著者
Seiji YUKIMOTO Yukimasa ADACHI Masahiro HOSAKA Tomonori SAKAMI Hiromasa YOSHIMURA Mikitoshi HIRABARA Taichu Y. TANAKA Eiki SHINDO Hiroyuki TSUJINO Makoto DEUSHI Ryo MIZUTA Shoukichi YABU Atsushi OBATA Hideyuki NAKANO Tsuyoshi KOSHIRO Tomoaki OSE Akio KITOH
出版者
Meteorological Society of Japan
雑誌
気象集誌. 第2輯 (ISSN:00261165)
巻号頁・発行日
vol.90A, pp.23-64, 2012 (Released:2012-06-07)
参考文献数
157
被引用文献数
354 362

A new global climate model, MRI-CGCM3, has been developed at the Meteorological Research Institute (MRI). This model is an overall upgrade of MRI’s former climate model MRI-CGCM2 series. MRI-CGCM3 is composed of atmosphere-land, aerosol, and ocean-ice models, and is a subset of the MRI’s earth system model MRI-ESM1. Atmospheric component MRI-AGCM3 is interactively coupled with aerosol model to represent direct and indirect effects of aerosols with a new cloud microphysics scheme. Basic experiments for pre-industrial control, historical and climate sensitivity are performed with MRI-CGCM3. In the pre-industrial control experiment, the model exhibits very stable behavior without climatic drifts, at least in the radiation budget, the temperature near the surface and the major indices of ocean circulations. The sea surface temperature (SST) drift is sufficiently small, while there is a 1 W m-2 heating imbalance at the surface. The model’s climate sensitivity is estimated to be 2.11 K with Gregory’s method. The transient climate response (TCR) to 1 % yr-1 increase of carbon dioxide (CO2) concentration is 1.6 K with doubling of CO2 concentration and 4.1 K with quadrupling of CO2 concentration. The simulated present-day mean climate in the historical experiment is evaluated by comparison with observations, including reanalysis. The model reproduces the overall mean climate, including seasonal variation in various aspects in the atmosphere and the oceans. Variability in the simulated climate is also evaluated and is found to be realistic, including El Niño and Southern Oscillation and the Arctic and Antarctic oscillations. However, some important issues are identified. The simulated SST indicates generally cold bias in the Northern Hemisphere (NH) and warm bias in the Southern Hemisphere (SH), and the simulated sea ice expands excessively in the North Atlantic in winter. A double ITCZ also appears in the tropical Pacific, particularly in the austral summer.
著者
村松 照男
出版者
Meteorological Society of Japan
雑誌
気象集誌. 第2輯 (ISSN:00261165)
巻号頁・発行日
vol.64, no.2, pp.259-272, 1986 (Released:2007-10-19)
参考文献数
17
被引用文献数
13 14

レーダーと衛星で決定した台風眼(T8019, WYNNE)の移動軌跡上にトロコイダル運動による顕著な周期変動が観測された。周期は5~8時間,最大振幅は23kmであった。周期の減少とともに振幅も減少した。レーダーエコーの解析の結果,台風眼の中心は台風系全体の中心とは一致せず,約20km偏位し系の中心に対し反時計回りに回転していることが明らかとなった。この間,外側と内側の eye wal1の直径が各々260kmと30kmである二重眼構造と,それに対応する風速分布の二重極大が観測された。特に,気圧と風速場で楕円状の循環が見られ,その結果としての矩形状エコー構造が外側 eye wal1の内側で観測された。この矩形と楕円状循環は台風系の中心に対しトロコイダル周期と同周期で,外側 eye wal1に内接しながら回転していた。台風眼は楕円の一方の焦点を追うように移動し,この結果としてトロコイダル軌跡となった。しかしながら,なぜ眼が系の中心から偏れるのかはまだ明らかとなっていない。
著者
ITO Kosuke WU Chun-Chieh CHAN Kelvin T. F. TOUMI Ralf DAVIS Chris
出版者
Meteorological Society of Japan
雑誌
気象集誌. 第2輯 (ISSN:00261165)
巻号頁・発行日
pp.2020-001, (Released:2019-10-08)

While the fundamental understanding of the movement of a tropical cyclone (TC) is fairly mature, there are still notable advancements being made. This paper summarizes new concepts and updates on existing fundamental theories on TC movement obtained from simplified barotropic models, full-physics models, and data analysis particularly since 2014. It includes the recent works on the interaction of the TC with its environment and the fundamental aspects of predictability related to TC movement. The conventional concepts of the steering flow, β-gyre, and diabatic heating remain important. Yet, a more complete understanding of mechanisms governing TC movement serves as an important basis toward the further improvement of track forecasts.
著者
Shinya KOBAYASHI Yukinari OTA Yayoi HARADA Ayataka EBITA Masami MORIYA Hirokatsu ONODA Kazutoshi ONOGI Hirotaka KAMAHORI Chiaki KOBAYASHI Hirokazu ENDO Kengo MIYAOKA Kiyotoshi TAKAHASHI
出版者
(公社)日本気象学会
雑誌
気象集誌. 第2輯 (ISSN:00261165)
巻号頁・発行日
vol.93, no.1, pp.5-48, 2015 (Released:2015-03-18)
参考文献数
128
被引用文献数
213 1198

The Japan Meteorological Agency (JMA) conducted the second Japanese global atmospheric reanalysis, called the Japanese 55-year Reanalysis or JRA-55. It covers the period from 1958, when regular radiosonde observations began on a global basis. JRA-55 is the first comprehensive reanalysis that has covered the last half-century since the European Centre for Medium-Range Weather Forecasts 45-year Reanalysis (ERA-40), and is the first one to apply four-dimensional variational analysis to this period. The main objectives of JRA-55 were to address issues found in previous reanalyses and to produce a comprehensive atmospheric dataset suitable for studying multidecadal variability and climate change. This paper describes the observations, data assimilation system, and forecast model used to produce JRA-55 as well as the basic characteristics of the JRA-55 product. JRA-55 has been produced with the TL319 version of JMA’s operational data assimilation system as of December 2009, which was extensively improved since the Japanese 25-year Reanalysis (JRA-25). It also uses several newly available and improved past observations. The resulting reanalysis products are considerably better than the JRA-25 product. Two major problems of JRA-25 were a cold bias in the lower stratosphere, which has been diminished, and a dry bias in the Amazon basin, which has been mitigated. The temporal consistency of temperature analysis has also been considerably improved compared to previous reanalysis products. Our initial quality evaluation revealed problems such as a warm bias in the upper troposphere, large upward imbalance in the global mean net energy fluxes at the top of the atmosphere and at the surface, excessive precipitation over the tropics, and unrealistic trends in analyzed tropical cyclone strength. This paper also assesses the impacts of model biases and changes in the observing system, and mentions efforts to further investigate the representation of low-frequency variability and trends in JRA-55.
著者
SAITO Kazuo KUNII Masaru ARAKI Kentaro
出版者
Meteorological Society of Japan
雑誌
気象集誌. 第2輯 (ISSN:00261165)
巻号頁・発行日
pp.2018-027, (Released:2018-02-11)
被引用文献数
4

Local heavy rainfall of about 100 mm h-1 occurred in Tokyo and Kanagawa Prefecture on 26 August 2011. This rain was brought by a mesoscale convective system (MCS) that developed near a stationary front that slowly moved southward. In an analysis using geostationary multi-purpose satellite rapid scan images and dense automated weather station networks, development of the MCS occurred after the merging of sea breezes from the east (Kashima-nada) and the south (Tokyo Bay). Numerical experiments by the Japan Meteorological Agency (JMA) nonhydrostatic model (NHM) with horizontal resolutions of 10 km and 2 km using mesoscale 4D-VAR analysis of JMA for initial conditions tended to predict the position of intense rainfall areas west of observed positions. In the mesoscale ensemble forecast using perturbations from JMA’s one-week global ensemble prediction system (EPS) forecast, some ensemble members showed enhanced precipitation around Tokyo, but false precipitation areas appeared north of the Kanto and Hokuriku Districts. As an attempt to improve the model forecast, we modified the model, reducing the lower limit of subgrid deviation of water vapor condensation to diagnose the cloudiness for radiation. In the modified model simulation, surface temperatures around Tokyo increased by about 1°C and the position of the intense precipitation was improved, but the false precipitation areas in the Hokuriku District were also enhanced in the ensemble member which brought a better forecast than the control run. We also conducted ensemble prediction using a singular vector method based on NHM. One of the ensemble members unstabilized the lower atmosphere on the windward side of the Kanto District and suppressed the false precipitation in the Hokuriku District, and observed characteristics of the local heavy rainfall were well reproduced by NHM with a horizontal resolution of 2 km. A conceptual model of the initiation of deep convection by the formation of a low-level convergence zone succeeding merging of the two sea breezes from the east and south is proposed based on observations, previous studies, and numerical simulation results. In this event, the northerly ambient wind played an important role on the occurrence of the local heavy rainfall around Tokyo by suppressing the northward intrusion of the sea breeze from the south.
著者
Axel GABRIEL Dieter PETERS
出版者
(公社)日本気象学会
雑誌
気象集誌. 第2輯 (ISSN:00261165)
巻号頁・発行日
vol.86, no.5, pp.613-631, 2008 (Released:2008-11-13)
参考文献数
16
被引用文献数
19 32 26

The long-term behavior of Rossby wave breaking (RWB) events is investigated by a diagnosis separating in different asymmetric types of RWB, i.e., cyclonically sheared waves breaking predominantly pole-ward (P1) or equatorward (LC2) and anticyclonically sheared waves breaking predominantly poleward (P2) or equatorward (LC1). Generally, RWB can be identified by meridional overturning of potential vorticity (PV) on specific isentropes, but a separation in poleward or equatorward asymmetry is too difficult based on PV maps alone. For this paper, we use that northward or southward direction of the meridional wave flux component for quasi-stationary Rossby waves indicates cyclonically or anticyclonically sheared RWB. We demonstrate that the magnitude of the meridional wave fluxes gives a reliable measure of the asymmetric types of RWB when combining with PV diagnostics as well as with the geometry of large-scale diffluent/ confluent flow. Based on 45 winter periods of ECMWF Reanalysis (ERA-40), we found two pronounced regions for P1- and LC2-type events, over the northern North Pacific and the northern North Atlantic, and two extended belts of P2- and LC1-type RWB events, over the North Pacific/North America region and the North Atlantic/European-West Asian region. The results reveal that the long-term mean occurrence of poleward RWB is generally as large as that of equatorward RWB with local differences. Since poleward or equatorward RWB events influence different regions efficiently, e.g., by associated cut-off cyclones or anticyclones, the proposed diagnosis gives an important tool for interpreting long-term general circulation patterns and large-scale weather regimes.
著者
YAMAZAKI Akira HONDA Meiji KAWASE Hiroaki
出版者
Meteorological Society of Japan
雑誌
気象集誌. 第2輯 (ISSN:00261165)
巻号頁・発行日
pp.2019-012, (Released:2018-11-16)
被引用文献数
2

This study found that regional snowfall distributions in a Japan-Sea side area of Japan are controlled by intraseasonal jet variability, particularly the 10-day-timescale quasi-stationary Rossby waves across the Eurasian continent and the atmospheric blocking over the East Asian region. This study mainly focused on the Niigata area, which is representative of heavy snowfall areas in Japan. Based on previous studies, three types of dominant snowfall distributions were defined: 1) the plain (P) type, which is characterized by heavy snowfall events predominant in coastal regions of the Niigata area, 2) the mountain (M) type, which occurs in the mountainous regions, and 3) the PM type, which occurs across the whole Niigata area. Our results revealed that all distribution types were related to the south-ward shift of the westerly jet over Japan associated with an intensified trough, i.e., cyclonic anomalies, originating from quasi-stationary Rossby waves along westerly jets over Eurasia (Eurasian jets). The cyclonic anomalies were found to be also related to blocking cyclones because the frequency of blocking events considerably increased in the East Siberian region. The mechanisms leading to the trough intensification were different among the events of the three snowfall types. The formation of Siberian blocking with relatively different positions and different paths of quasi-stationary Rossby wave packet propagation along Eurasian jets were evident in the distribution types. Therefore, local-scale snowfall distributions in the Japan-Sea side area are determined by anomalous large-scale circulations, which can be evidently distinguished in the global reanalysis data.
著者
Youichi KAMAE Wei MEI Shang-Ping XIE
出版者
(公社)日本気象学会
雑誌
気象集誌. 第2輯 (ISSN:00261165)
巻号頁・発行日
vol.95, no.6, pp.411-431, 2017 (Released:2017-11-14)
参考文献数
76
被引用文献数
7

Eddy transport of atmospheric water vapor from the tropics is important for rainfall and related natural disasters in the middle latitudes. Atmospheric rivers (ARs), intense moisture plumes that are typically associated with extratropical cyclones, often produce heavy precipitation upon encountering topography on the west coasts of mid-latitude North America and Europe. ARs also occur over the northwestern Pacific and sometimes cause floods and landslides over East Asia, but the climatological relationship between ARs and heavy rainfall in this region remains unclear. Here we evaluate the contribution of ARs to the hydrological cycle over East Asia using high-resolution daily rainfall observations and an atmospheric reanalysis during 1958-2007. Despite their low occurrence, ARs account for 14-44 % of the total rainfall and 20-90 % of extreme heavy-rainfall events during spring, summer, and autumn. AR-related extreme rainfall is especially pronounced over western-to-southeastern slopes of terrains over the Korean Peninsula and Japan, owing to strong orographic effects and a stable direction of low-level moisture flows. A strong relationship between warm-season AR heavy rainfall and preceding-winter El Niño is identified since the 1970s, suggesting the potential of predicting heavy-rainfall risk over Korea and Japan at seasonal leads.
著者
Toshinori AOYAGI Nobuyuki KAYABA Naoko SEINO
出版者
(公社)日本気象学会
雑誌
気象集誌. 第2輯 (ISSN:00261165)
巻号頁・発行日
vol.90B, pp.11-31, 2012 (Released:2012-06-09)
参考文献数
32
被引用文献数
10 14 4

We investigated a warming trend in the Kanto-Koshin area during a 30-year period (1976-2006). The warming trends at AMeDAS stations were estimated to average a little less than 1.3°C/30 years in both summer and winter. These warming trends were considered to include the trends of large-scale and local-scale warming effects. Because a regional climate model with 20-km resolution without any urban parameterization could not well express the observed warming trends and their daily variations, we investigated whether a mesoscale atmospheric model with an urban canopy scheme could express them.To make the simulations realistic, we used 3 sets of real data: National Land Numerical Information datasets for the estimation of the land use area fractions, anthropogenic heat datasets varying in space and time, and GIS datasets of building shapes in the Tokyo Metropolis for the setting of building aspect ratios. The time integrations over 2 months were executed for both summer and winter. A certain level of correlation was found between the simulated temperature rises and the observed warming trends at the AMeDAS stations. The daily variation of the temperature rises in urban grids was higher at night than in the daytime, and its range was larger in winter than in summer. Such tendencies were consistent with the observational results.From factor analyses, we figured out the classic and some unexpected features of urban warming, as follows: (1) Land use distribution change (mainly caused by the decrease of vegetation cover) had the largest daytime warming effect, and the effect was larger in summer than in winter; (2) anthropogenic heat had a warming effect with 2 small peaks owing to the daily variation of the released heat and the timing of stable atmospheric layer formation; and (3) increased building height was the largest factor contributing to the temperature rises, with a single peak in early morning.
著者
HOHENEGGER Cathy KORNBLUEH Luis KLOCKE Daniel BECKER Tobias CIONI Guido ENGELS Jan Frederik SCHULZWEIDA Uwe STEVENS Bjorn
出版者
Meteorological Society of Japan
雑誌
気象集誌. 第2輯 (ISSN:00261165)
巻号頁・発行日
pp.2020-005, (Released:2019-11-10)

Basic climate statistics, such as water and energy budgets, location and width of the InterTropical Convergence Zone (ITCZ), trimodal tropical cloud distribution, position of the polar jet and land-sea contrast remain either biased in coarse-resolution General Circulation Models or are tuned. Here we examine the horizontal resolution dependency of such statistics in a set of global convection-permitting simulations integrated with the ICOsahedral Non-hydrostatic (ICON) model, explicit convection and grid spacings ranging from 80 km down to 2.5 km. The impact of resolution is quantified by comparing the resolution-induced differences to the spread obtained in an ensemble of eight distinct global storm-resolving models. Using this metric, we find that, at least by 5 km, the resolution-induced differences become smaller than the spread in 26 out of the 27 investigated statistics. Even for 9 (18) of these statistics, a grid spacing of 80 (10) km does not lead to significant differences. Resolution down to 5 km matters especially for net shortwave radiation, which systematically increases with resolution due to reductions in low cloud amount over the subtropical oceans. Further resolution dependencies can be found in the land-to-ocean precipitation ratio, in the latitudinal position and width of the Pacific ITCZ and in the longitudinal position of the Atlantic ITCZ. Also in the tropics, the deep convective cloud population systematically increases at the expense of the shallow one, whereas the partition of congestus clouds remains fairly constant. Finally, refining the grid spacing systematically moves the simulations closer to observations, but climate statistics exhibiting weaker resolution dependencies are not necessarily associated with smaller biases.
著者
UEDA Hiroaki MIWA Kana KAMAE Youichi
出版者
Meteorological Society of Japan
雑誌
気象集誌. 第2輯 (ISSN:00261165)
巻号頁・発行日
pp.2018-044, (Released:2018-05-14)
被引用文献数
2

The response of tropical cyclone (TC) activity to the El Niño-Southern Oscillation (ENSO) and coherent sea surface temperate (SST) anomaly in the Indian Ocean (IO) is investigated with a particular focus on the decaying phase of El Niño. The TC anomalies are obtained from the database for Policy Decision making for Future climate change (d4PDF). This dataset is based on 100-member ensemble simulations for the period of 1951-2010 by use of the state-of-the-art atmospheric general circulation model (AGCM) forced with observed SST as well as the historical radiative forcing. AGCM utilized in the d4PDF is the Meteorological Research Institute Atmospheric General Circulation Model with about 60km horizontal resolution. Our analysis reveals a prolonged decrease in TC frequency over the tropical western Pacific during the post El Niño years until the boreal fall. Dominance of anomalous anticyclone (AAC) over the western Pacific induced by the delayed warming in the tropical Indian Ocean is the main factor for the suppressed TC activity rather than the local SST change. In contrast, the TC number over the South China Sea tends to increase during the post-El Niño fall (September to November). The physical reason can be ascribed to the weakening of AAC associated with the termination of IO warming. Thus we demonstrate that the effect of the IO warming should be taken into account when the ENSO is considered as an environmental factor for predicting TC activity.
著者
Hironobu IWABUCHI Nurfiena Sagita PUTRI Masanori SAITO Yuka TOKORO Miho SEKIGUCHI Ping YANG Bryan A. BAUM
出版者
Meteorological Society of Japan
雑誌
気象集誌. 第2輯 (ISSN:00261165)
巻号頁・発行日
vol.96B, pp.27-42, 2018 (Released:2018-03-16)
参考文献数
35
被引用文献数
9

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.
著者
YUKIMOTO Seiji KAWAI Hideaki KOSHIRO Tsuyoshi OSHIMA Naga YOSHIDA Kohei URAKAWA Shogo TSUJINO Hiroyuki DEUSHI Makoto TANAKA Taichu HOSAKA Masahiro YABU Shokichi YOSHIMURA Hiromasa SHINDO Eiki MIZUTA Ryo OBATA Atsushi ADACHI Yukimasa ISHII Masayoshi
出版者
Meteorological Society of Japan
雑誌
気象集誌. 第2輯 (ISSN:00261165)
巻号頁・発行日
pp.2019-051, (Released:2019-06-18)
被引用文献数
4

The new Meteorological Research Institute Earth System Model version 2.0 (MRI-ESM2.0) has been developed based on previous models, MRI-CGCM3 and MRI-ESM1, which participated in the fifth phase of the Coupled Model Intercomparison Project (CMIP5). These models underwent numerous improvements meant for highly accurate climate reproducibility. This paper describes model formulation updates and evaluates basic performance of its physical components. The new model has nominal horizontal resolutions of 100 km for atmosphere and ocean components, similar to the previous models. The atmospheric vertical resolution is 80 layers which is enhanced from 48 layers of its predecessor. Accumulation of various improvements concerning clouds, such as a new stratocumulus cloud scheme, led to remarkable reduction in errors in shortwave, longwave, and net radiation at the top of the atmosphere. The resulting errors are sufficiently small compared with those in the CMIP5 models. The improved radiation distribution brings the accurate meridional heat transport required for the ocean and contributes to a reduced surface air temperature (SAT) bias. MRI-ESM2.0 displays realistic reproduction of both mean climate and interannual variability. For instance, the stratospheric quasi-biennial oscillation can now be realistically expressed through the enhanced vertical resolution and introduction of non-orographic gravity wave drag parameterization. For the historical experiment, MRI-ESM2.0 reasonably reproduces global SAT change for recent decades; however, cooling in the 1950s through the 1960s and warming afterward are overestimated compared with observations. MRI-ESM2.0 has been improved in many aspects over the previous models, MRI-CGCM3/MRI-ESM1, and is expected to demonstrate superior performance in many experiments planned for CMIP6.
著者
SEO Jaemyeong Mango LEE Hyunho MOON Sungju BAIK Jong-Jin
出版者
Meteorological Society of Japan
雑誌
気象集誌. 第2輯 (ISSN:00261165)
巻号頁・発行日
pp.2020-003, (Released:2019-10-20)

This study examines how upslope geometry controls aerosol effects on orographic precipitation through two-dimensional idealized simulations of orographic precipitation from shallow warm convective clouds over a bell-shaped mountain with 1-km height. A total of nine cases are simulated by considering three different prescribed aerosol number concentrations and three different windward-widths of the mountain. For a detailed representation of drop size distributions, the Weather Research and Forecasting (WRF) model that includes a bin microphysics scheme is used with a horizontal grid size of 250 m and 401 terrain-following vertical levels. A higher aerosol number concentration leads to production of more cloud droplets, inhibiting the growth of cloud droplets into raindrops in the cases with the symmetric mountain (the windward-side half-width a1 = 10 km). As a result, the total and maximum surface precipitation amounts decrease and the location of the maximum surface precipitation amount shifts downstream. The aerosol effects on orographic precipitation are more clearly seen in the cases with the narrow windward-width (a1 = 5 km) compared to the cases with the symmetric mountain and the wide windward-width (a1 = 20 km). In the cases with the narrow windward-width, the steep upslope generates strong convection with a short advection timescale (∼ 600 s), resulting in more precipitation being concentrated over a narrow area of the mountain downslope compared to the cases with the symmetric mountain and the wide windward-width. On the other hand, in the cases with the wide windward-width, the gentle upslope generates weak convection with a sufficiently long advection timescale (∼ 2400 s), so that a large portion of liquid drops precipitates out on the wide mountain upslope before reaching the peak.
著者
YOSHIDA Mayumi KIKUCHI Maki NAGAO Takashi M. MURAKAMI Hiroshi NOMAKI Tomoyuki HIGURASHI Akiko
出版者
Meteorological Society of Japan
雑誌
気象集誌. 第2輯 (ISSN:00261165)
巻号頁・発行日
pp.2018-039, (Released:2018-04-15)
被引用文献数
22

We develop a common retrieval algorithm of aerosol properties such as aerosol optical thickness, single-scattering albedo, and Ångström exponent for various satellite sensors over both land and ocean. The three main features of this algorithm are as follows: (1) automatic selection of the optimum channels for aerosol retrieval by introducing a weight for each channel to the object function, (2) setting common candidate aerosol models over land and ocean, and (3) preparation of lookup tables for every 1 nm in the range from 300 to 2500 nm of wavelength and weighting the radiance using the response function for each sensor. This method was applied to the Advanced Himawari Imager (AHI) on board the Japan Meteorological Agency’s geostationary satellite Himawari-8, and the results depicted an approximately continuous estimate of aerosol optical thickness over land and ocean. Further, the aerosol optical thickness estimated using our algorithm was generally consistent with the products from Moderate Resolution Imaging Spectroradiometer (MODIS) and Aerosol Robotic Network (AERONET). Additionally, we applied our algorithm to MODIS on board the Aqua satellite and then compared the retrieval results to those that were obtained using AHI. The comparisons of the aerosol optical thickness retrieved from different sensors with different viewing angles on board the geostationary and polar-orbiting satellites suggest an underestimation of aerosol optical thickness at the backscattering direction (or overestimated in other directions). The retrieval of aerosol properties using a common algorithm allows us to identify a weakness in the algorithm, which includes the assumptions in the aerosol model (e.g. sphericity or size distiribution).
著者
AONO Kenji IWASAKI Toshiki SASAI Takahiro
出版者
Meteorological Society of Japan
雑誌
気象集誌. 第2輯 (ISSN:00261165)
巻号頁・発行日
pp.2020-017, (Released:2019-12-24)

This study examined the roles of wind-evaporation feedback in the tropical cyclone (TC) intensification, with special attention devoted to the feedback in weak wind areas (domains where the 10-m wind speed is smaller than 5, 10 and 15 m s−1). This was done by setting lower limits of the 10-m wind speed in the calculation of water vapor exchange between the atmosphere and the underlying ocean in a nonhydrostatic cloud-resolving model. As a result, the surface evaporation is enhanced in outer regions of a TC where the actual wind speed is smaller than the prescribed lower limit(s). Results show that increasing the lower limit reduces the radial water vapor contrast in the lower troposphere (below 100 m) and suppresses the TC size and intensity at the mature stage by 30-33 % and 5-14 %, respectively, compared to the control run with all standard model settings. The increased evaporation enhances the outer convective activity and reduces the radial pressure gradient in the lower troposphere. As a result, the inflow and thus the inward advection of angular momentum were reduced and the enhanced convection in the outer region suppressed eyewall updraft, and thus reduced the secondary circulation and finally the TC intensity. Moreover, the outer region convection suppresses the rainband activity (within a radius of 300 km from the TC center). The contribution of the wind-evaporation feedback to the enhancement of the radial contrast of water vapor in the lower troposphere is a fundamentally important element for TC intensification, suggesting that the TC development process can be revealed more accurately by elucidating the role of the weak wind area.
著者
SUEKI Kenta KAJIKAWA Yoshiyuki
出版者
Meteorological Society of Japan
雑誌
気象集誌. 第2輯 (ISSN:00261165)
巻号頁・発行日
pp.2019-063, (Released:2019-09-06)

During the recent catastrophic heavy rainfall event in western Japan in July 2018, both the Hiroshima and Keihanshin areas were subjected to unusual total rainfall amounts in 72 hours from 1200 UTC 4 July onward. However, the number of sediment disasters was significantly larger in the Hiroshima area. Among the possible reasons for the difference in the sediment disaster occurrences between the Hiroshima and Keihanshin areas, here, we focus on the differences in the rainfall characteristics in these two areas during the heavy rainfall event. Based on the radar observations, we investigate the characteristics of precipitation systems striking the Hiroshima and Keihanshin areas and find that significantly large precipitation systems with areas equal to or larger than 104 km2 were dominant in the Hiroshima area, which caused rapid accumulation of the rainfall amount and enhanced the risk of deadly sediment disasters in this area. On the other hand, in the Keihanshin area, rainfall of moderate intensity and relatively small precipitation systems were found to be dominant. We suggest that the difference in the amount of damage between the Hiroshima and Keihanshin areas was mainly caused by the size difference of the precipitation systems striking these two areas. Statistics relating to the background atmospheric conditions for the precipitation systems in the heavy rainfall event reveal that a high vertical wind shear environment provides preferable conditions for the formation of large precipitation systems.
著者
OTSUKA Shigenori KOTSUKI Shunji OHHIGASHI Marimo MIYOSHI Takemasa
出版者
Meteorological Society of Japan
雑誌
気象集誌. 第2輯 (ISSN:00261165)
巻号頁・発行日
pp.2019-061, (Released:2019-09-03)
被引用文献数
1

Since January 2016, RIKEN has been running an extrapolation-based nowcasting system of global precipitation in real time. Although our previous paper reported its advantage of the use of data assimilation in a limited verification period, long-term stability of its forecast accuracy through different seasons has not been investigated. In addition, the algorithm was updated seven times between January 2016 and March 2018. Therefore, this paper aims to present how motion vectors can be derived more accurately, and how data assimilation can constrain an advection-diffusion model for extrapolation stably for the long-term operation. The Japan Aerospace Exploration Agency's Global Satellite Mapping of Precipitation (GSMaP) Near-Real-Time product is the only input to the nowcasting system. Motion vectors of precipitation areas are computed by a cross-correlation method, and the Local Ensemble Transform Kalman Filter generates a smooth, complete set of motion vectors. Precipitation areas are moved by the motion vectors up to 12 hours, and the product, called “GSMaP RIKEN Nowcast”, is disseminated on a webpage in real time. Most of the algorithmic updates were related to better estimating motion vectors, and the forecast accuracy was gradually and consistently improved by these updates. Particularly, the threat scores increased the most around 40°S and 40°N. A performance drop in the northern hemisphere winter was also reduced by reducing noise in advection. The time series of ensemble spread showed that an increase in the number of available motion vectors by a system update led to a decrease in the ensemble spread, and vice versa.
著者
Bagtasa Gerry
出版者
Meteorological Society of Japan
雑誌
気象集誌. 第2輯 (ISSN:00261165)
巻号頁・発行日
pp.2019-052, (Released:2019-06-14)
被引用文献数
1

The influence of tropical cyclones (TC) on the western North Pacific (WNP) summer monsoon flow and its impact on rainfall in the Philippines during the months of June to September from 1958 to 2017 were investigated. High precipitation event (HPE) days with rainfall in the upper 85th, 95th, and 99th percentile were determined using daily rainfall averaged from eight synoptic stations in northwestern Philippines. More than 90 % of HPE days coincide with TC occurrence in the WNP and landfalling TCs only account for 12.8-15.1 % of HPE days. The present study looks at the non-landfalling TCs coincident with the HPEs. The result shows that these non-landfalling TCs are critical in remotely affecting almost all local HPEs in northwestern Philippines. Analysis of the TC tracks and their influence on the southwesterly of the summer monsoon flow in Southeast Asia during HPE days show that most of the TCs moved along a line segment connecting northern Luzon and Okinawa, Japan. The composite low-level flow of all HPE days is characterized by a zonally-oriented eastward trough of the 1005-1007 hPa sea level isobar along 20°N that extends to at least 135°E longitude over the northern half of the Philippines, and a deepening of the monsoon trough in northern South China Sea. The 1005-1007 hPa trough induces an eastward shift of the southwesterly that increased the mean zonal wind along western Luzon by 1.94-4.69 times and water vapor flux by 2.67-6.92 times by way of the ‘moisture conveyor belt’. In addition, significant increasing trends of 6.0 % per decade in the mean annual number of HPE days per decade and 12.7 % per decade in the annual total HPE precipitation are found for the upper 85th percentile daily rainfall. These are attributed to the recent changes in WNP TC tracks.