Uranus’ cloud structure and seasonal variability from Gemini-North and UKIRT observations

Observations of Uranus were made in September 2009 with the Gemini-North telescope in Hawaii, using both the NIFS and NIRI instruments. Observations were acquired in Adaptive Optics mode and have a spatial resolution of approximately 0.1″.NIRI images were recorded with three spectral filters to constrain the overall appearance of the planet: J, H-continuum and CH₄(long), and long slit spectroscopy measurements were also made (1.49-1.79 μm) with the entrance slit aligned on Uranus’ central meridian. To acquire spectra from other points on the planet, the NIFS instrument was used and its 3″ × 3″ field of view stepped across Uranus’ disc. These observations were combined to yield complete images of Uranus at 2040 wavelengths between 1.476 and 1.803 μm.The observed spectra along Uranus central meridian were analysed with the NEMESIS retrieval tool and used to infer the vertical/latitudinal variation in cloud optical depth. We find that the 2009 Gemini data perfectly complement our observations/conclusions from UKIRT/UIST observations made in 2006-2008 and show that the north polar zone at 45°N has continued to steadily brighten while that at 45°S has continued to fade. The improved spatial resolution of the Gemini observations compared with the non-AO UKIRT/UIST data removes some of the earlier ambiguities with our previous analyses and shows that the opacity of clouds deeper than the 2-bar level does indeed diminish towards the poles and also reveals a darkening of the deeper cloud deck near the equator, perhaps coinciding with a region of subduction. We find that the clouds at 45°N,S lie at slightly lower pressures than the clouds at more equatorial latitudes, which suggests that they might possibly be composed of a different condensate, presumably CH₄ ice, rather than H₂S or NH₃ ice, which is assumed for the deeper cloud. In addition, analysis of the centre-to-limb curves of both the Gemini/NIFS and earlier UKIRT/UIST IFU observations shows that the main cloud deck has a well-defined top, and also allows us to better constrain the particle scattering properties.Overall, Uranus appeared to be less convectively active in 2009 than in the previous 3 years, which suggests that now the northern spring equinox (which occurred in 2007) is passed the atmosphere is settling back into the quiescent state seen by Voyager 2 in 1986. However, a number of discrete clouds were still observed, with one at 15°N found to lie near the 500 mb level, while another at 30°N, was seen to be much higher at near the 200 mb level. Such high clouds are assumed to be composed of CH₄ ice.     

Latitudinal variations of HCN, HC3N, and C2N2 in Titan's stratosphere derived from Cassini CIRS data

Mid- and far-infrared spectra from the Composite InfraRed Spectrometer (CIRS) have been used to determine volume mixing ratios of nitriles in Titan's atmosphere. HCN, HC₃N, C₂H₂, and temperature were derived from 2.5 cm⁻¹ spectral resolution mid-IR mapping sequences taken during three flybys, which provide almost complete global coverage of Titan for latitudes south of 60° N. Three 0.5 cm⁻¹ spectral resolution far-IR observations were used to retrieve C₂N₂ and act as a check on the mid-IR results for HCN. Contribution functions peak at around 0.5-5 mbar for temperature and 0.1-10 mbar for the chemical species, well into the stratosphere. The retrieved mixing ratios of HCN, HC₃N, and C₂N₂ show a marked increase in abundance towards the north, whereas C₂H₂ remains relatively constant. Variations with longitude were much smaller and are consistent with high zonal wind speeds. For 90°-20° S the retrieved HCN abundance is fairly constant with a volume mixing ratio of around 1 × 10⁻⁷ at 3 mbar. More northerly latitudes indicate a steady increase, reaching around 4 × 10⁻⁷ at 60° N, where the data coverage stops. This variation is consistent with previous measurements and suggests subsidence over the northern (winter) pole at approximately 2 × 10⁻⁴ m s⁻¹. HC₃N displays a very sharp increase towards the north pole, where it has a mixing ratio of around 4 × 10⁻⁸ at 60° N at the 0.1-mbar level. The difference in gradient for the HCN and HC₃N latitude variations can be explained by HC₃N's much shorter photochemical lifetime, which prevents it from mixing with air at lower latitude. It is also consistent with a polar vortex which inhibits mixing of volatile rich air inside the vortex with that at lower latitudes. Only one observation was far enough north to detect significant amounts of C₂N₂, giving a value of around 9 × 10⁻¹⁰ at 50° N at the 3-mbar level.     

Core to corona: UKSP 2004

The UK solar physics community gathered with the MIST community in Edinburgh from 29 March – 1 April 2004, with a programme that reflected the strength and diversity of UK research in the field. Lyndsay Fletcher and Robert Erdelyi report.     

A comparison of the use of genetic and hill-climbing algorithms to fit low-l solar p-mode spectra

We present a comparative study of low-l solar p-mode parameters extracted by genetic-algorithm and ‘standard’ hill-climbing minimisation routines. To effect this we make use of observations made in integrated sunlight by the Birmingham Solar-Oscillations Network (BiSON) and the GOLF instrument on board the ESA/NASA SOHO satellite, in addition to artificial data. We find that over the central part of the p-mode range the two fitting routines return similar results. However, at low frequencies — where the S/N in the modes is low and their resonant peaks narrow — we find that the genetic routine appears to offer more robust estimates of the underlying parameters.     

Investigating the complex interface where bedrock transforms to regolith

The interface where bedrock transforms to regolith is not planar but rather has a roughness that varies with the scale of observation. The complexity of this surface is manifested in both element-depth and fragment size-depth distributions and may sometimes be related to the longitudinal profiles of watershed streams. The fractal nature of the bedrock-regolith interface means that the interface has a “thickness” which is >20 m in two ridgetop examples from Pennsylvania and Puerto Rico. Such weathering thicknesses, modeled as a function of one-dimensional fluid flow, are affected by the balance between rates of weathering and erosion. One-dimensional models are consistent with weathering advance rates that vary with equilibrium solubility and porefluid velocities (and not reaction kinetics). However, fluid flow is not strictly downward and one-dimensional. Permeability of regolith changes as particle size and bulk density changes with depth. Thus, both downward and lateral flow occurs especially at reaction fronts where reactions change permeability. The rate of weathering advance is, therefore, affected by the 3-dimensional distribution of reaction zones that affect permeability across the watershed. Quantitative models of such phenomena over a range of spatial and temporal scales are needed.     

Employing spatial information technologies to monitor biological control of saltcedar in West Texas

The saltcedar leaf beetle (Diorhadha spp.) has shown promise as a biocontrol agent for saltcedar (Tamarix spp.) invasions in the USA. In Texas, natural resource managers need assistance in monitoring biological control of invasive saltcedars. This study describes application of a medium-format, digital camera acquiring natural colour imagery and global positioning system (GPS) and geographic information system (GIS) technologies to check biological control of saltcedar in west Texas. On 8 July and 8 September 2011, natural colour airborne digital imagery was collected along a 155.8?km transect covering portions of Presidio and Brewster counties of Texas. The camera was tethered to a GPS receiver that geotagged each image and saved the coordinates to a key-hole marked up language file that was viewable on Google Earth. Saltcedar trees exhibiting severe feeding damage and those that were totally defoliated were easily identified in the imagery. The former appeared in orange to brown colour tones; the latter exhibited grey colour tones. Point distribution maps showing locations of saltcedar trees exhibiting feeding damage were developed from GPS information in the GIS. Coordinate points on the map were linked to the corresponding image, permitting the user to have quick access to view imagery. The results of this study show a practical method for monitoring biological control of saltcedar.     

Applying broadband spectra to assess biological control of saltcedar in west Texas

Broadband field spectra were assessed to discriminate invasive saltcedar (Tamarix spp.) trees exhibiting feeding damage caused by the saltcedar leaf beetle (Diorhadba spp.) from other land cover types. Data were collected at two study sites near Presidio, Texas in 2010 and 2011. Spectral bands evaluated were coastal blue (400–450?nm), blue (450–510?nm), green (510–580?nm), yellow (585–625?nm), red (630–690?nm), red-edge (705–745?nm), and near-infrared (770–895, 860–1040?nm). Data were evaluated with analysis of variance and Scheffe’s multiple comparison test (α?=?0.05). The red band generally separated severely damaged saltcedar trees from other land cover features. Near-infrared bands separated defoliated saltcedar trees. Broadband spectra has potential for distinguishing saltcedar trees exhibiting feeding damage caused by the saltcedar leaf beetle from other associated features, thus supporting future explorations of airborne and satellite-borne multispectral systems to monitor biological control of saltcedar within complex landscapes.     

Employing airborne multispectral digital imagery to map Brazilian pepper infestation in South Texas

A study was conducted in south Texas to determine the feasibility of using airborne multispectral digital imagery for differentiating the invasive plant Brazilian pepper (Schinus terebinthifolius) from other cover types. Imagery obtained in the visible, near-infrared, and mid-infrared regions of the light spectrum and a supervised classification approach were employed to develop thematic maps of two areas infested with Brazilian pepper. Map accuracies ranged from 84.2 to 100% for the Brazilian pepper class. Findings support using airborne multispectral digital imagery as a tool for separating Brazilian pepper from associated land cover types and further encourage exploration of airborne multispectral digital imagery and image processing techniques for developing maps of Brazilian pepper infestation in Texas and abroad.     

Do medical marijuana centers behave like locally undesirable land uses? Implications for the geography of health and environmental justice

As of 2013, medical marijuana is legal in 20 US States and the District of Columbia, but few studies have investigated the impact of the retail centers that sell the drug. We draw upon the social construction literature to frame our research and help us determine whether medical marijuana centers in Denver, Colorado, are considered locally undesirable land uses (LULUs). The geography of health and environmental justice frameworks lead us to hypothesize that marijuana centers are more likely to be opened in Hispanic, Black, and poor neighborhoods than in non-Hispanic White and affluent neighborhoods. We also hypothesize that marijuana centers will tend to increase the minority composition and poverty of the neighborhoods in which they are located. Contrary to expectations, we find no empirical support for these two hypotheses. Instead, results suggest that marijuana centers are likely to be situated in neighborhoods with higher crime rates and more retail employment. Thus, despite the view by many planners and law enforcement officials that these centers are problematic, they do not take on LULU characteristics in siting and demographic changes. This finding, while limited to Denver, has important implications for policymakers who are considering similar marijuana policies.