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 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 Equatorial Waves in Opposite QBO Phases

2011 ◽  
Vol 68 (4) ◽  
pp. 839-862 ◽  
Author(s):  
Gui-Ying Yang ◽  
Brian J. Hoskins ◽  
Julia M. Slingo
Keyword(s):  
Group Velocity ◽  
Lower Stratosphere ◽  
Phase Speed ◽  
Kelvin Waves ◽  
Western Hemisphere ◽  
Equatorial Waves ◽  
Vertical Wavelength ◽  
Quasi Biennial Oscillation ◽  
Zonal Wavenumber ◽  
The Waves

Abstract A methodology for identifying equatorial waves is used to analyze the multilevel 40-yr ECMWF Re-Analysis (ERA-40) data for two different years (1992 and 1993) to investigate the behavior of the equatorial waves under opposite phases of the quasi-biennial oscillation (QBO). A comprehensive view of 3D structures and of zonal and vertical propagation of equatorial Kelvin, westward-moving mixed Rossby–gravity (WMRG), and n = 1 Rossby (R1) waves in different QBO phases is presented. Consistent with expectation based on theory, upward-propagating Kelvin waves occur more frequently during the easterly QBO phase than during the westerly QBO phase. However, the westward-moving WMRG and R1 waves show the opposite behavior. The presence of vertically propagating equatorial waves in the stratosphere also depends on the upper tropospheric winds and tropospheric forcing. Typical propagation parameters such as the zonal wavenumber, zonal phase speed, period, vertical wavelength, and vertical group velocity are found. In general, waves in the lower stratosphere have a smaller zonal wavenumber, shorter period, faster phase speed, and shorter vertical wavelength than those in the upper troposphere. All of the waves in the lower stratosphere show an upward group velocity and downward phase speed. When the phase of the QBO is not favorable for waves to propagate, their phase speed in the lower stratosphere is larger and their period is shorter than in the favorable phase, suggesting Doppler shifting by the ambient flow and a filtering of the slow waves. Tropospheric WMRG and R1 waves in the Western Hemisphere also show upward phase speed and downward group velocity, with an indication of their forcing from middle latitudes. Although the waves observed in the lower stratosphere are dominated by “free” waves, there is evidence of some connection with previous tropical convection in the favorable year for the Kelvin waves in the warm water hemisphere and WMRG and R1 waves in the Western Hemisphere, which is suggestive of the importance of convective forcing for the existence of propagating coupled Kelvin waves and midlatitude forcing for the existence of coupled WMRG and R1 waves.

scholarly journals A Study of Multiple Tropopause Structures Caused by Inertia–Gravity Waves in the Antarctic

2015 ◽  
Vol 72 (5) ◽  
pp. 2109-2130 ◽  
Author(s):  
Ryosuke Shibuya ◽  
Kaoru Sato ◽  
Yoshihiro Tomikawa ◽  
Masaki Tsutsumi ◽  
Toru Sato
Keyword(s):  
Gravity Waves ◽  
General Circulation ◽  
Climate Models ◽  
Lower Stratosphere ◽  
Circulation Model ◽  
Cold Bias ◽  
Syowa Station ◽  
Dynamical Mechanism ◽  
The Antarctic ◽  
Inertia Gravity Waves

Abstract Multiple tropopauses (MTs) defined by the World Meteorological Organization are frequently detected from autumn to spring at Syowa Station (69.0°S, 39.6°E). The dynamical mechanism of MT events was examined by observations of the first mesosphere–stratosphere–troposphere (MST) radar in the Antarctic, the Program of the Antarctic Syowa MST/Incoherent Scatter (IS) Radar (PANSY), and of radiosondes on 8–11 April 2013. The MT structure above the first tropopause is composed of strong temperature fluctuations. By a detailed analysis of observed three-dimensional wind and temperature fluctuation components, it is shown that the phase and amplitude relations between these components are consistent with the theoretical characteristics of linear inertia–gravity waves (IGWs). Numerical simulations were performed by using a nonhydrostatic model. The simulated MT structures and IGW parameters agree well with the observation. In the analysis using the numerical simulation data, it is seen that IGWs were generated around 65°S, 15°E and around 70°S, 15°E, propagated eastward, and reached the region above Syowa Station when the MT event was observed. These IGWs were likely radiated spontaneously from the upper-tropospheric flow around 65°S, 15°E and were forced by strong southerly surface winds over steep topography (70°S, 15°E). The MT occurrence is attributable to strong IGWs and the low mean static stability in the polar winter lower stratosphere. It is also shown that nonorographic gravity waves associated with the tropopause folding event contribute to 40% of the momentum fluxes, as shown by a gravity wave–resolving general circulation model in the lower stratosphere around 65°S. This result indicates that they are one of the key components for solving the cold-bias problem found in most climate models.

scholarly journals Variability of the Stratospheric Quasi-Biennial Oscillation and Its Wave Forcing Simulated in the Beijing Climate Center Atmospheric General Circulation Model

2019 ◽  
Vol 77 (1) ◽  
pp. 149-165 ◽  
Author(s):  
Yixiong Lu ◽  
Tongwen Wu ◽  
Weihua Jie ◽  
Adam A. Scaife ◽  
Martin B. Andrews ◽  
...  
Keyword(s):  
General Circulation Model ◽  
General Circulation ◽  
Atmospheric General Circulation Model ◽  
Circulation Model ◽  
General Circulation Models ◽  
Kelvin Waves ◽  
Quasi Biennial Oscillation ◽  
Wave Forcing ◽  
Atmospheric General Circulation ◽  
Biennial Oscillation

Abstract It is well known that the stratospheric quasi-biennial oscillation (QBO) is forced by equatorial waves with different horizontal/vertical scales, including Kelvin waves, mixed Rossby–gravity (MRG) waves, inertial gravity waves (GWs), and mesoscale GWs, but the relative contribution of each wave is currently not very clear. Proper representation of these waves is critical to the simulation of the QBO in general circulation models (GCMs). In this study, the vertical resolution in the Beijing Climate Center Atmospheric General Circulation Model (BCC-AGCM) is increased to better represent large-scale waves, and a mesoscale GW parameterization scheme, which is coupled to the convective sources, is implemented to provide unresolved wave forcing of the QBO. Results show that BCC-AGCM can spontaneously generate the QBO with realistic periods, amplitudes, and asymmetric features between westerly and easterly phases. There are significant spatiotemporal variations of parameterized convective GWs, largely contributing to a great degree of variability in the simulated QBO. In the eastward wind shear of the QBO at 20 hPa, forcing provided by resolved waves is 0.1–0.2 m s−1 day−1 and forcing provided by parameterized GWs is ~0.15 m s−1 day−1. On the other hand, westward forcings by resolved waves and parameterized GWs are ~0.1 and 0.4–0.5 m s−1 day−1, respectively. It is inferred that the eastward forcing of the QBO is provided by both Kelvin waves and mesoscale convective GWs, whereas the westward forcing is largely provided by mesoscale GWs. MRG waves barely contribute to the formation of the QBO in the model.

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 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 Global Atmospheric Model Simulates Fine Details of Gravity Waves

Eos ◽  
2015 ◽  
Vol 96 ◽  
Author(s):  
Puneet Kollipara
Keyword(s):  
Gravity Wave ◽  
General Circulation Model ◽  
Gravity Waves ◽  
General Circulation ◽  
Circulation Model ◽  
Atmospheric Model ◽  
Global Atmospheric Model ◽  
Atmosphere General Circulation Model

Whole-atmosphere general circulation model captures many aspects of mesoscale gravity wave structures—down to the tens of kilometers—and resulting temperatures and tides.

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.

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