Parametric excitation of alfvén wave by magnetosonic wave with oblique propagation

A parametric excitation of the Alfvén wave (k^A, ω_a) by the magnetosonic wave (K₁^fs, ω_1fs), which propagates obliquely to the static magnetic field, has been analyzed. The theoretical model for a one-fluid with uniform, unbounded, ideally conducting and compressible plasma is employed. The resonance conditions are chosen such as, $\text{k}{}_1{}^{\mathrm{fs}}\text{=}\text{k}{}_1{}^{\mathrm{fs}}\text{+}\text{k}{}^{\mathrm{A}}$ and ω_1fs ? ω_A = δ ～ ω_2fs. The p wave is assumed to be strong enough, so that the pump wave is given as a constant. In both the case of the standing and the propagating pump the growth rates of the excited waves depend on not only the pump power but also the β-ratio. In the standing pump the threshold pump intensity of the oscillating instability is zero at the perfect matching. It is found that we can obtain a larger growth rate of the parametric excitation of Alfvén wave by the fast magnetosonic pump wave for θ_1f ～ 70–80° and the occurrence regions of parametric excitations are localized at the resonance point in the magnetosphere (β ～ m_e/m_i). It is concluded that the parametric instability of Pc3 range HM-waves is the more possible theory than the linear resonance theory.     

Predicting the effects of shade on water temperature in small streams

A computer model for stream water temperature was developed, and tested in a small pasture stream near Hamilton, New Zealand. The model quantifies shading by riparian vegetation, hillsides, and stream banks using three coefficients: canopy angle, topography angle, and canopy shade factor. Shade was measured directly and found to vary significantly along the channel. Using the maximum measured shade, a close match was achieved between observed and predicted daily maximum and minimum water and bed sediment temperature. Model predictions of incoming and outgoing long‐wave radiation flux closely matched measurements, but there were unexplained discrepancies in short‐wave radiation flux. Model predictions indicate that moderate shade levels (c. 70%) may be sufficient in temperate climates to restore headwater pasture stream temperatures to 20°C, an estimate of the thermal tolerance for sensitive invertebrates.     

New views of the lunar plasma environment

A rich set of new measurements has greatly expanded our understanding of the Moon–plasma interaction over the last sixteen years, and helped demonstrate the fundamentally kinetic nature of many aspects thereof. Photon and charged particle impacts act to charge the lunar surface, forming thin Debye-scale plasma sheaths above both sunlit and shadowed hemispheres. These impacts also produce photoelectrons and secondary electrons from the surface, as well as ions from the surface and exosphere, all of which in turn feed back into the plasma environment. The solar wind interacts with sub-ion-inertial-scale crustal magnetic fields to form what may be the smallest magnetospheres in the solar system. Proton gyro-motion, solar wind pickup of protons scattered from the dayside surface, and plasma expansion into vacuum each affect the dynamics and structure of different portions of the lunar plasma wake. The Moon provides us with a basic plasma physics laboratory for the study of fundamental processes, some of which we cannot easily observe elsewhere. At the same time, the Moon provides us with a test bed for the study of processes that also operate at many other solar system bodies. We have learned much about the Moon–plasma interaction, with implications for other space and planetary environments. However, many fundamental problems remain unsolved, including the details of the coupling between various parts of the plasma environment, as well as between plasma and the surface, neutral exosphere, and dust. In this paper, we describe our current understanding of the lunar plasma environment, including illustrative new results from Lunar Prospector and Kaguya, and outstanding unsolved problems.     

Anomalous deformation of the Earth's bow shock in the lunar wake: Joint measurement by Chang’E-1 and SELENE

Because the solar wind (SW) flow is usually super-sonic, a fast-mode bow shock (BS) is formed in front of the Earth's magnetosphere, and the Moon crosses the BS at both dusk and dawn flanks. On the other hand, behind of the Moon along the SW flow forms a tenuous region called lunar wake, where the flow can be sub-Alfvénic (and thus sub-sonic) because of its low-density status. Here we report, with joint measurement by Chang’E-1 and SELENE, that the Earth's BS surface is drastically deformed in the lunar wake. Despite the quasi-perpendicular shock configuration encountered at dusk flank under the Parker-spiral magnetic field, no clear shock surface can be found in the lunar wake, while instead gradual transition of the magnetic field from the upstream to downstream value was observed for a several-minute interval. This finding suggests that the ‘magnetic ramp’ is highly broadened in the wake where a fast-mode shock is no longer maintained due to the highly reduced density. On the other hand, observations at the 100 km altitude on the dayside show that the fast-mode shock is maintained even when the width of the downstream region is smaller than a typical scale length of a perpendicular shock. Our results suggest that the Moon is not so large to eliminate the BS at 100 km altitude on the dayside, while the magnetic field associated with the shock structure is drastically affected in the lunar wake.     

Improvement of GPS/acoustic seafloor positioning precision through controlling the ship’s track line

The precision of GPS/acoustic seafloor positioning was improved by introducing a hull-mounted onboard system in March 2008, which allows us to conduct acoustic ranging measurements with the vessel sailing along the pre-determined track lines, while the early system before 2008 could only adopt the uncontrollable drifting observation. The continuity of the positioning results due to the transition was first confirmed through the comparison between results from sailing and drifting observations conducted in parallel. Using the data acquired for about 3 years since 2008, the repeatability of the determined position for the sailing observation was evaluated to be about 2 cm in root mean squares in the horizontal component, significantly better than that for the early drifting observation. The improvement of positioning precision probably resulted from the improvement of geometric distribution of acoustic ranging data by controlling the track lines. It was also shown that the sailing observation allows to obtain reliable results with a smaller amount of data. Comparison between the results in different sea regions suggests that positioning precision is better in the region along the Nankai Trough than in the region along the Japan Trench, probably because of the complicated acoustic velocity structure of seawater often observed in the latter. Furthermore, the precision of height determination was also improved, which leads us to expect that vertical crustal movement will be detectable in the future through accumulation of data as well as further technology development.     

An Ecosystem Services Approach to Sustainable Livelihoods in the Homegardens of Kandy,Sri Lanka

ABSTRACT

The Kandyan homegardens, or forest gardens, of central Sri Lanka are diverse, smallholder agroforestry ecosystems that for 2000 years have reflected evolving environmental, economic, and social livelihood needs. An ecosystem services approach interrogated homegarden changes over the last 10 years in 31 Kandyan households. Livelihood strategies favouring homegardens were found to have broader benefits across household, national, and global scales than those favouring commercial simplification or those abandoning cultivation for alternative incomes. Livelihood benefits beyond income included resilience to economic and environmental shocks; food security; and higher stocks of biological and agricultural diversity. This revealed overlooked socio-ecological feedbacks between drivers that frustrated interventions to sustain homegarden livelihoods, including increased wild animal incursions thwarting household climate adaptation and disaster recovery; global organic and fair trade incentives reducing food security and livelihood resilience; and national seed and animal regulations counteracting homegarden sustainability programs. Despite these pressures, households maintained homegarden systems for their cultural, aesthetic and eating preferences. An ecosystem services approach can complement sustainable livelihood approaches by identifying overlooked environmental and cultural benefits; reveal livelihood feedbacks from drivers of ecosystem change; avoid unintended consequences from interventions; and capitalise on synergies between stakeholder priorities.     

Long-term variations in north-south asymmetry of solar activity

We present a new set of data on relative sunspot number (total, northern hemisphere, and southern hemisphere), taken for the 37-yr period 1947 to 1983; this constitutes a particularly coherent and consistent set of data, taken by the same observer (Hisako Koyama) using the same observing instrument. These data are combined with earlier data (White and Trotter, 1977) on the variation of sunspot areas for both solar hemispheres from 1874 to 1971. The combined data, covering 110 years and 10 solar cycles, are examined for periodicity in solar activity north-south asymmetry. We show that, in general, northern hemisphere activity, displayed as either An/(An + As) or Rn/(Rn + Rs), peaks about two years after sunspot minimum. This peak is greater during even cycles, pointing to a 22-yr periodicity in north-south asymmetry in solar activity, suggesting that the asymmetry is related to the 22-yr solar magnetic cycle. We demonstrate that the largest and most protracted period of northern-hemisphere activity excess in the last 110 years has occurred from 1959 to 1970; we show that there is a strong correlation between northern activity excess and a cosmic-ray density gradient perpendicular to the ecliptic plane, pointing southward, which is evident in cosmic-ray diurnal variation data from the Embudo underground cosmic-ray telescope.     

Analysis of a magnetohydrodynamic stellar wind

Characteristic features of solutions are analysed around the Alfvénic point. There are three types of solutions through the point.Paper presented at the IAU Third Asian-Pacific Regional Meeting, held in Kyoto, Japan, between 30 September–6 October, 1984.     

Substances of cometary grains estimated from evaporation and radiation pressure mechanisms

The shape and intensity distribution of tails for several large comets are estimated on the basis of grain properties in the solar radiation field. The following results are obtained: (1) The ratio of the maximum radiation pressure force to the gravitaional force acting on dust grains in cometary tails is found to be less than 2.5. This means that grains such as graphite particles in the size range 0.02–0.2 μm do not exist in them, because such particles would allow forces greater than 2.5 (2) Tail substances supplied near the time of perihelion passage for the Sun-grazing comet Ikeya-Seki (1965 VIII) and Comet Seki-Lines (1962 III) were composed of particular grains which had values of radiation pressure ratio less than 1.0. Therefore, it is concluded that the material was composed of silicate grains only, since iron grains had sublimated and there were no graphite particles.     

Effects of variability of sea ice transport through the Fram Strait on the intensity of the Atlantic deep circulation

Results from an ice-ocean coupled model are used to investigate the impact of long-term variability in sea ice transport at the Fram Strait on the intensity of the Atlantic deep circulation. An increase (or decrease) in sea ice transport through the Fram Strait leads to a stronger (or weaker) deep circulation in the Atlantic. Change in the sea ice transport is accompanied by a salinity anomaly in the surface layer of the Arctic Ocean. Such an anomaly could inversely affect the Atlantic circulation once it reaches deep water formation regions. If the Canadian Archipelago is closed, the anomaly is subsequently transported through the Fram Strait, and counters the initial changes in the Atlantic deep circulation. On the other hand, if the Canadian Archipelago is open, some of the anomaly is transported to the Canadian Archipelago, and the initial change in the Atlantic deep circulation persists. In the Arctic Ocean basin, the time scale and path of the salinity anomalys propagation depends on the large-scale flow at the surface of the Arctic Ocean. Our results suggest that the salinity anomaly transport and its propagation pathway out of the Arctic Ocean are important determinants of the role of sea ice transport variability through the Fram Strait in controlling the intensity of the Atlantic deep circulation.