著者

Alessandro Damiani Hitoshi Irie Tamio Takamura Rei Kudo Pradeep Khatri Hironobu Iwabuchi Ryosuke Masuda Takashi Nagao

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

vol.15, pp.198-204, 2019 (Released:2019-09-27)

参考文献数

39

被引用文献数

4

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We used observations recorded at Chiba University in November 2018 to examine the variability in cloud optical depth (COD) under overcast conditions. First, we conducted a careful evaluation of four COD datasets retrieved from three types of surface observations: i) zenith radiance recorded by two sky radiometers; ii) solar radiation data collected by a pyranometer; and iii) spatial distribution of radiance recorded using a sky camera system. Although the COD retrieved from the pyranometer (camera) slightly (moderately) overestimated the COD from zenith radiance, we found a satisfactory correlation among all surface estimates. This result suggests the efficacy of both pyranometer- and camera-based approaches and supports their broader use when dedicated cloud observations are not available. We then assessed satellite-based COD estimates retrieved from the recently launched Advanced Himawari Imager (AHI) aboard Himawari-8 (H-8) and Second-generation Global Imager (SGLI) on the Global Change Observation Mission for Climate (GCOM-C). Overall, we found good agreement between ground and satellite estimates; their correlation and root mean square error were virtually equivalent to values reported for co-located surface-based instruments. Nevertheless, the AHI-based COD was found to be slightly positively biased with respect to surface datasets.

著者

Takenari Kinoshita Koutarou Takaya Toshiki Iwasaki

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

vol.15, pp.193-197, 2019 (Released:2019-09-13)

参考文献数

16

---

The mass-weighted isentropic zonal mean (Z-MIM) equations derived by T. Iwasaki are powerful tools for diagnosing meridional circulation and wave-mean interaction, especially for the lower boundary and unstable waves. Recently, some studies have extended the equations to three dimensions by using the time mean instead of the zonal mean. However, the relation between wave activity flux and residual mean flow (not mass-weighed mean flow) is unclear. In the present study, we derive the three-dimensional (3D) wave activity flux and residual mean flow for Rossby waves on the mass-weighted isentropic time mean equations. Next, we discuss the relation between the obtained formulae and 3D transformed Eulerian-mean (TEM) equations.

著者

Jia Liu Xiaofeng Xu Xiangyang Luo

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

vol.15, pp.189-192, 2019 (Released:2019-09-11)

参考文献数

16

被引用文献数

2

---

Accurate estimation of tropical cyclone (TC) intensity is of great significance for serious natural disasters. A new method is presented to estimate intensity of TC using satellite infrared data. Firstly, TC region is calculated according to the location of TC center. Secondly, 2D-PCA algorithm is used to extract feature of bright temperature image, and historical data of TC intensity is matched with the k-nearest neighbor algorithm. Thirdly, the matching results are analyzed and the intensity information of TC is estimated. In addition, a TC intensity database, which contains historical data during 2006-2010, is developed for estimation of TC intensity. Experiments show that the proposed method is efficient for real-time estimation of TC intensity, average error of estimation is lower than 15 hPa.

著者

Shun-ichi I. Watanabe Hiroyuki Tsujino Akihiko Murata Masayoshi Ishii

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

vol.15, pp.183-188, 2019 (Released:2019-09-05)

参考文献数

31

被引用文献数

1

---

We evaluated the impact of sea surface temperature (SST) improvement realized by increasing horizontal resolution of an ocean model on dynamical downscaling (DDS) over Japan, focusing on the effects of the Kuroshio on summer precipitation in Japan. Two sets of SSTs were simulated using a high-resolution North Pacific (NP) model and a low-resolution global (GLB) ocean model. Using these SSTs as the lower boundary conditions for the atmosphere, two DDS experiments were conducted (NP-run and GLB-run). In NP-run, summer precipitation increases over the Kuroshio and reduces over Pacific coastal areas of Japan compared with GLB-run. Due to weaker southerly winds north of the Kuroshio in NP-run, the water vapor flux transported to Japan is smaller than in GLB-run. Both the pressure adjustment and the vertical mixing mechanisms weaken the southerly winds, with the latter being slightly more effective. Increasing the horizontal resolution of the ocean model, so that the Kuroshio is more realistically reproduced, improves the accuracy of simulated precipitation over Japan.

著者

Kazuo Saito

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

pp.2019-040, (Released:2019-10-10)

被引用文献数

8

---

It is well known that northward winds are often observed at southern coastal areas of Japan when a developed tropical cyclone is located off the south coast of Japan. These northward winds have been frequently referred to the northward emission of warm and humid air from the typhoon which cause pre-typhoon rainfalls, but their mechanism has not been clarified. In this paper, we show that the northward wind can be explained by the ageostrophic wind components dynamically induced by acceleration vector round the tropical cyclone.On 7th October 2009, when a developed typhoon (T0918 Melor) approached Japan, distinct northward winds were observed at aerological observations over western Japan. Using numerical simulations with the Japan Meteorological Agency nonhydrostatic model, we reproduced the observed northward wind and their mechanism were examined by numerical experiments.The origin of the northward winds is explained by the ageostrophic winds dynamically induced by the acceleration vectors. When a typhoon approaches a baroclinic zone from south, northeastward ageostrophic winds are induced by southeastward acceleration vectors. Other possible causes (diabatic heating and orographic effect) are examined by sensitivity experiments. Diabatic heating by moist process acts to enhance the ageostrophic winds but the role is not primary. Orography has little effect on the observed ageostrophic wind.Non-axisymmetric features of the upper level divergence flow of a tropical cyclone near a baroclinic zone can also be elucidated by the similar mechanism of the ageostrophic winds.

著者

Hanako Y. Inoue Kenichi Kusunoki Toru Adachi Chusei Fujiwara Naoki Ishitsu Ken-ichiro Arai

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

pp.2019-041, (Released:2019-10-18)

---

The characteristics and finescale evolution of misovortices within a snowband were examined using low-level high-resolution single- and dual-Doppler radar analysis. From 02:00 to 06:00 JST on 17 January 2017, many misovortices developed within three snowbands in the Japan Sea coastal region. The vortices developed along the shear line between the offshore north-northwesterly and the coastal northeasterly. As discussed in several previous studies of misovortices along airmass boundaries, horizontal shearing instability was considered to be a possible mechanism responsible for misovortex formation. A detailed investigation was performed on the most distinct snowband and misovortices embedded within it. Dual-Doppler analysis revealed a detailed behavior of vortex during merger, such as the morphological change from quasi-circular to elliptical shape, and the counterclockwise rotation which caused high-amplitude inflection of the shear line in less than 10 minutes. During the decay stage, the vortices weakened along with weakening convergence. The results suggest that evolution of the misovortex appears to have been closely tied to the low-level convergence within the vortex.

著者

Chiaki Kobayashi Ichiro Ishikawa

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

vol.15A, pp.31-36, 2019 (Released:2019-07-03)

参考文献数

11

被引用文献数

7

---

During summer 2018, zonally averaged tropospheric temperatures were higher than normal in the northern mid-latitudes, and this contributed to the extreme warmth experienced in eastern and western Japan. These northern-mid-latitudes warm anomalies, along with enhanced convective activity in the northern subtropics, persisted from autumn 2017 until autumn 2018. This paper demonstrates that both the persistent zonal pattern, and the circulation anomaly pattern, that developed during summer 2018 are well predicted by a reforecast experiment using an operational seasonal prediction system. As variation in zonally averaged convective activity in the northern subtropics is statistically closely related to northern-mid-latitude tropospheric warming in all seasons, we hypothesize that the former is likely to be a key influence on the latter. We found a weakening of northern-mid-latitude tropospheric warming in a sensitivity experiment in which tropical Pacific sea surface temperatures (SSTs) are nudged to the climatology and enhancement of convective activity in the northern tropics is weakened. These results suggest that SST anomalies in the tropical Pacific, which are well predicted by our reforecast experiment, contribute to the successful prediction of northern-mid-latitude tropospheric warming.

著者

Yuhei Takaya

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

vol.15A, pp.55-59, 2019 (Released:2019-08-24)

参考文献数

30

被引用文献数

15

---

The western North Pacific (WNP) exhibited markedly enhanced tropical cyclone (TC, typhoon) activity during the boreal summer (June–August) of 2018; 18 named typhoons were generated and 13 of these approached near Japan, causing serious damage and disruption in the country. During the summer of 2018, warm sea surface temperature persisted over the tropical Northeastern Pacific, which are typical oceanic conditions of a positive phase of the Pacific meridional mode (PMM), while no El Niño condition was observed. The Japan Meteorological Agency seasonal forecast system successfully predicted the enhanced TC activity in the WNP as well as associated seasonal characteristics such as a deep monsoon trough and active convection. Results of sensitivity experiments clearly indicate that the positive phase of the PMM played a major role in establishing the active TC conditions in the WNP during the summer of 2018 and reveal predictable seasonal processes of TC activity (genesis and tracks) during the summer of 2018, when there was no El Niño.

著者

Akiyo Yatagai Kotaro Minami Minami Masuda Naho Sueto

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

vol.15A, pp.43-48, 2019 (Released:2019-08-09)

参考文献数

10

被引用文献数

10

---

This study developed a rain-gauge-based hourly precipitation dataset to analyze the heavy precipitation event of July 2018 in Japan (H2018). We modified the APHRODITE algorithm to treat hourly precipitation data, and we detected orographically induced heavy precipitation patterns in western Japan. We compared the heavy precipitation pattern along with moisture transport with that of another disastrous precipitation event in 2014 over Hiroshima (H2014). It is evident that heavy precipitation occurred over a much wider area in Chugoku district during H2018 than in H2014, and extreme precipitation which exceeds 10mm/hr appeared three times in H2018 while at one time in H2014. Atmospheric rivers (ARs) were detected during two distinct episodes of heavy precipitation over Hiroshima, i.e., 19 August 2014 and 6 July 2018. Of the two events, the precipitation amount and the depth (height) of the AR were much greater in the latter. In the mid-troposphere, abundant moisture and high equivalent potential temperatures along the Meiyu frontal system can produce a large area of continuous heavy precipitation. The intensive hourly rainfall dataset developed in this study will be useful for investigations of AR and meso-scale system that affect heavy precipitation and validation of numerical models.

著者

Tomoe Nasuno

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

vol.15, pp.99-106, 2019 (Released:2019-05-16)

参考文献数

39

被引用文献数

5

---

Transport of moisture over the western Maritime Continent (MC) was examined using global cloud-system-resolving simulations for the Years of the Maritime Continent (YMC) field campaigns in 2015 and 2017, under peak El Niño and moderate La Niña conditions, respectively. We focused on the role of high- and low-frequency variability in the moistening over land and ocean, and their relationship with intraseasonal oscillation (ISO) events.The period-mean profiles indicate moistening by low-frequency upward motion in the deep troposphere and drying (moistening) in the lower (middle and upper) troposphere by high-frequency variability. The advection over ocean was greater in 2017 than in 2015, with the opposite occurring over land with smaller interannual differences. Over ocean, the roles of the high-frequency variability in the ISO life cycle, namely, the lower-to-middle-tropospheric moistening (enhanced upward transport of moisture) during the preconditioning (active) phases of the ISO, were common in both years, while over land, the high-frequency effects were nearly in phase (not correlated) with the ISO in the 2015 (2017) case. These results highlight clear land-ocean contrasts in the sensitivity of local convection to the background state and its link with the ISO life cycle.

著者

Van Q. Doan Van Nguyen Dinh Hiroyuki Kusaka Thanh Cong Ansar Khan Du Van Toan Nguyen Dinh Duc

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

vol.15, pp.113-118, 2019 (Released:2019-05-30)

参考文献数

32

被引用文献数

5

---

This study revealed great potential and shortcoming of offshore wind energy in Vietnam by numerical simulations with Weather Research and Forecasting (WRF) model at 10-km resolution for 10 years (2006-2015). The greatest energy potential was found in the offshore area of Phu Quy island (Binh Thuan province). The area, alone, can provide the 38.2 GW power generation capacity corresponding to the increasing renewable-energy demand by 2030 planned by the country. There is also a drawback of the wind resource, which is associated with strong multiple-scale temporal variabilities. The seasonal variability associated with monsoon onsets and daily variability associated with the wind diurnal cycles were found ranging 30-50%. Meanwhile, the inter-annual variability could reach up to 10%. These variabilities must be considered when designing wind farms and grids over the region. Additionally, due to the fact that the WRF model performed climatological features of the winds well against the observations, this results indicate that it can be useful tools for wind-power assessment as compared to other reanalysis or QuikSCAT data with coarser spatio-temporal resolutions.

著者

Hien Xuan Bui Jia-Yuh Yu Hsiao-Wei Liu Chia-Ying Tu Pin-Ging Chiu Huang-Hsiung Hsu

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

vol.15, pp.119-124, 2019 (Released:2019-05-30)

参考文献数

34

被引用文献数

6

---

While most studies have argued a slower increase of 1-3% K−1 of precipitation globally, others note that this is not necessarily the case from a regional perspective. In this study, we examine the convective structure changes over the equatorial Pacific with highly increased precipitation under global warming using simulations from the High Resolution Atmospheric Model (HiRAM). The moisture budget analysis shows that the precipitation increases must result from a significant enhancement of convection, with a minor modulation from the thermodynamic effect. Two different types of enhanced convection are identified. Over the mean ascending region, precipitation increases are associated with an enhancement of deep convection; while over the mean descending region, the precipitation increases are a result of enhanced shallow convection.

著者

Akifumi Nishi Hiroyuki Kusaka

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

vol.15, pp.149-153, 2019 (Released:2019-07-17)

参考文献数

23

被引用文献数

2

---

This study revealed that the Karakkaze events accompanied by rising temperature are more frequent than those accompanied by dropping temperature. This finding contrasted with the general belief for many years that the Karakkaze is a bora-type local wind. By focusing on the temporal evolution of temperature and wind, we were able to characterize three types of Karakkazes as follows: the surface wind speed and temperature both increase in the morning and then decrease in the afternoon (type Foehn-D); during the night, the temperature increases or stops decreasing, and the surface wind speed increases (type Foehn-N); and in the morning, the temperature decreases or stops increasing, and the surface wind speed increases (type Bora). As a result, we found that among the 238 Karakkazes that we identified, 103 were type Foehn-D events, 56 were type Foehn-N events, and 79 were type Bora events.

著者

Minghao Yang Ruiting Zuo Xin Li Liqiong Wang

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

vol.15, pp.166-171, 2019 (Released:2019-08-21)

参考文献数

40

被引用文献数

3

---

The Qian atmospheric forcing dataset is used to drive version 4.5 of the Community Land Model (CLM4.5) in off-line simulation tests. Based on the Global Land Evaporation Amsterdam Model (GLEAM) data, we attempt to ameliorate the canopy interception parameterization scheme in CLM4.5 by improving the empirical parameter and the physical structure. Considering that different plant functional types (PFTs) have different capacities to intercept rainfall is denoted as SEN1, and accounting for the influence of wind speed on canopy interception on the basis of SEN1 is denoted as SEN2. SEN1 shows obvious improvement in the simulated evaporation of intercepted water from vegetation canopy (Ec), not only greatly reduces the positive bias of the model to simulate Ec, especially in the equatorial region, but also significantly reduces the root mean square error (RMSE). SEN2 further improves the simulation of Ec by lowering the RMSE and increasing consistency with GLEAM data. In addition, the percentages of Ec over total evapotranspiration in both SEN1 and SEN2 are more reasonable and much closer to GLEAM data than that in CLM4.5.

著者

Jianbo Yang Min Shao Qingeng Wang Xu Yang

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

vol.15, pp.172-177, 2019 (Released:2019-08-24)

参考文献数

30

---

The relationships between the prediction of near-surface winds and the corresponding time of observations in eastern China were explored using the Advanced Weather Research and Forecasting (WRF) model and the three-dimensional variational (3D-Var) scheme in the gridpoint statistical interpolation (GSI) system. A series of one-month experiments was conducted in January 2018 with different time window configurations from 0.01 to 3.0 h. The relationship between the wind observation time and the model forecast was non-linear. An observational time closer to the initial time in the model usually have greater impact on the prediction of near-surface wind speeds. Observations in the 0.4-0.8 h time window associated with abnormally high with large near-surface wind speeds provide a negative impact. The predictions improved at a much smaller rate when the time window was increased from 0.8 to 3.0 h. No significant difference was seen as the time window increased in wind direction predictions, even with large wind increments. The optimum configuration of the time window in the GSI 3D-Var system for predicting near-surface winds should therefore be 0.2 or 0.4 h. A better understanding of the relationships between the observations and the predictions will help select more effective observations when using the 3D-Var scheme.

著者

Masaya Nosaka Hiroaki Kawase Hidetaka Sasaki Akihiko Murata

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

vol.15, pp.107-112, 2019 (Released:2019-05-22)

参考文献数

20

被引用文献数

3

---

High-frequency variations are excluded in the merged satellite and in-situ data global daily sea surface temperature (MGDSST) used in weather forecasting in Japan Meteorological Agency. We investigated the importance of temporal resolution on sea surface temperature (SST) when predicting winter precipitation using the Non-Hydrostatic Regional Climate Model. We used seven-day temporal smoothing to investigate the influence of temporal resolution on prediction. The Gaussian filter was used as spatial smoothing for comparison with the influence of spatial resolution. The influence of the temporal resolution of SST on monthly precipitation is smaller than that of spatial resolution. However, the influence of the temporal resolution on daily precipitation is comparable to that of spatial resolution. The temporal resolution of SST greatly affects precipitation, particularly in December, as the variations in SST are largest compared to the rest of the year. Furthermore, the winter monsoon promotes the effect of SST on winter precipitation. Our experiments using seven-day moving average smoothing indicates that the temporal resolution of the SST on precipitation become about 15 %/K under the winter monsoon.

著者

Kengo Arai Kazuaki Yasunaga

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

vol.15, pp.80-86, 2019 (Released:2019-04-12)

参考文献数

13

被引用文献数

1

---

This study examines dominant precipitation patterns during winter in the north-central region (Hokuriku District) of Japan, based on empirical orthogonal functions (EOFs) analysis. The pattern of the first leading component is similar to that of the mean precipitation, and the second leading component shows a dipole structure in which positive and negative regions are separated by the coast line. This dipole pattern across the coast line is robust regardless of data stratifications for the EOF calculation. Composites reveal that maritime and inland precipitation is relatively enhanced before and after the passage of a mid-level trough, respectively. In the former case, the temperature is higher and westerly or southwesterly wind prevails, while northwesterly wind dominates in the latter case. It is suggested that interactions between cold air over the land and warm air over the ocean are essentially important to the distinct precipitation patterns; offshore winds wedge the inland cold air under the maritime warm air, and intensifies the precipitation over the ocean. On the other hand, the northwesterly monsoonal flow pushes the maritime warm air onto the inland cold air, and more precipitation is brought about around the mountain range.

著者

Kazuto Takemura Akihiko Shimpo

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

vol.15, pp.75-79, 2019 (Released:2019-04-06)

参考文献数

20

被引用文献数

1

---

Herein, (i) the remote influence of positive Indian Ocean Dipole (P-IOD) events in enhancing Tibetan High and (ii) its impact on the East Asian climate, from July to September, is analyzed based on composite analysis and linear baroclinic model experiment. In the equatorial Indian Ocean, convective activity enhances over the western part and suppresses over the eastern, which is associated with the zonal contrast of the sea surface temperature anomaly during P-IOD events. A lower-tropospheric clockwise circulation anomaly is evident from the eastern equatorial Indian Ocean where the suppressed convection is seen to the Indochina Peninsula. The streamlines arrive at the seas east of the Philippines, contributing to the enhancement of the monsoon trough. In the upper troposphere, crucial divergence anomaly over a wide area in the western North Pacific and the associated stronger-than-normal northward divergent winds toward East Asia cause strong northward negative-vorticity advection over the northern part of East Asia, contributing to the northeastward extension of the Tibetan High. This circulation anomaly contributes to both the significantly hot conditions in boreal summer and the late-summer heat over East Asia.

著者

Hai Bui Shigeo Yoden Eriko Nishimoto

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

vol.15, pp.62-67, 2019 (Released:2019-03-21)

参考文献数

15

被引用文献数

4

---

We present a three-dimensional minimal model that produces a self-sustained oscillation reminiscent of the quasi-biennial oscillation (QBO) in a radiative–moist convective quasi-equilibrium state. The computational domain is rectangular (640 km × 160 km) with doubly periodic boundary conditions. After initial transient time, an oscillation with a period of about 300 days emerges in the stratosphere, both in the domain-averaged zonal wind and meridional wind. A synchronization of the zonal and meridional winds is observed and is characterized as an anti-clockwise rotation of a skewed spiral feature with height in the mean horizontal wind vectors. The QBO-like wind oscillations penetrate into the troposphere. Modulation of tropospheric temperature anomalies and precipitation occurs with an irregular period of about 100 days, in which heavy precipitation is associated with positive temperature anomalies. The simulation reveals three types of precipitation patterns: isolated quasi-stationary type clusters, fast-moving back-building type and squall-line type patterns. The quasi-stationary type is newly identified in this three-dimensional model. Intermittent self-organization of convective systems into quasi-stationary type and transition back to the fast-moving back-building type or squall-line type are fundamental characteristics of self-aggregation in the three-dimensional model.

著者

Wenkai Li Shuzhen Hu Zongmei Pan Xiaoyun Su Xinyue Luo Yijuan Wang

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

vol.15, pp.47-51, 2019 (Released:2019-02-28)

参考文献数

45

被引用文献数

2

---

The apparent temperature (APT), or human-perceived temperature, is commonly defined as a function of the surface air temperature (SAT), vapour pressure (or humidity) and wind speed. This paper demonstrates that the APT over China, as revealed by daily station-observed data, has generally increased faster than the SAT during summertime in the past 50 years (1968-2017). The rate of increase in APT was significantly faster than that of SAT in 60.1% of stations, and the difference between the average China-wide APT and SAT was 0.11°C decade−1. This phenomenon is occurring nationwide, but it is more intense over western, north-eastern and eastern coastal China. The more rapid increasing trend in APT indicates that human beings actually experience surplus heat stress under a certain change in SAT, and the increased SAT explains 67.0% of the average APT warming for the country, contributing to the change in the base APT. Apart from the increasing SAT, a decrease in surface wind speed and an increase in surface vapour pressure have also been observed, contributing to 21.6% of the increase in APT and explaining the remaining 11.4%, respectively.