scholarly journals Stratospheric Gravity Waves Generated by Typhoon Saomai (2006): Numerical Modeling in a Moving Frame Following the Typhoon

2010 ◽  
Vol 67 (11) ◽  
pp. 3617-3636 ◽  
Author(s):  
So-Young Kim ◽  
Hye-Yeong Chun
Keyword(s):  
Gravity Waves ◽  
Momentum Flux ◽  
Mesoscale Model ◽  
Horizontal Resolution ◽  
Moving Frame ◽  
Mature Stage ◽  
Small Scale ◽  
Background Wind ◽  
Spiral Bands ◽  
Typhoon Saomai

Abstract Stratospheric gravity waves generated by Typhoon Saomai (2006) were simulated using a mesoscale model in a moving frame of reference following the typhoon. Waves with large amplitudes appear near the domain center because of strong convection in the eyewall of the typhoon. Convection bands propagating outward from the storm center also generate waves propagating to the stratosphere. Convective forcing is significant in various propagation directions, with maximum power in slowly moving eastward components due to convection in the eyewall. The forcing exhibits large amplitude at a speed of 8–16 m s−1 in the eastward direction in which spiral bands are mainly developed. Induced gravity waves in the stratosphere are dominant in the eastward, northeastward, and southeastward propagation directions, since westward waves are mostly filtered by the background wind below z = 25 km. While the typhoon moves northwestward for 78 h, the wave characteristics vary through time depending on the evolution of the eyewall and spiral bands. Horizontal wavelengths of waves are longer in the mature and decaying stages than in the developing stage of the typhoon, likely because of a more dominant concentric eyewall in the mature and decaying stages. The spectral peak of the waves is at ∼20 km (∼50 km) horizontal wavelength in the developing (mature) stage, and the wave amplitudes are larger in the developing stages. The dominant contribution to the momentum flux is from waves with horizontal wavelengths longer than 80 km. Positive momentum flux decreases with overall height and the resultant positive drag can cause deceleration of northeasterly background wind. Sensitivity of the model results to horizontal resolution reveals that small-scale waves resolved in the present simulations with 3-km resolution cannot be fully represented with 9- or 27-km resolutions.

scholarly journals Intercomparison of AIRS and HIRDLS stratospheric gravity wave observations

2018 ◽  
Vol 11 (1) ◽  
pp. 215-232 ◽  
Author(s):  
Catrin I. Meyer ◽  
Manfred Ern ◽  
Lars Hoffmann ◽  
Quang Thai Trinh ◽  
M. Joan Alexander
Keyword(s):  
High Resolution ◽  
Gravity Wave ◽  
Gravity Waves ◽  
Momentum Flux ◽  
Wave Spectrum ◽  
Horizontal Resolution ◽  
Wave Activity ◽  
Large Variability ◽  
Wave Event ◽  
The Waves

Abstract. We investigate stratospheric gravity wave observations by the Atmospheric InfraRed Sounder (AIRS) aboard NASA's Aqua satellite and the High Resolution Dynamics Limb Sounder (HIRDLS) aboard NASA's Aura satellite. AIRS operational temperature retrievals are typically not used for studies of gravity waves, because their vertical and horizontal resolution is rather limited. This study uses data of a high-resolution retrieval which provides stratospheric temperature profiles for each individual satellite footprint. Therefore the horizontal sampling of the high-resolution retrieval is 9 times better than that of the operational retrieval. HIRDLS provides 2-D spectral information of observed gravity waves in terms of along-track and vertical wavelengths. AIRS as a nadir sounder is more sensitive to short-horizontal-wavelength gravity waves, and HIRDLS as a limb sounder is more sensitive to short-vertical-wavelength gravity waves. Therefore HIRDLS is ideally suited to complement AIRS observations. A calculated momentum flux factor indicates that the waves seen by AIRS contribute significantly to momentum flux, even if the AIRS temperature variance may be small compared to HIRDLS. The stratospheric wave structures observed by AIRS and HIRDLS often agree very well. Case studies of a mountain wave event and a non-orographic wave event demonstrate that the observed phase structures of AIRS and HIRDLS are also similar. AIRS has a coarser vertical resolution, which results in an attenuation of the amplitude and coarser vertical wavelengths than for HIRDLS. However, AIRS has a much higher horizontal resolution, and the propagation direction of the waves can be clearly identified in geographical maps. The horizontal orientation of the phase fronts can be deduced from AIRS 3-D temperature fields. This is a restricting factor for gravity wave analyses of limb measurements. Additionally, temperature variances with respect to stratospheric gravity wave activity are compared on a statistical basis. The complete HIRDLS measurement period from January 2005 to March 2008 is covered. The seasonal and latitudinal distributions of gravity wave activity as observed by AIRS and HIRDLS agree well. A strong annual cycle at mid- and high latitudes is found in time series of gravity wave variances at 42 km, which has its maxima during wintertime and its minima during summertime. The variability is largest during austral wintertime at 60∘ S. Variations in the zonal winds at 2.5 hPa are associated with large variability in gravity wave variances. Altogether, gravity wave variances of AIRS and HIRDLS are complementary to each other. Large parts of the gravity wave spectrum are covered by joint observations. This opens up fascinating vistas for future gravity wave research.

scholarly journals Mesospheric gravity wave activity estimated via airglow imagery, multistatic meteor radar, and SABER data taken during the SIMONe–2018 campaign

2020 ◽  
Author(s):  
Fabio Vargas ◽  
Jorge L. Chau ◽  
Harikrishnan Charuvil Asokan ◽  
Michael Gerding
Keyword(s):  
Gravity Waves ◽  
Momentum Flux ◽  
Large Scale ◽  
Lower Thermosphere ◽  
Small Scale ◽  
Meteor Radar ◽  
Mean Flow ◽  
Horizontal Scale ◽  
Momentum Fluxes ◽  
Mesosphere And Lower Thermosphere

Abstract. We describe in this study the analysis of small and large horizontal scale gravity waves from datasets composed of images from multiple mesospheric nightglow emissions as well as multistatic specular meteor radar (MSMR) winds collected in early November 2018, during the SIMONe–2018 campaign. These ground-based measurements are supported by temperature and neutral density profiles from TIMED/SABER satellite in orbits near Kühlungsborn, northern Germany (54.1° N, 11.8° E). The scientific goals here include the characterization of gravity waves and their interaction with the mean flow in the mesosphere and lower thermosphere and their relationship to dynamical conditions in the lower and upper atmosphere. We obtain intrinsic parameters of small and large horizontal scale gravity waves and characterize their impact in the mesosphere region via momentum flux and flux divergence estimations. We have verified that a small percent of the detected wave events are responsible for most of the momentum flux measured during the campaign from oscillations seen in the airglow brightness and MSMR winds. From the analysis of small-scale gravity waves in airglow images, we have found wave momentum fluxes ranging from 0.38 to 24.74 m2/s2 (0.88 ± 0.73 m2/s2 on average), with a total of 586.96 m2/s2 (sum over all 362 detected waves). However, small horizontal scale waves with flux > 3 m2/s2 (11 % of the events) transport 50 % of the total measured flux. Likewise, wave events having flux > 10 m2/s2 (2 % of the events) transport 20 % of the total flux. The examination of two large-scale waves seen simultaneously in airglow keograms and MSMR winds revealed relative amplitudes > 35 %, which translates into momentum fluxes of 21.2–29.6 m/s. In terms of gravity wave–mean flow interactions, these high momentum flux waves could cause decelerations of 22–41 m/s/day (small-scale waves) and 38–43 m/s/day (large-scale waves) if breaking or dissipating within short distances in the mesosphere and lower thermosphere region. The dominant large-scale waves might be the result of secondary gravity excited from imbalanced flow in the stratosphere caused by primary wave breaking.

scholarly journals Enhancing the spatiotemporal features of polar mesosphere summer echoes using coherent MIMO and radar imaging at MAARSY

2019 ◽  
Vol 12 (2) ◽  
pp. 955-969 ◽  
Author(s):  
Juan Miguel Urco ◽  
Jorge Luis Chau ◽  
Tobias Weber ◽  
Ralph Latteck
Keyword(s):  
Angular Resolution ◽  
Imaging Techniques ◽  
Radar Imaging ◽  
Horizontal Resolution ◽  
Atmospheric Dynamics ◽  
Small Scale ◽  
Polar Regions ◽  
Background Wind ◽  
Input Multiple Output ◽  
Summer Echoes

Abstract. Polar mesospheric summer echoes (PMSEs) are very strong radar echoes caused by the presence of ice particles, turbulence, and free electrons in the mesosphere over polar regions. For more than three decades, PMSEs have been used as natural tracers of the complicated atmospheric dynamics of this region. Neutral winds and turbulence parameters have been obtained assuming PMSE horizontal homogeneity on scales of tens of kilometers. Recent radar imaging studies have shown that PMSEs are not homogeneous on these scales and instead they are composed of kilometer-scale structures. In this paper, we present a technique that allows PMSE observations with unprecedented angular resolution (∼0.6∘). The technique combines the concept of coherent MIMO (Multiple Input Multiple Output) and two high-resolution imaging techniques, i.e., Capon and maximum entropy (MaxEnt). The resulting resolution is evaluated by imaging specular meteor echoes. The gain in angular resolution compared to previous approaches using SIMO (Single Input Multiple Output) and Capon is at least a factor of 2; i.e., at 85 km, we obtain a horizontal resolution of ∼900 m. The advantage of the new technique is evaluated with two events of 3-D PMSE structures showing: (1) horizontal wavelengths of 8–10 km and periods of 4–7 min, drifting with the background wind, and (2) horizontal wavelengths of 12–16 km and periods of 15–20 min, not drifting with the background wind. Besides the advantages of the implemented technique, we discuss its current challenges, like the use of reduced power aperture and processing time, as well as the future opportunities for improving the understanding of the complex small-scale atmospheric dynamics behind PMSEs.

scholarly journals Momentum Flux of Convective Gravity Waves Derived from an Offline Gravity Wave Parameterization. Part II: Impacts on the Quasi-Biennial Oscillation

2018 ◽  
Vol 75 (11) ◽  
pp. 3753-3775 ◽  
Author(s):  
Min-Jee Kang ◽  
Hye-Yeong Chun ◽  
Young-Ha Kim ◽  
Peter Preusse ◽  
Manfred Ern
Keyword(s):  
Shear Zone ◽  
Gravity Waves ◽  
Momentum Flux ◽  
Large Scale ◽  
Reanalysis Data ◽  
Equatorial Region ◽  
Small Scale ◽  
Quasi Biennial Oscillation ◽  
Convective Gravity Waves ◽  
Biennial Oscillation

Abstract The characteristics of small-scale convective gravity waves (CGWs; horizontal wavelengths <100 km) and their contributions to the large-scale flow in the stratosphere, including the quasi-biennial oscillation (QBO), are investigated using an offline calculation of a source-dependent, physically based CGW parameterization with global reanalysis data from 1979 to 2010. The CGW momentum flux (CGWMF) and CGW drag (CGWD) are calculated from the cloud top (source level) to the upper stratosphere using a Lindzen-type wave propagation scheme. The 32-yr-mean CGWD exhibits large magnitudes in the tropical upper stratosphere and near the stratospheric polar night jet (~60°). The maximum positive drag is 0.1 (1.5) m s−1 day−1, and the maximum negative drag is −0.9 (−0.7) m s−1 day−1 in January (July) between 3 and 1 hPa. In the tropics, the momentum forcing by CGWs at 30 hPa associated with the QBO in the westerly shear zone is 3.5–6 m s−1 month−1, which is smaller than that by Kelvin waves, while that by CGWs in the easterly shear zone (3.1–6 m s−1 month−1) is greater than that by any other equatorial planetary waves or inertio-gravity waves (inertio-GWs). Composite analyses of the easterly QBO (EQBO) and westerly QBO (WQBO) phases reveal that the zonal CGWMF is concentrated near 10°N and that the negative (positive) CGWD extends latitudinally to ±20° (±10°) at 30 hPa. The strongest (weakest) negative CGWD is in March–May (September–November) during the EQBO, and the strongest (weakest) positive CGWD is in June–August (March–May) during the WQBO. The CGWMF and CGWD are generally stronger during El Niño than during La Niña in the equatorial region.

scholarly journals Vertical resolution dependence of gravity wave momentum flux simulated by an atmospheric general circulation model

2015 ◽  
Vol 8 (6) ◽  
pp. 1637-1644 ◽  
Author(s):  
S. Watanabe ◽  
K. Sato ◽  
Y. Kawatani ◽  
M. Takahashi
Keyword(s):  
Gravity Wave ◽  
Gravity Waves ◽  
Momentum Flux ◽  
General Circulation ◽  
Horizontal Resolution ◽  
Sensitivity Test ◽  
Vertical Resolution ◽  
Time Step ◽  
Atmospheric General Circulation ◽  
Wave Momentum

Abstract. The dependence of the gravity wave spectra of energy and momentum flux on the horizontal resolution and time step of atmospheric general circulation models (AGCMs) has been thoroughly investigated in the past. In contrast, much less attention has been given to the dependence of these gravity wave parameters on models' vertical resolutions. The present study demonstrates the dependence of gravity wave momentum flux (GWMF) in the stratosphere and mesosphere on the model's vertical resolution, which is evaluated using an AGCM with a horizontal resolution of about 0.56°. We performed a series of sensitivity test simulations changing only the model's vertical resolution above a height of 8 km, and found a global reduction of GWMF with increasing vertical resolution. Inertial gravity waves with short vertical wavelengths simulated at higher vertical resolutions might play an important role in determining GWMF in the summertime stratosphere. The sensitivity test simulation also demonstrated the importance of the model's vertical resolution on representing realistic behaviors of gravity waves near their critical level.

Momentum Fluxes of Gravity Waves Generated by Variable Froude Number Flow over Three-Dimensional Obstacles

2010 ◽  
Vol 67 (7) ◽  
pp. 2260-2278 ◽  
Author(s):  
Stephen D. Eckermann ◽  
John Lindeman ◽  
Dave Broutman ◽  
Jun Ma ◽  
Zafer Boybeyi
Keyword(s):  
Froude Number ◽  
Gravity Waves ◽  
Momentum Flux ◽  
Mesoscale Model ◽  
Three Dimensional ◽  
Wave Drag ◽  
Analytical Relation ◽  
Far Field ◽  
Pressure Drag ◽  
Momentum Fluxes

Abstract Fully nonlinear mesoscale model simulations are used to investigate the momentum fluxes of gravity waves that emerge at a “far-field” height of 6 km from steady unsheared flow over both an axisymmetric and elliptical obstacle for nondimensional mountain heights ĥm = Fr−1 in the range 0.1–5, where Fr is the surface Froude number. Fourier- and Hilbert-transform diagnostics of model output yield local estimates of phase-averaged momentum flux, while area integrals of momentum flux quantify the amount of surface pressure drag that translates into far-field gravity waves, referred to here as the “wave drag” component. Estimates of surface and wave drag are compared to parameterization predictions and theory. Surface dynamics transition from linear to high-drag (wave breaking) states at critical inverse Froude numbers Frc−1 predicted to within 10% by transform relations. Wave drag peaks at Frc−1 < ĥm ≲ 2, where for the elliptical obstacle both surface and wave drag vacillate owing to cyclical buildup and breakdown of waves. For the axisymmetric obstacle, this occurs only at ĥm = 1.2. At ĥm ≳ 2–3 vacillation abates and normalized pressure drag assumes a common normalized form for both obstacles that varies approximately as ĥm−1.3. Wave drag in this range asymptotes to a constant absolute value that, despite its theoretical shortcomings, is predicted to within 10%–40% by an analytical relation based on linear clipped-obstacle drag for a Sheppard-based prediction of dividing streamline height. Constant wave drag at ĥm ∼ 2–5 arises despite large variations with ĥm in the three-dimensional morphology of the local wave momentum fluxes. Specific implications of these results for the parameterization of subgrid-scale orographic drag in global climate and weather models are discussed.

scholarly journals Gravity wave reflection and its influence on the consistency of temperature- and wind-based momentum fluxes simulated above Typhoon Ewiniar

2012 ◽  
Vol 12 (22) ◽  
pp. 10787-10795 ◽  
Author(s):  
Y.-H. Kim ◽  
H.-Y. Chun ◽  
P. Preusse ◽  
M. Ern ◽  
S.-Y. Kim
Keyword(s):  
Gravity Wave ◽  
Momentum Flux ◽  
Wave Reflection ◽  
Mesoscale Model ◽  
Background Wind ◽  
Stability Change ◽  
Propagating Waves ◽  
Momentum Fluxes ◽  
Flux Profile

Abstract. For a case study of Typhoon Ewiniar performed with a mesoscale model, we compare stratospheric gravity wave (GW) momentum flux determined from temperature variances by applying GW polarization relations and by assuming upward propagating waves, with GW momentum flux calculated from model winds which is considered as a reference. The temperature-based momentum-flux profile exhibits positive biases relative to the reference, which fluctuate significantly with altitude. The vertically-averaged magnitude of the positive biases is about 14% of the reference momentum flux. We found that this deviation from the reference stems from the interference between upward and downward propagating waves. The downward propagating GWs are due mainly to partial reflections of upward propagating waves at altitudes where the background wind and stability change with height. When the upward and downward propagating waves are decomposed and their momentum fluxes are calculated separately from temperature perturbations, the fraction of the momentum flux arising from the downward propagating waves is about 4.5–8.2% of that from the upward propagating waves. The net momentum flux of upward and downward propagating GWs agrees well with the reference from the model wind perturbations. The implications of this study for the GW momentum-flux observations from satellites are discussed.

scholarly journals Short-period mesospheric gravity waves and their sources at the South Pole

2017 ◽  
Vol 17 (2) ◽  
pp. 911-919 ◽  
Author(s):  
Dhvanit Mehta ◽  
Andrew J. Gerrard ◽  
Yusuke Ebihara ◽  
Allan T. Weatherwax ◽  
Louis J. Lanzerotti
Keyword(s):  
Gravity Waves ◽  
Baroclinic Instability ◽  
Significant Proportion ◽  
Polar Vortex ◽  
Small Scale ◽  
South Pole ◽  
Background Wind ◽  
Wind Fields ◽  
Short Period ◽  
Spatial And Temporal Characteristics

Abstract. The sourcing locations and mechanisms for short-period, upward-propagating gravity waves at high polar latitudes remain largely unknown. Using all-sky imager data from the Amundsen–Scott South Pole Station, we determine the spatial and temporal characteristics of 94 observed small-scale waves in 3 austral winter months in 2003 and 2004. These data, together with background atmospheres from synoptic and/or climatological empirical models, are used to model gravity wave propagation from the polar mesosphere to each wave's source using a ray-tracing model. Our results provide a compelling case that a significant proportion of the observed waves are launched in several discrete layers in the tropopause and/or stratosphere. Analyses of synoptic geopotentials and temperatures indicate that wave formation is a result of baroclinic instability processes in the stratosphere and the interaction of planetary waves with the background wind fields in the tropopause. These results are significant for defining the influences of the polar vortex on the production of these small-scale, upward-propagating gravity waves at the highest polar latitudes.

scholarly journals Intercomparison of AIRS and HIRDLS stratospheric gravity wave observations

2017 ◽  
Author(s):  
Catrin I. Meyer ◽  
Manfred Ern ◽  
Lars Hoffmann ◽  
Quang Thai Trinh ◽  
M. Joan Alexander
Keyword(s):  
High Resolution ◽  
Gravity Wave ◽  
Gravity Waves ◽  
Momentum Flux ◽  
Wave Spectrum ◽  
Horizontal Resolution ◽  
Wave Activity ◽  
Large Variability ◽  
Wave Event ◽  
The Waves

Abstract. We investigate stratospheric gravity wave observations by the Atmospheric InfraRed Sounder (AIRS) aboard NASA's Aqua satellite and the High Resolution Dynamics Limb Sounder (HIRDLS) aboard NASA's Aura satellite. AIRS operational temperature retrievals are typically not used for studies of gravity waves, because their horizontal resolution is rather limited. This study uses data of a high-resolution retrieval which provides stratospheric temperature profiles for each individual satellite footprint. Therefore the horizontal sampling of the high-resolution retrieval is nine times better than that of the operational retrieval. HIRDLS provides 2D spectral formation of observed gravity waves in terms of along-track and vertical wavelengths. AIRS as a nadir sounder is more sensitive to short horizontal wavelength gravity waves and HIRDLS as a limb sounder is more sensitive to short vertical wavelength gravity waves. Therefore HIRDLS is ideally suited to complement AIRS observations. A calculated momentum flux factor indicates that the waves seen by AIRS contribute significantly to momentum flux, even if the AIRS temperature variance may be small compared to HIRDLS. The stratospheric wave structures observed by AIRS and HIRDLS agree often very well. Case studies of a mountain wave event and a non-orographic wave event demonstrate that the observed phase structures of AIRS and HIRDLS are conform. AIRS has a coarser vertical resolution, which results in an attenuation of the amplitude and coarser vertical wavelengths compared to HIRDLS. However, AIRS has a much higher horizontal resolution and the propagation direction of the waves can be clearly identified in geographical maps. The horizontal orientation of the phase fronts can be deduced from AIRS 3D temperature fields. This is a restricting factor for gravity wave analyses of limb measurements. Additionally, temperature variances with respect to stratospheric gravity wave activity are compared on a statistical basis. The complete HIRDLS measurement period from January 2005 to March 2008 is covered. The seasonal and latitudinal distributions of gravity wave activity as observed by AIRS and HIRDLS fit well. A strong annual cycle at mid and high latitudes is found in time series of gravity wave variances at 42 km, which has during wintertime its maxima and during summertime its minima. During austral wintertime at 60° S the variability is largest. Variations in the zonal winds at 2.5 hPa are associated with large variability in gravity wave variances. Altogether, gravity wave variances of AIRS and HIRDLS are conform and complementary to each other. Thereby large parts of the gravity wave spectrum are covered by joint observations. This opens up fascinating vistas for future gravity wave research.

scholarly journals Mesospheric gravity wave activity estimated via airglow imagery, multistatic meteor radar, and SABER data taken during the SIMONe–2018 campaign

2021 ◽  
Vol 21 (17) ◽  
pp. 13631-13654
Author(s):  
Fabio Vargas ◽  
Jorge L. Chau ◽  
Harikrishnan Charuvil Asokan ◽  
Michael Gerding
Keyword(s):  
Gravity Wave ◽  
Gravity Waves ◽  
Momentum Flux ◽  
Large Scale ◽  
Lower Thermosphere ◽  
Small Scale ◽  
Meteor Radar ◽  
Mean Flow ◽  
Flux Divergence ◽  
Mesosphere And Lower Thermosphere

Abstract. We describe in this study the analysis of small and large horizontal-scale gravity waves from datasets composed of images from multiple mesospheric airglow emissions as well as multistatic specular meteor radar (MSMR) winds collected in early November 2018, during the SIMONe–2018 (Spread-spectrum Interferometric Multi-static meteor radar Observing Network) campaign. These ground-based measurements are supported by temperature and neutral density profiles from TIMED/SABER (Thermosphere, Ionosphere, Mesosphere Energetics and Dynamics/Sounding of the Atmosphere using Broadband Emission Radiometry) satellite in orbits near Kühlungsborn, northern Germany (54.1∘ N, 11.8∘ E). The scientific goals here include the characterization of gravity waves and their interaction with the mean flow in the mesosphere and lower thermosphere and their relationship to dynamical conditions in the lower and upper atmosphere. We have obtained intrinsic parameters of small- and large-scale gravity waves and characterized their impact in the mesosphere via momentum flux (FM) and momentum flux divergence (FD) estimations. We have verified that a small percentage of the detected wave events is responsible for most of FM measured during the campaign from oscillations seen in the airglow brightness and MSMR winds taken over 45 h during four nights of clear-sky observations. From the analysis of small-scale gravity waves (λh < 725 km) seen in airglow images, we have found FM ranging from 0.04–24.74 m2 s−2 (1.62 ± 2.70 m2 s−2 on average). However, small-scale waves with FM > 3 m2 s−2 (11 % of the events) transport 50 % of the total measured FM. Likewise, wave events of FM > 10 m2 s−2 (2 % of the events) transport 20 % of the total. The examination of large-scale waves (λh > 725 km) seen simultaneously in airglow keograms and MSMR winds revealed amplitudes > 35 %, which translates into FM = 21.2–29.6 m2 s−2. In terms of gravity-wave–mean-flow interactions, these large FM waves could cause decelerations of FD = 22–41 m s−1 d−1 (small-scale waves) and FD = 38–43 m s−1 d−1 (large-scale waves) if breaking or dissipating within short distances in the mesosphere and lower thermosphere region.

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