scholarly journals Concentric gravity waves in the mesosphere generated by deep convective plumes in the lower atmosphere near Fort Collins, Colorado

2009 ◽  
Vol 114 (D6) ◽  
Author(s):  
Jia Yue ◽  
Sharon L. Vadas ◽  
Chiao-Yao She ◽  
Takuji Nakamura ◽  
Steven C. Reising ◽  
...  
Keyword(s):  
Gravity Waves ◽  
Lower Atmosphere ◽  
Fort Collins

scholarly journals Frequency variations of gravity waves interacting with a time-varying tide

2013 ◽  
Vol 31 (10) ◽  
pp. 1731-1743 ◽  
Author(s):  
C. M. Huang ◽  
S. D. Zhang ◽  
F. Yi ◽  
K. M. Huang ◽  
Y. H. Zhang ◽  
...  
Keyword(s):  
Gravity Waves ◽  
High Frequency ◽  
Lower Atmosphere ◽  
Horizontal Wind ◽  
Frequency Variation ◽  
Time Varying ◽  
Transient Nature ◽  
Critical Layers ◽  
Favorable Conditions ◽  
Frequency Variations

Abstract. Using a nonlinear, 2-D time-dependent numerical model, we simulate the propagation of gravity waves (GWs) in a time-varying tide. Our simulations show that when a GW packet propagates in a time-varying tidal-wind environment, not only its intrinsic frequency but also its ground-based frequency would change significantly. The tidal horizontal-wind acceleration dominates the GW frequency variation. Positive (negative) accelerations induce frequency increases (decreases) with time. More interestingly, tidal-wind acceleration near the critical layers always causes the GW frequency to increase, which may partially explain the observations that high-frequency GW components are more dominant in the middle and upper atmosphere than in the lower atmosphere. The combination of the increased ground-based frequency of propagating GWs in a time-varying tidal-wind field and the transient nature of the critical layer induced by a time-varying tidal zonal wind creates favorable conditions for GWs to penetrate their originally expected critical layers. Consequently, GWs have an impact on the background atmosphere at much higher altitudes than expected, which indicates that the dynamical effects of tidal–GW interactions are more complicated than usually taken into account by GW parameterizations in global models.

scholarly journals Spatial and seasonal variability of medium- and high-frequency gravity waves in the lower atmosphere revealed by US radiosonde data

2014 ◽  
Vol 32 (9) ◽  
pp. 1129-1143 ◽  
Author(s):  
S. D. Zhang ◽  
C. M. Huang ◽  
K. M. Huang ◽  
F. Yi ◽  
Y. H. Zhang ◽  
...  
Keyword(s):  
Energy Density ◽  
Gravity Waves ◽  
Seasonal Variability ◽  
High Frequency ◽  
Lower Atmosphere ◽  
Radiosonde Data ◽  
High Latitudes ◽  
Middle Latitudes ◽  
Momentum Fluxes ◽  
Horizontal Momentum

Abstract. We extended the broad spectral method proposed by Zhang et al. (2013) for the extraction of medium- and high-frequency gravity waves (MHGWs). This method was applied to 11 years (1998–2008) of radiosonde data from 92 stations in the Northern Hemisphere to investigate latitudinal, continuous vertical and seasonal variability of MHGW parameters in the lower atmosphere (2–25 km). The latitudinal and vertical distributions of the wave energy density and horizontal momentum fluxes as well as their seasonal variations exhibit considerable consistency with those of inertial gravity waves. Despite the consistency, the MHGWs have much larger energy density, horizontal momentum fluxes and wave force, indicating the more important role of MHGWs in energy and momentum transportation and acceleration of the background. For the observed MHGWs, the vertical wavelengths are usually larger than 8 km; the horizontal wavelengths peak in the middle troposphere at middle–high latitudes. These characteristics are obviously different from inertial gravity waves. The energy density and horizontal momentum fluxes have similar latitude-dependent seasonality: both of them are dominated by a semiannual variation at low latitudes and an annual variation at middle latitudes; however at high latitudes, they often exhibit more than two peaks per year in the troposphere. Compared with the inertial GWs, the derived intrinsic frequencies are more sensitive to the spatiotemporal variation of the buoyancy frequency, and at all latitudinal regions they are higher in summer. The wavelengths have a weaker seasonal variation; an evident annual cycle can be observed only at middle latitudes.

scholarly journals A Two-Layer Model for Steady-Amplitude Gravity Waves and Convection Generated by a Thermal Forcing

2018 ◽  
Vol 75 (7) ◽  
pp. 2199-2216 ◽  
Author(s):  
A. A. M. Sayed ◽  
L. J. Campbell
Keyword(s):  
Gravity Waves ◽  
Lower Layer ◽  
Stable Stratification ◽  
Internal Gravity Waves ◽  
Conservation Equation ◽  
Lower Atmosphere ◽  
Thermal Forcing ◽  
Energy Conservation Equation ◽  
Vertical Location ◽  
Convective Cells

Abstract A two-dimensional two-layer mathematical model is described representing internal gravity waves and convection generated by a thermal forcing in the lower atmosphere. The model consists of an upper layer with stable stratification, a lower layer with unstable stratification, and a thermal forcing in the form of a nonhomogeneous term in the energy conservation equation. Exact analytical solutions are derived for some simple configurations. Depending on the vertical location and depth of the thermal forcing, the model can be used to represent different configurations in which gravity waves are generated by diabatic heating. When the thermal forcing is centered in the lower layer, convective cells are generated in the lower layer, and gravity waves are forced and propagate upward from the interface between the two layers. When the thermal forcing is centered at the interface, the convection in the lower layer is weaker, and gravity waves are forced by the direct effect of the thermal forcing in the upper layer and the influence of the convective cells below. Steady-amplitude solutions for the vertical profile of the gravity waves and convection are derived and generalized to include cases where there is a spectrum of horizontal wavenumbers or vertical wavenumbers or frequencies present.

Dynamical phenomena in the atmosphere of Mars imaged with the Visual Monitoring Camera onboard Mars Express

2020 ◽  
Author(s):  
Teresa del Río-Gaztelurrutia ◽  
Agustín Sánchez-Lavega ◽  
Jorge Hernández-Bernal ◽  
Ricardo Hueso ◽  
Alejandro Cardesín-Moinelo ◽  
...  
Keyword(s):  
Gravity Waves ◽  
Dust Storms ◽  
Lower Atmosphere ◽  
Temperature Fields ◽  
Polar Regions ◽  
Storm Activity ◽  
Visual Monitoring ◽  
Mars Express ◽  
Wide Range ◽  
Monitoring Camera

<p>The Visual Monitoring Camera on board Mars Express provides images of varied resolutions, covering a wide range of locations and seasons, and has been taking images for several Martian years. This large image database can be exploited to study various dynamical phenomena, and in this work, we concentrate on the study of cloud and dust storm activity in the polar regions, describing vortices, cloud evolution, and regional dust storms as well as the presence of gravity waves. Tracking the motions of details in the images, we estimate local winds, compare our results with predictions from the Mars Climate Database in different scenari, and study their seasonal evolution and potential inter annual variability. Further, resolution of images captured near pericenter is sufficient to allow the detection of gravity waves in the troposphere, identified as regular patterns in the cloud fields. We measure some of the basic properties of these waves, such as horizontal wave vector and extension of wave trains. We analyse those properties in relation to their aerographic location, local time and season, in the context of a recent study of the distribution of gravity waves on the lower atmosphere of Mars as inferred from the analysis of temperature fields by the Mars Climate Sounder onboard the Mars Reconnaissance Orbiter (MRO) (Heavens et al. ICARUS 2020).</p>

scholarly journals Studies on atmospheric gravity wave activity in the troposphere and lower stratosphere over a tropical station at Gadanki

2005 ◽  
Vol 23 (10) ◽  
pp. 3237-3260 ◽  
Author(s):  
I. V. Subba Reddy ◽  
D. Narayana Rao ◽  
A. Narendra Babu ◽  
M. Venkat Ratnam ◽  
P. Kishore ◽  
...  
Keyword(s):  
Gravity Wave ◽  
Gravity Waves ◽  
Lower Stratosphere ◽  
Wave Length ◽  
Wave Activity ◽  
Lower Atmosphere ◽  
Wind Fields ◽  
Atmospheric Gravity Wave ◽  
Short Period ◽  
Atmospheric Gravity

Abstract. MST radars are powerful tools to study the mesosphere, stratosphere and troposphere and have made considerable contributions to the studies of the dynamics of the upper, middle and lower atmosphere. Atmospheric gravity waves play a significant role in controlling middle and upper atmospheric dynamics. To date, frontal systems, convection, wind shear and topography have been thought to be the sources of gravity waves in the troposphere. All these studies pointed out that it is very essential to understand the generation, propagation and climatology of gravity waves. In this regard, several campaigns using Indian MST Radar observations have been carried out to explore the gravity wave activity over Gadanki in the troposphere and the lower stratosphere. The signatures of the gravity waves in the wind fields have been studied in four seasons viz., summer, monsoon, post-monsoon and winter. The large wind fluctuations were more prominent above 10 km during the summer and monsoon seasons. The wave periods are ranging from 10 min-175 min. The power spectral densities of gravity waves are found to be maximum in the stratospheric region. The vertical wavelength and the propagation direction of gravity waves were determined using hodograph analysis. The results show both down ward and upward propagating waves with a maximum vertical wave length of 3.3 km. The gravity wave associated momentum fluxes show that long period gravity waves carry more momentum flux than the short period waves and this is presented.

scholarly journals Intensive radiosonde observations of gravity waves in the lower atmosphere over Yichang (111°18´ E, 30°42´ N), China

2008 ◽  
Vol 26 (7) ◽  
pp. 2005-2018 ◽  
Author(s):  
◽  
◽  
◽  
Keyword(s):  
Energy Density ◽  
Gravity Waves ◽  
Lower Stratosphere ◽  
Daily Basis ◽  
Lower Atmosphere ◽  
Wave Number ◽  
Kinetic Energy Density ◽  
Seasonal Differences ◽  
Seasonal Characteristics ◽  
The Mean

Abstract. The characteristics of dynamical and thermal structures and inertial gravity waves (GWs) in the troposphere and lower stratosphere (TLS) over Yichang (111°18´ E, 30°42´ N) were statistically studied by using the data from intensive radiosonde observations in August 2006 (summer month) and January 2007 (winter month) on an eight-times-daily basis. The background atmosphere structures observed in different months exhibit evident seasonal differences, and the zonal wind in winter has a prominent tropospheric jet with a maximum wind speed of about 60 ms−1 occurring at the height of 11.5 km. The statistical results of the inertial GWs in our two-month observations are generally consistent with previous observations in the mid-latitudes. In the summer month, the mean intrinsic frequency and vertical wavelength of the inertial GWs in the troposphere are still larger than those in the lower stratosphere with the absence of intensive tropospheric jets, suggesting that the Doppler shifting due to the tropospheric jets cannot completely account for the differences between the GWs in the troposphere and lower stratosphere. Compared with the observations in the summer month, some interesting seasonal characteristics of the GWs are revealed by the observations in the winter month: 1) more and stronger tropospheric GWs are observed in the winter month; 2) less and weaker GWs are observed in the lower stratosphere in winter; 3) the ratio of the mean GW kinetic energy density to potential energy density is smaller than 1 in winter, which contrasts to that in summer. Most of the seasonal differences can be explained by the intensive tropospheric jets in winter. In both the summer and winter months, the fitted spectral slopes of the vertical wave number spectra for GWs are generally smaller than the canonical spectral slope of −3. Correlation analyses suggest that the tropospheric jet induced wind shear is the dominant source for GWs in both the troposphere and lower stratosphere. Moreover, the tropospheric (lower stratospheric) GWs are found to be modulated by the quasi-7-day (10-day) PW, and the impacts of the diurnal tide on the GWs are relatively weak.

scholarly journals Satellite observations of middle atmosphere–thermosphere vertical coupling by gravity waves

2018 ◽  
Vol 36 (2) ◽  
pp. 425-444 ◽  
Author(s):  
Quang Thai Trinh ◽  
Manfred Ern ◽  
Eelco Doornbos ◽  
Peter Preusse ◽  
Martin Riese
Keyword(s):  
Ocean Circulation ◽  
Gravity Waves ◽  
Middle Atmosphere ◽  
Density Fluctuations ◽  
Lower Atmosphere ◽  
Research Approach ◽  
Vertical Coupling ◽  
Broadband Emission ◽  
Momentum Fluxes ◽  
Positive Correlations

Abstract. Atmospheric gravity waves (GWs) are essential for the dynamics of the middle atmosphere. Recent studies have shown that these waves are also important for the thermosphere/ionosphere (T/I) system. Via vertical coupling, GWs can significantly influence the mean state of the T/I system. However, the penetration of GWs into the T/I system is not fully understood in modeling as well as observations. In the current study, we analyze the correlation between GW momentum fluxes observed in the middle atmosphere (30–90 km) and GW-induced perturbations in the T/I. In the middle atmosphere, GW momentum fluxes are derived from temperature observations of the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) satellite instrument. In the T/I, GW-induced perturbations are derived from neutral density measured by instruments on the Gravity field and Ocean Circulation Explorer (GOCE) and CHAllenging Minisatellite Payload (CHAMP) satellites. We find generally positive correlations between horizontal distributions at low altitudes (i.e., below 90 km) and horizontal distributions of GW-induced density fluctuations in the T/I (at 200 km and above). Two coupling mechanisms are likely responsible for these positive correlations: (1) fast GWs generated in the troposphere and lower stratosphere can propagate directly to the T/I and (2) primary GWs with their origins in the lower atmosphere dissipate while propagating upwards and generate secondary GWs, which then penetrate up to the T/I and maintain the spatial patterns of GW distributions in the lower atmosphere. The mountain-wave related hotspot over the Andes and Antarctic Peninsula is found clearly in observations of all instruments used in our analysis. Latitude–longitude variations in the summer midlatitudes are also found in observations of all instruments. These variations and strong positive correlations in the summer midlatitudes suggest that GWs with origins related to convection also propagate up to the T/I. Different processes which likely influence the vertical coupling are GW dissipation, possible generation of secondary GWs, and horizontal propagation of GWs. Limitations of the observations as well as of our research approach are discussed. Keywords. Ionosphere (ionosphere–atmosphere interactions)

scholarly journals The QBO as potential amplifier and conduit to lower altitudes of solar cycle influence

2007 ◽  
Vol 25 (5) ◽  
pp. 1071-1092 ◽  
Author(s):  
H. G. Mayr ◽  
J. G. Mengel ◽  
C. L. Wolff ◽  
F. T. Huang ◽  
H. S. Porter
Keyword(s):  
Solar Cycle ◽  
Gravity Waves ◽  
Radiative Forcing ◽  
Model Simulation ◽  
Equatorial Region ◽  
Lower Atmosphere ◽  
Quasi Biennial Oscillation ◽  
Wave Forcing ◽  
Wind Measurements ◽  
Solar Uv

Abstract. In several papers, the solar cycle (SC) effect in the lower atmosphere has been linked observationally to the Quasi-biennial Oscillation (QBO) of the zonal circulation. Salby and Callaghan (2000) in particular analyzed the QBO wind measurements, covering more than 40 years, and discovered that they contain a large SC signature at 20 km. We present here the results from a study with our 3-D Numerical Spectral Model (NSM), which relies primarily on parameterized gravity waves (GW) to describe the QBO. In our model, the period of the SC is taken to be 10 years, and the relative amplitude of radiative forcing varies exponentially with height, i.e., 0.2% at the surface, 2% at 50 km, and 20% at 100 km and above. Applying spectral analysis to identify the SC signature, the model generates a relatively large modulation of the QBO, which reproduces the observations qualitatively. The numerical results demonstrate that the QBO modulation, closely tracking the phase of the SC, is robust and persists at least for 70 years. The question is what causes the SC effect, and our analysis shows that four interlocking processes are involved: (1) In the mesosphere at around 60 km, the solar UV variations generate in the zonal winds a SC modulation of the 12-month annual oscillation, which is hemispherically symmetric and confined to equatorial latitudes like the QBO. (2) Although the amplitude of this equatorial annual oscillation (EAO) is relatively small, its SC modulation is large and extends into the lower stratosphere under the influence of, and amplified by, wave forcing. (3) The amplitude modulations of both EAO and QBO are essentially in phase with the imposed SC heating for the entire time span of the model simulation. This indicates that, due to positive feedback in the wave mechanism, the EAO apparently provides the pathway and pacemaker for the SC modulation of the QBO. (4) Our analysis demonstrates that the SC modulations of the QBO and EAO are amplified by tapping the momentum from the upward propagating gravity waves. Influenced and amplified by wave processes, the QBO thus acts as conduit to transfer to lower altitudes the larger SC variations in the UV absorbed in the mesosphere. Our model produces in the temperature variations of the QBO and EAO measurable SC modulations at polar latitudes near the tropopause. The effects are apparently generated by the meridional circulation, and planetary waves presumably, which redistribute the energy from the equatorial region where the waves are very effective in amplifying the SC influence.

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