Modeling Studies of Gravity Wave Dynamics in Highly Structured Environments: Reflection, Trapping, Instability, Momentum Transport, Secondary Gravity Waves, and Induced Flow Responses

A compressible numerical model is applied for three-dimensional (3-D) gravity wave (GW) packets undergoing momentum deposition, self-acceleration (SA), breaking, and secondary GW (SGW) generation in the presence of highly-structured environments enabling thermal and/or Doppler ducts, such as a mesospheric inversion layer (MIL), tidal wind (TW), or combination of MIL and TW. Simulations reveal that ducts can strongly modulate GW dynamics. Responses modeled here include reflection, trapping, suppressed transmission, strong local instabilities, reduced SGW generations, higher altitude SGW responses, and induced large-scale flows. Instabilities that arise in ducts experience strong dissipation after they emerge, while trapped smaller-amplitude and smaller-scale GWs can survive in ducts to much later times. Additionally, GW breaking and its associated dynamics enhance the local wind along the GW propagation direction in the ducts, and yield layering in the wind field. However, these dynamics do not yield significant heat transport in the ducts. The failure of GW breaking to induce stratified layers in the temperature field suggests that such heat transport might not be as strong as previously assumed or inferred from observations and theoretical assessments. The present numerical simulations confirm previous finding that MIL generation may not be caused by the breaking of a transient high-frequency GW packet alone.

Updated Climatology of Mesospheric Temperature Inversions Detected by Rayleigh Lidar above Observatoire de Haute Provence, France, Using a K-Mean Clustering Technique

A climatology of Mesospheric Inversion Layers (MIL) has been created using the Rayleigh lidar located in the south of France at L’Observatoire de Haute Provence (OHP). Using criteria based on lidar measurement uncertainties and climatological mean gravity wave amplitudes, we have selected significant large temperature anomalies that can be associated with MILs. We have tested a novel approach for classifying MILs based on a k-mean clustering technique. We supplied different parameters such as the MIL amplitudes, altitudes, vertical extension, and lapse rate and allowed the computer to classify each individual MIL into one of three clusters or classes. For this first proof of concept study, we selected k = 3 and arrived at three distinct MIL clusters, each of which can be associated with different processes generating MILs in different regimes. All clusters of MIL exhibit a strong seasonal cycle with the largest occurrence in winter. The four decades of measurements do not reveal any long-term changes that can be associated with climate changes and only show an inter-annual variability with a quasi-decadal oscillation.

Assessment of ERA-5 Temperature Variability in the MiddleAtmosphere Using Rayleigh LiDAR Measurements between 2005 and 2020

In this study, the temperature biases and the ability of the ERA-5 product to reproduce the LiDAR variability in the 30–80 km altitude range were evaluated for the period 2005–2020, both for the winter and the summer months. During winter, temperatures from the ERA-5 dataset were in good agreement with LiDAR observations up to 45 km, while in the mesosphere, almost 70% of the ERA-5 profiles were cooler than those from LiDAR, except around 65 km. During summer, negative biases of −3 K were observed up to the stratopause, while significant positive biases of more than +10 K were found in the mesosphere. For the winter months, the variability observed by LiDAR, even during sudden stratospheric warming (SSWs) events, was reproduced accurately by the model in the upper stratosphere, but not in the mesosphere. Surprisingly, the LiDAR variability mainly due to propagating gravity waves in the summertime was also not reproduced by ERA-5 in the whole middle atmosphere. The model uncertainty associated with this variability, evaluated afterward with a new method, grew as expected with altitude and was more significant in winter than summer. A principal component analysis of the fluctuations of the temperature differences between the LiDAR and ERA-5 was performed to investigate the vertical coupling between 30 km and 70 km. The three first vertical modes illustrated 76% and 78% of the fluctuations of the temperature difference profiles in summer and winter, respectively, confirming the connection between the studied layers. The leading modes of the summer (49%) and winter (42%) possessed an anti-correlation between the upper stratosphere and the mesosphere, where fluctuations increased (at least ±5 K at 65 km) for both seasons due to the coarse vertical resolution in the model. The other modes showed an agreement between the LiDAR and ERA-5 fluctuations in the upper stratosphere and had a wave-like structure mainly located in the mesosphere, confirming that the model either overlooked or simulated imprecisely the gravity waves, leading to mesospheric inversions. Finally, SSWs impacted the ERA-5 temperature (deviation of ±3K) some days before and after its trigger around the stratopause.

Gravity Wave Breaking Associated with Mesospheric Inversion Layers as Measured by the Ship-Borne BEM Monge Lidar and ICON-MIGHTI

During a recent 2020 campaign, the Rayleigh lidar aboard the Bâtiment d’Essais et de Mesures (BEM) Monge conducted high-resolution temperature measurements of the upper Mesosphere and Lower Thermosphere (MLT). These measurements were used to conduct the first validation of ICON-MIGHTI temperatures by Rayleigh lidar. A double Mesospheric Inversion Layer (MIL) as well as shorter-period gravity waves was observed. Zonal and meridional wind speeds were obtained from locally launched radiosondes and the newly launched ICON satellite as well as from the European Centre for Medium-Range Weather Forecasts (ECMWF-ERA5) reanalysis. These three datasets allowed us to see the evolution of the winds in response to the forcing from the MIL and gravity waves. The wavelet analysis of a case study suggests that the wave energy was dissipated in small, intense, transient instabilities about a given wavenumber in addition to via a broad spectrum of breaking waves. This article will also detail the recent hardware advances of the Monge lidar that have allowed for the measurement of MILs and gravity waves at a resolution of 5 min with an effective vertical resolution of 926 m.

Comprehensive Study on Tropical (10°N-15°N) Mesospheric Inversion Layers Using Lidar and Satellite (Timed-Saber) Observations

One of the interesting and poorly understood features of mesosphere and lower thermosphere (MLT) region is the phenomenon of Mesospheric Inversion Layers (MILs). The poor understanding of MILs is due to limited access of their occurrence height region, however the lidars are more efficient tools which provide stratosphere and mesosphere nocturnal temperatures with high temporal and vertical resolutions. The state-of-the-art lidar system comprising Mie, Rayleigh lidars installed at National Atmospheric Research Laboratory (NARL), Gadanki (13.5°N, 79.2°E), India has provided an excellent opportunity to undertake this study. The Nd:YAG laser source with lower power (11W) has been replaced by the one with higher power (30W) in January 2007. As the laser power has been increased, the molecular back scatter signal is also increased and consequently the top height level of the temperature retrieval has been increased to ~90-95 km. In the present study, the role of dominant causative mechanisms for the occurrence of MILs has been discussed using mainly the lidar and satellite (TIMED-SABER) observations over Gadanki region.

Rayleigh lidar observation of tropical mesospheric inversion layer: a comparison between dynamics and chemistry

The Rayleigh lidar at National Atmospheric Research Laboratory, Gadanki (13.5°N, 79.2°E), India operates at 532 nm green laser with ~600 mJ/pulse since 2007. The vertical temperature profiles are derived above ~30 km by assuming the atmosphere is in hydrostatic equilibrium and obeys ideal gas law. A large mesospheric inversion layer (MIL) is observed at ~77.4-84.6 km on the night of 22 March 2007 over Gadanki. Although dynamics and chemistry play vital role, both the mechanisms are compared for the occurrence of the MIL in the present study.