ALBERT

Description: The low frequency radio sky shows the locations of electromagnetic radio sources with a characteristic dilution of precision. Here we report a thorough high resolution analysis of radio waves from low frequency (∼20-150 kHz) radio communication transmitters which are recorded with a small aperture array of radio receivers during the day. It is found that the observed dilution of precision results from the array geometry of the radio receivers, a birefringent wave propagation and the correlated multipath propagation of low frequency radio waves. The influence of the array geometry on the dilution of precision is reduced by taking into account the impulse response of the array. This procedure reveals for the very first time the splitting of one single radio source into two distinct source locations separated by ∼0.2°-1.9° which result from a birefringent wave propagation. The two locations are yet more clearly identified by using the polarity of the modulated wave number vectors of the radio waves. This polarity is also used to quantify the dilution of precision arising from correlated multipath propagation which is discriminated against wave number fluctuations arising from the timing accuracy of the radio receivers. It is found that ∼69% of the wave number variability is of natural origin and ∼31% originates from the timing accuracy of the receivers. The wave number variability from correlated multipath propagation results in a standard deviation ∼2-8% relative to the source location. This compact measurement of correlated multipath propagation is used to characterize the uncertainty of source locations in the radio sky. The identification of correlated multipath propagation strongly suggests the existence of very fast processes acting on time scales 〈1 ms in the D-region ionosphere with physically meaningful effects on low frequency radio wave propagation. This important result has implications for practical applications in that the observed multipath propagation enables the determination of natural limits for the accuracy of navigation and lightning location methods using low frequency radio waves.

Description: The expansion of coniferous trees into sagebrush ecosystems is a major driver of habitat loss and fragmentation, resulting in negative impacts to wildlife. Greater sage-grouse ( Centrocercus urophasianus ) respond directly to conifer expansion through decreased breeding activity, nesting, and overall survival; thus, small amounts of conifer expansion can have significant impacts on sage-grouse habitat and populations. To this end, conservation partners have collaborated across private and public lands to reduce the threat of conifer expansion through targeted removal of conifer trees. Here, we demonstrate the use of the Marxan framework to incorporate important ecosystem attributes in the prioritization of conifer removal within the Oregon range of sage-grouse. We prioritized conifer removal relative to three separate goals: (1) enhancement of existing sage-grouse breeding, nesting, and early brood-rearing habitats; (2) facilitation of sage-grouse movement between breeding and brood-rearing habitats; and (3) improvement of connectivity among sage-grouse priority areas for conservation (PACs). Optimization models successfully identified areas with low conifer canopy cover, high resilience and resistance to wildfire and annual grass invasion, and high bird abundance to enhance sage-grouse habitat. The inclusion of mesic resources resulted in further prioritization of areas that were closer to such resources, but also identified potential pathways that connected breeding habitats to the late brood-rearing habitats associated with mesic areas. Examining areas outside of PACs resulted in the selection of potential corridors to facilitate connectivity; although areas with low conifer cover were selected similarly to the other optimization models, areas with high cover were also chosen to be able to enhance connectivity. Areas identified by optimization models were largely consistent with and overlapped ongoing conifer removal efforts in the Warner Mountains of south-central Oregon. Land ownership of preferential areas selected by models varied with priority goals and followed general ownership patterns of the region, with public lands managed by the Bureau of Land Management and private lands being selected the most. The increased availability of landscape-level datasets and assessment tools in sagebrush ecosystems can reduce the time and cost of both planning and implementation of habitat projects involving conifer removal. Most importantly, incorporating these new datasets and tools can supplement expert-based knowledge to maximize benefits to sagebrush and sage-grouse conservation.

Description: Single particle mass spectral data, collected in Paris, France during the MEGAPOLI winter campaign, have been used to predict hygroscopic growth at the single particle level. The mass fractions of black carbon, organic aerosol, ammonium, nitrate and sulphate present in each particle were estimated using a combination of single particle mass spectrometer and bulk aerosol chemical composition measurements. The Zdanovskii-Stokes-Robinson (ZSR) approach was then applied to predict hygroscopic growth factors based on these mass fraction estimates. Smaller particles with high black carbon mass fractions and low inorganic ion mass fractions exhibited the lowest predicted growth factors, while larger particles with high inorganic ion mass fractions exhibited the highest growth factors. Growth factors were calculated for subsaturated relative humidity (90%) to enable comparison with hygroscopic tandem differential mobility analyser (HTDMA) measurements. Mean predicted and measured hygroscopic growth factors for 110, 165 and 265 nm particles were found to agree within 6%. Single particle-based ZSR hygroscopicity estimates offer an advantage over bulk aerosol composition-based hygroscopicity estimates by providing additional chemical mixing state information. External mixing can be determined for particles of a given diameter through examination of the predicted hygroscopic growth factor distributions. 110 nm and 265 nm particles were found to be predominantly internally mixed using this approach, however external mixing of 165 nm particles was observed periodically when thinly coated and thickly coated BC particles were simultaneously detected. Single particle-resolved chemical information will be useful for modelling efforts aimed at constraining cloud condensation nuclei activity and hygroscopic growth.

Description: Using the Mars Atmospheric and Volatile EvolutioN Mission (MAVEN) Imaging Ultraviolet Spectrograph (IUVS), we found periodic longitudinal variations in CO 2 density in the Martian atmosphere. These density variations are derived from observations of the emission from limb scans in the 100 − 190 km altitude range. The variations exhibit significant structure with longitudinal wavenumbers 1, 2 and 3 in an effectively constant local solar time frame, and we attribute this structure to non-migrating tides. The wave-2 component is dominated by the diurnal eastward-moving DE1 tide at the equator and the semidiurnal stationary S0 tide at the midlatitudes. Wave-3 is dominated by the diurnal eastward-moving DE2 tide, with possibly the semidiurnal eastward-moving SE1 tide causing an amplitude increase at the midlatitudes. Structure in the wave-1 component can be explained by the semidiurnal westward-moving SW1 tide.