in a Stratospheric Model (original) (raw)
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Annales Geophysicae, 2010
Three datasets (the NCEP-NCAR reanalysis, the ERA-40 reanalysis and the LMDz-GCM), are used to analyze the relationships between large-scale dynamics of the stratosphere and the tropospheric planetary waves during the Northern Hemisphere (NH) winter. First, a crossspectral analysis clarifies the time scales at which downward propagation of stratospheric anomalies occurs in the lowfrequency band (that is at periods longer than 50 days). At these periods the strength of the polar vortex, measured by the 20-hPa Northern Annular Mode (NAM) index and the wave activity flux, measured by the vertical component of the Eliassen-Palm flux (EPz) from both the troposphere and the stratosphere, are significantly related with each other and in lead-lag quadrature. While, in the low-frequency band of the downward propagation, the EPz anomalies of the opposite sign around NAM extremes drive the onset and decay of NAM events, we found that the EPz anomalies in the troposphere, are significantly larger after stratospheric vortex anomalies than at any time before. This marked difference in the troposphere is related to planetary waves with zonal wavenumbers 1-3, showing that there is a tropospheric planetary wave response to the earlier state of the stratosphere at low frequencies. We also find that this effect is due to anomalies in the EPz issued from the northern midlatitudes and polar regions.
A Study of Stationary Wave-Wave Interactions in a Low Order Stratospheric Model
Journal of the Meteorological Society of Japan. Ser. II
Interactions among stationary planetary waves in a low-order spherical stratospheric model are studied both analytically and numerically. A triad of interacting waves is examined using a steadystate hemispheric quasi-geostrophic model with a mean zonal wind in solid body rotation. Due to the structure of the model basic state, dissipation is required for the waves to interact. It is found that the nonlinear structure of the two gravest forced modes is independent of their relative position only if the third mode is unforced at the lower boundary. In this case the degree to which the nonlinearities act to amplify or phase shift the linear waves is shown to be dependent upon the vertical propagation characteristics of the waves. Large horizontal scale waves and weak zonal westerlies are found to be conditions which can result in significant amplitude changes due to the wave-wave interaction. As the scale of the wave is reduced and/or the speed of the mean zonal westerlies is increased, the predominant changes occur in the wave phases. Numerical solutions using realistic boundary forcing amplitudes and realistic dissipation are found to be only weakly nonlinear, despite the fact that the planetary waves distort considerably the polar vortex.
Stratospheric wave-mean flow interaction: Simple modeling
Journal of Atmospheric and Solar-Terrestrial Physics, 2006
We show that the interaction between planetary waves and the stratospheric zonal mean flow results in bi-modal (directreverse flow) or unimodal state depending on wave number of the waves. First we demonstrate this using a simple nonlinear dynamic system of the wave-flow interaction, which has two stable equilibrium states and one unstable state (attractors) in its phase space. Then we compare this model dynamics with the stratosphere dynamics using the same dynamical variables and a similar parameter range in the National Centers for Environmental Prediction (NCEP) Reanalysis data. This comparison supports the tendency for the states of planetary wave-zonal mean flow in the upper stratosphere to be bi-modal for wave number 2 and unimodal for wave number 1. Crown
Planetary wave activity in the Arctic and Antarctic lower stratospheres during 2007 and 2008
Atmospheric Chemistry and Physics Discussions, 2009
Temperature data from the COSMIC GPS-RO satellite constellation are used to study planetary wave activity in both polar stratospheres from September 2006 until November 2008. One major and several minor sudden stratospheric warmings (SSWs) were recorded during the boreal winters of phology is studied using space-time spectral analysis while individual waves are extracted using a linear least squares fitting technique. Results show the planetary wave frequency and zonal wavenumber distribution varying between hemisphere and altitude. Most of the large Northern Hemisphere wave activity is associated with the winter SSWs, while the largest amplitude waves in the Southern Hemisphere occur during 10 spring. Planetary wave activity during the 2006/2007 and 2007/2008 Arctic SSWs is due largely to travelling waves with zonal wavenumbers |s|=1 and |s|=2 having periods of 12, 16 and 23 days and stationary waves with s=1 and s=2. The latitudinal variation of wave amplification during the two Northern Hemisphere winters is studied. Most planetary waves show different structure and behaviour during each winter. Abrupt 15 changes in the latitude of maximum amplitude of some planetary waves is observed co-incident in time with some of the SSWs. 2005). However, planetary waves generally propagate westward relative to the zonal 14602 ACPD 9Abstract Introduction Conclusions References Tables Figures Back Close Full Screen / Esc Printer-friendly Version Interactive Discussion mean flow (Holton, 2004).
Topographically forced planetary wave breaking in the stratosphere
Geophysical Research Letters, 1995
The effects of topographi•y forced planetary wave Ixeaking on eddy translxxt in the smu•here are examined for zca• • 1 and 2. •y averaged basic states represent•ve ofN• • (NH) and Southern Hemisphere (Sift) wimer conditions are used. Waves 1 and 2 each have significant wave breaking effects in the extratropical smU•ahere during NH winter, whereas only wave 1 is important during SH winter. During NH winta', eddy•
On the presence of equatorial waves in the lower stratosphere of a general circulation model
Atmospheric Chemistry and Physics, 2014
To challenge the hypothesis that equatorial waves in the lower stratosphere are essentially forced by convection, we use the LMDz atmospheric model extended to the stratosphere and compare two versions having very different convection schemes but no quasi-biennial oscillation (QBO). The two versions have realistic time mean precipitation climatologies but very different precipitation variabilities. Despite these differences, the equatorial stratospheric Kelvin waves at 50 hPa are almost identical in the two versions and quite realistic. The Rossby gravity waves are also very similar but significantly weaker than in observations. We demonstrate that this bias on the Rossby gravity waves is essentially due to a dynamical filtering occurring because the model zonal wind is systematically westward. During a westward phase of the QBO, the ERA-Interim Rossby gravity waves compare well with those in the model. These results suggest that (i) in the model the effect of the convection scheme on the waves is in part hidden by the dynamical filtering, and (ii) the waves are produced by other sources than equatorial convection. For the Kelvin waves, this last point is illustrated by an Eliassen and Palm flux analysis, showing that in the model they come more from the subtropics and mid-latitude regions, whereas in the ERA-Interim reanalysis the sources are more equatorial. We show that non-equatorial sources are also significant in reanalysis data sets as they explain the presence of the Rossby gravity waves in the stratosphere. To illustrate this point, we identify situations with large Rossby gravity waves in the reanalysis middle stratosphere for dates selected when the stratosphere is dynamically separated from the equatorial troposphere. We refer to this process as a stratospheric reloading.
Geophysical Research Letters, 2007
1] The paper presents clear evidence of zonally symmetric planetary waves with very large amplitudes present in the UK Met Office zonal wind data of the Northern Hemisphere stratosphere in the winter of 2003 -2004. The spectral analysis reveals that three prevailing periods of $23, 17 and 11 days contribute to the observed zonally symmetric oscillations. These waves are extracted from the data and their amplitudes and phases are studied in detail depending on height and latitude. The wave amplitudes -particularly those of the 11-and the 17-day zonally symmetric wavesclearly indicate the presence of two latitudinal branches of amplifications centred at 50-60°N and 20-30°N. The phase analysis shows that these waves are vertically upward propagating waves and that the waves from the high-latitude and tropical branches are almost out of phase. A possible forcing mechanism is suggested. The zonally symmetric waves play an important role in coupling the dynamical regimes of the high-and low-latitude stratosphere particularly during the major stratwarm event in the Arctic winter of 2003 -2004. Citation: Pancheva, D. V., P. J. Mukhtarov, and B. A. Andonov (2007), Zonally symmetric oscillations in the Northern Hemisphere stratosphere during the winter of
The Annual Wave in the Temperature of the Low Stratosphere
J Atmos Sci, 1970
A quantitative examination of the annual cycle in the tropical tropopause temperatures, tropical ascent, momentum balance, and wave driving is performed using ECMWF analyses to determine how the annual cycle in tropical tropopause temperatures arises. Results show that the annual cycle in tropical tropopause temperatures is driven by the annual variation in ascent and consequent dynamical (adiabatic) cooling at the tropical tropopause. Mass divergence local to the tropical tropopause has the dominant contribution to ascent near the tropical tropopause. The annual cycle in mass divergence, and the associated meridional flow, near the tropical tropopause is driven by Eliassen-Palm (EP) flux divergence, that is, wave dissipation. The EP flux divergence near the tropical tropopause is dominated by stationary waves with both the horizontal and vertical components of the EP flux contributing. However, the largest annual cycle is in the divergence of the vertical EP flux and in particular from the contribution in the vertical flux of zonal momentum. These results do not match the existing theory that the annual cycle is driven by the wave dissipation in the extratropical stratosphere, that is, the stratospheric pump. It is suggested that the annual cycle is linked to equatorial Rossby waves forced by convective heating in the tropical troposphere.
Quasi-Stationary Planetary Waves in Mid-Latitude Stratosphere–Mesosphere in Winter 2011-2020
ГРААЛЬ НАУКИ, 2021
The 10-year climatology (2011–2020) of quasi-stationary planetary waves in the mid-latitude stratosphere and mesosphere (40–50N, up to 90 km) has been analyzed. Longitude–altitude sections of geopotential height and ozone have been obtained using the Aura MLS satellite data. It is found that stationary wave 1 propagates into the mesosphere from the North American High and Icelandic Low, which are adjacent surface pressure anomalies in the structure of stationary wave 2. Unexpectedly, the strongest pressure anomaly in the Aleutian Low region does not contribute to the stationary wave 1 formation in the mesosphere. The vertical phase transformations of stationary waves in geopotential height and ozone show inconsistencies that should be studied separately.
Planetary wave activity in the polar lower stratosphere
Atmospheric Chemistry and Physics, 2010
Temperature data from the COSMIC GPS-RO satellite constellation are used to study the distribution and variability of planetary wave activity in the low to midstratosphere (15-40 km) of the Arctic and Antarctic from September 2006 until March 2009. Stationary waves are separated from travelling waves and their amplitudes, periods and small-scale vertical distribution then examined. COS-MIC observed short lived (less than two weeks and less than 5 km vertically) but large enhancements in planetary wave amplitudes occurring regularly throughout all winters in both hemispheres. In contrast to recent Arctic winters, eastward wave activity during 2008-2009 was significantly reduced during the early part of the winter and immediately prior to the major SSW. The eastward waves which did exist had similar periods to the two preceding winters (∼ 16-20 days). A westward wave with zonal wavenumber two, with distinct peaks at 22 km and 35 km and period around 16-24 days, as well as a stationary wave two were associated with the 2009 major SSW. In the Southern Hemisphere, the height structure of planetary wave amplitudes also exhibited fluctuations on short time and vertical scales superimposed upon the broader seasonal cycle. Significant inter-annual variability in planetary wave amplitude and period are noticed, with the times of cessation of significant activity also varying.