Baroclinic Rossby Wave Forcing and Barotropic Rossby Wave Response to Stratospheric Vortex Variability

Castanheira, J. M.; Liberato, Margarida L. R.; Torre, Laura de la; Graf, Hans F.; DaCamara, Carlos C.

doi:10.1175/2008jas2862.1

Cited by 17 publications

(14 citation statements)

References 20 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…PV-based algorithms have been developed for the multilevel isentropic-coordinate primitive equations on the sphere, providing an opportunity to address the question of internal variability in a more realistic setting. This appears to be an essential next step, especially as the SW model likely misrepresents the transition between strong and weak vortex states, which is a baroclinic process in the real stratosphere (see, e.g., Castanheira et al 2009;Matthewman et al 2009). Further, compared to PV dissipation in the SW model, vertical shear and verticalscale-selective radiative damping (Haynes and Ward 1993) may provide a different way of removing small-scale PV structures, with the potential to alter the phase relation between the diabatic and dissipative fluxes critical to the vacillations.…”

Section: Discussionmentioning

confidence: 99%

Revisiting Vacillations in Shallow-Water Models of the Stratosphere Using Potential-Vorticity-Based Numerical Algorithms

MirRokni

Mohebalhojeh

Dritschel

2011

Journal of the Atmospheric Sciences

View full text Add to dashboard Cite

Polar vortex vacillations are investigated using long-term simulations of potential-vorticity (PV)-based shallow-water (SW) models for the stratosphere. In the models examined, mechanical forcing is applied through a time-independent topography mimicking tropospheric excitation of the stratosphere. Thermal forcing is applied through a linear relaxation of the mass field to a time-independent equilibrium state mimicking the radiative relaxation taking place in the stratosphere. The SW equations in the PV, velocity divergence, and acceleration divergence representation are solved for a range of resolutions using the ''diabatic contour-advective semi-Lagrangian'' (DCASL) algorithm and a standard pure semi-Lagrangian (SL) algorithm. Using very different numerical algorithms enables the determination of the degree of numerical sensitivity and the properties of the vacillations with much greater accuracy than in previous related studies.The focus here is on the Lagrangian or material evolution of the polar vortex. The authors examine quasiLagrangian diagnostics based on equivalent latitude, the mass enclosed by PV contours, and the terms involved in its time evolution. The PV field forms the basis for calculating quasi-Lagrangian diagnostics. Variations in the mass enclosed by a PV contour are associated with nonconservative processes such as diabatic heating, friction, and irreversible small-scale mixing. Generally, the mass of the polar vortex increases under the action of diabatic mass fluxes, whereas it decreases under the action of dissipative mass fluxes.The results herein differ from previous results reported at T42 resolution by Rong and Waugh in which a spectral transform algorithm is used to solve the SW equations in a vorticity-divergence-mass representation, and in which dissipation is provided by explicitly damping vorticity using hyperdiffusion. Except for the first large-amplitude oscillation, there is little sign of a clear, systematic phase shift between the dissipative and diabatic mass fluxes across the edge of the polar vortex, as proposed by Rong and Waugh as the main mechanism responsible for the vacillations. Concomitant with the absence of a phase shift, the vacillations tend to decay and occur intermittently. Rather than a phase shift, inherent fluctuations in both the diabatic and mass fluxes across the edge of the polar vortex appear to be responsible for the vacillations.

show abstract

Section: Discussionmentioning

confidence: 99%

Revisiting Vacillations in Shallow-Water Models of the Stratosphere Using Potential-Vorticity-Based Numerical Algorithms

MirRokni

Mohebalhojeh

Dritschel

2011

Journal of the Atmospheric Sciences

View full text Add to dashboard Cite

show abstract

“…It is known that stratospheric vortex anomalies are preceded by positive poleward anomalies in the zonal-mean heat fluxes in the lower stratosphere (Polvani and Waugh 2004) and increased baroclinic wave energy associated with planetary-scale waves (Liberato et al 2007;Castanheira et al 2009). However, the relationship between anomalous tropospheric planetary wave amplitudes and subsequent stratospheric variability is complex and dependent on the state of the stratosphere-troposphere system at the time of the generation of planetary wave anomalies (Reichler et al 2005).…”

Section: Introductionmentioning

confidence: 99%

Observed and simulated precursors of stratospheric polar vortex anomalies in the Northern Hemisphere

Kolstad

Charlton‐Perez

2010

Clim Dyn

View full text Add to dashboard Cite

The Northern Hemisphere stratospheric polar vortex is linked to surface weather. After Stratospheric Sudden Warmings in winter, the tropospheric circulation is often nudged towards the negative phase of the Northern Annular Mode (NAM) and the North Atlantic Oscillation (NAO). A strong stratospheric vortex is often associated with subsequent positive NAM/NAO conditions. For stratosphere-troposphere associations to be useful for forecasting purposes it is crucial that changes to the stratospheric vortex can be understood and predicted. Recent studies have proposed that there exist tropospheric precursors to anomalous vortex events in the stratosphere and that these precursors may be understood by considering the relationship between stationary wave patterns and regional variability. Another important factor is the extent to which the inherent variability of the stratosphere in an atmospheric model influences its ability to simulate stratosphere-troposphere links. Here we examine the lower stratosphere variability in 300-year pre-industrial control integrations from 13 coupled climate models. We show that robust precursors to stratospheric polar vortex anomalies are evident across the multi-model ensemble. The most significant tropospheric component of these precursors consists of a height anomaly dipole across northern Eurasia and large anomalies in upward stationary wave fluxes in the lower stratosphere over the continent. The strength of the stratospheric variability in the models was found to depend on the variability of the upward stationary wave fluxes and the amplitude of the stationary waves.

show abstract

“…There has been much discussion on the inter-relationships between PNA, NAO and AO and also on the influence of the stratospheric vortex variability in the troposphere (e.g. Baldwin and Dunkerton 1999;Ambaum and Hoskins 2002;Thompson et al 2002;Scaife et al 2005;Orsolini et al 2008;Castanheira et al 2009). For example, Baldwin and Dunkerton (2001) provided evidence that strength of the stratospheric vortex affects not only the phase of the AO/NAO indexes, but also the location of the mid-latitude storm tracks and the likelihood of storms.…”

Section: Introductionmentioning

confidence: 99%

The variable link between PNA and NAO in observations and in multi-century CGCM simulations

2010

View full text Add to dashboard Cite

The link between the Pacific/North American pattern (PNA) and the North Atlantic Oscillation (NAO) is investigated in reanalysis data (NCEP, ERA40) and multicentury CGCM runs for present day climate using three versions of the ECHAM model. PNA and NAO patterns and indices are determined via rotated principal component analysis on monthly mean 500 hPa geopotential height fields using the varimax criteria. On average, the multicentury CGCM simulations show a significant anti-correlation between PNA and NAO. Further, multi-decadal periods with significantly enhanced (high anti-correlation, active phase) or weakened (low correlations, inactive phase) coupling are found in all CGCMs. In the simulated active phases, the storm track activity near Newfoundland has a stronger link with the PNA variability than during the inactive phases. On average, the reanalysis datasets show no significant anti-correlation between PNA and NAO indices, but during the sub-period 1973-1994 a significant anti-correlation is detected, suggesting that the present climate could correspond to an inactive period as detected in the CGCMs. An analysis of possible physical mechanisms suggests that the link between the patterns is established by the baroclinic waves forming the North Atlantic storm track. The geopotential height anomalies associated with negative PNA phases induce an increased advection of warm and moist air from the Gulf of Mexico and cold air from Canada. Both types of advection contribute to increase baroclinicity over eastern North America and also to increase the low level latent heat content of the warm air masses. Thus, growth conditions for eddies at the entrance of the North Atlantic storm track are enhanced. Considering the average temporal development during winter for the CGCM, results show an enhanced Newfoundland storm track maximum in the early winter for negative PNA, followed by a downstream enhancement of the Atlantic storm track in the subsequent months. In active (passive) phases, this seasonal development is enhanced (suppressed). As the storm track over the central and eastern Atlantic is closely related to the NAO variability, this development can be explained by the shift of the NAO index to more positive values.

show abstract

Baroclinic Rossby Wave Forcing and Barotropic Rossby Wave Response to Stratospheric Vortex Variability

Cited by 17 publications

References 20 publications

Revisiting Vacillations in Shallow-Water Models of the Stratosphere Using Potential-Vorticity-Based Numerical Algorithms

Revisiting Vacillations in Shallow-Water Models of the Stratosphere Using Potential-Vorticity-Based Numerical Algorithms

Observed and simulated precursors of stratospheric polar vortex anomalies in the Northern Hemisphere

The variable link between PNA and NAO in observations and in multi-century CGCM simulations

Contact Info

Product

Resources

About