Evidence of the Excitation of a Ring-Like Gravity Wave in the Mesosphere over the Andes Lidar Observatory

On 23 March 2012, our all-sky imager recorded a concentric, ring-like gravity wave pattern. The wave arose within the area covered by images of both OH and O(1S) nightglow emissions taken at the Andes Lidar Observatory (ALO), Chile (30.3°S, 70.7°W). We have estimated the observed and intrinsic parameters of the event and located the wave source within the lower mesosphere altitude range using a reverse ray tracing method. By the analysis of GOES and LIS satellite images, we have not found evidence of neither convective nor lightning activity nearby ALO, indicating that the source of the ring-like wave was not directly in the troposphere. The absence of tropospheric activity and the height of the source of the event suggest that a secondary wave generation mechanism might be the cause of the ring-like wave. The secondary wave mechanism was likely triggered by a breaking, larger-scale primary wave excited by deep convection ∼1400 km northeast of ALO over Bolivia, as determined by a forward ray tracing scheme

Evidence of the excitation of a ring-like gravity wave in the mesosphere over the Andes Lidar Observatory

On 23 March 2012, our all-sky imager recorded a concentric, ring-like gravity wave pattern. The wave arose within the area covered by images of both OH and O(1S) nightglow emissions taken at the Andes Lidar Observatory (ALO), Chile (30.3ÁS, 70.7ÁW). We have estimated the observed and intrinsic parameters of the event and located the wave source within the lower mesosphere altitude range using a reverse ray tracing method. By the analysis of GOES and LIS satellite images, we have not found evidence of neither convective nor lightning activity nearby ALO, indicating that the source of the ring-like wave was not directly in the troposphere. The absence of tropospheric activity and the height of the source of the event suggest that a secondary wave generation mechanism might be the cause of the ring-like wave. The secondary wave mechanism was likely triggered by a breaking, larger-scale primary wave excited by deep convection _1400ækm northeast of ALO over Bolivia, as determined by a forward ray tracing scheme. ©2016. American Geophysical Union. All Rights Reserved

First Observed Temporal Development of a Noctilucent Cloud Ice Void

Noctilucent clouds are ice clouds that appear high in the atmosphere, about 80 km above the summer pole. By observing them we have learned a lot about the remote and inaccessible region where they form. Recently, a satellite borne instrument discovered nearly circular ice-free regions within the clouds, denoted as “ice voids.” The origin of these voids is a mystery—we do not know what causes the clouds to disappear in large circular areas. So far these voids have only been observed from satellites, which only can take pictures of the clouds when they pass above once every 1.5 hr—longer than most ice voids exist. This means that until now we completely lack observations of the development and disappearance of the voids. Here we therefore present the first full temporal development of a void, as observed by our ground-based camera taking images every 30 s. Surprisingly, the void did not drift with the wind as cloud features around it, but it remained notably stationary for approximately 1 hr. These observations give important clues to help us solve the mystery of the origin of these voids—they suggest a steady local heating of the atmosphere as the cause

Winter Climatology of Short-Period Polar Mesospheric Gravity Waves Observed Over Poker Flat Research Range, Alaska (65 o N, 147 o W)

Short-period gravity wave observations over the Arctic region are few and their impact on the Arctic mesosphere lower thermosphere region via momentum deposition is of high interest. The Mesospheric Airglow Imaging and Dynamics project was initiated in January 2011 to investigate the presence and dynamics of these waves over the interior of Alaska. Observations were made from Poker Flat Research Range (PFRR) using an all-sky imager. This site provides an exceptional opportunity to establish a long-term climatology of short-period gravity waves in the Arctic Region. We present summary measurements of prominent gravity waves over two consecutive winters and compare their characteristics with recent observations at Resolute Bay, Canada (75o N), ALOMAR Station, Norway (69o N), Svalbard (78o N), and Rothera Station (76o S). The wave parameters measured at PFRR were found to be similar to the other high-latitude sites, except for the wave headings. The waves at PFRR exhibited dominant eastward motion, while the other observations reported westward motion. To investigate this wave directionality, we look at the effects of critical level filtering

Electron Densities in the Lower Thermosphere From GUVI 135.6 nm Tomographic Inversions in Support of SpreadFEx

The SpreadFEx campaign was conducted with the goal of investigating potential neutral atmospheric dynamics influences in seeding plasma instabilities and bubbles extending to higher altitudes from September to November 2005, with primary measurements in Brazil. In this paper, we present the results of space-based UV and ground-based optical observations in support of this campaign. Specifically, we present multi-dimensional electron density images obtained tomographically from the 135.6 nm emissions measured by the GUVI instrument aboard the TIMED satellite that result from radiative recombination of O+ and compare those with the corresponding 630.0 nm OI images recorded in the Brazilian sector. The GUVI results provide altitude vs. longitude information on depleted regions in the ionospheric plasma density that are complementary to the single-height latitude-longitude images obtained with the airglow imager

Regional Distribution of Mesospheric Small‐Scale Gravity Waves During DEEPWAVE

The Deep Propagating Gravity Wave Experiment project took place in June and July 2014 in New Zealand. Its overarching goal was to study gravity waves (GWs) as they propagate from the ground up to ~100 km, with a large number of ground‐based, airborne, and satellite instruments, combined with numerical forecast models. A suite of three mesospheric airglow imagers operated onboard the NSF Gulfstream V (GV) aircraft during 25 nighttime flights, recording the GW activity at OH altitude over a large region (\u3e7,000,000 km2). Analysis of this data set reveals the distribution of the small‐scale GW mean power and direction of propagation. GW activity occurred everywhere and during every flight, even over open oceans with no neighboring tropospheric sources. Over the mountainous regions (New Zealand, Tasmania, isolated islands), mean power reached high values (more than 100 times larger than over the waters), but with a considerable variability. This variability existed from day to day over the same region, but even during the same flight, depending on forcing strength and on the middle atmosphere conditions. Results reveal a strong correlation between tropospheric sources, satellite stratospheric measurements, and mesosphere lower thermosphere airglow observations. The large‐amplitude GWs only account for a small amount of the total (~6%), even though they carry the most momentum and energy. The weaker wave activity measured over the oceans might originate from distance sources (polar vortex, weather fronts), implying that a ducted mechanism helped for their long range propagation

Chemical and dynamical processes in the mesospheric emissive layer. First results of stereoscopic observations

[1] The mesospheric emissive layer is an efficient tracer of the dynamical processes propagating in the atmosphere at that level. CCD images in the near infrared taken from the ground at slant angles often reveal the existence of wavy fields. A series of such images has been transformed, using matrix operations, producing a downward satellite-type view that covers a circular area of radius ∼1000 km at the altitude of the layer. The Fourier characteristics of the wave system are measured using a Morlet-type wavelet generator function with horizontal wavelengths of mostly ∼20–40 km and 100–150 km and temporal periods of ∼15–30 min. An oxygen-hydrogen model is used to evaluate the response of the emissive layer to a progressive density wave. The altitude of the layer is modulated with an amplitude of ∼0.8–1.8 km when a density wave propagates vertically. The layer thickness is slightly modulated and is equal to ∼7 km. Stereoscopic pairs of photographs taken simultaneously on 8–9 September 2000 at the Château-Renard and Pic du Midi observatories are used to obtain surface maps of the emission layer barycenter altitude. A stereocorrelation method suitable for low contrast objects without discrete contours is employed. Preliminary results for areas ∼50 × 50 km2 are presented. The surface maps of the layer barycenter altitude depict the existence of waves. They show the same wavy structure and compare favorably with the maps showing the emission intensity

Investigating Mesospheric Gravity Wave Dynamics Over McMurdo Station, Antarctica (77° S)

The ANtarctic Gravity Wave Instrument Network (ANGWIN) is an NSF sponsored international program designed to develop and utilize a network of gravity wave observatories using existing and new instrumentation operated at several established research stations around the continent. The primary goal is to better understand and quantify large-scale gravity wave climatology and their effects on the upper atmosphere over Antarctica. ANGWIN currently comprises research measurements from five nations (U.S., U.K., Australia, Japan, and Brazil) at seven international stations. Utah State University’s Atmospheric Imaging Lab operates an all-sky CCD, all-sky infrared imagers and an Advanced Mesospheric Temperature Mapper (AMTM) imager at several research stations (Davis, Halley, Rothera, McMurdo, and South Pole). In this poster we present new measurements, mainly focusing on short-period (\u3c 1 hour) mesospheric gravity waves, imaged from McMurdo Station (77°S, 166°E) on Ross Island, Antarctica. The infrared camera has operated successfully from the NSF Arrival Heights Facility alongside the University of Colorado Fe Lidar during the past three winter seasons (March-September 2012-2014). Image data were recorded every ~10 seconds enabling detailed measurements of individual gravity wave events in the infrared OH emission layer (peak altitude ~87 km). Here we present example data illustrating the broad range of wave activity observed at this site and summarize novel measurements of the wave characteristics observed during the first two winter seasons. The results are contrasted with other emerging ANGWIN wave measurements from around the continent

Mountain Wave Propagation under Transient Tropospheric Forcing: A DEEPWAVE Case Study

The impact of transient tropospheric forcing on the deep vertical mountain wave propagation is investigated by a unique combination of in-situ and remote-sensing observations and numerical modeling. The temporal evolution of the upstream low-level wind follows approximately a cos2 shape and was controlled by a migrating trough and connected fronts. Our case study reveals the importance of the time-varying propagation conditions in the upper troposphere, lower stratosphere (UTLS). Upper-tropospheric stability, the wind profile as well as the tropopause strength affected the observed and simulated wave response in the UTLS. Leg-integrated along-track momentum fluxes (−MFtrack) and amplitudes of vertical displacements of air parcels in the UTLS reached up to 130 kN m−1 and 1500 m, respectively. Their maxima were phase-shifted to the maximum low-level forcing by ≈ 8 h. Small-scale waves (λx ≈ 20–30 km) were continuously forced and their flux values depended on wave attenuation by breaking and reflection in the UTLS region