scholarly journals Effects of the planetary waves on the MLT airglow

2017 ◽  
Vol 35 (5) ◽  
pp. 1023-1032 ◽  
Author(s):  
Fabio Egito ◽  
Hisao Takahashi ◽  
Yasunobu Miyoshi
Keyword(s):  
General Circulation ◽  
Atomic Oxygen ◽  
Lower Thermosphere ◽  
Lower Boundary ◽  
Circulation Model ◽  
Vertical Transport ◽  
Transport Processes ◽  
Planetary Waves ◽  
Emission Rates ◽  
Middle Latitudes

Abstract. The planetary-wave-induced airglow variability in the mesosphere and lower thermosphere (MLT) is investigated using simulations with the general circulation model (GCM) of Kyushu University. The model capabilities enable us to simulate the MLT OI557.7 nm, O2b(0–1), and OH(6–2) emissions. The simulations were performed for the lower-boundary meteorological conditions of 2005. The spectral analysis reveals that at middle latitudes, oscillations of the emission rates with the period of 2–20 days appear throughout the year. The 2-day oscillations are prominent in the summer and the 5-, 10-, and 16-day oscillations dominate from the autumn to spring equinoxes. The maximal amplitude of the variations induced by the planetary waves was 34 % in OI557.7 nm, 17 % in O2b(0–1), and 8 % in OH(6–2). The results were compared to those observed in the middle latitudes. The GCM simulations also enabled us to investigate vertical transport processes and their effects on the emission layers. The vertical transport of atomic oxygen exhibits similar periodic variations to those observed in the emission layers induced by the planetary waves. The results also show that the vertical advection of atomic oxygen due to the wave motion is an important factor in the signatures of the planetary waves in the emission rates.

scholarly journals A study into the effect of the diurnal tide on the structure of the background mesosphere and thermosphere using the new coupled middle atmosphere and thermosphere (CMAT) general circulation model

2002 ◽  
Vol 20 (2) ◽  
pp. 225-235 ◽  
Author(s):  
M. J. Harris ◽  
N. F. Arnold ◽  
A. D. Aylward
Keyword(s):  
General Circulation Model ◽  
General Circulation ◽  
Atomic Oxygen ◽  
Middle Atmosphere ◽  
Lower Thermosphere ◽  
Lower Boundary ◽  
Circulation Model ◽  
Diurnal Tide ◽  
Temperature Structure ◽  
The Mean

Abstract. A new coupled middle atmosphere and thermosphere general circulation model has been developed, and some first results are presented. An investigation into the effects of the diurnal tide upon the mean composition, dynamics and energetics was carried out for equinox conditions. Previous studies have shown that tides deplete mean atomic oxygen in the upper mesosphere-lower thermosphere due to an increased recombination in the tidal displaced air parcels. The model runs presented suggest that the mean residual circulation associated with the tidal dissipation also plays an important role. Stronger lower boundary tidal forcing was seen to increase the equatorial local diurnal maximum of atomic oxygen and the associated 0(1S) 557.7 nm green line volume emission rates. The changes in the mean background temperature structure were found to correspond to changes in the mean circulation and exothermic chemical heating.Key words. Atmospheric composition and structure (middle atmosphere – composition and chemistry) Meterology and atmospheric dynamics (middle atmosphere dynamics; waves and tides)

scholarly journals Accuracy issues of the existing thermospheric wind models: can we rely on them in seeking solutions to wind-driven problems?

2009 ◽  
Vol 27 (6) ◽  
pp. 2277-2284 ◽  
Author(s):  
M. F. Larsen ◽  
C. G. Fesen
Keyword(s):  
General Circulation Model ◽  
General Circulation ◽  
Lower Thermosphere ◽  
Lower Boundary ◽  
Circulation Model ◽  
Horizontal Wind ◽  
Wind Model ◽  
Model Predictions ◽  
Statistical Sense ◽  
Wind Profiles

Abstract. We address the question of the ability of empirical and general circulation model neutral wind profiles in the lower thermosphere to reproduce the observed characteristics of the winds in that part of the atmosphere. The winds in that altitude range are critical for electrodynamic processes, but evaluations of the model winds are generally difficult because of the sparse observational data, which makes an evaluation of the wind predictions over large areas difficult or impossible. In this paper, we use a recently identified characteristic of the winds in the lower thermosphere, namely the enhanced winds and strong shears between 95 and 115 km altitude, as a test of the models, at least in a statistical sense. Our results show that the Horizontal Wind Model (HWM) significantly underestimates the maximum winds and shears in the lower thermosphere, although it has reasonable agreement with the average winds. The NCAR general circulation model used in this study also underestimates the maximum winds and shears significantly when run with standard resolution, as well as producing an unrealistic increase of the wind speed with height. The agreement between the model and the observations improves significantly however, in a statistical sense, when the altitude resolution is increased. The improved height resolution in the model appears to produce a greater improvement in the model predictions than any of the other factors that we examined, such as improving the geomagnetic forcing or the forcing at the lower boundary.

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>

Modelling high-latitude explosive eruptions and their atmospheric and environmental impacts

2021 ◽  
Author(s):  
Herman Fuglestvedt ◽  
Zhihong Zhuo ◽  
Michael Sigl ◽  
Matthew Toohey ◽  
Michael Mills ◽  
...  
Keyword(s):  
Environmental Impacts ◽  
High Latitude ◽  
Radiative Forcing ◽  
General Circulation ◽  
Lower Thermosphere ◽  
Circulation Model ◽  
Ice Cores ◽  
Volcanic Eruptions ◽  
Explosive Eruptions ◽  
Sulphate Deposition

<p>Large explosive volcanic eruptions inject sulphur into the stratosphere where it is converted to sulphur dioxide and sulphate aerosols. Due to atmospheric circulation patterns, aerosols from high-latitude eruptions typically remain concentrated in the hemisphere in which they are injected. Eruptions in the high-latitude Northern Hemisphere could thus lead to a stronger hemispheric radiative forcing and surface climate response than tropical eruptions, a claim that is supported by a previous study based on proxy records and the coupled aerosol-general circulation model MAECHAM5-HAM. Additionally, the subsequent surface deposition of volcanic sulphate is potentially harmful to humans and ecosystems, and an improved understanding of the deposition over polar ice sheets can contribute to better reconstructions of historical volcanic forcing. On this basis, we model Icelandic explosive eruptions in a pre-industrial atmosphere, taking both volcanic sulphur and halogen loading into account. We use the fully coupled Earth system model CESM2 with the atmospheric component WACCM6, which extends to the lower thermosphere and has prognostic stratospheric aerosols and full chemistry. In order to study the volcanic impacts on the atmosphere, environment, and sulphate deposition, we vary eruption parameters such as sulphur and halogen loading, and injection altitude and season. The modelled volcanic sulphate deposition is compared to the deposition in ice cores following comparable historical eruptions. Furthermore, we evaluate the potential environmental impacts of sulphate deposition. To study inter-model differences, we also compare the CESM2-WACCM6 simulations to similar Icelandic eruption experiments simulated with MAECHAM5-HAM. </p>

scholarly journals Bayesian calibration of the Thermosphere-Ionosphere Electrodynamics General Circulation Model (TIE-GCM)

2009 ◽  
Vol 2 (2) ◽  
pp. 137-144 ◽  
Author(s):  
S. Guillas ◽  
J. Rougier ◽  
A. Maute ◽  
A. D. Richmond ◽  
C. D. Linkletter
Keyword(s):  
Electron Density ◽  
General Circulation Model ◽  
General Circulation ◽  
Lower Boundary ◽  
Circulation Model ◽  
Computer Simulation Model ◽  
Data Types ◽  
Night Time ◽  
Pressure Surface ◽  
Calibration Parameters

Abstract. In this paper, we demonstrate a procedure for calibrating a complex computer simulation model having uncertain inputs and internal parameters, with application to the NCAR Thermosphere-Ionosphere-Electrodynamics General Circulation Model (TIE-GCM). We compare simulated magnetic perturbations with observations at two ground locations for various combinations of calibration parameters. These calibration parameters are: the amplitude of the semidiurnal tidal perturbation in the height of a constant-pressure surface at the TIE-GCM lower boundary, the local time at which this maximises and the minimum night-time electron density. A fully Bayesian approach, that describes correlations in time and in the calibration input space is implemented. A Markov Chain Monte Carlo (MCMC) approach leads to potential optimal values for the amplitude and phase (within the limitations of the selected data and calibration parameters) but not for the minimum night-time electron density. The procedure can be extended to include additional data types and calibration parameters.

scholarly journals Sensitivity of Late-Glacial and Holocene Climates to the Combined Effects of Orbital Parameter Changes and Lower Boundary Condition Changes: “Snapshot” Simulations with A General Circulation Model for 18, 9, AND 6 ka BP

1984 ◽  
Vol 5 ◽  
pp. 85-87 ◽  
Author(s):  
John E. Kutzbach ◽  
P. J. Guetter
Keyword(s):  
Solar Radiation ◽  
Boundary Conditions ◽  
General Circulation ◽  
Ice Sheet ◽  
Lower Boundary ◽  
Circulation Model ◽  
Late Glacial ◽  
Orbital Parameter ◽  
Ocean Temperature ◽  
Parameter Values

Sensitivity experiments can be used to illustrate the response of the general circulation to prescribed changes in lower boundary conditions (such as ocean temperature) or external forcing conditions (such as solar radiation). The climatic record from the late-glacial and the Holocene provides examples for both types of prescribed change experiments. A number of general circulation model experiments have been carried out. These are reviewed.At 18 ka 8P, orbital parameter values were very much like those of today, but the lower boundary conditions (ocean temperature, ice-sheet extent, etc.) were very different. The change in ocean temperature, and ice-sheet extent and thickness, were prescribed from the results of the Climate: Long-range Investigation Mapping and Prediction (CLIMAP) project.At 9 ka BP, orbital parameter values were very different from present, leading to increased radiation in July and decreased radiation in January (compared to present). The North American ice sheet still covered a significant area, so that lower boundary conditions also differed from the present ones. The combined and individual effects of these prescribed changes on the general circulation are reviewed, particularly in the context of changes of the monsoon circulation.At 6 ka BP, the solar radiation distribution differed from that of today in much the same fashion as at 9 ka BP, although the magnitude of the change was reduced. Lower boundary conditions were probably very similar to those of today.A series of experimental results from 18, 9, and 6 ka BP are presented as “snapshot” estimates of the paleoclimate of those times. The results are based upon simulations with the community climate model of the National Center for Atmospheric Research.

An Analysis of the Linkage of Pacific Subtropical Cells with the Recharge–Discharge Processes in ENSO Evolution

2015 ◽  
Vol 28 (9) ◽  
pp. 3786-3805 ◽  
Author(s):  
Han-Ching Chen ◽  
Chung-Hsiung Sui ◽  
Yu-Heng Tseng ◽  
Bohua Huang
Keyword(s):  
El Niño ◽  
General Circulation ◽  
El Nino ◽  
Causal Relation ◽  
Circulation Model ◽  
Transport Processes ◽  
Water Volume ◽  
Time Lags ◽  
Wind Stress Curl ◽  
Time Intervals

Abstract The Simple Ocean Data Assimilation, version 2.2.4 (SODA 2.2.4), analysis for the period of 1960–2010 is used to study the variability of Pacific subtropical cells (STCs) and its causal relation with tropical climate variability. Results show that the interior STC transport into the equatorial basin through 9°S and 9°N is well connected with equatorial sea surface temperature (SST) (9°S–9°N, 180°–90°W). The highest correlation at interannual time scales is contributed by the western interior STC transport within 160°E and 130°W. It is known that the ENSO recharge–discharge cycle experiences five stages: the recharging stage, recharged stage, warmest SST stage, discharging stage, and discharged stage. A correlation analysis of interior STC transport convergence, equatorial warm water volume (WWV), wind stress curl, and SST identifies the time intervals between the five stages, which are 8, 10, 2, and 8 months, respectively. A composite analysis for El Niño–developing and La Niña–developing events is also performed. The composited ENSO evolutions are in accordance with the recharge–discharge theory and the corresponding time lags between the above denoted five stages are 4–12, 6, 2, and 4 months, respectively. For stronger El Niño events, the discharge due to interior STC transport at 9°N terminates earlier than that at 9°S because of the southward migration of westerly winds following the El Niño peak phase. This study clarifies subsurface transport processes and their time intervals, which are useful for refinement of theoretical models and for evaluating coupled ocean–atmosphere general circulation model results.

scholarly journals The Three-Dimensional Steady Circulation in a Homogenous Ocean Induced by a Stationary Hurricane

2010 ◽  
Vol 40 (7) ◽  
pp. 1441-1457 ◽  
Author(s):  
Zhu Min Lu ◽  
Rui Xin Huang
Keyword(s):  
Analytical Solution ◽  
General Circulation ◽  
Numerical Solutions ◽  
Three Dimensional ◽  
Circulation Model ◽  
Ocean General Circulation Model ◽  
Coriolis Parameter ◽  
Middle Latitudes ◽  
Oceanic Response ◽  
Stratified Ocean

Abstract Based on the classical Ekman layer theory, a simple analytical solution of the steady flow induced by a stationary hurricane in a homogenous ocean is discussed. The model consists of flow converging in an inward spiral in the deeper layer and diverging in the upper layer. The simple analytical model indicates that both the upwelling flux and the horizontal transport increase linearly with increasing radius of maximum winds. Furthermore, they both have a parabolic relationship with the maximum wind speed. The Coriolis parameter also affects the upwelling flux: the response to a hurricane is stronger at low latitudes than that at middle latitudes. Numerical solutions based on a regional version of an ocean general circulation model are similar to the primary results obtained through the analytical solution. Thus, the simplifications made in formulating the analytical solution are reasonable. Although the analytical solution in this paper is sought for a rather idealized ocean, it can help to make results from the more complicated numerical model understandable. These conceptual models provide a theoretical limit structure of the oceanic response to a moving hurricane over a stratified ocean.

scholarly journals Influence of the sudden stratospheric warming on quasi-2-day waves

2016 ◽  
Vol 16 (8) ◽  
pp. 4885-4896 ◽  
Author(s):  
Sheng-Yang Gu ◽  
Han-Li Liu ◽  
Xiankang Dou ◽  
Tao Li
Keyword(s):  
General Circulation ◽  
Phase Speed ◽  
Circulation Model ◽  
Meridional Wind ◽  
Equatorial Region ◽  
Wave Number ◽  
Stratospheric Warming ◽  
Sudden Stratospheric Warming ◽  
Middle Latitudes ◽  
Zonal Wave Number

Abstract. The influence of the sudden stratospheric warming (SSW) on a quasi-2-day wave (QTDW) with westward zonal wave number 3 (W3) is investigated using the Thermosphere–Ionosphere–Mesosphere Electrodynamics General Circulation Model (TIME-GCM). The summer easterly jet below 90 km is strengthened during an SSW, which results in a larger refractive index and thus more favorable conditions for the propagation of W3. In the winter hemisphere, the Eliassen–Palm (EP) flux diagnostics indicate that the strong instabilities at middle and high latitudes in the mesopause region are important for the amplification of W3, which is weakened during SSW periods due to the deceleration or even reversal of the winter westerly winds. Nonlinear interactions between the W3 and the wave number 1 stationary planetary wave produce QTDW with westward zonal wave number 2 (W2). The meridional wind perturbations of the W2 peak in the equatorial region, while the zonal wind and temperature components maximize at middle latitudes. The EP flux diagnostics indicate that the W2 is capable of propagating upward in both winter and summer hemispheres, whereas the propagation of W3 is mostly confined to the summer hemisphere. This characteristic is likely due to the fact that the phase speed of W2 is larger, and therefore its waveguide has a broader latitudinal extension. The larger phase speed also makes W2 less vulnerable to dissipation and critical layer filtering by the background wind when propagating upward.

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