scholarly journals On one technique of the analysis of oscillation processes for the geophysical problems

2019 ◽  
Vol 55 (1) ◽  
pp. 35-40
Author(s):  
E. M. Volodin
Keyword(s):  
Evolution Equation ◽  
Phase Change ◽  
Gravity Wave ◽  
Zonal Wind ◽  
Climate Model ◽  
Wave Drag ◽  
Main Mechanism ◽  
Vertical Advection ◽  
Change Impact ◽  
The Impact

A technique is proposed for evolution equation that estimates the impact of different terms in phase change for oscillations with different frequencies. The impact is normalized in such way that sum of impacts for all terms equals 1. Proposed technique is applied for study of quasibiannual oscillation of zonal wind in equatorial stratosphere produced in 500 year preindustrial run with climate model of Institute of Numerical Mathematics RAS. The impact of nonorographic and orographic gravity wave drag and advection by zonal mean vertical wind to the phase change of model quasibiannual oscillation. It is shown that nonorographic wave drag is main mechanism responsible for phase change (the impact equals 1.58), vertical advection slows down phase change (impact is –0.74), and the impacts of other terms are small.

scholarly journals Compensation between Resolved Wave Driving and Parameterized Orographic Gravity Wave Driving of the Brewer–Dobson Circulation and Its Response to Climate Change

2014 ◽  
Vol 27 (14) ◽  
pp. 5601-5610 ◽  
Author(s):  
Michael Sigmond ◽  
Theodore G. Shepherd
Keyword(s):  
Climate Change ◽  
Gravity Wave ◽  
Northern Hemisphere ◽  
Rossby Wave ◽  
Climate Model ◽  
Wave Drag ◽  
High Latitudes ◽  
Remarkable Degree ◽  
The Impact

Abstract Following recent findings, the interaction between resolved (Rossby) wave drag and parameterized orographic gravity wave drag (OGWD) is investigated, in terms of their driving of the Brewer–Dobson circulation (BDC), in a comprehensive climate model. To this end, the parameter that effectively determines the strength of OGWD in present-day and doubled CO2 simulations is varied. The authors focus on the Northern Hemisphere during winter when the largest response of the BDC to climate change is predicted to occur. It is found that increases in OGWD are to a remarkable degree compensated by a reduction in midlatitude resolved wave drag, thereby reducing the impact of changes in OGWD on the BDC. This compensation is also found for the response to climate change: changes in the OGWD contribution to the BDC response to climate change are compensated by opposite changes in the resolved wave drag contribution to the BDC response to climate change, thereby reducing the impact of changes in OGWD on the BDC response to climate change. By contrast, compensation does not occur at northern high latitudes, where resolved wave driving and the associated downwelling increase with increasing OGWD, both for the present-day climate and the response to climate change. These findings raise confidence in the credibility of climate model projections of the strengthened BDC.

scholarly journals Is Missing Orographic Gravity Wave Drag near 60°S the Cause of the Stratospheric Zonal Wind Biases in Chemistry–Climate Models?

2012 ◽  
Vol 69 (3) ◽  
pp. 802-818 ◽  
Author(s):  
Charles McLandress ◽  
Theodore G. Shepherd ◽  
Saroja Polavarapu ◽  
Stephen R. Beagley
Keyword(s):  
Gravity Wave ◽  
Zonal Wind ◽  
Climate Models ◽  
Middle Atmosphere ◽  
Wave Drag ◽  
Early Summer ◽  
Systematic Bias ◽  
Stratospheric Polar Vortex ◽  
Column Ozone ◽  
The Impact

Abstract Nearly all chemistry–climate models (CCMs) have a systematic bias of a delayed springtime breakdown of the Southern Hemisphere (SH) stratospheric polar vortex, implying insufficient stratospheric wave drag. In this study the Canadian Middle Atmosphere Model (CMAM) and the CMAM Data Assimilation System (CMAM-DAS) are used to investigate the cause of this bias. Zonal wind analysis increments from CMAM-DAS reveal systematic negative values in the stratosphere near 60°S in winter and early spring. These are interpreted as indicating a bias in the model physics, namely, missing gravity wave drag (GWD). The negative analysis increments remain at a nearly constant height during winter and descend as the vortex weakens, much like orographic GWD. This region is also where current orographic GWD parameterizations have a gap in wave drag, which is suggested to be unrealistic because of missing effects in those parameterizations. These findings motivate a pair of free-running CMAM simulations to assess the impact of extra orographic GWD at 60°S. The control simulation exhibits the cold-pole bias and delayed vortex breakdown seen in the CCMs. In the simulation with extra GWD, the cold-pole bias is significantly reduced and the vortex breaks down earlier. Changes in resolved wave drag in the stratosphere also occur in response to the extra GWD, which reduce stratospheric SH polar-cap temperature biases in late spring and early summer. Reducing the dynamical biases, however, results in degraded Antarctic column ozone. This suggests that CCMs that obtain realistic column ozone in the presence of an overly strong and persistent vortex may be doing so through compensating errors.

scholarly journals Influence of Gravity Waves in the Tropical Upwelling: WACCM Simulations

2011 ◽  
Vol 68 (11) ◽  
pp. 2599-2612 ◽  
Author(s):  
Hye-Yeong Chun ◽  
Young-Ha Kim ◽  
Hyun-Joo Choi ◽  
Jung-Yoon Kim
Keyword(s):  
Gravity Wave ◽  
Gravity Waves ◽  
Zonal Wind ◽  
Annual Cycle ◽  
Climate Model ◽  
Wave Drag ◽  
Flux Divergence ◽  
Relative Contribution ◽  
The Tropics ◽  
Convective Gravity Waves

Abstract The annual cycle of tropical upwelling and contributions by planetary and gravity waves are investigated from climatological simulations using the Whole Atmosphere Community Climate Model (WACCM) including three gravity wave drag (GWD) parameterizations (orographic, nonstationary background, and convective GWD parameterizations). The tropical upwelling is estimated by the residual mean vertical velocity at 100 hPa averaged over 15°S–15°N. This is well matched with an upwelling estimate from the balance of the zonal momentum and the mass continuity. A clear annual cycle of the tropical upwelling is found, with a Northern Hemispheric (NH) wintertime maximum and NH summertime minimum determined primarily by the Eliassen–Palm flux divergence (EPD), along with a secondary contribution from the zonal wind tendency. Gravity waves increase tropical upwelling throughout the year, and of the three sources the contribution by convective gravity wave drag (CGWD) is largest in most months. The relative contribution by all three GWDs to tropical upwelling is not larger than 5%. However, when tropical upwelling is estimated by net upward mass flux between turnaround latitudes where upwelling changes downwelling, annual mean contribution by all three GWDs is up to 19% at 70 hPa by orographic and convective gravity waves with comparable magnitudes. Effects of CGWD on upwelling are investigated by conducting an additional WACCM simulation without CGWD parameterization. It was found that including CGWD parameterization increases tropical upwelling not only directly by adding CGWD forcing, but also indirectly by modulating EPD and zonal wind tendency terms in the tropics.

Self-Acceleration in the Parameterization of Orographic Gravity Wave Drag

2010 ◽  
Vol 67 (8) ◽  
pp. 2537-2546 ◽  
Author(s):  
John F. Scinocca ◽  
Bruce R. Sutherland
Keyword(s):  
Gravity Wave ◽  
Middle Atmosphere ◽  
Wave Train ◽  
Leading Edge ◽  
Wave Theory ◽  
Wave Drag ◽  
Tuning Parameter ◽  
Mean Flow ◽  
Propagating Waves ◽  
The Impact

Abstract A new effect related to the evaluation of momentum deposition in conventional parameterizations of orographic gravity wave drag (GWD) is considered. The effect takes the form of an adjustment to the basic-state wind about which steady-state wave solutions are constructed. The adjustment is conservative and follows from wave–mean flow theory associated with wave transience at the leading edge of the wave train, which sets up the steady solution assumed in such parameterizations. This has been referred to as “self-acceleration” and it is shown to induce a systematic lowering of the elevation of momentum deposition, which depends quadratically on the amplitude of the wave. An expression for the leading-order impact of self-acceleration is derived in terms of a reduction of the critical inverse Froude number Fc, which determines the onset of wave breaking for upwardly propagating waves in orographic GWD schemes. In such schemes Fc is a central tuning parameter and typical values are generally smaller than anticipated from conventional wave theory. Here it is suggested that self-acceleration may provide some of the explanation for why such small values of Fc are required. The impact of Fc on present-day climate is illustrated by simulations of the Canadian Middle Atmosphere Model.

COnstraining ORographic Drag Effects (COORDE): A model intercomparison of resolved and parametrized orographic drag

2020 ◽  
Author(s):  
Annelize VanNiekerk ◽  
Irina Sandu
Keyword(s):  
Gravity Wave ◽  
Complex Terrain ◽  
Spatial Scales ◽  
Wave Drag ◽  
Large Spread ◽  
Numerical Experimentation ◽  
Wave Effects ◽  
Atmospheric Gravity ◽  
The Impact ◽  
Orographic Drag

<p>Mountains are know to impact the atmospheric circulation on a variety of spatial scales and through a number of different processes. They exert a drag force on the atmosphere both locally through deflection of the flow and remotely through the generation of atmospheric gravity waves. The degree to which orographic drag parametrizations are able to capture the complex impacts on the circulation from realistic orography in high resolution simulations is examined here. We present results from COnstraing ORographic Drag Effects (COORDE), a project joint with the Working Group on Numerical Experimentation (WGNE) and Global Atmospheric System Studies (GASS). The aim of COORDE is to validate parametrized orographic drag in several operational models in order to determine both systematic and model dependent errors over complex terrain. To do this, we compare the effects of parametrized orographic drag on the circulation with those of the resolved orographic drag, deduced from km-scale resolution simulations which are able to resolve orographic low-level blocking and gravity-wave effects. We show that there is a large spread in the impact from parametrized orographic drag between the models but that the impact from resolved orography is much more robust. This is encouraging as it means that the km-scale simulations can be used to evaluate the caveats of the existing orographic drag parametrizations. Analysis of the parametrized drag tendencies and stresses shows that much of the spread in the parametrized orographic drag comes from differences in the partitioning of the drag into turbulent and flow blocking drag near the surface. What is more, much of the model error over complex terrain can be attributed to deficiencies in the parametrized orographic drag, particularly coming from the orographic gravity wave drag.</p>

scholarly journals Effects of Convective Gravity Wave Drag in the Southern Hemisphere Winter Stratosphere

2013 ◽  
Vol 70 (7) ◽  
pp. 2120-2136 ◽  
Author(s):  
Hyun-Joo Choi ◽  
Hye-Yeong Chun
Keyword(s):  
Gravity Wave ◽  
Southern Hemisphere ◽  
Climate Models ◽  
Climate Model ◽  
Global Climate ◽  
Storm Track ◽  
Wave Drag ◽  
Global Climate Models ◽  
Systematic Biases ◽  
Hemisphere Winter

Abstract The excessively strong polar jet and cold pole in the Southern Hemisphere winter stratosphere are systematic biases in most global climate models and are related to underestimated wave drag in the winter extratropical stratosphere—namely, missing gravity wave drag (GWD). Cumulus convection is strong in the winter extratropics in association with storm-track regions; thus, convective GWD could be one of the missing GWDs in models that do not adopt source-based nonorographic GWD parameterizations. In this study, the authors use the Whole Atmosphere Community Climate Model (WACCM) and show that the zonal-mean wind and temperature biases in the Southern Hemisphere winter stratosphere of the model are significantly alleviated by including convective GWD (GWDC) parameterizations. The reduction in the wind biases is due to enhanced wave drag in the winter extratropical stratosphere, which is caused directly by the additional GWDC and indirectly by the increased existing nonorographic GWD and resolved wave drag in response to the GWDC. The cold temperature biases are alleviated by increased downwelling in the winter polar stratosphere, which stems from an increased poleward motion due to enhanced wave drag in the winter extratropical stratosphere. A comparison between two simulations separately using the ray-based and columnar GWDC parameterizations shows that the polar night jet with a ray-based GWDC parameterization is much more realistic than that with a columnar GWDC parameterization.

scholarly journals The Impact of Air–Sea Interactions on the Predictability of the Tropical Intraseasonal Oscillation

2008 ◽  
Vol 21 (22) ◽  
pp. 5870-5886 ◽  
Author(s):  
Kathy Pegion ◽  
Ben P. Kirtman
Keyword(s):  
Zonal Wind ◽  
Climate Model ◽  
Intraseasonal Oscillation ◽  
Coupled Model ◽  
Longwave Radiation ◽  
Boreal Winter ◽  
Potential Predictability ◽  
Key Factor ◽  
The Impact ◽  
Tropical Intraseasonal Oscillation

Abstract This study investigates whether air–sea interactions contribute to differences in the predictability of the boreal winter tropical intraseasonal oscillation (TISO) using the NCEP operational climate model. A series of coupled and uncoupled, “perfect” model predictability experiments are performed for 10 strong model intraseasonal events. The uncoupled experiments are forced by prescribed SST containing different types of variability. These experiments are specifically designed to be directly comparable to actual forecasts. Predictability estimates are calculated using three metrics, including one that does not require the use of time filtering. The estimates are compared between these experiments to determine the impact of coupled air–sea interactions on the predictability of the tropical intraseasonal oscillation and the sensitivity of the potential predictability estimates to the different SST forcings. Results from all three metrics are surprisingly similar. They indicate that predictability estimates are longest for precipitation and outgoing longwave radiation (OLR) when the ensemble mean from the coupled model is used. Most importantly, the experiments that contain intraseasonally varying SST consistently predict the control events better than those that do not for precipitation, OLR, 200-hPa zonal wind, and 850-hPa zonal wind after the first 10 days. The uncoupled model is able to predict the TISO with similar skill to that of the coupled model, provided that an SST forecast that includes these intraseasonal variations is used to force the model. This indicates that the intraseasonally varying SSTs are a key factor for increased predictability and presumably better prediction of the TISO.

scholarly journals Differing responses of the QBO to SO<sub>2</sub> injections in two global models

2020 ◽  
Author(s):  
Ulrike Niemeier ◽  
Jadwiga H. Richter ◽  
Simone Tilmes
Keyword(s):  
General Circulation ◽  
Climate Model ◽  
Numerical Models ◽  
General Circulation Models ◽  
Injection Rate ◽  
Equatorial Region ◽  
Quasi Biennial Oscillation ◽  
Vertical Advection ◽  
Model Studies ◽  
The Impact

Abstract. Artificial injections of sulfur dioxide (SO2) into the stratosphere show in several model studies an impact on stratospheric dynamics. The quasi-biennial oscillation (QBO) has been shown to slow down or even vanish, under higher SO2 injections in the equatorial region. But the impact is only qualitatively, but not quantitatively consistent across the different studies using different numerical models. The aim of this study is to understand the reasons behind the differences in the QBO response to SO2 injections between two general circulation models, the Whole Atmosphere Community Climate Model (WACCM-110L) and MAECHAM5-HAM. We show that the response of the QBO to injections with the same SO2 injection rate is very different in the two models, but similar when a similar stratospheric heating rate is induced by SO2 injections of different amounts. The reason for the different response of the QBO corresponding to the same injection rate is very different vertical advection in the two models, even in the control simulation. The stronger vertical advection in WACCM results in a higher aerosol burden and stronger heating of the aerosols, and, consequently in a vanishing QBO at lower injection rate than in simulations with MAECHAM5-HAM.

scholarly journals Effect of latitudinally displaced gravity wave forcing in the lower stratosphere on the polar vortex stability

2019 ◽  
Author(s):  
Nadja Samtleben ◽  
Christoph Jacobi ◽  
Petr Pišoft ◽  
Petr Šácha ◽  
Aleš Kuchař
Keyword(s):  
Refractive Index ◽  
Gravity Wave ◽  
Zonal Wind ◽  
Polar Region ◽  
Middle Atmosphere ◽  
Negative Refractive Index ◽  
Baroclinic Instability ◽  
Polar Vortex ◽  
Circulation Model ◽  
The Impact

Abstract. In order to investigate the impact of a locally confined gravity wave (GW) hotspot, a sensitivity study based on simulations of the middle atmosphere circulation during northern winter was performed with a nonlinear, mechanistic, global circulation model. To this end, for the hotspot region we selected a fixed longitude range in the East Asian region (120° E–170° E) and a latitude range from 22.5° N–52.5° N between 18 km and 30 km, which was then shifted northward in steps of 5°. For the southernmost hotspots, we observe a decreased stationary planetary wave (SPW) 1 activity in the upper stratosphere/lower mesosphere, i.e. less SPWs 1 are propagating upwards. These GW hotspots are leading to a negative refractive index inhibiting SPW propagation at midlatitudes. The decreased SPW 1 activity is connected with an increased zonal mean zonal wind at lower latitudes. This in turn decreases the meridional potential vorticity gradient (qy) from midlatitudes towards the polar region. A reversed qy indicates local baroclinic instability which generates SPWs 1 in the polar region, where we observe a strong positive Eliassen-Palm (EP) divergence. Thus, the EP flux is increasing towards the polar stratosphere (corresponding to enhanced SPW 1 amplitudes) where the SPWs 1 are breaking and the zonal mean zonal wind is decreasing. Thus, the local GW forcing is leading to a displacement of the polar vortex towards lower latitudes. The effect of the local baroclinic instability indicated by the reversed qy also produces SPWs 1 in the lower mesosphere. The effect on the dynamics in the middle atmosphere by GW hotspots which are located northward of 50° N is negligible because the refractive index of the atmosphere is strongly negative in the polar region. Thus, any changes in the SPW activity due to the local GW forcing are quite ineffective.

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