SOLA
Online ISSN : 1349-6476
ISSN-L : 1349-6476
Volume 18
Displaying 1-19 of 19 articles from this issue
Editorial
  • Tetsuya Takemi
    2022 Volume 18 Pages i
    Published: 2022
    Released on J-STAGE: February 03, 2022
    JOURNAL OPEN ACCESS
    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. A rapid review cycle is the first priority of SOLA.
    Last year, everyone in the world suffers from the crisis of the coronavirus disease 2019 (COVID-19). Even under this difficult situation, we have published special editions on “Typhoons in 2018-2019” and “Research on Extreme Weather Events That Occurred around East Asia in 2017-2021” as well as the regular issue in 2021. The COVID-19 pandemic stimulated new directions in meteorology and atmospheric sciences. We presented the SOLA Award in 2020 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).
    We have been making continuous efforts to organize special editions coordinated jointly with Journal of the Meteorological Society of Japan. The special edition on “Research on Extreme Weather Events That Occurred around East Asia in 2017-2021” is welcoming submissions on relevant studies. With these efforts, the impact factor provided by Clarivate Analytics last year was 2.245, 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.
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  • Tetsuya Takemi
    2022 Volume 18 Pages ii-iii
    Published: 2022
    Released on J-STAGE: February 04, 2022
    JOURNAL OPEN ACCESS
    The Editorial Committee of Scientific Online Letters on the Atmosphere (SOLA) gives The SOLA Award to outstanding paper(s) published each year. We are pleased to announce that The SOLA Award in 2021 will be presented to the paper by Drs. Koichi Shiraishi and Takashi Shibata, entitled “Seasonal variation in high arctic stratospheric aerosols observed by lidar at Ny Ålesund, Svalbard between March 2014 and February 2018” (Shiraishi and Shibata 2021).
    Stratospheric aerosols play essential roles in radiative and chemical processes in the atmosphere and impact the climate of the Earth. The lidar observations of the temporal and spatial variations of the aerosols will provide essential information to understand the atmospheric processes related to the aerosols. Thus, there have been many studies on lidar observations of aerosols in the low and middle latitude regions. However, the observations in the Arctic are limited. In particular, there are no long-term observations of stratospheric aerosols throughout the year in the high Arctic. This study investigates the seasonal variations of stratospheric aerosols in the high Arctic by using long-term observations for about four years at Ny Ålesund, Svalbard. By carefully removing data affected by polar stratospheric clouds and volcanic eruption, the analysis shows the robust characteristics of the seasonal variations of background aerosols in the stratosphere. It is found that the backscattering ratio takes maximum values at altitudes between 13 and 16 km from December to March and at altitudes between 17 and 20 km from April to November. This observational evidence is highly evaluated in presenting the seasonal variations of stratospheric aerosols in the high Arctic, which will be helpful to understand the dynamical and chemical processes in the stratosphere.
    The Editorial Committee of SOLA highly evaluates the significance of this study and therefore presents “The SOLA Award.”
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Article
  • Koichi Watanabe, Hirohito Satoh, Teruya Maki
    2022 Volume 18 Pages 104-109
    Published: 2022
    Released on J-STAGE: May 24, 2022
    Advance online publication: April 12, 2022
    JOURNAL OPEN ACCESS
    Supplementary material

    The number concentrations of microbial (counted as viable) particles and size-separated particles were measured continuously in Imizu City, Toyama, in the coastal region of the Sea of Japan, in 2015 using a commercial real time viable particle counter. From February to June, large increases in the number concentrations of coarse particles with rapid increases of viable particles were observed during Asian dust events. In mid-July, a phenomenon was observed in which the number concentrations of viable particles decreased, although coarse particles significantly increased. From the results of the backward trajectory analysis, the phenomenon was considered to be due to the transport of volcanic ash from Nishinoshima. The monthly average number concentrations of the viable particles were highest in September, whereas the average concentrations of coarse particles were at a maximum in April.

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  • Michiya Hayashi, Hideo Shiogama
    2022 Volume 18 Pages 96-103
    Published: 2022
    Released on J-STAGE: May 17, 2022
    Advance online publication: March 28, 2022
    JOURNAL OPEN ACCESS
    Supplementary material

    The technique for composing a small subset of global climate models is critical to provide climate scenarios for impact and adaptation studies of regional climate changes. A recent study developed a novel statistical method for selecting a mini-ensemble of five climate models from the Coupled Model Intercomparison Project Phase 6 for widely capturing different future projections of Japanese climate across eight atmospheric variables at the surface. However, it remains unclear which mini-ensemble model contributes to efficiently covering the full projection ranges. Here, we rank each mini-ensemble projection around Japan among a full ensemble, showing that the selected five models capture the full ranges without systematic biases, except for relative humidity. Furthermore, we find that the widespread global warming level contributes to covering well the projection uncertainties in the daily-mean, maximum and minimum air temperatures and downward longwave radiation but not in precipitation, solar radiation, relative humidity, or wind speed. As the last four variables are sensitive to various factors, such as large-scale circulation and aerosol-forcing changes, rather than global-mean temperature changes, the model selection method featured here is preferable for capturing the wide future projection ranges in Japan.

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  • Tomoe Nasuno, Masuo Nakano, Hiroyuki Murakami, Kazuyoshi Kikuchi, Yohe ...
    2022 Volume 18 Pages 88-95
    Published: 2022
    Released on J-STAGE: May 13, 2022
    Advance online publication: April 01, 2022
    JOURNAL OPEN ACCESS
    Supplementary material

    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.

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  • Kazuo Saito, Takumi Matsunobu, Tsutao Oizumi
    2022 Volume 18 Pages 81-87
    Published: 2022
    Released on J-STAGE: April 25, 2022
    Advance online publication: April 06, 2022
    JOURNAL OPEN ACCESS
    Supplementary material

    As a complement work to the authors' previous studies, we examined the pre-typhoon rainfalls (PRE) ahead of typhoon T0918 (Melor) in October 2009. The influence of moistening in the upper atmosphere induced by the northward ageostrophic winds on PRE precipitation was examined by a sensitivity experiment using a cloud resolving model with a horizontal resolution of 2 km.

    The cloud resolving simulation showed a large impact of the water vapor in the upper atmosphere on the precipitation over western Japan. In the sensitivity experiment where the moisture in the middle and upper layers was reduced over the area off the south coast of western Japan, the water vapor reduction area was advected northward, and the snow in the middle and upper layers and the cloud ice in the upper layer decreased, reducing the rain below the melting level. The intrusion of drying air into the upper atmosphere reduced the thickness of the moist absolutely unstable layer (MAUL), and the maximum intensity of convective updrafts decreased by about 10% in the test experiment. In this case, the increase of rain in PRE was primarily caused by the deep northward water vapor transport which yielded a large amount of condensation in the middle and upper layers, and change of moist instability in the upper atmosphere subsidiarily enhanced the convective updrafts.

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  • Yaokun Li, Yanyan Kang
    2022 Volume 18 Pages 76-80
    Published: 2022
    Released on J-STAGE: April 25, 2022
    Advance online publication: March 17, 2022
    JOURNAL OPEN ACCESS

    The energy dispersion process of westward propagating Rossby waves in tropical easterlies are investigated in the linear nondivergent barotropic atmosphere. The variations in wave energy and amplitude along energy dispersion paths are calculated by solving the wave action conservation equation. The results suggest that a westward marching ray can form a cycle-like path near the turning latitude that is located in easterlies. Waves with shorter periods propagate between two turning latitudes, which are located in either the easterlies or westerlies and have the largest meridional propagation range. Waves with longer periods propagate between a turning latitude in westerlies and a critical latitude in easterlies. Both wave energy and amplitude can simultaneously increase to their maximum values at the turning latitudes that are located in easterlies. This implies that waves may develop significantly. Wave energy and amplitude do not always have an in-phase variation when the ray moves toward the turning latitude that is located in westerlies. The oscillating ranges of wave energy and amplitude are also limited. In this case, waves may not develop significantly.

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  • Asami Komatsu, Kouichi Nishimura
    2022 Volume 18 Pages 71-75
    Published: 2022
    Released on J-STAGE: April 22, 2022
    Advance online publication: March 08, 2022
    JOURNAL OPEN ACCESS
    Supplementary material

    We introduce a new procedure to evaluate the snowdrift distribution over complex topography and improve the accuracy of snow avalanche warning systems. We select the Niseko region, Japan, as the target area, and first obtain the wind distribution map at a 50-m grid spacing for 16 wind directions. We then employ these maps to calculate the amount of snow erosion and deposition. We present a case study to demonstrate that the model output agrees fairly well with measurements of local wind speed and observed snowdrift distribution. While improvements can be made to improve the accuracy of the model results, including more comprehensive calculation procedures and quantitative comparisons of snowdrift formation and evolution, it appears that the presented snowdrift analysis is an effective tool that can be incorporated into a snow avalanche warning system that employs a simple snow-cover model.

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  • Haruka Sasaki, Tatsuo Motoi
    2022 Volume 18 Pages 65-70
    Published: 2022
    Released on J-STAGE: April 08, 2022
    Advance online publication: March 03, 2022
    JOURNAL OPEN ACCESS

    Previous studies suggested that increases in ocean heat content result in strengthening of tropical cyclone (TC) and causing the associated disasters. In the western North Pacific (WNP), acceleration of increasing rates of tropical cyclone heat potential (TCHP: ocean heat content above 26°C from the surface) in the TC rapidly intensifying (RI: a 24-h intensity change of ≥ 30 kt) zone may have contributed to increases in TC intensity. However, there is no research on the relation of the acceleration of increasing rates to the variations in TCHP in a climatological view, differently from the relation to decadal variations such as Pacific Decadal Oscillation (PDO). This study focused on the relation of the variations in TCHP anomalies (TCHPA) to RITCs over the past six decades.

    Although the annual mean TCHPA in the global ocean was not accelerated, the TCHPA accelerated recently in the late 1990s over the RI zone particularly in fall (October-December) in the WNP. The acceleration of the increase in TCHPA was possibly explained by the intensification of trade wind-driven ocean general circulation and the combination of the linear trend of TCHPA with PDO phase change.

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  • Hirokazu Endo, Akio Kitoh, Ryo Mizuta
    2022 Volume 18 Pages 58-64
    Published: 2022
    Released on J-STAGE: March 29, 2022
    Advance online publication: March 01, 2022
    JOURNAL OPEN ACCESS
    Supplementary material

    Future changes in extreme precipitation over the western North Pacific and East Asia (WNP-EA) are investigated using a 20 km mesh atmospheric general circulation model (AGCM). Time-slice simulations are performed under low- and high-emission scenarios using different spatial patterns of changes in sea surface temperature. In the WNP-EA region, future changes in the climatological mean of the annual maximum 1 day precipitation total (Rx1d) are characterized by a large meridional variation, where the higher the latitude, the greater the rate of increase in Rx1d, although this pattern is not so clear under the low emission scenario. This feature probably results from a combination of two factors: a greater warming in high latitudes and a decrease in tropical cyclone (TC) frequency in the subtropics. The future changes in Rx1d climatology for the 20 km AGCM show a marked difference in comparison with those of the lower-resolution AGCM and conventional climate models. Part of this discrepancy may come from differences in model resolution through representation of TCs, suggesting that coarse-resolution models may have some systematic bias in future projections of extreme precipitation in the WNP-EA region.

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  • Shinta Seto
    2022 Volume 18 Pages 53-57
    Published: 2022
    Released on J-STAGE: March 23, 2022
    Advance online publication: February 10, 2022
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    Supplementary material

    For over 20 years, precipitation measurement has continued with spaceborne radars including the Precipitation Radar (PR) operating at 13.8 GHz on the Tropical Rainfall Measuring Mission and the Ku-band Precipitation Radar (KuPR) operating at 13.6 GHz on the Global Precipitation Measurement mission core satellite. PR and KuPR have essentially the same hardware designs and the same algorithm to make standard products (PRV8 and KuPRV06, respectively). The surface precipitation rate estimates (R) and related variables are statistically compared between PR and KuPR for a common observation area (within 35°N and 35°S) and period (April to September 2014). Due to the difference in sensitivity, the total precipitation amount recorded by KuPR is larger than recorded by PR by approximately 1.3%. For heavy precipitation, PR shows a smaller measured radar reflectivity factor (Zm) and a larger R than KuPR. Zm is affected by the attenuation and it is smaller for PR than KuPR, as the frequency is slightly higher. The attenuation corrected radar reflectivity factor is almost the same for PR and KuPR. However, the adjustment factor is larger for PR, which results in a larger R. Direct comparison between PR and KuPR during matchup cases demonstrates similar results.

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  • Yuhji Kuroda, Miho Toryu, Hiroaki Naoe
    2022 Volume 18 Pages 47-52
    Published: 2022
    Released on J-STAGE: March 18, 2022
    Advance online publication: January 27, 2022
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    Supplementary material

    This study examined the influence of stratospheric variability on the polar winter tropospheric climate. The winter-mean tropospheric condition can be well represented by a winter-mean stratospheric index (the Polar-night Jet Oscillation (PJO) index) defined from profiles of monthly polar temperature anomalies. In winters with a positive (negative) index, the winter-mean surface pressure anomaly tends to acquire a positive (negative) pattern resembling the Arctic Oscillation (AO). This tropospheric condition tends to become a persistent polarity of the AO index throughout the winter. This tendency is also found when the PJO index for each month is used. Although the PJO index in January shows the best results, those in early winter can be used as predictors for the entire winter troposphere. Use of the PJO index for the stratospheric effect on winter troposphere is compared with that associated with the occurrence of the major stratospheric sudden warmings. The origin of the decadal variability of the index is also discussed.

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  • Ju-Young Shin, Kyu Rang Kim, Yong Hee Lee
    2022 Volume 18 Pages 41-46
    Published: 2022
    Released on J-STAGE: March 18, 2022
    Advance online publication: January 26, 2022
    JOURNAL OPEN ACCESS

    Determining the thresholds for risk assessment is critical for the successful implementation of thermal health warning systems. A risk assessment methodology with multiple thresholds must be developed to provide detailed warning information to the public and decision makers. This study developed a new methodology to identify multiple thresholds for different risk levels for heat or cold wave events by considering simultaneously impact on public health. A new objective function was designed to optimize segmented Poisson regression, which relates public health to temperature indicators. Thresholds were identified based on the values of the objective functions for all threshold candidates. A case study in identifying thresholds for cold and heat wave events in Seoul, South Korea, from 2014 to 2018, was conducted to evaluate the appropriateness of the proposed methodology. Daily minimum or maximum air temperature, mortality, and morbidity data were used for threshold identification and evaluation. The proposed methodology can successfully identify multiple thresholds to simultaneously represent different risk levels. These thresholds show comparable performance to those using the relative frequency approach.

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  • Chih-Chien Chang, Shu-Chih Yang, Stephen G. Penny
    2022 Volume 18 Pages 33-40
    Published: 2022
    Released on J-STAGE: March 18, 2022
    Advance online publication: January 20, 2022
    JOURNAL OPEN ACCESS

    A regional hybrid gain data assimilation (HGDA) system is newly developed using Weather Research and Forecasting model (WRF). The WRF-HGDA augments an ensemble-based Kalman filter (WRF-LETKF) with information from the variational analysis system (WRF-3DVAR) by combining their gain matrices. The performance of WRF-HGDA is evaluated by assimilating the GNSS radio occultation (RO) observations from the FORMOSAT-3/COSMIC (FS3/C) and the FORMOSAT-7/COSMIC2 (FS7/C2) under an Observing System Simulation Experiment (OSSE) framework. The results demonstrate that the variational correction improves the WRF-LETKF, with the equal-weighted WRF-HGDA outperforming its component DA systems in the moisture and wind fields when only conventional observations are assimilated. Assimilating additional RO data from FS7/C2 further improves the WRF-LETKF and WRF-HGDA systems. Although the variational correction for the mid-level temperature causes degradation in the WRF-HGDA analysis, this can be alleviated by adjusting the combination weight to include more flow-dependent information in WRF-HGDA at these levels. Further tuning of the static background error covariance used in WRF-3DVAR also brings some improvement in the WRF-HGDA wind analysis. Our results imply that a well-tuned variational system is critical for the accuracy of the regional HGDA analysis.

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  • Yasumitsu Maejima, Takuya Kawabata, Hiromu Seko, Takemasa Miyoshi
    2022 Volume 18 Pages 25-32
    Published: 2022
    Released on J-STAGE: March 07, 2022
    JOURNAL OPEN ACCESS
    Supplementary material

    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.

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  • Kazuto Takemura, Hitoshi Mukougawa, Yuhei Takaya, Shuhei Maeda
    2022 Volume 18 Pages 19-24
    Published: 2022
    Released on J-STAGE: February 11, 2022
    Advance online publication: January 13, 2022
    JOURNAL OPEN ACCESS

    Seasonal predictability of summertime Asian jet deceleration near Japan is examined using monthly mean data of hindcasts based on an operational seasonal prediction system of the Japan Meteorological Agency. Interannual variabilities of the Asian jet deceleration averaged during July–August are generally well predicted with moderate to high forecast skill starting from initial months from January to June. The seasonal predictability of the Asian jet deceleration in specific years is, by contrast, limited with large forecast errors. An inter-member regression analysis for the forecast errors of the Asian jet deceleration using ensembles shows that the forecast errors of the Asian jet are associated with those of the Asian jet deceleration near Japan. Furthermore, the forecast errors of El Niño Southern Oscillation (ENSO)-related excessive upper-tropospheric divergence near Southeast Asia can account for the errors of the northward shifted Asian jet. The above-mentioned results indicate that more accurate seasonal prediction of ENSO can further improve the seasonal prediction skill of the Asian jet deceleration and summer climate near Japan.

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  • Yasutaka Hirockawa, Teruyuki Kato
    2022 Volume 18 Pages 13-18
    Published: 2022
    Released on J-STAGE: February 02, 2022
    Advance online publication: December 28, 2021
    JOURNAL OPEN ACCESS
    Supplementary material

    We propose a new application method in which radar/raingauge-analyzed precipitation amounts (RAP) produced by the Japan Meteorological Agency are spatially converted into 5km-resolution data, in addition to a three-hourly accumulation procedure, in order to statistically analyze localized heavy rainfall areas (HRAs) for a long period. A long-term trend and homogeneity in the appearance frequency of RAP with 5km-resolution converted by several methods, including the conventional method, are statistically evaluated in comparison with rain-gauge observations. The results indicate that the following application method is the most suitable to represent long-term variations in the appearance frequency of HRAs; (1) the converted value of RAP from 1 km to 5 km resolution is set to the 90th percentile value in 30 segments with 1km-resolution included in a grid with 5km-resolution, and (2) this spatial conversion is conducted after accumulating original RAP with 1km-resolution for three hours. Statistical analyses were performed for the appearance frequency of HRAs extracted from 5km-resolution RAP that were produced by the new application method, which indicates that the number of HRAs of the linear-stationary type could be increased without compromising the characteristics of HRAs extracted by the conventional method.

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  • Yusuke Goto, Naoki Sato
    2022 Volume 18 Pages 8-12
    Published: 2022
    Released on J-STAGE: February 02, 2022
    Advance online publication: December 21, 2021
    JOURNAL OPEN ACCESS

    The horizontal movement vectors of the maximum rainfall area associated with local heavy rainfall around Tokyo in the afternoon of high-temperature summer days were analyzed using a numerical algorithm in order to investigate their relationship to the wind vectors in the free atmosphere. First, the movement vectors were objectively identified every 10 minutes from radar echo intensity data, and their time average from the onset to the termination of a heavy rainfall event was calculated. The results show that the maximum areas of localized heavy rainfall around Tokyo most frequently move to the east-southeast and southeast. Moreover, the direction of movement is shifted to the right relative to the mean direction of the free atmospheric winds in most cases. It is also implied that water vapor supply from the south in the boundary layer plays a role in the rightward movement.

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  • Chiaki Kobayashi, Shuhei Maeda, Yuki Kanno, Toshiki Iwasaki
    2022 Volume 18 Pages 1-7
    Published: 2022
    Released on J-STAGE: January 29, 2022
    Advance online publication: November 30, 2021
    JOURNAL OPEN ACCESS
    Supplementary material

    We examine the relationship between the record-warm winter (DJF) 2019/2020 over East Asia and the extremely weak hemispheric circulation anomaly. During this period, the polar cold-air mass (PCAM) flux over East Asia was the weakest on record since the DJF 1958/1959 due to the weak Siberian High. The zonal averaged surface temperature over the Northern Hemisphere mid-latitudes in DJF 2019/2020 was the highest since DJF 1958/1959 and was linked to the weakest PCAM flux at the mid-latitudes. The zonal mean field during this period was characterized by weak stationary waves, weak wave activity as diagnosed by Eliassen-Palm flux, and, to balance with this, record-weak extratropical direct meridional circulation (EDC). The weak EDC corresponded to weaker-than-normal meridional heat exchange and was consistent with warm anomalies in the Northern Hemisphere mid-latitudes, since the lower branch of EDC corresponds to zonally averaged cold air outflow. In addition, the statistical relationship also indicates the EDC intensity is negatively correlated with the surface temperature anomaly over East Asia.

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