On the Vertical Thermal Structure of Pluto's Atmosphere

A radiative–conductive model for the vertical thermal structure of Pluto's atmosphere is developed with a non-LTE treatment of solar heating in the CH₄3.3 μm and 2.3 μm bands, non-LTE radiative exchange and cooling in the CH₄7.6 μm band, and LTE cooling by CO rotational line emission. The model includes the effects of opacity and vibrational energy transfer in the CH₄molecule. Partial thermalization of absorbed solar radiation in the CH₄3.3 and 2.3 μm bands by rapid vibrational energy transfer from the stretch modes to the bending modes generates high altitude heating at sub-microbar pressures. Heating in the 2.3 μm bands exceeds heating in 3.3 μm bands by approximately a factor of 6 and occurs predominantly at microbar pressures to generate steep temperature gradients ∼10–20 K km⁻¹forp> 2 μbar when the surface or tropopause pressure is ∼3 μbar and the CH₄mixing ratio is a constant 3%. This calculated structure may account for the “knee” in the stellar occultation lightcurve. The vertical temperature structure in the first 100 km above the surface is similar for atmospheres with Ar, CO, and N₂individually as the major constituent. If a steep temperature gradient ∼20 K km⁻¹is required near the surface or above the tropopause, then the preferred major constituent is Ar with 3% CH₄mixing ratio to attain a calculated ratio ofT/(= 3.5 K amu⁻¹) in agreement with inferred values from stellar occultation data. However, pure Ar and N₂ices at the same temperature yield an Ar vapor pressure of only ∼0.04 times the N₂vapor pressure. Alternative scenarios are discussed that may yield acceptable fits with N₂as the dominant constituent. One possibility is a 3 μbar N₂atmosphere with 0.3% CH₄that has 106 K isothermal region (T/= 3.8 K amu⁻¹) and ∼8 K km⁻¹surface/tropopause temperature gradient. Another possibility would be a higher surface pressure ∼10 μbar with a scattering haze forp> 2 μbar. Our model with appropriate adjustments in the CH₄density profile to Triton's inferred profile yields a temperature profile consistent with the UVS solar occultation data (Krasnopolsky, V. A., B. R. Sandel, and F. Herbert 1992.J. Geophys. Res.98, 3065–3078.) and ground-based stellar occultation data (Elliot, J. L., E. W. Dunham, and C. B. Olkin 1993.Bull. Am. Astron. Soc.25, 1106.).     

Wind environment in the Lee of Kauai Island,Hawaii during trade wind conditions: weather setting for the Helios Mishap

On 26 June 2003 (approximately 1030 local time) the Helios ultralight aircraft broke apart off the west coast of Kauai Island, Hawaii as it was climbing out of the Kauai wind shadow. Following the aircraft mishap, a study was carried out to understand the conditions on the day of the crash and to better characterize the wind in the lee of Kauai. As part of this effort, both aircraft measurements and numerical modelling studies were carried out. Measurements and models showed the trade wind flow was enhanced around the island creating a region of wind shear surrounding the leeside calm zone. This wind shear region was found to be vertically oriented along the south side but tilted northward with height along the northern side of the calm zone. Several other factors on the day of the crash were investigated including water vapour gradients, diurnal Island heating, and gravity waves but their possible influences on the crash could not be confirmed. While the numerical model captured the general features of the Kauai leeside winds, the orientation of the calm zone was north of the observed one.     

Tourism and deforestation in the Mt Everest region of Nepal

Over the past 50 years the Sherpa-inhabited Mt Everest region of Nepal has become a premier international mountaineering and trekking destination. Tourism development has brought prosperity to many Sherpas. It has also, however, had adverse impacts on regional forests and alpine vegetation because of the use of firewood by camping groups and inns and the felling of trees to construct inns and other tourist facilities. Concern that tourism was causing widespread deforestation helped catalyse the 1976 establishment of an inhabited protected area, Sagarmatha (Mt Everest) National Park, in the Khumbu region and spurred the implementation of a series of forest conservation and alternative energy development measures both within the national park and in a recently declared buffer zone in the adjacent Pharak region. This paper examines the changing pressures that tourism has placed on regional forests and alpine vegetation over the past half century and their role in regional vegetation change. This analysis is based primarily on detailed accounts of past and present forest use and change obtained during fieldwork conducted in all Khumbu and Pharak villages, along with corroborating evidence from early foreign visitors' accounts and photographs. Contrary to some early reports it now appears there has actually been little deforestation since 1950. The continuing use of firewood by inns, however, has contributed to the thinning of forests in some parts of the national park and to the depletion of shrub juniper in the most heavily visited alpine regions. There has been a greater impact on forests just outside the national park, which have been heavily thinned over an extensive area in order to provide timber to build inns within the national park.     

Sedimentation and erosion in connection with ship traffic,Göteborg Harbour,Sweden

Two detailed bathymetric surveys document the effects of increased turbulence due to jet-propelled ferries and other ship traffic in Göteborg Harbour. Sedimentation is enhanced in areas where the water stratification is disturbed by harbour design and ship traffic. However, accumulation is dependent on bottom conditions, and erosion is prevalent in areas with heavy ship traffic, especially at turning sites. A geostatistical analysis of spatial bathymetric data indicates greater variability but a longer range of dependence between sites within areas of accumulation in comparison with those characterised by erosion or mixed erosion and accumulation. Changes in the geostatistical relationships induced by directing the comparison of sites along or across the channel are also possible to interpret in connection with the sedimentation conditions. Bathymetric variations, mineralogical trends, and contaminant changes support the interpretation of high bottom sediment mobility and the focusing of accumulation and erosion in specific areas.