scholarly journals Modelling the residual mean meridional circulation at different stages of stratospheric warming events

2020 ◽  
Author(s):  
Andrey V. Koval ◽  
Anna N. Bakhareva ◽  
Ksenia A. Didenko ◽  
Tatiana S. Ermakova ◽  
Nikolai M. Gavrilov ◽  
...  
Keyword(s):  
Northern Hemisphere ◽  
Meridional Circulation ◽  
Lower Thermosphere ◽  
Boreal Winter ◽  
Stratospheric Warming ◽  
Mean Flow ◽  
Middle Latitudes ◽  
Mean Meridional Circulation ◽  
First Time ◽  
Transformed Eulerian Mean

Abstract. Ensemble simulation of the general atmospheric circulation of the middle and upper atmosphere up to the lower thermosphere is performed using the 3-D nonlinear mechanistic numerical model MUAM. Residual mean meridional circulation (RMC) in terms of the Transformed Eulerian Mean is calculated for the boreal winter and changes in its vertical and meridional velocity components during different phases of simulated composite stratospheric warming (SW) events are studied. The simulation results show general decrease in RMC velocity components up to 30 % during and after SW in the mesosphere and lower thermosphere of the Northern Hemisphere. There are also increases in the downward and northward velocities at altitudes 50–70 km at the northern high latitudes. Associated changes in adiabatic heating/cooling rates can contribute to heating the stratosphere and cooling the mesosphere during the composite SW. The changes in the transport of conservative species (like ozone) during SWs are estimated. Weakening of ozone fluxes at the middle latitudes of the Northern Hemisphere may reach 30 % during SWs and 30–40 % after the events at the altitudes of stratospheric maximum of ozone concentration. Such statistically confident simulations of RMC reactions on SWs at altitudes up to the lower thermosphere are performed for the first time. The study of the residual meridional circulation is useful for effective analysis of wave impacts on the mean flow and for diagnostics of the transport of atmospheric gas species in the atmosphere.

scholarly journals Tropospheric circulation response to sudden stratospheric warming observed in January 2013

2020 ◽  
pp. 241-254
Author(s):  
A.I. Pogoreltsev ◽  
O.G. Aniskina ◽  
A.Y. Kanukhina ◽  
T.S. Ermakova ◽  
A.I. Ugryumov ◽  
...  
Keyword(s):  
Winter Season ◽  
Wave Activity ◽  
Cold Weather ◽  
Synoptic Situation ◽  
Dynamical Regime ◽  
Stratospheric Warming ◽  
Mean Flow ◽  
Sudden Stratospheric Warming ◽  
Middle Latitudes ◽  
Tropospheric Circulation

Analysis of the dynamical regime changes in the stratosphere during different phases of the Sudden Stratospheric Warming (SSW) that has been observed in January 2013 is presented. The different mechanisms of SSW influence on the tropospheric circulation through the stationary planetary waves (SPWs) reflection and/or increase in SPWs activity due to nonlinear interaction with the mean flow and their subsequent propagation into the troposphere are discussed. Three-dimensional wave activity flux and its divergence are determined using the UK Met Office data; the synoptic situation and its changes during the SSW events are analyzed. The wave activity penetrates downward from stratosphere into the troposphere and can affect weather processes during the SSW and right afterwards. It is this time that polar anticyclones can be formed at high latitudes, which quickly go southward along meridional directions and then deviate to the East at middle latitudes. Interestingly, the locations of polar anticyclone formations and subsequent displacements correspond to the regions of maximal horizontal wave activity fluxes connected with stratospheric processes. The results obtained allow us to suggest that accounting of stratospheric processes and their influence on the troposphere in winter season can improve the middle-range forecast of anticyclone formation and cold weather events at middle latitudes.

scholarly journals Coupled Interannual Variability of the Hadley and Ferrel Cells

2018 ◽  
Vol 31 (12) ◽  
pp. 4757-4773 ◽  
Author(s):  
Pablo Zurita-Gotor ◽  
Pablo Álvarez-Zapatero
Keyword(s):  
Angular Momentum ◽  
Meridional Circulation ◽  
Reanalysis Data ◽  
Hadley Cell ◽  
Boreal Winter ◽  
Austral Winter ◽  
Momentum Fluxes ◽  
Mean Meridional Circulation ◽  
Eddy Fluxes ◽  
The Mean

This work investigates the covariability in the strength of the Hadley and Ferrel cells on interannual time scales using reanalysis data. A significant correlation is found in both hemispheres only during boreal winter. For other seasons, only the outermost (subtropical) part of the Hadley cell is correlated with changes in the extratropical eddy momentum fluxes, as the eddies are unable to penetrate into the deep tropics. During boreal winter, the northern Hadley cell variability is driven by extratropical planetary momentum fluxes, but the mean meridional circulation response is primarily found below the level of maximum climatological outflow. Instead, at upper levels, changes in the zonal wind dominate the response to the anomalous eddy forcing. During austral winter, the southern Hadley cell is shielded from the extratropical eddy fluxes and its variability displays some of the characteristics of the angular momentum–conserving solution.

Wavenumber Decomposition and Extremes of Atmospheric Meridional Energy Transport in the Northern Hemisphere Midlatitudes

2020 ◽  
Author(s):  
Valerio Lembo ◽  
Gabriele Messori ◽  
Rune Graversen ◽  
Valerio Lucarini
Keyword(s):  
Northern Hemisphere ◽  
Energy Transport ◽  
Meridional Circulation ◽  
Planetary Waves ◽  
Destructive Interference ◽  
Constructive Interference ◽  
Total Transport ◽  
Mean Meridional Circulation ◽  
The Mean ◽  
Seasonal Dependence

<p>The atmospheric meridional energy transport in the Northern Hemisphere midlatitudes is mainly accomplished by planetary and synoptic waves. A decomposition into wave components highlights the strong seasonal dependence of the transport, with both the total transport and the contributions from planetary and synoptic waves peaking in winter. In both winter and summer months, poleward transport extremes primarily result from a constructive interference between planetary and synoptic motions. The contribution of the mean meridional circulation is close to climatology. Equatorward transport extremes feature a mean meridional equatorward transport in winter, while the planetary and synoptic modes mostly transport energy poleward. In summer, a systematic destructive interference occurs, with planetary modes mostly transporting energy equatorward and synoptic modes again poleward. This underscores that baroclinic conversion dominates regardless of season in the synoptic wave modes, whereas the planetary waves can be either free or forced, depending on the season.</p>

scholarly journals Modelling the residual mean meridional circulation at different stages of sudden stratospheric warming events

2021 ◽  
Vol 39 (2) ◽  
pp. 357-368
Author(s):  
Andrey V. Koval ◽  
Wen Chen ◽  
Ksenia A. Didenko ◽  
Tatiana S. Ermakova ◽  
Nikolai M. Gavrilov ◽  
...  
Keyword(s):  
Planetary Wave ◽  
Polar Region ◽  
Meridional Circulation ◽  
Lower Thermosphere ◽  
High Latitudes ◽  
Sudden Stratospheric Warming ◽  
The North ◽  
Mean Meridional Circulation ◽  
The Mean ◽  
Wave Induced

Abstract. Ensemble simulation of the atmospheric general circulation at altitudes up to the lower thermosphere is performed using the 3-D nonlinear mechanistic numerical model MUAM. The residual mean meridional circulation (RMC), which is the superposition of the mean Eulerian and wave-induced eddy components, is calculated for the boreal winter. Changes in the vertical and meridional RMC velocity components are analysed at different stages of a simulated composite sudden stratospheric warming (SSW) event averaged over 19 model runs. The simulation results show a general decrease in RMC velocity components up to 30 % during and after SSW in the mesosphere and lower thermosphere of the Northern Hemisphere. There are also increases in the downward and northward velocities at altitudes of 20–50 km at the northern polar latitudes during SSW. Associated vertical transport and adiabatic heating can contribute to warming the stratosphere and downward shifting of the stratopause during the composite SSW. The residual mean and eddy mass fluxes are calculated for different SSW stages. It is shown that before the SSW, planetary wave activity creates wave-induced eddy circulation cells in the northern upper stratosphere, which are directed upwards at middle latitudes, northward at high latitudes and downwards near the North Pole. These cells increase heat transport and adiabatic heating in the polar region. During SSW, the region of upward eddy vertical velocity is shifted to high latitudes, but the velocity is still downward near the North Pole. After SSW, upward eddy-induced fluxes span the entire polar region, producing upward transport and adiabatic cooling of the stratosphere and providing the return of the stratopause to higher altitudes. The obtained statistically significant results on the evolution of RMC and eddy circulation at different SSW stages at altitudes up to the lower thermosphere can be useful for a better understanding the mechanisms of planetary wave impacts on the mean flow and for the diagnostics of the transport of conservative tracers in the atmosphere.

scholarly journals Northern Hemisphere stratospheric winds in higher midlatitudes: longitudinal distribution and long-term trends

2015 ◽  
Vol 15 (4) ◽  
pp. 2203-2213 ◽  
Author(s):  
M. Kozubek ◽  
P. Krizan ◽  
J. Lastovicka
Keyword(s):  
Northern Hemisphere ◽  
Zonal Wind ◽  
Meridional Circulation ◽  
Meridional Wind ◽  
Reanalysis Data ◽  
Core Structure ◽  
Middle Latitudes ◽  
Meridional Winds ◽  
Long Term Trends

Abstract. The Brewer–Dobson circulation (mainly meridional circulation) is very important for stratospheric ozone dynamics and thus for the overall state of the stratosphere. There are some indications that the meridional circulation in the stratosphere could be longitudinally dependent, which would have an impact on the ozone distribution. Therefore, we analyse here the meridional component of the stratospheric wind at northern middle latitudes to study its longitudinal dependence. The analysis is based on the NCEP/NCAR-1 (National Centers for Environmental Prediction and the National Center for Atmospheric Research), MERRA (Modern Era-Retrospective Analysis) and ERA-Interim (European Centre for Medium-Range Weather Forecasts (ECMWF) Re-Analysis Interim) reanalysis data. The well-developed two-core structure of strong but opposite meridional winds, one in each hemisphere at 10 hPa at higher northern middle latitudes, and a less pronounced five-core structure at 100 hPa are identified. In the central areas of the two-core structure the meridional and zonal wind magnitudes are comparable. The two-core structure at 10 hPa is almost identical for all three different reanalysis data sets in spite of the different time periods covered. The two-core structure is not associated with tides. However, the two-core structure at the 10 hPa level is related to the Aleutian pressure high at 10 hPa. Zonal wind, temperature and the ozone mixing ratio at 10 hPa also exhibit the effect of the Aleutian high, which thus affects all parameters of the Northern Hemisphere middle stratosphere. Long-term trends in the meridional wind in the "core" areas are significant at the 99% level. Trends of meridional winds are negative during the period of ozone depletion development (1970–1995), while they are positive after the ozone trend turnaround (1996–2012). Meridional wind trends are independent of the sudden stratospheric warming (SSW) occurrence and the quasi-biennial oscillation (QBO) phase. The influence of the 11-year solar cycle on stratospheric winds has been identified only during the west phase of QBO. The well-developed two-core structure in the meridional wind illustrates the limitations of application of the zonal mean concept in studying stratospheric circulation.

scholarly journals Cross-Seasonal Influence of the December–February Southern Hemisphere Annular Mode on March–May Meridional Circulation and Precipitation

2015 ◽  
Vol 28 (17) ◽  
pp. 6859-6881 ◽  
Author(s):  
Fei Zheng ◽  
Jianping Li ◽  
Lei Wang ◽  
Fei Xie ◽  
Xiaofeng Li
Keyword(s):  
Southern Hemisphere ◽  
General Circulation ◽  
Large Scale ◽  
Meridional Circulation ◽  
Circulation Model ◽  
Annular Mode ◽  
Southern Hemisphere Annular Mode ◽  
Middle Latitudes ◽  
Mean Meridional Circulation ◽  
Sst Anomalies

Abstract New evidence suggests that interannual variability in zonal-mean meridional circulation and precipitation can be partially attributed to the Southern Hemisphere annular mode (SAM), the dominant mode of climate variability in the Southern Hemisphere (SH) extratropics. A cross-seasonal correlation exists between the December–February (DJF) SAM and March–May (MAM) zonal-mean meridional circulation and precipitation. This correlation is not confined to the SH: it also extends to the Northern Hemisphere (NH) subtropics. When the preceding DJF SAM is positive, counterclockwise, and clockwise meridional cells, accompanied by less and more precipitation, occur alternately between the SH middle latitudes and NH subtropics in MAM. In particular, less precipitation occurs in the SH middle latitudes, the SH tropics, and the NH subtropics, but more precipitation occurs in the SH subtropics and the NH tropics. A framework is built to explain the cross-seasonal impact of SAM-related SST anomalies. Evidence indicates that the DJF SAM tends to lead to dipolelike SST anomalies in the SH extratropics, which are referred to in this study as the SH ocean dipole (SOD). The DJF SOD can persist until the following MAM when it begins to modulate MAM meridional circulation and large-scale precipitation. Atmospheric general circulation model simulations further verify that MAM meridional circulation between the SH middle latitudes and the northern subtropics responds to the MAM SOD.

scholarly journals A Statistical Generalization of the Transformed Eulerian-Mean Circulation for an Arbitrary Vertical Coordinate System

2011 ◽  
Vol 68 (8) ◽  
pp. 1766-1783 ◽  
Author(s):  
Olivier Pauluis ◽  
Tiffany Shaw ◽  
Frédéric Laliberté
Keyword(s):  
Coordinate System ◽  
Heat Transport ◽  
Latent Heat ◽  
Meridional Circulation ◽  
Potential Temperature ◽  
Explicit Calculation ◽  
Vertical Coordinate ◽  
Mean Meridional Circulation ◽  
The Mean ◽  
Transformed Eulerian Mean

Abstract A new method is derived for approximating the mean meridional circulation in an arbitrary vertical coordinate system using only the time-mean and zonally averaged meridional velocity, meridional eddy transport, and eddy variance. The method is called the statistical transformed Eulerian mean (STEM) and can be viewed as a generalization of the transformed Eulerian mean (TEM) formulation. It is shown that the TEM circulation can be obtained from the STEM circulation in the limit of small eddy variance. The main advantage of the STEM formulation is that it can be applied to nonmonotonic coordinate systems such as the equivalent potential temperature. In contrast, the TEM formulation can only be applied to stratified variables. Reanalysis data are used to compare the STEM circulation to an explicit calculation of the mean meridional circulation on dry and moist isentropic surfaces based on daily data. It is shown that the STEM formulation accurately captures all the key features of the circulation. The error in the streamfunction is less than 10%. The STEM formulation is subsequently used to analyze the circulation induced by latent heat transport and to understand the processes responsible for setting the effective stratification in the troposphere. The eddy sensible heat transport dominates in the midlatitudes and in the winter hemisphere, while the eddy latent heat transport dominates in the subtropical regions and in the summer hemisphere. For the dry isentropic circulation, the approximate effective stratification is dominated by the vertical stratification, whereas for the moist isentropic circulation it is dominated by the eddy variance contribution. The importance of the eddy variance in setting the stratification is in agreement with previous work.

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