著者

高藪 出

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.70, no.2, pp.733-738, 1992 (Released:2007-10-19)

参考文献数

12

被引用文献数

5

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

15

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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

HAYNES Peter HITCHCOCK Peter HITCHMAN Matthew YODEN Shigeo HENDON Harry KILADIS George KODERA Kunihiko SIMPSON Isla

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.2021-040, (Released:2021-03-24)

被引用文献数

32

---

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.

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 18 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

NAKANISHI Mikio NIINO Hiroshi ANZAI Taro

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.2022-013, (Released:2021-11-05)

---

It is desirable that a surface layer scheme in an atmospheric numerical model is consistent with an atmospheric boundary layer scheme incorporated in the same model. In this study, stability functions based on Monin–Obukhov similarity theory for momentum and heat, ϕm and ϕh, in the stable surface layer are derived from the Mellor–Yamada–Nakanishi–Niino (MYNN) scheme modified so that turbulent diffusivity coefficients have no critical gradient Richardson number. The resulting stability functions are approximated by ϕm = 1 + 4.8z/L and ϕh = 0.74 + 6.0z/L, which can be analytically integrated with respect to height z to obtain momentum and heat fluxes, where L is the Obukhov length. The fluxes thus obtained are compared with those obtained from stability functions in four previous studies: they turn out to be nearly the same as those from two of them, and show better agreement with observational data of the Surface Heat Budget of the Arctic Ocean experiment (SHEBA) over sea ice than those from the other two studies. Detailed comparisons of the results of the MYNN scheme with the SHEBA data suggest that significant variations of the fluxes observed for a period of “winter” when the ice was covered with dry snow may have been caused by those of the surface roughness around the observational site. The stability functions obtained from the MYNN scheme predict that the bulk and flux Richardson numbers approach critical values of 0.26 and 0.21, respectively, in the limit of z/L → ∞. These critical values result from Kolmogorov hypothesis applied to the turbulent dissipation in the MYNN scheme and are considered to correspond to a transition from Kolmogorov to non-Kolmogorov turbulence.

著者

NAOI Moeka KAMAE Youichi UEDA Hiroaki MEI Wei

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.2020-027, (Released:2020-02-10)

被引用文献数

15

---

Atmospheric rivers (ARs), narrow water vapor transport bands over the mid-latitudes, often cause great socio-economic impacts over East Asia. While it has been shown that summertime AR activity over East Asia is strongly induced by preceding-winter El Niño development, it remains unclear the extent to which seasonal transitions of El Niño Southern Oscillation (ENSO) from winter to summer affect the AR activity. Here we examine the relationship between the seasonal transitions of ENSO and the summertime AR activity over East Asia using an atmospheric reanalysis and high-resolution atmospheric general circulation model (AGCM) ensemble simulations. A rapid transition from preceding-winter El Niño to summertime La Niña results in more AR occurrence over northern East Asia via northward expansion of an anomalous low-level anticyclone over the western North Pacific compared to sustained or decayed El Niño cases. The northward expansion of the anticyclone is consistent with a steady response of the atmosphere to the anomalous condensation heating over the Maritime Continent and equatorial Pacific. Meridional positions of the extratropical AR occurrence and circulation anomalies are different between the reanalysis and AGCM simulations, which is possibly contributed by a limited sample size and/or AGCM biases and suggests that seasonal prediction of AR-related natural disaster risk over East Asia on a regional scale remains a challenge.

著者

MIYAMOTO Yoshiaki NISHIZAWA Seiya TOMITA Hirofumi

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.2020-023, (Released:2020-02-06)

被引用文献数

2

---

The impacts of the number density of cloud condensation nuclei (CCN) and other thermodynamic quantities on moist Rayleigh convection were examined. A numerical model, consisting of a simple two–dimensional equation for Boussinesq air and a sophisticated double moment microphysics scheme, was developed. The impact of the number of CCN is most prominent in the initially formed convection, whereas the convection in the quasi–steady state does not significantly depend on the number of CCN. It is suggested that the former convection is driven by a mechanism without a background circulation, such as parcel theory. In contrast, the latter convection appears to be driven by the statically unstable background layer.  Incorporating the cloud microphysics reduces the integrated kinetic energy and number of convective cell (increases the distance between the cells), with some exceptions, which are consistent with previous studies. These features are not largely sensitive to the number of CCN. It is shown in this study that the reduction in kinetic energy is mainly due to condensation (evaporation) in the upper (lower) layer, which tends to stabilize the fluid. The ensemble simulation shows that the sensitivity of the moist processes to changes the temperature at the bottom boundary, temperature lapse rate, water vapor mixing ratio, and CCN is qualitatively similar to that in the control simulation. The impact becomes strong with increasing temperature lapse rate. The number of convective cell in a domain decreases with the degree of supersaturation or an increase in the domain–integrated condensate.

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)

被引用文献数

53

---

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

13

---

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

46

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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

Bh. V. Ramana Murty K. R. Biswas

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.46, no.3, pp.160-165, 1968 (Released:2008-05-27)

参考文献数

9

被引用文献数

2 4

---

Experiments on artificial stimulation of clouds using warm cloud seeding technique have been conducted, on randomized basis, from ground for 4 monsoon periods at Jaipur, 6 monsoon periods at Agra and 9 monsoon periods at Delhi, in North India. The seedings were also conducted from aircraft, during one monsoon period at Delhi. Orographic clouds have been seeded for two summer seasons at Munnar in South India.Results have been evaluated on the basis of rainfall amounts obtainedd from raingauges in the respective target and control sectors in each region. Evaluation has also been done on the basis of data obtained by high power microwave radar in the case of a few series of trials conducted at Delhi.A net increase in precipitation was suggested in each area as a result of seeing. The percentage increase in rainfall as a result of ground-based seeding varied from 18.6 to 58.5 according to the area. Statistical evaluation indicated that the results obtained could be significant.

著者

KAWAI Hideaki SHIGE Shoichi

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.2020-059, (Released:2020-08-03)

被引用文献数

3 9

---

This review paper aims to provide readers with a broad range of meteorological backgrounds with basic information on marine low clouds and the concept of their parameterizations used in global climate models. The first part of the paper presents basic information on marine low clouds and their importance in climate simulations in a comprehensible way. It covers the global distribution and important physical processes related to the clouds, typical examples of observational and modeling studies of such clouds, and the considerable importance of changes in low cloud for climate simulations. In the latter half of the paper, the concept of cloud parameterizations that determine cloud fraction and cloud water content in global climate models, which is sometimes called cloud “macrophysics”, is introduced. In the parameterizations, the key element is how to assume or determine the inhomogeneity of water vapor and cloud water content in model grid boxes whose size is several tens to several hundreds of kilometers. Challenges related to cloud representation in such models that must be tackled in the next couple of decades are discussed.

著者

加藤 輝之

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.98, no.3, pp.485-509, 2020 (Released:2020-06-20)

参考文献数

50

被引用文献数

19 49

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日本では3時間積算降水量200mmを超える集中豪雨がしばしば観測され、過酷な地滑りや洪水をもたらす。そのような事例は主に、日本語で「線状降水帯」と名付けられた準停滞線状降水システムによってもたらされる。線状降水帯は次々と発生する発達した対流セルが列をなした、組織化した積乱雲群によって、数時間にわたってほぼ同じ場所を通過または停滞することで作り出される、線状に伸びる長さ50~300km程度、幅20~50km程度の強い降水をともなう雨域として定義される。線状降水帯の形成過程としては主に、暖湿流がほぼ停滞している局地前線に流入することで、対流セルが前線上で同時に発生する破線型と、下層風の風上側に新しい対流セルが繰り返し発生し、既存のセルと線状に組織化するバックビルディング型の2つに分類される。 本研究では、線状の降水システムについての過去研究のレビューに加えて、線状降水帯の数値モデルによる再現性および線状降水帯の発生しやすい条件について調査した。2014年8月20日の広島豪雨の事例の再現では、対流セルの形成・発達過程をおおよそ再現できる少なくとも水平解像度2kmが必要であったが、その内部構造を正確に再現するには水平解像度250~500mが必要であった。2㎞のモデルは10時間前の初期値を用いることで広島の事例を量的に再現したが、予想された最大積算降水量は初期時刻が線状降水帯の発生時刻に近づくにつれてかなり減少した。この減少は過度の下層乾燥空気の流入が新たな積乱雲群が発生する領域を移動させたためであった。 線状降水帯を診断的に予測するために、線状降水帯の発生しやすい条件を過去の集中豪雨事例における大気環境場から統計的に構築した。500m高度データをベースに判断する下層水蒸気場を代表して、(1)大量の水蒸気フラックス量(>150g m-2 s-1)と(2)自由対流高度までの距離が短いこと(<1000 m)の2つの条件を選択した。ほかの4つとして、(3)中層(500hPa と 700hPa)の相対湿度が高い(>60%)、(4)ストームに相対的なヘリシティで判断する大きな鉛直シア(>100m2 s-2)、(5)総観スケール(700hPa で空間 400km平均)の上昇流場で判断する上昇流域と(6)700~850hPaに度々みられる暖気移流を除外するための平衡高度が3000m以上の条件を選択した。

著者

MIN Kyeong-Seok TSUBOKI Kazuhisa YOSHIOKA Mayumi K. MORODA Yukie KANADA Sachie

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.2021-017, (Released:2020-12-04)

被引用文献数

3

---

A stationary line-shaped precipitation system (SLPS), which is one type of mesoscale convective systems (MCSs), is a typical heavy-rain-producing weather system formed during warm seasons in Japan. Although the Kinki district, western Japan, is known as a frequent occurrence region for SLPSs, their formation mechanisms in the region have not been sufficiently clarified yet because of their complex formation processes. This study investigated a SLPS event that occurred on 1 September 2015, using observational data and high-resolution numerical experiments. We also carried out numerical sensitivity experiments with regard to the orography and initial time.  The observational data showed that the relative humidity at lower levels was high during the SLPS event. The southwesterly was dominant at middle levels over the Kinki district during the formation of the SLPS. The formation of the SLPS was associated with neither a mesoscale low-pressure system nor a synoptic-scale cold front, demonstrating that these were not necessary conditions for the formation of the SLPS.  In the numerical experiments, we found that the SLPS was formed in a low-level convergence zone of the westerly with the warm and moist south-southwesterly from the Kii Channel. New convective cells formed over the north of Awaji Island and are propagated northeastward by the middle-level southwesterly. This cell formation process was repeated and resulted in the formation of the SLPS. The sensitivity experiments for the orography around the occurrence area of the SLPS indicated that the orography was not a significant factor for the formation of the SLPS in this event. The orography can modify the location of the SLPS.

著者

S. Manabe

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.35, no.6, pp.311-326, 1957-12-25 (Released:2007-10-19)

参考文献数

20

被引用文献数

69 71

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Japan Sea is generally considered to be one of the places where the most rapid airmass transformation takes place in winter season.As it is surrounded by the dense network of radiosonde and surface observation stations, quantitative investigation about the modification of airmass is possible.Selecting the period of a typical continuous outburst of cold air from 20 Dec.'54 to 3 Jan.'55 during which the air-sea temperature difference exceeded 10°C, we computed the integrated netflux divergence of enthalpy and water vapor and the vertical transport of them at the standard levels in the lower half of the troposphere, and further estimated the amount of heating and cooling due to radiation and condensation.Then, based upon the balance requirement, the amount of heat or water vapor supplied from the sea to the atmosphere was obtained.According to the results of above computations, it is concluded that the amount of supplied heat is as much as 1000ly/day in such a typical unstable situation, and is 2.3 times as large as that of supplied latent heat in spite of the fact that mean Bowen's ratio expected from mixing length theory was nearly equal, to unity.Finally, for several periods when no remarkable cyclone passed over the Japan Sea, the amount of evaporation computed by the scheme above-mentioned are compared with the results obtained by use of climatological evaporation equation after Jacobs.

著者

野田 彰 時岡 達志

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.67, no.6, pp.1057-1069, 1989 (Released:2007-10-19)

参考文献数

27

被引用文献数

37 43

著者

DUEBEN Peter D. WEDI Nils SAARINEN Sami ZEMAN Christian

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.2020-016, (Released:2020-03-17)

被引用文献数

2 24

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Global simulations with 1.45 km grid-spacing are presented that were performed with the Integrated Forecasting System (IFS) of the European Centre for Medium-Range Weather Forecasts (ECMWF). Simulations are uncoupled (without ocean, sea-ice or wave model), using 62 or 137 vertical levels and the full complexity of weather forecast simulations including recent date initial conditions, real-world topography, and state-of-the-art physical parametrizations and diabatic forcing including shallow convection, turbulent diffusion, radiation and five categories for the water substance (vapour, liquid, ice, rain, snow). Simulations are evaluated with regard to computational efficiency and model fidelity. Scaling results are presented that were performed on the fastest supercomputer in Europe - Piz Daint (Top 500, Nov 2018). Important choices for the model configuration at this unprecedented resolution for the IFS are discussed such as the use of hydrostatic and non-hydrostatic equations or the time resolution of physical phenomena which is defined by the length of the time step. Our simulations indicate that the IFS model — based on spectral transforms with a semi-implicit, semi-Lagrangian time-stepping scheme in contrast to more local discretisation techniques — can provide a meaningful baseline reference for O(1) km global simulations.

著者

HUANG Xiaogang PENG Xudong FEI Jianfang CHENG Xiaoping DING Juli YU Dandan

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.2021-008, (Released:2020-11-19)

被引用文献数

19

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This study systematically evaluates the accuracy, trends and error sources for western North Pacific tropical cyclone intensity forecasts between 2005 and 2018. The study uses homogeneous samples from TC intensity official forecasts issued by the China Meteorological Administration (CMA), the Joint Typhoon Warning Center (JTWC), and the Regional Specialized Meteorological Center Tokyo-Typhoon Center (RSMC-Tokyo). The TC intensity forecast accuracy performances are: 24-48 h, JTWC > RSMC-Tokyo > CMA; 72 h, JTWC > CMA > RSMC-Tokyo; and 96-120 h, JTWC > CMA. Improvements in TC intensity forecasting are marginal but steady for all the three centers. The 24-72 h improvement rate is approximately 1-2 % yr−1. The improvement rates are statistically significant at the 95 % level for almost half of the verification times from 0-120 h. The three centers tend to overestimate weak TCs over the northern South China Sea, but strong TCs are sometimes underestimated over the area east of the Philippines. The three centers generally have higher skill scores associated with forecasting of rapid weakening (RW) events than rapid intensification (RI) events. Overall, the three centers are not skillful in forecasting RI events more than three days in advance. Fortunately, RW events could be forecasted five days in advance with an accuracy order of CMA > RSMC-Tokyo > JTWC.

著者

YAMAGUCHI Munehiko MAEDA Shuhei

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.2020-068, (Released:2020-08-27)

被引用文献数

15

---

Global warming already affects weather and climate worldwide; accordingly, various studies have been conducted to understand the effects of climate change on tropical cyclones (TCs). The translation speed of a tropical cyclone is a particularly important feature, as a slower translation speed lengthens the duration of a cyclone's impact. Here, on the basis of observational data, we report that tropical cyclone translation speeds in the middle latitudes of the western North Pacific basin have significantly decreased during September over the last 40 years. Historical model simulations with and without observational global warming trends reveal two main factors responsible for translation speed slowdown: natural decadal climate variabilities (such as the Pacific Decadal Oscillation) and global warming. Both factors produce an anticyclonic anomaly in the westerly jet over western Japan; this anomaly relaxes the latitudinal geopotential height gradient, weakening the environmental synoptic winds by which tropical cyclones are steered. Furthermore, model simulations for a future warmer climate show that global warming further reduces the steering flows, leading to more slowly-moving TCs in autumn in the future.

著者

SONG Hwan-Jin KIM Sunyoung ROH Soonyoung LEE Hyesook

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.2020-044, (Released:2020-06-02)

被引用文献数

6

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This study compares the regional characteristics of heavy rain clouds in terms of Cloud Top Height (CTH) and Storm Height (SH) from long-term Tropical Rainfall Measuring Mission (TRMM) observations. The SH is derived from Precipitation Radar reflectivity and the CTH is estimated using Visible and InfraRed Scanner brightness temperature (10.8 μm) and reanalysis temperature profiles. As the rain rate increases, the average CTH and average SH increase, but by different degrees in different regions. Heavy rainfall in continental rainfall regimes such as Central Africa and the United States is characterized by high SH, in contrast to oceanic rainfall regions such as the northwestern Pacific, Korea, and Japan; the increase of atmospheric instability in dry environments is interpreted as a mechanism of continental floods. Conversely, heavy rain events in Korea and Japan occur in a thermodynamically near-neutral environment with large amounts of water vapor; these are characterized by the lowest CTH, SH, and ice water content. The northwestern Pacific exhibits the lowest SH in humid environments, similar to Korea and Japan; however, this region also characteristically exhibits the highest convective instability condition as well as high CTH and CTH–SH values, in contrast to Korea and Japan. The observed CTH and SH characteristics of heavy rain clouds are expected to be useful for the evaluation and improvement of satellite-based precipitation estimation and numerical model cloud parameterization.