Andrew MacKinnon | University of Adelaide (original) (raw)

Papers by Andrew MacKinnon

This work contains no material which has been accepted for the award of any other degree or diplo... more This work contains no material which has been accepted for the award of any other degree or diploma in any university or other tertiary institution and, to the best of my knowledge and belief, contains no material previously published or written by another person, except where due reference has been made in the text. I give consent to this copy of my thesis, when deposited in the University Library, being available for loan and photocopying.

Advances in Space Research, Jul 1, 2017

Based on the one-month (October, 2014) wind observations of 11 radars distributed in both hemisph... more Based on the one-month (October, 2014) wind observations of 11 radars distributed in both hemispheres along the 120°E meridian during a radar campaign, this article reports on improvements of the tidal mapping technique proposed before [Yu et al., 2013] by extending the latitude coverage to the global scale (from pole to pole). We first present the tidal components decomposed from the wind observations at different stations. It is revealed that the tidal components are stronger at stations in the Northern Hemisphere than in the Southern Hemisphere. Then, Hough mode decomposition is performed to extract the contributions of different tidal modes for each decomposed tidal component. The expected dominant mode, (1, 1) mode, is the strongest. The trapped (1,-2) mode also contributes a lot to the diurnal component.

43rd COSPAR Scientific Assembly. Held 28 January - 4 February, 2021

AGU Fall Meeting Abstracts, Dec 1, 2019

Journal Of Geophysical Research: Atmospheres, Sep 17, 2018

During the Deep Propagating Gravity Wave Experiment (DEEPWAVE) 13 July 2014 research flight over ... more During the Deep Propagating Gravity Wave Experiment (DEEPWAVE) 13 July 2014 research flight over the South Island of New Zealand, a multiscale spectrum of mountain waves (MWs) was observed. High-resolution measurements of sodium densities were available from~70 to 100 km for the duration of this flight. A comprehensive technique is presented for obtaining temperature perturbations, T 0 , from sodium mixing ratios over a range of altitudes, and these T 0 were used to calculate the momentum flux (MF) spectra with respect to horizontal wavelengths, λ H , for each flight segment. Spectral analysis revealed MWs with spectral power centered at λ H of~80, 120, and 220 km. The temperature amplitudes of these MWs varied between the four cross-mountain flight legs occurring between 6:10UT and 9:10UT. The average spectral T 0 amplitudes near 80 km in altitude ranged from 7-13 K for the 220 km λ H MW and 4-8 K for the smaller λ H MWs. These amplitudes decayed significantly up to 90 km, where a critical level for MWs was present. The average MF per unit mass near 80 km in altitude ranged from~13 to 60 m 2 /s 2 across the varying spectra over the duration of the research flight and decayed to~0 by 88 km in altitude. These MFs are large compared to zonal means and highlight the importance of MWs in the momentum budget of the mesosphere and lower thermosphere at times when they reach these altitudes.

Annales Geophysicae, Jun 12, 2017

Mesospheric gravity wave (GW) momentum flux estimates using data from multibeam Buckland Park MF ... more Mesospheric gravity wave (GW) momentum flux estimates using data from multibeam Buckland Park MF radar (34.6 • S, 138.5 • E) experiments (conducted from July 1997 to June 1998) are presented. On transmission, five Doppler beams were symmetrically steered about the zenith (one zenith beam and four off-zenith beams in the cardinal directions). The received beams were analysed with hybrid Doppler interferometry (HDI) (Holdsworth and Reid, 1998), principally to determine the radial velocities of the effective scattering centres illuminated by the radar. The methodology of Thorsen et al. (1997), later reintroduced by Hocking (2005) and since extensively applied to meteor radar returns, was used to estimate components of Reynolds stress due to propagating GWs and/or turbulence in the radar resolution volume. Physically reasonable momentum flux estimates are derived from the Reynolds stress components, which are also verified using a simple radar model incorporating GW-induced wind perturbations. On the basis of these results, we recommend the intercomparison of momentum flux estimates between co-located meteor radars and verticalbeam interferometric MF radars. It is envisaged that such intercomparisons will assist with the clarification of recent concerns (e.g. Vincent et al., 2010) of the accuracy of the meteor radar technique. Keywords. Meteorology and atmospheric dynamics (waves and tides; instruments and techniques)-radio science (remote sensing)

Atmospheric Measurement Techniques, Sep 6, 2019

This paper assesses the ability of a recently-installed 55 MHz multistatic meteor radar to measur... more This paper assesses the ability of a recently-installed 55 MHz multistatic meteor radar to measure gravity wave-driven momentum fluxes around the mesopause, and applies it in a case study of measuring gravity wave forcing on the diurnal tide during a period following the autumnal equinox of 2018. The radar considered is in the vicinity of Adelaide, South Australia (34.9 • S, 138.6 • E) and consists of a monostatic radar and bistatic receiver separated by approximately 55 km. The assessment shows that the inclusion of the bistatic receiver reduces the relative uncertainty of the momentum flux estimate from about 75% to 65% (for a flux magnitude of ∼ 20 m 2 s −2 , one day's worth of integration, and for a gravity wave field synthesized from a realistic spectral model). This increase in precision appears to be entirely attributable to the increased number of meteor detections associated with the combined monostatic and bistatic receivers, rather than changes in the meteors' spatial distribution. The case study reveals large modulations in the diurnal tidal amplitudes, with a maximum tidal amplitude of ∼ 50 ms −1 and an associated maximum zonal wind velocity of around 140 ms −1. While the observed gravity wave forcing exhibits a complex relationship with the tidal winds during this period, the components of the forcing are seen to be approximately out of phase with the tidal winds above 88 km. No clear phase relationship has been observed below 88 km.

This article reports the ongoing development of the lidar facility at Buckland Park (35 • S, 138 ... more This article reports the ongoing development of the lidar facility at Buckland Park (35 • S, 138 • E), the first of its kind in Australia. Within The University of Adelaide, the Atmospheric Physics Group, in collaboration with the Optics and Photonics Group, is setting up a facility with the potential to host three lidar systems. The aim of this facility is to measure atmospheric temperature and dynamical processes with high spatial and temporal resolution from 15 to 110 km altitude. In addition, this project provides students with the unique opportunity to participate in a real world experiment and to benefit from the education and training gained by access to these instruments. The current work focuses on the development of a Rayleigh/Mie/Raman (RMR) backscatter lidar for temperature measurements in the altitude range from approximately 15 to 75 km. The derived temperature profiles will be used to establish a climatology and to study dynamical processes such as gravity waves at this unique geographic location. Although the RMR lidar technique is well established, most of these lidars are predominantly situated in the northern hemisphere. There are very few lidar stations in the southern hemisphere with the capability to investigate the middle atmosphere. The scientific outcomes of this project will greatly enhance our understanding of the middle atmosphere and will contribute to the evaluation of meteorological satellites and models in this southern subtropical region.

Radio Science, Sep 1, 2018

A network of oblique angle-of-arrival (AoA) ionosondes was installed as part of the Elevationscan... more A network of oblique angle-of-arrival (AoA) ionosondes was installed as part of the Elevationscanned Oblique Incidence Sounder Experiment (ELOISE) in September 2015. The ELOISE experimental campaign was designed to study the spatial and temporal structure of ionospheric variability at midlatitudes, of which traveling ionospheric disturbances are a key component. The new AoA sounder makes use of Defence Science and Technology Group's direct-digital high-frequency transmitter and receiver technology, to enable multichannel collection of both ionograms and channel scattering functions (Doppler spectra) on a common 2-D array. In this paper, the array design and onboard signal processing for the AoA sounder is described, along with a sample of results showing typical disturbance signatures across the delay, Doppler frequency, bearing, and elevation measurements. Realistic parameterized models of electron density perturbations, along with geometric ray tracing, were used to synthesize the effects of medium-to large-scale traveling ionospheric disturbances on the sounder observables and aid in interpreting the measured signatures. Plain Language Summary The ionosphere is an outer charged layer of the Earth's atmosphere that is used by technologies such as over-the-horizon radar to "bounce" (refract) high-frequency radio waves out to very long distances beyond the horizon. However, as a propagation medium, the ionosphere is far from uniform, and to improve the performance of such radars, it is necessary to better understand the nature and sources of variability that affect high-frequency propagation. One of the aims of the Elevation-scanned Oblique Incidence Sounder Experiment (ELOISE), conducted by Defence Science and Technology Group in September 2015, was to study the wave-like perturbations known as traveling ionospheric disturbances by receiving a network of low-power ionospheric sounder (or ionosonde) transmissions on two new antenna arrays. These were designed to measure path delay, angle-of-arrival and Doppler shifts simultaneously on multiple paths. This paper describes the ELOISE array and its signal processing and provides examples of typical observations. It is shown that the characteristic signatures of traveling ionospheric disturbances in the measurements, combined with realistic synthetic models, can provide information about the structure and behavior of such ionospheric disturbances in space and time.

Journal of Geophysical Research, Sep 29, 2009

During the Tropical Warm Pool International Cloud Experiment (TWPICE) an intense tropical low was... more 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.

IEEE Transactions on Antennas and Propagation, 2021

The Earth's magnetic field causes the ionosphere to be birefringent at radio frequencies, which m... more The Earth's magnetic field causes the ionosphere to be birefringent at radio frequencies, which means that any system using ionospherically propagated radio waves, such as long-distance broadcasting, high-frequency (HF) skywave communications, over-the-horizon radar, and oblique incidence sounders (OIS) will receive pairs of waves with different polarizations. In this article, we develop a model for the polarization of ionospherically propagated radio waves; the polarization is dependent only upon the strength and direction of the magnetic field at the location where the radio wave exits the ionosphere. This leads to the hemisphere of possible incoming directions of arrival to any particular receiver being divided into three distinct regions. We then use this model to predict the response of a polarimetric antenna to a transmitted OIS signal and validate the model against real ionograms, including cases where all three polarization regions can be clearly observed.

Journal of Geophysical Research: Atmospheres, 2013

The Tropical Warm Pool International Cloud Experiment campaign centered on Darwin (12°S, 131°E) i... more The Tropical Warm Pool International Cloud Experiment campaign centered on Darwin (12°S, 131°E) in northern Australia in January-February 2006 provided an opportunity to study gravity wave generation by convection and the associated wave propagation and momentum transport. In this study, we discuss wave generation by a single mesoscale convective system (MCS) that occurred on 23 January. The project used a variety of radars to study the spatial and temporal variability of rainfall and the associated latent heat release during the storm. A high-resolution numerical model utilized the latent heat release derived from radar rainfall measurements to compute the spatial and geographic variation of gravity wave generation and propagation into the lower stratosphere. Gravity wave ray-tracing techniques were then used to estimate the wave energy flux penetrating to heights near 90 km, where the results were compared with direct measurements made with a meteor wind radar. This comparison is used to calibrate the momentum fluxes derived from the model and the ray-tracing results using an iterative technique. The momentum was deposited in a relatively compact region. Body forces computed from the flux divergences had their maximum values at heights near 98 km with a peak values of about 400 m s-1 h-1. The effects of secondary gravity wave generation are discussed, as is the overall contribution of gravity waves generated by MCSs to the momentum budget of the tropical middle atmosphere.

Journal of Geophysical Research: Atmospheres, 2015

The Southern Hemisphere summer 2 day wave (TDW) is the most dramatic large-scale event of the upp... more 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.

IEEE Transactions on Antennas and Propagation

Over-the-horizon radars (OTHRs) utilize the refractive properties of the ionosphere to illuminate... more Over-the-horizon radars (OTHRs) utilize the refractive properties of the ionosphere to illuminate targets beyond the Earth's horizon. Consequently, the performance of this type of radar is highly dependent on the ionosphere. Reliable models of the radar ground backscatter are required to accurately assess the ionospheric propagation conditions and, thus, the expected performance of OTHRs. The ground backscatter coefficient characterizes the amount of radiation scattered back from a surface toward a receiver per unit area. While the backscatter coefficient of the sea is well understood and may be calculated from theory if the sea state is known, the backscatter coefficient of land at high frequencies is not well understood. To calculate the land backscatter coefficients over Northern Australia, a methodology that compares observed backscatter ionograms to those synthesized using high-frequency (HF) radio wave raytracing techniques through model ionospheres was developed. Maps of the backscatter coefficients across Northern Australia were produced. The effects of surface properties, including topography, soil moisture, and vegetation cover on the backscatter coefficients, were investigated. A weak positive correlation between the backscatter coefficient and the soil moisture and surface roughness was observed; however, it was found that the vegetation had the largest effect on the backscatter coefficient. Index Terms-Backscatter coefficient, backscatter sounder (BSS), high-frequency (HF) radar, over-the-horizon radar (OTHR). I. INTRODUCTION O VER-THE-HORIZON radars (OTHRs) are a class of radars that operate in the high-frequency (HF) band and are important for long-range surveillance. These radars utilize the refractive properties of the ionosphere to illuminate

Advances in Space Research, 2017

Based on the one-month (October, 2014) wind observations of 11 radars distributed in both hemisph... more Based on the one-month (October, 2014) wind observations of 11 radars distributed in both hemispheres along the 120°E meridian during a radar campaign, this article reports on improvements of the tidal mapping technique proposed before [Yu et al., 2013] by extending the latitude coverage to the global scale (from pole to pole). We first present the tidal components decomposed from the wind observations at different stations. It is revealed that the tidal components are stronger at stations in the Northern Hemisphere than in the Southern Hemisphere. Then, Hough mode decomposition is performed to extract the contributions of different tidal modes for each decomposed tidal component. The expected dominant mode, (1, 1) mode, is the strongest. The trapped (1,-2) mode also contributes a lot to the diurnal component.

Journal of Geophysical Research, 2004

We conducted radiosonde soundings during three intensive observation periods (IOP) of the Darwin ... more We conducted radiosonde soundings during three intensive observation periods (IOP) of the Darwin Area Wave Experiment (DAWEX) campaign in October to December 2001 and measured humidity, temperature, and wind velocity up to $30-35 km every 3 hours for 40 times at three sites in each IOP. We analyzed height profiles of kinetic (E k) and potential (E p) energy per unit mass caused by gravity waves with vertical wavelengths less than 3 km. The wave energy was clearly enhanced between 15-20 km and 25-30 km, and it was considerably depressed at 20-25 km between the two height regions. This feature was seen at all the sites during the three IOPs. Different types of wave activity seem to contribute to the enhancement of E k and E p below 20 km and at 25-30 km. Height distribution of the wave energy at 20-30 km seems to correlate with the structure of the mean zonal wind shear. We also analyzed a latitude-height section of E p in October to December 2001 using GPS occultation data with the CHAMP satellite collected around the DAWEX sites (80-180°E and 30°N to 30°S). Compared with the latitude distribution of E p with GPS, the DAWEX results were slightly smaller and larger at 20-25 km and 25-30 km, respectively. The longitude variation of E p is also analyzed from the GPS data at 10-15°S, which generally agreed well with the DAWEX results at both 20-25 km and 25-30 km.

AGU Fall Meeting Abstracts, Dec 1, 2011

The TWPICE campaign centered on Darwin (12 S, 131 E) in northern Australia in January-February 20... more The TWPICE campaign centered on Darwin (12 S, 131 E) in northern Australia in January-February 2006 provided an opportunity to study gravity wave generation by convection and the associated wave propagation and momentum transport. The project used a variety of radars to study the spatial and temporal variability of rainfall and the associated latent heat release during large thunderstorms. A high-resolution numerical model utilized the latent heat release to compute the spatial and geographic variation of ...

43rd COSPAR Scientific Assembly. Held 28 January - 4 February, 2021

Atmosphere, 2020

The Calbuco volcano in southern Chile (41.3° S, 72.6° W) underwent three separate eruptions on 22... more The Calbuco volcano in southern Chile (41.3° S, 72.6° W) underwent three separate eruptions on 22–23 April 2015. Following the eruptions, distinct layers of enhanced lidar backscatter at 532 nm were observed in the lower stratosphere above Buckland Park, South Australia (34.6° S, 138.5° E), and Kingston, Tasmania (43.0° S, 147.3° E), during a small set of observations in April–May 2015. Using atmospheric trajectory modelling and measurements from the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) space-borne lidar and the Ozone Mapping Profiler Suite (OMPS) instrument on the Suomi National Polar-orbiting Partnership (NPP) satellite, we show that these layers were associated with the Calbuco eruptions. Buckland Park measurements on 30 April and 3 May detected discrete aerosol layers at and slightly above the tropopause, where the relative humidity was well below saturation. Stratospheric aerosol layers likely associated with the eruptions were observed at Kingston on 17 an...

This work contains no material which has been accepted for the award of any other degree or diplo... more This work contains no material which has been accepted for the award of any other degree or diploma in any university or other tertiary institution and, to the best of my knowledge and belief, contains no material previously published or written by another person, except where due reference has been made in the text. I give consent to this copy of my thesis, when deposited in the University Library, being available for loan and photocopying.

Advances in Space Research, Jul 1, 2017

Based on the one-month (October, 2014) wind observations of 11 radars distributed in both hemisph... more Based on the one-month (October, 2014) wind observations of 11 radars distributed in both hemispheres along the 120°E meridian during a radar campaign, this article reports on improvements of the tidal mapping technique proposed before [Yu et al., 2013] by extending the latitude coverage to the global scale (from pole to pole). We first present the tidal components decomposed from the wind observations at different stations. It is revealed that the tidal components are stronger at stations in the Northern Hemisphere than in the Southern Hemisphere. Then, Hough mode decomposition is performed to extract the contributions of different tidal modes for each decomposed tidal component. The expected dominant mode, (1, 1) mode, is the strongest. The trapped (1,-2) mode also contributes a lot to the diurnal component.

43rd COSPAR Scientific Assembly. Held 28 January - 4 February, 2021

AGU Fall Meeting Abstracts, Dec 1, 2019

Journal Of Geophysical Research: Atmospheres, Sep 17, 2018

During the Deep Propagating Gravity Wave Experiment (DEEPWAVE) 13 July 2014 research flight over ... more During the Deep Propagating Gravity Wave Experiment (DEEPWAVE) 13 July 2014 research flight over the South Island of New Zealand, a multiscale spectrum of mountain waves (MWs) was observed. High-resolution measurements of sodium densities were available from~70 to 100 km for the duration of this flight. A comprehensive technique is presented for obtaining temperature perturbations, T 0 , from sodium mixing ratios over a range of altitudes, and these T 0 were used to calculate the momentum flux (MF) spectra with respect to horizontal wavelengths, λ H , for each flight segment. Spectral analysis revealed MWs with spectral power centered at λ H of~80, 120, and 220 km. The temperature amplitudes of these MWs varied between the four cross-mountain flight legs occurring between 6:10UT and 9:10UT. The average spectral T 0 amplitudes near 80 km in altitude ranged from 7-13 K for the 220 km λ H MW and 4-8 K for the smaller λ H MWs. These amplitudes decayed significantly up to 90 km, where a critical level for MWs was present. The average MF per unit mass near 80 km in altitude ranged from~13 to 60 m 2 /s 2 across the varying spectra over the duration of the research flight and decayed to~0 by 88 km in altitude. These MFs are large compared to zonal means and highlight the importance of MWs in the momentum budget of the mesosphere and lower thermosphere at times when they reach these altitudes.

Annales Geophysicae, Jun 12, 2017

Mesospheric gravity wave (GW) momentum flux estimates using data from multibeam Buckland Park MF ... more Mesospheric gravity wave (GW) momentum flux estimates using data from multibeam Buckland Park MF radar (34.6 • S, 138.5 • E) experiments (conducted from July 1997 to June 1998) are presented. On transmission, five Doppler beams were symmetrically steered about the zenith (one zenith beam and four off-zenith beams in the cardinal directions). The received beams were analysed with hybrid Doppler interferometry (HDI) (Holdsworth and Reid, 1998), principally to determine the radial velocities of the effective scattering centres illuminated by the radar. The methodology of Thorsen et al. (1997), later reintroduced by Hocking (2005) and since extensively applied to meteor radar returns, was used to estimate components of Reynolds stress due to propagating GWs and/or turbulence in the radar resolution volume. Physically reasonable momentum flux estimates are derived from the Reynolds stress components, which are also verified using a simple radar model incorporating GW-induced wind perturbations. On the basis of these results, we recommend the intercomparison of momentum flux estimates between co-located meteor radars and verticalbeam interferometric MF radars. It is envisaged that such intercomparisons will assist with the clarification of recent concerns (e.g. Vincent et al., 2010) of the accuracy of the meteor radar technique. Keywords. Meteorology and atmospheric dynamics (waves and tides; instruments and techniques)-radio science (remote sensing)

Atmospheric Measurement Techniques, Sep 6, 2019

This paper assesses the ability of a recently-installed 55 MHz multistatic meteor radar to measur... more This paper assesses the ability of a recently-installed 55 MHz multistatic meteor radar to measure gravity wave-driven momentum fluxes around the mesopause, and applies it in a case study of measuring gravity wave forcing on the diurnal tide during a period following the autumnal equinox of 2018. The radar considered is in the vicinity of Adelaide, South Australia (34.9 • S, 138.6 • E) and consists of a monostatic radar and bistatic receiver separated by approximately 55 km. The assessment shows that the inclusion of the bistatic receiver reduces the relative uncertainty of the momentum flux estimate from about 75% to 65% (for a flux magnitude of ∼ 20 m 2 s −2 , one day's worth of integration, and for a gravity wave field synthesized from a realistic spectral model). This increase in precision appears to be entirely attributable to the increased number of meteor detections associated with the combined monostatic and bistatic receivers, rather than changes in the meteors' spatial distribution. The case study reveals large modulations in the diurnal tidal amplitudes, with a maximum tidal amplitude of ∼ 50 ms −1 and an associated maximum zonal wind velocity of around 140 ms −1. While the observed gravity wave forcing exhibits a complex relationship with the tidal winds during this period, the components of the forcing are seen to be approximately out of phase with the tidal winds above 88 km. No clear phase relationship has been observed below 88 km.

This article reports the ongoing development of the lidar facility at Buckland Park (35 • S, 138 ... more This article reports the ongoing development of the lidar facility at Buckland Park (35 • S, 138 • E), the first of its kind in Australia. Within The University of Adelaide, the Atmospheric Physics Group, in collaboration with the Optics and Photonics Group, is setting up a facility with the potential to host three lidar systems. The aim of this facility is to measure atmospheric temperature and dynamical processes with high spatial and temporal resolution from 15 to 110 km altitude. In addition, this project provides students with the unique opportunity to participate in a real world experiment and to benefit from the education and training gained by access to these instruments. The current work focuses on the development of a Rayleigh/Mie/Raman (RMR) backscatter lidar for temperature measurements in the altitude range from approximately 15 to 75 km. The derived temperature profiles will be used to establish a climatology and to study dynamical processes such as gravity waves at this unique geographic location. Although the RMR lidar technique is well established, most of these lidars are predominantly situated in the northern hemisphere. There are very few lidar stations in the southern hemisphere with the capability to investigate the middle atmosphere. The scientific outcomes of this project will greatly enhance our understanding of the middle atmosphere and will contribute to the evaluation of meteorological satellites and models in this southern subtropical region.

Radio Science, Sep 1, 2018

A network of oblique angle-of-arrival (AoA) ionosondes was installed as part of the Elevationscan... more A network of oblique angle-of-arrival (AoA) ionosondes was installed as part of the Elevationscanned Oblique Incidence Sounder Experiment (ELOISE) in September 2015. The ELOISE experimental campaign was designed to study the spatial and temporal structure of ionospheric variability at midlatitudes, of which traveling ionospheric disturbances are a key component. The new AoA sounder makes use of Defence Science and Technology Group's direct-digital high-frequency transmitter and receiver technology, to enable multichannel collection of both ionograms and channel scattering functions (Doppler spectra) on a common 2-D array. In this paper, the array design and onboard signal processing for the AoA sounder is described, along with a sample of results showing typical disturbance signatures across the delay, Doppler frequency, bearing, and elevation measurements. Realistic parameterized models of electron density perturbations, along with geometric ray tracing, were used to synthesize the effects of medium-to large-scale traveling ionospheric disturbances on the sounder observables and aid in interpreting the measured signatures. Plain Language Summary The ionosphere is an outer charged layer of the Earth's atmosphere that is used by technologies such as over-the-horizon radar to "bounce" (refract) high-frequency radio waves out to very long distances beyond the horizon. However, as a propagation medium, the ionosphere is far from uniform, and to improve the performance of such radars, it is necessary to better understand the nature and sources of variability that affect high-frequency propagation. One of the aims of the Elevation-scanned Oblique Incidence Sounder Experiment (ELOISE), conducted by Defence Science and Technology Group in September 2015, was to study the wave-like perturbations known as traveling ionospheric disturbances by receiving a network of low-power ionospheric sounder (or ionosonde) transmissions on two new antenna arrays. These were designed to measure path delay, angle-of-arrival and Doppler shifts simultaneously on multiple paths. This paper describes the ELOISE array and its signal processing and provides examples of typical observations. It is shown that the characteristic signatures of traveling ionospheric disturbances in the measurements, combined with realistic synthetic models, can provide information about the structure and behavior of such ionospheric disturbances in space and time.

Journal of Geophysical Research, Sep 29, 2009

During the Tropical Warm Pool International Cloud Experiment (TWPICE) an intense tropical low was... more 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.

IEEE Transactions on Antennas and Propagation, 2021

The Earth's magnetic field causes the ionosphere to be birefringent at radio frequencies, which m... more The Earth's magnetic field causes the ionosphere to be birefringent at radio frequencies, which means that any system using ionospherically propagated radio waves, such as long-distance broadcasting, high-frequency (HF) skywave communications, over-the-horizon radar, and oblique incidence sounders (OIS) will receive pairs of waves with different polarizations. In this article, we develop a model for the polarization of ionospherically propagated radio waves; the polarization is dependent only upon the strength and direction of the magnetic field at the location where the radio wave exits the ionosphere. This leads to the hemisphere of possible incoming directions of arrival to any particular receiver being divided into three distinct regions. We then use this model to predict the response of a polarimetric antenna to a transmitted OIS signal and validate the model against real ionograms, including cases where all three polarization regions can be clearly observed.

Journal of Geophysical Research: Atmospheres, 2013

The Tropical Warm Pool International Cloud Experiment campaign centered on Darwin (12°S, 131°E) i... more The Tropical Warm Pool International Cloud Experiment campaign centered on Darwin (12°S, 131°E) in northern Australia in January-February 2006 provided an opportunity to study gravity wave generation by convection and the associated wave propagation and momentum transport. In this study, we discuss wave generation by a single mesoscale convective system (MCS) that occurred on 23 January. The project used a variety of radars to study the spatial and temporal variability of rainfall and the associated latent heat release during the storm. A high-resolution numerical model utilized the latent heat release derived from radar rainfall measurements to compute the spatial and geographic variation of gravity wave generation and propagation into the lower stratosphere. Gravity wave ray-tracing techniques were then used to estimate the wave energy flux penetrating to heights near 90 km, where the results were compared with direct measurements made with a meteor wind radar. This comparison is used to calibrate the momentum fluxes derived from the model and the ray-tracing results using an iterative technique. The momentum was deposited in a relatively compact region. Body forces computed from the flux divergences had their maximum values at heights near 98 km with a peak values of about 400 m s-1 h-1. The effects of secondary gravity wave generation are discussed, as is the overall contribution of gravity waves generated by MCSs to the momentum budget of the tropical middle atmosphere.

Journal of Geophysical Research: Atmospheres, 2015

The Southern Hemisphere summer 2 day wave (TDW) is the most dramatic large-scale event of the upp... more 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.

IEEE Transactions on Antennas and Propagation

Over-the-horizon radars (OTHRs) utilize the refractive properties of the ionosphere to illuminate... more Over-the-horizon radars (OTHRs) utilize the refractive properties of the ionosphere to illuminate targets beyond the Earth's horizon. Consequently, the performance of this type of radar is highly dependent on the ionosphere. Reliable models of the radar ground backscatter are required to accurately assess the ionospheric propagation conditions and, thus, the expected performance of OTHRs. The ground backscatter coefficient characterizes the amount of radiation scattered back from a surface toward a receiver per unit area. While the backscatter coefficient of the sea is well understood and may be calculated from theory if the sea state is known, the backscatter coefficient of land at high frequencies is not well understood. To calculate the land backscatter coefficients over Northern Australia, a methodology that compares observed backscatter ionograms to those synthesized using high-frequency (HF) radio wave raytracing techniques through model ionospheres was developed. Maps of the backscatter coefficients across Northern Australia were produced. The effects of surface properties, including topography, soil moisture, and vegetation cover on the backscatter coefficients, were investigated. A weak positive correlation between the backscatter coefficient and the soil moisture and surface roughness was observed; however, it was found that the vegetation had the largest effect on the backscatter coefficient. Index Terms-Backscatter coefficient, backscatter sounder (BSS), high-frequency (HF) radar, over-the-horizon radar (OTHR). I. INTRODUCTION O VER-THE-HORIZON radars (OTHRs) are a class of radars that operate in the high-frequency (HF) band and are important for long-range surveillance. These radars utilize the refractive properties of the ionosphere to illuminate

Advances in Space Research, 2017

Based on the one-month (October, 2014) wind observations of 11 radars distributed in both hemisph... more Based on the one-month (October, 2014) wind observations of 11 radars distributed in both hemispheres along the 120°E meridian during a radar campaign, this article reports on improvements of the tidal mapping technique proposed before [Yu et al., 2013] by extending the latitude coverage to the global scale (from pole to pole). We first present the tidal components decomposed from the wind observations at different stations. It is revealed that the tidal components are stronger at stations in the Northern Hemisphere than in the Southern Hemisphere. Then, Hough mode decomposition is performed to extract the contributions of different tidal modes for each decomposed tidal component. The expected dominant mode, (1, 1) mode, is the strongest. The trapped (1,-2) mode also contributes a lot to the diurnal component.

Journal of Geophysical Research, 2004

We conducted radiosonde soundings during three intensive observation periods (IOP) of the Darwin ... more We conducted radiosonde soundings during three intensive observation periods (IOP) of the Darwin Area Wave Experiment (DAWEX) campaign in October to December 2001 and measured humidity, temperature, and wind velocity up to $30-35 km every 3 hours for 40 times at three sites in each IOP. We analyzed height profiles of kinetic (E k) and potential (E p) energy per unit mass caused by gravity waves with vertical wavelengths less than 3 km. The wave energy was clearly enhanced between 15-20 km and 25-30 km, and it was considerably depressed at 20-25 km between the two height regions. This feature was seen at all the sites during the three IOPs. Different types of wave activity seem to contribute to the enhancement of E k and E p below 20 km and at 25-30 km. Height distribution of the wave energy at 20-30 km seems to correlate with the structure of the mean zonal wind shear. We also analyzed a latitude-height section of E p in October to December 2001 using GPS occultation data with the CHAMP satellite collected around the DAWEX sites (80-180°E and 30°N to 30°S). Compared with the latitude distribution of E p with GPS, the DAWEX results were slightly smaller and larger at 20-25 km and 25-30 km, respectively. The longitude variation of E p is also analyzed from the GPS data at 10-15°S, which generally agreed well with the DAWEX results at both 20-25 km and 25-30 km.

AGU Fall Meeting Abstracts, Dec 1, 2011

The TWPICE campaign centered on Darwin (12 S, 131 E) in northern Australia in January-February 20... more The TWPICE campaign centered on Darwin (12 S, 131 E) in northern Australia in January-February 2006 provided an opportunity to study gravity wave generation by convection and the associated wave propagation and momentum transport. The project used a variety of radars to study the spatial and temporal variability of rainfall and the associated latent heat release during large thunderstorms. A high-resolution numerical model utilized the latent heat release to compute the spatial and geographic variation of ...

43rd COSPAR Scientific Assembly. Held 28 January - 4 February, 2021

Atmosphere, 2020

The Calbuco volcano in southern Chile (41.3° S, 72.6° W) underwent three separate eruptions on 22... more The Calbuco volcano in southern Chile (41.3° S, 72.6° W) underwent three separate eruptions on 22–23 April 2015. Following the eruptions, distinct layers of enhanced lidar backscatter at 532 nm were observed in the lower stratosphere above Buckland Park, South Australia (34.6° S, 138.5° E), and Kingston, Tasmania (43.0° S, 147.3° E), during a small set of observations in April–May 2015. Using atmospheric trajectory modelling and measurements from the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) space-borne lidar and the Ozone Mapping Profiler Suite (OMPS) instrument on the Suomi National Polar-orbiting Partnership (NPP) satellite, we show that these layers were associated with the Calbuco eruptions. Buckland Park measurements on 30 April and 3 May detected discrete aerosol layers at and slightly above the tropopause, where the relative humidity was well below saturation. Stratospheric aerosol layers likely associated with the eruptions were observed at Kingston on 17 an...