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. In order to rapidly publish papers as quickly as possible, SOLA aims to make a first decision within one month and a decision upon resubmission within a further month. A rapid review cycle is the first priority of SOLA as a rapid publication journal.
Recently, we have been making efforts to organize special editions to welcome submissions on specific topics. We published special editions on “Extreme Rainfall Events in 2017 and 2019” in 2019 and on “Years of the Maritime Continent (YMC)” in 2020. This year, the special edition on “Typhoons in 2018-2019” has been launched. A unique feature of these special editions is that they are organized jointly with Journal of the Meteorological Society of Japan. We are planning to issue another special edition this year in response to advance studies on extreme weather events that occurred last year. We hope that the readers would know the recent developments in research on specific topics dealt in those special editions.
The special editions encourage submissions on relevant topics. The number of submissions exceeded 100 last year. With the increasing tendency of the submissions, the impact factor provided by Clarivate Analytics last year was 1.632, which is a rapid growth from the previous year.
We hope that readers would be our next authors. SOLA welcomes submission from the international community in meteorology, atmospheric sciences, and the related fields.
The Editorial Committee of Scientific Online Letters on the Atmosphere (SOLA) gives The SOLA Award to outstanding paper(s) published each year. I am pleased to announce that The SOLA Award in 2020 is going to be presented to the paper by Dr. Fumiaki Fujibe, entitled “Temperature anomaly in the Tokyo metropolitan area during the COVID-19 (coronavirus) self-restraint period” (Fujibe 2020).
In response to the rapid spread of the coronavirus disease 2019 (COVID-19) in spring 2020, human activities were strongly regulated and restricted in many parts of the world. The Japanese government set a nationwide self-restraint period from March to June in 2020 to prevent and contain the COVID-19 infection. This study investigated the impact of the reduced human activities during the self-restraint period on the temperature in the Tokyo metropolitan area. By using surface station data, the author revealed negative temperature anomaly in the central district of Tokyo from April to May, corresponding to the strong restraint period imposed by the government. It was demonstrated that the temperature anomaly in central Tokyo is about −0.5°C and is larger in the nighttime than in the daytime. It was also shown that a weak negative anomaly of about −0.2°C is found in the weak restraint period from late February to early April. The present result implies that the reduction of anthropogenic heat release affects significantly the temperature decrease in densely populated urban areas such as central Tokyo. The finding of this study is highly evaluated in revealing the impacts of human activities and the resulting anthropogenic heat release on the temperature in urban areas. With the growing concern on the urban heat island under climate change, it is critically important to quantify the influences of anthropogenic heat release on the urban atmospheric environment. This study would contribute to assessing the impacts of human activities on climate change at urban scales.
The Editorial Committee of SOLA highly evaluates the significance of this study and therefore presents The SOLA Award.
Forecast performances of the July 2020 Kyushu heavy rain have been revisited with the aim of improving the forecasts for this event. While the Japan Meteorological Agency's (JMA) deterministic forecasts were relatively good, the JMA's ensemble forecasts somehow missed this event. Our approach is to introduce flow-dependence into assimilation by running a 1000-member local ensemble transform Kalman filter (LETKF1000) to extract more information from observations and to better quantify forecast uncertainties. To save computational costs, vertical localization is removed in running LETKF1000. Qualitative and quantitative verifications show that the LETKF1000 forecasts outperform the operational forecasts both in deterministic and probabilistic forecasts.
Rather than a trick to save computational costs, removal of vertical localization is shown to be the main contribution to the outperformance of LETKF1000. If vertical localization is removed, forecasts with similar performances can be obtained with 100 ensemble members. We hypothesize that running ensemble Kalman filters with around 1000 ensemble members is more effective if vertical localization is removed at the same time. Since this study examines only one case, to assess benefit of removing vertical localization rigorously when the number of ensemble members is around 1000, a larger set of cases needs to be considered in future.
This study developed a volume scan-type disdrometer and investigated the size distribution of solid-precipitation particles observed by flux- and volume-scan type disdrometers, installed in 2016-2017 winter in Sapporo, Japan. The former disdrometer detected particles, by line sensors, of which frequency is proportional to the particle number per area. On the other hand, the latter directly observed the particle number per volume using an image sensor. The flux-scan data are known to have the bias of more frequency in higher-speed (or larger-size) particles, but this bias was hardly corrected due to the error of estimated particles' velocity. It was first validated that the volume scan-type disdrometer could observe particle size between 0.5 mm and 13 mm, consistently with the flux scan-type one. Then, we examined how many events showed the difference of the size distribution between the two disdrometers with the Kolmogorov-Smirnov test. The result showed that 84% of the total events examined fell into the class where they were significantly different, partially due to fast-falling graupels.
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.
While global warming may expand suitable places for potato cultivation in cold regions, it may reduce the yield due to the increase of hot days during the tuber growth period. This study evaluated the effects of global warming on potato cultivation over Hokkaido by dynamically-downscaled ensemble experiments called d4PDF and assessed applicability of possible adaptive measures. In this study, we define the suitable area based on the accumulated temperature and deduced a relationship between the potato yield per unit area and the number of hot days (maximum temperature > 28°C) from crop statistic data. In a warming environment with 2K or 4K increase in global-mean temperature relative to the present climate (1981-2010), the accumulated temperatures likely satisfied the criterion on potato production almost over Hokkaido. The risk of growth delay due to cold weather was projected to reduce. However, hot days in the tuber growth period would increase, reducing potato yield by 7% in a plus 2-K climate and 16% in a plus 4-K climate. This risk of yield loss would not be avoidable by moving up planting by 30 days, and the development of varieties that are tolerant to 31-33°C would be a possible way to adaptation.
This study investigated characteristics of atmospheric environmental fields in the occurrence of quasi-stationary convective bands (QSCBs) in Kyushu, western Japan during the July 2020 heavy rainfall event. We performed case studies of extreme rainfall subevents in the Kumamoto and Kagoshima prefectures on 3-4 July (2020KK) and northern Kyushu on 6-7 July 2020 (2020NK), compared with two heavy rainfall events in northern Kyushu in 2017 and 2018.
Nine QSCBs were objectively extracted during the July 2020 heavy rainfall event, causing hourly precipitation amounts exceeding 100 mm twenty times. In 2020KK, the environmental field with extremely large precipitable water due to low-level and middle-level humidity was affected by the upper-level cold airflow, which resulted in favorable condition for the deep convection development. Consequently, the lightning activity became high, and cloud tops were the highest in comparison to previous events. QSCBs in 2020KK and 2020NK were located along a low-level convergence line/zone associated with an inflow that had extremely large water vapor flux on the south side of the mesoscale Baiu frontal depressions. In most of the QSCB cases in 2020, mesoscale depressions were observed and enhanced horizontal winds, which led to extremely large low-level water vapor flux to produce short-term heavy rainfall.
We investigate regional characteristics of future changes in snowfall in Japan under two emission scenarios—RCP2.6 and RCP8.5—using a high-resolution regional climate model with 5km grid spacing and discuss the influence of changes in atmospheric circulation. The high-resolution model can simulate details of changes in distributions of total snowfall in Japan. Under RCP2.6, the annual total snowfall decreases in most parts of Japan except for Japan's northern island, Hokkaido. In Hokkaido, the winter snowfall increases even under RCP8.5, especially in January and February. The snowfall peak is delayed from early December to late January in Hokkaido. Along the Sea of Japan in eastern Japan, the winter-total snowfall decreases even if the winter mean temperature is below 0°C in the future climate. The different snowfall changes in Hokkaido and on the Sea of Japan side of eastern Japan are caused by precipitation changes in each region. Future changes in atmospheric circulation related to the Aleutian low cause the enhancement and the inhibition of winter precipitation in Hokkaido and the Sea of Japan side of eastern Japan, respectively, contributing to changes in the regional characteristics of snowfall and snow cover in addition to moistening due to atmospheric and ocean warming.
Relationship between diurnal convection and the intraseasonal oscillation (ISO) over the western Maritime Continent (MC) was investigated by a case study of an ISO event that occurred during the Years of the Maritime Continent (YMC)-Sumatra 2017 campaign. Two sets of global cloud-permitting simulations using cloud microphysics settings for ISO prediction (CTL) and for climate simulation (MOD) were performed to clarify their impacts. CTL had biases of weaker diurnal variation and smaller precipitation amounts over land than in observations; these were reduced in MOD by higher probabilities of local intense convection in the middle troposphere and higher precipitation efficiency. The enhanced convection over land coincided with suppressed convection over the surrounding ocean, especially at the diurnal peak time of land convection. Exception is the onset period of the ISO convection, when upward moisture advection and precipitation increased also over ocean in MOD than in CTL at the diurnal peak time of oceanic convection. These results suggest that the enhancement of local convection over the MC by the cloud microphysical processes basically hinders the ISO convection by the activation of land convection, but it also favors the ISO convection development over ocean during the onset period.