scholarly journals Diurnal Characteristics of Gravity Waves over the Tibetan Plateau in 2015 Summer Using 10-km Downscaled Simulations from WRF-EnKF Regional Reanalysis

Atmosphere ◽  
2020 ◽  
Vol 11 (6) ◽  
pp. 631
Author(s):  
Tingting Qian ◽  
Fuqing Zhang ◽  
Junhong Wei ◽  
Jie He ◽  
Yinghui Lu
Keyword(s):  
Tibetan Plateau ◽  
Gravity Waves ◽  
Power Spectra ◽  
Reanalysis Data ◽  
Small Scale ◽  
The Tibetan Plateau ◽  
Wave Source ◽  
Momentum Fluxes ◽  
Regional Reanalysis ◽  
Meso Scale

Diurnal variations of gravity waves over the Tibetan Plateau (TP) in summer 2015 were investigated based on high-resolution downscaled simulations from WRF-EnKF (Weather Research and Forecasting model and an ensemble Kalman filter) regional reanalysis data with particular emphasis on wave source, wave momentum fluxes and wave energies. Strong diurnal precipitations, which mainly happen along the south slope of the TP, tend to excite upward-propagating gravity waves. The spatial and temporal distributions of the momentum fluxes of small-scale (10–200 km) and meso-scale (200–500 km) gravity waves agree well with the diurnal precipitation distributions. The power spectra of momentum fluxes also show that the small- and meso-scale atmospheric processes become important during the period of the strongest rainfall. Eastward momentum fluxes and northward momentum fluxes are dominant. Wave energies are described in terms of kinetic energy (KE), potential energy (PE) and vertical fluctuation energy (VE). The diurnal variation and spatial distribution of VE in the lower stratosphere correspond to the diurnal rainfall in the troposphere.

scholarly journals Contributions of equatorial planetary waves and small-scale convective gravity waves to the 2019/20 QBO disruption

2021 ◽  
Author(s):  
Min-Jee Kang ◽  
Hye-Yeong Chun
Keyword(s):  
Gravity Waves ◽  
Rossby Wave ◽  
Rossby Waves ◽  
Reanalysis Data ◽  
Small Scale ◽  
Negative Wave ◽  
Quasi Biennial Oscillation ◽  
Wave Forcing ◽  
Equatorial Wave ◽  
Convective Gravity Waves

Abstract. In January 2020, unexpected easterly winds developed in the downward-propagating westerly quasi-biennial oscillation (QBO) phase. This event corresponds to the second QBO disruption in history, and it occurred four years after the first disruption that occurred in 2015/16. According to several previous studies, strong midlatitude Rossby waves propagating from the Southern Hemisphere (SH) during the SH winter likely initiated the disruption; nevertheless, the wave forcing that finally led to the disruption has not been investigated. In this study, we examine the role of equatorial waves and small-scale convective gravity waves (CGWs) in the 2019/20 QBO disruption using MERRA-2 global reanalysis data. In June–September 2019, unusually strong Rossby wave forcing originating from the SH decelerated the westerly QBO at 0°–5° N at ~50 hPa. In October–November 2019, vertically (horizontally) propagating Rossby waves and mixed Rossby–gravity (MRG) waves began to increase (decrease). From December 2019, contribution of the MRG wave forcing to the zonal wind deceleration was the largest, followed by the Rossby wave forcing originating from the Northern Hemisphere and the equatorial troposphere. In January 2020, CGWs provided 11 % of the total negative wave forcing at ~43 hPa. Inertia–gravity (IG) waves exhibited a moderate contribution to the negative forcing throughout. Although the zonal-mean precipitation was not significantly larger than the climatology, convectively coupled equatorial wave activities were increased during the 2019/20 disruption. As in the 2015/16 QBO disruption, the increased barotropic instability at the QBO edges generated more MRG waves at 70–90 hPa, and westerly anomalies in the upper troposphere allowed more westward IG waves and CGWs to propagate to the stratosphere. Combining the 2015/16 and 2019/20 disruption cases, Rossby waves and MRG waves can be considered the key factors inducing QBO disruption.

COSMIC GPS observations of topographic gravity waves in the stratosphere around the Tibetan Plateau

2016 ◽  
Vol 60 (1) ◽  
pp. 188-197 ◽  
Author(s):  
XuanYun Zeng ◽  
XiangHui Xue ◽  
XianKang Dou ◽  
Chen Liang ◽  
MingJiao Jia
Keyword(s):  
Tibetan Plateau ◽  
Gravity Waves ◽  
The Tibetan Plateau ◽  
Gps Observations

scholarly journals Gravity wave amplitudes and momentum fluxes inferred from OH airglow intensities and meteor radar winds during SpreadFEx

2009 ◽  
Vol 27 (6) ◽  
pp. 2361-2369 ◽  
Author(s):  
F. Vargas ◽  
D. Gobbi ◽  
H. Takahashi ◽  
L. M. Lima
Keyword(s):  
Gravity Waves ◽  
Horizontal Wind ◽  
Small Scale ◽  
Meteor Radar ◽  
Plasma Bubble ◽  
Spatial And Temporal Scales ◽  
Analysis Technique ◽  
Momentum Fluxes ◽  
Different Types ◽  
Wave Directionality

Abstract. We show in this report the momentum flux content input in the mesosphere due to relatively fast and small scale gravity waves (GWs) observed through OH airglow images. The acquisition of OH NIR images was carried out in Brazil at Brasilia (14.8° S, 47.6° W) and Cariri (7.4° S, 36.5° W) from September 2005 to November 2005 during the SpreadFEx Campaign. Horizontal wind information from meteor radar was available in Cariri only. Our findings showed strong wave activity in both sites, mainly in Cariri. High wave directionality was also observed in both sites during SpreadFEx, which have been observed by other investigators using different analysis' techniques and different types of data during the campaign. We discuss also the possibility of plasma bubble seeding by gravity waves presenting spatial and temporal scales estimated with our novel analysis technique during the SpreadFEx campaign.

scholarly journals Seasonal Features and a Case Study of Tropopause Folds over the Tibetan Plateau

2019 ◽  
Vol 2019 ◽  
pp. 1-12 ◽  
Author(s):  
Jiali Luo ◽  
Wenjun Liang ◽  
Pingping Xu ◽  
Haiyang Xue ◽  
Min Zhang ◽  
...  
Keyword(s):  
Tibetan Plateau ◽  
High Frequency ◽  
Reanalysis Data ◽  
The Tibetan Plateau ◽  
Transport Pathway ◽  
Westerly Jet ◽  
Meridional Winds ◽  
Surrounding Areas ◽  
High Potential Vorticity

Tropopause fold is the primary mechanism for stratosphere-troposphere exchange (STE) at the midlatitudes. Investigation of the features of tropopause folds over the Tibetan Plateau (TP) is important since the TP is a hotspot in global STE. In this study, we investigated seasonal features of the tropopause fold events over the TP using the 40-year ERA-Interim reanalysis data. The development of a tropopause folding case is specifically examined. The results show that shallow tropopause folds occur mostly in spring, while medium and deep folds occur mostly in winter. The multiyear mean monthly frequency of shallow tropopause folds over the TP reaches its maximum value of about 7% in May and then decreases gradually to its minimum value of 1% in August and increases again since September. Deep folds rarely occur in summer and autumn. Both the seasonal cycle and seasonal distribution of total tropopause folds over the TP are dominated by shallow folds. The relative high-frequency areas of medium and deep folds are located over the southern edge of the TP. The westerly jet movement controls the displacement of the high-frequency folding region over the TP. The region of high-frequency tropopause folds is located in the southern portion of the plateau in spring and moves northward in summer. The jet migrates back to the south in autumn and is located along about 30°N in winter, and the region where folds occur most frequently also shifts southward correspondingly. A medium fold event that occurred on 29 December 2018 is used to demonstrate the evolution of a tropopause fold case over the TP in winter; that is, the folding structure moves from west to east, the tropopause pressure is greater than 320 hPa over the folding region, while it is about 200 hPa in the surrounding areas, and the stratospheric air with high potential vorticity (PV) is transported from the high latitudes to the plateau by meridional winds. A trajectory model result verifies the transport pathway of the air parcels during the intrusion event.

Numerical Modeling of Nonlinear Interactions of Spectral Components of Acoustic-Gravity Waves in the Middle and Upper Atmosphere

2020 ◽  
Author(s):  
Nikolai M. Gavrilov ◽  
Sergej P. Kshevetskii
Keyword(s):  
Gravity Waves ◽  
Upper Atmosphere ◽  
Jet Flows ◽  
Small Scale ◽  
Nonlinear Interactions ◽  
Mean Flow ◽  
Wave Source ◽  
Acoustic Gravity Waves ◽  
The Mean ◽  
Wave Modes

<p>Acoustic-gravity waves (AGWs) measuring at big heights may be generated in the troposphere and propagate upwards. A high-resolution three-dimensional numerical model was developed for simulating nonlinear AGWs propagating from the ground to the upper atmosphere. The model algorithms are based on the finite-difference analogues of the main conservation laws. This methodology let us obtaining the physically correct generalized wave solutions of the nonlinear equations. Horizontally moving sinusoidal structures of vertical velocity on the ground are used for the AGW excitation in the model. Numerical simulations were made in an atmospheric region having horizontal dimensions up to several thousand kilometers and the height extention up to 500 km. Vertical distributions of the mean temperature, density, molecular viscosity and thermal conductivity are specified using standard models of the atmosphere.</p><p>Simulations were made for different horizontal wavelengths, amplitudes and speeds of the wave sources at the ground. After “switch on” the tropospheric wave source, an initial AGW pulse very quickly (for several minutes) could propagate to heights up to 100 km and above. AGW amplitudes increase with height and waves may break down in the middle and upper atmosphere. Wave instability and dissipation may lead to formations of wave accelerations of the mean flow and to producing wave-induced jet flows in the middle and upper atmosphere. Nonlinear interactions may lead to instabilities of the initial wave and to the creation of smaller-scale perturbations. These perturbations may increase temperature and wind gradients and could enhance the wave energy dissipation.</p><p>In this study, the wave sources contain a superposition of two AGW modes with different periods, wavelengths and phase speeds. Longer-period AGW modes served as the background conditions for the shorter-period wave modes. Thus, the larger-scale AGWs can modulate amplitudes of small-scale waves. In particular, interactions of two wave modes could sharp vertical temperature gradients and make easier the wave breaking and generating  turbulence. On the other hand, small-wave wave modes might increase dissipation and modify the larger-scale modes.This study was partially supported by the Russian Basic Research Foundation (# 17-05-00458).</p>

scholarly journals Small-scale gravity waves in ER-2 MMS/MTP wind and temperature measurements during CRYSTAL-FACE

2005 ◽  
Vol 5 (6) ◽  
pp. 11377-11412
Author(s):  
L. Wang ◽  
M. J. Alexander ◽  
T. P. Bui ◽  
M. J. Mahoney
Keyword(s):  
Gravity Waves ◽  
Temperature Measurements ◽  
Small Scale ◽  
Maximum Magnitude ◽  
Horizontal Scale ◽  
Crystal Face ◽  
Cloud Models ◽  
S Transform ◽  
Momentum Fluxes ◽  
The Cross

Abstract. ER-2 MMS and MTP wind and temperature measurements during the CRYSTAL-FACE campaign in July 2002 were analyzed to retrieve information on small scale gravity waves (GWs) at aircraft's flight level. For a given flight segment, the S-transform was used to search for and identify small horizontal scale GW events, and to estimate the apparent horizontal wavelengths of the events. The horizontal propagation directions of the events were determined using the Stokes parameters method combined with the cross S-transform analysis. The MTP temperature gradient method was used to determine the vertical wavelengths of the events. GW momentum fluxes were calculated from the cross S-transform. Other wave parameters such as intrinsic frequencies were calculated using the GW dispersion relation. More than 100 GW events were identified. They were generally short horizontal scale and high frequency waves with λz of ~5 km and λh generally shorter than 20 km. Their intrinsic propagation directions were predominantly toward the east, whereas their ground-based propagation directions were primarily toward the west. Among the events, ~20% of them had very short horizontal wavelength (<10 km), very high intrinsic frequency (ω/N≥0.8), and relatively small momentum fluxes, and thus they were likely trapped in the lower stratosphere. The averaged magnitude of vertical flux of horizontal momentum was ~0.026 kg m−1 s−2, and the maximum magnitude was ~0.13 kg m−1 s−2. Using the estimated GW parameters and the background winds and stabilities from the NCAR/NCEP reanalysis data, we were able to trace the sources of the events using a simple reverse ray-tracing. More than 70% of the events were traced back to convective sources in the troposphere, and the sources were generally located upstream to the events. Finally, a probability density function of GW cooling rates was obtained in this study, which may be used in cirrus cloud models.

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 Role of equatorial planetary and gravity waves in the 2015–16 quasi-biennial oscillation disruption

2020 ◽  
Author(s):  
Min-Jee Kang ◽  
Hye-Yeong Chun ◽  
Rolando R. Garcia
Keyword(s):  
Gravity Waves ◽  
Rossby Waves ◽  
Wave Mode ◽  
Reanalysis Data ◽  
Small Scale ◽  
Negative Wave ◽  
Quasi Biennial Oscillation ◽  
Rossby Wave Breaking ◽  
Wave Forcing ◽  
Biennial Oscillation

Abstract. In February 2016, the descent of the westerly phase of the quasi-biennial oscillation (QBO) was unprecedentedly disrupted by the development of easterly winds. Previous studies have shown that extratropical Rossby waves propagating into the deep Tropics were the major cause of the 2015–16 QBO disruption. However, a large portion of the negative momentum forcing associated with the disruption still stems from equatorial planetary and small-scale gravity waves, which calls for detailed analyses by separating each wave mode compared with climatological QBO cases. Here, the contributions of resolved equatorial planetary waves [Kelvin, Rossby, mixed-Rossby gravity (MRG), and inertia-gravity (IG) waves] and small-scale convective gravity waves (CGWs) obtained from an offline CGW parameterization to the 2015–16 QBO disruption are investigated using MERRA-2 global reanalysis data from October 2015 to February 2016. In October and November 2015, anomalously strong negative forcing by MRG and IG waves weakened the QBO jet at 0°–5° S near 40 hPa, leading to Rossby wave breaking at the QBO jet core in the southern hemisphere. From December 2015 to January 2016, exceptionally strong Rossby waves propagating horizontally (vertically) continuously decelerated the southern (northern) flank of the jet. In February 2016, when the westward CGW momentum flux at the source level was much stronger than its climatology, CGWs began to exert considerable negative forcing at 40–50 hPa near the equator, in addition to the Rossby waves. The enhancement of the negative wave forcing in the Tropics stems mostly from strong wave activity in the troposphere associated with increased convective activity and the strong westerlies (or weaker easterlies) in the troposphere, except that the MRG wave forcing is more likely associated with increased barotropic instability in the lower stratosphere.

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