Comparison of Data from Four Current Meters
Obtained by Long-Term Deep-Sea Moorings

長期係留による 4 種類の流速計観測結果の比較

Toshiya Nakano*1, Hiroshi Ishizaki*2 and Nobuyuki Shikama*3
中野俊也*1・石崎 廣*2・四竈信行*3*1

Oceanographic Research Department, Meteorological Research Institute
気象研究所 海洋研究部
Present affiliation: Marine Division, Global Environment and Marine Department,
Japan Meteorological Agency
現所属: 気象庁 地球環境･海洋部 海洋気象課*2

Oceanographic Research Department, Meteorological Research Institute
気象研究所 海洋研究部*3

Institute of Observational Research for Global Change,
Japan Agency for Marine-Earth Science and Technology
独立行政法人 海洋研究開発機構 地球環境観測研究センター

序
気象研究所海洋研究部では 1979 年以来、気象庁及び神戸海洋気象台の協力の下に、
海洋大循環の解明のための一手段として、流速計を用いた海中設置型の係留系による直接測流観測を実施してきた。これらの観測に用いた流速計は、1990 年代後半まではアーンデラー社製のもので、測定原理としてはローターとベーンを用いて器械的に流速(スピード)と流向を測定するものであった。当時、アーンデラー社製品の評価は高く、全世界で類似製品のうち 90％に及ぶ普及率であった。しかし、その測定原理の故に、微弱な流速に対しては感度が悪いという欠点があり、当研究部の観測でも流速の弱い海洋深層での測流においては相対的に低い測定精度であった。
1990 年代以降、器械的運動を伴わない新たな測定原理による流速計が次々と開発された。当研究部においても経常研究「西太平洋における中・深層循環の定量化」(平成 10〜14 年度)での赤道域における深層測流の開始を機に、超音波の位相のずれを測定原理とする FSI 社製の流速計を次期の主力とすべく整備していった。ここで問題はそれら新旧２種の流速計のキャリブレーションであった。それを行うために、赤道域での深層測流用係留系において約１年に及ぶ比較観測を延べ５回にわたって、上記経常研究及び後続の「高解像度（渦解像）海洋大循環モデルの開発とそれによる水塊の形成、維持、及び変動機構の解明」（平成 15〜19 年度）において実施した。その内の１回ではさらに他の新機種２台を加えて４機種による比較観測を行った。
本技術報告はそれらの比較観測結果を示すものである。そこから見えてくるのは、
旧来型はもちろんのこと、新機種においてもそれぞれに特有の測定誤差を含んでいるということである。特に、大きな水圧のかかる深海では予想外に大きな誤差を生じる場合もあることが示された。これらのテスト結果は深層測流を行っている研究者には貴重な情報である。旧来型の流速計もまだ多く使用されているのが実情であり、その誤差に関する情報は内外の関係者に役立つものと考えられる。
これらの観測の実施に当り、多大のご協力をいただいた、気象庁、神戸海洋気象台の関係者の方々、また、一部流速計の借用を快諾していただいた企業の方々にこの場を借りて御礼申し上げる。
海洋研究部長石崎廣PrefaceIn the Oceanographic Research Department of the Meteorological Research Institute(MRI), we have long made direct observations of in situ currents at various depths toelucidate the ocean general circulation, by means of moored current meter systems since 1979,
under the cooperative efforts by Japan Meteorological Agency (JMA) and Kobe Marine
Observatory (KMO). The current meters used until the 1990s were manufactured by Aanderaa
Instruments, and use a mechanical rotor and vane system to measure current speed anddirection. In those days, the Aanderaa current meters were well appreciated, having aworldwide market share greater than 90%. However, they have a low sensitivity to weakcurrents because of the principle behind their current measurements. Therefore, in our
measurements of deep-sea currents, they were not accurate because the current speeds there
were usually very weak.
In the 1990s, development began of current meters based on new principles ofmeasurement, without mechanical movement. One of them was a current meter using thephase shift of supersonic waves as the principle for current measurements, manufactured by
Falmouth Scientific Inc. (FSI; Cataumet, MA, USA). In our research department we preparedthis kind of current meters as the next generation of current meters in time to take advantageof the start of mooring observations near the equator in 1998. However, there arose theproblem of calibration between the two kinds of current meters. To accomplish this calibration,
we made parallel observations five times in the deep mooring system near the equator, witheach set of observations lasting about one year. In one of the five comparisons, two othertypes of current meters were added, so four types of current meters were used for that set ofparallel observations.
This report presents the results of the comparisons from the parallel observations. We
found that even the new types of current meters have their own inherent measurement errors.
In particular, a few cases showed that unexpectedly large errors occurred in the deep ocean
under conditions with extreme pressure. We think the results of our comparison contain
important information for researchers occupied in field observations at home and abroad. The
classic type of current meter is often used even today, in addition to the new types, so that
information about their operating characteristics is useful.
The parallel observations were carried out as part of two projects funded by MRI’s

ordinary budget: ‘Quantitative study of the intermediate and deep circulation in the western
Pacific’ (1998–2002) and ‘Development of high-resolution (eddy-resolving) ocean generalcirculation model, and study on formation, maintenance, and variation mechanisms of water
masses based on the model’ (2003–2007). We thank the people at JMA and KMO for theircooperative efforts in carrying out the observations. We also thank Alec Electronics Company
for providing us two other types of current meters for our parallel observations.
Hiroshi Ishizaki
Director
Oceanographic Research Department

概要4 種類の流速計（RCM8：アーンデラー社製・ローターとベーンタイプ、3D-ACM：
FSI 社製・超音波位相差、Compact-EM (EM)：アレック電子社製・電磁式、RCM11：
アーンデラー社製・超音波ドップラー式）のデータの比較を、赤道近傍の約 1 年間の深層測流観測結果をもとに行った。また、4 回の RCM8 と 3D-ACM の比較観測結果もあわせて解析した。平均流速は、RCM8 が最も弱く、RCM11 は、3D-ACM と EM
よりやや弱かった。3D-ACM と EM の平均的な流速と流向はよく一致していた。RCM8の流向には、他の流速計と比較して系統的に非対称的な差があった。すなわち、RCM8と他の流速計の流向の差（RCM8 の流向−他の流速計の流向）は、流速との間（2〜10 cm s-1）に負の相関があった。流速が弱いほど、流向の差が大きい。さらに、RCM8と 3D-ACM の比較では、10 cm s-1 より強い流れの時における流向の差が零ではなく、
15°〜30°の範囲で 安定して存在する場合があった。時間平均流の流向差は、これらの差を反映している。3D-ACM と EM の流向については、異なったトレンド及び突然の背景誤差変移がみられた。

Abstract
We compared the data from four types of current meter: rotor and vane (model
RCM8; Aanderaa), acoustic phase shift (3D-ACM), electromagnetic (Compact-EM [EM]),and Doppler backscatter (RCM11; Aanderaa). The data were obtained from deep-ocean
moorings near the equator for a period of one year. We also analyzed data from four
additional parallel observations by RCM8 and 3D-ACM meters. The mean current speed of
the RCM8 meter was the lowest, and that of the RCM11 was lower than the EM and3D-ACM. The mean current speed and direction data of the 3D-ACM and EM current meters
were in good agreement. There was a systematically asymmetric difference in the current
direction indicated by the RCM8 as compared to the other meters; that is, the difference indirection between the RCM8 and the others is inversely correlated with the current speed in
the medium velocity range of 2 to 10 cm s–1. We found that the lower the current speed, thegreater the difference in direction. Furthermore, a comparison of paired RCM8 and 3D-ACM
meters indicated that the difference in direction for large speeds exceeding 10 cm s–1 wasconsistently high, ranging from 15° to 30° in some situations, not near zero. The
time-averaged difference in direction reflects these differences. Two current meters, models
3D-ACM and EM, exhibited different temporal trends and abrupt offsets in direction during
the observations.

Contents
1. Introduction･･･････････････････････････････････････････

2. Data and observations･････････････････････････････････････

1
2

3. Results･････････････････････････････････････････････････ 6
3.1 First set of observations ･･････････････････････････････････ 6
3.2 Second and third sets of observations ･･･････････････････････ 13
4. Summary and discussion
Acknowledgements
References････････････････････････････････････ 17･･･････････････････････････････････････････ 21･････････････････････････････････････････････････ 22

Technical Reports of the MRI, No. 55

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1. Introduction
It is important to describe the long-term mean flow in the deep ocean to understand the ocean
general circulation, which plays an important role in the climate system. Many oceanographers have
deployed long-term mooring systems at key places in the deep to bottom layers to measure the deep-ocean
circulation. Current meters used in deep-ocean moorings must be very sensitive since the deep flow is
generally weak. The RCM8 current meter manufactured by Aanderaa Instruments (Aanderaa Instruments,
Attleboro, MA, USA: Aanderaa Instruments, 1987), with a mechanical rotor and vane, has long been themost widely used current meter. However, the RCM8 has problems related to its mechanical workings. For–

example, its response to a weak flow is slow, and a flow of 1.1 cm s 1 or less cannot be measured.
Many oceanographers have recently begun to use new current meter designs, such as acoustic
Doppler backscatter-based current meters, those based on the measurement and comparison of direct-pathacoustic phase shifts along multiple paths, and electromagnetic current meters. It is necessary to know thecharacteristics of each current meter in observations where current meters based on different principles ofmeasurement principles must be used. This requires a comparison of observations obtained during fieldtests. Since mooring observations are expensive and require substantial effort, there is not muchinformation for inter-calibrating current meters with different measurement principles. The limited
literature includes Frye (2002) and Frye et al. (2004), who reported the results of a comparison of several
current meters in newly developed mooring systems. Their research revealed unexpected differences inmeasured speed and direction among those current meters. A similar but more thorough analysis of thesame data appeared in Hogg and Frye (2007), where they added the results from the comparison between
the appropriate velocity component of each instrument and the rate of change of pressure when they werelowered from a ship. They stressed that the RCM11 (Aanderaa; acoustic Doppler backscatter) records lower
current speeds than those indicated by their referenced instruments, the VACM/VMCM (the vector
averaging current meter/vector measuring current meter), although its direction records are of high quality(Minken, 2000). Gilboy et al. (2000) compared the results obtained by three systems, the three-dimensional
acoustic current meter (3D-ACM; Falmouth Scientific, Inc., Cataumet, MA, USA; Falmouth ScientificInc., 1999), VMCM, and acoustic Doppler current profiler (ADCP ) and found that they are in agreement
within statistical error except for a 20°–30° directional discrepancy attributed to the 3D-ACM. In addition,
a European group in the French Research Institute for Exploitation of the Sea (IFREMER) recently
collected several global datasets of parallel observations with different current meters (including part of our-1－－Technical Reports of the MRI, No. 55

2008data) and completed a comparative study that focused on the differences between mechanical instruments(mainly the RCM8) and newer ones (A. Tengberg, personal communication). They also found fairly large
differences in the current direction indicated, particularly at low current speeds. The same group also
conducted a tow-tank test for various current meters in IFREMER (A. Tengberg, unpublished data), whichindicated that errors in current speed and direction are generally substantial at low current speeds, not onlywith mechanical instruments but also with other newer designs.
We have had a series of mooring systems deployed in the western equatorial Pacific since 1998 toobserve deep currents below 2000 m. The purpose and background of this series of deep-mooring
observations are described in section 2. In 2000 during this series of observations, we introduced a new
type of current meter in this series of mooring observations, the 3D-ACM, in addition to the RCM8 alreadyin use. We needed to compare the results of the two current meters to assess the accuracy of theobservations. We also introduced two additional current meters, the RCM11 and the Compact-EM (EM;Alec Electronics, Kobe, Japan), to further clarify the characteristics of our two primary current meters, theRCM8 and 3D-ACM.
We made parallel observations using either two or four different current meters on five mooring
systems to compare the results. Four different current meters were deployed on the first mooring of the five
(Oct 2000 to Nov 2001) for a comparison at about 2500 m. Only two current meters, the RCM8 and3D-ACM, were deployed at 2750 m on each of the remaining four moorings, two starting in July 2003 andtwo more in February 2004.
We compared the data to clarify the characteristics of each current meter type. Section 2 briefly
explains the nominal features of the four kinds of current meters and the data-processing procedures. Thissection also includes a description of the purpose and background of the series of deep-mooring
observations. The results are described in section 3. Finally, section 4 summarizes our conclusions andprovides a discussion.

2. Data and observations
Figure 1 depicts the mooring locations and the design of the mooring system for the first set of-2－－Technical Reports of the MRI, No. 55

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observations. Summary information for all three sets of observations is presented in Table 1. The firstmooring was at 3°00.82'S, 162°12.40'E, with a bottom depth of 3261 m and an observation depth of 2500
m. The duration of observations was about one year, from 19 October 2000 to 7 November 2001. The
current meters deployed were the RCM8, RCM11, 3D-ACM, and EM. The specifications of each current
meter and observation setting are presented in Table 2. Three current meters, the RCM8, 3D-ACM, and EM
were connected one over the other, separated by 10 m of rope. The RCM11 was connected with a stainlesssteel shackle directly below the EM (Figure 1b). The record length for the comparison was set to a uniform
353 days to match the duration of data collection of the 3D-ACM, which had battery trouble. The data forcomparison (raw data) were obtained every two hours, and that data set was subsampled once a day at 1200–

JST after smoothing twice using a 25-h running mean (filtered data). A recorded value of 1.1 cm s 1 was––treated as 0.0 cm s 1 because the RCM8 cannot measure flow slower than 1.1 cm s 1, recording it as 1.1 cm–

s 1.

Figure 1.

(a) Location of mooring sites. The light (dark) shading indicates regions with a depth between 3000

and 4000 m (between 0 and 3000 m). Isobaths are indicated between 2000 and 4000 m with a 200-m interval
based on ETOPO2 (2-minute Gridded Global Relief Data, NGDC, NOAA, USA). (b) Design of the mooring at
Stn. B for the first set of observations.

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Each mooring in the second and third sets of observations included a 3D-ACM and an RCM8
current meter separated by 10 m at a depth of about 2750 m. The respective sampling intervals for the
3D-ACM and RCM8 meters were 20 minutes and 1 h. The original 3D-ACM data were sampled every
hour at the same time as the RCM8 data point for comparison (raw data). The data were filtered andsubsampled using the same procedure as described for the first set of observations. The duration of datacollection was only 65 days for the RCM8 at Stn. E (Table 1). The duration of the data record used forcomparison at each mooring was set to the shortest period of recorded observations.

Table 1.

Locations of the mooring systems, mooring configurations, and numbers of data points for raw andfiltered data.
Depth

Sampling
interval(a)Sampling

Record length

Record lengthmode(raw data: hours)(Filtered data: days)

First Observation

Stn.B (3-00.82S, 162-12.40E : Water depth 3261 m) 2000/10/19 - 2001/11/7

(b)

RCM8

2490 m2 hourAveraging

4606

381

3D-ACM

2500 m

1 hour

Burst

4261

353

EM

2510 m2 hour

Burst

4606

381

RCM11

2510 m2 hour

Burst

4606

381

Second Observation

Stn.D (4-35.01S, 165-12.00E : Water depth 2730 m) 2003/07/23 - 2004/07/14
3D-ACM

2670 m20 min.

Burst

8564

354

RCM8

2680 m

1 hourAveraging

8564

354

Stn.E (4-14.90S, 165-24.60E : Water depth 3300m)(c)

2003/07/23 - 2004/07/14

3D-ACM

2750 m20 min.

Burst

8563

354

RCM8

2760 m

1 hourAveraging

1600

65

Third Observation

Stn.B (3-00.05S, 162-13.63E : Water depth 3349 m) 2004/02/14 - 2005/02/12
3D-ACM

2750 m20 min.

Burst

8730

361

RCM8

2760m

1 hourAveraging

8730

361

Stn.C’ (2-39.01S, 162-10.28E : Water depth 3718 m)

2004/02/13 - 2005/02/12

3D-ACM

750 m

20 min.

Burst

8757

362

RCM8

2760 m

1 hourAveraging

8757

362

-4－－

Technical Reports of the MRI, No. 55

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The present series of deep-mooring observations are designed to answer a specific question
concerning deep-water circulation in the Pacific Ocean. Historical hydrographic and mooring data indicatesthat Lower Circumpolar Deep Water (LCDW) flows northward, crossing the equator, and enters the North
Pacific (Johnson and Toole., 1993; Roemmich et al., 1996; Kawabe et al., 2003; Siedler et al., 2004). It isthen vertically mixed with upper-layer waters to form North Pacific Deep Water (NPDW) (Mantyla, 1975).
The NPDW, which fills the deep layer (2000 to 3000 m) over the North Pacific, travels south, crossing theequator again back into the South Pacific (Mantyla, 1975; Fiadeiro, 1980). Ishizaki (1994) presented thiscirculation image using a simulation based on a Pacific Ocean model. The results of this model indicatethat NPDW crosses the equator in the Melanesia Basin, northeast of Papua, New Guinea, but this is notevident from field observations. We have had mooring systems deployed near the equator since 1998 toclarify the location where NPDW crosses the equator. The results from these deployments will be presented
in forthcoming papers.

Table 2.

Specifications of the four current meters.

RCM8

3D-ACMEM

RCM11

AANDERAA Instruments

Falmouth Scientific, Inc.

ALEC Electronics

AANDERAA Instruments(NORWAY)(U.S.A)(JAPAN)(NORWAY)

Type

Rotor

Acoustic (Phase shift)2-axis electro-magnetic

Acoustic (Doppler)

Range (cm s-1)

2 to 295(a) Current speed

Accuracy

0 to 300

0 to ±500

0 to 300

1 cm s-1 or ±2%±1 cm s-1 or ±2%±0.15 cm s-1 or ±1%

-

0.01

0.02

0.3

Magnetic compass

3-axis fluxgate

Hall-element compass

0 to 360

0 to 360

0 to 360±2±2±1 cm s-1 or ±2%

Resolution (cm s-1)(b) Direction
Type
Range (degree)
Accuracy (degree)±5 (5 to 100 cm s-1)

±7.5 (2.5 to 5 and 100 to 200 cm s-1)
Resolution (degree)

0.35

Hall-element compass
0 to 360±5 (0 to 15 degree tilt)±7 (15 to 35 degree tilt)

0.01

0.01

-5－－

0.35

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3. Results
Stick diagrams of the filtered data and their time-averaged vectors are shown in Figures 2 and 3,
respectively. The values of the time-averaged vector components from the raw data and the filtered data are
given in Table 3. Direction is clockwise degree from true north (°T). The time-averaged values for the raw
data and those for the filtered data are almost the same; the difference is less than 9% in speed and less than
1° in direction. We hereafter primarily discuss the filtered data. The temporal flow patterns recorded by thefour current meters in the first set of observations show a similar tendency over the entire period, but thecurrent speeds recorded by the RCM8 and RCM11 meters were lower than those of the other two (Figure2a). This same tendency is also reflected in the time-averaged flow vectors (Figure 3a), in which the current
speed and direction from the 3D-ACM and EM appear to be almost the same and the current speeds fromthe RCM8 and RCM11 are lower.
The current speeds recorded by the 3D-ACM were greater than those of RCM8 in all of themoorings except at Stn. B during the third set of observations. It is noteworthy that the time-averaged
current direction of the RCM8 is always rotated clockwise from that of the 3D-ACM (Figure 3). The
directional difference ranged from 10.6° at Stn. B in the first set of observations to 42.2° at Stn. B during
the third set of observation. Following subsections present a more detailed examination of these different
results.

3.1 First set of observations
The filtered data from the first set of observations were used to compare the current speed anddirection recorded by the 4 types of meters by pairs (Figure 4). The current speeds indicated by the RCM8
were lower than those of each of the other three with an almost linear relationship. The RCM8 current
direction was rotated clockwise relative to the others over the entire direction range except in a relatively
narrow range between 330° and 120°, from north-northwest to east-southeast, in which the flow vector of
the RCM8 was rotated slightly counterclockwise from those of the other meters (Figures 4a, b, and c). The
EM current speeds showed a nonlinear relationship with those of the 3D-ACM and RCM11, suggesting a–slower increase in the difference between recorded velocities for currents exceeding 10 cm s 1 (Figures 4d
and f).

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Figure 2.

2008

Stick diagrams of the filtered data for all current meters. (a) The first set of observations (Stn. B),(b) the second set of observations (Stns. D and E), and (c) the third set of observations (Stns B and C’). The
abscissa is the day number, beginning on the first day of the first month in which data were recorded.

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Figure 3. Time-averaged velocity vectors for all current meters. (a) The first set of observations, at Stn. B; (b)second set of observations, at Stns. D (left) and E (right); and (c) third set of observations, at Stns. B (left) andC' (right). Velocities are in cm s-1. R8: RCM8; 3D: 3D-ACM; E: EM; R1: RCM11.

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Table 3. Time-averaged flow statistics from raw and filtered data. The east–west and south–north components
are given by u and v. Direction is clockwise degree from true north (°T).
Raw datauv(cm s-1)(a)Filtered data

Direction

Speed(degree)(cm s-1)uv(cm s-1)

Direction

Speed(degree)(cm s-1)

First observation

Stn.B (2000/10/19 - 2001/11/7)
RCM8

-2.16

0.83

291.0

2.31

-1.99

0.76

291.0

2.13

3D-ACM

-3.55

0.66

280.5

3.61

-3.28

-0.60

280.4

3.33

EM

-3.42

0.39

276.6

3.44

-3.16

0.35

276.5

3.18

RCM11

-2.60

0.16

273.4

2.61

-2.40

0.14

273.3

2.41

(b)

Second observation

Stn.D (2003/07/23 - 2004/07/14)
3D-ACM

-1.36

0.50

290.4

1.45

-1.36

0.51

290.3

1.46

RCM8

-0.69

0.49

305.4

0.85

-0.70

0.49

304.9

0.85

Stn.E (2003/07/23 - 2004/07/14)
3D-ACM

-0.20

-0.89

193.2

0.91

-0.20

-0.88

192.8

0.91

RCM8

-0.44

-0.37

230.8

0.58

-0.44

-0.36

230.8

0.57

(c)

Third observation

Stn.B (2004/02/14 - 2005/02/12)
3D-ACM

0.92

-0.80

131.1

1.22

0.92

-0.81

131.1

1.23

RCM8

0.15

-1.31

173.5

1.32

0.15

-1.32

173.3

1.33

Stn.C’ (2004/02/13 - 2005/02/12)
3D-ACM

-0.14

-1.70

184.8

1.70

-0.11

-1.72

183.8

1.72

RCM8

-0.59

-1.36

203.6

1.48

-0.57

-1.36

202.7

1.47

-9－－

Technical Reports of the MRI, No. 55

Figure 4.

2008

Scatter plots of current speed and direction, using filtered data, for each pair of the four current

meters used in the first set of observations. (a) RCM8 vs. 3D-ACM, (b) RCM8 vs. RCM11, (c) RCM8 vs. EM,(d) EM vs. 3D-ACM, (e) RCM11 vs. 3D-ACM, and (f) EM vs. RCM11. Direction is clockwise degree from true
north (°T).

We also performed a time-series comparison of current speed and directional difference for eachpair of current meters, based on the filtered data (Figure 5). Significant differences in direction, whichappear as spikes, generally corresponded to weak flows. We first compared the RCM8 with the other threecurrent meters (Figures 5a, b, and c). The current speed of the RCM8 was always less than that of each of
the other three, as expected (see Figures 2 and 3). The directional difference between the RCM8 and eachof the other three meters exhibited similar temporal patterns, with the difference being generally positive,
also as expected (see Figure 3). Note that the magnitude of the difference in direction appeared to be
inversely correlated with the current speed, except for the spike-like variations; the higher the current speed,
the smaller the difference in direction. This inverse relationship is evident in the long-term variation overthe first half of the observation period, or about 120 days. This relationship was also evident in the
short-term variations with a period of about 10 days.

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Technical Reports of the MRI, No. 55

2008

Figure 5. Time-series of current speed and the difference in direction for each pair of current meters used in thefirst set of observations. The order of the pairs is the same as in Figure 4. Thick lines in the panels for speed
denote (a) RCM8, (b) RCM11, (c) EM, (d) EM, (e) RCM11, and (f) RCM11. The directional difference is definedas the direction of the first listed current meter minus that of the second in each pair. The abscissa is the day
number, beginning on the first day of the first month in which data were recorded.

In the three remaining comparisons (Figures 5d, e, and f), the temporal patterns in the current
speed of the 3D-ACM and EM were almost the same; the current speed of RCM11 was somewhat lower
than those of both the 3D-ACM and EM (see Figures 2 and 3). The differences in direction were generally
small compared to those relative to the RCM8. However, there is a trend with a descending slope in thepaired comparison between the EM and 3D-ACM and the RCM11 and 3D-ACM (Figures 5d and e). By theend of the observation period, these differences had reached approximately –30° and –15°, respectively. In
addition, the comparison between the EM and RCM11 demonstrated discontinuous changes in the
directional difference around days 100, 225, and 300, at about 10° each (Figure 5f). These changes appear- 11 － 11 －

Technical Reports of the MRI, No. 55

2008

to be related to low current speeds. The difference in direction was stable at other times. These
discontinuous changes can also be seen in the comparison between the EM and 3D-ACM, superposed on
the descending trend (Figure 5d). Thus, we deduce that the temporal trend in the difference in direction inthis comparison came from the 3D-ACM and that the discontinuous changes originated from the EM
current meter.
For each pair of current meter types, we compared the directional difference with the current
speed of one current meter of the pair, using the filtered data (Figure 6). It is noteworthy that incomparisons between the RCM8 and the other three meters, there is an inverse relationship between themagnitude of difference in current direction and the current speed of the RCM8 over the entire current
range (Figures 6a, b, and c). The directional differences were all positive values for higher current speeds,
or at least greater than that at the highest current speeds. The directional difference was zero or evennegative at the highest current speeds; however, the difference in direction of the time-averaged flows was
positive (Figure 3a) because of the inverse correlation between current speed and the directional difference.
In the comparisons between the EM and 3D-ACM and the EM and RCM11, two clusters of–

directional differences, separated by about 10°, can be clearly seen at current speeds greater than 5 cm s 1(Figures 6d and f). These two clusters correspond to the periods before and after the discontinuous change–

in the directional difference around day 100 (Figures 5d and f). The current speed did not exceed 5 cm s 1
for the period after day 300; thus, the corresponding points do not form a clear peak at high current speed
but rather appear as a clump with negative values (Figures 6d and f). The paired comparison between the–

RCM11 and 3D-ACM also displayed increased scatter for current speeds between 2 and 7 cm s 1, and thisseems to come from the temporal trend in the direction record of the 3D-ACM as was deduced before(Figure 5d and e). Unlike the comparisons that included the RCM8, we could not identify any definite
relationship between current speed and the difference in direction in the comparisons that did not include
the RCM8.

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Technical Reports of the MRI, No. 55

Figure 6.

2008

Scatter plots of the difference in direction versus the speed recorded by one current meter of each pair.

The order of the pairs is the same as in Figure 4.

3.2 Second and third sets of observations
The second and third sets of observations involved a comparison only between the RCM8 and3D-ACM. The scatter diagrams for speed in Figure 7 reveals various deviations from the linear relationship.
The only obvious linear relationship was at Stn. E, but the duration of data collection there was very short(65 days). At Stn. D, the speed measured by the 3D-ACM was generally greater than that measured by the- 13 － 13 －Technical Reports of the MRI, No. 55

2008

–

RCM8; at the highest current velocities (>8 cm s 1), there was an almost linear relationship with a slope ofone. This general relationship was reversed at Stn. B, with the speed measured by the 3D-ACM less than–that of the RCM8 for currents weaker than 7 cm s 1. Station B was unique in that the time-averaged flow
speed from the RCM8 was greater than that of the 3D-ACM (see Figure 3c). At station C'1 there were two–different patterns evident at speeds greater than 5 cm s 1 that can be deduced from the time series for
current speed for this station (Figure 8d), in which the speed measured by the 3D-ACM was generally
greater than that of the RCM8 over the entire observation period, except for between days 200 and 260,
when the two curves almost coincided. The scatter in the directional data indicates a linear relationship witha consistent difference over the entire range of observations for all stations except Stn. D, where most of thepoints fall near the line indicating equality between the two meters, with some scattered points (Figure 7a).
Some points just below the central declined line for Stn. C' (Figure 7d) came from the initial 15-day period(Figure 8d), when the sign of the directional difference was reversed.

Figure 7.

Scatter plots of current speed and direction for the filtered data from the second and third sets ofobservations. (a) Stn. D and (b) Stn. E from the second set of observations and (c) Stn. B and (d) Stn. C' from thethird set.

1

We made a mooring observation at station C near station C’ but as different station in the same period as
the first set of observation mentioned in this report. Therefore, we identify the location in the third sets ofobservation C’.
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Technical Reports of the MRI, No. 55

2008

During the second observation period, at Stn. D, the current speed was relatively low and thedifference in current direction between the two meters exhibited many spike-like variations without any
clear, steady positive bias (Figure 8a). In contrast, the other three comparisons showed high, steady positive
values for the directional difference between the two meters, with a short-term shift over the first 50 days at
Stn. C' during the third observational period (Figures 8b, c, and d). There is a clear, inverse relationshipbetween current speed and the difference in direction for all comparisons except at Stn. D, where the points
scatter almost evenly around the current speed peak at about +5° (Figure 9). The difference in direction at–

the highest current speeds, around 10 cm s 1, was a relatively high positive value for the three cases with aclear inverse relationship, that is, about +30°, +25°, and +15° for Stns. E, B, and C', respectively (Figure 9).
The actual directional differences for the time-averaged flows listed in Table 3 for these three stations were+38.0°, +42.2°, and +18.9°, respectively, which are greater than those at the highest current speeds, as was
also noted for the comparisons between the RCM8 and other meters during the first set of observations(Table 3 and Figures 6a, b, and c). In addition, the difference in direction for the time-averaged flow for Stn.
D, +14.6°, was greater than that for the peak current flow, +5°. A comparison of the difference in current
direction and current speed as measured by the 3D-ACM, using raw data, shows that the difference in–direction was stable for speeds greater than 10 cm s 1 (Figure 10).

Figure 8. Time-series of current speed and the difference in direction for each pair of current meters during thesecond and third sets of observations. Thick lines in the panels for speed denote the RCM8, and thin lines, the3D-ACM. The difference in direction is defined as the direction recorded by the RCM8 minus that recorded by
the 3D-ACM. The abscissa is the day number, beginning on the first day of the first month in which data wererecorded.

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Technical Reports of the MRI, No. 55

Figure 9.

2008

The difference in recorded current direction versus current speed recorded by the RCM8, using

filtered data from the second and third sets of observations.

Figure 10.

The difference in recorded current direction versus current speed recorded by the RCM8, using raw datafrom the second and third sets of observations. The abscissa is the current speed recorded by the 3D-ACM.

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Technical Reports of the MRI, No. 55

2008

4. Summary and discussion
We compared current meter data obtained from deep-ocean moorings near the equator. There
were three sets of observations, each with a duration of about one year. Four different models of current
meter, the RCM8, RCM11, EM, and 3D-ACM, were set at approximately 2500 m at Stn. B for the first setof observations (Figure 1). For the second set of observations, moorings at Stns. D and E each had a
3D-ACM and an RCM8 meter at 2750 m. For the third set of observations, moorings at Stns. B and C' each
had a 3D-ACM and an RCM8 meter at 2750 m. There were a total of four paired meter deployments in the
2nd and 3rd sets of observations. The primary results are as follows:(1)

The results from the first set of observations indicate that the temporal flow patterns recorded by thefour current meters exhibited a similar tendency over the whole observation period, but that thecurrent speed indicated by the RCM8 was the lowest and that of the RCM11 was lower than the
3D-ACM and EM (Figure 2a). This tendency is also reflected in the time-averaged flow vectors(Figure 3a), in which the current speed and direction of the 3D-ACM and EM are almost the sameand the current speeds of the RCM8 and RCM11 are lower.

(2)

The speed of the time-averaged flow of the RCM8 was generally lower than that of the 3D-ACM
during the second and third observations, except at Stn. B during the third set of observations (Figures
3b and c).

(3)

The direction of the time-averaged flow of the RCM8 was always rotated substantially clockwisefrom those of the other current meters. The difference in direction from the 3D-ACM ranged from
10.6° at Stn. B during the first set of observations to 42.2° at Stn. B during the third (Figure 3 andTable 3).

(4)

A paired comparison of current speed data from the RCM8 with each of the other three current meters,
using data from the first set of observations, indicates that the speed measured by the RCM8 wasalways lower than that of the other meters with an almost linear relationship (Figures 4a, b, and c;
Figures 5a, b, and c). However, the speed measured by the RCM8 in the second and third sets ofobservations revealed various deviations from the linear relationship compared with the speed
measured by the 3D-ACM (Figure 7a, c, and d). The deviations seem to be dependent upon the- 17 － 17 －Technical Reports of the MRI, No. 55

2008particular conditions at each station.
(5)

The directional difference between the RCM8 and the other meters (the direction indicated by the
RCM8 minus the direction indicated by each of the other meters) in the first set of observations wasinversely correlated with the current speed; the lower the current speed, the greater the difference indirection (Figures 5a, b, and c; Figures 6a, b, and c). This difference in direction was asymmetrically
positive and consistent with the relationship among the time-averaged current vectors (Figure 3a).

(6)

A similar inverse correlation between speed and directional difference can be seen in three of the fourparallel observations by the RCM8 and 3D-ACM meters in the second and third sets of observations(Figures 9 and 10). The difference in direction in those observations for the highest speeds, around 10–

cm s 1, was consistently a high positive value ranging from 15° to 30°, not near zero. The current
direction indicated by each RCM8 clearly had a consistent bias compared to that of the 3D-ACM. The
directional difference between the time-averaged flows was greater than that for the highest current
speeds because of the inverse relationship between the speed and the difference in direction.
(7)

A comparison among the three current meters other than the RCM8 during the first set ofobservations suggests that observational errors occurred, including a temporal trend in current
direction in the 3D-ACM and discontinuous changes in current direction in the EM. The RCM11
appeared to be the most robust against errors in current direction. No definite relationship between
speed and the difference in direction was noted in any paired comparison among these three current
meters, as was observed in pairs that included the RCM8.
There are two factors to consider in the finding that the RCM8 generally had a positive bias incurrent direction relative to the other current meters. The first is the inverse relationship between current
speed and directional difference from the other current meters (Figures 6, 9, and 10). This relationshipclearly resulted from directional measurement errors by the RCM8 alone, since this correlation was notdetected in any other comparison between pairs of the other current meters from the first set of observations.
Although we do not have proof, we think one possible reason for the asymmetric distortion in current
direction may be the existence of the shield for the rotor, which is located on the right side of the
instrument, facing into the current. The inverse relationship was observed for current speeds below 10 cm–

s 1 both in the raw and filtered data; this means that the current speed threshold for correct functioning of- 18 － 18 －

Technical Reports of the MRI, No. 55

2008

the RCM8 meter is around this value.
The second factor in the apparent directional bias of the RCM8 is the steady positive bias understrong currents in three of the comparisons in the second and third sets of observations (Figures 9 and 10).
Only the RCM8 and 3D-ACM were compared in these observations, and thus we cannot directly determine
from which current meter the errors originated solely from our observations. Following our field studies,
we performed a laboratory calibration of the direction sensors of all RCM8 and 3D-ACM instruments used
for the comparisons in the second and the third sets of observation and found errors on the order of ±2°
against magnetic north in every instrument, but not errors as large as 15°–30° as were observed in the deep
ocean. Both Gilboy et al. (2000) and Hogg and Frye (2007) reported similar phenomena about the steadydirectional bias of the 3D-ACM. Gilboy et al. (2000), while attempting to detect the current velocity at 72
m over a 110-day period, indicated that the direction measured by a 3D-ACM set at a depth of 72 m was up
to 20°–30° offset from those of a VMCA at 73 m and an ADCP set at 209 m. Hogg and Frye (2007) founda mean difference in direction of 15°–20° over 54 days at 4000 m between their referenced VMCA/RCM11
and 3D-ACM against the reference direction. These values fall within the range of directional differencesthat we observed. Furthermore, the direction of offset is the same, that is, the current direction recorded by
the 3D-ACM is rotated anticlockwise from those measured by the other instruments, as it was in ourcomparisons. Therefore, we deduce that the steady positive bias in direction for strong currents seen inthree of the four comparisons in the second and third sets of observations (Figures 9 and 10) may comefrom the 3D-ACM. We believe that some of the laboratory calibration values installed into the instrumentby the manufacturer (zero adjustment) may not have been correct for real ocean conditions of high pressure
and low temperature.
Tow-tank tests indicate that the average direction errors not only for the RCM8 but also for the
EM and 3D-ACM may be more than 10°, and often more than 40°, below current speeds of about 3 cm s–1(Tengberg et al., unpublished data). However, the systematically asymmetric difference in direction of theRCM8 (Figures 6, 9, and 10) cannot be seen in the tow-tank tests. The duration of each tow-tank test was
short, that is, several hours; thus, the average response of each current meter may differ from that duringlong-term moorings. These comparisons between meters may be complementary.
The RCM11 works by measuring the Doppler shift of back-scattered super-sonic sound signals
first released in four directions; its measurement window is between 0.4 and 2.2 m from the sensor. This

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Technical Reports of the MRI, No. 55

2008

differs from the EM and 3D-ACM, which measure the current near the sensor. The reduced current speed
measured by the RCM11 may be a result of this spatial averaging. Hogg and Frye (2007) also stressed that
the RCM11 speed values are generally less than those indicated by their referenced VACM/VMCM
instruments, although its direction records are of high quality, observations consistent with our results.
We do not know the causes for observational errors such as the temporal trends and discontinuouschanges in current direction that occurred in the 3D-ACM and EM. At Stn. C', where two distinct
relationships between current meter speeds are evident (Figure 7d), the flow was predominantly southward
during the period in which the speeds of the two current meters coincided. A certain range of current
directions may generate errors in current speed measurements for either of the two current meters, but again
we do not know the cause.
New current meter designs (acoustic or electromagnetic) provide superior performance and areeasy to handle and care for, with increased battery capacity, substantial data-storage memory, shorter
recording intervals if required, and simplified data processing. These new current meters are becoming
more widely used. However, they also have specific characteristics and inherent errors that counteract theirnominal accuracy, as reported in this report. Therefore, interaction and information exchange between
manufacturers and field observers are important for improving instruments to obtain high accuracy data.

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Technical Reports of the MRI, No. 55

2008

Acknowledgements
The Compact-EM, manufactured by Alec Electronics, and the RCM-11, manufactured byAanderaa Instruments, were provided by Mr. S. Konashi of Alec Electronics. Technical support was given
by Mr. M. Kodama of Alec Electronics. The authors thank them both. The authors are grateful to Captain N.
Kosuge, formerly of R/V Ryofu Maru, Captain K. Mizumoto of R/V Keifu Maru, S. Yasutomi of R/V
Ryofu Maru, and the officers and crew of R/V Ryofu Maru and R/V Keifu Maru. The authors also thank thetechnical officials of the Japan Meteorological Agency and Kobe Marine Observatory for their on-board
work on the mooring systems. We also thank Mr. T. Uchiyama and Ms. A. Yamada for their data processingwork.

- 21 － 21 －

References
Aanderaa Instruments, 1987: RCM 7 & 8. Technical Description 159.
Falmouth Scientific, Inc., 1999: 3DACM configuration, acquisition software and operating manual for the
2D-ACM, 3D-ACM and 3D-ACM Wave.
Fiadeiro, M. H., 1980: The alkalinity of the deep Pacific. Earth Planet. Sci. Lett., 49, 499-505.
Frye, D., 2002: New-generation mooring system allows longer deployment. EOS, 83, 34365-34380.
Frye, D., N. Hogg, and C. Wunsch, 2004: A long duration mooring for ocean observation. Sea Technology,
45, 6, 29-39.
Gilboy, T. P., T. D. Dickey, D. E. Sigurdson, X. Yu, and D. Manov, 2000: An intercomparison of current
measurements using a vector measuring current meter, an acoustic Doppler current profiler, and a
recently developed acoustic current meter. J. Atmos. Oceanic Technol., 17, 561-574.
Hogg, N. G. and D. E. Frye, 2007: Performance of a new generation of acoustic current meters. J. Phys.
Oceanogr., 37, 148-161.
Ishizaki, H., 1994: A simulation of the abyssal circulation in the North Pacific Ocean (Part I: Flow field andcomparison with observations). J. Phys. Oceanogr., 24, 9, 1921-1939.
Johnson, G. C. and J. M. Toole, 1993: Flow of deep and bottom waters in the Pacific at 10N. Deep-Sea Res.,38, 637-652.
Kawabe, M., S. Fujio, and D. Yanagimoto, 2003: Deep-water circulation at low latitude in the western
North Pacific. Deep-Sea Res. I., 50, 631-656.
Mantyla, A. W., 1975: On the potential temperature in the abyssal Pacific Ocean. J. Mar. Res., 81,1163-1176.
Minken, H., 2000: The design of the new RCM-9 Mk II and RCM-11 Doppler current sensor. Technical
Description 212.
Roemmich, D., S. Hautala, and D. Rudnick, 1996: Northward abyssal transport through the Samoan
Passage and adjacent regions. J. Geophys. Res., 101, 14039-14055.
Siedler, G., J. Holfort, W. Zenk, T. J. Muller, and T. Csernok, 2004: Deep-water flow in the Mariana andCaroline Basins. J. Phys. Oceanogr., 34, 3, 566-58.

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気象研究所技術報告一覧表
第１号

バックグラウンド大気汚染の測定法の開発（地球規模大気汚染特別研究班，1978）
Development of Monitoring Techniques for Global Background Air Pollution. (MRI Special Research Group on Global
Atmospheric Pollution, 1978)
第２号 主要活火山の地殻変動並びに地熱状態の調査研究（地震火山研究部，1979）
Investigation of Ground Movement and Geothermal State of Main Active Volcanoes in Japan. (Seismology andVolcanology Research Division, 1979)
第３号 筑波研究学園都市に新設された気象観測用鉄塔施設（花房龍男・藤谷徳之助・伴野 登・魚津 博，1979）
On the Meteorological Tower and Its Observational System at Tsukuba Science City. (T. Hanafusa, T. Fujitani, N. Banno,and H. Uozu, 1979)
第４号 海底地震常時観測システムの開発（地震火山研究部，1980）
Permanent Ocean−Bottom Seismograph Observation System. (Seismology and Volcanology Research Division, 1980)
第５号 本州南方海域水温図−400m（又は 500m）深と 1,000m 深−（1934−1943 年及び 1954−1980 年）（海洋研究部，
1981）
Horizontal Distribution of Temperature in 400m (or 500m) and 1,000m Depth in Sea South of Honshu, Japan and Western−North Pacific Ocean from 1934 to 1943 and from 1954 to 1980. (Oceanographical Research Division, 1981)
第６号 成層圏オゾンの破壊につながる大気成分及び紫外日射の観測（高層物理研究部，1982）
Observations of the Atmospheric Constituents Related to the Stratospheric ozon Depletion and the Ultraviolet Radiation.
(Upper Atmosphere Physics Research Division, 1982)
第７号 83 型強震計の開発（地震火山研究部，1983）
Strong−Motion Seismograph Model 83 for the Japan Meteorological Agency Network. (Seismology and Volcanology
Research Division, 1983)
第８号 大気中における雪片の融解現象に関する研究（物理気象研究部，1984）
The Study of Melting of Snowflakes in the Atmosphere. (Physical Meteorology Research Division, 1984)
第９号 御前崎南方沖における海底水圧観測（地震火山研究部・海洋研究部，1984）
Bottom Pressure Observation South off Omaezaki, Central Honsyu. (Seismology and Volcanology Research Division andOceanographical Research Division, 1984)
第 10 号 日本付近の低気圧の統計（予報研究部，1984）
Statistics on Cyclones around Japan. (Forecast Research Division, 1984)
第 11 号 局地風と大気汚染質の輸送に関する研究（応用気象研究部，1984）
Observations and Numerical Experiments on Local Circulation and Medium−Range Transport of Air Pollutions.
(Applied Meteorology Research Division, 1984)
第 12 号 火山活動監視手法に関する研究（地震火山研究部，1984）
Investigation on the Techniques for Volcanic Activity Surveillance. (Seismology and Volcanology Research Division,
1984)
第 13 号 気象研究所大気大循環モデル−Σ（MRI・GCM−㸇）（予報研究部，1984）
A Description of the MRI Atmospheric General Circulation Model (The MRI・GCM−Σ). (Forecast Research Division,
1984)
第 14 号 台風の構造の変化と移動に関する研究−台風 7916 の一生−（台風研究部，1985）
A Study on the Changes of the Three - Dimensional Structure and the Movement Speed of the Typhoon through its Life
Time. (Typhoon Research Division, 1985)
第 15 号 波浪推算モデル MRI と MRI−Τの相互比較研究−計算結果図集−（海洋気象研究部，1985）
An Intercomparison Study between the Wave Models MRI and MRI − Τ − A Compilation of Results −(Oceanographical Research Division, 1985)
第 16 号 地震予知に関する実験的及び理論的研究（地震火山研究部，1985）
Study on Earthquake Prediction by Geophysical Method. (Seismology and Volcanology Research Division, 1985)
第 17 号 北半球地上月平均気温偏差図（予報研究部，1986）
Maps of Monthly Mean Surface Temperature Anomalies over the Northern Hemisphere for 1891−1981. (Forecast
Research Division, 1986)
第 18 号 中層大気の研究（高層物理研究部・気象衛星研究部・予報研究部・地磁気観測所，1986）
Studies of the Middle Atmosphere. (Upper Atmosphere Physics Research Division, Meteorological Satellite Research
Division, Forecast Research Division, MRI and the Magnetic Observatory, 1986)
第 19 号 ドップラーレーダによる気象・海象の研究（気象衛星研究部・台風研究部・予報研究部・応用気象研究部・海洋研究部，1986）
Studies on Meteorological and Sea Surface Phenomena by Doppler Radar. (Meteorological Satellite Research Division,
Typhoon Research Division, Forecast Research Division, Applied Meteorology Research Division, and OceanographicalResearch Division, 1986)
第 20 号 気象研究所対流圏大気大循環モデル（MRI・GCM−Σ）による 12 年間分の積分（予報研究部，1986）
Mean Statistics of the Tropospheric MRI・GCM−Σbased on 12−year Integration. (Forecast Research Division, 1986)

第 21 号
第 22 号
第 23 号
第 24 号
第 25 号
第 26 号
第 27 号
第 28 号
第 29 号

第 30 号
第 31 号

第 32 号
第 33 号
第 34 号
第 35 号
第 36 号
第 37 号
第 38 号
第 39 号
第 40 号

第 41 号

第 42 号

宇宙線中間子強度 1983−1986（高層物理研究部，1987）
Multi−Directional Cosmic Ray Meson Intensity 1983−1986. (Upper Atmosphere Physics Research Division, 1987)
静止気象衛星「ひまわり」画像の噴火噴煙データに基づく噴火活動の解析に関する研究（地震火山研究部， 1987）
Study on Analysis of Volcanic Eruptions based on Eruption Cloud Image Data obtained by the Geostationary
Meteorological satellite (GMS). (Seismology and Volcanology Research Division, 1987)
オホーツク海海洋気候図（篠原吉雄・四竃信行，1988）
Marine Climatological Atlas of the sea of Okhotsk. (Y. Shinohara and N. Shikama, 1988)
海洋大循環モデルを用いた風の応力異常に対する太平洋の応答実験（海洋研究部，1989）
Response Experiment of Pacific Ocean to Anomalous Wind Stress with Ocean General Circulation Model.
(Oceanographical Research Division, 1989)
太平洋における海洋諸要素の季節平均分布（海洋研究部，1989）
Seasonal Mean Distribution of Sea Properties in the Pacific. (Oceanographical Research Division, 1989)
地震前兆現象のデータベース（地震火山研究部，1990）
Database of Earthquake Precursors. (Seismology and Volcanology Research Division, 1990)
沖縄地方における梅雨期の降水システムの特性（台風研究部，1991）
Characteristics of Precipitation Systems During the Baiu Season in the Okinawa Area. (Typhoon Research Division, 1991)
気象研究所・予報研究部で開発された非静水圧モデル（猪川元興・斉藤和雄，1991）
Description of a Nonhydrostatic Model Developed at the Forecast Research Department of the MRI. (M. Ikawa and K.
Saito, 1991)
雲の放射過程に関する総合的研究（気候研究部・物理気象研究部・応用気象研究部・気象衛星・観測システム研究部・台風研究部，1992）
A Synthetic Study on Cloud−Radiation Processes. (Climate Research Department, Physical Meteorology Research
Department, Applied Meteorology Research Department, Meteorological Satellite and Observation System Research
Department, and Typhoon Research Department, 1992)
大気と海洋・地表とのエネルギー交換過程に関する研究（三上正男・遠藤昌宏・新野 宏・山崎孝治，1992）
Studies of Energy Exchange Processes between the Ocean−Ground Surface and Atmosphere. (M. Mikami, M. Endoh, H.
Niino, and K. Yamazaki, 1992)
降水日の出現頻度からみた日本の季節推移−30 年間の日降水量資料に基づく統計−（秋山孝子，1993）
Seasonal Transition in Japan, as Revealed by Appearance Frequency of Precipitating-Days. −Statistics of Daily
Precipitation Data During 30 Years−(T. Akiyama, 1993)
直下型地震予知に関する観測的研究（地震火山研究部，1994）
Observational Study on the Prediction of Disastrous Intraplate Earthquakes. (Seismology and Volcanology Research
Department, 1994)
各種気象観測機器による比較観測（気象衛星・観測システム研究部，1994）
Intercomparisons of Meteorological Observation Instruments. (Meteorological Satellite and Observation System Research
Department, 1994)
硫黄酸化物の長距離輸送モデルと東アジア地域への適用（応用気象研究部，1995）
The Long−Range Transport Model of Sulfur Oxides and Its Application to the East Asian Region. (Applied Meteorology
Research Department, 1995)
ウインドプロファイラーによる気象の観測法の研究（気象衛星・観測システム研究部，1995）
Studies on Wind Profiler Techniques for the Measurements of Winds. (Meteorological Satellite and Observation System
Research Department, 1995)
降水・落下塵中の人工放射性核種の分析法及びその地球化学的研究（地球化学研究部，1996）
Geochemical Studies and Analytical Methods of Anthropogenic Radionuclides in Fallout Samples. (Geochemical
Research Department, 1996)
大気と海洋の地球化学的研究（1995 年及び 1996 年）（地球化学研究部，1998）
Geochemical Study of the Atmosphere and Ocean in 1995 and 1996. (Geochemical Research Department, 1998)
鉛直２次元非線形問題（金久博忠，1999）
Vertically 2-dmensional Nonlinear Problem (H. Kanehisa, 1999)
客観的予報技術の研究（予報研究部，2000）
Study on the Objective Forecasting Techniques（Forecast Research Department, 2000）
南関東地域における応力場と地震活動予測に関する研究（地震火山研究部，2000）
Study on Stress Field and Forecast of Seismic Activity in the Kanto Region（Seismology and Volcanology Research
Department, 2000）
電量滴定法による海水中の全炭酸濃度の高精度分析および大気中の二酸化炭素と海水中の全炭酸の放射性炭素
同位体比の測定（石井雅男・吉川久幸・松枝秀和，2000）
Coulometric Precise Analysis of Total Inorganic Carbon in Seawater and Measurements of Radiocarbon for the Carbon
Dioxide in the Atmosphere and for the Total Inorganic Carbon in Seawater（I.Masao, H.Y.Inoue and H.Matsueda, 2000）
気象研究所／数値予報課統一非静力学モデル（斉藤和雄・加藤輝之・永戸久喜・室井ちあし，2001）
Documentation of the Meteorological Research Institute / Numerical Prediction Division Unified Nonhydrostatic Model(Kazuo Saito, Teruyuki Kato, Hisaki Eito and Chiashi Muroi，2001)

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大気および海水中のクロロフルオロカーボン類の精密測定と気象研究所クロロフルオロカーボン類標準ガスの確立（時枝隆之・井上(吉川)久幸，2004）
Precise measurements of atmospheric and oceanic chlorofluorocarbons and MRI chlorofluorocarbons calibration scale(Takayuki Tokieda and Hisayuki Y. Inoue，2004)
PostScript コードを生成する描画ツール"PLOTPS"マニュアル（加藤輝之，2004）
Documentation of "PLOTPS": Outputting Tools for PostScript Code (Teruyuki Kato，2004)
気象庁及び気象研究所における二酸化炭素の長期観測に使用された標準ガスのスケールとその安定性の再評価に関する調査・研究（松枝秀和・須田一人・西岡佐喜子・平野礼朗・澤 庸介・坪井一寛・堤 之智・神谷ひとみ・根本和宏・長井秀樹・吉田雅司・岩野園城・山本 治・森下秀昭・鎌田匡俊・和田 晃，2004）
Re-evaluation for scale and stability of CO2 standard gases used as long-term observations at the Japan Meteorological
Agency and the Meteorological Research Institute (Hidekazu Matsueda, Kazuto Suda, Sakiko Nishioka, Toshirou Hirano,
Yousuke, Sawa, Kazuhiro Tuboi, Tsutumi, Hitomi Kamiya, Kazuhiro Nemoto, Hideki Nagai, Masashi Yoshida, Sonoki
Iwano, Osamu Yamamoto, Hideaki Morishita, Kamata, Akira Wada，2004)
地震発生過程の詳細なモデリングによる東海地震発生の推定精度向上に関する研究（地震火山研究部, 2005）
A Study to Improve Accuracy of Forecasting the Tokai Earthquake by Modeling the Generation Processes (Seismology
and Volcanology Research Department, 2005)
気象研究所共用海洋モデル（MRI.COM）解説（海洋研究部, 2005）
Meteorological Research Institute Community Ocean Model (MRI.COM) Manual (Oceanographical Research Department,
2005)
日本海降雪雲の降水機構と人工調節の可能性に関する研究（物理気象研究部・予報研究部, 2005）
Study of Precipitation Mechanisms in Snow Clouds over the Sea of Japan and Feasibility of Their Modification by
Seeding (Physical Meteorology Research Department, Forecast Research Department, 2005)
2004 年日本上陸台風の概要と環境場（台風研究部, 2006）
Summary of Landfalling Typhoons in Japan, 2004 (Typhoon Research Department, 2006)
栄養塩測定用海水組成標準の 2003 年国際共同実験報告（青山道夫, 2006）
2003 Intercomparison Exercise for Reference Material for Nutrients in Seawater in a Seawater Matrix (Michio Aoyama,2006)
大気および海水中の超微量六フッ化硫黄(SF6)の測定手法の高度化と SF6 標準ガスの長期安定性の評価（時枝隆之、石井雅男、斉藤 秀、緑川 貴, 2007）
Highly developed precise analysis of atmospheric and oceanic sulfur hexafluoride (SF6) and evaluation of SF6 standard
gas stability (Takayuki Tokieda, Masao Ishii, Shu Saito and Takashi Midorikawa, 2007)
地球温暖化による東北地方の気候変化に関する研究（仙台管区気象台, 環境・応用気象研究部, 2008）
Study of Climate Change over Tohoku District due to Global Warming (Sendai District Meteorological Observatory,
Atmospheric Environment and Applied Meteorology Research Department, 2008)
火山活動評価手法の開発研究（地震火山研究部, 2008）
Studies on Evaluation Method of Volcanic Activity (Seismology and Volcanology Research Department, 2008)
日本における活性炭冷却捕集およびガスクロ分離による気体計数システムによる 85Kr の測定システムの構築および 1995 年から 2006 年の測定結果（青山道夫, 藤井憲治, 廣瀬勝己, 五十嵐康人, 磯貝啓介, 新田済, Hartmut
Sartorius, Clemens Schlosser, Wolfgang Weiss, 2008）
Establishment of a cold charcoal trap-gas chromatography-gas counting system for 85Kr measurements in Japan and resultsfrom 1995 to 2006 (Michio Aoyama, Kenji Fujii, Katsumi Hirose, Yasuhito Igarashi, Keisuke Isogai, Wataru Nitta,
Hartmut Sartorius, Clemens Schlosser, Wolfgang Weiss, 2008)