The prospect of studying atmospheric gravity waves with balloon lidars

Long duration balloons are ideal platforms to study atmospheric gravity waves with remote sensing Rayleigh lidar instruments. Using a laser beam and receiving telescope, atmospheric density and temperature are sounded throughout the stratosphere and mesosphere at high vertical and temporal resolution. Sources of gravity waves that induce temperature perturbations are flow over orography, convection or jet imbalances. Under optimal wind conditions such as in the vicinity of the polar vortex edge, gravity waves can propagate long distances both vertically and horizontally and deposit momentum and exert drag in regions where they break. Successive balloon launches of several identical payloads from Antarctica would allow for mapping gravity wave sources, characterize their horizontal and vertical distribution and observe their evolution in different background conditions. Our group has developed high-power lidar instruments and flown them on a NASA long duration balloon in the Arctic (PMC-Turbo) and on the High altitude Long Distance (HALO) aircraft in South America (SouthTRAC-GW). As HALO cannot operate in Antarctica due to logistical constraints, only balloons can fill this gap in observations from ground-based stations that lack the spatial coverage and satellite measurements of coarse vertical and temporal resolution. Based on our experience with building the first Rayleigh lidar to fly successfully on a balloon, we propose to take this next step in miniaturizing lidar instruments to be carried by smaller hand-launched balloons

Signatures of gravity wave-induced instabilities in balloon lidar soundings of polar mesospheric clouds

The Balloon Lidar Experiment (BOLIDE), which was part of the Polar Mesospheric Cloud Turbulence (PMC Turbo) Balloon Mission has captured vertical profiles of PMCs during a 6 d flight along the Arctic circle in July 2018. The high-resolution soundings (20 m vertical and 10 s temporal resolution) reveal highly structured layers with large gradients in the volume backscatter coefficient. We systematically screen the BOLIDE dataset for small-scale variability by assessing these gradients at high resolution. We find longer tails of the probability density distributions of these gradients compared to a normal distribution, indicating intermittent behaviour. The high occurrence rate of large gradients is assessed in relation to the 15 min averaged layer brightness and the spectral power of short-period (5–62 min) gravity waves based on PMC layer altitude variations. We find that variability on small scales occurs during weak, moderate, and strong gravity wave activity. Layers with below-average brightness are less likely to show small-scale variability in conditions of strong gravity wave activity. We present and discuss the signatures of this small-scale variability, and possibly related dynamical processes, and identify potential cases for future case studies and modelling efforts.</p

Waves and clouds in the atmosphere above the southern Andes as seen by the CORAL Rayleigh lidar

Das CORAL-Lidar misst seit November 2017 in Tierra del Fuego, Argentinien (54°S) die Temperatur der Atmosphäre bis in 100 km Höhe. In der Stratosphäre treten über den südlichen Anden durch Gebirgswellen verursachte Temperaturstörungen von über 20 K Amplitude auf. In den kalten Phasen der Wellen können auf diese Weise polare Stratosphärenwolken auch in mittleren Breiten entstehen. In größeren Höhen, am oberen Rand der Mesosphäre, ist die Temperatur im Sommer kalt genug für die Bildung von Eiswolken, den sogenannten leuchtenden Nachtwolken. Sie werden durch die Gezeitenwinde beeinflusst, sind stark durch Schwerewellen moduliert, und treten in der Südhemisphäre nicht seltener auf als in der Nordhemisphäre, was man aufgrund der höheren Hintergrundtemperatur der südlichen polaren Mesosphäre erwarten könnte. Wir zeigen eine Übersicht und ausgewählte Beobachtungen von Wellen und Wolken in der mittleren Atmosphäre aus fünf Jahren Lidar-Messungen

A technical description of the Balloon Lidar Experiment (BOLIDE)

The Balloon Lidar Experiment (BOLIDE) was the first high-power lidar flown and operated successfully onboard a balloon platform. As part of the PMC Turbo payload, the instrument acquired high resolution backscatter profiles of Polar Mesospheric Clouds (PMCs) from an altitude of ∼38 km during its maiden ∼6 day flight from Esrange, Sweden, to Northern Canada in July 2018. We describe the BOLIDE instrument and its development and report on the predicted and actual in-flight performance. Although the instrument suffered from excessively high background noise, we were able to detect PMCs with a volume backscatter coefficient as low as 0.6 × 10^−10 m^−1 sr^−1 at a vertical resolution of 100 m and a time resolution of 30 s

Influences of source conditions on mountain wave penetration into the stratosphere and mesosphere

We present atmospheric gravity wave (GW) measurements obtained by a Rayleigh/Raman lidar at Lauder, New Zealand (45∘ S, 170∘ E) during and after the DEEPWAVE campaign. GW activity and characteristics are derived from 557 hours of high-resolution lidar data recorded between June and November 2014 in an altitude range between 28 and 76 km. In this period, strong GW activity occurred in sporadic intervals lasting a few days. Enhanced stratospheric GW potential energy density is detected during periods with high tropospheric wind speeds perpendicular to New Zealand's Southern Alps. These enhancements are associated with the occurrence of quasi-stationary GW (mountain waves). Surprisingly, the largest response in the mesosphere is observed for conditions with low to moderate lower tropospheric wind speeds (2–12 m/s). On the other hand, large-amplitude mountain waves excited by strong tropospheric forcings often do not reach mesospheric altitudes, either due to wave breaking and dissipation in the stratosphere or refraction away from New Zealand

The polar mesospheric cloud dataset of the Balloon Lidar Experiment (BOLIDE)

The Balloon Lidar Experiment (BOLIDE) observed polar mesospheric clouds (PMCs) along the Arctic circle between Sweden and Canada during the balloon flight of PMC Turbo in July 2018. The purpose of the mission was to study small-scale dynamical processes induced by the breaking of atmospheric gravity waves by high-resolution imaging and profiling of the PMC layer. The primary parameter of the lidar soundings is the time- and range-resolved volume backscatter coefficient β. These data are available at high resolutions of 20 m and 10 s (Kaifler, 2021, https://doi.org/10.5281/zenodo.5722385). This document describes how we calculate β from the BOLIDE photon count data and balloon floating altitude. We compile information relevant for the scientific exploration of this dataset, including statistics, mean values, and temporal evolution of parameters like PMC brightness, altitude, and occurrence rate. Special emphasis is given to the stability of the gondola pointing and the effect of resolution on the signal-to-noise ratio and thus the detection threshold of PMC. PMC layers were detected during 49.7 h in total, accounting for 36.8 % of the 5.7 d flight duration and a total of 178 924 PMC profiles at 10 s resolution. Up to the present, published results from subsets of this dataset include the evolution of small-scale vortex rings, distinct Kelvin–Helmholtz instabilities, and mesospheric bores. The lidar soundings reveal a wide range of responses of the PMC layer to larger-scale gravity waves and breaking gravity waves, including the accompanying instabilities, that await scientific analysis

High-Cadence Lidar Observations of Middle Atmospheric Temperature and Gravity Waves at the Southern Andes Hot Spot

Middle atmospheric lidar temperature measurements were performed at the Southern Andes gravity wave hot spot with unprecedented cadence. Exceptional wave events were observed in winter, resulting in temperature deviations from the monthly mean of 25K to 55K. GW potential energies show conservative growth rates in the stratosphere and a saturation limit in the mesosphere during winter

Gravity-Wave-Driven Seasonal Variability of Temperature Differences Between ECMWF IFS and Rayleigh Lidar Measurements in the Lee of the Southern Andes

Long-term high-resolution temperature data of the Compact Rayleigh Autonomous Lidar (CORAL) is used to evaluate temperature and gravity wave (GW) activity in ECMWF Integrated Forecasting System (IFS) over Río Grande (53.79°S, 67.75°W), which is a hot spot of stratospheric GWs in winter. Seasonal and altitudinal variations of the temperature differences between the IFS and lidar are studied for 2018 with a uniform IFS version. Moreover, interannual variations are considered taking into account updated IFS versions. We find monthly mean temperature differences ±10 K) and increase with altitude. We relate this seasonal variability to middle atmosphere GW activity. In the upper stratosphere and lower mesosphere, the observed temperature differences result from both GW amplitude and phase differences. The IFS captures the seasonal cycle of GW potential energy (Ep) well, but underestimates Ep in the middle atmosphere. Experimental IFS simulations without damping by the model sponge for May and August 2018 show an increase in the monthly mean Ep above 45 km from only ≈10% of the Ep derived from the lidar measurements to 26% and 42%, respectively. GWs not resolved in the IFS are likely explaining the remaining underestimation of the Ep

Multi-Scale Kelvin-Helmholtz Instability Dynamics Observed by PMC Turbo on 12 July 2018: 2. DNS Modeling of KHI Dynamics and PMC Responses

Kjellstrand et al. (2021) describes the evolution and dynamics of a strong, large-scale Kelvin-Helmholtz instability (KHI) event observed in polar mesospheric clouds (PMCs) on 12 July 2018 by high-resolution imagers aboard the PMC Turbulence (PMC Turbo) stratospheric long-duration balloon experiment. The imaging provides evidence of KH billow interactions and instabilities that are strongly influenced by gravity waves at larger scales. Specific features include initially separated regions of KHI, secondary convective and KH instabilities of individual billows, and “tubes” and “knots” that arise where billow cores are mis-aligned or discontinuous along their axes. This study describes a direct numerical simulation of KH billow interactions in a periodic domain seeded with random initial noise that enables excitation of multiple KH billows exhibiting variable phase structures that capture multiple features of the observed KHI dynamics. Variable KH billow phases along their axes yield initial vortex tubes having diagonal alignments that link adjacent, but mis-aligned, billow cores. Weak initial vortex tubes and billow cores having nearly orthogonal alignments amplify, interact strongly, and drive intense vortex knots at these sites. These vortex tube & knot (T&K) dynamics excite “twist waves” that unravel the initial vortex tubes, and drive increasingly strong vortex interactions and a cascade of energy and enstrophy to successively smaller scales in the turbulence inertial range. The implications of T&K dynamics are much more rapid and intense breakdown and decay of the KH billows, and significantly enhanced energy dissipation rates, where these interactions occur