
Vol 119 (10) ◽  
pp. 5966-5985 ◽  
Author(s):  
Madeleine L. Smith ◽  
Adrian J. McDonald
Keyword(s):  
Polar Vortex ◽  
Quantitative Measure ◽  
Vortex Strength

scholarly journals Extending the Modular Earth Submodel System (MESSy v2.54) model hierarchy: the ECHAM/MESSy IdeaLized (EMIL) model setup

2020 ◽  
Vol 13 (11) ◽  
pp. 5229-5257
Author(s):  
Hella Garny ◽  
Roland Walz ◽  
Matthias Nützel ◽  
Thomas Birner
Keyword(s):  
Climate Model ◽  
Polar Vortex ◽  
Equilibrium Temperature ◽  
Earth System ◽  
Tracer Transport ◽  
Dynamical Core ◽  
Vortex Strength ◽  
Model Hierarchy ◽  
Model Setup ◽  
The Impact

Abstract. As models of the Earth system grow in complexity, a need emerges to connect them with simplified systems through model hierarchies in order to improve process understanding. The Modular Earth Submodel System (MESSy) was developed to incorporate chemical processes into an Earth System model. It provides an environment to allow for model configurations and setups of varying complexity, and as of now the hierarchy ranges from a chemical box model to a fully coupled chemistry–climate model. Here, we present a newly implemented dry dynamical core model setup within the MESSy framework, denoted as ECHAM/MESSy IdeaLized (EMIL) model setup. EMIL is developed with the aim to provide an easily accessible idealized model setup that is consistently integrated in the MESSy model hierarchy. The implementation in MESSy further enables the utilization of diagnostic chemical tracers. The setup is achieved by the implementation of a new submodel for relaxation of temperature and horizontal winds to given background values, which replaces all other “physics” submodels in the EMIL setup. The submodel incorporates options to set the needed parameters (e.g., equilibrium temperature, relaxation time and damping coefficient) to functions used frequently in the past. This study consists of three parts. In the first part, test simulations with the EMIL model setup are shown to reproduce benchmarks provided by earlier dry dynamical core studies. In the second part, the sensitivity of the coupled troposphere–stratosphere dynamics to various modifications of the setup is studied. We find a non-linear response of the polar vortex strength to the prescribed meridional temperature gradient in the extratropical stratosphere that is indicative of a regime transition. In agreement with earlier studies, we find that the tropospheric jet moves poleward in response to the increase in the polar vortex strength but at a rate that strongly depends on the specifics of the setup. When replacing the idealized topography to generate planetary waves by mid-tropospheric wave-like heating, the response of the tropospheric jet to changes in the polar vortex is strongly damped in the free troposphere. However, near the surface, the jet shifts poleward at a higher rate than in the topographically forced simulations. Those results indicate that the wave-like heating might have to be used with care when studying troposphere–stratosphere coupling. In the third part, examples for possible applications of the model system are presented. The first example involves simulations with simplified chemistry to study the impact of dynamical variability and idealized changes on tracer transport, and the second example involves simulations of idealized monsoon circulations forced by localized heating. The ability to incorporate passive and chemically active tracers in the EMIL setup demonstrates the potential for future studies of tracer transport in the idealized dynamical model.

scholarly journals The North Atlantic variability structure, storm tracks, and precipitation depending on the polar vortex strength

2004 ◽  
Vol 4 (5) ◽  
pp. 6127-6148 ◽  
Author(s):  
K. Walter ◽  
H.-F. Graf
Keyword(s):  
North Atlantic ◽  
Storm Track ◽  
Polar Vortex ◽  
The State ◽  
Storm Tracks ◽  
The Arctic ◽  
Ample Evidence ◽  
Vortex Strength ◽  
The North ◽  
The North Atlantic

Abstract. There is ample evidence that the state of the northern polar stratospheric vortex in boreal winter influences tropospheric variability. Therefore, the main teleconnection patterns over the North Atlantic are defined separately for winter episodes in which the zonal mean wind at 50 hPa and 65° N is above or below the critical Rossby velocity for zonal planetary wave one. It turns out that the teleconnection structure in the middle and upper troposphere differs considerably between the two regimes of the polar vortex, while this is not the case at sea level. If the "polar vortex is strong", there exists "one" meridional dipole structure of geopotential height in the upper and middle troposphere, which is situated in the central North Atlantic. If the "polar vortex is weak", there exist "two" such dipoles, one over the western and one over the eastern North Atlantic. Storm tracks (and precipitation related with these) are determined by mid and upper tropospheric conditions and we find significant differences of these parameters between the stratospheric regimes. For the strong polar vortex regime, in case of a negative upper tropospheric "NAO" index we find a blocking height situation over the Northeast Atlantic and the strongest storm track of all. It is reaching far north into the Arctic Ocean and has a secondary maximum over the Denmark Strait. Such storm track is not found in composites based on a classic NAO defined by surface pressure differences between the Icelandic Low and the Azores High. Our results show that it is essential to include the state of the upper dynamic boundary conditions (the polar vortex strength) in any study of the variability over the North Atlantic. Climate forecast based solely on the forecast of a "classic NAO" and further statistical downscaling may lead to the wrong conclusions if the state of the polar vortex is not considered as well.

scholarly journals The North Atlantic variability structure, storm tracks, and precipitation depending on the polar vortex strength

2005 ◽  
Vol 5 (1) ◽  
pp. 239-248 ◽  
Author(s):  
K. Walter ◽  
H.-F. Graf
Keyword(s):  
North Atlantic ◽  
Storm Track ◽  
Polar Vortex ◽  
The State ◽  
Storm Tracks ◽  
The Arctic ◽  
Boreal Winter ◽  
Vortex Strength ◽  
The North ◽  
The North Atlantic

Abstract. Motivated by the strong evidence that the state of the northern hemisphere vortex in boreal winter influences tropospheric variability, teleconnection patterns over the North Atlantic are defined separately for winter episodes where the zonal wind at 50hPa and 65° N is above or below the critical velocity for vertical propagation of zonal planetary wave 1. We argue that the teleconnection structure in the middle and upper troposphere differs considerably between the two regimes of the polar vortex, while this is not the case at sea level. If the polar vortex is strong, there exists one meridional dipole structure of geopotential height in the upper and middle troposphere, which is situated in the central North Atlantic. If the polar vortex is weak, there exist two such dipoles, one over the western and one over the eastern North Atlantic. Storm tracks (and precipitation related with these) are determined by mid and upper tropospheric conditions and we find significant differences of these parameters between the stratospheric regimes. For the strong polar vortex regime, in case of a negative upper tropospheric "NAO" index we find a blocking height situation over the Northeast Atlantic and the strongest storm track of all. It is reaching far north into the Arctic Ocean and has a secondary maximum over the Denmark Strait. Such storm track is not found in composites based on a classic NAO defined by surface pressure differences between the Icelandic Low and the Azores High. Our results suggest that it is important to include the state of the polar vortex strength in any study of the variability over the North Atlantic.

Wave Energy Associated with the Variability of the Stratospheric Polar Vortex

2007 ◽  
Vol 64 (7) ◽  
pp. 2683-2694 ◽  
Author(s):  
M. L. R. Liberato ◽  
J. M. Castanheira ◽  
L. de la Torre ◽  
C. C. DaCamara ◽  
L. Gimeno
Keyword(s):  
Rossby Wave ◽  
Wave Energy ◽  
General Circulation ◽  
Polar Vortex ◽  
Stratospheric Polar Vortex ◽  
Vortex Strength ◽  
Wave Forcing ◽  
Zonal Wavenumber ◽  
Baroclinic Modes ◽  
The Waves

Abstract A study is performed on the energetics of planetary wave forcing associated with the variability of the northern winter polar vortex. The analysis relies on a three-dimensional normal mode expansion of the atmospheric general circulation that allows partitioning the total (i.e., kinetic + available potential) atmospheric energy into the energy associated with Rossby and inertio-gravity modes with barotropic and baroclinic vertical structures. The analysis mainly departs from traditional ones in respect to the wave forcing, which is here assessed in terms of total energy amounts associated with the waves instead of heat and momentum fluxes. Such an approach provides a sounder framework than traditional ones based on Eliassen–Palm (EP) flux diagnostics of wave propagation and related concepts of refractive indices and critical lines, which are strictly valid only in the cases of small-amplitude waves and in the context of the Wentzel–Kramers–Brillouin–Jeffries (WKBJ) approximation. Positive (negative) anomalies of the energy associated with the first two baroclinic modes of the planetary Rossby wave with zonal wavenumber 1 are followed by a downward progression of negative (positive) anomalies of the vortex strength. A signature of the vortex vacillation is also well apparent in the lagged correlation curves between the wave energy and the vortex strength. The analysis of the correlations between individual Rossby modes and the vortex strength further confirmed the result from linear theory that the waves that force the vortex are those associated with the largest zonal and meridional scales. The two composite analyses of displacement- and split-type stratospheric sudden warming (SSW) events have revealed different dynamics. Displacement-type SSWs are forced by positive anomalies of the energy associated with the first two baroclinic modes of planetary Rossby waves with zonal wavenumber 1; split-type SSWs are in turn forced by positive anomalies of the energy associated with the planetary Rossby wave with zonal wavenumber 2, and the barotropic mode appears as the most important component. In respect to stratospheric final warming (SFW) events, obtained results suggest that the wave dynamics is similar to the one in displacement-type SSW events.

scholarly journals Global distribution of total ozone and lower stratospheric temperature variations

2003 ◽  
Vol 3 (4) ◽  
pp. 3411-3449 ◽  
Author(s):  
W. Steinbrecht ◽  
B. Hassler ◽  
H. Claude ◽  
P. Winkler ◽  
R. S. Stolarski
Keyword(s):  
Solar Cycle ◽  
Total Ozone ◽  
Southern Oscillation ◽  
Linear Trend ◽  
Polar Vortex ◽  
High Latitudes ◽  
Least Squares Regression ◽  
Quasi Biennial Oscillation ◽  
Vortex Strength ◽  
Low Latitudes

Abstract. This study gives an overview of interannual variations of total ozone and 50hPa temperature. It is based on newer and longer records from the 1979 to 2001 Total Ozone Monitoring Spectrometer (TOMS) and Solar Backscatter Ultraviolet (SBUV) instruments, and on US National Center for Environmental Prediction (NCEP) reanalyses. Multiple linear least squares regression is used to quantify various natural and anthropogenic influences. For most influences the total ozone and 50hPa temperature responses look very similar, reflecting a very close coupling. As a rule of thumb, a 10 Dobson Unit (DU) change in total ozone corresponds to a 1K change of 50hPa temperature. Large influences come from the linear trend term, up to −30 DU or −1.5 K/decade, from terms related to polar vortex strength, up to 50 DU or 5 K (typical, minimum to maximum), from tropospheric meteorology, up to 30 DU or 3 K, or from the Quasi-Biennial Oscillation (QBO), up to 25 DU or 2.5 K. The 11-year solar cycle, up to 25 DU or 2.5 K, El Niño/Southern Oscillation (ENSO), up to 10 DU or 1 K, are somewhat smaller influences. Stratospheric aerosol after the 1991 Pinatubo eruption lead to warming up to 3 K at low latitudes and to ozone depletion up to 40 DU at high latitudes. Response to QBO, polar vortex strength, and to a lesser degree to ENSO, exhibit an inverse correlation between low latitudes and higher latitudes. Responses to the solar cycle or 400 hPa temperature, however, have the same sign over most of the globe. Responses are usually zonally symmetric at low and mid-latitudes, but asymmetric at high latitudes. There, solar cycle, QBO or ENSO influence position and strength of the stratospheric anti-cyclones over the Aleutians and south of Australia.

scholarly journals Persistence of ozone anomalies in the Arctic stratospheric vortex in autumn

2012 ◽  
Vol 12 (11) ◽  
pp. 4817-4823 ◽  
Author(s):  
D. Blessmann ◽  
I. Wohltmann ◽  
R. Lehmann ◽  
M. Rex
Keyword(s):  
Potential Temperature ◽  
Initial Perturbation ◽  
Vortex Formation ◽  
Polar Vortex ◽  
Quantitative Measure ◽  
The Arctic ◽  
Early Winter ◽  
Dynamical Processes ◽  
Vertical Range ◽  
Formation Phase

Abstract. Dynamical processes during the formation phase of the Arctic stratospheric vortex in autumn (from September to December) can introduce considerable interannual variability in the amount of ozone that is incorporated into the vortex. Chemistry in autumn tends to remove part of this variability because ozone relaxes towards equilibrium. As a quantitative measure of how important dynamical variability during vortex formation is for the winter ozone abundances above the Arctic we analyze which fraction of an ozone anomaly induced during vortex formation persists until early winter (3 January). The work is based on the Lagrangian Chemistry Transport Model ATLAS. In a case study, model runs for the winter 1999–2000 are used to assess the fate of an ozone anomaly artificially introduced during the vortex formation phase on 16 September. In addition, runs with reduced resolution explore the sensitivity of the results to interannual changes in transport, mixing, temperatures and NOx. The runs provide information about the persistence of the induced ozone anomaly as a function of time, potential temperature and latitude. The induced ozone anomaly survives longer inside the polar vortex than outside the vortex. Half of the initial perturbation survives until 3 January at 550 K inside the polar vortex, with a rapid fall off towards higher levels, mainly due to NOx induced chemistry. Above 750 K the signal falls to values below 0.5%. Hence, dynamically induced ozone variability from the early vortex formation phase cannot significantly contribute to early winter variability above 750 K. At lower levels increasingly larger fractions of the initial perturbation survive, reaching 90% at 450 K. In this vertical range dynamical processes during the vortex formation phase are crucial for the ozone abundance in early winter.

scholarly journals Interaction of chemical and transport processes during the formation of the Arctic stratospheric polar vortex

2011 ◽  
Vol 11 (12) ◽  
pp. 32283-32300
Author(s):  
D. Blessmann ◽  
I. Wohltmann ◽  
R. Lehmann ◽  
M. Rex
Keyword(s):  
Initial Perturbation ◽  
Vortex Formation ◽  
Polar Vortex ◽  
Quantitative Measure ◽  
Transport Processes ◽  
The Arctic ◽  
Dynamical Processes ◽  
Stratospheric Polar Vortex ◽  
Relevant Variable ◽  
Formation Phase

Abstract. Dynamical processes during the formation phase of the Arctic polar vortex can introduce considerable interannual variability in the amount of ozone that is incorporated into the vortex. Chemistry in autumn and early winter tends to remove part of that variability because ozone relaxes towards equilibrium. As a quantitative measure of how relevant variable dynamical processes during vortex formation are for the winter ozone abundances above the Arctic we analyze which fraction of an ozone anomaly induced dynamically during vortex formation persists until mid-winter. The work is based on the Lagrangian Chemistry Transport Model ATLAS. Model runs for the winter 1999–2000 are used to assess the fate of an ozone anomaly artificially introduced during the vortex formation phase. From these runs we get detailed information about the persistence of the induced ozone variability over time, height and latitude. Induced ozone variability survives longer inside the polar vortex compared to outside. At 540 K inside the polar vortex half of the initial perturbation survives until mid-winter (3 January) with a rapid fall off towards higher levels, mainly due to NOx induced chemistry. At 660 K 10% of the initial perturbation survives. Above 750 K the signal falls to values below 0.5%. Hence, dynamically induced ozone variability from the vortex formation phase can not significantly contribute to mid-winter variability at levels above 750 K. At lower levels increasingly larger fractions of the initial perturbation survive, reaching 90% at 450 K. In this vertical range dynamical processes during the vortex formation phase are crucial for the ozone abundance in mid-winter.

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