|2020||Fumiaki Fujibe||Temperature Anomaly in the Tokyo Metropolitan Area during the COVID-19 (coronavirus) Self-Restraint Period|
|2019||Yukiko Imada, Masahiro Watanabe, Hiroaki Kawase, Hideo Shiogama, Miki Arai||The July 2018 High Temperature Event in Japan Could Not Have Happened without Human-Induced Global Warming|
|2018||Kosuke Ito, Hiroyuki Yamada, Munehiko Yamaguchi, Tetsuo Nakazawa, Norio Nagahama, Kensaku Shimizu, Tadayasu Ohigashi, Taro Shinoda and Kazuhisa Tsuboki||Analysis and Forecast Using Dropsonde Data from the Inner-Core Region of Tropical Cyclone Lan (2017) Obtained during the First Aircraft Missions of T-PARCII|
|2017||Hiroaki Miura||“Coupling the Hexagonal B1-grid and B2-grid to Avoid Computational Mode Problem of the Hexagonal ZM-Grid”, SOLA, Vol. 13, 069-073. (2017)|
|Daisuke Goto, Shinji Morimoto, Shuji Aoki, Satoshi Sugawara, Shigeyuki Ishidoya, Yoichi Inai, Sakae Toyoda, Hideyuki Honda, Gen Hashida, Takashi Yamanouchi, and Takakiyo Nakazawa||“Vertical Profiles and Temporal Variations of Greenhouse Gases in the Stratosphere over Syowa Station, Antarctica”, SOLA, Vol. 13, 224-229. (2017)|
|2016||Toru Adachi, Kenichi Kusunoki, Satoru Yoshida, Hanako Inoue, Ken-ichiro Arai, and Tomoo Ushio||“Rapid Volumetric Growth of Misocyclone and Vault-Like Structure in Horizontal Shear Observed by Phased Array Weather Radar”, SOLA, Vol. 12, 314-319. (2016)|
|2015||Satoshi Masuda and Keiichi Ishioka||“A Method to Calculate Steady Lee-Wave Solutions with High-Accuracy”, SOLA, Vol. 11, 085-089. (2015)|
|2014||Toru Miyama and Takuya Hasegawa||“Impact of Sea Surface Temperature on Westerlies over the Western Pacific Warm Pool: Case Study of an Event in 2001/02”, SOLA, Vol. 10, 5-9. (2014)|
|2013||Qoosaku Moteki and Atsuyoshi Manda||“Seasonal Migration of the Baiu Frontal Zone over the East China Sea: Sea Surface Temperature Effect”, SOLA, Vol. 9, 019-022. (2013)|
|2012||Toshiki Iwasaki and Yasushi Mochizuki||“Mass-Weighted Isentropic Zonal Mean Equatorward Flow in the Northern Hemispheric Winter”, SOLA, Vol. 8, 115-118. (2012)|
|2011||Hirokazu Endo||“Long-Term Changes of Seasonal Progress in Baiu Rainfall Using 109 Years (1901—2009) Daily Station Data”, SOLA, Vol. 7, 005-008. (2011)|
|Jun Inoue, Masatake E. Hori, Takeshi Enomoto, and Takashi Kikuchi||“Intercomparison of Surface Heat Transfer Near the Arctic Marginal Ice Zone for Multiple Reanalyses: A Case Study of September 2009”, SOLA, Vol. 7, 057-060. (2011)|
|2010||Junshi Ito, Hiroshi Niino, and Mikio Nakanishi||“Large Eddy Simulation on Dust Suspension in a Convective Mixed Layer”, SOLA, Vol. 6, 133-136. (2010)|
The Temperature Anomaly in the Tokyo Metropolitan Area during the COVID-19 (coronavirus) Self-Restraint Period
- Research Center for Climatology, Department of Geography, Tokyo Metropolitan University
Japan underwent a nationwide self-restraint of human activities in spring 2020 to prevent the spread of the COVID-19 infection. In order to evaluate the effect of suppressed human activities on temperature in the Tokyo Metropolitan area, a statistical analysis was made for temperature anomalies during the self-restraint period using hourly data on the AMeDAS network. The temperature anomaly was defined by the departure from the value that would have been observed without self-restraint, estimated from regression analysis for temperatures at surrounding non-urban stations. It was found that the temperature in central Tokyo (Kitanomaru Park) had a negative anomaly of −0.49°C with a 95% confidence range of ±0.19°C on the average over the strong self-restraint period from April to May. The anomaly was larger in the nighttime than in the daytime, and was found in an area spreading for several tens of kilometers, with a decreasing magnitude according to the distance from Tokyo. These facts indicate a possibility that the reduction of anthropogenic heat release during the self-restraint period resulted in substantial decrease of temperature in the Tokyo Metropolitan area.
The July 2018 High Temperature Event in Japan Could Not Have Happened without Human-Induced Global Warming
Yukiko Imada(1), Masahiro Watanabe(2), Hiroaki Kawase(1),Hideo Shiogama(3), and Miki Arai(2)
- Meteorological Research Institute, Japan Meteorological Agency
- Atmosphere and Ocean Research Institute, University of Tokyo
- National Institute for Environmental Studies
The high temperature event in July 2018 caused record-breaking human damage throughout Japan. Large-ensemble historical simulations with a high-resolution atmospheric general circulation model showed that the occurrence rate of this event under the condition of external forcings in July 2018 was approximately 20%. This high probability was a result of the high-pressure systems both in the upper and lower troposphere in July 2018. The event attribution approach based on the large-ensemble simulations with and without human-induced climate change indicated the following: (1) The event would never have happened without anthropogenic global warming. (2) The strength of the two-tiered high-pressure systems was also at an extreme level and at least doubled the level of event probability, which was independent of global warming. Moreover, a set of the large-ensemble dynamically downscaled outputs revealed that the mean annual occurrence of extremely hot days in Japan will be expected to increase by 1.8 times under a global warming level of 2°C above pre-industrial levels.
Analysis and Forecast Using Dropsonde Data from the Inner-Core Region of Tropical Cyclone Lan (2017) Obtained during the First Aircraft Missions of T-PARCII
Kosuke Ito(1)(2)(6), Hiroyuki Yamada(1), Munehiko Yamaguchi(2), Tetsuo Nakazawa(2), Norio Nagahama(3), Kensaku Shimizu(3), Tadayasu Ohigashi(4), Taro Shinoda(5), Kazuhisa Tsuboki(5)
- University of the Ryukyus
- Meteorological Research Institute
- Meisei Electric Co., LTD.
- National Research Institute for Earth Science and Disaster Resilience
- Nagoya University
- Japan Agency for Marine–Earth Science and Technology
The inner core of Tropical Cyclone Lan was observed on 21-22 October 2017 by GPS dropsondes during the first aircraft missions of the Tropical Cyclones-Pacific Asian Research Campaign for the Improvement of Intensity Estimations/Forecasts (T-PARCII). To evaluate the impact of dropsondes on forecast skill, 12 36-h forecasts were conducted using a Japan Meteorological Agency non-hydrostatic model (JMA-NHM) with a JMA-NHM-based mesoscale four-dimensional data assimilation (DA) system. Track forecast skill improved over all forecast times with the assimilation of the dropsonde data. The improvement rate was 8-16% for 27-36-h forecasts. Minimum sea level pressure (Pmin) forecasts were generally degenerated (improved) for relatively short-term (long-term) forecasts by adding the dropsonde data, and maximum wind speed (Vmax) forecasts were degenerated. Some of the changes in the track and Vmax forecasts were statistically significant at the 95% confidence level. It is notable that the dropsonde-derived estimate of Pmin was closer to the real-time analysis by the Regional Specialized Meteorological Center (RSMC) Tokyo than the RSMC Tokyo best track analysis. The degeneration in intensity forecast skill due to uncertainties in the best track data is discussed.
Vertical Profiles and Temporal Variations of Greenhouse Gases in the Stratosphere over Syowa Station, Antarctica
Daisuke Goto(1), Shinji Morimoto(2), Shuji Aoki(2), Satoshi Sugawara(3), Shigeyuki Ishidoya(4), Yoichi Inai(2), Sakae Toyoda(5), Hideyuki Honda(6), Gen Hashida(1), Takashi Yamanouchi(1), Takakiyo Nakazawa(2)
- National Institute of Polar Research (NIPR)
Department of Polar Science, The Graduate University for Advanced Studies (SOKENDAI)
- Center for Atmospheric and Oceanic Studies, Tohoku University
- Miyagi University of Education
- National Institute of Advanced Industrial Science and Technology (AIST)
- Department of Chemical Science and Engineering, School of Materials and Chemical Technology, Tokyo Institute of Technology
- Institute of Space and Astronautical Science (ISAS), Japan Aerospace Exploration Agency (JAXA)
Stratospheric air sampling using balloon-borne cryogenic air samplers was conducted over Syowa Station, Antarctica in four austral summers between 1998 and 2013. The CH4 and N2O mole fractions decreased with increasing altitude due to chemical reactions and photodissociation in the stratosphere, and a compact positive correlation between CH4 and N2O was found in their vertical profiles. The vertical profiles of CO2 and SF6 mole fractions showed high values in the lower stratosphere, decreasing gradually with altitude, and then becoming almost constant at altitudes above 18 km. Stratospheric CO2 and SF6 above 18km over Antarctica increased secularly at the respective average rates of 1.82 ± 0.31 ppm yr−1 and 0.26 ± 0.01 ppt yr−1 during the study period. The CO2 and SF6 mole fractions increased in the Antarctic stratosphere, but were delayed 4.5 ± 0.5 and 5.6 ± 0.2 years, respectively, compared to the tropical troposphere. The secular increase in stratospheric CH4 was also detected by classifying the measured mole fractions in terms of the N2O depletion in the stratosphere.
Coupling the Hexagonal B1-grid and B2-grid to Avoid a Computational Mode Problem of the Hexagonal ZM-grid
- Department of Earth and Planetary Science, Graduate School of Science, The University of Tokyo
A shallow water model is developed on the regular hexagonal mesh by combining the hexagonal B1-grid and B2-grid schemes. The new scheme called as the hexagonal synchronized B-grid (SB-grid) scheme in this work allows avoiding a computational mode problem of the ZM-grid scheme. It is known that the problem is caused by the mismatch of degrees of freedoms of the prognostic variables. The SB-grid uses the same variable arrangement as the ZM-grid, placing fluid depths and fluid velocities at the centers and corners of hexagonal cells, respectively, but the nonlinear terms of the momentum equation are discretized using wider spatial stencils than those of the ZM-grid. This change results in the inhibition of extra interactions in the velocity fields that enhances a computational mode in the ZM-grid. Geostrophic adjustment tests on a regular hexagonal mesh confirm that the SB-grid shallow water model behaves almost equivalently to the Z-grid model, and the computational mode problem is certainly settled down.
Rapid Volumetric Growth of Misocyclone and Vault-Like Structure in Horizontal Shear Observed by Phased Array Weather Radar
Toru Adachi(1), Kenichi Kusunoki(1), Satoru Yoshida(1), Hanako Inoue(1), Ken-ichiro Arai(1), Tomoo Ushio(2)
- Meteorogical Research Institute, Japan Meteorological Agency, Tsukuba, Japan
- Faculty of Engineering, Osaka University, Suita, Japan
The present paper reports a sub-minute scale growth of a misocyclone and vault-like structure in a horizontal shear environment observed by a phased array weather radar (PAWR). Between 0756 and 0801 Japan Standard Time on 25 August 2013, dual radar synthesis shows a signature of significant low-level convergence at 0.6-0.8 km above sea level (ASL). PAWR data show a coincident rapid growth of a misocyclone with top altitude increasing from 1.2 to 1.8 km ASL in two minutes. A small vault-like structure with the maximum height of 1.3 km is formed following to the development of misocyclone with a delay time of about two minutes. One possible explanation is the role of vorticity stretching associated with horizontal shear instability. Fast and volumetric seamless observation of such a small spatiotemporal-scale phenomena opens up a way to progress our understanding of misocyclone that is of importance for convection initiation and severe weather phenomena.
A Method to Calculate Steady Lee-Wave Solutions with High-Accuracy
Satoshi Masuda(1) and Keiichi Ishioka(1)
- Graduate School of Science, Kyoto University, Kyoto Japan
This study proposes a new numerical method to compute highly accurate, full-nonlinear, two-dimensional steady lee-wave solutions. The method is based on the charge simulation method and enables to obtain numerical solutions of steady lee wave over arbitrary topography. The accuracy of the proposed method is evaluated for the steady flow and lee wave over a semicircular mountain through the comparison with the exact solution based on a lee-wave theory. It is demonstrated that compared with an existing boundary element method the proposed method is able to provide a highly accurate solution for the semicircular mountain test. The present method is further applied to obtain a well-behaved numerical solution of lee wave over a Gaussian-shaped, steep mountain.
Numerical modeling of the atmosphere over complex topography is a challenging task in order to improve the accuracy of high-resolution atmospheric models. There are recently some new developments of high-resolution atmospheric models. In order to evaluate such high-resolution models, a basic test case for flows over arbitrary complex topography should be useful. The method proposed by the present study is very unique in the sense that it provides a standard solution for flows and lee waves over complex topography and a useful guidance for high-resolution modeling. The proposed method is also helpful for the theoretical understanding of lee waves over topography. Therefore, the Editorial Committee of SOLA highly evaluates the excellence of the authors’ study.
Impact of Sea Surface Temperature on Westerlies over the Western Pacific Warm Pool: Case Study of an Event in 2001/02
Toru Miyama(1), and Takuya Hasegawa(2)
- Application Laboratory and Research Institute for Global Change, Japan Agency for Marine-Earth Science and Technology, Kanagawa, Japan
- Research Institute for Global Change, Japan Agency for Marine-Earth Science and Technology, Kanagawa, Japan
This study examines a tropical western Pacific westerly wind event observed in 2001/02 boreal winter, which contributed to a subsequent El Niño development in 2002, with the use of both regional atmospheric and oceanic models. From regional atmospheric model experiments, the authors show that zonal sea surface temperature gradient in the equatorial western Pacific, which is caused by cold water upwelling to the north of New Guinea and the eastward extension of warm pool, locally reinforced the surface westerly winds. They estimate that this local SST gradient accounts for the half of the westerly anomaly. Through regional ocean model experiments, they further present triggering of an oceanic Kelvin wave by the intensified surface westerly winds, highlighting the role of regional sea surface temperature gradient in a subsequent El Niño development. These numerical experiments are well designed and make a strong case for their hypothesis. This study reveals a unique air-sea interaction, and a variety of applications are expected to emerge, including an improved understanding and prediction of El Niño development and a unique air-sea coupled mode in the western Pacific warm pool. Therefore, the Editorial Committee of SOLA highly evaluates of the excellence of the authors’ study.
Seasonal Migration of the Baiu Frontal Zone over the East China Sea: Sea Surface Temperature Effect
Qoosaku Moteki(1), Atsuyoshi Manda(2)
- Research Institute for Global Change (RIGC), Japan Agency for Marine-Earth Science and Technology (JAMSTEC)
- Nagasaki University
We propose a new scenario for the seasonal migration of the Baiu frontal zone over the East China Sea in which this migration is affected by variations in the sea surface temperature (SST). Using atmospheric and oceanic objective analysis datasets, a relationship was determined between the seasonal migration of the Baiu frontal zone and the decaying process of the cold high over the East China Sea. Before the middle of June, the cold high, cooled by the low SST, is present over the continental shelf, and the position of the Baiu frontal zone corresponds to that of the Kuroshio Front. After the middle of June, the cold high decays and is shifted northward in association with the warming SST over the shelf. As a result, the Baiu frontal zone migrates northward and ends in the middle of July due to the dissipation of the cold high.
Mass-Weighted Isentropic Zonal Mean Equatorward Flow in the Northern Hemispheric Winter
Toshiki Iwasaki(1), Yasushi Mochizuki(2)
- Graduate School of Science, Tohoku University
- Okinawa Meteorological Observatory
In the diagnosis of mass-weighted isentropic zonal mean (MIM), the mean- meridional circulation has a strong extratropical direct (ETD) cell in the northern- hemispheric winter, which turns from downward to equatorward around 45°N and isentropic zonal mean pressure of 850 hPa. The January mean equatorward flow in the extratopical lower troposphere is almost in balance with Eliassen-Palm (E-P) flux divergence for both climatology and interannual variability. This means that the zonal mean equatorward flow in the extratropical lower troposphere is the wave-induced circulation as well as the poleward flow in the stratosphere is.
The interannual variation of January mean mass stream functions at (45°N, 850 hPa) positively (negatively) correlates with the zonal mean temperature in the lower troposphere north (south) of about 45°N, respectively. This is consistent with a simple thermodynamic consideration that the strong ETD circulation adiabatically warms up the lower troposphere due to the descending flow in the higher latitudes but cools it down due to the heat advection by the equatorward flow in the middle latitudes (～35°N).
Long-Term Changes of Seasonal Progress in Baiu Rainfall Using 109 Years (1901-2009) Daily Station Data
- Meteorological Research Institute
This study investigates long-term changes in Baiu rainfall in Eastern and Western Japan using daily precipitation records at 37 stations for the years 1901 through 2009, focusing on its seasonal progress. This period is much longer than various data analyzed in previous observational studies. In the early Baiu season (early to mid June), significant long-term decreasing trends are observed in Eastern and Western Japan, accompanying large inter-decadal variation in the former half of the 20th century. In the late Baiu season (mid to late July), in contrast, significant long-term increasing trends are observed on the Japan Sea side of Eastern and Western Japan. No significant trends are recognized either in the mid Baiu season (late June to early July) or in the entire Baiu season (June to July) over all regions. It is interesting to note that the observed tendency of delayed Baiu withdrawal in the last 109 years, when global warming has been in progress, is similar to its future changes projected by climate models.
Intercomparison of Surface Heat Transfer Near the Arctic Marginal Ice Zone for Multiple
Reanalyses: A Case Study of September 2009
Jun Inoue(1), Masatake E. Hori(1), Takeshi Enomoto(2), Takashi Kikuchi(1)
- Research Institute for Global Change, JAMSTEC
- The Earth Simulator Center, JAMSTEC
This study evaluated surface heat fluxes in reanalyses (ERA-Interim, JCDAS, and NCEP/NCAR) at the marginal ice zone during September 2009, a month in which intensive radiosonde soundings were performed during an Arctic cruise by the Japanese R/V Mirai. Two surface conditions are compared: very new ice cover during a period of low temperature and ice-free conditions. ERA-Interim reproduces the observed temperature profiles well because the turbulent heat fluxes are realistic, due to the explicit treatment of the ice concentration. With the relatively simplified treatment in JCDAS, the temperature is significantly underestimated (overestimated) in the quasi-ice-covered (ice-free) area. Although NCEP/NCAR has characteristics between ERA-Interim and JCDAS, the satellite-derived sea surface temperature (SST) distribution near the ice edge efficiently controls the heat fluxes.
Large Eddy Simulation on Dust Suspension in a Convective Mixed Layer
Junshi Ito(1), Hiroshi Niino(1), Mikio Nakanishi(2)
- Atmosphere and Ocean Research Institute, The University of Tokyo
- National Defense Academy
Observations show that optical depth over desert increase during daytime when a convective mixed layer develops under a light general wind condition. This implies that dust suspension by horizontal winds associated with convective motions occur even in the absence of general winds. In the present paper, a large eddy simulation is performed to study how much dust is suspended in a convective mixed layer without a general wind. The results show that dust particle concentration in the convective mixed layer can reach on the order of 10 μg m-3, which is in reasonable agreement with observations. Tiny dust particles that have small terminal velocities are easily brought up by convective winds during daytime and remain in the atmosphere throughout night. If a similar weather continues for several days, dust particles concentration on the evening of the second day can reach 1.8 times as large as that on the evening of the first day, accordingly.