scholarly journals The climatology, propagation and excitation of ultra-fast Kelvin waves as observed by meteor radar, Aura MLS, TRMM and in the Kyushu-GCM

2011 ◽  
Vol 11 (10) ◽  
pp. 29479-29525 ◽  
Author(s):  
R. N. Davis ◽  
Y.-W. Chen ◽  
S. Miyahara ◽  
N. J. Mitchell
Keyword(s):  
General Circulation ◽  
Lower Thermosphere ◽  
Central Africa ◽  
Circulation Model ◽  
Kelvin Waves ◽  
Convective Heating ◽  
Rainfall Time Series ◽  
Meteor Radar ◽  
Zonal Wavenumber ◽  
The Waves

Abstract. Wind measurements from a meteor radar on Ascension Island (8° S, 14° W) and simultaneous temperature measurements from the Aura MLS instrument are used to characterise ultra-fast Kelvin waves (UFKW) of zonal wavenumber 1 (E1) in the mesosphere and lower thermosphere (MLT) in the years 2005–2010. These observations are compared with some predictions of the Kyushu-general circulation model. Good agreement is found between observations of the UFKW in the winds and temperatures, and also with the properties of the waves in the Kyushu-GCM. UFKW are found at periods between 2.5–4.5 days with amplitudes of up to 40 m s−1 in the zonal winds and 6 K in the temperatures. The average vertical wavelength is found to be 44 km. Amplitudes vary with latitude in a Gaussian manner with the profiles centred over the equator. Dissipation of the waves results in monthly-mean eastward accelerations of 0.2–0.9 m s−1 day−1 at heights around 95 km, with 5-day mean peak values of 4 m s−1 day−1. Largest wave amplitudes and variances are observed over Indonesia and central Africa and may be a result of very strong moist convective heating over those regions. Rainfall data from TRMM are used as a proxy for latent-heat release in an investigation of the excitation of these waves. No strong correlation is found between the occurrence of large-amplitude mesospheric UFKW events and either the magnitude of the equatorial rainfall or the amplitudes of E1 signatures in the rainfall time series, indicating that either other sources or the propagation environment are more important in determining the amplitude of UFKW in the MLT. A strong semiannual variation in wave amplitudes is observed. Intraseasonal oscillations (ISOs) with periods 25–60 days are evident in the zonal background winds, zonal-mean temperature, UFKW amplitudes, UFKW accelerations and the rainfall rate. This suggests that UFKW play a role in carrying the signature of tropospheric ISOs to the MLT region.

scholarly journals The climatology, propagation and excitation of ultra-fast Kelvin waves as observed by meteor radar, Aura MLS, TRMM and in the Kyushu-GCM

2012 ◽  
Vol 12 (4) ◽  
pp. 1865-1879 ◽  
Author(s):  
R. N. Davis ◽  
Y.-W. Chen ◽  
S. Miyahara ◽  
N. J. Mitchell
Keyword(s):  
General Circulation ◽  
Lower Thermosphere ◽  
Central Africa ◽  
Circulation Model ◽  
Kelvin Waves ◽  
Convective Heating ◽  
Rainfall Time Series ◽  
Meteor Radar ◽  
Zonal Wavenumber ◽  
The Waves

Abstract. Wind measurements from a meteor radar on Ascension Island (8° S, 14° W) and simultaneous temperature measurements from the Aura MLS instrument are used to characterise ultra-fast Kelvin waves (UFKW) of zonal wavenumber 1 (E1) in the mesosphere and lower thermosphere (MLT) in the years 2005–2010. These observations are compared with some predictions of the Kyushu-general circulation model. Good agreement is found between observations of the UFKW in the winds and temperatures, and also with the properties of the waves in the Kyushu-GCM. UFKW are found at periods between 2.5–4.5 days with amplitudes of up to 40 m s−1 in the zonal winds and 6 K in the temperatures. The average vertical wavelength is found to be 44 km. Amplitudes vary with latitude in a Gaussian manner with the maxima centred over the equator. Dissipation of the waves results in monthly-mean eastward accelerations of 0.2–0.9 m s−1 day−1 at heights around 95 km, with 5-day mean peak values of 4 m s−1 day−1. Largest wave amplitudes and variances are observed over Indonesia and central Africa and may be a result of very strong moist convective heating over those regions. Rainfall data from TRMM are used as a proxy for latent-heat release in an investigation of the excitation of these waves. No strong correlation is found between the occurrence of large-amplitude mesospheric UFKW events and either the magnitude of the equatorial rainfall or the amplitudes of E1 signatures in the rainfall time series, indicating that either other sources or the propagation environment are more important in determining the amplitude of UFKW in the MLT. A strong semiannual variation in wave amplitudes is observed. Intraseasonal oscillations (ISOs) with periods 25–60 days are evident in the zonal background winds, zonal-mean temperature, UFKW amplitudes, UFKW accelerations and the rainfall rate. This suggests that UFKW play a role in carrying the signature of tropospheric ISOs to the MLT region.

scholarly journals On the presence of equatorial waves in the lower stratosphere of a general circulation model

2013 ◽  
Vol 13 (8) ◽  
pp. 22607-22637 ◽  
Author(s):  
P. Maury ◽  
F. Lott
Keyword(s):  
Gravity Waves ◽  
General Circulation ◽  
Lower Stratosphere ◽  
Circulation Model ◽  
Atmospheric Model ◽  
Kelvin Waves ◽  
Flux Analysis ◽  
Equatorial Waves ◽  
Quasi Biennial Oscillation ◽  
The Waves

Abstract. 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 close 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 Rossby-gravity waves in ERA-Interim compare well with those in the model. These results suggest that in the model the effect of the convection scheme on the waves is in part hidden by the dynamical filtering and 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 also show that non-equatorial sources are significant in reanalysis data, and we consider the case of the Rossby-gravity waves. We identify situations in the reanalysis where here are large Rossby-gravity waves in the middle stratosphere, and for dates when the stratosphere is dynamically separated from the equatorial troposphere. We refer to this process as a "stratospheric reloading".

scholarly journals Impact of Gravity wave drag on the thermospheric circulation: Implementation of a nonlinear gravity wave parameterization in a whole atmosphere model

2019 ◽  
Author(s):  
Yasunobu Miyoshi ◽  
Erdal Yiğit
Keyword(s):  
Gravity Wave ◽  
General Circulation ◽  
Lower Thermosphere ◽  
Circulation Model ◽  
Wave Drag ◽  
Zonal Wavenumber ◽  
Semidiurnal Variation ◽  
Solar Tide ◽  
Atmosphere General Circulation Model ◽  
Thermospheric Dynamics

Abstract. To investigate the effects of the gravity wave (GW) drag on the general circulation in the thermosphere, a nonlinear GW parameterization that estimates the GW drag in the whole atmosphere system is implemented in a whole atmosphere general circulation model (GCM). Comparing the simulation results obtained with the whole atmosphere scheme with the ones obtained with a conventional linear scheme, we study the GW effects on the thermospheric dynamics for solstice conditions. The GW drag significantly decelerates the mean zonal wind in the thermosphere. The GWs attenuate the migrating semidiurnal solar tide (SW2) amplitude in the lower thermosphere, and modifies the latitudinal structure of the SW2 above 150 km height. The SW2 simulated by the GCM based on the nonlinear whole atmosphere scheme agrees well with the observed SW2. The GW drag in the lower thermosphere has zonal wavenumber 2 and semidiurnal variation, while the GW drag above 150 km height is enhanced in high latitude. The GW drag in the thermosphere is a significant dynamical and plays an important role in the momentum budget of the thermosphere. Therefore, a GW parameterization accounting for thermospheric processes is essential for coarse-grid whole atmosphere GCMs in order to more realistically simulate the atmosphere-ionosphere system.

scholarly journals On the presence of equatorial waves in the lower stratosphere of a general circulation model

2014 ◽  
Vol 14 (4) ◽  
pp. 1869-1880 ◽  
Author(s):  
P. Maury ◽  
F. Lott
Keyword(s):  
Gravity Waves ◽  
General Circulation ◽  
Lower Stratosphere ◽  
Circulation Model ◽  
Atmospheric Model ◽  
Kelvin Waves ◽  
Flux Analysis ◽  
Equatorial Waves ◽  
Quasi Biennial Oscillation ◽  
The Waves

Abstract. 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.

scholarly journals Impact of gravity wave drag on the thermospheric circulation: implementation of a nonlinear gravity wave parameterization in a whole-atmosphere model

2019 ◽  
Vol 37 (5) ◽  
pp. 955-969 ◽  
Author(s):  
Yasunobu Miyoshi ◽  
Erdal Yiğit
Keyword(s):  
Gravity Wave ◽  
General Circulation ◽  
Lower Thermosphere ◽  
Circulation Model ◽  
Wave Drag ◽  
Zonal Wavenumber ◽  
Semidiurnal Variation ◽  
Solar Tide ◽  
Dynamical Factor ◽  
Thermospheric Dynamics

Abstract. To investigate the effects of the gravity wave (GW) drag on the general circulation in the thermosphere, a nonlinear GW parameterization that estimates the GW drag in the whole-atmosphere system is implemented in a whole-atmosphere general circulation model (GCM). Comparing the simulation results obtained with the whole-atmosphere scheme with the ones obtained with a conventional linear scheme, we study the GW effects on the thermospheric dynamics for solstice conditions. The GW drag significantly decelerates the mean zonal wind in the thermosphere. The GWs attenuate the migrating semidiurnal solar-tide (SW2) amplitude in the lower thermosphere and modify the latitudinal structure of the SW2 above a 150 km height. The SW2 simulated by the GCM based on the nonlinear whole-atmosphere scheme agrees well with the observed SW2. The GW drag in the lower thermosphere has zonal wavenumber 2 and semidiurnal variation, while the GW drag above a 150 km height is enhanced in high latitude. The GW drag in the thermosphere is a significant dynamical factor and plays an important role in the momentum budget of the thermosphere. Therefore, a GW parameterization accounting for thermospheric processes is essential for coarse-grid whole-atmosphere GCMs in order to more realistically simulate the atmosphere–ionosphere system.

scholarly journals Convectively Coupled Kelvin Waves in an Idealized Moist General Circulation Model

2007 ◽  
Vol 64 (6) ◽  
pp. 2076-2090 ◽  
Author(s):  
Dargan M. W. Frierson
Keyword(s):  
Relaxation Time ◽  
General Circulation Model ◽  
General Circulation ◽  
Large Scale ◽  
Circulation Model ◽  
Kelvin Waves ◽  
Convection Scheme ◽  
Gross Moist Stability ◽  
The Tropics ◽  
The Waves

The dynamics of convectively coupled Kelvin waves and their dependence on convection scheme parameters are studied within a simplified moist general circulation model. The model consists of the primitive equations on the sphere over zonally symmetric aquaplanet, slab mixed layer ocean boundary conditions, and idealized physical parameterizations including gray radiative transfer and a simplified Betts–Miller convection scheme. This framework allows the authors to study the dependence of Kelvin waves on quantities such as the gross moist stability in a clean manner. A control simulation with the model produces convectively coupled Kelvin waves that are remarkably persistent and dominate the variability within the Tropics. These waves propagate with an equivalent depth of ≈40 m. Linear regression analysis with respect to a Kelvin-filtered time series shows that the waves are driven by evaporation–wind feedback and have structures broadly consistent with theoretical predictions for Kelvin waves. Next, the determination of the speed and structure of the Kelvin waves is studied by examining the response of the waves to changes in convection scheme parameters. When the convective relaxation time is lengthened, the waves are damped and eventually are completely eliminated. The propagation speed additionally increases with longer relaxation time. Then changes to a convection scheme parameter that essentially controls the fraction of convective versus large-scale precipitation are examined. When some large-scale precipitation occurs, the waves increase in strength, propagate more slowly, and move to larger scales. However, when mostly large-scale precipitation occurs, the Kelvin wave disappears, and the Tropics are dominated by tropical storm–like variability. The decrease in speed is related here to the gross moist stability of the atmosphere, which is reduced with increased large-scale precipitation.

Validation of multi-static meteor radar analysis using realistic mesospheric dynamics from UA-ICON model: Reliability of gradients and vertical velocities

2021 ◽  
Author(s):  
Harikrishnan Charuvil Asokan ◽  
Jorge Luis Chau ◽  
Juan Federico Conte ◽  
Gerd Baumgarten ◽  
Juha Vierinen ◽  
...  
Keyword(s):  
Spread Spectrum ◽  
General Circulation ◽  
Lower Thermosphere ◽  
Circulation Model ◽  
Horizontal Wind ◽  
Meteor Radar ◽  
Wind Fields ◽  
Network Systems ◽  
Mlt Dynamics ◽  
Static Approach

<p>Specular meteor radars (SMRs) are a major ground-based instrument to study the mesosphere and the lower thermosphere (MLT) dynamics. The recently developed multi-static approach of SMRs allows maximising the number of measurements from different viewing angles, hence enabling the estimation of horizontal wind fields and their second-order statistics (power spectrum, momentum fluxes). We have installed the operational versions of these techniques in Germany, Peru and Argentina, called SIMONe (Spread-spectrum Interferometric Multistatic meteor radar Observing Network) systems. Here, we present a validation study of multi-static meteor radar analysis by using virtual radar systems on the upper-atmosphere extension of the ICOsahedral Non-hydrostatic (UA-ICON) general circulation model with a horizontal grid spacing of 5 km. This particular study is focusing on the estimates of gradients and vertical velocities with these multi-static systems.</p>

Formation of the double stratopause and elevated stratopause associated with the major stratospheric sudden warming in 2018/19

2021 ◽  
Author(s):  
Haruka Okui ◽  
Kaoru Sato ◽  
Dai Koshin ◽  
Shingo Watanabe
Keyword(s):  
General Circulation ◽  
Middle Atmosphere ◽  
Baroclinic Instability ◽  
Lower Thermosphere ◽  
Circulation Model ◽  
Lower Atmosphere ◽  
Temperature Structure ◽  
Residual Circulation ◽  
Stratospheric Sudden Warming

<p>After several recent stratospheric sudden warming (SSW) events, the stratopause disappeared and reformed at a higher altitude, forming an elevated stratopause (ES). The relative roles of atmospheric waves in the mechanism of ES formation are still not fully understood. We performed a hindcast of the 2018/19 SSW event using a gravity-wave (GW) permitting general circulation model containing the mesosphere and lower thermosphere (MLT), and analyzed dynamical phenomena throughout the entire middle atmosphere. An ES formed after the major warming on 1 January 2019. There was a marked temperature maximum in the polar upper mesosphere around 28 December 2018 prior to the disappearance of the descending stratopause associated with the SSW. This temperature structure with two maxima in the vertical is referred to as a double stratopause (DS). We showed that adiabatic heating from the residual circulation driven by GW forcing (GWF) causes barotropic and/or baroclinic instability before DS formation, causing in situ generation of planetary waves (PWs). These PWs propagate into the MLT and exert negative forcing, which contributes to DS formation. Both negative GWF and PWF above the recovered eastward jet play crucial roles in ES formation. The altitude of the recovered eastward jet, which regulates GWF and PWF height, is likely affected by the DS structure. Simple vertical propagation from the lower atmosphere is insufficient to explain the presence of the GWs observed in this event.</p>

scholarly journals The wintertime two-day wave in the polar stratosphere, mesosphere and lower thermosphere

2008 ◽  
Vol 8 (3) ◽  
pp. 749-755 ◽  
Author(s):  
D. J. Sandford ◽  
M. J. Schwartz ◽  
N. J. Mitchell
Keyword(s):  
Lower Thermosphere ◽  
Radar Data ◽  
The Arctic ◽  
Horizontal Wind ◽  
Meteor Radar ◽  
Polar Night ◽  
Zonal Wavenumber ◽  
Mesosphere And Lower Thermosphere ◽  
Polar Stratosphere ◽  
Striking Contrast

Abstract. Recent observations of the polar mesosphere have revealed that waves with periods near two days reach significant amplitudes in both summer and winter. This is in striking contrast to mid-latitude observations where two-day waves maximise in summer only. Here, we use data from a meteor radar at Esrange (68° N, 21° E) in the Arctic and data from the MLS instrument aboard the EOS Aura satellite to investigate the wintertime polar two-day wave in the stratosphere, mesosphere and lower thermosphere. The radar data reveal that mesospheric two-day wave activity measured by horizontal-wind variance has a semi-annual cycle with maxima in winter and summer and equinoctial minima. The MLS data reveal that the summertime wave in the mesosphere is dominated by a westward-travelling zonal wavenumber three wave with significant westward wavenumber four present. It reaches largest amplitudes at mid-latitudes in the southern hemisphere. In the winter polar mesosphere, however, the wave appears to be an eastward-travelling zonal wavenumber two, which is not seen during the summer. At the latitude of Esrange, the eastward-two wave reaches maximum amplitudes near the stratopause and appears related to similar waves previously observed in the polar stratosphere. We conclude that the wintertime polar two-day wave is the mesospheric manifestation of an eastward-propagating, zonal-wavenumber-two wave originating in the stratosphere, maximising at the stratopause and likely to be generated by instabilities in the polar night jet.

scholarly journals Interhemispheric differences of mesosphere/lower thermosphere winds and tides investigated from three whole atmosphere models and meteor radar observations

2021 ◽  
Author(s):  
Gunter Stober ◽  
Ales Kuchar ◽  
Dimitry Pokhotelov ◽  
Huixin Liu ◽  
Han-Li Liu ◽  
...  
Keyword(s):  
General Circulation ◽  
Climate Models ◽  
Climate Model ◽  
Lower Thermosphere ◽  
Winter Season ◽  
General Circulation Models ◽  
Meteor Radar ◽  
Radar Observations ◽  
Seasonal Characteristics

Abstract. Long-term and continuous observations of mesospheric/lower thermospheric winds are rare, but they are important to investigate climatological changes at these altitudes on time scales of several years, covering a solar cycle and longer. Such long time series are a natural heritage of the mesosphere/lower thermosphere climate, and they are valuable to compare climate models or long term runs of general circulation models (GCMs). Here we present a climatological comparison of wind observations from six meteor radars at two conjugate latitudes to validate the corresponding mean winds and atmospheric diurnal and semidiurnal tides from three GCMs, namely Ground-to-Topside Model of Atmosphere and Ionosphere for Aeronomy (GAIA), Whole Atmosphere Community Climate Model Extension (Specified Dynamics) (WACCM-X(SD)) and Upper Atmosphere ICOsahedral Non-hydrostatic (UA-ICON) model. Our results indicate that there are interhemispheric differences in the seasonal characteristics of the diurnal and semidiurnal tide. There also are some differences in the mean wind climatologies of the models and the observations. Our results indicate that GAIA shows a reasonable agreement with the meteor radar observations during the winter season, whereas WACCM-X(SD) shows a better agreement with the radars for the hemispheric zonal summer wind reversal, which is more consistent with the meteor radar observations. The free running UA-ICON tends to show similar winds and tides compared to WACCM-X(SD).

Sign in / Sign up

Export Citation Format

Share Document