The stemflow of trees in a Bornean lowland tropical forest

Stemflow volume generation in lowland tropical forests was measured over a 1‐year period in the Malaysian state of Sarawak. The stemflow volume generated by 66 free‐standing trees with a diameter at breast height (DBH) over 1 cm and a tree height over 1 m were measured daily in a representative 10 m × 10 m plot of the forest. Throughfall in the plot was also measured using 20 gauges in a fixed position. Of the 2292 mm of total rainfall observed during the year‐long period, stemflow accounted for 3·5%, throughfall for 82% and there was an interception loss of 14·5%. Understory trees (DBH < 10 cm) played an important role in stemflow generation, producing 77% of the overall stemflow volume and 90% during storms with less than 20 mm of rainfall. Also, owing to their efficiency at funneling rainfall or throughfall water received by their crowns, some understory trees noticeably reduced the catches of the throughfall gauges situated under the reach of their crown areas. During storms producing greater than 20 mm of rainfall, 80% of the total stemflow occurred; trees with a large DBH or height and for which the ratio between crown's diameter and depth is less than 1, tended to generate more stemflow volume in these storms. Mean areal stemflow as a fraction of rainfall in this lowland tropical forest was 3·4%, but may range from 1–10% depending upon the proportion of trees that are high or poor stemflow yielders. Trees with DBH greater than 10 cm were likely to contribute less than 1% of the 3·4% mean areal stemflow in the forest. Copyright © 2004 John Wiley & Sons, Ltd.     

Estimation of water requirement per unit carbon fixed byEucalyptus camaldulensis in semi-arid land of Western Australia

Afforestation in arid land is a promising method for carbon fixation, but the effective utilization of water is highly important and required. Thus, the evaluation of the amount of water per unit carbon fixed with the tree growth is required to minimize the amount of water supplied to the plants. In this research, a tree is regarded as a carbon fixation reactor with inflows of water and nutrients from roots, and CO₂ as the carbon source from leaves with outflow of water vapor from leaves and accumulation in the tree itself. In the process of photosynthesis and respiration nutritional elements are dissolved in water flow in trees. They do not flow out by these reactions, but are accumulated in trees. Thus, we have treated the behaviour of nutrients as a marker to evaluate the water/carbon ratio.

Assuming that nutrient concentration is constant in sap, and the differences in the ratios of nutrient to carbon in living trees and dead (i.e. litter fall, etc.) are neglected, the ratio of the used water to fixed carbon is given as the ratio of nutrient to carbon in the tree body divided by the ratio of nutrient to water in sap. However, some nutrients are translocated and concentrated within the tree and some may be discarded through litter fall. Thus it is important to examine which nutrient element is the most suitable as the tracer.

In this paper, the results of the above method applied toEucalyptus camaldulensis in semiarid land of Western Australia are shown. The value of water requirement per unit carbon fixation determined from potassium balance is between 421 kg-H₂O/kg-C for mature trees and 285 kg-H₂O/kg-C for young trees, while the values from calcium balance are much larger than these. The cause of the discrepancy between these values is discussed based on the measured element concentrations in sap and trees and the plant physiology. Finally, the actual average value through the life of a tree is suggested to fall between the two values.

     

Gravitational interaction between a planet and an optically thin disc

We investigate the gravitational interaction between a planet and an optically thin protoplanetary disc, performing local three-dimensional hydrodynamical simulations. In the present study, we take account of radiative energy transfer in optically thin discs. Before the stage of planetary accretion, dust opacity is expected to decrease significantly because of grain growth and planetesimal formation. Thus, it would be reasonable to consider optically thin discs in the disc–planet interaction. Furthermore, we focus on small planets that can neither capture disc gas nor open a disc gap. The one-sided torque exerted on a planet by an optically thin disc is examined for various values of the disc optical thickness (<1). In optically thin discs, the temperature behind the density waves is lower than the unperturbed value because of radiative cooling. Heating due to shock dissipation is less effective than radiative cooling. Because of radiative cooling, the density distribution around the planet is not axisymmetric, which exerts an additional torque on the planet. The torque enhancement becomes maximum when the cooling time is comparable with the Keplerian period. The enhancement is significant for low-mass planets. For planets with  3 M_⊕  , the additional one-sided torque can be 40 per cent of the torque in the isothermal case. The radiative cooling is expected to change the differential torque and the migration speed of planets, too.     

Quick triggering of magnetic reconnection in magnetotail

Recently, quick triggering of magnetic reconnection (QMRT) even in an ion-scale current sheet is found to be possible with the help of the nonlinear evolution of the lower hybrid drift instability (LHDI). The details of the QMRT mechanism are reviewed mostly based on three-dimensional full-particle simulation results of our group. QMRT is mediated by LHDI and its time scale is comparable to the saturation time scale of LHDI. Depending on the initial current sheet thickness, two types of QMRT, so-called Type-I and Type-II QMRT, are demonstrated.     

Formation and disruption of aquifers in southwestern Chryse Planitia, Mars

We present geologic evidence suggesting that after the development of Mars' cryolithosphere, the formation of aquifers in southwestern Chryse Planitia and their subsequent disruption led to extensive regional resurfacing during the Late Hesperian, and perhaps even during the Amazonian. In our model, these aquifers formed preferentially along thrust faults associated with wrinkle ridges, as well as along fault systems peripheral to impact craters. The characteristics of degraded wrinkle ridges and impact craters in southwestern Chryse Planitia indicate a profound role of subsurface volatiles and especially liquid water in the upper crust (the upper one hundred to a few thousands of meters). Like lunar wrinkle ridges, the martian ones are presumed to mark the surface extensions of thrust faults, but in our study area the wrinkle ridges are heavily modified. Wrinkle ridges and nearby plains have locally undergone collapse, and in other areas they are associated with domical intrusions we interpret as mud volcanoes and mud diapirs. In at least one instance, a sinuous valley emanates from a modified wrinkle ridge, further indicating hydrological influences on these thrust-fault-controlled features. A key must be the formation of volatile-rich crust. Primary crustal formation and differentiation incorporated juvenile volatiles into the global crust, but the crustal record here was then strongly modified by the giant Chryse impact. The decipherable rock record here begins with the Chryse impact and continues with the resulting basin's erosion and infilling, which includes outflow channel activity. We propose that in Simud Vallis surface flow dissection into the base of the cryolithosphere-produced zones where water infiltrated and migrated along SW-dipping strata deformed by the Chryse impact, thereby forming an extensive aquifer in southwestern Chryse Planitia. In this region, compressive stresses produced by the rise of Tharsis led to the formation of wrinkle ridges. Zones of high fracture density within the highly strained planes of the thrust faults underlying the wrinkle ridges formed regions of high permeability; thus, groundwater likely flowed and gathered along these tectonic structures to form zones of elevated permeability. Volatile depletion and migration within the upper crustal materials, predominantly along fault systems, led to structurally controlled episodic resurfacing in southwestern Chryse Planitia. The erosional modification of impact craters in this region is linked to these processes. This erosion is scale independent over a range of crater diameters from a few hundred meters to tens of kilometers. According to our model, pressurized water and sediment intruded and locally extruded and caused crustal subsidence and other degradational activity across this region. The modification of craters across this wide range of sizes, according to our model, implies that there was intensive mobilization of liquid water in the upper crust ranging from about one hundred to several thousand meters deep.     

A numerical study of the contributions of dust source regions to the global dust budget

Contributions of the nine potential dust source regions (North and South Africa, the Arabian Peninsula, Central Asia, eastern and western China, North and South America, and Australia) to the global dust budget are investigated with a global dust transport model. A six-year simulation (1990 to 1995) indicates that the greatest contributor to the global dust budget is found to be North Africa (the Sahara Desert), which accounts for 58% of the total global dust emission and 62% of the total global dust load in the atmosphere. Australian dust dominates the southern hemisphere. The dust emission and atmospheric dust load originating from East Asia (eastern and western China) are estimated to be 214 Tg yr^− 1 and 1.1 Tg, respectively, which are 11% and 6% of the total global dust emission and dust load. Dust from East Asia dominates the atmospheric load over China and Mongolia (about 70%), Korea (60%), Japan (50%), and the North Pacific Ocean (40%). The contribution of dust originating from regions other than East Asia to the dust load over these East Asian countries and the North Pacific Ocean cannot be ignored. The simulated total dust deposition flux on Greenland suggests a possible overestimation of the Saharan dust and an underestimation of the East Asian dust in the Arctic region, which may be a common problem with global dust transport models. Possible reasons for the underestimation of the East Asian dust are discussed.     

春季亚洲地面湿度异常对月、季气候影响的模拟研究

通过大气环流模式试验,研究了春季亚洲中纬带地面湿度异常对其后4个月月平均气候参数的影响.结果发现:正的地面湿度异常对其后气候参数的影响在第1个月最弱,第3个月最强;它导致欧亚中高纬带在第2～4个月对流层内的高度和温度都降低,低值系统发展,副热带高压亦发展,中纬度西风急流相应增强;同时北美东岸有明显的遥相关响应.     

Open boundary value problems in ocean dynamics by finite elements

This paper presents recent results of application of the finite element models to wave overtopping and wave run-up problems in ocean dynamics. Open boundaries are prescribed as natural boundary condition obtained from the continuity equation of the Galerkin finite element formulation. The numerical results are, in general, reasonably good agreements with the histrical field data.     

An upper limit of visible emission from the plume generated by the impact of the K fragment of SL9

We monitored Jupiter with a video movie camera attached to a 1.3 m reflector during the impact event of the K fragment of D/Shoemaker-Levy 9. The camera was sensitive to visible radiation. A plume, which was generated by the impact and prominent in infrared wavelength, was not detected. Jovian images with hypothetical plumes were synthesized to examine how luminous the plume should have been to be recognized. It has been revealed that the plume was no more than twice as bright as Io in visible wavelength.