Spectrum Analysis of Gravity Waves Based on Sensors Mounted on a New Round-Trip Airborne Flat-Floating Sounding System

In this study, sensors mounted on a new type of round-trip airborne flat-floating sounding system (RTAFSS) were used to obtain the observation data of the three stages of "rising, flat-floating and falling". This new sounding method has a good application prospect. We performed spectrum analysis on the normalized temperature fluctuation, and the vertical wavenumber spectrum from the rising and falling stages and the horizontal wavenumber spectrum from the flat-floating stage were obtained. This is the first time the complete gravity wave spectrum characteristics were obtained from three consecutive stages: rising, flat-floating and falling. The results show that the gravity wave spectrum of the three stages can be well obtained by RTAFSS. For the horizontal wavenumber spectrum, the spectral slope is basically around -2, and the difference in the spectral structure of the horizontal wave number spectrum may be due to the intermittent turbulent activity and the variable intensity of the gravitational wave during its propagation. This study aims to make experimental exploration of the spectrum characteristics of gravity waves by this new type of observation data. It is expected to reveal the spectrum characteristics of horizontal wavenumber in the stratosphere region of China, providing a theoretical basis for spectrum analysis in a wider space-time range after further network observation of RTAFSS.

Coupled Stratospheric Chemistry–Meteorology Data Assimilation. Part I: Physical Background and Coupled Modeling Aspects

A coupled stratospheric chemistry–meteorology model was developed by combining the Canadian operational weather prediction model Global Environmental Multiscale (GEM) with a comprehensive stratospheric photochemistry model from the Belgian Assimilation System for Chemical ObsErvations (BASCOE). The coupled model was called GEM-BACH for GEM-Belgian Atmospheric CHemistry. The coupling was made across a chemical interface that preserves time-splitting while being modular, allowing GEM to run with or without chemistry. An evaluation of the coupling was performed by comparing the coupled model, refreshed by meteorological analyses every 6 h, against the standard offline chemical transport model (CTM) approach. Results show that the dynamical meteorological consistency between meteorological analysis times far outweighs the error created by the jump resulting from the meteorological analysis increments at regular time intervals, irrespective of whether a 3D-Var or 4D-Var meteorological analysis is used. Arguments in favor of using the same horizontal resolution for chemistry, meteorology, and meteorological and chemical analysis increments are also presented. GEM-BACH forecasts refreshed by meteorological analyses every 6 h were compared against independent measurements of temperature, long-lived species, ozone and water vapor. The comparison showed a relatively good agreement throughout the stratosphere except for an upper-level warm temperature bias and an ozone deficit of nearly 15%. In particular, the coupled model simulation during an ozone hole event gives better ozone concentrations than a 4D-Var chemical assimilation at a lower resolution.

Quantifying gravity wave forcing using scale invariance

Despite the increasing resolution, forcing on the mean circulation by resolved waves in general circulation models is not yet converging. Parameterization of the forcing remains a major source of model uncertainty. This study examines the scale invariance of zonal spectra of momentum flux and wave forcing, and shows that it can be used to quantify the forcing by unresolved waves with knowledge of the resolved ones in global models. The result reveals the leading order importance of the small-scale wave forcing, which is in general agreement with that required for obtaining the zonal mean wind climatology. It is also found that wave and mean flow interaction is important in maintaining the robust spectral structure. This method may provide a strategy to design physically consistent and scale-aware parameterization schemes for scale invariant quantities, when a model has sufficient resolution to partially resolve their spectra.

Parametrizations of unresolved small-scale atmospheric waves are an important source of uncertainty in climate models. Scale invariance is used to estimate the forcing of these small-scale waves and it is shown to have a leading order effect on the mean flow.

Gravity Wave Spectra in the Lower Stratosphere Diagnosed from Project Loon Balloon Trajectories

Project Loon has been launching super-pressure balloons since January 2013 to provide worldwide Internet coverage. These balloons typically fly between 18-21 km and provide measurements of winds and pressure fluctuations in the lower stratosphere. We divide 1,560 Loon flights into 3,405 two-day segments for gravity wave analysis. We derive the kinetic energy spectrum from the horizontal balloon motion and estimate the temperature perturbation spectrum (proportional to the potential energy spectrum) from the pressure variations. We fit the temperature (and kinetic energy) data to the functional form T , 2 = T O , 2 ( ω / ω O ) α where ω is the wave frequency, ω _o is daily frequency, T' _o is the base temperature amplitude and α is the slope. Both the kinetic energy and temperature spectra show -1.9±0.2 power-law dependence in the intrinsic frequency window 3 - 50 cycles/day. The temperature spectrum slope is weakly anti-correlated with the base temperature amplitude. We also find that the wave base temperature distribution is highly skewed. The average tropical modal temperature is 0.77 K. The highest amplitude waves occur over the mountainous regions, the tropics, and the high southern latitudes. Temperature amplitudes show little height variation over our 18-21 km domain. Our results are consistent with other limited super-pressure balloon analyses. The modal temperature is higher than the temperature currently used in Lagrangian model gravity wave parameterizations.

Modeling propagation of infrasound signals observed by a dense seismic network

The long-range propagation of infrasound from a surface explosion with an explosive yield of about 17.6 t TNT that occurred on June 16, 2008 at the Utah Test and Training Range (UTTR) in the western United States is simulated using an atmospheric model that includes fine-scale layered structure of the wind velocity and temperature fields. Synthetic signal parameters (waveforms, amplitudes, and travel times) are calculated using parabolic equation and ray-tracing methods for a number of ranges between 100 and 800 km from the source. The simulation shows the evolution of several branches of stratospheric and thermospheric signals with increasing range from the source. Infrasound signals calculated using a G2S (ground-to-space) atmospheric model perturbed by small-scale layered wind velocity and temperature fluctuations are shown to agree well with recordings made by the dense High Lava Plains seismic network located at an azimuth of 300° from UTTR. The waveforms of calculated infrasound arrivals are compared with those of seismic recordings. This study illustrates the utility of dense seismic networks for mapping an infrasound field with high spatial resolution. The parabolic equation calculations capture both the effect of scattering of infrasound into geometric acoustic shadow zones and significant temporal broadening of the arrivals.