Journal of the Meteorological Society of Japan. Ser. II
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Showing 1-13 articles out of 13 articles from Advance online publication
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  • Miho SEKIGUCHI, Hironobu IWABUCHI, Takashi M. NAGAO, Teruyuki NAKAJIMA
    Type: Articles : Special issue on Meteorology and Climate Change Studies by Using the Geostationary Meteorological Satellite Himawari-8
    Article ID: 2018-007
    [Advance publication] Released: December 08, 2017
    JOURNALS FREE ACCESS ADVANCE PUBLICATION

     We developed an atmospheric gas absorption table for the Advanced Himawari Imager (AHI) based on the correlated k-distribution (CKD) method with the optimization method, which was used to determine quadrature weights and abscissas. We incorporated the table and band information of the AHI into a multi-purpose atmospheric radiative transfer package, Rstar. We updated the package so that users could easily specify the satellite and band number. Use of this update made it possible for the optimized CKD method to carry out calculations rapidly and accurately. Rstar is easy for beginners to use and facilitates comparison of results. Cloud retrieval tests using different numbers of quadrature points showed that cloud retrievals could be significantly affected by the accuracy of the CKD model.

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  • Teruyuki KATO
    Type: Articles
    Article ID: 2018-008
    [Advance publication] Released: December 08, 2017
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     This study investigated the representative height of low-level water vapor field that can be used to examine the occurrence possibility of heavy rainfall in East Asia. First, cloud base heights (CBHs) of moist convection were statistically examined by performing simulations with a 1-km-resolution numerical model during April–August 2008, with a focus on Kyushu and Shikoku Islands, western Japan. CBHs of moist convection with strong updrafts were simulated mainly around 500 and 300 m heights above sea level over land and over the ocean, respectively. This result indicates that low-level humid air below a height of 500 m is very important for the initiation of strong moist convection. Moreover, the equivalent potential temperature θe at the CBHs was examined to clarify θe values of lifted air parcels initiating cumulonimbus development. This result showed that below the CBHs, θe was usually around 355 K.

     Next, given these results for the CBHs, θe at 500 m height from 10-km-resolution objective analysis data was statistically compared with θe at various heights and pressure levels over the ocean south of 35 °N in East Asia during June–September 2008. These comparisons showed that analyses at the 850-hPa level could not represent the low-level water vapor field, while the θe field at 850 hPa in the Baiu season was strongly influenced by convective activity over the Baiu frontal zone. The θ e field at 925 hPa also could not adequately represent the low-level water vapor field, but the difference in θ e between heights of 250 and 500 m was very small. Because high θ e layers must have some thickness, data at 500 m height can be considered representative of the low-level water vapor field in analyses examining the initiation of moist convection leading to heavy rainfall.

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  • Tsutao OIZUMI, Kazuo SAITO, Junshi ITO, Thoru KURODA, Le DUC
    Type: Articles
    Article ID: 2018-006
    [Advance publication] Released: November 30, 2017
    JOURNALS FREE ACCESS ADVANCE PUBLICATION

     An intense rainband associated with Typhoon 1326 (Wipha) induced a fatal debris flow on Izu Oshima, Japan, on October 15-16, 2013. This rainband formed along a local front between the southeasterly humid warm air around the typhoon and the northeasterly cold air from the Kanto Plain. In this paper, the Japan Meteorological Agency Nonhydrostatic Model was optimized for the “K computer,” and ultra-high-resolution (500-250 m grid spacing) numerical simulations of the rainband with a large domain were conducted.

     Two of main factors that affect a numerical weather prediction (NWP) model, (1) grid spacing and (2) planetary boundary layer (PBL) schemes [Mellor–Yamada–Nakanishi–Niino (MYNN) and Deardorff (DD)], were investigated. Experiments with DD (Exps_DD: grid spacings of 2 km, 500 m, and 250 m) showed better reproducibility of the rainband position than experiments with MYNN (Exps_MYNN: grid spacings of 5 km, 2 km, and 500 m). Exps_DD simulated distinct convective-scale up/downdraft pairs on the southeast/northwest sides of the front, whereas those of Exps_MYNN were not clear. Exps_DD yielded stronger cold pools near the surface than did Exps_MYNN. These differences in the boundary layer structures likely had a large impact on the position of the front and the associated rainband. Exps_DD with the 500-m grid spacing showed the best precipitation performance according to the Fractions Skill Score.

     To check other factors of the precipitation forecast, model domain sizes, lateral boundary conditions in nesting simulations, and terrain representations were investigated. In the small domain experiments, the rainband shapes were very different from the observations. In the experiment using a nesting procedure, the deterioration of the forecast performance was acceptably reduced. The model with fine terrains better reproduced the intense rain over the island. These results demonstrate that the ultra-high-resolution NWP model with a large domain has the possibility to improve predictions of heavy rain.

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  • Yuhei YAMAMOTO, Hirohiko ISHIKAWA
    Type: Articles : Special issue on Meteorology and Climate Change Studies by Using the Geostationary Meteorological Satellite Himawari-8
    Article ID: 2018-004
    [Advance publication] Released: November 24, 2017
    JOURNALS FREE ACCESS ADVANCE PUBLICATION
     The land surface emissivity (LSE) in the thermal infrared (TIR) is an essential parameter in the retrieving the land surface temperature (LST) from space. This paper describes the LSE maps in TIR three bands (centered at 10.4, 11.2 and 12.4 μm) used for retrieving the LST from Himawari-8. Himawari-8, a next-generation geostationary satellite has high spatial and temporal resolutions compared to previous geostationary satellites. Due to these improvements, it is expected that the Himawari-8 LST product contribute to observe small-scale environments in high-frequency. In this study, the LSE is estimated by a semi-empirical method, which is a combination of the classification based method and the normalized difference vegetation index (NDVI) thresholds method. The land cover classification information is taken from the Global Land Cover by National Mapping Organizations version3 (GLCNMO 2013). Material emissivities of soil, vegetation and others are taken from the MODIS UCSB emissivity library and the ASTER spectral library. This method is basically following to Peres and DaCamara (2005) but advanced considerations are added. They are phenology of vegetation, flooding of paddy field, snow/ice coverage and the internal reflections (cavity effect) in the urban area. The average cavity effect on LSE in urban canopy is approximately 0.01, but it reaches 0.02 in built-up area. The sensitivity analysis shows that the total LSE errors for three bands are less than 0.02. The LSE estimation is especially stable at the vegetation area, where the error is less than 0.01.
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  • Yuhei YAMAMOTO, Hirohiko ISHIKAWA, Yuichiro OKU, Zeyong HU
    Type: Articles : Special issue on Meteorology and Climate Change Studies by Using the Geostationary Meteorological Satellite Himawari-8
    Article ID: 2018-005
    [Advance publication] Released: November 24, 2017
    JOURNALS FREE ACCESS ADVANCE PUBLICATION
     This paper presents a method to estimate the land surface temperature (LST) from Himawari-8 data. The Advanced Himawari Imager (AHI) onboard Himawari-8 has three thermal infrared bands in the spectral range of 10–12.5 μm. We developed a nonlinear three-band algorithm (NTB) that makes the best use of these bands to estimate the LST. The formula of the algorithm includes ten coefficients. The optimum values of these coefficients were derived using a statistical regression method from the simulated data, as obtained by a radiative-transfer model. The simulated data sets corresponding to a variety of values of LST, surface emissivity, type and season of temperature and water vapor profiles. Viewing zenith angles (VZAs) from 0° to 60° were considered. For the coefficients obtained in this way, we checked the root-mean-square error (RMSE) in terms of the VZA, LST and precipitable water dependence. We showed that the NTB can accurately estimate the LST with the RMSE less than 0.9 K by comparison with the nonlinear split-window algorithm developed by Sobrino and Romaguera (2004). Moreover, we evaluated the sensitivities of the LST algorithms to the uncertainties in input data by using the dataset independent of dataset used to obtain coefficients. Consequently, we showed that the NTB has the highest robustness against the uncertainties in input data. Finally, the stepwise LST retrieval method were constructed. This method includes a simple cloud mask procedure and the LSE estimation. The LST product was evaluated using in-situ data over the Tibetan Plateau, and then the validity was confirmed.
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  • Shusuke NISHIMOTO, Hirotada KANEHISA
    Type: Articles
    Article ID: 2018-003
    [Advance publication] Released: November 16, 2017
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     We analytically solve a forced linear problem of vortex Rossby waves (VRWs) associated with vortex resiliency of tropical cyclones. We consider VRWs on a basic barotropic axisymmetric vortex. The VRWs, which are initially absent, are successively forced by a vertically sheared unidirectional environmental flow. The problem is formulated in the quasigeostrophic equations, linearized about the basic vortex. The basic potential vorticity (PV) is assumed to be piecewise constant in the radial direction so that the problem can be analytically solved. The obtained solutions show the following.

     When the vertical interaction (VI) between the VRWs is weak, a stationary mode (called the pseudo mode) is selectively forced and grows linearly in time, and the vortex is eventually destroyed by the environmental vertical shear. When the VI is moderate, an almost form-preserving quasi-mode (simply called the quasi mode) of the VRWs appears and precesses about a downshear-left tilt equilibrium (DSLTE). The precession is not growing and the vortex maintains the vertical coherence. In particular, in the presence of the inward radial gradient of the basic PV at the critical radius, the precession damps and the quasi mode eventually approaches the DSLTE. When the VI is strong, the VRWs are simply advected by the basic angular velocity at each radius to be axisymmetrized to some extent about the DSLTE, and the vortex maintains the vertical coherence.

     In order to examine the diabatic effect near the eyewall, the solution with the basic buoyancy frequency being small in the central region and large in the outer region is also obtained. The small and large buoyancy frequencies imply the strong and weak VIs, respectively. The central VRWs are simply advected by the basic vortex flow. While, the outer VRWs precess about the DSLTE just like a quasi mode, and the vortex maintains the vertical coherence.

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  • Woosub ROH, Masaki SATOH
    Type: Notes and Correspondence
    Article ID: 2018-002
    [Advance publication] Released: September 29, 2017
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     As an alternative approach to the previous multisensor satellite evaluation method of cloud system resolving models, a method is presented using combined infrared and microwave channels for precipitation clouds in cloud system resolving models over the ocean. This method determines characteristics of cloud-top temperatures and ice scatterings for clouds using infrared 11-μm and microwave high frequencies (89.0 GHz) brightness temperatures (TBs). The threshold of the TB at low frequencies (18.7 GHz) is also used to identify precipitation regions. This method extends the previous approach via the wider swath of the passive microwave sensor and sensitivities to ice clouds compared to the previous Tropical Rainfall Measuring Mission (TRMM)-based analysis method using the narrower coverage of the Precipitation Radar.

     The numerical results of the non-hydrostatic icosahedral atmospheric model (NICAM) with two cloud microphysics schemes are evaluated over the tropical open ocean using this method. The intensities of the scatterings in the two simulations at 89.0 GHz are different due to the parameterizations of the snow and graupel size distributions. A bimodal size distribution of the snow improved the underestimation of the TBs at 89.0 GHz. These results have a similar structure to the joint histograms of cloud-top temperatures and precipitation-top heights in the previous method: the overestimated intensity of scattering and the frequencies of high precipitation-top heights above 12 km in the control experiment. We find that the change in the snow size distribution in the cloud microphysics scheme can lead to better agreements of simulated TBs at 89.0 GHz with observations. We further investigate impacts of non-spherical assumptions for snow using a satellite simulator. The effect of a non-spherical shape of snow in the radiative transfer model causes a smaller change of TBs at 89.0 GHz compared to the difference between the TBs of the two simulations without non-spherical assumptions.

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  • Hironobu IWABUCHI, Nurfiena Sagita PUTRI, Masanori SAITO, Yuka TOKORO, ...
    Type: Articles : Special issue on Meteorology and Climate Change Studies by Using the Geostationary Meteorological Satellite Himawari-8
    Article ID: 2018-001
    [Advance publication] Released: September 15, 2017
    JOURNALS FREE ACCESS ADVANCE PUBLICATION

      An algorithm for retrieving the macroscopic, physical and optical properties of clouds from thermal infrared measurements is applied to the Himawari-8 multiband observations. A sensitivity study demonstrates that the addition of the single CO2 band of Himawari-8 is effective for the estimation of cloud top height. For validation, retrieved cloud properties are compared systematically with collocated active remote sensing counterparts with small time lags. While retrievals agree reasonably for single-layer clouds, multilayer cloud systems with optically thin upper clouds overlying lower clouds are the major source of error in the present algorithm. Validation of cloud products is critical for identifying the characteristics, advantages and limitation of each product and should be continued in the future.

     As an application example, data are analyzed for eight days in the vicinity of the New Guinea to study the diurnal cycle of the cloud system. The present cloud property analysis investigates cloud evolution through separation of different cloud types and reveals typical features of diurnal cycles related to the topography. Over land, middle clouds increase from 0900 to 1200 local solar time (LST), deep convective clouds develop rapidly during 1200–1700 LST with a subsequent increase in cirrus and cirrostratus cloud amounts. Over the ocean near coastlines, a broad peak of convective cloud fraction is seen in the early morning. The present study demonstrates the utility of frequent observations by Himawari-8 for life cycle study of cloud systems, owing to the ability to capture their continuous temporal variations.

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  • Ryo OYAMA, Masahiro SAWADA, Kazuki SHIMOJI
    Type: Articles : Special issue on Weather and Environmental Studies Using the Geostationary Meteorological Satellite Himawari-8
    Article ID: 2017-024
    [Advance publication] Released: August 10, 2017
    JOURNALS FREE ACCESS ADVANCE PUBLICATION
     The high temporal and spatial resolutions of geostationary satellite observations achieved by recent technological advances have facilitated derivation of atmospheric motion vectors (AMVs), even in a tropical cyclone (TC) where the winds abruptly change. This study used TCs in the western North Pacific basin to investigate the ability of upper tropospheric AMVs to estimate TC intensity and structure. We first examined the relationships between the cloud-top wind fields captured by 6-hourly upper tropospheric AMVs derived from images of the Multi-functional Meteorological Satellite (MTSAT) and the surface maximum sustained wind (MSW) of the Japan Meteorological Agency best-track data for 44 TCs during 2011–2014. The correlation between the maximum tangential winds of the upper tropospheric AMVs (UMaxWinds) and MSWs was high, about 0.73, the suggestion being that the cyclonic circulation near the cloud top was intensified by the upward transport of absolute angular momentum within the TC inner core. The upper tropospheric AMVs also revealed that the mean radii of UMaxWinds and the maximum radial outflows shifted inward as the TC intensification rate became large, the implication being that low-level inflow was strong for TCs undergoing rapid intensification. We further examined the possibility of estimating the MSW by using 30-min-interval UMaxWinds derived from Himawari-8 target observations, which have been used to track TCs throughout their lifetimes. A case study using Typhoon Lionrock (1610) showed that the UMaxWinds captured changes of the cyclonic circulation near the cloud top within the inner core on a time scale shorter than one day. It was apparent that the increase of UMaxWind was associated with intensification of the TC warm core and shrinkage of UMaxWind radius. These results suggest that the Himawari-8 AMVs include useful information on TC intensification and related structural changes to support the TC intensity analysis and structure monitoring.
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  • Shin-ichi SUZUKI, Takeshi MAESAKA, Koyuru IWANAMI, Shingo SHIMIZU, Kao ...
    Type: Articles : Special issue on Tokyo Metropolitan Area Convection Study for Extreme Weather Resilient Cities (TOMACS)
    Article ID: 2017-019
    [Advance publication] Released: July 21, 2017
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     X-band dual-polarization (multi-parameter) radars observed the supercell storm that generated an F3 tornado in Ibaraki Prefecture, Japan on 6 May 2012. The observational data collected for the storm clearly show typical polarimetric features of a supercell storm, such as the ZDR (differential reflectivity) arc, ZDR column, and K DP (specific differential phase) column, and their time evolution. The ZDR arc emerged 10 or 15 min before tornadogenesis. The ZDR column appeared about 1 hour before ZDR arc formation and developed intermittently until tornadogenesis. Just when the ZDR arc appeared, the column was becoming taller and stable, and lasted until the dissipation of the tornado. These ZDR signatures of the supercell storm lasted around half an hour.
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  • Yoshihito SETO, Hitoshi YOKOYAMA, Tsuyoshi NAKATANI, Haruo ANDO, Nobum ...
    Type: Articles : Special issue on Tokyo Metropolitan Area Convection Study for Extreme Weather Resilient Cities (TOMACS)
    Article ID: 2017-020
    [Advance publication] Released: July 21, 2017
    JOURNALS FREE ACCESS ADVANCE PUBLICATION
     The relationships between the occurrence of intense rainfall and the convergence of surface winds and water vapor concentration for typical heavy-rainfall cases were examined using data from July to August in 2011–2013 obtained from high-density meteorological observations in Tokyo, Japan. Additionally, the temporal variations in wind convergence and water vapor between days with and without heavy rainfall events were compared. Corresponding to the heavy-rainfall area, the convergence of surface winds tended to increase for several tens of minutes prior to the heavy rainfall. The peak of convergence was observed 10–30 min before the heavy rainfall occurrence, and convergence continued to increase for approximately 30 min until the convergence peak time. Around the heavy-rainfall area, the increase in the water vapor concentration index coincided with the increase in convergence. From these results, by monitoring the temporal variations and distributions of these parameters using a high-density observation network, it should be possible to predict the occurrence of heavy rainfall rapidly and accurately.
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  • Ryohei MISUMI, Namiko SAKURAI, Takeshi MAESAKA, Shin-ichi SUZUKI, Shin ...
    Type: Articles : Special issue on Tokyo Metropolitan Area Convection Study for Extreme Weather Resilient Cities (TOMACS)
    Article ID: 2017-021
    [Advance publication] Released: July 21, 2017
    JOURNALS FREE ACCESS ADVANCE PUBLICATION
     Convective storms are frequently initiated over mountains under weak synoptic forcing conditions. However, the initiation process of such convective storms is not well understood due to a lack of observations, especially of the transition process from non-precipitating cumuli to precipitating convective clouds. In order to investigate the initiation process, we conducted observations around the mountains in the Kanto region, Japan on 18 August 2011 using a 35 GHz (Ka-band) Doppler radar and a pair of digital cameras. The evolution of convective clouds was classified into three stages: convective clouds were visible but not detected by the Ka-band radar (stage 0), convective clouds were detectable by the Ka-band radar with reflectivity below 15 dBZ (stage 1), and convective clouds were accompanied by descending echoes corresponding to precipitation (stage 2). During the transition process from stage 1 to stage 2, weak radar echoes rose to the higher level and reflectivity rapidly increased. This phenomenon suggests that drizzle particles produced in a pre-existing convective cloud were lifted by a newly developed updraft, and raindrops were formed rapidly by coalescence of the drizzle particles and cloud droplets. This hypothetical process explains the precipitation echo formation in the lower layer frequently observed in the mountainous area in the Kanto region.
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  • Hironori IWAI, Shoken ISHII, Seiji KAWAMURA, Eiichi SATO, Kenichi KUSU ...
    Type: Article : Special issue on Tokyo Metropolitan Area Convection Study for Extreme Weather Resilient Cities (TOMACS)
    Article ID: 2017-014
    [Advance publication] Released: April 26, 2017
    JOURNALS FREE ACCESS ADVANCE PUBLICATION
     During the Tokyo Metropolitan Area Convection Study for Extreme Weather Resilient Cities (TOMACS), many isolated convective storms developed in the southern Kanto Plain on August 17, 2012. The aim of this study was to clarify the dynamics leading to the convection initiation of one of them using different remote sensing instruments.

     Before the convection initiation, a southeasterly flow transported water vapor inland from Tokyo Bay and the well-mixed and a cumulus-cloud-topped convective boundary layer developed. A convergence line in the form of a sea breeze front (SBF) also moved inland from Tokyo Bay. A near-surface air parcel was lifted to its lifting condensation level (LCL) by an updraft in a convergence zone with a 3 km horizontal scale, which formed the west edge of the convergence line. The saturated air parcel at the LCL was then lifted to its level of free convection (LFC) by the updrafts associated with thermals below the cumulus cloud base. The first echo of hydrometeors was detected by a Ku-band radar about 6 minutes after the air parcel reached its LFC, then the convective cell developed rapidly. When an SBF arriving from Sagami Bay passed under the cell, the updraft over the nose of the SBF triggered a new precipitation cell, but no intensification of the preexisting cell was observed.

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