Thebarton, Australia
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Li G.,CAS Institute of Geology and Geophysics | Ning B.,CAS Institute of Geology and Geophysics | Hu L.,CAS Institute of Geology and Geophysics | Chu Y.-H.,National Central University | And 4 more authors.
Journal of Geophysical Research: Space Physics | Year: 2012

Interferometry measurements of range spread meteor trail echoes (RSTEs; also known as nonspecular echoes) have provided new insights into both the irregularity structures in meteor trails and lower-thermospheric winds (LTWs). In this study, we used trail echoes observed with the newly installed Sanya (18.4°N, 109.6°E) 47.5 MHz VHF coherent radar and the Sanya all-sky meteor radar to estimate instantaneous zonal and hourly averaged meridional winds from RSTEs and hourly averaged zonal and meridional winds from large numbers of specular meteor echoes. The mean height variations in both the zonal and meridional winds estimated from the RSTEs were generally consistent with those estimated from specular meteor echoes below 96 km. This gives validity to the technique proposed recently by Oppenheim et al. (2009) and suggests that RSTE measurements made with a small radar can be used to investigate LTWs, whereas this had previously been limited to larger radars such as the Jicamarca radar. However, some observations show significant differences in wind magnitude at individual heights at times. The results of RSTE measurements show the presence of an intense westward wind with a speed near 100 ms-1. In contrast, the specular meteor zonal winds were generally less than 50 ms -1. On the other hand, the meridional drift of RSTEs derived from the meridional Doppler velocity at higher altitudes shows a very poor correlation with the specular meteor meridional wind. Potential causes for the discrepancy in wind estimates obtained from RSTE and specular meteor trail echoes are discussed.

Verrall G.,South Australian Institute | Dolman B.,ATRAD Pty Ltd. | Dolman B.,University of Adelaide
Muscles, Ligaments and Tendons Journal | Year: 2016

Background: The mechanism of musculoskeletal (MSK) injuries is not well understood. This research applies principles of elastic motion to the anatomy and movement patterns of MSK structures. From this an insight into the application and timing of forces on MSK structures can be established and the mechanism/s of injury derived. Methods (Current Knowledge): All MSK structures demonstrate varying degrees of elasticity. Movement occurs primarily as a consequence of Muscle Tendon Unit (MTU) shortening. The application of an applied external force results in MSK structure lengthening. Results: The MTU acts as a non-idealised Hookean Spring. The resting length of MSK structures is the minimum distance between attachment points. The anatomical constraints results in MSK structures having adequate compressive strength during shortening. Thus MSK injuries only occur during lengthening of the MSK structure. From this with knowledge of MSK movement cycles, we can derive the mechanism of injury. Conclusions: MSK injuries result from an inability to counter applied forces whilst lengthening. Muscles, tendons and ligaments can only injure during their lengthening contraction phase. Insertional tendons and bone near attachment points injure during the MTU shortening phase. Injuries to other MSK structures can occur independent of the lengthening and shortening phases such as direct contact injuries. © 2016 CIC Edizioni Internazionali Unauthorized reproduction of this article is prohibited.

Dolman B.K.,ATRAD Pty Ltd | Dolman B.K.,University of Adelaide | Reid I.M.,University of Adelaide
Journal of Atmospheric and Solar-Terrestrial Physics | Year: 2014

Wind profiling radars are now in general use by a number of weather agencies worldwide. These use the Doppler Beam Swinging approach exclusively. The Australian Government Bureau of Meteorology has adopted a Boundary Layer wind profiling radar using the Spaced Antenna technique. This paper describes the performance of these radars and discusses some of the issues that needed to be addressed for appropriate performance in an operational environment, namely the known wind magnitude underestimation. The underestimation was successfully addressed with an empirical correction. Quality control and hardware improvements to minimize internal clutter have been implemented, resulting in largely outlier free wind estimates on presentation to forecasters, and excellent height coverage. © 2014 Elsevier Ltd.

Reid I.M.,University of Adelaide | Spargo A.J.,University of Adelaide | Woithe J.M.,ATRAD Pty Ltd
Journal of Geophysical Research: Atmospheres | Year: 2014

We analyze 15years of atomic oxygen (OI) 558nm and hydroxyl (OH) (8-3) 730nm nightglow emission intensities from heights near 96 and 87km, respectively, measured using filter photometers at the Buckland Park Field Station (34.6S, 138.6E) near Adelaide, Australia. The intensity of both emissions exhibits clear seasonal and interannual periodicities, with annual, semiannual, and quasi-biennial oscillations, as well as a solar cycle influence. In addition, there is a terannual and 4.1year component in the OI airglow intensity and both a quasi-biennial and quasi-triennial oscillation in the OH intensity. The results are in very good agreement with simultaneous collocated measurements made with an imager, and with global satellite climatologies of OI and OH intensities reported for the Wind Imaging Interferometer instrument. The mean value of the OI annual oscillation intensity is the same as that of the semiannual oscillation at this location to within the experimental uncertainty. The OI annual oscillation maximizes in summer, and the semiannual oscillation maximizes in autumn and spring, with the largest maximum in autumn. The terannual component in the OI nightglow maximizes in early summer, autumn, and spring. The quasi-biennial oscillation in the OI nightglow takes its first maximum value in autumn 1996, and the 4.1year period in this emission first maximizes in summer 1998. The OH annual and semiannual oscillation intensities also agree to within the experimental uncertainties and are observed to peak in early winter. The quasi-biennial and quasi-triennial oscillations in this emission take their first maximum value in summer 1996. Key Points Fifteen years of airglow intensity measurements Seasonal and interseasonal variations Similarity to conjugate observations ©2014. American Geophysical Union. All Rights Reserved.

Walterscheid R.L.,The Aerospace Corporation | Hecht J.H.,The Aerospace Corporation | Gelinas L.J.,The Aerospace Corporation | Mackinnon A.,University of Adelaide | And 7 more authors.
Journal of Geophysical Research D: Atmospheres | Year: 2015

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. ©2015. American Geophysical Union. All Rights Reserved.

Younger J.P.,University of Adelaide | Younger J.P.,ATRAD Pty. Ltd. | Reid I.M.,University of Adelaide | Reid I.M.,ATRAD Pty. Ltd. | Vincent R.A.,University of Adelaide
Radio Science | Year: 2013

Meteor radars have become common and important tools in the study of the climate and dynamics of the mesosphere/lower thermosphere (MLT) region. These systems depend on accurate angle-of-arrival measurements to locate the positions of meteor trails in the atmosphere. Mutual coupling between antennas, although small, produces a measurable error in the antenna pair phase differences used to deduce the angle of arrival of incident radiation. Measurements of the scattering parameter matrix for antennas in an interferometric meteor radar array have been made and applied to the existing angle-of-arrival calculation algorithm. The results indicate that mutual coupling of antennas in the array produces errors in the zenith angle estimate of less than ± 0.5°. This error is primarily in the form of a gradient across the field of view of the radar, which can be removed using existing phase calibration methods. The remaining error is small but will produce small systematic variations in the height estimates for detected meteors. Key PointsMutual coupling in meteor radar is small, but non-negligible.Antenna mutual coupling can be easily measured.Antenna mutual coupling can be corrected for. ©2013. American Geophysical Union. All Rights Reserved.

Younger J.P.,University of Adelaide | Younger J.P.,ATRAD Pty. Ltd. | Reid I.M.,University of Adelaide | Reid I.M.,ATRAD Pty. Ltd. | And 2 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2012

Single-station meteor shower detections produce distributions of shower meteor speeds that can be used to estimate the velocity of shower meteoroids entering the atmosphere. Meteor shower velocity is used to calculate the orbital parameters of the debris streams that are responsible for meteor showers, so it is important to understand the accuracy of shower velocity estimation techniques. An analysis of the distribution of speeds of shower meteors can also be used to assess the precision and accuracy of the speed estimation technique used. The velocity estimates of 522 shower detections obtained during a survey of 33 MHz meteor radar data from 2006 to 2007 have been compared to velocity values in the IAU data base and used to assess the performance of the Fresnel transform method of speed estimation. It is shown that the estimates for high-velocity showers are strongly influenced by the angle-of-entry of the meteors due to the removal of early-stage ablation meteors in shallow trajectories by the underdense echo high-altitude cut-off phenomenon. © 2012 The Authors Monthly Notices of the Royal Astronomical Society © 2012 RAS.

Younger J.P.,ATRAD Pty Ltd. | Younger J.P.,University of Adelaide | Reid I.M.,ATRAD Pty Ltd. | Reid I.M.,University of Adelaide | And 2 more authors.
Geophysical Research Letters | Year: 2015

A new technique for determining the height of a constant density surface at altitudes of 78-85 km is presented. The first results are derived from a decade of observations by a meteor radar located at Davis Station in Antarctica and are compared with observations from the Microwave Limb Sounder instrument aboard the Aura satellite. The density of the neutral atmosphere in the mesosphere/lower thermosphere region around 70-110 km is an essential parameter for interpreting airglow-derived atmospheric temperatures, planning atmospheric entry maneuvers of returning spacecraft, and understanding the response of climate to different stimuli. This region is not well characterized, however, due to inaccessibility combined with a lack of consistent strong atmospheric radar scattering mechanisms. Recent advances in the analysis of detection records from high-performance meteor radars provide new opportunities to obtain atmospheric density estimates at high time resolutions in the MLT region using the durations and heights of faint radar echoes from meteor trails. Previous studies have indicated that the expected increase in underdense meteor radar echo decay times with decreasing altitude is reversed in the lower part of the meteor ablation region due to the neutralization of meteor plasma. The height at which the gradient of meteor echo decay times reverses is found to occur at a fixed atmospheric density. Thus, the gradient reversal height of meteor radar diffusion coefficient profiles can be used to infer the height of a constant density level, enabling the observation of mesospheric density variations using meteor radar. © 2015. American Geophysical Union. All Rights Reserved.

Lee C.S.,Chungnam National University | Lee C.S.,University of Adelaide | Younger J.P.,University of Adelaide | Younger J.P.,ATRAD Pty. Ltd. | And 4 more authors.
Journal of Geophysical Research: Atmospheres | Year: 2013

Estimates of the ambipolar diffusion coefficient producedusing meteor radar echo decay times display an increasing trend below 80-85 km, which is inconsistent with a diffusion-only theory of the evolution of meteor trails. Data from the 33 MHz meteor radar at King Sejong Station, Antarctica, have been compared with observations from the Aura Earth Observing System Microwave Limb Sounder satellite instrument. It has been found that the height at which the diffusion coefficient gradient reverses follows the height of a constant neutral atmospheric density surface. Numerical simulations of meteor trail diffusion including dissociative recombination with atmospheric ions and three-body attachment of free electrons to neutral molecules indicate that three-body attachment is responsible for the distortion of meteor radar diffusion coefficient profiles at heights below 90 km, including the gradient reversal below 80-85 km. Further investigation has revealed that meteor trails with low initial electron line density produce decay times more consistent with a diffusion-only model of meteor trail evolution. © 2013. American Geophysical Union. All Rights Reserved.

Dolman B.,ATRAD Pty Ltd | Dolman B.,University of Adelaide | Reid I.,ATRAD Pty Ltd | Reid I.,University of Adelaide
2014 International Radar Conference, Radar 2014 | Year: 2014

The Australian Government Bureau of Meteorology is in the process of installing a network of 9 wind profiling radars across Australia, including four stratospheric tropospheric profilers. To meet forecasting standards, these radars were required to produce averaged horizontal wind profiles, free from outliers, through as much of the atmosphere as possible. This research is concerned with the development of a radar to meet these requirements. © 2014 IEEE.

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