Scientific Online Letters on the Atmosphere (SOLA) is a fully Open Access journal under the terms of the Creative Commons Attribution 4.0 International (CC BY 4.0) License, and aims to make a first decision within one month and a decision upon resubmission within a further month.
Last year, we published 44 papers including those in the Special Editions of Research on Extreme Weather Events That Occurred around East Asia in 2017-2021 and of the Frontier of Atmospheric Science with High Performance Computing. There is also a new special edition on Advances in Studies of Torrential-Rain-Producing Quasi-Stationary Band-Shaped Precipitating Systems, or ‘Senjo-Kousuitai’, which currently welcomes submissions. Those who are interested in this topic are encouraged to submit papers to this special edition.
The Editorial Committee of SOLA presents the SOLA Award to one or two outstanding papers published in each year. The SOLA Award in 2022 were presented to two papers: Maejima et al. (2022) and Nasuno et al. (2022). The SOLA Award in 2023 will be announced shortly, by the end of January 2024.
There is a change in the word count limitation for papers submitted in 2024 and afterwards. This is because Journal of the Meteorological Society of Japan, the sister journal, will cease publishing "Note" paper. In order to accommodate needs to publish short articles, SOLA will increase the word count limitation up to 3500 at the time of the acceptance. The current word count limitation of 3100 words still applies at the time of the initial submission, based on the total words included in the abstract and in the main body of the manuscript; but with the title, authors’ names and affiliations excluded in the word count.
We hope that SOLA is one of your preferred platforms where you can disseminate your research achievements. SOLA welcomes submission from the international community in meteorology, atmospheric sciences, and the related fields.

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The Editorial Committee of Scientific Online Letters on the Atmosphere (SOLA) presents the SOLA Award to one or two outstanding papers published each year. We are pleased to announce that The SOLA Award in 2023 will be given to the paper by Drs. Sachie Kanada and Akira Nishii, entitled "Observed Concentric Eyewalls of Supertyphoon Hinnamnor (2022)" (Kanada and Nishii 2023) and to the paper by Dr. Kenji Suzuki et al., entitled "Development of a New Particle Imaging Radiosonde with Particle Fall Velocity Measurements in Clouds" (Suzuki et al. 2023).

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Temperature trends in Japanese cities were analyzed using data at 433 stations on the AMeDAS network from April 1979 to March 2023. It was found that urban warming, defined by a temperature increase at an urban station relative to the surrounding non-urban stations, had slowed down in the latter part of the analysis period. The deceleration of urban warming was commonly found for northern, eastern, and western Japan, and not only for stations in densely inhabited areas but also those at weakly urbanized sites where the surrounding population density was 100-300 km⁻². The deceleration was observed in all seasons and time of the day, although it tended to be more conspicuous in winter than in other seasons, and in the nighttime than in the daytime.

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An extreme rainfall event with 48-h accumulated precipitation amounts exceeding 500 mm on the north (Japan Sea) side of western Japan occurred when Typhoon Lan (2023) approached and passed over Japan in a weak baroclinic environment. The rainfall event included two local heavy precipitation peaks. In the present study, we perform numerical simulations with a cloud-system-resolving model to investigate the potential roles of two factors in the first event peak: (1) an abnormally high sea surface temperature (AHSST) anomaly (∼ +4°C) and (2) a mesoscale low formed over the Sea of Japan. The results of sensitivity experiments showed that the AHSST increased the total rainfall amount by about 100 mm. The mesoscale low, which was generated by southeasterly flows over the mountain ranges of central Japan, determined the location of the heavy rainfall by controlling the direction and intensity of low-level flows. The role of this terrain-induced mesoscale low provided new insight into the mechanisms producing heavy rainfall in association with typhoons approaching Japan in a weak baroclinic environment.

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Field observations were conducted at Ibaraki Airport, Japan, to determine the vertical development speed of shallow radiation fog. The development speed in shallow (less than several meters) fog was 3-16 cm min⁻¹, and was slower at higher wind speeds. The speed decreased when the air above the fog layer became drier, possibly due to the mixing of the fog layer with the dry air above it. The speed data presented here can be used in nowcasting fog development for aviation decision making.

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In this study, we introduce a new seasonal prediction system using an atmosphere–ocean-coupled general circulation model called CFES (hereafter referred to as CFES ESPreSSO). We compare its prediction skill of the interannual variability of the surface air temperature (SAT) and precipitation anomalies with that of the SINTEX-F2 seasonal prediction system. We find that CFES ESPreSSO has a higher skill in predicting the SAT variability in January-February-March over East Asia and northeastern North America than SINTEX-F2, while the following season (April-May-June), SINTEX-F2 provides better predictions of the SAT variability over the Maritime Continent and subtropical North Pacific. Meanwhile, CFES better predicts the SAT variability in July-August-September over Eurasia and Arctic, and it continues to be so over the following season (October-November-December) over Eurasia. However, the prediction skill of SINTEX-F2 is generally better in the tropics (e.g., SAT in the subtropical North Pacific, SAT and precipitation in the Maritime Continent). Regarding climate indices, CFES shows a better prediction skill for the Atlantic Niño and Ningaloo Niño indices, whereas SINTEX-F2 is generally better for El Niño and the Indian Ocean dipole mode. These results suggest that for improved seasonal forecasting, it is beneficial to consider a multi-model approach, leveraging the respective strengths of each model.

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Typhoon HAISHEN, Typhoon No. 10 in 2020, was weaker than forecasts as it moved north over the western coast of Kyushu. The typhoon intensity forecasting scheme called TIFS operated at the Japan Meteorological Agency (JMA) tended to predict HAISHEN's intensity more strongly than the observed one, resulting in large errors in JMA's operational forecasts. One possible reason for the large errors is that TIFS does not include the effect of ocean cooling associated with tropical cyclones. Here, we investigated whether the accuracy of the typhoon intensity predictions can be improved by replacing static sea surface temperature and ocean heat content used in the conventional TIFS by those predicted by an ocean model. The results of prediction experiments using the pseudo-ocean-coupled TIFS show that the over-intensification of HAISHEN was suppressed and that the prediction errors were significantly reduced. We also extended the evaluation to all typhoons in 2020 and found that the pseudo-ocean-coupled TIFS reduced the prediction errors by about 10% compared to the conventional TIFS for prediction times of 3 to 5 days. This indicates that pseudo-ocean coupling of the conventional TIFS can improve the accuracy of typhoon intensity forecasts.

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Drylands, which occupy 41% of Earth's land area, have large effects on Earth's climate via land-atmosphere interactions, and simulations of future climate indicate that drylands will be very sensitive to climate changes associated with global warming. Monitoring of drylands is therefore necessary to help guide sustainable development in drylands and to protect the global environment. This study examined changes of the global distribution of the aridity index from 2000 to 2020 and compared them to changes from 1951 to 1980. The regions with relatively wet climates, that is, semi-arid and dry sub-humid regions, became drier from 2000 to 2020. The largest use of land in drylands was grassland, followed by open shrubland, cropland, savanna, and woody savanna. More than 50% of dry land was accounted for by grasslands (18,651,109 km²) and dryland forests including shrubland and savanna (13,331,231 km²). The relationship between the aridity index and the normalized difference vegetation index indicated that the value of the aridity index of dryland forests and grasslands equaled the threshold for climatically stable existence, although the range of the aridity index was wide in both cases. We also made rough assessments of soil organic carbon sequestration in dryland forests and grasslands.

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In summer 2023, record-high temperatures were observed in many parts of the Northern Hemisphere, including Japan, where summer-mean temperature was the highest over the last 126 years. Under an unprecedented heatwave in late July through September, record-high temperatures were successively observed particularly over northern and eastern Japan. The late-July heatwave is attributable primarily to the markedly-intensified North Pacific Subtropical High over Japan, accompanied by the poleward-deflected subtropical jet (STJ). This situation occurred under the influence of the Pacific–Japan pattern driven by northwestward-moving enhanced tropical convection over the western North Pacific and the Silk-Road pattern. The enhanced convection was influenced by upper-level cyclonic vortices detached from the intensified mid-Pacific trough. Seemingly, it was also under the remote influence from positive sea-surface temperature (SST) anomalies in the western equatorial Pacific as well as negative ones in the central–eastern equatorial Indian Ocean, considered as remnant and delayed impacts of long-lasted La Niña until the preceding winter. The August heatwave occurred under the persistent poleward-shift of STJ as well as warm, moist low-level southerlies and their downslope-wind effects. Both extremely high SST around northern Japan and a long-term warming trend in air temperature could also contribute to the record-setting air temperature.

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An eyewall replacement cycle is often seen in tropical cyclones, when a secondary eyewall forms outside the inner eyewall, and the inner eyewall disappears. Although this cycle significantly affects the intensity of tropical cyclones, the mechanisms of secondary eyewall formation (SEF) are diverse, and most are complementary. Some studies have suggested that dry air inflow and diabatic cooling may have an important role in SEF via the mesoscale descending inflow (MDI). Here, we use numerical experiments to investigate the role of the middle tropospheric dry inflow in SEF. Idealized experiments were conducted using the plane version of the Nonhydrostatic Icosahedral Atmospheric Model. The control experiment produced SEF with a dry air inflow in the middle troposphere and associated MDI. In sensitivity experiments, in which the water vapor in the middle troposphere was increased in the outer areas of the tropical cyclone, the onset of SEF was delayed. These results reveal the two distinct processes of SEF: the angular momentum transport by MDI and the unbalanced dynamics in the boundary layer.

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Shallow coastal seawater response during the passage of near-landfall intensification (NLI) tropical cyclones (TCs) and non-NLI TCs was examined using oceanic and atmospheric reanalysis data and observations. The sea surface temperature ahead of the NLI-TC track is maintained or even increases when NLI-TC is approaching the land. The magnitude of the wind stress, which plays an important role in the NLI process, is related to the zonal surface wind on the right side of the tracks. Coastal mixed layer warming can be explained by Ekman transport under sustained wind stress due to surface wind forcing. The successive deepening of the coastal ocean boundary layer and the increase in warming in the subsurface seawater temperature by an average of 0.3°C, could maintain thermal capacity in a certain degree. This shallow coastal water response could partly explain the NLI progress in the northern South China Sea, indicating the importance of coastal ocean dynamics and air-sea interactions.

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This study investigated three-dimensional structure of an equilibrium drop size distribution within a convective system that spawned heavy rainfall over northern Kyushu in western Japan on 10 July 2023. Ground-based optical disdrometer observations showed that the drop size distribution shape became bimodal (the peaks are at 0.7 and 1.0 mm in diameter) and then reached an equilibrium state during the rapid increase in precipitation intensity. Analyses of vertical profiles of polarimetric measurements showed that within the convective system collisional coalescence was dominant mainly at 1.5-4 km height, whereas collisional breakup was dominant below 1.5 km height. These processes were inferred to enhance the precipitation intensity. The equilibrium drop size distribution continued at least one minute during the event, and its spatial scale, diagnosed by a radar-derived parameter to be several kilometers, suggested that the equilibrium drop size distribution was a meso-γ-scale phenomenon.

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At a site on the Sea of Japan side of central Japan, the concentrations of ionic components in PM_2.5 were measured semi-continuously for about 15 months using filter collection and ion chromatography (filter method). Continuous measurements of sulfate particles were simultaneously performed in summer and autumn using a commercial sulfate monitor (Sulfate Particle Analyzer, SPA). High concentrations of sulfate ion (SO₄²⁻) were sometimes observed from spring to summer, and the high SO₄²⁻ was thought to be due not only to trans-boundary pollution from the Asian continent but also the influence of volcanic plumes. A comparison between the SPA and the filter method showed that the sulfate concentrations measured by the SPA method tended to be about 20% lower than those by the filter method. High concentrations of sulfate particles were observed not only from volcanoes from the Kyushu District such as Sakurajima, but also from volcanic smoke derived from Nishinoshima in the Ogasawara Islands. In recent times, sulfate particles from volcanos may be important contributors to PM_2.5 in Japan.

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Ensemble dynamical downscaling experiments were performed to investigate the influence of East Siberian blocking on a heavy snowfall event that occurred over Fukui City, Japan, in early February 2018 and was associated with the development of the Japan Sea Polar airmass Convergence Zone (JPCZ). The downscaling experiments simulated the enhancement of the East Asian cold air stream and its flow along two routes: the western route, which runs from the Eurasian Continent via the Yellow Sea and the Korean Peninsula; and the northern route, which originates in the Sea of Okhotsk and runs via the northern Japan Sea. As a result, the location and strength of the simulated JPCZ in the downscaling experiments are consistent with those in the Japanese regional reanalysis dataset. For the sensitivity experiments, the blocking that develops over East Siberia just prior to the formation of the JPCZ was removed, and the results indicate that the East Siberian blocking contributes significantly to JPCZ development by enhancing the East Asian cold air stream along the western route. Additional data analyses based on the 20-year reanalysis revealed that East Siberian blocking can enhance both the western and northern routes of the cold air streams.

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The relationship between maximum sustained wind speed (V_max) and minimum sea level pressure (P_min) of tropical cyclones (TC), which is called the wind–pressure relationship (WPR), is investigated by using best track data in which aircraft observations are used. On average, for given V_max (P_min), P_min (V_max) varies by 8.5 hPa (11.0 kt) between the 25th and 75th percentiles, and it varies by 17.1 hPa (22.6 kt) between the 10th and 90th percentiles; corresponding variations in the Dvorak Current Intensity (CI) numbers are also quantified. Also investigated is an adjusted WPR in which environmental conditions are incorporated through multiple linear regression. Its utilization reduces the variations to 6.9 hPa (9.5 kt) between the 25th and 75th percentiles and 13.0 hPa (18.9 kt) between the 10th and 90th percentiles. These remaining variations indicate intrinsic variability of WPR, suggesting a need for further utilization of observations to improve the intensity estimation of TCs.

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This study investigates the precipitation characteristics and disturbances of widespread heavy rainfall during the Akisame using meteorological data from the Japanese 55-year Reanalysis, precipitation data from the Automated Meteorological Data Acquisition System (AMeDAS), the Global Satellite Mapping of Precipitation (GSMaP) and the Global Precipitation Measurement (GPM) data. First, in the climatological field during the Akisame, northward water vapor transports (WVTs) prevail over eastern Japan (EJPN) due to the eastward shift of the North Pacific subtropical high and the existence of an anticyclone over the continent. This situation differs from the Baiu. Under humid conditions during the Akisame, well-organized precipitation systems with large stratiform precipitation area accompanying strong convective precipitation bring heavy rainfall, as in the Baiu. Second, the analysis of widespread extreme precipitation events (WEPEs) conducted for the Baiu in WJPN (Baiu/WJPN) by Shibuya et al. (2021) is performed for 4 cases: Baiu/EJPN, Baiu/WJPN, Akisame/EJPN and Akisame/WJPN. In the composite of the Akisame/EJPN case, WVTs toward EJPN is enhanced by a northeast-southwest dipole structure of geopotential height anomaly. We newly revealed that WEPEs occur during the Akisame associated with the overlap of the climatological field with anomalous disturbances that are different from those in the Baiu.

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It is generally considered that warm rain is less likely to occur in urban areas where the air is polluted. However, heavy precipitation from shallow convective clouds is occasionally reported in Tokyo. In this study, we observed microphysical characteristics of warm convective precipitation in Tokyo on 19-20 August 2019 using an X-band polarimetric radar, a Ka-band radar, a cloud droplet spectrometer and an optical disdrometer. The radar reflectivity and the specific differential phase from the X-band radar tended to increase in the lower layers, suggesting accretion growth of raindrops. On the other hand, the differential reflectivity decreased in the lower layers, suggesting the presence of low concentrations of large raindrops near the echo top. According to range height indicators, precipitation clouds were composed of streak-like echoes. The Z-R relationship on the ground was close to that of the Marshall-Palmer raindrop size distribution. Mean cloud number concentration (N_c) was 370 cm⁻³, which was larger than the average of low-level clouds in Tokyo (213 cm⁻³). Parcel model simulations suggested that warm rain could be initiated when N_c < 1200 cm⁻³, although the threshold of N_c depends on the cloud base temperature.

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On 4 July 2020, a quasi-stationary band-shaped area of heavy precipitation occurred near the center of Kyushu, Japan. The contribution of shallow convection to the localization of the precipitation area is examined using the Weather Research and Forecasting model. Two turbulent transport schemes, the Yonsei University scheme and the Mellor–Yamada–Nakanishi–Niino (MYNN) scheme, are selected. Simulations are performed for a 5-km horizontal resolution domain (SIM1) and a 1-km horizontal resolution domain nested within the 5-km resolution domain (SIM2). The results show that SIM1 predicts a more northerly bias than a radar/raingauge-analyzed precipitation area but provides a relatively small bias for the MYNN scheme, and SIM2 predicts the analyzed precipitation area reasonably well for both schemes. They also suggest that the improvement in SIM2s is due to the transition from shallow to deep convection upwind of the southwesterly wind, and the MYNN scheme with a partial condensation scheme in SIM1 reasonably simulates the growth of shallow convection by parameterizing the buoyancy production of turbulence associated with cloud formation. It is expected that the accurate prediction of shallow convection can improve the reproduction of the location of heavy precipitation areas.

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