Journal of the Meteorological Society of Japan. Ser. II
Online ISSN : 2186-9057
Print ISSN : 0026-1165
ISSN-L : 0026-1165
Advance online publication
Showing 1-27 articles out of 27 articles from Advance online publication
  • Ryosuke SHIBUYA, Masuo NAKANO, Chihiro KODAMA, Tomoe NASUNO, Kazuyoshi ...
    Type: Article : Special Edition on DYAMOND: The DYnamics of the Atmospheric general circulation Modeled On Non-hydrostatic Domains
    Article ID: 2021-046
    Published: 2021
    [Advance publication] Released: April 08, 2021
    JOURNALS OPEN ACCESS ADVANCE PUBLICATION
    Supplementary material

     In this study, we assess the prediction skill of the Boreal Summer Intra-Seasonal Oscillation (BSISO) mode of one-month simulations using a global Non-hydrostatic Icosahedral Atmospheric Model (NICAM) with explicit cloud microphysics and a grid spacing of 14 km. The simulations were run as a series of hindcast experiments every day of August from 2000 to 2014. A total of 465 simulations were run with a 13950-day integration. Using forecast skill scores for statistical measurements, it was found that the model showed an overall BSISO prediction skill of approximately 24 days. The prediction skill tended to be slightly higher (~ 2 days) when BSISO events began in the initial phases 7 to 1, which corresponded to the re-initiation phase of the BSISO, during which a major convective center over the Philippine Sea decayed and a new convective envelope began aggregating over the western Indian Ocean. The phase speed and the evolution of the amplitude of the BSISO were well simulated by the model with a clear northwest–southeastward tilted outgoing longwave radiation (OLR) structure over the Maritime Continent and the western Pacific. However, the propagation speed was slower during phases 6 and 7, and the amplitude of the BSISO largely decayed during phases 8–1, which is likely to have been associated with the stagnant behavior of the convective cells over the Philippines sea. Based on a regression coefficient analysis using the moist static energy, the stagnation of the propagation over the Philippines was found to be largely attributable to the small southerly background bias in the model over the Philippines. The bias in the large-scale circulation was likely to have been associated with the bias in the moisture field and the background monsoonal circulation. We concluded that the model physics controlling the background fields are important factors in improving BSISO prediction skill.

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  • Kenji NAKAMURA, Yuki KANEKO, Katsuhiro NAKAGAWA, Hiroshi HANADO
    Type: Article : Special Edition on Global Precipitation Measurement (GPM): 5th Anniversary
    Article ID: 2021-053
    Published: 2021
    [Advance publication] Released: May 14, 2021
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     Specific attenuation and equivalent radar reflectivity in a melting layer were measured using a dual Ka-band radar system. The system consists of two identically designed Ka-radars. When the two radars are arranged to face each other and a precipitation system comes between the two radars, they observe the system from opposite directions. The radar echoes suffer from rain attenuation, which appears symmetrically in both radar echo profiles. By differentiating measured radar reflectivity with range, the specific attenuation (k) can be estimated. After obtaining the specific attenuation, the equivalent radar reflectivity (Ze) is estimated. Melting layer observations were conducted on a slope of Mt. Zao, Japan. In the melting layer, the specific attenuation and the equivalent radar reflectivity vary considerably along the radio path. The relationship between k and Ze showed interesting characteristics which appears in a loop-shape on a k-Ze diagram. A simple theoretical study using the Rayleigh and Mie scattering theories for melting snow spheres showed that the basic loop-shape is resulted from the change in permittivity of precipitation particles during melting. The loop-shape is greatly expanded by change of the particle size. The Mie effect which is significant for large precipitation particles slightly modifies the loop-shape by reducing backscattering cross sections. The results also explain that the shelf-like profile instead of the peak-like in Ze.

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  • Kunio YONEYAMA, Mikiko FUJITA, Ayako SEIKI, Ryuichi SHIROOKA, Satoru Y ...
    Type: Article : Special Edition on Years of the Maritime Continent (YMC)
    Article ID: 2021-054
    Published: 2021
    [Advance publication] Released: May 14, 2021
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    Supplementary material

     This short article describes humidity data correction based on intercomparison between the two manufacturers' radiosondes with the assessment using precipitable water vapor (PWV) derived from Global Navigation Satellite System (GNSS) signals. In addition, we propose a method to determine whether the same correction procedure can be applied for the case that such intercomparison cannot be conducted.

     During the intensive observation called Years of the Maritime Continent - Boreal Summer Monsoon study in 2018 (YMC-BSM 2018), intercomparison of radiosonde between Lockheed Martin LMS6 and Vaisala RS41-SGP was conducted at Laoag, Ilocos Norte, Philippines from late July to early August 2018. While their mean difference of relative humidity (RH) showed better than 5 %, dry bias was confirmed for LMS6 only during clear sky daytime soundings based on the comparison of PWV with that derived from GNSS signals. To use different radiosonde data with the same research-quality, we developed a correction table for LMS6 RH data.

     While a direct intercomparison between different radiosondes and independently developed observational tools such as GNSS-receiver is ideal to evaluate the data quality, it is not always able to be performed. Indeed, we obtained LMS6 radiosonde data at different site at Yap Island, Federated States of Micronesia from another field campaign YMC-BSM 2020, where any intercomparison could not be conducted. In order to decide whether the same correction procedure obtained from YMC-BSM 2018 can be applied to those data, we assessed their similarity based on a relationship between specific humidity from surface meteorological station data that was obtained independently prior to launch and radiosonde specific humidity averaged over 300 m from the initial radiosonde measurement point. This method allowed us to confirm the same behavior between Laoag data in 2018 and Yap data in 2020, thus we applied our correction method to RH data in YMC-BSM 2020.

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  • Kunihiko KODERA, Nawo EGUCHI, Rei UEYAMA, Beatriz M. FUNATSU, Marco GA ...
    Type: Notes and Correspondence
    Article ID: 2021-055
    Published: 2021
    [Advance publication] Released: May 14, 2021
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     Previous studies have suggested that the recent increase in tropical extreme deep convection, in particular over Asia and Africa during the boreal summer, has occurred in association with a cooling in the tropical lower stratosphere. The present study is focused on the Sahel region of West Africa, where an increased occurrence of extreme precipitation events has been reported over recent decades. The results show that the changes over West Africa since the 1980s involve a cooling trend in the tropical lower stratosphere and tropopause layer, combined with a warming in the troposphere. This feature is similar to that which might result from increased greenhouse gas levels, but is distinct from the interannual variation of precipitation associated with the transport of water vapor from the Atlantic Ocean. It is suggested that the decrease in the vertical temperature gradient in the tropical tropopause region enhances extreme deep convection over the Sahel, where penetrating convection is frequent, whereas tropospheric warming suppresses the shallower convection over the Guinea Coast. The essential feature of the recent changes over West Africa is therefore the depth of convection, rather than the total amount of surface precipitation.

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  • Tsuyoshi Thomas SEKIYAMA, Mizuo KAJINO
    Type: Notes and Correspondence
    Article ID: 2021-052
    Published: 2021
    [Advance publication] Released: May 10, 2021
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     This study examined the performance of Eulerian models in simulating dispersion fields at two coastal monitoring stations in the vicinity of a pollutant source (3.2 and 17.5 km distant) under the situation of the Fukushima 2011 nuclear accident using two horizontal resolutions (3 km and 250 m). A 250-m grid simulation was newly performed for the examination and was able to reproduce the wind and concentration fields in detail over complex terrain. The 3-km grid model could not reproduce the details of the winds and plumes around the Fukushima Daiichi Nuclear Power Plant but occasionally yielded a higher performance with a lower undetected error rate than the 250-m grid model due to the large numerical diffusion of the former. A disadvantage of Eulerian dispersion models is expected to be the artificial numerical diffusion in the advection process near emission sources. The artificial numerical diffusion increases the false alarm ratio (number of strikeouts while swinging) but fortunately decreases the undetected error rate (number of strikeouts while looking). This characteristic is appropriate for environmental emergency response (EER) systems. Furthermore, the 250-m grid model result was robustly improved by a plume augmentation (i.e., max pooling) process, which enlarged the plume widths and masked short time lags and small plume drifts. Plume augmentation was advantageous to the high-resolution model to improve statistical scores, which is beneficial for EER systems.

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  • Marylis BARREYAT, Philippe CHAMBON, Jean-François MAHFOUF, Ghislain FA ...
    Type: Article : Special Edition on Global Precipitation Measurement (GPM): 5th Anniversary
    Article ID: 2021-050
    Published: 2021
    [Advance publication] Released: April 30, 2021
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     The assimilation of cloudy and rainy microwave observations is under investigation at Météo-France with a method called ‘1D-Bay+3D/4D-Var’. This method consists of two steps: (i) a Bayesian inversion of microwave observations and (ii) the assimilation of the retrieved relative humidity profiles in a 3D/4D-Var framework. In this paper, two estimators for the Bayesian inversion are used: either a weighted average (WA) or the maximum likelihood (ML) of a kernel density function. Sensitivity studies over the first step of the method are conducted for different degrees of freedom: the observation error, the channel selection and the scattering properties of frozen hydrometeors in the observation operator. Observations over a two-month period of the Global Precipitation Measurement (GPM) Microwave Imager (GMI) on-board the GPM-Core satellite and forecasts of the convective scale model Application of Research to Operations at Mesoscale (AROME) have been chosen to conduct these studies. Two different meteorological situations are analysed: those predicted cloudy in AROME but clear in the observations and, on the contrary, those predicted clear in AROME but cloudy in the observations.Main conclusions are as follows. First, low observational errors tend to be associated with the profiles with the highest consistency with the observations. Second, the validity of the retrieved profiles varies vertically with the set of channels used. Third, the radiative properties used in the radiative transfer simulations have a strong influence on the retrieved atmospheric profiles. Finally, the ML estimator has the advantage of being independent of the observation error but is less constrained than the WA estimator when few frequencies are considered. While the presented sensitivities have been conducted to incorporate the scheme in a data assimilation system, the results may be generalized for geophysical retrieval purposes.

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  • Takuto SATO, Hiroyuki KUSAKA
    Type: Notes and Correspondence
    Article ID: 2021-047
    Published: 2021
    [Advance publication] Released: April 14, 2021
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     In this study, we compare the accuracy of five representative similarity metrics in extracting sea level pressure (SLP) patterns for accurate weather chart classification: correlation coefficient, Euclidean distance (EUC), S1-score (S1), structural similarity (SSIM), and average hash. We use a large amount of teacher data to statistically evaluate the accuracy of each metric. The evaluation results reveal that S1 and SSIM have the highest accuracy in terms of both average and maximum scores. Their accuracy does not change even when non-ideal data are used as the teacher data. In addition, S1 and SSIM can reproduce the subjective resemblance between two maps better than EUC. However, EUC reproduces the central position of the signal in a sample case. This study can serve as a reference for identifying the most useful similarity metric for the classification of SLP patterns, especially when using non-ideal teacher data.

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  • Chiu Tung CHENG, Kentaroh SUZUKI
    Type: Articles
    Article ID: 2021-031
    Published: 2021
    [Advance publication] Released: February 18, 2021
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    J-STAGE Data Supplementary material

     The transport and removal processes of aerosol particles, as well as their potential impacts on clouds and climate, are strongly dependent on the particle sizes. Recent advances in computational capabilities enable us to develop sectional aerosol schemes for general circulation models and chemical transport models. The sectional aerosol modeling framework provides a capacity to explicitly simulate the variations in size distributions due to microphysical processes such as nucleation and coagulation, based on the mechanisms suggested from laboratory studies and field observations. Here, we develop a two-moment sectional aerosol scheme for Spectral Radiation-Transport Model for Aerosol Species (SPRINTARS-bin) for use in NICAM (Nonhydrostatic ICosahedral Atmospheric Model) as an alternative to the original mass-based (single-moment) SPRINTARS-orig aerosol module. NICAM-SPRINTARS is a seamless multiscale model that has been used for regional-to-global simulations of different resolutions based on the same model framework. In this study, we performed global simulations with NICAM-SPRINTARS-bin at typical climate model resolution (Δx ∼ 230 km) with nudging to a meteorological re-analysis. We compared our results with equivalent simulations for the original model (NICAM-SPRINTARS-orig) and observations including 500 nm aerosol optical depth and 440-870 nm Angstrom Exponent in AErosol RObotic NETwork (AERONET) measurements, particle number concentrations measured at Global Atmospheric Watch (GAW) sites and size-resolved number concentrations measured at European Supersites for Atmospheric Aerosol Research (EUSAAR) and German Ultrafine Aerosol Network (GUAN) sites. We found that compared to NICAM-SPRINTARS-orig, NICAM-SPRINTARS-bin demonstrates the long-range transport of ultra-fine particles to high latitudes and predicts higher Angstrom Exponent and total number concentrations that better agrees with observations. The latter underscores the importance of resolving the microphysical processes that determine concentrations of ultra-fine aerosol particles and explicitly represent size-dependent deposition in predicting these properties. However, number concentrations of coarse particles are still underestimated by both the original mass-based and the new microphysical schemes. Further efforts are needed to understand the reasons for the differences with the observed size distributions, including testing different emission and secondary organic aerosol production schemes, incorporating inter-species coagulation and black carbon aging, as well as performing simulations with higher spatial resolutions.

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  • Jinjie SONG, Philip J. KLOTZBACH, Yihong DUAN
    Type: Article
    Article ID: 2021-051
    Published: 2021
    [Advance publication] Released: April 27, 2021
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     This study shows that the impact of El Niño-Southern Oscillation (ENSO) Modoki on boreal summer tropical cyclone (TC) formation over the western North Pacific (WNP) has experienced decadal changes during the past few decades. The correlation between the ENSO Modoki index (EMI) and TC frequency over the WNP is weak between 1975-1989, becomes strong and significant between 1990-2004, and becomes weak again between 2005-2019. Over the eastern part of the WNP, ENSO Modoki enhanced TC formation during 1990-2004 but did not significantly impact on the TC formation during 1975-1989 and 2005-2019. The difference in correlation strength primarily results from changes in large-scale features related to ENSO Modoki among the three sub-periods (1975-1989, 1990-2004 and 2005-2019). El Niño Modoki from 1990-2004 was characterized by a tripole SST pattern with maximum SST anomalies in the equatorial central Pacific, while from 1975-1989 and 2005-2019, the maximum SST anomalies were located over the subtropical northeastern Pacific. The two primary environmental variables likely leading to these observed relationships between ENSO Modoki and TCs were mid-level moisture (RH600) and low-level vorticity (VOR850). From 1990-2004, TC formation was enhanced both south of 20°N and north of 20°N. The increase in TC activity during El Niño Modoki south of 20°N was likely tied to greater RH600 and north of 20°N to larger cyclonic VOR850. In contrast, ENSO Modoki's impacts on both VOR850 and RH600 were weak from 1975-1989 and 2005-2019.

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  • Kensuke K. KOMATSU, Yoshihiro IIJIMA, Yuki KANEKO, Dambaravjaa OYUNBAA ...
    Type: Article : Special Edition on Global Precipitation Measurement (GPM): 5th Anniversary
    Article ID: 2021-048
    Published: 2021
    [Advance publication] Released: April 20, 2021
    JOURNALS OPEN ACCESS ADVANCE PUBLICATION

     This paper focuses on the uncertainty of summer precipitation estimations produced by Global Satellite Mapping of Precipitation (GSMaP) over Mongolia, a region that has complex terrain and sparse weather observation networks. We first compared average summer precipitation over Mongolian territory as reported by several precipitation products. Although the interannual variability of the product was comparable, the amount of recorded precipitation differed among the various products. The rain-gauge-based analysis reported the lowest amount of precipitation, while the satellite-based GSMaP_MVK reported the highest amount. Our results represent a first estimate of the characteristic differences among the various precipitation-monitoring products, including GPM-based products, as they relate to climatic and hydro-meteorological assessments in Mongolia. We then made a detailed comparison using a case study in which a heavy rainfall event was captured by the Global Precipitation Measurement (GPM) mission's core observatory near Ulaanbaatar in July 2016. In this case, gauged and ungauged GSMaP estimates of the precipitation over the mountain area differed substantially between algorithm versions 6 and 7. An intercomparison of atmospheric numerical modeling, the GPM core observatory, and rain gauge observation showed that the rain gauge calibration of GSMaP effectively moderates the large error of the ungauged GSMaP data. The source of the significant ungauged GSMaP error is likely to be the rain rate estimates in version 7 of the algorithm. However, GSMaP gauge-calibrated estimates of the precipitation over mountainous areas may be affected by a potential underestimation of gauge analysis due to the missing localized precipitation occurring in the large gaps of the routine observation network. We expect that these findings will be helpful for developers seeking to further improve the GSMaP algorithm.

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  • Ying-Jhang WU, Yu-Chieng LIOU, Yi-Chuan LO, Sheng-Lun TAI, Shao-Fan CH ...
    Type: Article
    Article ID: 2021-049
    Published: 2021
    [Advance publication] Released: April 20, 2021
    JOURNALS OPEN ACCESS ADVANCE PUBLICATION

     The evolution of a heavy rainfall event occurred on 19 August 2014 in northern Taiwan is investigated with observed data and analyses from a newly-developed system named IBM_VDRAS, which is based on a four-dimensional Variational Doppler Radar Assimilation System (VDRAS) with the capability to assimilate radar observations and surface station data over a complex terrain by adopting the Immersed Boundary Method (IBM). This event possesses different precipitating processes and track from those frequently observed in that region.

     From the surface observations and the high spatiotemporal resolution analysis fields generated by IBM_VDRAS, it is found that the rainfall process started with the initiation of two individual convective cells triggered through the interaction between land-sea breeze and terrain in two different cities (Taoyuan and Taipei). The outflow of one of the convective cells developed in Taoyuan City at an earlier time merged with another convective system which grew in Taipei Basin, and provided favorable conditions to intensify the latter. The enhanced major convective cell moved into the Taipei City metropolitan area and produced 80 mm of precipitation within approximately 2.5 h. The kinematic, thermodynamic, and microphysical fields of the convective cells are analyzed in details to explain the mechanisms which helped to maintain the structure of the rainfall system. Sensitivity experiments of quantitative precipitation forecast (QPF) show that the terrains prevent the location of major rainfall from shifting outside of Taipei Basin. By assimilating surface data, the model can better predict the position of the rainfall.

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  • Hien X. BUI, Jia-Yuh YU
    Type: Article
    Article ID: 2021-039
    Published: 2021
    [Advance publication] Released: April 08, 2021
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    Supplementary material

     In this study, we examine the resolution dependence of the convective spectrum in Community Atmospheric Model version 5 (CAM5) simulations, focusing on the transition from shallow to deep convection and the associated cloud-radiative effect (CRE) change. We first apply the bin method (percentile binning) on precipitation intensity to obtain the convective spectrum in the tropics. The same approach is also used in the column-integrated moist static energy (MSE) budget analysis. The binning results show that over the light-rain regime, the convective structure is dominated by shallow convection, functioning to destabilize the atmosphere by importing column-integrated MSE. The heavy-rain regime shows the coexistence of deep and shallow convection, which inclines to stabilize the atmosphere by exporting the column-integrated MSE. Moreover, we also note that the longwave (LW) component of CRE (LWCRE) is more sensitive to the change of model spatial resolution than the shortwave (SW) component of CRE (SWCRE), characterized by a stronger response in the coarser resolution run over the heavy-rain regime. The resolution dependence of convective spectrum and CRE changes presented in this study highlights the importance of scale-aware cumulus parameterization design in climate models, which is not yet implemented in CAM5.

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  • Hidetaka HIRATA, Ryuichi KAWAMURA, Masami NONAKA, Kazuhisa TSUBOKI
    Type: Article
    Article ID: 2021-043
    Published: 2021
    [Advance publication] Released: March 25, 2021
    JOURNALS OPEN ACCESS ADVANCE PUBLICATION

     This study examined the roles of heat fluxes from the Kuroshio Current in enhancing a frontal convective rainband associated with an extratropical cyclone that brought record-breaking heavy rainfall to Miyake Island, Japan, in January 2017. A simulation of the rainband (control experiment) and sensitivity experiments without the sensible and latent heat fluxes from the Kuroshio Current were conducted using a regional cloud-resolving model. The rainband developed along a non-classic front (outer front), which formed to the north of a warm front associated with the cyclone. The control experiment reproduced the intensity and migration of the rainband well. As the rainband developed, the heat fluxes from the Kuroshio Current became evident around the cold conveyor belt of the cyclone to the south of the rainband. The latent heat fluxes were ~2.3 times larger than the sensible heat fluxes. Comparisons between the control and sensitivity experiments demonstrated that the heat fluxes, especially the latent heat fluxes, enhanced the rainband. The sensible heat fluxes slightly intensified convective instability in the lower troposphere, whereas the latent heat fluxes significantly increased the near-surface moisture content and the convective instability. A frontal updraft along the outer front released the increased convective instability, which intensified the moisture convergence, condensation, and updraft, enhancing the rainband. The findings show that the heat fluxes from the Kuroshio Current, especially the latent heat fluxes, enhanced the heavy rainfall-producing rainband by increasing the moisture content and the convective instability.

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  • Kazuyoshi KIKUCHI
    Type: Review Article
    Article ID: 2021-045
    Published: 2021
    [Advance publication] Released: March 30, 2021
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     The boreal summer intraseasonal oscillation (BSISO) is among the most pronounced subseasonal variability in the tropics during boreal summer. Compared to its wintertime counterpart, the so-called Madden-Julian oscillation (MJO), the BSISO convection displays more complicated spatio-temporal evolution, characterized by northward propagation over the northern Indian Ocean and western North Pacific as well as eastward propagation along the equator. It exerts a strong influence on a broad range of tropical weather and climate phenomena such as tropical cyclogenesis, monsoon onset and active/break cycles, among others. Our fundamental understanding of the BSISO has steadily advanced: so far various aspects of the BSISO have been described and several theories aiming to explain its northward propagation have been proposed. Yet, our skill to simulate the BSISO by general circulation models remains unsatisfactory, though it has been improved. This paper reviews some fundamental aspects of the BSISO from the viewpoint of observation, theory, and modeling.

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  • Fang-Ching CHIEN, Yen-Chao CHIU, Chih-Hua TSOU
    Type: Article
    Article ID: 2021-044
    Published: 2021
    [Advance publication] Released: March 25, 2021
    JOURNALS OPEN ACCESS ADVANCE PUBLICATION

     This paper examined southwesterly flows and rainfall around the Taiwan area during the mei-yu seasons from 1979 to 2018. The occurrence percentage of the southwesterly flow events in southern Taiwan was highly correlated with 6-h accumulated rainfall and heavy precipitation in Taiwan, while those in northern Taiwan showed little correlation. Low pressure to the north of Taiwan and high pressure to the south exerted a large northward pressure gradient force across the Taiwan area, favoring the formation of southwesterly flows and rainfall in southern Taiwan. During an active year of southwesterly flow events, the Pacific high weakens and moisture is transported along two paths in the early mei-yu season: one from the Bay of Bengal and the other from the south of the Pacific high. The moisture-laden air results in high equivalent potential temperature near Taiwan, which in turn creates a large equivalent potential temperature gradient to the north of Taiwan. This setting favors the activity of mei-yu fronts and produces a low pressure environment. The pressure gradient thus increases, supporting the formation of southwesterly flows. The southwesterly flows then help to transport more moisture toward the Taiwan area, resulting in heavy rainfall as well as a further increase of equivalent potential temperature. This kind of positive feedback produces more fronts, stronger southwesterly flows, and heavier rainfall during the mei-yu season. The study also suggests that the meridional component of vertically integrated water vapor transport over the South China Sea and the Philippines in the early mei-yu season can be used to predict the occurrence of southwesterly flows and heavy rain for the entire mei-yu season.

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  • Peter HAYNES, Peter HITCHCOCK, Matthew HITCHMAN, Shigeo YODEN, Harry H ...
    Type: Review Article
    Article ID: 2021-040
    Published: 2021
    [Advance publication] Released: March 24, 2021
    JOURNALS OPEN ACCESS ADVANCE PUBLICATION

     Observational and model studies suggest that the stratosphere exerts a significant influence on the tropical troposphere. The corresponding influence, through dynamical coupling, of the stratosphere on the extratropical troposphere has over the last 15-20 years been intensively investigated, with consequent improvement in scientific understanding which is already being exploited by weather forecasting and climate prediction centres. The coupling requires both communication of dynamical effects from stratosphere to troposphere and feedbacks within the troposphere which enhance the tropospheric response. Scientific understanding of the influence of the stratosphere on the tropical troposphere is far less developed. This review summarises the current observational and modelling evidence for that influence, on timescales ranging from diurnal to centennial. The current understanding of potentially relevant mechanisms for communication and for feedbacks within the tropical troposphere and the possible implications of the coupling for weather and climate prediction are discussed. These include opportunities for model validation and for improved subseasonal and seasonal forecasting and the effects, for example, of changes in stratospheric ozone and of potential geoengineering approaches. Outstanding scientific questions are identified and future needs for observational and modelling work to resolve these questions are suggested.

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  • Brian MAPES
    Type: Review Article
    Article ID: 2021-041
    Published: 2021
    [Advance publication] Released: March 24, 2021
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     Mesoscale patterns in atmospheric convection (between the inner scale of convecting-layer depth and the outer scales of domain constraints) are fascinating and ubiquitous. This review asks whether some aspects of that form (normalized for a given amount of convective activity) play a meaningful role or function in the total flow, especially in its more-predictable larger scales. Do some mesoscale features deserve to be called organization in its stronge sense, acting like multi-cellular organs in an organism? After enumerating hypotheses from null (mesoscale arrangement doesn't matter) to various detailed ideas (rectification of nonlinear processes with spatial agglomeration, size-dependent top-heaviness of heating, vertical momentum flux effects, adjustment roles, and the character of stochastic noise), a tabular framework for categorizing form-function research is offered. Function measures are divided into micro (mere quantification of budget terms averaged over mesoscale patches) vs. macro (roles played through time in larger-scale phenomena). Tools and approaches are arrayed from literal and explicit (case observations) to conceptualized (models, ranging from theory to numerical to statistical depictions), on timelines both historical (contacting case observations in some way) and synthetic (theory, simulation, and composites). Efforts are further distinguished by whether their inferences are associative (derived from conditional sampling of either form or function) or causal (involving controlled experimentation). Literature examples are surveyed, albeit incompletely, and future research strategies are suggested across this tabular landscape or framework. One spotlighted result is an apparent internal optimum in the horizontal geometry continuum between isotropic horizontal two-dimensionality and horizontally one-dimensional squall lines. Form-function questions could help justify, orient, and capitalize scientifically on the field's costly multiscale activities (requiring both coverage and resolution) in both observational and modeling realms. Data assimilation is a motivating application, and also a potentially powerful research tool for achieving greater synthesis. An observant human sensibility remains crucial for discovering and interpreting form-function relationships, at the very least to design more salient algorithms in the age of big data and computing.

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  • Kazuto TAKEMURA, Hitoshi MUKOUGAWA, Shuhei MAEDA
    Type: Article
    Article ID: 2021-042
    Published: 2021
    [Advance publication] Released: March 22, 2021
    JOURNALS OPEN ACCESS ADVANCE PUBLICATION

     Future change of Rossby wave breaking (RWB) frequency over the middle North Pacific (MNP) in August and the related features of large-scale atmospheric circulation are examined using large-ensemble simulations of current and future climates with a global circulation model. Correlation analysis indicates that the RWB frequency over the MNP in the current climate can show a relationship to El-Niño Southern Oscillation as reanalysis. The RWB frequency in the future climate shows significant decreases over the MNP, compared to that in the current climate. The large-scale atmospheric circulation in the upper troposphere in the future climate indicates a significant weakening of the Asian summer monsoon circulation and the consequent southward shifted Asian jet. The decreased RWB frequency over the MNP is associated with the modulated Asian jet, through reduced diffluence and deceleration of the jet in the basic-state over the region. Rossby wave propagation over Eurasia and the North Pacific in mid-latitudes is also clearly reduced in the future climate, consistent with the decreased RWB frequency over the MNP. Correlation and histogram analyses of the current and future experiments indicate that the significantly decreased RWB frequency over the MNP is associated with significantly suppressed convective activities east of the Philippines in the future climate. The diagnosis using ω-equation further shows the dynamical impact of the decreased RWB frequency on the suppressed convective activities, through the weakened extension of the Mid-Pacific trough and the consequent weakening of dynamically induced ascent east of the Philippines.

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  • Yukie MORODA, Kazuhisa TSUBOKI, Shinsuke SATOH, Katsuhiro NAKAGAWA, To ...
    Type: Article
    Article ID: 2021-038
    Published: 2021
    [Advance publication] Released: March 16, 2021
    JOURNALS OPEN ACCESS ADVANCE PUBLICATION
    Supplementary material

     A phased array weather radar (PAWR) can complete one volume scan in 30 seconds, thus enabling us to obtain high spatiotemporal resolution echo intensities and wind fields of storms. Using its rapid scanning capability, we investigated the evolution of a convective storm in detail. To describe evolution of convective storms, we used the following definitions. The precipitation cell is defined as a three-dimensionally contiguous region of 40 dBZ or greater. The precipitation core is defined by a threshold of positive deviation greater than 7 dBZ, which is a difference from the average reflectivity during the mature stage of the cell. An updraft core is defined as an updraft region of 1 m s−1 or stronger at a height of 2 km.

     An isolated convective storm was observed by two PAWRs on 7 August 2015 in the Kinki District, western Japan. The storm was judged as a single cell, according to the above definition. We identified nine precipitation cores and five updraft cores within 49 minutes in the mature stage of the cell. A long-lasting updraft core and its branches moved southwestward or southeastward. Around these updraft cores, the precipitation cores were generated successively. The updraft core with the longest duration lasted 73.5 minutes; in contrast, the lifetimes of precipitation cores were from 4.5 to 14.5 minutes. The precipitation cell was maintained by the successive generations of updraft cores which lifted humid air associated with a low-level southwesterly inflow. The total amounts of water vapor inflow supplied by all the identified updraft cores were proportional to the volumes of the precipitation cell, with a correlation coefficient of 0.75. Thus, the extremely high spatiotemporal resolution of the PAWR observations provides us with new evidence that an isolated convective storm can be formed by multiple precipitation cores and updraft cores.

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  • Kenji NAKAMURA
    Type: Review Articles : Special Edition on Global Precipitation Measurement (GPM): 5th Anniversary
    Article ID: 2021-035
    Published: 2021
    [Advance publication] Released: March 12, 2021
    JOURNALS OPEN ACCESS ADVANCE PUBLICATION

     The Tropical Rainfall Measuring Mission (TRMM) satellite was launched in 1997 and the observations continued for more than 17 years. The features of TRMM observation were as follows: (a) it followed a non-sun synchronized orbit that enabled diurnal variation of precipitation to be investigated, (b) it carried a precipitation radar and microwave and infrared radiometers, along with two instruments of opportunity in the form of a lighting sensor and a radiation budget sensor, and (c) it worked as a standard reference for precipitation measurements for other spaceborne microwave radiometers, which enabled global rain maps to be developed. For science, TRMM provided precise and accurate rain distributions over tropical and subtropical regions. The rainfall results are primarily important for the study of the precipitation climatologies, while the three-dimensional images of precipitation systems enabled the study of the global characteristics of precipitation systems. Technologically, the spaceborne rain radar onboard TRMM demonstrated the effectiveness of radars in space, while the combination with other rain observation instruments showed its effectiveness as a calibration source. Multi-satellite rain maps in which TRMM was the reference standard have been developed, and they became prototypes of the multi-satellite Earth observation systems. Based on the great success of TRMM, the Global Precipitation Measurement (GPM) was designed to expand TRMM's coverage to higher latitudes. The core satellite of GPM is equipped with a dual frequency precipitation radar (DPR) and a microwave radiometer. DPR consists of a Ku-band radar (KuPR) and a Ka-band radar (KaPR) and has a capability to discriminate solid from liquid precipitation. The period of the precipitation measurement with spaceborne radars extended to more than 23 years which may make it possible to detect the change of precipitation climatology related to change in the global environment. While TRMM's and GPM's accomplishments are very broad, this paper tries to highlight Japan's contributions to the science of these missions.

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  • Yoshinori YAMADA
    Type: Notes and Correspondence
    Article ID: 2021-036
    Published: 2021
    [Advance publication] Released: March 12, 2021
    JOURNALS OPEN ACCESS ADVANCE PUBLICATION

     This paper presents an efficient, practical post-processing algorithm for the quality control of dual-pulse repetition frequency (dual-PRF) Doppler velocity data observed in Plan Position Indicator (PPI) mode. Quality control refers to the enhancement of the quality of the Doppler velocities through the re-assignment of an appropriate Nyquist interval number to an erroneous velocity datum and the elimination of unreliable data. The proposed algorithm relies on the local continuity of velocity data, as do most of the preexisting algorithms. Its uniqueness, however, lies both in the preparation of more reliable reference velocity data and its applicability to PPI data at higher elevation angles. The performance of the proposed algorithm is highlighted by its application to observed data from C- and X-band Doppler radars. This algorithm is practical, efficient, and not time consuming. It may be of great help in the derivation of accurate wind information from dual-PRF Doppler velocities.

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  • Prashant KUMAR, Rakesh GAIROLA, Takuji KUBOTA, Chandra KISHTAWAL
    Type: Articles : Special Edition on Global Precipitation Measurement (GPM): 5th Anniversary
    Article ID: 2021-037
    Published: 2021
    [Advance publication] Released: March 12, 2021
    JOURNALS OPEN ACCESS ADVANCE PUBLICATION

     Accurate rainfall estimation during Indian summer monsoon (ISM) is one of the most crucial activities in and around the Indian Sub-continent. Japan Aerospace Exploration Agency (JAXA) provides a couple of Global Satellite Mapping of Precipitation (GSMaP) rainfall products viz. the GSMaP_MVK, which is a satellite based product calculated with ancillary data including global objective analysis data, and the GSMaP_Gauge, which is adjusted by global rain gauges. In this study, the daily rainfall amount from the GSMaP rainfall product (version 7) is validated against a dense rain gauge network over Karnataka, one of southwestern states of India, during ISM 2016–2018. Further, as the primary objective, these dense rain gauge observations are assimilated in the GSMaP rainfall product using hybrid assimilation method to improve the final rainfall estimate. The hybrid assimilation method is a combination of two-dimensional variational (2D-Var) method and Kalman filter, in which 2D-Var method is used to merge rain gauge observations and Kalman filter is used to update background error in the 2D-Var method. Preliminary verification results suggest that GSMaP_Gauge rainfall has sufficient skill over north interior Karnataka (NIK) and south interior Karnataka (SIK) regions, with large errors over the orographic heavy rainfall region of the Western Ghats. These errors are larger in the GSMaP_MVK rainfall product over orographic heavy rainfall regions. Hybrid assimilation results of randomly selected rain gauge observations improve the skill of GSMaP_Gauge and GSMaP_MVK rainfall products, when compared with independent rain gauges observations. These improvements in daily rainfall are more prominent over orographic heavy rainfall regions. GSMaP_MVK rainfall product shows larger improvement due to absence of the gauge adjustment in the JAXA operational processing. The superiority of hybrid assimilation method against Cressman and optimal interpolation methods for impacts of utilized rain gauge numbers are also presented in this study.

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  • Takahisa KOBAYASHI, Mitsuharu NOMURA, Ahoro ADACHI, Soichiro SUGIMOTO, ...
    Type: Articles : Special Edition on Global Precipitation Measurement (GPM): 5th Anniversary
    Article ID: 2021-030
    Published: 2021
    [Advance publication] Released: February 24, 2021
    JOURNALS OPEN ACCESS ADVANCE PUBLICATION

     A new method that retrieves attenuation profiles using a Dual-Frequency Precipitation Radar (DPR) equipped on the Global Precipitation Mission (GPM) is proposed. The DPR operates at Ka and Ku-bands and provides profiles of a differential frequency ratio, which is the difference of the measured or attenuated reflectivity in decibel scale between Ka and Ku bands. For accurate measurements of precipitation, hydrometeor classification is essential. Attenuation of radio wave due to precipitation is closely related to microphysical properties and available for hydrometeor classification. The proposed method estimates range variations of relative values of differential attenuation between two frequencies and can be used for identifying hydrometeor types along the radar propagation path. Numerical simulations indicate that the proposed method performs well for rain, melted snow, mixed-phase precipitation, and some cases of the melting layer. The method was also evaluated for GPM DPR measurements. Results indicate that the method works well for identifying rain and snow and also provides useful information for melting layer detection and attenuation, even for the melting layer in which no enhancement of reflectivity is observed.

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  • Kumiko TAKATA, Naota HANASAKI
    Type: Notes and Correspondence
    Article ID: 2021-034
    Published: 2021
    [Advance publication] Released: February 22, 2021
    JOURNALS OPEN ACCESS ADVANCE PUBLICATION

     The Minimal Advanced Treatments of Surface Interaction and RunOff (MATSIRO), which has been used as a land-surface scheme in the global climate model, the Model for Interdisciplinary Research On Climate (MIROC), calculates Dunne runoff and base runoff using the TOPography-based MODEL (TOPMODEL). In past experiments that used MATSIRO, the runoff and its response to precipitation were too low compared to observation. We conjectured that those biases could be attributed to the water table's excessive depth. Its depth was diagnosed based on grid-mean soil moisture, using a saturation threshold that was originally set to almost equal the porosity. In this study, sensitivity experiments, in which the threshold was decreased to 75 %, 50 %, 25 %, and less than 13 % of the porosity, were conducted, and the subsequent effects on river flow were investigated in the Chao Phraya River basin, Thailand, as a case study. As a result, both Dunne and base runoff increased along with the response of river flow to precipitation. The simulated river flow matched observations most closely with the threshold of 50 % saturation. In addition, soil moisture and the Bowen ratio also changed significantly with the runoff changes induced by the threshold changes. These results suggested the importance of the relationship between grid-mean soil moisture and groundwater level for TOPMODEL. Preliminary global experiments indicate that the runoff sensitivity might be dependent on climate zone.

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  • Moeka YAMAJI, Takuji KUBOTA, Munehisa K. YAMAMOTO
    Type: Notes and Correspondence: Special Edition on Global Precipitation Measurement (GPM): 5th Anniversary
    Article ID: 2021-033
    Published: 2021
    [Advance publication] Released: February 17, 2021
    JOURNALS OPEN ACCESS ADVANCE PUBLICATION
    Supplementary material

     Reliability information of satellite precipitation products is required for various applications. This study describes and evaluates a reliability flag of the Global Satellite Mapping of Precipitation Near-Real-Time precipitation product (GSMaP_NRT). This flag was developed to characterize the reliability of GSMaP_NRT data simply and qualitatively by considering its algorithm characteristics. The reliability at each pixel is represented by any one of ten levels (10 being the best and 1 the worst) by considering three major factors: 1) “surface type reliability”—which takes into account that estimation of rainfall using passive microwave sensors is better over the oceans than over land and coastal areas; 2) “low-temperature reliability”—which takes into account the lower reliability due to surface snow cover in low-temperature conditions; and 3) “Moving Vector with Kalman Filter (MVK) propagation reliability”—which means that the reliability gets worse with the increase in time since the last overpass of the passive microwave sensor.

     To evaluate the utility of the reliability flag, statistical indices are calculated for each reliability level using gauge-calibrated ground radar data around Japan. It is found that the reliability flag represents the differences in GSMaP accuracy: the accuracy worsens as the reliability decreases. The GSMaP errors exhibit seasonal changes that are well represented by the ten levels of the reliability flag, indicating that the reliability flag can be used to catch seasonal variations in GSMaP accuracy due to changes in environmental factors.

     This study also raises the possibility of improving the reliability flag by using information related to heavy orographic rainfall. It is shown how the error features of heavy orographic rainfall differ from those of the total rainfall, and it is suggested that heavy orographic rainfall information can be utilized to further improve the reliability flag.

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  • Falko JUDT, Daniel KLOCKE, Rosimar RIOS-BERRIOS, Benoit VANNIERE, Flor ...
    Type: Articles : Special Edition on DYAMOND: The DYnamics of the Atmospheric general circulation Modeled On Non-hydrostatic Domains
    Article ID: 2021-029
    Published: 2021
    [Advance publication] Released: January 21, 2021
    JOURNALS OPEN ACCESS ADVANCE PUBLICATION

     Recent progress in computing and model development has initiated the era of global storm-resolving modeling and with it the potential to transform weather and climate prediction. Within the general theme of vetting this new class of models, the present study evaluates nine global-storm resolving models in their ability to simulate tropical cyclones (TCs). Results show that, broadly speaking, the models produce realistic TCs and remove longstanding issues known from global models such as the deficiency to accurately simulate TC intensity. However, TCs are strongly affected by model formulation, and all models suffer from unique biases regarding the number of TCs, intensity, size, and structure. Some models simulated TCs better than others, but no single model was superior in every way. The overall results indicate that global storm-resolving models are able to open a new chapter in TC prediction, but they need to be improved to unleash their full potential.

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  • Ye CUI, Zheng RUAN, Ming WEI, Feng LI, Runsheng GE, Yong HUANG
    Type: Articles
    Article ID: 2021-032
    Published: 2021
    [Advance publication] Released: January 21, 2021
    JOURNALS OPEN ACCESS ADVANCE PUBLICATION

     This study applied the C-band vertically pointing radar with frequency-modulation continuous-wave technology to obtain the continuous observation data of four shallow and two deep snow events during the winter of 2015-2016 in the midlatitudes of China. Generating cells (GCs) were found near the echo tops in every event. The ice particle number concentration (N), ice water content (IWC), and median mass diameter (Dm) retrieved from radar Doppler spectra were used to analyze the microphysical properties in the snow clouds. The clouds were divided into upper GC and lower stratiform (St) regions according to their vertical structure. The fall streaks (FSs) associated with GCs were embedded in the St regions. In the GC regions, the N values in shallow events were smaller compared with deep events, while Dm and IWC were larger. In the St regions, N decreased compared with the GC regions, while the Dm and IWC increased, implying the existence of aggregation and deposition growth. The growth of particle size and mass mainly occurred in the St regions. The increases of N were usually observed near −5°C accompanied by bimodal Doppler spectra, which might be caused by ice multiplication. The average ratios of the median N, Dm, and IWC inside GCs to those outside GCs are 2, 1.3, and 2.5 respectively for shallow events, with 1.7, 1.2, and 2.3 respectively for deep events. These values were basically the same as those for the FSs, implying the importance of GCs to the enhanced ice growth subsequently found in FSs. The larger values of N, Dm, and IWC inside GCs could be related to the upward air motions inside GCs. The first Ze–IWC relationship suitable for snow clouds in the midlatitudes of China was also established.

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