Stationary waves in the wintertime mesosphere: Evidence for gravity wave filtering by stratospheric planetary waves (original) (raw)
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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.
Characterisation of quasi-stationary planetary waves in the Northern MLT during summer
Journal of Atmospheric and Solar-Terrestrial Physics, 2015
Observations of planetary wave (PW) activity in the northern hemisphere, polar summer mesosphere and lower thermosphere (MLT) are presented. Meteor winds from a northern hemisphere chain of Su-perDARN radars have been used to monitor the meridional wind along a latitude band (51-66°N) in the MLT. A stationary PW-like longitudinal structure with a strong zonal PW number 1 characteristic is persistently observed year-to-year during summer. Here we characterize the amplitude and the phase structure of this wave in the MLT. The Modern-Era Retrospective Analysis for Research and Application (MERRA) of the NASA Global Modelling and Assimilation Office has been used to evaluate possible sources of the observed longitudinal perturbation in the mesospheric meridional wind by investigating the amplitudes and phases of PWs in the underlying atmosphere. The investigation shows that neither gravity wave modulation by lower atmospheric PWs nor direct propagation of PWs from the lower atmosphere are a significant cause of the observed longitudinal perturbation. However, the data are not of sufficient scope to investigate longitudinal differences in gravity wave sources, or to separate the effects of instabilities and inter-hemispheric propagation as possible causes for the large PW present in the summer MLT.
Trends of mesospheric gravity waves at northern middle latitudes during summer
Journal of Geophysical Research, 2011
Recent investigations of the seasonal variation of the activity of gravity waves in the mesosphere/lower thermosphere (MLT) at middle and high latitudes suggest a semiannual variation with maxima during winter and summer and minima during the equinoxes. It is generally assumed that this annual cycle is determined by filtering processes due to the background winds in the stratosphere and lower mesosphere. On the other side, long-term observations of mesospheric winds at Juliusruh (55°N, 13°E) since 1990 indicate a stable increase of westward directed winds below 80 km (negative trends) during summer, as, e.g., clearly evident in monthly means in July. Here, we are studying how these long-term changes of winds are related to trends of the activity of gravity waves (GW) with periods between 3-6 hours. Our results show that the observed zonal wind trend at about 75 km during July goes along with an enhancement of the GW activity at altitudes above 80 km. Indeed, also the year-to-year variation of maxima of the observed westward directed winds at altitudes near 75 km and the GW activity at about 80 km are significantly correlated. Our results stimulate the further study of long-term wind changes and corresponding gravity wave trends.
Modeling study of mesospheric planetary waves: genesis and characteristics
Annales Geophysicae, 2004
The Numerical Spectral Model (NSM) extends from the ground into the thermosphere and incorporates Hines' Doppler Spread Parameterization for smallscale gravity waves (GWs). In the present version of the model we account for a tropospheric heat source in the zonal mean (m=0), which reproduces qualitatively the observed zonal jets near the tropopause and the accompanying reversal in the latitudinal temperature variations. In the study presented here, we discuss the planetary waves (PWs) that are solely generated internally, i.e. without the explicit excitation sources related to tropospheric convection or topography. Our analysis shows that PWs are not produced when the zonally averaged heat source into the atmosphere is artificially suppressed, and that the PWs are generally weaker when the tropospheric source is not applied. Instabilities associated with the zonal mean temperature, pressure and wind fields, which still need to be explored, are exciting PWs that have amplitudes in the mesosphere comparable to those observed. Three classes of PWs are generated in the NSM. (1) Rossby type PWs, which slowly propagate westward relative to the mean zonal flow, are carried by the winds so that they appear (from the ground) to propagate, respectively, eastward and westward in the winter and summer hemispheres below 80 km. Depending on the zonal wave number and magnitudes of the zonal winds, and under the influence of the equatorial oscillations, these PWs typically have periods between 2 and 20 days. Their horizontal wind amplitudes can exceed 40 m/s in the lower mesosphere. (2) Rossby-gravity waves, which propagate westward at low latitudes and have periods around 2 days for zonal wave numbers m=2 to 4. (3) Eastward propagating equatorial Kelvin waves, which are generated in the upper mesosphere with periods between 1 and 3 days depending on m. A survey of the PWs reveals that the largest wind amplitudes tend to occur below 80 km in the winter hemisphere; but above that altitude the amplitudes
Atmospheric Chemistry and Physics, 2015
This study investigates the effect of stratospheric sudden warmings (SSWs) on planetary wave (PW) activity in the mesosphere-lower thermosphere (MLT). PW activity near 95 km is derived from meteor wind data using a chain of eight SuperDARN radars at high northern latitudes that span longitudes from 150 • W to 25 • E and latitudes from 51 to 66 • N. Zonal wave number 1 and 2 components were extracted from the meridional wind for the years 2000-2008. The observed wintertime PW activity shows common features associated with the stratospheric wind reversals and the accompanying stratospheric warming events. Onset dates for seven SSW events accompanied by an elevated stratopause (ES) were identified during this time period using the Specified Dynamics Whole Atmosphere Community Climate Model (SD-WACCM). For the seven events, a significant enhancement in wave number 1 and 2 PW amplitudes near 95 km was found to occur after the wind reversed at 50 km, with amplitudes maximizing approximately 5 days after the onset of the wind reversal. This PW enhancement in the MLT after the event was confirmed using SD-WACCM. When all cases of polar cap wind reversals at 50 km were considered, a significant, albeit moderate, correlation of 0.4 was found between PW amplitudes near 95 km and westward polar-cap stratospheric winds at 50 km, with the maximum correlation occurring ∼ 3 days after the maximum westward wind. These results indicate that the enhancement of PW amplitudes near 95 km is a common feature of SSWs irrespective of the strength of the wind reversal.
Journal of Geophysical Research, 2011
In this work absolute values of gravity wave (GW) momentum flux are derived from global temperature measurements by the satellite instruments High Resolution Dynamics Limb Sounder (HIRDLS) and Sounding of the Atmosphere using Broadband Emission Radiometry (SABER). Momentum fluxes in the stratosphere are derived for both instruments and for SABER in the whole mesosphere. The large-scale atmospheric background state is removed by a two-dimensional Fourier decomposition in longitude and time, covering even planetary-scale waves with periods as short as 1-2 days. Therefore, it is possible to provide global distributions of GW momentum flux from observations for the first time in the mesosphere. Seasonal as well as longer-term variations of the global momentum flux distribution are discussed. GWs likely contribute significantly to the equatorward tilt of the polar night jet and to the poleward tilt of the summertime mesospheric jet. Our results suggest that GWs can undergo large latitudinal shifts while propagating upward. In particular, GWs generated by deep convection in the subtropical monsoon regions probably contribute significantly to the mesospheric summertime wind reversal at mid-and high latitudes. Variations in the GW longitudinal distribution caused by those convectively generated GWs are still observed in the mesosphere and could be important for the generation of the quasi two-day wave. Indications for quasi-biennial oscillation (QBO) induced variations of GW momentum flux are found in the subtropics. Also variations at time scales of about one 11-year solar cycle are observed and might indicate a negative correlation between solar flux and GW momentum flux.
Seasonal variation of mesospheric waves at northern middle and high latitudes
Journal of Atmospheric and Solar-Terrestrial Physics, 2010
The seasonal variation of the wave activity in the mesosphere/lower thermosphere is investigated using wind measurements with meteor and MF radars at Juliusruh (551N, 131E) and Andenes (691N, 161E), as well as on the basis of the simulated annual cycle using a gravity-wave resolving mechanistic general circulation model. For the observations, proxies for the activity of gravity waves (GWs) and waves with longer periods are computed from wind variances for defined bandwidths. Our corresponding proxy for the simulated GWs is the non-rotational kinetic energy due to the resolved mesoscales. Both observational and computational results show the strongest GW energy during winter and a secondary maximum during summer. Additional observational analysis of short-period GWs yields a more pronounced summer maximum. The semi-annual variation is consistent with the selective filtering of westward and eastward GWs by the mean zonal wind. The latitudinal dependence during summer is characterized by stronger GW energy between 65 and 85 km at middle latitudes than at polar latitudes, and a corresponding upward shift of the wind reversal towards the pole which is also reflected by the simulated GW drag. Also the observed oscillations with periods from 2 to 4 days show a latitudinal dependence and a clear seasonal cycle which is related to the mean zonal wind shear.
Journal of Atmospheric and Terrestrial Physics, 1996
A linearised numerical model has been used to simulate the stationary planetary waves (SPW) structure and investigate its influence on a zonally averaged circulation in the mesosphere and lower thermosphere. The wave-activity density, Eliassen-Palm flux, and its divergence cross-sections are used as a diagnostic of wave propagation and wave-mean flow interaction. The results of numerical simulations show that SPW can provide the substantial accelerations of the mean flow which are comparable with the accelerations due to the breakdown of internal gravity waves and atmospheric tides, and it is necessary to develop three-dimensional models of the general circulation of the lower thermosphere, taking account of the effects of gravity wave and tidal drag. The influence of the eddy thermal conduction and viscosity on the formation of SPW structure in the mesosphere and lower thermosphere and on the distribution of the mean flow accelerations due to SPW dissipation is discussed.
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).