Andrew D. MacKinnon

A VHF boundary layer radar: First results

The development of a novel VHF radar designed to measure winds and temperatures in the planetary boundary layer is described. The radar operates at 54.1 MHz and is compact and easily transportable. The antenna system consists of 12 Yagis grouped into three subarrays arranged in the form of an equilateral triangle. Transmission takes place on the whole array, and reception takes place on the three subarrays, with winds measured by the spaced antenna technique over a height range between 300 and 3000 m. Results from field trials conducted in southern Australia in a variety of meteorological conditions are presented. Comparisons with high-resolution radiosondes launched from the radar site show excellent agreement, with rms differences between radiosonde and radar wind components being about 1.5 m s−1. Observations carried out in rain show that echoes from precipitation are clearly distinguishable from clear-air echoes. Unlike UHF radars, this means that vertical air velocities can be measured during precipitation, and the evolution of drop-size distributions can be studied down to low altitudes. It is shown that temperatures derived from a radio acoustic sounding system are measured up to heights near 2 km, depending on background wind conditions.

Raindrop Size Distribution Retrievals from a VHF Boundary Layer Profiler

Abstract The retrieval of raindrop size distributions (DSDs) in precipitation using boundary layer wind profiler operating at VHF is described. To make the retrievals, a Fourier transform–based deconvolution technique, optimized to run with little human input, is used. The sensitivities of the technique and its overall accuracy are investigated using simulated spectra. The retrievals have an error that depends on the drop diameter, with relative errors varying between ∼10% and 35%. An overall average negative bias of about ∼20% is also found. The magnitude and direction of this bias depend on the spectral width of the input spectrum. The radar and methodology are applied to a case study of a convective cell. Retrievals are made with ∼300 m resolution between 800 and 4600 m. The temporal resolution is 2 min. Comparisons with a rain gauge show that both the magnitude and timing of the precipitation are well captured by the radar. The relationship between the observed rain rate and exponential fits applied t...

Momentum flux estimates accompanying multiscale gravity waves over Mount Cook, New Zealand, on 13 July 2014 during the DEEPWAVE campaign

Observations performed with a Rayleigh lidar and an Advanced Mesosphere Temperature Mapper aboard the National Science Foundation/National Center for Atmospheric Research Gulfstream V research aircraft on 13 July 2014 during the Deep Propagating Gravity Wave Experiment (DEEPWAVE) measurement program revealed a large-amplitude, multiscale gravity wave (GW) environment extending from ~20 to 90 km on flight tracks over Mount Cook, New Zealand. Data from four successive flight tracks are employed here to assess the characteristics and variability of the larger- and smaller-scale GWs, including their spatial scales, amplitudes, phase speeds, and momentum fluxes. On each flight, a large-scale mountain wave (MW) having a horizontal wavelength ~200–300 km was observed. Smaller-scale GWs over the island appeared to correlate within the warmer phase of this large-scale MW. This analysis reveals that momentum fluxes accompanying small-scale MWs and propagating GWs significantly exceed those of the large-scale MW and the mean values typical for these altitudes, with maxima for the various small-scale events in the range ~20–105 m2 s−2.

Simultaneous observations of the phase‐locked 2 day wave at Adelaide, Cerro Pachon, and Darwin

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.

Observations and modeling of traveling ionospheric disturbance signatures from an Australian network of oblique angle-of-arrival sounders

An Australian network of oblique angle-of-arrival (AoA) ionosondes was installed as part of the ELOISE experimental campaign in September 2015, aimed at an improved understanding of the spatial and temporal structure of traveling ionospheric disturbances (TIDs) at mid-latitudes. In this paper, the array design and signal processing for the AoA sounder is described, along with a sample of results showing typical disturbance signatures. Realistic parameterized models of electron density perturbations, along with geometric ray tracing, were used to synthesize the effects of medium to large scale TIDs on the sounder observables and aid in classifying the measurements.