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<p>Seasonal cycle including day-to-day fluctuations shows great variety from region to region even among the middle/higher latitudes. Thus to know such detailed seasonal cycle for each region is the common basis for deeper understanding of (1) seasonal backgrounds of extreme meteorological or climatological events and (2) that of cultural generation leading to the cultural understanding education through the “seasonal feeling”. For example, the “seasonal feeling” of the severe winter relating to the traditional event for driving the winter away (“Fasnacht”) around Germany might be greatly reflected by the intermittent appearance of the extremely low temperature events, although the winter mean temperature there is lower only by about 3~5℃than in the southern part of the Japan Islands area.</p><p>Hamaki et al.(2018, although written in Japanese) suggested, based on the case study for 2000/01 winter, that the appearance of such events with large intraseasonal variation are greatly controlled by that of the Icelandic low. Furthermore, a case study for the same winter by Miyake and Kato (EGU2020 Assembly) pointed out that the rapid seasonal increase in the appearance frequency of extremely low temperature events there as the intraseasonal variation around mid-December, although the seasonal mean the Icelandic low already appeared in mid-October.</p><p>However, the climatological appearance features of the extremely low temperature events for longer periods should be examined further. Thus we will describe the detailed synoptic climatological features for 1971/72 to 2010/11 winters, based on the NCEP/NCAR reanalysis data. In this study, the days with daily mean surface air temperature less than or equal to -7℃ are referred to as the "extremely low temperature days".</p><p>Amplitude of the intraseasonal variation of the surface air temperature around Germany increased seasonally in association with the beginning of the nearly minimum seasonal mean temperature period (around December to February), resulting in the seasonal increase in the appearance frequency of the extremely low temperature days from around December. Such features are clearly found for the 10 winters (referred to as the "typical years") of the total 40 winters.</p><p>In the typical years, amplitude of the intrasesaonal variation increased rapidly around December (although this timing is somewhat different among the typical winters) and the persistent extremely low temperature days for about a week appeared two or three cycles in a winter. According to the case study for a typical winter (e.g., 1984/85 winter), while the temperature around Germany was relatively higher at the eastward shift phase of the Icelandic low due to the strong warm air advection by the SW-ly wind, the temperature was extremely low there when the Icelandic low was weakened and retreated westward as pointed out for the case study for 2000/2001 by Hamaki et al. (2018). It is also noted that the low corresponding to a part of the equivalent barotropic wave train lined up zonally was located around Germany in the extremely low temperature phase in 1984/85 winter.</p>

<p>   In East Asia, a significant subtropical front called the Baiu/Meiyu front appears just before midsummer and brings the huge rainfall there, greatly influenced by the Asian summer monsoon. However, large-scale atmospheric features and rainfall characteristics (such as convective or stratiform rain) as well as the total rainfall amount around the front show rather great differences between the western and eastern portions. For example, in the western part of the Japan Islands (especially around Kyushu District, the most western part) and the Changjiang River Basin in Central China, the more frequent appearance of the heavy rainfall events due to the organized deep convective clouds than in the eastern Japan results in the larger climatological precipitation amount there. This is greatly related to the larger moisture transport toward the western part of the Baiu front than toward the eastern part. On the other hand, the rainfall characteristics around the front in the eastern Japan tend to be largely influenced by the cool Okhotsk air mass with rather stable stratification. Furthermore, their year-to-year, intraseasonal and short-period variations including the diversity of the “heavy rainfall types” are also very large.</p> <p>The extreme events in association with the Baiu/Meiyu activity are greatly reflected by the above variability of the frontal activity. Inversely, it would be also important viewpoint that detailed examination of some extreme events could lead to the better understanding of the “dynamic climatological features” of the Baiu/Meiyu system itself.</p> <p>In such concept, the present study will examine the frontal-scale rainfall features and the atmospheric conditions for the extremely heavy rainfall event around the Baiu front in western to central Japan during 5-7 July 2018. Although it is the common feature for the Baiu frontal rainfall heavy in western Japan that the frequent appearance of the meso-scale intense rain bands results in the huge total rainfall amount there, it is noted that the extremely large total rainfall area was distributed much more widely up to the central Japan with also considerable contribution of the long-persistent “not-so-intense rain” there, as often found in the heavy rainfall in the eastern Japan. Our analyses of the atmospheric fields suggest that this extreme event seems to be characterized by the strong mixture both of the large-scale factors for activating the “western Japan Baiu” and the “eastern Japan Baiu”.</p> <p>As for the precipitation analyses, the 10-minute precipitation data at many meteorological stations in the Japan Islands area were used to discuss on the frontal-scale “rainfall characteristics” as well as the total rainfall amounts.</p>

<p>  To know the detailed seasonal cycle in various regions, confined only to the middle and higher latitudes, is the common basis for deeper understanding of the seasonal backgrounds of (1) extreme meteorological or climatological events and (2) cultural generation through the “seasonal feeling” leading to cultural understanding education. For example, our previous studies (e.g., Kato et al. 2017) pointed out that the “seasonal feeling” on the severe winter relating to the traditional event for driving the winter away (“Fasnacht”) around Germany might be due to the intermittent appearance of the extremely low temperature events, although the winter mean temperature there is lower only by about 3~5℃ than in southern Japan. Hamaki et al.(2018) suggested the appearance of such events to be controlled greatly by the intraseasonal behaviors of the Icelandic low. Furthermore, Kuwana et al. (EGU2018 and 2019) pointed out the asymmetric seasonal progression of the behaviors of the Icelandic low including its intraseasonal variation from the autumn to the next spring. However, it has not been clarified yet what kind of seasonal transition of the dominant large-scale daily fields was related to the increase in appearance frequency of such extremely low temperature events after mid-December. Thus the present study will further examine the detailed features on the above processes, mainly for the 2000/2001 winter based on the NCEP/NCAR reanalysis data.</p><p>  Appearance frequency of extremely low temperature events (e.g., below -5℃) rapidly increased around mid-December of 2000 with the large amplitude of its intraseasonal variation although the seasonal mean the Icelandic low appeared from mid-October. It is interesting that the daily mean temperature decreased gradually with shorter-period fluctuation until mid-December, even after the seasonal formation of the Icelandic low.</p><p>  As for the seasonal mean fields from mid-December to the next March, the northeastern portion of the Icelandic low area extended more closely to the northwestern Europe and the baroclinicity was enhanced especially to the south of ~55°N. Composite analyses suggest that the extremely low temperature events after mid-December around Germany was related not only to the weakening and westward retreat of the Icelandic low but also to the cold air advection by the low-level easterly wind along the southeastern edge of the intraseasonal-scale surface high to the north of Germany.</p>

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