2022

Observing System Simulation Experiments of a Rich Phased Array Weather Radar Network Covering Kyushu for the July 2020 Heavy Rainfall Event

Yasumitsu Maejima(1), Takuya Kawabata(2), Hiromu Seko(2), and Takemasa Miyoshi(1,3,4,5,6)

1. RIKEN Center for Computational Science (R-CCS)
2. Meteorological Research Institute, Japan Meteorological Agency
3. RIKEN interdisciplinary Theoretical and Mathematical Sciences Program
4. RIKEN Cluster for Pioneering Research
5. Department of Atmospheric and Oceanic Science, University of Maryland, College Park
6. Application Laboratory, Japan Agency for Marine-Earth Science and Technology

SOLA, Vol. 18, pp. 25−32, doi:10.2151/sola.2022-005

Citation: The SOLA Award in 2022

Abstract
This study investigates a potential impact of a rich phased array weather radar (PAWR) network covering Kyushu, Japan on numerical weather prediction (NWP) of the historic heavy rainfall event which caused a catastrophic disaster in southern Kumamoto on 4 July 2020. Perfect-model, identical-twin observing system simulation experiments (OSSEs) with 17 PAWRs are performed by the local ensemble transform Kalman filter (LETKF) with a regional NWP model known as the Scalable Computing for Advanced Library and Environment-Regional Model (SCALE-RM) at 1-km resolution. The nature run is generated by running the SCALE-RM initialized by the Japan Meteorological Agency (JMA) mesoscale model (MSM) analysis at 1800 JST 3 July 2020, showing sustained heavy rainfalls in southern Kumamoto on 4 July. Every 30-second synthetic reflectivity and radial winds are generated from the nature run at every model grid point below 20-km elevation within 60-km ranges from the 17 PAWRs. Two different control runs are generated, both failing to predict the heavy rainfalls in southern Kumamoto. In both cases, assimilating the PAWR data improves the heavy rainfall prediction mainly up to 1-hour lead time. The improvement decays gradually and is lost in about 3-hour lead time likely because the large-scale Baiu front dominates.

Impacts of Midlatitude Western North Pacific Sea Surface Temperature Anomaly on the Subseasonal to Seasonal Tropical Cyclone Activity: Case Study of the 2018 Boreal Summer

Tomoe Nasuno(1), Masuo Nakano(1), Hiroyuki Murakami(2), Kazuyoshi Kikuchi(2), and Yohei Yamada(1)

1. Japan Agency for Marine-Earth Science and Technology
2. Geophysical Fluid Dynamics Laboratory

SOLA, Vol. 18, pp. 88−95, doi:10.2151/sola.2022-015

Citation: The SOLA Award in 2022

Abstract
In this study, we explored the impacts of midlatitude western North Pacific (WNP) sea surface temperature (SST) on tropical cyclone (TC) activity at intraseasonal to seasonal time scales during the 2018 boreal summer. During this period, a positive SST anomaly occurred in the midlatitude WNP and subtropical central Pacific; TC activity was abnormally high under the influence of the strong Asian summer monsoon. We performed sensitivity experiments using a global cloud system-resolving model for global SST (control, CTL) and SST that were regionally restored according to midlatitude WNP climatology (MWNPCLM). TC track density in the eastern WNP was higher in CTL than in MWNPCLM, in association with large-scale atmospheric responses; enhanced monsoon westerlies in the subtropical WNP, moist rising (dry subsiding) tendencies, and reduced (enhanced) vertical wind shear in the eastern (western) WNP. Enhanced TC activity in the eastern WNP was more distinct for intense TCs and during the active phase of intraseasonal oscillation (ISO). These results suggest that the impacts of midlatitude SST anomalies can reach lower latitudes to affect TC activity via large-scale atmospheric responses and ISO, which are usually overwhelmed by the impacts of SST anomalies in the tropics and subtropics.

2021

Seasonal variation in high arctic stratospheric aerosols observed by lidar at Ny Ålesund, Svalbard between March 2014 and February 2018

Koichi Shiraishi(1) and Takashi Shibata(2)

1. Faculty of Science, Fukuoka University
2. Nagoya University

SOLA, Vol.17, pp. 30-34, doi:10.2151/sola.2021-005

Citation: The SOLA Award in 2021

Abstract
Stratospheric aerosols over the high Arctic at Ny Ålesund, Svalbard (79°N, 12°E) were observed continuously for four years from March 2014 by a lidar system using the second harmonic wavelength (532 nm) of the Nd:YAG laser. Our observations reveal the seasonal features of stratospheric aerosols and the arrival of the smoke at the high Arctic from Canadian forest-fire in August 2017. We estimated the seasonal variation for three years before the Canadian forest-fire when there was no apparent volcanic effect. In the estimation, we removed polar stratospheric clouds by the threshold temperature of their formation. The seasonal variation for the three years is that the vertical profiles of the backscattering ratio take a maximum value of about 1.05-1.06 at altitudes between 13 and 16 km from December to March, and about 1.02-1.04 at altitudes between 17 and 20 km from April to November. These results are compared with the results observed at the low Arctic, northern Norway. We also present the increases in the backscattering ratio and the volume depolarization ratio from September to December 2017 caused by the smoke from the Canadian forest-fire.

2020

The Temperature Anomaly in the Tokyo Metropolitan Area during the COVID-19 (coronavirus) Self-Restraint Period

Fumiaki Fujibe(1)

1. Research Center for Climatology, Department of Geography, Tokyo Metropolitan University

SOLA, Vol.16, pp. 175-179, doi:10.2151/sola.2020-030

Citation: The SOLA Award in 2020

Abstract
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.

2019

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)

1. Meteorological Research Institute, Japan Meteorological Agency
2. Atmosphere and Ocean Research Institute, University of Tokyo
3. National Institute for Environmental Studies

SOLA, Vol.15A, pp. 8-12, doi:10.2151/sola.15A-002

Citation: The SOLA Award in 2019

Abstract
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.

2018

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)

1. University of the Ryukyus
2. Meteorological Research Institute
3. Meisei Electric Co., LTD.
4. National Research Institute for Earth Science and Disaster Resilience
5. Nagoya University
6. Japan Agency for Marine–Earth Science and Technology

SOLA, Vol.14, pp. 105-110, doi:10.2151/sola.2018-018

Citation: The SOLA Award in 2018

Abstract
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.

2017

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)

1. National Institute of Polar Research (NIPR)
   Department of Polar Science, The Graduate University for Advanced Studies (SOKENDAI)
2. Center for Atmospheric and Oceanic Studies, Tohoku University
3. Miyagi University of Education
4. National Institute of Advanced Industrial Science and Technology (AIST)
5. Department of Chemical Science and Engineering, School of Materials and Chemical Technology, Tokyo Institute of Technology
6. Institute of Space and Astronautical Science (ISAS), Japan Aerospace Exploration Agency (JAXA)

SOLA, Vol. 13, pp. 224-229, doi:10.2151/sola.2017-041.

Citation: The SOLA Award in 2017

Abstract
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

Hiroaki Miura(1)

1. Department of Earth and Planetary Science, Graduate School of Science, The University of Tokyo

SOLA, Vol. 13, pp. 69-73, doi: 10.2151/sola.2017-013.

Citation: The SOLA Award in 2017

Abstract
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.

2016

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)

1. Meteorogical Research Institute, Japan Meteorological Agency, Tsukuba, Japan
2. Faculty of Engineering, Osaka University, Suita, Japan

SOLA, Vol. 12, pp. 314-319, doi: 10.2151/sola.2016-061.

Citation: The SOLA Award in 2016

Abstract
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.

2015

A Method to Calculate Steady Lee-Wave Solutions with High-Accuracy

Satoshi Masuda(1) and Keiichi Ishioka(1)

1. Graduate School of Science, Kyoto University, Kyoto Japan

SOLA, Vol. 11, pp. 85-89, doi: 10.2151/sola.2015-021.

Citation: The SOLA Award in 2015

Abstract
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.

2014

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)

1. Application Laboratory and Research Institute for Global Change, Japan Agency for Marine-Earth Science and Technology, Kanagawa, Japan
2. Research Institute for Global Change, Japan Agency for Marine-Earth Science and Technology, Kanagawa, Japan

SOLA, Vol. 10, pp. 5−9, doi: 10.2151/sola.2014-002.

Citation: The SOLA Award in 2014

Abstract
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.

2013

Seasonal Migration of the Baiu Frontal Zone over the East China Sea: Sea Surface Temperature Effect

Qoosaku Moteki(1), Atsuyoshi Manda(2)

1. Research Institute for Global Change (RIGC), Japan Agency for Marine-Earth Science and Technology (JAMSTEC)
2. Nagasaki University

SOLA, Vol. 9, pp. 19-22, doi: 10.2151/sola.2013-005.

Abstract
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.

2012

Mass-Weighted Isentropic Zonal Mean Equatorward Flow in the Northern Hemispheric Winter

Toshiki Iwasaki(1), Yasushi Mochizuki(2)

1. Graduate School of Science, Tohoku University
2. Okinawa Meteorological Observatory

SOLA, Vol. 8, pp. 115-118, doi: 10.2151/sola.2012-029.

Abstract
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).

2011

Long-Term Changes of Seasonal Progress in Baiu Rainfall Using 109 Years (1901-2009) Daily Station Data

Hirokazu Endo(1)

1. Meteorological Research Institute

SOLA, Vol. 7, pp. 5-8, doi: 10.2151/sola.2011-002.

Abstract
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)

1. Research Institute for Global Change, JAMSTEC
2. The Earth Simulator Center, JAMSTEC

SOLA, Vol. 7, pp. 57-60, doi: 10.2151/sola.2011-015.

Abstract
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.

2010

Large Eddy Simulation on Dust Suspension in a Convective Mixed Layer

Junshi Ito(1), Hiroshi Niino(1), Mikio Nakanishi(2)

1. Atmosphere and Ocean Research Institute, The University of Tokyo
2. National Defense Academy

SOLA, Vol. 6, pp. 133-136, doi: 10.2151/sola.2010-034.

Abstract
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.