Journal of the Meteorological Society of Japan. Ser. II
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Volume 73 , Issue 2B
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  • Atusi Numaguti, Riko Oki, Kozo Nakamura, Kazuhisa Tsuboki, Nobuhiko Mi ...
    Volume 73 (1995) Issue 2B Pages 267-290
    Released: September 15, 2009
    JOURNALS FREE ACCESS
    A significant 4-5-day-period variation was observed in surface and aerological data obtained at the equator, 156E during November 1992. The time-height structure of the variation is determined by use of spectral and composite analysis. The 4-5-day period variation can be basically explained by westward-propagating mixed Rossby-gravity wave disturbances. However, the structure of the circulation was significantly distorted by the presence of a tropical depression. Further, two distinctive events of extremely dry air in the lower troposphere were observed. The vertical profiles of specific humidity as well as the equivalent potential temperature had distinct minima at about the 3km level. The trajectory analysis revealed that the dry-air parcels were brought from a subtropical area by tropical disturbances, especially by the intense meridional flow associated with 4-5-day period disturbances. These events of dry-air intrusion are detected in the precipitable water data derived from SSM/I satellite imageries and the zonal scale of the intrusion is estimated to be about 1000km. Convection was strongly suppressed over the dry air, and the latter was maintained to about 4 days due to very weak vertical mixing.
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  • Kunio Yoneyama, Tokunosuke Fujitani
    Volume 73 (1995) Issue 2B Pages 291-304
    Released: September 15, 2009
    JOURNALS FREE ACCESS
    Based on the R/V Natsushima stationary observations at (0°, 156°E) during the TOGA-COARE Intensive Observing Period, the atmospheric features for the period from February 5th to 14th were examined.
    The radiosonde sounding results show the existence of dry westerly air at an altitude of 2-4km from February 6th to 9th. In particular, this dry air region subsided during this period and then became not well defined on February 10th. The convection was inactive from February 6th to 9th, while a deep convection developed on the 10th.
    It is found that the inversion layer existed at 800hPa and the dry low potential temperature layer above the inversion suppressed the convective activity for the former period. This dry low potential temperature air mass was traced back to the northeast trade wind region. The subsidence of this air mass was associated with the existence of an inversion layer above and the compensating subsidence among the cloud clusters that existed to the north and/or to the south of this observational site where the inversion layer was formed.
    The change of the wind direction at the lower level from northwesterly to westerly before and after February 10th may have accompanied the suppression and the development of the convective activity. It is suggested that the dry westerly air intrusion and the associated variation of the convective activity may be a part of the several-days scale atmospheric disturbances over the equatorial Pacific Ocean.
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  • Tetsuo Nakazawa
    Volume 73 (1995) Issue 2B Pages 305-319
    Released: September 15, 2009
    JOURNALS FREE ACCESS
    We examined the behavior of the convective activity and other meteorological variables such as divergence, velocity potential and total precipitable water, associated with the intraseasonal oscillation (ISO) during the TOGA-COARE IOP from November 1992 to February 1993.
    During the IOP, there are two major ISOs, one in December and another in January. We confirmed that there is a hierarchic structure of the tropical convection: planetary-scale ISO, eastward-moving synoptic-scale super cluster, and westward-moving meso-scale cloud cluster. Each ISO has two super clusters. The maximum of the total precipitable water (tpw) delineated from the SSM/I data is leading the convective activity from the GMS IR TBB data by about 5-10 days. The SST is also leading the convection about by 12-13 days, which is the same as for previous results.
    We also checked the surface radiation budget. The SST change is closely related with the ISO passage. The clear sky and the calm wind condition leads to the warming up of the SST east of the active convection associated with the ISO (that is, before the passage of the active convection of the ISO). During the passage of the active convection associated with the ISO, the SST decreases due to less insolation and enhanced latent heat flux from the sea surface under the disturbed wind condition.
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  • Noriyuki Nishi, Akimasa Sumi
    Volume 73 (1995) Issue 2B Pages 321-337
    Released: September 15, 2009
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    The three eastward-moving disturbances localized near the tropopause during January and February 1993 were investigated using JMA (Japan Meteorological Agency) global analysis data and the rawinsonde data at some stations during the TOGA COARE IOP (November 1992-February 1993). These events are considered to be part of the equatorial trapped internal Kelvin waves with upward energy propagation. These waves have large amplitude only in the several ten degree longitudes around the western Pacific. In January, the wave form is far from a sinusoidal one when the amplitude becomes very large. Change from the easterly to the westerly is much more rapid than change from the westerly to the easterly.
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  • Y. H. Ding, Akimasa Sumi
    Volume 73 (1995) Issue 2B Pages 339-351
    Released: September 15, 2009
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    The present paper analyzed the large-scale aspects of the atmospheric circulation features during the TOGA-COARE IOP period (November 1, 1992-February 28, 1993). Atmospheric conditions were in many ways similar to those typical of a developing warm episode over the equatorial eastern Pacific, including the frequent occurrence of the low-level westerly wind or westerly wind bursts and the upper-level easterly wind in the western and central Pacific, a moderate eastward shift of the major atmospheric heat source in winter and the Walker circulation, and continuous eastward propagation of 30-60 day low-frequency oscillation into the central and eastern Pacific.
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  • Atusi Numaguti
    Volume 73 (1995) Issue 2B Pages 353-377
    Released: September 15, 2009
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    Several types of westward-propagating equatorial disturbances within a 4-to-20-day-period range in the equatorial Pacific are detected from an objective analysis data during November and December 1992. Their horizontal structures are determined by composite analysis. A signal of 4-to-5-day period is detected in the 850hPa meridional wind field and a signal of a 7-day period is detected in the 200hPa meridional wind field. The associated structure of both signals has a characteristic of the mixed Rossby-gravity wave. Further, a 15-to-20-day signal is detected in equatorial zonal wind variation, both at 200hPa and 850hPa. The structure and westward phase speed can be interpreted as the equatorial Rossby wave of n=1. The signals at the 200hPa and 850hPa levels are coherent and baroclinic near the equator but nearly barotropic in the subtropics. These disturbances have a relation to the cloud activity and have a equivalent depth of the order of 10m. However, the equivalent depth of the 15-day signal in the 200hPa level is estimated to be an order of magnitude larger.
    It is suggested that the development of tropical cyclones in the tropical western Pacific is affected by both the 4-5-day mixed Rossby-gravity type waves and 15-day Rossby type waves. A possible excitation mechanism of the 15-day Rossby type waves through an intensification of 200hPa trough by midlatitude forcing is also suggested.
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  • Tomoki Ushiyama, Shinsuke Satoh, Kensuke Takeuchi
    Volume 73 (1995) Issue 2B Pages 379-392
    Released: September 15, 2009
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    We examine the relationship between mesoscale rainfalls and large-scale atmospheric fields in the western Pacific using data obtained in the TOGA-COARE IOP (Tropical Ocean and Global Atmosphere-Coupled Ocean Atmosphere Research Experiment, Intensive Observation Phase). The data used for our analysis were a two-months period of successive x-band radar data taken at Manus island P. N. G. (2S, 147E), sounding data and GANAL (Global Analysis by Japan Meteorological Agency) data. Radar observation data were converted into rainfall rates as an index of local connective activity, and averaged into two horizontal areas: land area and sea area, and into three vertical layers to evaluate the island effect and the vertical distribution.
    The rainfall rates of the land area were dominated by a strong diurnal variation. On the other hand, diurnal variation in the sea area was much weaker than the land area. In the spectrum of rainfall rates in the sea area, 1.5 to 2-days and 3 to 5-days-period peaks were more significant than those of the land area.
    Lagged correlation analysis and cross spectral analysis was done to examine the relationship between the local rainfalls and large-scale atmospheric fields. The correlation between the rainfall rates and the CAPE showed that before a rainfall event the CAPE increased for two days, and then decreased after it. The correlation between the rainfall rates and the zonal wind or mixing ratio showed an eastward propagation of the correlation that may correspond to a Madden-Julian oscillation. The phase relation of this correlation was such that, when the lower tropospheric wind changed its direction from easterly to westerly, a rainfall event started. After a rainfall event, the mixing ratio at 500hPa increased. This relationship between the mixing ratio and the rainfall rates was also found in the sounding data.
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  • Toshitaka Tsuda, Shoichiro Fukao, Mamoru Yamamoto, Takuji Nakamura, Ma ...
    Volume 73 (1995) Issue 2B Pages 393-406
    Released: September 15, 2009
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    Through collaboration between Japan and Indonesia, a radar observatory was established near Jakarta, Indonesia in November 1992, where we installed a meteor wind radar (MWR) and a boundary layer radar (BLR). Horizontal wind velocity and temperature fluctuations at 75-100km were determined with the MWR with time and height resolution of 1 hour and 4km, respectively. The BLR provided three components of wind velocity every minute in the planetary boundary layer (0.3-5km) with a height resolution of 100m. In addition, by combining an acoustic transmitter, temperature profiles were also obtained with the BLR by means of the RASS (radio acoustic sounding system) technique. Observations with the radars have been continued over 2 years since November 1992.
    Profiles of horizontal wind velocity, temperature and humidity were measured with radiosondes up to 35km, with a height resolution of 150m, four times a day during November 1992-April 1993 at LAPAN in Bandung. Further, radiosonde sounding has been routinely continued once a day after October 1993.
    Preliminary data analysis showed some new aspects of the equatorial atmosphere dynamics over Indonesia, such as the structure of the tropical planetary boundary layer and the behavior of atmospheric waves in the middle atmosphere. We report in this paper a description of the radar equipment, the current status of observations and the fundamental characteristics of equatorial atmosphere dynamics during the TOGA/COARE campaign.
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  • S. Ogino, M. D. Yamanaka, S. Fukao
    Volume 73 (1995) Issue 2B Pages 407-413
    Released: September 15, 2009
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    Meridional variation of the lower stratospheric gravity wave activity in the western Pacific region (14°S-25°N)is investigated on the basis of vertical wavenumber spectra analyzed from temperature and wind data observed by rawinsondes of the Hakuho-maru J-COARE cruise during November 1 and December 4, 1992. The dominant vertical wavelength of gravity waves is ∼2.7km, which is distinguished from that of Kelvin waves (∼4km). The power spectral densities of the 4.0km, 2.7km and 2.0km wavelength components for temperature, zonal wind and meridional wind in an altitude range of 14-22km are plotted as functions of latitude. In general, they are obviously larger than those obtained in the mid-latitude regions and seem to have maxima near the equator.
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  • Hiroshi Uyeda, Yoshio Asuma, Nobuhiro Takahashi, Shuji Shimizu, Osamu ...
    Volume 73 (1995) Issue 2B Pages 415-426
    Released: September 15, 2009
    JOURNALS FREE ACCESS
    Observations of tropical convection and cloud clusters with two X-band Doppler radars were carried out on Manus Island, Papua New Guinea for two and a half months from 12 November 1992 during the Intensive Observation Period (IOP) of the TOGA-COARE. Several different types of clouds were observed by Doppler radars during the period, such as squall lines, convective clouds and stratiform clouds associated with cloud clusters, isolated convective clouds over the island in the day time, etc. Outlines of the observations on Manus Island and brief reviews of the results of these observations are described. Preliminary summaries of the analyses on the observations are: 1) A warm rain process dominates at the beginning stage of radar echo development and the maximum radar reflectivity is recognized at this stage, 2) The maximum echo top height is observed within 3 hours from the first echo, 3) The maximum echo area within the radar range was analyzed a few to several hours later than the time of maximum echo top height corresponding to the size of cloud cluster, 4) In the long-lasting stratiform echo, updrafts independent from those below the melting layer were identified above the melting layer. It is concluded that further studies utilizing these observational data may reveal the structure and the evolution mechanism of tropical cloud clusters.
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  • Nobuhiro Takahashi, Hiroshi Uyeda
    Volume 73 (1995) Issue 2B Pages 427-442
    Released: September 15, 2009
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    During the TOGA-COARE intensive observation period (IOP), many types of clouds were observed around Manus Island, Papua New Guinea, by X-band Doppler radars. This paper analyzes several characteristics of three types of tropical convective clouds, an isolated echo cell and two types of rainbands. The common characteristics, from the viewpoint of echo area, echo-top height and maximum reflectivity, in association with the development process are that 1) the peak of maximum reflectivity appeared in the early stage in the lower-level circulation, 2) the peak of the maximum echo top height appeared shortly after the maximum reflectivity caused by a development of upper-level circulation, and 3) the maximum echo area appeared at a later stage because of the appearance of anvil clouds.
    In the case of the isolated echo, the above-mentioned characteristics were examined with kinematics in detail. The development of low-level circulation into upper-level circulation appeared successively and coexisted in the case of an isolated echo. In all cases, a strong reflectivity core appeared at the lower altitude, indicating the effectiveness of the warm-rain process. The echo-top height did not increase continuously to the maximum height; stable echo-top heights appeared during the echo development. This tendency was common to all cases of rainband. Anvil clouds contributed to the extension of the upper tropospheric cloud area in the later stage of its life cycle and formed a stratiform echo.
    Rainbands are categorized as non-squall type from the GATE criteria (Barnes and Sieckman, 1984; Houze, 1977). Both rainbands developed parallel to the low-level shear vector. The first case was slow-moving: the rainband had a clear leading edge and continuous rear-to-front flow to maintain the circulation during the mature stage. The second case was relatively fast-moving: it had intermittent rear-to-front flow. These are somewhat different characteristics from rainbands during GATE. Convective outflows were also observed in all cases. In particular, gust fronts were observed in the rainband cases. The gust front in the second rainband had a thickness of 0.5 to 1.0km, and a propagation speed of 8 to 10m/s, which was slightly faster than the rainband's propagation speed.
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  • Shinsuke Satoh, Atsushi Kinoshita, Hiroshi Uyeda
    Volume 73 (1995) Issue 2B Pages 443-459
    Released: September 15, 2009
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    Three distinct mesoscale convective systems (MCSs), composing a tropical cloud cluster, observed on January 18-19, 1993 were investigated. This event was observed by two Doppler radars on Manus Island (2°S, 147°E), Papua New Guinea, during the TOGA-COARE TOP. The cloud cluster was formed within the radar range, and extended to a diameter of about 200km. The environmental wind was weak, but a strong vertical shear existed at the middle level (3-8km).
    The first characteristic MCS moved faster than the environmental wind, and thus is referred to as a fast-moving convective system (FMCS). The orientation of this FMCS was nearly perpendicular to the direction of the dominant vertical shear. Behind the convective cell of the FMCS, an anvil echo extended to upper levels. The front inflow had two branching sub-flows in front of the convective cell with a strong downdraft. The lower level outflow from the downdraft also branched out to southward and northward flows. The branching inflow and outflow were associated with symmetrically-arranged strong convergence regions. These features were similar to a structure produced by the storm splitting, and is recognized as a squall line system with a three-dimensional structure. The second MCS was composed of individual convective cells, moving at a slower speed than the first system. This slow-moving convective system (SMCS) was associated with the south-easterly inflow at lower levels, and extended in a line parallel to the vertical shear direction from north to south. The last system was a stratiform-looking echo system marked by an obvious bright band at the melting level. This system brought more precipitation than the other MCSs. In the echo system, a vortex with a diameter of 20km was found at the middle layer (4-6km). In the middle layer, some vertical circulations were also found, and vertical circulations with a maximum velocity of 5ms-1 were found in the upper layer (>6km). These circulations seemed to cause the heavy precipitation.
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  • Ryuichi Shirooka, Hiroshi Uyeda
    Volume 73 (1995) Issue 2B Pages 461-470
    Released: September 15, 2009
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    We observed global solar radiation changes through two months during the IOP of TOGA-COARE from 19 November 1992 to 19 January 1993 on Manus Island, Papua New Guinea, in the western tropical Pacific. The whole observation period was divided into four stages through consideration of the daily variations of solar radiation. Significant features of each period were also presented in terms of the activity of cloud convection derived from TBB data of GMS and zonal wind changes observed by a wind profiler. Surface winds were changeable throughout the observation period; however, an episodic strong westerly wind was observed from the end of December to early January. The most active stage of cloud convection, which was characterized by a decrease of solar radiation in the afternoon, was observed before the westerly wind episode. Morning convection was, however, prominent during the period of the strong westerly wind. A diurnal change of solar radiation was also compared with the change of latent and sensible heat fluxes obtained using the eddy correlation method. Energy fluxes on a ground surface indicated a quick response within about 30 minutes to solar radiation change. Latent and sensible heat fluxes were almost zero at nighttime, but the maximum value of latent and sensible heat fluxes in the daytime were about 270 and 200Wm-2, respectively.
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  • Yasushi Fujiyoshi, Biao Geng
    Volume 73 (1995) Issue 2B Pages 471-490
    Released: September 15, 2009
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    The structure and evolution of a small, isolated convective rainband, which developed over the warm pool between January 5 and 6, 1993, were examined in detail using sounding and dual-Doppler radar data from Manus Island, Papua New Guinea, during the TOGA-COARE IOP. The rainband developed from two small convective cells and decayed within the dual-Doppler radar coverage area.
    The rainband was oriented parallel to the low-level environmental shear with a lower magnitude of 2.5×10-3 s-1 and the CAPE was as small as 342 J kg-1. It moved from 320° to 140° at a speed of 5.5m s-1. During its mature stage, it was 30km long and 15km wide. Rain water within the rainband was mainly concentrated below the 3.0km level and decreased rapidly with height. The maximum updraft was about 4∼5m s-1 and the maximum radar reflectivity was about 35∼40 dBZ.
    The number of convective cells changed with time as follows: two at the initial stage, five at the developing stage, and one at the mature stage. The low-level front inflow was lifted upward within the cells, formed the main updrafts over the reflectivity cores, and then moved toward the trailing region. There were no strong downdrafts below the heavy rainfall area, and there was no widespread stratiform region behind the convective region. Convective-scale rear inflows were observed in the early stage. These rear inflows aggregated with each other, increased in area and depth, and developed into a flow like a gravity current. The aggregated rear inflow with a gravity current “head” moved faster than the rainband, caused strong low-level convergence, and triggered explosive development of a convective cell in the mature stage, according to a detailed analysis of the dual Doppler radar data. The aggregation of convective-scale rear inflows appears to be important in the organization of a rainband.
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  • Kazumasa Mori
    Volume 73 (1995) Issue 2B Pages 491-508
    Released: September 15, 2009
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    During the TOGA COARE IOP (Tropical Ocean-Global Atmosphere, Coupled Ocean-Atmosphere Response Experiment, Intensive Observation Period), 7.5-minute-interval weather radar observations and 6-hourly radiosonde observations were conducted by the Keifu Maru, a research vessel of the Japan Meteorological Agency (JMA) at a point of (0.5S, 154.5E), near the center of the Intensive Flux Array (IFA), from 3 to 16 November, 1992. The radar echo intensity is digitized on a 2.5km mesh over a square of 500km×500km.
    The observed equatorial convection was documented focusing on mesoscale precipitation systems (MPSs). According to the radar echo coverage, the observation period was divided into four periods. On 3-4 November, convection was inactive and organization of MPSs was suppressed. On 5-8 November, convection was activated and echoes were organized into MPSs with a horizontal scale of about 100-300km. The convection showed diurnal variation with enhancement in the midnight to early morning (14-20 UTC, 00-06 Local Time (LT)). Major MPSs formed as convective cells at early night around 10 UTC (20 LT) and matured into large echoes with embedded strong echoes around midnight to early morning (14-20 UTC, 00-06 LT), then dissipated into scattered weak echoes by the morning around 23 UTC (09 LT). Life histories of major MPSs were similar those of mesoscale precipitation features (MPFs) presented by Leary and Houze (1979). On 10-12 November, an active convective event containing larger MPSs occurred for 1.5 days associated with the westward passage of a large (1500-2000km) scale rapid westward-moving cloud disturbance. The MPSs moved eastward but the field of development of the MPSs seemed to move westward, corresponding to the westward passage of the large-scale cloud disturbance. The MPSs took the form of a multiple-line structure oriented northeast to southwest with a length over 300-500km in the developing stages. The longer lifetime of MPSs covered up the diurnal variation of convection. On 13-14 November, convection was completely suppressed.
    The nighttime enhancement of convection on 5-8 November suggests that even over an open warm water pool region, intense convection circumstantially behaves as diurnal cyclic through the nighttime appearances of MPSs depending on large-scale conditions. Tightly bound and successively westward appearances of eastward-moving MPSs on 10-12 November implies an interaction between the grouped MPSs and the westward-moving large-scale cloud disturbance. Characteristics of the large-scale cloud disturbance were examined.
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  • Tsutomu Takahashi, Kenji Suzuki, Masayuki Orita, Masami Tokuno, Robert ...
    Volume 73 (1995) Issue 2B Pages 509-534
    Released: September 15, 2009
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    Twenty one Precipitation Particle Image Sensors (PPIS) were launched into various clouds at Manus Is., Papua New Guinea (2°S, 147°E) during the Tropical Ocean and Global Atmosphere-Coupled Ocean Atmosphere Response Experiments (TOGA-COARE) international project.
    Cloud system development varied with the vertical humidity profiles. These seemed to form in relation to areal convergence and divergence. It is suggested that typhoons are the most effective modifiers of wind field profiles.
    Two distinct rain system types were typically observed at Manus Is.: rainbands composing cloud clusters from which intense rainfall fell, and thick, upper layer clouds covering a broad area from which weak but steady rain fell.
    The most outstanding result was the finding of a dominant warm rain process in the Manus rainbands. On the other hand, small graupel, including aggregates, fell from thick, upper layer clouds. Subtle differences in precipitation particles from thin anvil clouds and those from stratified typhoon clouds, lead to the conclusion that these thick upper layer clouds are formed by additional lifting of mid-level air. In both cloud types, ice crystal concentration in the equatorial area was minimal in comparison to other tropical regions.
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  • Hiroyuki Hashiguchi, Shoichiro Fukao, Manabu D. Yamanaka, Toshitaka Ts ...
    Volume 73 (1995) Issue 2B Pages 535-548
    Released: September 15, 2009
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    An L-band (1357.5MHz) boundary layer radar (BLR) has been in continuous successful operation at Serpong, Indonesia (6.4°S, 106.7°E) for more than two years from November 1992, including the Intensive Observation Period (IOP) of TOGA COARE (November 1992-February 1993). We found a striking reversal of the wind direction from easterly to westerly at the beginning of December 1992. It was confirmed from geostationary meteorological satellite (GMS) observation data that this reversal was associated with an eastward movement of the convection center (a super cluster) situated between the Indian Ocean monsoon (westerly) dominant area and the Pacific Ocean trade wind (easterly) dominant area. The lower-tropospheric wind variations associated with (super) cloud clusters are presented, and some differences are found between the eastern and western sides of the convection center (corresponding respectively to the easterly and westerly regimes; or to the dry and rainy seasons).
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  • Ken-ichiro Muramoto, Takashi Fujiki, Masaki Kaneda, Tatsuo Endoh
    Volume 73 (1995) Issue 2B Pages 549-556
    Released: September 15, 2009
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    To offer precise data for a more quantitative analysis of the data obtained by the dual Doppler radar system, a specially designed raindrop size distribution meter was utilized at Manus Island, Papua New Guinea, in the TOGA/COARE project. The measuring device consists of an optical system with a light source and two video cameras. The raindrops that fall through a slit are illuminated against a uniform surface light source by means of a frosted glass plate immediately next to them and their shadow images are photographed by two video cameras with different shutter speeds for simultaneously measuring size and velocity of fall of the same raindrop. Fall velocity is used to examine the size measured and provides a highly reliable measurement of size for even the smaller raindrops.
    In this paper, two different types of size distribution of raindrops are shown by a single modal Gamma function and a bimodal distribution corresponding to relatively weak and relatively strong convective clouds, respectively. The bimodal case is discussed in comparison with the radar data analyzed in a few instances of a series of rainfall periods and some of the results provide possible evidence for the warm-rain mechanism and evaporation processes.
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  • Osamu Tsukamoto, Hiroshi Ishida
    Volume 73 (1995) Issue 2B Pages 557-568
    Released: September 15, 2009
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    Turbulent flux measurements were carried out on board the R/V Hakuhomaru during TOGA-COARE IOP in Nov., 1992. She stayed at the station of 156°E on the equator, north of the Intensive Flux Array (IFA) of COARE region for more than 2 weeks (Asai, 1993). Turbulent fluxes were evaluated by the eddy correlation method, including ship motion corrections for wind velocity fluctuations. The weather situation was relatively calm for most of the period. Convective activity developed in the latter half of the period with occasional showers. It was found that heat fluxes from the sea surface were about 14Wm-2 and 88Wm-2 for sensible and latent heat fluxes, respectively, as mean values of the period when Brook's correction was accepted. However they increased to almost double when a gust front developed from the precipitating cumulus as a downdraft.
    Bulk transfer coefficients were estimated from eddy fluxes and bulk meteorological values. The average values of CH=1.32×10-3 and CE=1.16×10-3 were evaluated. The wind speed dependencies of the coefficients were investigated and increases in the low wind speed region were observed, which supports the previous prediction. The surface energy budget was investigated based on radiation and turbulent flux measurements. The net heat flux into the water was estimated to be about 68Wm-2 in this period.
    The present data of eddy correlation measurements are considered to be one of the sea truth standards, as well as the ones from the R/V Moana Wave, Franklin and Natsushima.
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  • Y. H. Ding, Akimasa Sumi, X. S. Shen
    Volume 73 (1995) Issue 2B Pages 569-583
    Released: September 15, 2009
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    The surface and aerological observations made by the Japanese research vessel Hakuho-maru on 11-27 November, 1992 at 0°, 156°E during TOGA-COARE IOP period were used to analyze the evolution and structure of mixed layer over the ocean, and to estimate surface fluxes by using bulk schemes. The Part I of this study is devoted to the problem of the mixed layer. The main finding is that the regional wind field can greatly modify the structure of the mixed layer. For the east trade régime, the mixed layer had a relatively great depth, mostly reaching 800-900m. Above this level was a dry layer without any significant inversion. For the west wind régime created by four westerly wind bursts, the height of the mixed layer was considerably depressed, or even disappeared. A deep saturation layer was often observed.
    Two events of the intrusion of the extremely dry air layer greatly enhanced and elevated the mixed layer, up to about 1.5km. The reason for these events was discussed.
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  • Y. H. Ding, Akimasa Sumi, X. S. Shen
    Volume 73 (1995) Issue 2B Pages 585-596
    Released: September 15, 2009
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    The present paper is the second part of our study on features of the boundary layer during TOGA-COARE IOP. Utilizing the observational dataset obtained by the Japanese R/V Hakuho-maru for 11-27 November, 1992 during TOGA-COARE IOP at 0°, 156°E, the ocean surface fluxes were estimated by three different bulk schemes. Firstly, a near-linear relation between the neutral drag coefficient and wind speed was used. Then, the stability-dependent drag and heat transfer coefficients were iteratively solved. Based on the thus-derived transfer coefficients the momentum, sensible, and latent heat fluxes were estimated, which amount to 0.0316N/m2, 10.2W/m2 and 190.3W/m2, respectively. The regional wind field strongly modulated the magnitude of surface fluxes, with four westerly wind episodes corresponding to much greater fluxes than those for the east trade wind. The magnitude of surface fluxes is also dependent upon the atmospheric stability, in particular for a weak wind condition. The net surface heat flux was estimated, indicating that a considerable amount of heat was transported from the underlying ocean into the atmosphere. Finally, an accuracy analysis was made through a comparison with direct measurements by the eddy-correlation method and other bulk method estimates, showing that the bulk-derived fluxes are acceptable with high confidence.
    Through this study, it has been realized that the full range of wind structures and conditions, from the ambient trade-wind regime through the episodic westerly wind regime, may exert a significant impact on the structures of mixed layers and the ocean-atmosphere fluxes of heat, moisture and momentum.
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  • Sei-ichi Kanari, Chikashi Kobayashi, Hirotaka Otobe
    Volume 73 (1995) Issue 2B Pages 597-609
    Released: September 15, 2009
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    Estimates of turbulent heat flux and heat budget in a time-dependent mixed layer and a surface slab layer are presented using the microstructure data measured during the cruise of the R/V Hakuho-maru at the fixed location of 0°, 156°E. Repeated profilings of the microstructure measurements with 3- or 6-hour intervals were carried out from November 12 to 27 in 1992.
    The maximum turbulent heat flux at the bottom of the time-dependent mixed layer, which was determined as the depth with temperature difference of 0.1° from temperature at 5m layer, is 239.1W/m2 downward. Mean heat flux at the bottom of the time-dependent mixed layer averaged over the analyzed period of eleven days, however, was only 31.4W/m2 downward. Heat budget in the time-dependent mixed layer is greatly affected by advective heat flux, which reaches more than 50 percent of the net heat stored in the layer.
    On the other hand, accumulated heat budget in the surface slab layer (surface layer) about 70m thick, defined as the layer between sea surface and 28°C isotherm, is also evaluated. Accumulated net heat input estimated from the surface meteorological data for eleven days is 80MJ/m2. The maximum components of turbulent heat flux in the surface layer were 50W/m2 upward and 250W/m2 downward. However, the mean flux for eleven days averaged over the surface layer was only 9.1W/m2. The total heat flow at the bottom of the surface layer for eleven days was 9.3MJ/m2 downward. Therefore, if we neglect the advective heat, the residue of 70.7MJ/m2 could contribute to a rise in temperature of the surface layer. The net heat input estimated from mean temperature change in the surface layer was 84MJ/m2. The difference of 13.3MJ/m2 could be attributed to advective heat, which corresponds to 16 percent of the surface net heat input.
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  • Akimasa Sumi, X. S. Shen
    Volume 73 (1995) Issue 2B Pages 611-629
    Released: September 15, 2009
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    Sensitivity of parameterization schemes for upper ocean mixing in a large-scale ocean model has been examined by using observational data of the R/V Hakuho-maru during the TOGA-COARE IOP, which was conducted from November, 1992 until February, 1993 in the equatorial Western Pacific region. The turbulent energy dissipation rate (ε) and mixed-layer structure have been intensively observed, associated with surface fluxes at (Equator, 156°E) from 12-26 November, 1992.
    Time evolution of the mixed layer has been simulated by using 1-dimensional level 2, 2.5, 3 and 4 of the Mellor-Yamada closure model (Mellor and Yamada, 1974; Yamada and Mellor, 1975), and has been compared to the observations conducted by the R/V Hakuho-maru. A special emphasis was placed on the comparison of the turbulent energy dissipation rate, because it is an observed quantity directly related to a turbulent process. In general, the results of the four models are similar and, if compared to the observation, it is noted that the mixing is weak. Especially, when the surface wind is very weak, the discrepancy becomes prominent. It is concluded that there are few differences between these schemes as long as a 1-dimensional model is applied.
    Sensitivity of the results to vertical resolution has been investigated. General features of the upper mixing layer (∼100m) are not different between high vertical resolution (Δz=1m) and ordinary resolution (Δz=20m), although the diurnal variation of SST (0.2°C) cannot be simulated by Δz=20m.
    Time evolution of the mixed layer was simulated by using the level-2 model with eddy diffusion coefficients derived by the observed ε. This result explains approximately 70% of the increase of heat content during this period.
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  • Eiji Ohtaki, Eiji Yamashita, Kunimitsu Ishida, Haruna Ito, Xiaohu Liu
    Volume 73 (1995) Issue 2B Pages 631-637
    Released: September 15, 2009
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    The carbon dioxide in seawater (pCO2) was measured at the equatorial station (0.0°N, 156.0°E) during the R/V Hakuho Maru Cruise as part of the TOGA COARE program extending from October 31 to December 7, 1992. There is no significant equatorial upwelling during whole experimental period. The pCO2 shows the diurnal variation with low values in the daylight hours and high values at nighttime. The mean value of pCO2 in the morning (9h) is smaller by about 4.8ppm (standard deviation=4.6ppm) than that in the evening (21h). The maximum value of downward transport of carbon dioxide (4×10-4 mol m-2d-1) is obtained when the wind speed is 4.1ms-1. The downward transport of carbon dioxide results in the increase in pCO2 by about 0.06ppm. This is negligibly small compared with the real diurnal change in pCO2. The vertical profile of pCO2 shows that there is a depletion layer of pCO2 at around 50m depth. This depletion layer of pCO2 is roughly coincident with the layer of high chlorophyll-a concentration, high dissolved oxygen concentration, and low nitrate concentration measured during the Sagittarius Expedition near our station (0.0°S, 150.0°E). These results denote that the biological activity plays an important rôle in causing the diurnal variation of pCO2 in seawater. pCO2 values measured at the equatorial station are undersaturated with respect to the atmospheric carbon dioxide. This denotes the possibility that the equatorial oceans act as a sink of the atmospheric carbon dioxide under conditions of high seawater temperature during cessation periods of upwelling.
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  • Hideo Nakajima, Arata Kaneko, Noriaki Gohda, Kazuo Kawatate
    Volume 73 (1995) Issue 2B Pages 639-643
    Released: September 15, 2009
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    Self-contained upward-looking ADCP data obtained at station (2°0.21′N, 156°0.11′E) during the TOGA/COARE TOP were carefully analyzed to extract the echo amplitude (AGC) returning from the sea surface. The AGC values at the surface were found to have a good correlation with the wind speed data obtained from the ATLAS buoy at the same site and ranging from 0 to 13ms-1. This study opened the possibility of predicting the wind speed from the surface AGC although the reason why backscatter from the sea surface increased with the wind speed was not sufficiently elucidated.
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  • Tatsuo Suzuki, Shinichi Ito, Kensuke Takeuchi, Hirotaka Otobe
    Volume 73 (1995) Issue 2B Pages 645-652
    Released: September 15, 2009
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    Variations of temperature and salinity in the upper ocean are observed by the R/V Hakuho-Maru, when she stayed at the fixed station at the equator, 156°E, for 15 days in November 1992. The weather was calm for most of the period, and the temperature of the surface mixed layer increased slightly. Analyses suggest that heat fluxes through the sea surface and meridional advection explain most of the change of the heat storage in the mixed layer. EOF and isopycnal analyses suggest wave motion and intrusion of off-equatorial water are the main processes for the variation of temperature and salinity in the upper ocean, along with fluxes through the sea surface and mixing process in the mixed layer.
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  • Kentaro Ando, Yoshifumi Kuroda, Kunio Yoneyama, Kei Muneyama, Kensuke ...
    Volume 73 (1995) Issue 2B Pages 653-663
    Released: September 15, 2009
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    Continuous CTD casts and meteorological observations were made from a station at 0°, 156°E from February 5 to February 14, 1993 during the TOGA-COARE Intensive Observation Period. Large temperature variations were found around 240, 340, 570 and 760dbar. These variations affect the surface geopotential anomaly (dynamic height) with a standard deviation of ±0.28m2/s2 at the sea surface.
    In the ocean surface layer (0-60dbar), the 10 day average “heat storage rate (the rate of change of heat content)” was -27.1Watt/m2 (positive means cooling), and the similarly averaged surface heat flux calculated from the meteorological data on the ship was -24.2Watt/m2 (positive means upward with heat loss of the ocean). This balance suggests that the mixed layer temperature was mainly controlled by the local surface heat flux during the 10 days of our observation period, although the residual (defined as heat storage rate minus surface heat flux) was large in the calculation for each 6 hours.
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  • Kunio Kutsuwada, Hideo Inaba
    Volume 73 (1995) Issue 2B Pages 665-675
    Released: September 15, 2009
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    Measurements of oceanic currents were performed at two sites (0°, 147°E and 0°, 154°E) in the western equatorial Pacific by upward-looking moored Acoustic Doppler Current Profilers (ADCPs) during about one year in 1992-93 to investigate current variabilities in the surface layer of a warm-pool region. The zonal currents are always eastward except in the uppermost layer above 100m, in which the current direction changed frequently. Mean eastward currents corresponding to the Equatorial Undercurrent (EUC) have two maxima at 70-90m and 210m. The depth of the EUC's core tends to shift in the vertical direction with time scales from several days to a few months.
    These layered structures of the zonal currents are represented by those of empirical orthogonal function (EOF) modes. At the western site, the first EOF mode contributing about 60% of the total variance has no nodes in the depth range with a maximum of 90m, meaning that the entire layer changes with the same phase, while the second EOF mode, contributing about 20%, has a node at about 110m, meaning that the upper and lower currents change with an out-of-phase relation. In the uppermost layer above 100m, strong eastward currents reaching about 80cm s-1 are found in January 1992, and are related to the third mode which has two nodes, one at 70m and the other at 130m. The meridional current has a time average of about zero in almost all layers, its change being about half of the zonal change in magnitude. Spectral analyses indicate that dominant changes are found at periods of about 10 days, 15-20 days, and 30-60 days.
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