A Flexible Prism used as an Image Stabilizer

An image stabilizer was constructed by making use of a flexible prism, which is widely used as an anti-vibration mechanism in handheld video cameras. The prism responds to frequencies up to 20 Hz, and can be simply inserted into existing optics. The performance of the prism has been confirmed by observing the Sun through it.     

High belowground biomass allocation in an upland black spruce (Picea mariana) stand in interior Alaska

The root system of forest trees account for a significant proportion of the total forest biomass. However, data is particularly limited for forests in permafrost regions. In this study, therefore, we estimated the above- and belowground biomass of a black spruce (Picea mariana) stand underlain with permafrost in interior Alaska. Allometric equations were established using 4–6 sample trees to estimate the biomass of the aboveground parts and the coarse roots (roots >5 mm in diameter) of P. mariana trees. The aboveground biomass of understory plants and the fine-root biomass were estimated by destructive sampling. The aboveground and coarse-root biomasses of the P. mariana trees were estimated to be 3.97 and 2.31 kg m^?2, respectively. The aboveground biomass of understory vascular plants such as Ledum groenlandicum and the biomass of forest floor mosses and lichens were 0.10 and 0.62 kg m^?2, respectively. The biomass of fine roots <5 mm in diameter was 1.27 kg m^?2. Thus, the above- and belowground biomasses of vascular plants in the P. mariana stand were estimated to be 4.07 and 3.58 kg m^?2, respectively, indicating that belowground biomass accounted for 47% of the total biomass of vascular plants. Fine-root biomass was 36% of the total root biomass, of which 90% was accumulated in the surface organic layer. Thus, this P. mariana stand can be characterized as having extremely high belowground biomass allocation, which would make it possible to grow on permafrost with limited soil resource availability.     

Temporal variations of the net Kuroshio transport and its relation to atmospheric variations

Temporal variations of the net Kuroshio transport are investigated using long-term hydrographic data from repeat section of the 137°E meridian from the south of Japan (34°N) to New Guinea (1°S) conducted by the Japan Meteorological Agency. In this study, boundaries of the Kuroshio and the Kuroshio Counter Current (KCC) are defined based on the sea surface dynamic height distribution. Westward flows associated with the KCC and cold-core eddy north of the Kuroshio are removed from the eastward flow associated with the Kuroshio in order to estimate the net Kuroshio transport strictly. The net Kuroshio transport reveals low-frequency variations: significant signals on a decadal (about 10-year) timescale. The variations of net Kuroshio transport are predominantly caused by changes in the magnitude of oceanic current speed fields associated with a vertical movement of the main pycnocline depth around the southern boundary of the Kuroshio: deepening of the main pycnocline around the southern boundary of the Kuroshio forms a sharp northern upward-tilting slope of the isopycnal surfaces at the Kuroshio region, and eventually the net Kuroshio transport increases together with the Kuroshio eastward transport. By using a wind-driven hindcast model, it is found that the main pycnocline depth variation results from the first-mode baroclinic Rossby waves attributable to two types of Aleutian Low (AL) changes: a change in the magnitude of AL and meridional movement of AL.     

Quasi-decadal modulations of North Pacific Intermediate Water area in the cross section along the 137°E meridian: impact of the Aleutian Low activity

Temporal variations of area of the North Pacific Intermediate Water (NPIW), in the repeat hydrographic section along 137°E meridian conducted by the Japan Meteorological Agency, are investigated using the de-trended variables from 1972 to 2008. Variations of NPIW area show a clear quasi-decadal (about 10 years) modulation and it is caused by the vertical displacement of isopycnal surfaces in the lower portion of NPIW around the northern boundary of its distribution (30–32°N): The downward (upward) movement of isopycnal surfaces in the lower portion of NPIW as a result of the first-mode baroclinic ocean response stretches (shrinks) the density layer equivalent of NPIW and causes strengthening (weakening) of westward flows associated with the Kuroshio Counter Current, and then it can induce an increase (decrease) of volume transport of NPIW from the east. Consequently, the NPIW northern boundary shifts northward (southward) and an increase (decrease) of the NPIW area is induced. Large-scale atmospheric forcing controlling the vertical displacements of isopycnal surfaces is explored using a wind-driven hindcast ocean model. The vertical displacements stem from the first-mode baroclinic ocean response to the two types of Aleutian Low (AL) activities: in particular, the meridional movement of the AL imparts more potential influence on them than the AL intensity variation does.     

Variation of water system distribution in the Sanriku Coastal Area

We analyzed hydrographic data obtained monthly by the Iwate Prefectural Fisheries Laboratory during 1977–1981. Our attention was focussed on the classification of waters based on the Temperature-Salinity (T-S) scatter diagram analyses, and on the extraction of the mean state of their distribution for each season. The water system was defined as all waters occupying some specific region on the T-S plane, and the mean state for each season was expressed by the distribution of the mode water systems (i.e., the most commonly occuring water system).Because of the coexistence of the Tsugaru Warm Current, the Oyashio and the Kuroshio, and their large seasonal variability, the sea waters had a wide variety of T-S combinations. The detailed T-S scatter diagram analyses allowed us to classify the waters into six water systems. A time-longitude diagram of water systems and the distribution of mode water systems are presented. The latter showed clear seasonal variations of the Tsugaru Warm Current and the Oyashio.Though the water system analysis was successfully able to present the distribution of the various waters in the Sanriku Coastal Area and to clearly extract the mean state of sea conditions, it was found that the classification of water systems on the T-S plane was not complete in all cases for this area.     

Comparison of upper ocean thermal conditions in the western North Pacific between two pentads: 1938–42 and 1978–82

In order to understand long-term changes in the temperature structure of the upper western North Pacific, we compared thermal conditions in two pentads, 1938–42 (P34) and 1978–82 (P78). The 1938–42 data were taken mostly by the Japanese Imperial Navy in a series of hydrographic surveys. The 1978–82 data were mostly XBT data taken as part of the TRANSPAC program. For each pentad, the data were interpolated to a set of standard depths, put through quality control procedures and averaged on a 1^o×1^o grid. A large area of the central subtropical gyre was warmer during P78, while the southern subtropical gyre, in the area of the North Equatorial Current was warmer during P34. This suggests that the transports of the Kuroshio and North Equatorial currents were larger during P78. Properties of North Pacific subtropical mode water (NPSTMW) were compared between pentads. It was found that NPSTMW was thicker, more uniform in temperature and more confined geographically during P34. A greater thickness is shown to result from stronger wintertime cooling during P34. Changes in the geographic extent of NPSTMW probably result from reduced advection by the Kuroshio current system during P34. The reason for the reduced advection maybe the Kuroshio was in a large meander state for a larger fraction of the earlier pentad, which can cut off advection west of the Izu Ridge.     

Impact of quasi-decadal variability in the tropical Pacific on ENSO modulations

The impact of quasi-decadal (QD: 8 to 18 years) variability in the tropical Pacific on ENSO events is investigated. It is found that there is a significant difference in the behavior of ENSO events between the phases of positive and negative anomalies of the QD Niño-3.4 index. During the period of negative QD-scale Niño-3.4 index, ENSO events, especially La Niña events, occur more frequently, and larger amplitudes of thermal anomalies related to El Niño events appear over the central to eastern equatorial Pacific. Furthermore, propagations of upper ocean heat content anomaly and a phase relationship between upper ocean heat content and Niño-3 index in the equatorial Pacific, which have been pointed out by previous studies, are clearly detected during the period of negative QD Niño-3.4 index.