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Gravity waves generated by flow over the steep topography of the Antarctic Peninsula transport significant amounts of zonal and meridional momentum into the stratosphere. Quantitative determination of this transport has been carried out for wave periods of 1 h or greater using data from a previous Antarctic superpressure balloon campaign in austral spring 2005 (VORCORE). The present study uses data from the later Concordiasi campaign (2010) to extend the momentum flux determination to shorter periods. Maps of the vertical fluxes of meridional and zonal momentum are presented for periods down to 12 min. We find that the momentum fluxes for periods below 1 h are comparable to those at longer periods, despite larger variances at longer periods. The momentum fluxes in the vicinity of the peninsula provide a significant zonal acceleration of the lower stratosphere, confirming a conclusion from the VORCORE data. The geographical distribution of fluxes around the peninsula has peaks both leeward and windward of the main terrain features. Numerical simulations suggest that the separate peaks may be related to wave transience caused by unsteady winds over the peninsula. Momentum fluxes comprise a main distribution maximizing at moderate flux values and a secondary distribution maximizing at high values exhibiting a high degree of intermittency. The high flux events account for the largest part of the average flux and suggest that drag parameterizations should take them into account. It is found that waves generated by the jet stream are also a significant source of momentum flux.

The prediction of tropical cyclone rapid intensification is one of the most pressing unsolved problems in hurricane forecasting. The signatures of gravity waves launched by strong convective updrafts are often clearly seen in airglow and carbon dioxide thermal emission spectra under favorable atmospheric conditions. By continuously monitoring the Atlantic hurricane belt from the main development region to the vulnerable sections of the continental United States at high cadence, it will be possible to investigate the utility of storm-induced gravity wave observations for the diagnosis of impending storm intensification. Such a capability would also enable significant improvements in our ability to characterize the 3D transient behavior of upper-atmospheric gravity waves and point the way to future observing strategies that could mitigate the risk to human life caused by severe storms. This paper describes a new mission concept involving a midinfrared imager hosted aboard a geostationary satellite positioned at approximately 80°W longitude. The sensor’s 3-km pixel size ensures that the gravity wave horizontal structure is adequately resolved, while a 30-s refresh rate enables improved definition of the dynamic intensification process. In this way the transient development of gravity wave perturbations caused by both convective and cyclonic storms may be discerned in near–real time.

The Southern Hemisphere summer 2 day wave (TDW) is the most dramatic large-scale event of the upper mesosphere. The winds accelerate over ~1 week, may attain > 70 m/s, and are often accompanied by a near disappearance of the diurnal tide and stabilization of the period close to 48 h. We denote this as the phase-locked 2 day wave (PL/TDW). We have examined airglow and meteor radar (MR) wind data from the Andes Lidar Observatory (Cerro Pachon, Chile:30°S, 289.3°E), MR data from Darwin (12.5°S, 131°E) and airglow and medium frequency radar data from the University of Adelaide (34.7°S, 138.6°E) for the behavior of the TDW during the austral summers of 2010, 2012, and 2013. The Cerro Pachon and Adelaide sites are located at similar latitudes separated in longitude by about 120°. We find a remarkable coincidence between the TDW oscillations at Chile and Adelaide for the period January–February 2010. The oscillations are nearly in phase in terms of local time and the minima and maxima repeat at nearly the same local time from cycle to cycle consistent with a phase-locked wave number 3 TDW. Data for this and other years (including Darwin) show that the amplitude of the diurnal tide decreases when the TDW is largest and that this occurs when the period is close to 48 h. These observations support the proposal that the PL/TDW is a subharmonic parametric instability wherein the diurnal tide transfers energy to a TDW that is resonant at nearly 48 h.

The Hotel Payload 2 rocket was launched on January 31st 2008 at 20.14 LT from the Andøya Rocket Range in northern Norway (69.31° N, 16.01° E). Measurements in the 75–105 km region of atomic O, negatively-charged dust, positive ions and electrons with a suite of instruments on the payload were complemented by lidar measurements of atomic Na and temperature from the nearby ALOMAR observatory. The payload passed within 2.58 km of the lidar at an altitude of 90 km. A series of coupled models is used to explore the observations, leading to two significant conclusions. First, the atomic Na layer and the vertical profiles of negatively-charged dust (assumed to be meteoric smoke particles), electrons and positive ions, can be modelled using a self-consistent meteoric input flux. Second, electronic structure calculations and Rice–Ramsperger–Kassel–Markus theory are used to show that even small Fe–Mg–silicates are able to attach electrons rapidly and form stable negatively-charged particles, compared with electron attachment to O2 and O3. This explains the substantial electron depletion between 80 and 90 km, where the presence of atomic O at concentrations in excess of 1010 cm−3 prevents the formation of stable negative ions.

The Aerospace Corporation's Nightglow Imager (ANI) observes nighttime OH emission (near 1.6 μm) every 2 s over an approximate 73° field of view. ANI had previously been used to study instability features seen over Maui. Here we describe observations of instabilities seen from 5 to 8 UT on 24 March 2012 over Cerro Pachon, Chile, and compare them with previous results from Maui, with theory, and with Direct Numerical Simulations (DNS). The atmosphere had reduced stability because of the large negative temperature gradients measured by a Na lidar. Thus, regions of dynamical and convective instabilities are expected to form, depending on the value of the Richardson number. Bright primary instabilities are formed with a horizontal wavelength near 9 km and showed the subsequent formation of secondary instabilities, rarely seen over Maui, consistent with the primaries being dynamical instabilities. The ratio of the primary to secondary horizontal wavelength was greater over Chile than over Maui. After dissipation of the instabilities, smaller-scale features appeared with sizes in the buoyancy subrange between 1.5 and 6 km. Their size spectra were consistent with the model of Weinstock (1978) if the turbulence is considered to be increasing. The DNS results produce secondary instabilities with sizes comparable to what is seen in the images although their spectra are somewhat steeper than is observed. However, the DNS results also show that after the complete decay of the primary features, scale sizes considerably smaller than 1 km are produced and these cannot be seen by the ANI instrument.

[1] The commonly used criteria for shear and convective instabilities were developed for steady horizontally uniform background flows. However, the formalism that rigorously addresses the instability of waves on a basic state modulated by a primary wave is Floquet theory in which the basic state includes a wave. A Floquet system supports parametric instabilities when conventional Richardson number (Ri) criteria indicate that the system is stable. In a study of small-scale instability structures during the Maui MALT campaign, Hecht et al. (2005) noted that there were occurrences of ripple (instability) structure when the conventional criteria indicated stable conditions. We have followed up this work with a detailed survey of the occurrence of ripple structure over Maui during periods that were both stable and unstable according to conventional criteria. Values of Ri were calculated from lidar data. We have found frequent occurrence of ripple structure when Ri > 14. We have focused on a period when there are clear indications of waves and ripple structure exhibiting two-dimensional instability structure when Ri ~ 1 or greater. These results are analyzed in terms of Floquet theory and interpreted as parametric instabilities occurring for modest primary wave amplitudes.

Spectral analyses of time series of zonal winds derived from locations of balloons drifting in the Southern Hemisphere polar vortex during the Vorcore campaign of the Stratéole program reveal a peak with a frequency near 0.10 h−1, more than 25% higher than the inertial frequency at locations along the trajectories. Using balloon data and values of relative vorticity evaluated from the Modern Era Retrospective-Analyses for Research and Applications (MERRA), the authors find that the spectral peak near 0.10 h−1 can be interpreted as being due to inertial waves propagating inside the Antarctic polar vortex. In support of this claim, the authors examine the way in which the low-frequency part of the gravity wave spectrum sampled by the balloons is shifted because of effects of the background flow vorticity. Locally, the background flow can be expressed as the sum of solid-body rotation and shear. This study demonstrates that while pure solid-body rotation gives an effective inertial frequency equal to the absolute vorticity, the latter gives an effective inertial frequency that varies, depending on the direction of wave propagation, between limits defined by the absolute vorticity plus or minus half of the background relative vorticity.

Ionospheric plasmas containing density gradients are subject to a gradient drift instability under the influence of an externally applied electric field or neutral wind. In this paper we present electric field wave data from the Sudden Atom Layers sounding rocket showing a pure gradient drift instability on the topside of a 1 km thick sporadic E layer. An outer scale of 50 m was determined. Considering the local linear growth rate and the mapping of the electric field structures along magnetic field lines, we conclude that structures with scales larger than 50 m perpendicular to the magnetic field map into regions of linear stability where they are damped. The free energy is localized in wavenumber space, yielding peak fluctuating fields of 6 mV/m, corresponding to electron drifts over 190 m/s and a cascade of energy to meter scales.

We discuss a recent sounding rocket experiment which found charged dust in the Earth's tropical mesosphere. The dust detector was designed to measure small (5000–10000 amu) charged dust particles, most likely of meteoric origin. A 5 km thick layer of positively charged dust was found at an altitude of 90 km, in the vicinity of an observed sporadic sodium layer and sporadic E layer. The observed dust was positively charged in the bulk of the dust layer, but was negatively charged near the bottom.

[1] The Aerospace Corporation's Nightglow Imager observed a large step function change in airglow in the form of a traveling front in the OH Meinel (OHM) and O2atmospheric (O2A) airglow emissions over Alice Springs, Australia, on 2 February 2003. The front exhibited nearly a factor of 2 stepwise increase in the OHM brightness and a stepwise decrease in the O2A brightness. There was significant (∼25 K) cooling behind the airglow fronts. The OHM airglow brightness behind the front was among the brightest for Alice Springs that we have measured in 7 years of observations. The event was associated with a strong phase-locked 2 day wave (PL/TDW). We have analyzed the wave trapping conditions for the upper mesosphere and lower thermosphere using a combination of data and empirical models and found that the airglow layers were located in a region of ducting. The PL/TDW-disturbed wind profile was effective in supporting a high degree of ducting, whereas without the PL/TDW the ducting was minimal or nonexistent. The change in brightness in each layer was associated with a strong leading disturbance followed by a train of weak barely visible waves. In OHM the leading disturbance was an isolated disturbance resembling a solitary wave. The characteristics of the wave train suggest an undular bore with some turbulent dissipation at the leading edge.

[1] Expressions for momentum and heat fluxes using density as the vertical coordinate are derived. These are applied in the evaluation of fluxes using data from super-pressure balloons drifting on constant density surfaces in the Antarctic lower stratosphere during the VORCORE campaign (September 2005 to February 2006). We focus on the core months of October and November. Vertical fluxes of zonal and meridional momentum are calculated using wind, pressure and height data and the vertical flux of sensible heat is calculated using temperature and height data. Calculations were performed in three band passes covering 1–13 h. We find that the largest fluxes are in the vicinity of the Antarctic Peninsula. In October the fluxes in the low period band pass (1–5 h) account for the main part of the total flux of zonal momentum, consistent with topographically forced waves. During November the vertical fluxes of zonal momentum are found mainly in longer period band passes, consistent with weaker winds. The peak campaign-averaged flux of zonal momentum in the vicinity of the Antarctic Peninsula is ∼−30 mPa. These values are ∼60% larger over the peninsula than those inferred by other authors. The flux of zonal momentum provides a zonal body force of ∼5 m s−1 day−1 assuming a saturated spectrum. We infer downward sensible heat fluxes of ∼3 W m−2. The corresponding cooling rates assuming a saturated spectrum are ∼0.6 K day−1, a significant fraction of the net radiative imbalance in the springtime Antarctic lower stratosphere.

[1] The quasi 2 day wave, with a nominal mean period just above 50 h, is a significant feature of the 80–100 km altitude region in both hemispheres. It becomes particularly prominent in the Southern Hemisphere summer at midlatitudes where, a short time after summer solstice, its amplitude rapidly increases and its mean period is found to be approximately 48 h, producing an oscillation phase locked in local time. This lasts for a few weeks. Presented here are observations of the meridional winds and airglow over two sites in Australia, for 4 years during the austral summers of 2003–2006. We show that during those times when the large-amplitude phase-locked 2 day wave (PL-TDW) is present the diurnal tide greatly decreases. This is consistent with the Walterscheid and Vincent (1996) model in which the PL-TDW derives its energy from a parametric excitation by the diurnal tide. These data also show that the diurnal tide is more suppressed and the PL-TDW amplitude is larger in odd-numbered years, suggesting a biannual effect. The airglow data indicated that, for the PL-TDW, the winds and temperature are nearly out of phase. When the PL-TDW is present airglow amplitudes can become quite large, a result dependent on the local time of the PL-TDW maximum. The airglow intensity response was, in general, much larger than what would be expected from the airglow temperature response, suggesting that the PL-TDW is causing a significant composition change possibly due to minor constituent transport.

[1] During the Tropical Warm Pool International Cloud Experiment (TWPICE) an intense tropical low was situated between Darwin and Alice Springs, Australia. Observations made on 31 January 2006 by the Atmospheric Infrared Sounder instrument on the NASA Aqua satellite imaged the presence of atmospheric gravity waves (AGWs), at approximately 40 km altitude, with horizontal wavelengths between 200 and 400 km that were originating from the region of the storm. Airglow images obtained from Alice Springs (about 600 km from the center of the low) showed the presence of similar waves with observed periods of 1 to 2 h. The images also revealed the presence of 30- to 45-km-horizontal-wavelength AGWs with shorter observed periods of near 15 to 25 min. Ray tracing calculations show that (1) some of the long wavelength waves traveled on rays, without ducting, to the altitudes where the observations were obtained, and (2) shorter-period waves rapidly reached 85 km altitude at a horizontal distance close to the storm, thus occurring over Alice Springs only if they were trapped or ducted. The mesospheric inversion layer seen in the measured temperature data almost forms such a trapped region. The winds therefore critically control the formation of the trapped region. Wind profiles deduced from the available data show the plausibility for the formation of such a trapped region. Variations in the wind, however, would make ideal trapped region conditions short-lived, and this may account for the sporadic nature of the short-period wave observations.

[1] An artificial aurora was generated during a trimethyl aluminum (TMA) release from the October 2000 TOMEX rocket launch. Cameras in several locations filmed the optical emissions, believed to be associated with small amounts of kerosene added to the TMA liquid. The geometry of the launch trajectory with respect to the magnetic field and camera viewing angles has provided new insight on the source of the emissions. Surprisingly, the aurora appears to be associated with the vertical footprint of the rocket, rather than the magnetic footprint of the rocket, as previously assumed. The new observations favor a generation mechanism involving large particles >1 μm falling to 90 km altitude.

[1] We present data from a winter 2002 sounding rocket campaign for multiple observations of mesospheric charged dust. The campaign consisted of four identically instrumented payloads carrying detectors for charged mesospheric dust particles. The payloads reached an altitude of 100 km in the nighttime mesosphere and were flown from Poker Flat Research Range, Alaska, in conjunction with observations by the UAF sodium and iron resonance lidar system. Three of the four flights flew in sequence during the course of one night to study the temporal evolution of dust layers. Observations show good correlations between structure seen in the charged dust altitude profile, structure seen in the neutral metal layers observed by the lidars, and structure in the plasma density seen by the onboard Langmuir probes. The dust detector is sensitive to positively and negatively charged dust particles with ram energies of 1 to 11 eV for negatively and 3–11 eV for positively charged dust; that is, particles of approximately 5000 amu. The charged dust densities seen (estimated to be approximately 5 to 10 percent of the total dust density) are approximately 100 particles per cc, and the dust is negatively charged. Variations in the dust density of about 10% are seen in conjunction with structure in the plasma density and with the neutral metal layers. In this paper we present the details of the dust data and instrumentation; a companion paper explores the implications of the correlations seen between the dust and other mesospheric layers.