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

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.

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A study of the dynamical characteristics of inertia–gravity waves in the Antarctic mesosphere combining the PANSY radar and a non-hydrostatic general circulation model

10.5194/acp-2018-1023 ◽

2018 ◽

Author(s):

Ryosuke Shibuya ◽

Kaoru Sato

Keyword(s):

General Circulation Model ◽

Gravity Waves ◽

General Circulation ◽

Initial Conditions ◽

Circulation Model ◽

Reanalysis Data ◽

Wind Fields ◽

High Latitude Region ◽

The Antarctic ◽

Inertia Gravity Waves

Abstract. The first long-term simulation using the high-top non-hydrostatic general circulation model (NICAM) was executed to analyze mesospheric gravity waves in the period from April to August in 2016. Successive runs lasting 7 days are performed using initial conditions from the MERRA reanalysis data with an overlap of 2 days between consecutive runs. The data for the analyses were compiled from the last 5 days of each run. The simulated wind fields were closely compared to the MERRA reanalysis data and to the observational data collected by a complete PANSY (Program of the Antarctic Syowa MST/IS Radar) radar system installed at Syowa Station (39.6° E 69.0° S). It is shown that the NICAM mesospheric wind fields are realistic, even though the amplitudes of the wind disturbances appear to be larger than the radar observations. The power spectrum of the meridional wind fluctuations at a height of 70 km has an isolated and broad peak at frequencies slightly lower than the inertial frequency, f, for latitudes from 30° S to 75° S, while another isolated peak is observed at frequencies of approximately 2π/8 h at latitudes from 78° S to 90° S. The spectrum of the vertical fluxes of the zonal momentum also has an isolated peak at frequencies slightly lower than f at latitudes from 30° S to 75° S at a height of 70 km. It is shown that these isolated peaks are primarily composed of gravity waves with horizontal wavelengths of more than 1000 km. The latitude–height structure of the momentum fluxes indicates that the isolated peaks at frequencies slightly lower than f originate from two branches of gravity wave propagation paths. It is thought that one branch originates from 75° S due to topographic gravity waves generated over the Antarctic Peninsula and its coast, while more than 80 % of the other branch originates from 45° S and includes contributions by non-orographic gravity waves. The existence of isolated peaks in the high-latitude region in the mesosphere is likely explained by the poleward propagation of quasi-inertia–gravity waves and by the accumulation of wave energies near the inertial frequency at each latitude.

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A study of the dynamical characteristics of inertia–gravity waves in the Antarctic mesosphere combining the PANSY radar and a non-hydrostatic general circulation model

Atmospheric Chemistry and Physics ◽

10.5194/acp-19-3395-2019 ◽

2019 ◽

Vol 19 (5) ◽

pp. 3395-3415 ◽

Cited By ~ 5

Author(s):

Ryosuke Shibuya ◽

Kaoru Sato

Keyword(s):

General Circulation Model ◽

Gravity Waves ◽

General Circulation ◽

Circulation Model ◽

Reanalysis Data ◽

Wind Fields ◽

Dynamical Characteristics ◽

High Latitude Region ◽

The Antarctic ◽

Inertia Gravity Waves

Abstract. This study aims to examine the dynamical characteristics of gravity waves with relatively low frequency in the Antarctic mesosphere via the first long-term simulation using a high-top high-resolution non-hydrostatic general circulation model (NICAM). Successive runs lasting 7 days are performed using initial conditions from the MERRA reanalysis data with an overlap of 2 days between consecutive runs in the period from April to August in 2016. The data for the analyses were compiled from the last 5 days of each run. The simulated wind fields were closely compared to the MERRA reanalysis data and to the observational data collected by a complete PANSY (Program of the Antarctic Syowa MST/IS radar) radar system installed at Syowa Station (39.6∘ E, 69.0∘ S). It is shown that the NICAM mesospheric wind fields are realistic, even though the amplitudes of the wind disturbances appear to be larger than those from the radar observations. The power spectrum of the meridional wind fluctuations at a height of 70 km has an isolated and broad peak at frequencies slightly lower than the inertial frequency, f, for latitudes from 30 to 75∘ S, while another isolated peak is observed at frequencies of approximately 2π∕8 h at latitudes from 78 to 90∘ S. The spectrum of the vertical fluxes of the zonal momentum also has an isolated peak at frequencies slightly lower than f at latitudes from 30 to 75∘ S at a height of 70 km. It is shown that these isolated peaks are primarily composed of gravity waves with horizontal wavelengths of more than 1000 km. The latitude–height structure of the momentum fluxes indicates that the isolated peaks at frequencies slightly lower than f originate from two branches of gravity wave propagation paths. It is thought that one branch originates from 75∘ S due to topographic gravity waves generated over the Antarctic Peninsula and its coast, while more than 80 % of the other branch originates from 45∘ S and includes contributions by non-orographic gravity waves. The existence of isolated peaks in the high-latitude region in the mesosphere is likely explained by the poleward propagation of quasi-inertia–gravity waves and by the accumulation of wave energies near the inertial frequency at each latitude.

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Stratospheric temperatures and tracer transport in a nudged 4-year middle atmosphere GCM simulation

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-5-961-2005 ◽

2005 ◽

Vol 5 (1) ◽

pp. 961-1006 ◽

Cited By ~ 2

Author(s):

M. K. van Aalst ◽

J. Lelieveld ◽

B. Steil ◽

C. Brühl ◽

P. Jöckel ◽

...

Keyword(s):

Interannual Variability ◽

General Circulation ◽

Middle Atmosphere ◽

Circulation Model ◽

Detailed Comparison ◽

The Arctic ◽

Cold Bias ◽

Tracer Transport ◽

Quasi Biennial Oscillation ◽

The Antarctic

Abstract. We have performed a 4-year simulation with the Middle Atmosphere General Circulation Model MAECHAM5/MESSy, while slightly nudging the model’s meteorology in the free troposphere (below 113 hPa) towards ECMWF analyses. We show that the nudging 5 technique, which leaves the middle atmosphere almost entirely free, enables comparisons with synoptic observations. The model successfully reproduces many specific features of the interannual variability, including details of the Antarctic vortex structure. In the Arctic, the model captures general features of the interannual variability, but falls short in reproducing the timing of sudden stratospheric warmings. A 10 detailed comparison of the nudged model simulations with ECMWF data shows that the model simulates realistic stratospheric temperature distributions and variabilities, including the temperature minima in the Antarctic vortex. Some small (a few K) model biases were also identified, including a summer cold bias at both poles, and a general cold bias in the lower stratosphere, most pronounced in midlatitudes. A comparison 15 of tracer distributions with HALOE observations shows that the model successfully reproduces specific aspects of the instantaneous circulation. The main tracer transport deficiencies occur in the polar lowermost stratosphere. These are related to the tropopause altitude as well as the tracer advection scheme and model resolution. The additional nudging of equatorial zonal winds, forcing the quasi-biennial oscillation, sig20 nificantly improves stratospheric temperatures and tracer distributions.

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

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-13-22607-2013 ◽

2013 ◽

Vol 13 (8) ◽

pp. 22607-22637 ◽

Cited By ~ 1

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".

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Improved sea-ice prediction in the Weddell Sea using sea-ice thickness initialization

10.5194/egusphere-egu21-3638 ◽

2021 ◽

Author(s):

Yushi Morioka ◽

Doroteaciro Iovino ◽

Andrea Cipollone ◽

Simona Masina ◽

Swadhin Behera

Keyword(s):

Sea Ice ◽

General Circulation ◽

Climate Models ◽

Circulation Model ◽

Weddell Sea ◽

Ice Thickness ◽

Austral Spring ◽

Sea Ice Concentration ◽

Sea Ice Thickness ◽

The Antarctic

Skillful sea-ice prediction in the Antarctic Ocean remains a big challenge due to paucity of sea-ice observations and insufficient representation of sea-ice processes in climate models. This study demonstrates that the Antarctic sea-ice concentration (SIC) prediction is significantly improved using a coupled general circulation model (SINTEX-F2) in which the model&#8217;s SIC and sea-ice thickness (SIT) are initialized with the ocean/sea-ice reanalysis product (C-GLORSv7). It is found that the wintertime SIT initialization adds positive values to the prediction skills of the summertime SIC, most effectively in the Weddell Sea where the SIT climatology and variability are the largest among the Antarctic Seas. Examination of the SIT balance during low sea-ice years of the Weddell Sea shows that negative SIT anomalies initialized in June retain the memory throughout austral winter (July-September) owing to horizontal advection of the SIT anomalies by sea-ice velocities. The negative SIT anomalies continue to develop in austral spring (October-December) owing to more incoming solar radiation via ice-albedo feedback and the associated warming of mixed layer. This results in further sea-ice decrease during austral summer (January-March). Concomitantly, the model reasonably reproduces atmospheric circulation anomalies in the Amundsen-Bellingshausen Seas as well as the Weddell Sea during the development of the negative sea-ice anomalies. These results provide solid evidence that the wintertime SIT initialization benefits skillful summertime sea-ice prediction in the Antarctic Seas.

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Improved Simulation of the Antarctic Stratospheric Final Warming by Modifying the Orographic Gravity Wave Parameterization in the Beijing Climate Center Atmospheric General Circulation Model

Atmosphere ◽

10.3390/atmos11060576 ◽

2020 ◽

Vol 11 (6) ◽

pp. 576

Author(s):

Yixiong Lu ◽

Tongwen Wu ◽

Xin Xu ◽

Li Zhang ◽

Min Chu

Keyword(s):

Gravity Wave ◽

General Circulation Model ◽

General Circulation ◽

Climate Models ◽

Atmospheric General Circulation Model ◽

Circulation Model ◽

Wave Drag ◽

Atmospheric General Circulation ◽

Stratospheric Final Warming ◽

The Antarctic

The Antarctic stratospheric final warming (SFW) is usually simulated with a substantial delay in climate models, and the corresponding temperatures in austral spring are lower than observations, implying insufficient stratospheric wave drag. To investigate the role of orographic gravity wave drag (GWD) in modeling the Antarctic SFW, in this study the orographic GWD parameterization scheme is modified in the middle-atmosphere version of the Beijing Climate Center Atmospheric General Circulation Model. A pair of simulations are conducted to compare two orographic GWD schemes in simulating the breakdown of the stratospheric polar vortex over Antarctica. The control simulation with the default orographic GWD scheme exhibits delayed vortex breakdown and the cold-pole bias seen in most climate models. In the simulation with modified orographic GWD scheme, the simulated vortex breaks down earlier by 8 days, and the associated cold-pole bias is reduced by more than 2 K. The modified scheme provides stronger orographic GWD in the lower stratosphere, which drives an accelerated polar downwelling branch of the Brewer–Dobson circulation and, in turn, produces adiabatic warming. Our study suggests that modifying orographic GWD parameterizations in climate models would be a valid way of improving the SFW simulation over Antarctica.

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

Atmospheric Chemistry and Physics ◽

10.5194/acp-14-1869-2014 ◽

2014 ◽

Vol 14 (4) ◽

pp. 1869-1880 ◽

Cited By ~ 7

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.

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Summertime sea-ice prediction in the Weddell Sea improved by sea-ice thickness initialization

Scientific Reports ◽

10.1038/s41598-021-91042-4 ◽

2021 ◽

Vol 11 (1) ◽

Author(s):

Yushi Morioka ◽

Doroteaciro Iovino ◽

Andrea Cipollone ◽

Simona Masina ◽

Swadhin K. Behera

Keyword(s):

Sea Ice ◽

General Circulation ◽

Climate Models ◽

Circulation Model ◽

Weddell Sea ◽

Ice Thickness ◽

Austral Spring ◽

Sea Ice Concentration ◽

Sea Ice Thickness ◽

The Antarctic

AbstractSkillful sea-ice prediction in the Antarctic Ocean remains a big challenge due to paucity of sea-ice observations and insufficient representation of sea-ice processes in climate models. Using a coupled general circulation model, this study demonstrates skillful prediction of the summertime sea-ice concentration (SIC) in the Weddell Sea with wintertime SIC and sea-ice thickness (SIT) initializations. During low sea-ice years of the Weddell Sea, negative SIT anomalies initialized in June retain the memory throughout austral winter owing to horizontal advection of the SIT anomalies. The SIT anomalies continue to develop in austral spring owing to more incoming solar radiation and the associated warming of mixed layer, contributing to further sea-ice decrease during late austral summer-early autumn. Concomitantly, the model reasonably reproduces atmospheric circulation anomalies during austral spring in the Amundsen-Bellingshausen Seas besides the Weddell Sea. These results provide evidence that the wintertime SIT initialization benefits skillful summertime sea-ice prediction in the Antarctic Seas.

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Tropical Atmospheric Variability Forced by Oceanic Internal Variability

Journal of Climate ◽

10.1175/jcli4044.1 ◽

2007 ◽

Vol 20 (4) ◽

pp. 765-771 ◽

Cited By ~ 17

Author(s):

Markus Jochum ◽

Clara Deser ◽

Adam Phillips

Keyword(s):

General Circulation ◽

Climate Models ◽

Rainfall Variability ◽

Circulation Model ◽

Internal Variability ◽

Tropical Pacific ◽

Atmospheric Variability ◽

Instability Waves ◽

Tropical Instability Waves ◽

The Tropical Pacific

Abstract Atmospheric general circulation model experiments are conducted to quantify the contribution of internal oceanic variability in the form of tropical instability waves (TIWs) to interannual wind and rainfall variability in the tropical Pacific. It is found that in the tropical Pacific, along the equator, and near 25°N and 25°S, TIWs force a significant increase in wind and rainfall variability from interseasonal to interannual time scales. Because of the stochastic nature of TIWs, this means that climate models that do not take them into account will underestimate the strength and number of extreme events and may overestimate forecast capability.

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Atmospheric general circulation and waves simulated by a Venus AORI GCM with topographical and radiative forcings

10.5194/egusphere-egu21-3657 ◽

2021 ◽

Author(s):

Masaru Yamamoto ◽

Takumi Hirose ◽

Kohei Ikeda ◽

Masaaki Takahashi

Keyword(s):

Gravity Waves ◽

General Circulation ◽

Circulation Model ◽

Stationary Wave ◽

Static Stability ◽

Small Scale ◽

Mean Flow ◽

Short Period ◽

Low Latitudes ◽

Thermal Tides

General circulation and waves are investigated using a T63 Venus general circulation model (GCM) with solar and thermal radiative transfer in the presence of high-resolution surface topography. This model has been developed by Ikeda (2011) at the Atmosphere and Ocean Research Institute (AORI), the University of Tokyo, and was used in Yamamoto et al. (2019, 2021). In the wind and static stability structures similar to the observed ones, the waves are investigated. Around the cloud-heating maximum (~65 km), the simulated thermal tides accelerate an equatorial superrotational flow with a speed of ~90 m/swith rates of 0.2&#8211;0.5 m/s/(Earth day) via both horizontal and vertical momentum fluxes at low latitudes. Over the high mountains at low latitudes, the vertical wind variance at the cloud top is produced by topographically-fixed, short-period eddies, indicating penetrative plumes and gravity waves. In the solar-fixed coordinate system, the variances (i.e., the activity of waves other than thermal tides) of flow are relatively higher on the night-side than on the dayside at the cloud top. The local-time variation of the vertical eddy momentum flux is produced by both thermal tides and solar-related, small-scale gravity waves. Around the cloud bottom, the 9-day super-rotation of the zonal mean flow has a weak equatorial maximum and the 7.5-day Kelvin-like wave has an equatorial jet-like wind of 60-70 m/s. Because we discussed the thermal tide and topographically stationary wave in Yamamoto et al. (2021), we focus on the short-period eddies in the presentation.

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