著者

UCHIYAMA Akihiro CHEN Bin YAMAZAKI Akihiro SHI Guangyu KUDO Rei NISHITA-HARA Chiharu HAYASHI Masahiko HABIB Ammara MATSUNAGA Tsuneo

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.2018-026, (Released:2018-02-05)

被引用文献数

1

---

The aerosol optical characteristics in the East Asian cities of Fukuoka and Beijing were measured from 2010 to 2014. These long-term season-crossing data were compared to understand the differences between the aerosol characteristics at a source and a downstream region. Previously, few long-term, season-crossing observations have been reported. Using a method developed by one of the present authors, the measurement data were analyzed so that the retrieved optical properties can be more accurate than those obtained in previous studies. Using these data, the aerosol characteristics and their frequency distributions were reliably obtained. In Fukuoka, the annual means of the extinction, scattering, and absorption coefficients Cext (525 nm), Csca (525 nm), and Cabs (520 nm) were 74.6, 66.1, and 8.1 M m−1, respectively, whereas those in Beijing were 412.1, 367.2, and 42.4 M m−1, respectively. The coefficients in Fukuoka were approximately one-fifth of those in Beijing. The single-scattering albedos ω 0 (525 nm) in Fukuoka and Beijing were 0.877 and 0.868, respectively. The asymmetry factors G (525 nm) in the two cities were 0.599 and 0.656, respectively. The extinction Ångström exponents αext in the two cities were 1.555 and 0.855, respectively. The absorption Ångström exponents αabs in the two cities were 1.106 and 0.977, respectively. The fine and coarse mode volume fractions in Fukuoka were approximately 80 % and 20 %, and those in Beijing were both approximately 50 % except in the summer. The Cext , Csca , and Cabs showed seasonal variation in both cities. Some other properties showed also seasonal variation. In particular, the seasonal variation in αabs was clear in both cities; it tended to be small in the summer and large in the winter. The frequency distributions of various parameters were also investigated. The frequency of Cext >500 M m−1 in Fukuoka was very low, and large Cext values were recorded more frequently in the spring than in other seasons. In Beijing, Cext > 1000 M m−1 values were recorded more frequently, and the frequency of 10 M m−1 ≤ Cabs ≤ 60 M m−1 was high in the spring and summer. Furthermore, αabs < 1.0 values were recorded frequently, which cannot be explained by the simple external mixture of absorbing aerosols. To demonstrate the usefulness of the data obtained in this study, the relationships among αabs , αext , the volume size distribution, the imaginary part of the refractive index and ω 0 were investigated, and two characteristic cases in Beijing (winter) and Fukuoka (spring) were preliminarily analyzed.

著者

LONG Jingchao WANG Yuqing ZHANG Suping

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.2018-018, (Released:2018-01-15)

被引用文献数

1

---

The cloud variability and regime transition from-stratocumulus-to-cumulus across the sea surface temperature front in the Kuroshio region over the East China Sea are important regional climate features and may affect the earth’s energy balance. However, because of large uncertainties among available cloud products, it is unclear which cloud datasets are more reliable for use in studying the regional cloud features and to validate cloud simulations in the region by climate models. In this study, the monthly low cloud amount (LCA) and total cloud amount (TCA) datasets in the region from Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO), Moderate-resolution Imaging Spectroradiometer (MODIS) and International Comprehensive Ocean-Atmosphere Data Set (ICOADS) are validated against the combined product of CloudSat+CALIPSO (CC) in terms of the consistency and discrepancy in the climatologically mean, seasonal cycle, and interannual variation. The results show that LCA and TCA derived from MODIS and CALIPSO present relatively high consistency with CC data in the climatological annual mean and show similar behavior in seasonal cycle. The consistency in LCA between the three datasets and the CC is generally good in cold seasons (winter, spring and fall) but poor in summer. MODIS shows the best agreement with CC in fall with the correlation coefficient of 0.77 at the confidence level over 99%. CALIPSO and MODIS can provide competitive description of TCA in all seasons while ICOADS is good in terms of the climatological seasonal mean of TCA in winter only. Moreover, the interannual variation of LCA and TCA from all datasets is highly correlated with that from CC in both winter and spring with the Matching Score ranging between 2/3 and 1. Further analysis with long-term data suggests that both LCA and TCA from ICOADS and MODIS can be good references for the studies of cloud interannual variability in the region.

著者

Tsutao OIZUMI Kazuo SAITO Junshi ITO Thoru KURODA Le DUC

出版者

Meteorological Society of Japan

雑誌

Journal of the Meteorological Society of Japan. Ser. II (ISSN:00261165)

巻号頁・発行日

pp.2018-006, (Released:2017-11-30)

被引用文献数

9

---

An intense rainband associated with Typhoon 1326 (Wipha) induced a fatal debris flow on Izu Oshima, Japan, on October 15-16, 2013. This rainband formed along a local front between the southeasterly humid warm air around the typhoon and the northeasterly cold air from the Kanto Plain. In this paper, the Japan Meteorological Agency Nonhydrostatic Model was optimized for the “K computer,” and ultra-high-resolution (500-250 m grid spacing) numerical simulations of the rainband with a large domain were conducted. Two of main factors that affect a numerical weather prediction (NWP) model, (1) grid spacing and (2) planetary boundary layer (PBL) schemes [Mellor–Yamada–Nakanishi–Niino (MYNN) and Deardorff (DD)], were investigated. Experiments with DD (Exps_DD: grid spacings of 2 km, 500 m, and 250 m) showed better reproducibility of the rainband position than experiments with MYNN (Exps_MYNN: grid spacings of 5 km, 2 km, and 500 m). Exps_DD simulated distinct convective-scale up/downdraft pairs on the southeast/northwest sides of the front, whereas those of Exps_MYNN were not clear. Exps_DD yielded stronger cold pools near the surface than did Exps_MYNN. These differences in the boundary layer structures likely had a large impact on the position of the front and the associated rainband. Exps_DD with the 500-m grid spacing showed the best precipitation performance according to the Fractions Skill Score. To check other factors of the precipitation forecast, model domain sizes, lateral boundary conditions in nesting simulations, and terrain representations were investigated. In the small domain experiments, the rainband shapes were very different from the observations. In the experiment using a nesting procedure, the deterioration of the forecast performance was acceptably reduced. The model with fine terrains better reproduced the intense rain over the island. These results demonstrate that the ultra-high-resolution NWP model with a large domain has the possibility to improve predictions of heavy rain.

著者

TERASAKI Koji MIYOSHI Takemasa

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

pp.2017-028, (Released:2017-09-15)

被引用文献数

18

---

An observation operator to assimilate satellite radiances with the Non-hydrostatic Icosahedral Atmospheric Model (NICAM)-based Local Ensemble Transform Kalman Filter (LETKF) is newly developed using the radiative transfer model RTTOV (Radiative Transfer for the TOVS (TIROS Operational Vertical Sounder)) version 11.1. Here we assimilate the Advanced Microwave Sounding Unit-A (AMSU-A) brightness temperature observations which are known to bring a large improvement to global numerical weather prediction. We apply the online estimation of bias correction for both airmass and scan biases, or the biases originating from the atmospheric state and scan position. Comparing the two experiments with and without the AMSU-A radiances, we find that the adaptive bias correction methods work appropriately, and that the analysis is significantly improved by assimilating the AMSU-A radiances. This is an important step toward assimilating different types of satellite radiances with NICAM-LETKF.

著者

Nurfiena Sagita PUTRI Tadahiro HAYASAKA Kim Dionne WHITEHALL

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.391-409, 2017 (Released:2017-11-14)

参考文献数

30

被引用文献数

11

---

A mesoscale convective system (MCS) is organized thunderstorms with connected anvils, which has a significant impact on the global climate. By focusing on MCSs over the Maritime Continent of Indonesia, this study aims to gain a better understanding on the properties of the MCSs over the study area. The “Grab ‘em Tag ‘em Graph ‘em” (GTG) tracking algorithm is applied to hourly Multi-functional Transport Satellite-1R data for two years to observe the distribution of MCSs and the evolution of MCSs along their lifetime. The results of MCS identification by using GTG are combined with CloudSat data products to study the vertical structure of the MCSs at various MCS life stages: developing, mature, and dissipating. The distribution of MCSs over Indonesia has a seasonal variation and distinct diurnal cycle. The life stages of the observed MCSs are characterized by distinct cloud microphysics at each stage. In the developing stage, the upper level of the MCS raining region shows the presence of precipitating ice particles. As the MCS progresses to the mature stage, the proportion of the raining area becomes small and the intensity of rain is reduced, accompanied by increasing occurrence of small-sized ice particles at the upper level. In the dissipating stage, large hydrometeors no longer exist at the upper part of the raining region. Within the MCS anvils, the dissipating stage shows a more uniform distribution of ice-particle effective radius compared to that shown by the developing and mature stages. MCS characteristics over the land and ocean differ on the basis of the minimum brightness temperature, the equivalent radius, the maximum rain rate, and the rain fraction that varies along the MCS evolution.

著者

ROH Woosub SATOH Masaki

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

pp.2018-002, (Released:2017-09-29)

被引用文献数

10

---

As an alternative approach to the previous multisensor satellite evaluation method of cloud system resolving models, a method is presented using combined infrared and microwave channels for precipitation clouds in cloud system resolving models over the ocean. This method determines characteristics of cloud-top temperatures and ice scatterings for clouds using infrared 11-μm and microwave high frequencies (89.0 GHz) brightness temperatures (TBs). The threshold of the TB at low frequencies (18.7 GHz) is also used to identify precipitation regions. This method extends the previous approach via the wider swath of the passive microwave sensor and sensitivities to ice clouds compared to the previous Tropical Rainfall Measuring Mission (TRMM)-based analysis method using the narrower coverage of the Precipitation Radar. The numerical results of the non-hydrostatic icosahedral atmospheric model (NICAM) with two cloud microphysics schemes are evaluated over the tropical open ocean using this method. The intensities of the scatterings in the two simulations at 89.0 GHz are different due to the parameterizations of the snow and graupel size distributions. A bimodal size distribution of the snow improved the underestimation of the TBs at 89.0 GHz. These results have a similar structure to the joint histograms of cloud-top temperatures and precipitation-top heights in the previous method: the overestimated intensity of scattering and the frequencies of high precipitation-top heights above 12 km in the control experiment. We find that the change in the snow size distribution in the cloud microphysics scheme can lead to better agreements of simulated TBs at 89.0 GHz with observations. We further investigate impacts of non-spherical assumptions for snow using a satellite simulator. The effect of a non-spherical shape of snow in the radiative transfer model causes a smaller change of TBs at 89.0 GHz compared to the difference between the TBs of the two simulations without non-spherical assumptions.

著者

Eigo TOCHIMOTO Tetsuya KAWANO

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.4, pp.217-237, 2017 (Released:2017-07-04)

参考文献数

39

被引用文献数

4

---

In Part I of this study, the development processes of Baiu frontal depressions (BFDs) have been examined through case-study numerical experiments. The numerical simulations revealed that latent heating is dominant for the development of BFDs in the western part of the Baiu frontal zone (W-BFDs), west of approximately 140°E, while both latent heating and baroclinicity are important for the development of BFDs in the eastern part of the zone (E-BFDs), east of approximately 140°E. In this study, idealized numerical simulations with zonally homogeneous basic fields are conducted to obtain a more generalized perspective of the development processes of BFDs. The basic fields for the idealized simulations are made from the composites of the environments under which 28 W-BFDs and 43 E-BFDs developed. The idealized simulations successfully reproduce a realistic W-BFD and E-BFD. The W-BFD has a slightly westward-tilted vertical structure, modulated by latent heating at low levels of the atmosphere. In contrast, the E-BFD has a westward-tilted structure through the troposphere, similar to the well-known baroclinic wave structure. Results of available potential energy diagnosis for the effects of latent heating and baroclinicity on the BFD development are consistent with those in Part I. The W-BFD has a mechanism mainly driven by latent heating yielding strong convection, while the E-BFD develops through baroclinic instability in moist atmosphere.

著者

Yasuko OKADA Tetsuya TAKEMI Hirohiko ISHIKAWA Shoji KUSUNOKI Ryo MIZUTA

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.4, pp.239-260, 2017 (Released:2017-07-04)

参考文献数

45

被引用文献数

19

---

This study investigates future changes in atmospheric circulation during the Baiu in Japan using 20-km-mesh atmospheric general circulation model (AGCM) simulations for the present-day (1979-2003) and the future (2075-2099) climates under the Representative Concentration Pathways 8.5 scenario. The simulated future climates include the outputs obtained with one control sea surface temperature (SST) and three different SST patterns. The Baiu frontal zone, defined as the meridional gradient of equivalent potential temperature, gradually moves northward during June–July–August in the present-day climate. In the future climate simulations using the control SST, the Baiu frontal zone is projected to stay to the south of Japan in June. Thus, precipitation is projected to increase over this region, while decreasing in the western part of Japan. Future changes in precipitation and atmospheric circulations in June are consistent across all four SST patterns. However, precipitation and atmospheric circulation in July and August in the future climate simulation depends on the SST patterns as follows: in non-El Niño-like SST pattern, the Baiu terminates in late July, similar to that of the present-day climate; a result with an El Niño-like SST pattern shows that sufficient amount moisture is transported to the Japanese islands and leads in a delay of the Baiu termination until August; and in the SST pattern with strong warming in the western North Pacific (WNP), a sufficient amount of moisture is transported to the south of Japan from June until August. The difference in the SST pattern leads to a variation in sea-level pressure in the WNP and affects a variation of the Northern Pacific subtropical high around the Japanese islands in July and August.

著者

岡田 武松

出版者

METEOROLOGICAL SOCIETY OF JAPAN

雑誌

氣象集誌. 第1輯 (ISSN:00261165)

巻号頁・発行日

vol.32, no.11, pp.478-479, 1913

著者

Seiji KATO Norman G. LOEB David A. RUTAN Fred G. ROSE

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.6, pp.597-612, 2015 (Released:2016-01-13)

参考文献数

107

被引用文献数

11

---

NASA’s Clouds and the Earth’s Radiant Energy System (CERES) project integrates CERES, Moderate Resolution Imaging Spectroradiometer (MODIS), and geostationary satellite observations to provide top-of-atmosphere (TOA) irradiances derived from broadband radiance observations by CERES instruments. It also uses snow cover and sea ice extent retrieved from microwave instruments as well as thermodynamic variables from reanalysis. In addition, these variables are used for surface and atmospheric irradiance computations. The CERES project provides TOA, surface, and atmospheric irradiances in various spatial and temporal resolutions. These data sets are for climate research and evaluation of climate models. Long-term observations are required to understand how the Earth system responds to radiative forcing. A simple model is used to estimate the time to detect trends in TOA reflected shortwave and emitted longwave irradiances.

著者

大野 久雄 鈴木 修 韮澤 浩 吉崎 正憲 長谷川 直之 田中 芳男 村松 良夫 小倉 義光

出版者

社団法人日本気象学会

雑誌

気象集誌 (ISSN:00261165)

巻号頁・発行日

vol.72, no.2, pp.197-222, 1994-04-25

被引用文献数

13

---

太平洋高気圧の北辺に位置する岡山地方で1991年6月27日午後発生した雷雨嵐は同地方に激しい雨や雷および強い突風をもたらせた。中でも岡山市の北東部で発生した突風は特に強く、単体では51m/sの風に耐えられるコンクリート製電柱18本を倒壊させた。この研究は、電柱の倒壊をもたらせた突風の原因を調べるために始められた。利用可能なすべてのデータが集められ、解析された。データ源は、通常レーダー、気象庁のシステム、密に展開された自治体の大気汚染監視用風向風速計、民間航空機、テレビ局のビデオ画像、被害調査結果等と多岐にわたった。これらを複合利用してメソ解析を行った結果、少なくとも4つのダウンバースト(マイクロバーストとマクロバーストの両方)の発生が明らかになった。電柱を倒壊させたのはそのうちの1つで、雷を伴っていた。当時大気成層は、湿マイクロバーストを発生させるのに適したもので、Atkins and Wakimoto(1991)が報告した米国北アラバマの事例と類似していた。また、ダウンバースト発生の潜在的危険性が太平洋高気圧の北辺にあるとの指摘がなされた。

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.1-2, 2015 (Released:2015-03-18)

参考文献数

5

著者

土屋 清

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.47, no.6, pp.457-465, 1969 (Released:2008-05-27)

参考文献数

14

被引用文献数

26

---

約4時間の時間間隔で撮影した気象衛星エッサ7号と8号の写真に現われた済州島風下のKarman鋤うず列状の雲を解析した結果,次のことがわかった.雲のうず列から得られた無次元パラメーターは,これまで2次元流の流体実験から得られたKarman鋤うず列発生の限界値を満足しており,Karmanうず列の理論で説明できる.島の抵抗とうず列のwakeによる抵抗を考慮して,うず列の間隔と個々のうずの間隔の比だけから,うず列の移動速度を求める計算式を導いた.結果実況とかなりよく合い,比が0.332のとき.一般流の約76%であった.済州島の風下に,このような雲のうず列のできるのは,晩秋から初春にかけて,比較的強い(10ノット以上)北風が持続し,1000m付近(島の中央部の山の高さの半分)に顕著な逆転のある時である.

著者

Hiroshige TSUGUTI Teruyuki KATO

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.92, no.2, pp.163-183, 2014 (Released:2014-05-16)

参考文献数

32

被引用文献数

4 22

---

On 20 October 2010, a heavy rainfall event occurred on Amami-Oshima Island, Japan, delivering a record 622 mm of rainfall in one day. To clarify the factors underlying this event, the supply mechanism and formation process of low-level humid air and the formation and maintenance mechanisms of the precipitation systems causing the heavy rainfall were examined using observation data, objective analysis data, and numerical simulation results. These investigations showed that low-level humid air, carried to Amami-Oshima Island during the rainfall event by strong east-northeasterly winds, originated more than 500 km to the east-northeast as low-level dry air on the northern side of a stationary front. This dry air was transformed into humid air on the way to the island by receiving large latent heat flux from the sea surface (air-parcel transformation). Warm sea surface temperatures around Amami-Oshima Island, about 2°C higher than the annual mean, contributed to this air-parcel transformation. At Amami-Oshima Island, the collision of the humid flows with a cold pool formed under earlier precipitation systems contributed significantly to the formation and maintenance of the precipitation systems, supplemented by topographic effects of the island.

著者

DUC Le SAWADA Yohei

出版者

公益社団法人 日本気象学会

雑誌

気象集誌. 第2輯 (ISSN:00261165)

巻号頁・発行日

pp.2024-003, (Released:2023-09-19)

---

It is well-known in rainfall ensemble forecasts that ensemble means suffer substantially from the diffusion effect resulting from the averaging operator. Therefore, ensemble means are rarely used in practice. The use of the arithmetic average to compute ensemble means is equivalent to the definition of ensemble means as centers of mass or barycenters of all ensemble members where each ensemble member is considered as a point in a high-dimensional Euclidean space. This study uses the limitation of ensemble means as evidence to support the viewpoint that the geometry of rainfall distributions is not the familiar Euclidean space, but a different space. The rigorously mathematical theory underlying this space has already been developed in the theory of optimal transport (OT) with various applications in data science. In the theory of OT, all distributions are required to have the same total mass. This requirement is rarely satisfied in rainfall ensemble forecasts. We, therefore, develop the geometry of rainfall distributions from an extension of OT called unbalanced OT. This geometry is associated with the Gaussian-Hellinger (GH) distance, defined as the optimal cost to push a source distribution to a destination distribution with penalties on the mass discrepancy between mass transportation and original mass distributions. Applications of the new geometry of rainfall distributions in practice are enabled by the fast and scalable Sinkhorn-Knopp algorithms, in which GH distances or GH barycenters can be approximated in real-time. In the new geometry, ensemble means are identified with GH barycenters, and the diffusion effect, as in the case of arithmetic means, is avoided. New ensemble means being placed side-by-side with deterministic forecasts provide useful information for forecasters in decision-making.

著者

Yoshiharu IWASA Takashi ARAKAWA Akimasa SUMI

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.90, no.1, pp.11-33, 2012-02-29 (Released:2012-02-29)

参考文献数

31

被引用文献数

1 1

---

Time integration using the Regional Atmospheric Modeling System (RAMS), a non-hydrostatic cloud-resolving model, was performed for 12 days over a low-latitude band (45°S–45°N) circling an aqua planet with 5-km horizontal grid-point intervals. Tropical and subtropical regions with active precipitation and clear sky, respectively, were clearly divided at 10° latitudes. The numerical experiments derived obvious tropospheric mid-level detrainment (TMD) flows near the 0°C level (z ∼ 5 km) out of the tropics into the subtropics. The TMD flows became largest near the border (10° latitude). In this paper, the time-longitudinal mean field was spotlighted and the atmospheric structure accompanying the TMD flow was investigated. When averaged over time and longitude, the subtropical mid-level troposphere, into which the TMD flows move, is approximately in a state of local thermodynamic equilibrium sustained mainly by the balance between the net radiative cooling and adiabatic heating due to mean subsidence flow. Considering the heat balance, a thermodynamic diagnosis of the mean subsidence flow field suggests the following mechanisms for the mean TMD flow: (1) The mean atmosphere near the melting level has stronger radiative cooling and a larger temperature lapse rate than the atmosphere above it. (2) Free subsidence in the mean subtropical mid-level troposphere, which is consistent with the vertical variation of thermal structure and suffers from no direct dynamic forcings, such as buoyancy, involves a vertically mass-divergent layer just above the melting level. (3) The steady poleward mean TMD flow out of the convective tropic atmosphere exists so as to compensate for the vertical mass divergence in the subtropical atmosphere. Because net meridional transports of sensible heat and water vapor in the middle troposphere are influenced by the mean TMD flow, the existence and the maintaining mechanisms of the mean TMD flow could be important elements of the climate system.

著者

Gerald STANHILL Shabtai COHEN

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.86, no.1, pp.57-67, 2008 (Released:2008-05-12)

参考文献数

28

被引用文献数

44 47

---

Annual values of sunshine duration (SS) measured in Japan between 1890 and 2002 were used as a proxy for global irradiance (Eg↓) to study trends and changes in solar forcing at the Earth's surface. Proxy relationships established for the two SS recorders used in the JMA network both yielded estimates of mean annual values of Eg↓ with RMS &1t; 6%. A first order integrated moving average model (ARIMA) adequately described the time course of SS and Eg↓, which indicated a small, irregular but significant annual increase in solar forcing during the 20th century averaging 0.08 W m-2 or 2.3 hours of Jordan SS recorder sunshine, equivalent to 0.5% per decade. The rate of increase was four times the average in the first four and last three decades of the century reaching a maximum after 1980. The negative effect of the five major volcanic eruptions on Eg↓ was shown to yield a significant linear negative forcing of -41 W m-2 per unit AOD stratospheric aerosol optical depth). The degree of negative solar forcing was related to latitude: between 25° and 44°N each degree shift to the North was associated with an annual increase in Eg↓averaging 0.02%. The time course of changes in solar radiation in Japan during the 20th century resembled that measured in air temperature; correlations between annual values of Eg↓and those in the air temperature of the Northern Hemisphere were very highly significant (P < 0.001) both for the concurrent and preceding year.

著者

Kenneth Sassen

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.58, no.5, pp.422-429, 1980 (Released:2007-10-19)

参考文献数

14

被引用文献数

64 69

---

大気中を自然落下している板状氷晶の落下姿勢と氷晶の大きさとの関係を知るため,氷晶によって生ずる光学現象である光柱(light pillars)の拡がり角および散乱光強度の分布を光柱写真の解析から求めた。その結果,レイノルズ数(Re)にして1.0<Re<100の範囲氷晶は,基底面(basal plane)を落下方向に対して垂直,すなわち水平方向に保つような落下姿勢が卓越し,特にRe=10前後ではこの姿勢が最も安定な落下姿勢であることが判った。落下中の板状結晶の基底面の水平方向からの傾き角は,大気中の乱れのため一般的には,水平方向を中心にガウス分布をしている。これら観測結果と,大気光学現象との関係や雲構成要素の性質のアクチブリモートセンシングについて議論を行った。

著者

Kensuke NAKAJIMA Eizi TOYODA Masaki ISHIWATARI Shin-ichi TAKEHIRO Yoshi-Yuki HAYASHI

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.82, no.6, pp.1483-1504, 2004 (Released:2005-03-02)

参考文献数

23

被引用文献数

6 9 7

---

For the purpose of examining the initial development of the atmospheric response to a warm SST anomaly placed at the equator, an ensemble switch-on experiment is conducted with an aqua-planet GCM. An ensemble average of the size of 128 significantly reduces the transient noises caused by both small scale convective activity and large scale intraseasonal variability.In the first three days after the switch-on of the SST anomaly, a convection center develops above the warm SST area. As a barotropic response to the heating of convection center, a global increase of surface pressure occurs outside the low pressure region around the warm SST area. The response after the emergence of the high pressure anomaly is consistent with Gill (1980); a warm Kelvin wave-like anomaly is emitted to the east of the convection center, while a warm Rossby wave-like anomaly is emitted to the west.The Kelvin wave-like signal propagates at a speed slower than that of free Kelvin wave expected from its vertical wavelength, suggesting that the signal is a “moist” Kelvin wave. Transient decrease of precipitation occurs at the moist Kelvin wave front; a decrease of convection associated with the downward motion at the wave front is consistent with its slow propagation. After several days, precipitation recovers and is even intensified because of the surface frictional convergence associated with the Kelvin wave-like equatorial low pressure anomaly. To the west of the warm SST area, on the other hand, precipitation decreases monotonically. The continuous reduction of precipitation is caused by the equatorial surface frictional divergence associated with the relatively high pressure anomaly at the equator of the Rossby wave structure.Finally, there appears a slow zonally symmetric response within the Hadley cell characterized with surface pressure rise in the tropics and westerly wind anomaly in the troposphere. The change of eddy zonal momentum transport, together with the transport toward the lower level by the Hadley circulation and the geostrophic adjustment to the resulting low level westerly acceleration, seems to be responsible for the response.

著者

Takeshi ENOMOTO Hirokazu ENDO Yayoi HARADA Wataru OHFUCHI

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.87, no.1, pp.139-156, 2009 (Released:2009-03-07)

参考文献数

43

被引用文献数

13 14

---

In July 2004, torrential rainfalls caused significant damages in parts of Japan, followed by heat waves. Our data analysis shows that both rainfall and heat wave events in late Baiu season were caused by the intensification of the subtropical anticyclone near Japan (Bonin high) and that intensity of the Bonin high was significantly influenced by propagation of Rossby waves along the subtropical jet. Hindcast experiments from 15 July were conducted to study the mechanisms and predictability of these high-impact weather events. On 17-18 July, localized rainfalls at a few locations along the coast of the Sea of Japan including Sakata and Fukui were successfully simulated in a high-resolution (21-km mesh) global hindcast simulation. These rainfall events were found to occur near the leading edge of a filament of moist and warm air advected clockwise. On 20 July, anomalously high temperature was reproduced in the high-resolution hindcast simulation. With a moderate resolution of 83 km, the intensification of the subtropical anticyclone was reproduced although the föhn was much weaker. This result indicates that temperature distribution associated with föhn requires a resolution high enough to resolve major mountains. In order to investigate the predictability of propagation of Rossby waves and intensification of the Bonin high, 25-member ensemble experiments from 1 July 2004 were conducted using the moderate-resolution model. It is shown that the region along the Asian jet has twice as long predictability as the entire Northern Hemisphere. This case study suggests that the intensification of the Bonin high associated with the propagation of Rossby waves along the Asian jet could be predicted a few weeks in advance with an ensemble forecast at a moderate resolution.