Masatoshi Yoshino

Thermal belt and cold air drainage on the mountain slope and cold air lake in the basin at quiet, clear night

This paper reviews results of recent observations on the thermal belt, cold air drainage and cold air lake, which are striking in local climatic phenomena in mountain areas.The height (A) of the warmer part, the thermal belt, of the mountain slopes changes with time from early evening, midnight to early morning and also seasonally and differs according to the velocity of the upper general wind and cloudiness, but is generalized by the height difference (H) between the bottom of the basin and the surrounding mountain ridges. Roughly speaking, A = (0.25–0.30) H.On the mountain slopes, cold air flows down intermittently. The air temperature shows positive correlation to the wind speed of cold air drainage in the source region of cold air drainage. On the other hand, however, there is a negative correlation between the wind speed and air temperature in the drainage region at the lower part of the slope. Above the downslope cold air drainage, there is an anti-down-slope wind. The relatively large drainages are formed at frequencies corresponding to periods of oscillation of 1–2 hours and the smaller ones are of several minutes.In the basin or valley bottom, cold air lakes are formed. They are well defined by a strong inversion in air temperature. In most cases, the stagnant air in the cold air lake flows down slowly in accordance with inclination of the basin or valley floor. Above the cold air lake, we find the neutral or weak inversion layer. In some periods the drained cold air flows into this layer from the side slopes of the mountains. However, the radiation cooling of the basin or valley floor seems to be more effective for the formation of the cold air lake. Above the neutral or weak inversion layer, there is a layer of the general wind caused by the synoptic scale circulation systems. Their effects are controlled by the surrounding topography as well as the basin or the valley itself.In short, the structure of thermal belt, cold air drainage and cold air lake is a good example of the small-scale climatic processes under the influence of the synoptic scale phenomena and the one-order-greater scale topography.

Climatology of yellow sand (Asian sand, Asian dust or Kosa) in East Asia

In order to study climatology of yellow sand (Asian sand, Asian dust or Kosa) in East Asia, secular fluctuation in China, Korea and Japan in the recent 30 years was presented. The number of days with sand-dust storm at five stations in China—Hotan, Zhangye, Minqin, Jurh and Beijing, decreases a lot at the former three stations, but changed little at the latter two stations. Suggesting that the recent global warming is more evident in Xinjiang and Gansu, where the frequency of cold air invasions from the higher latitudes is decreasing. But, the eastern parts of Mongolia, inner Mongolia, and North China encounter stronger cyclones in early spring as a result of global warming. These cyclones bring cold air from higher latitudes, causing severe dust storms. Secular variation in the annual days with sand-dust storms in China and Kosa days in Korea and Japan show a parallel change with higher frequency from 1975 to 1985. This may be related to the higher frequency of La Nina years. However, different tendency was shown in the period from 1986 to 1996. Since 1996 or 1997, a sharp increase is clear, which may be caused by the developed cyclones in East Asia as well as human activities, and stronger land degradation under La Nina conditions. Anomalies of the total number of stations with Kosa days were discussed in accordance with some synoptic meteorological conditions such as the differences between Siberian anticyclone and Aleutian cyclone center at 500 hPa level during the previous winter.In order to study climatology of yellow sand (Asian sand, Asian dust or Kosa) in East Asia, secular fluctuation in China, Korea and Japan in the recent 30 years was presented. The number of days with sand-dust storm at five stations in China—Hotan, Zhangye, Minqin, Jurh and Beijing, decreases a lot at the former three stations, but changed little at the latter two stations. Suggesting that the recent global warming is more evident in Xinjiang and Gansu, where the frequency of cold air invasions from the higher latitudes is decreasing. But, the eastern parts of Mongolia, inner Mongolia, and North China encounter stronger cyclones in early spring as a result of global warming. These cyclones bring cold air from higher latitudes, causing severe dust storms. Secular variation in the annual days with sand-dust storms in China and Kosa days in Korea and Japan show a parallel change with higher frequency from 1975 to 1985. This may be related to the higher frequency of La Nina years. However, different tendency was shown in the period from 1986 to 1996. Since 1996 or 1997, a sharp increase is clear, which may be caused by the developed cyclones in East Asia as well as human activities, and stronger land degradation under La Nina conditions. Anomalies of the total number of stations with Kosa days were discussed in accordance with some synoptic meteorological conditions such as the differences between Siberian anticyclone and Aleutian cyclone center at 500 hPa level during the previous winter.

Development of urban climatology and problems today

Abstract Development of urban climatology is reviewed in relation to the history of small-scale climatology. At the beginning of the 20th century comparison was made between the stations in and outside of Tokyo and then mobile observation using cars was introduced in Japan from Austria and Germany in the 1930s. In the 1940s, many comprehensive studies were made: for example, wind-sock observations at about 180 stations located in every 1 km × 1 km area in Tokyo and its suburbs were continuously made for more than 1 year. In the 1950s, project studies on urban climatology were tried and the results have been published in the late 1950s and 1960s. In this stage, physical and synoptic climatological backgrounds of heat islands came in the main theme of the studies. Also, the other climatic elements such as solar radiation, number of drizzle days, and air pollution or three dimensions of heat islands over cities were taken up. During the last 10–20 years, the following have been studied: heat islands — population relationship according to the city size, different tendency of number of fog days, relative humidity or visibility according to the development of cities, change in frequency of strong and weak rainfall and heat islands in relation to sea-breeze front or local convergence. These developments of urban climatology in Japan are compared with those in the world. Lastly, the problems today are summarized.

Heat island of a small city and its influences on the formation of a cold air lake and radiation fog in Xishuangbanna, Tropical China

Abstract In Xishuangbanna, Yunnan Province, China, cold air lakes and radiation fog are formed in basins at frequencies of 70–90% of winter days. In January, 1989, mobile observations were carried out in order to clarify the urban effects on these local climatic phenomena. The small city, Jinghong, is located in the northwestern part of the Jinghong basin. The basin bottom has an area of about 76 km2. The city had a population of about 40 000 in 1988. Heat islands with an intensity higher than 1 °C were clearly observed in the city. The formation of radiation fog was also observed simultaneously on the slope located in the northeastern part of the basin. It was found that radiation fog was formed first in an air layer at a height of several tens of meters above the city and then it spread over the whole basin within about one hour. It disappeared from the northwestern part of the basin, where the city is located. The mechanism of the urban effect on radiation fog is discussed. On the other hand, some previous studies have pointed out that the local climate in Xishuangbanna has been changing; it has become drier, sunshine duration has increased, and the number of fog-days and the duration of fog at night have decreased. By comparing the meteorological data in the 1960s, when the population of the city was less than 10 000, and in the 1980s, when it was about 40 000, the effects of urbanization and deforestation on the local climate phenomena, such as cold air lakes and radiation fog, are analyzed.

Winter and summer monsoons and the navigation in East Asia in historical age

In order to make clear a problem in the human impact on the East Asian monsoons, navigation in the period from the 7th century to the 19th century was studied from the standpoint of historical climatology. 1. are described the periods of winter and summer monsoons over East Asia in relation to the division of the natural season. 2. based on the characteristics of the wind direction and velocity during the monsoons, it is shown that the winter monsoon is extremely unfavorable for navigation in contrast to the favorable summer monsoon. 3. statistical results on the possible frequency of navigation over the East China Sea by small boats are dealt with according to the meteorological records. 4. it is indicated that the navigations of the missions between Japan and China, Korea or Po Hai in the 7th – 9th centuries showed clear relations to the monsoon seasons. Lastly, the navigation mainly in 17th, 18th and 19th centuries around Ryukyu Islands, on the Chinese coast and the Japanese Islands are mentioned in detail. Even in this period the winter monsoon affected strongly on the navigation, that is, sailing and entries kept away the winter monsoon season almost completely.

Conclusions and Recommendations of the Working Groups

On the final afternoon of the symposium, participants divided into five working groups to draw up summary statements of the symposium’s deliberations. These statements take the form both of conclusions and recommendations.

Classification and Chronology of Monthly Mean Topography Patterns at the 100mb-Level in the Northern Hemisphere

SummaryAn attempt was made to classify the monthly mean topography patterns of the 100mb-level in the Northern Hemisphere from January 1956 to December 1970. The winter types are classified into eight by the range and height of circumpolar low pressure and by the range and height of high pressure area in middle or lower latitudes. The summer types are classified into five by the absolute height of anticyclone in the Eastern Hemisphere and its latitudinal range. According to this classification criteria, the chronology was made and the normal annual change of the types was shown. Lastly, discussions about the relations between the types at the 100mb-level and at the 500mb-level, 50mb-level and 10mb-level are presented. It was made clear that some winter types at the 100mb-level have a close relation to the zonal or meridional circulation types of the 500mb-level. A positional relation of the centers of the circumpolar low pressure was found between the 50mb-level and 100mb-level. Among the relationships as far as analysed, the phenomena shown as the topography patterns at the 100mb-level occur earlier than those shown as the circulation type at the 10mb-level with some exception.ZusammenfassungEs wird versucht, die Formen der Monatsmittel der Topographie der 100mb-Fläche auf der Nordhalbkugel von Januar 1956 bis Dezember 1970 zu klassifizieren. Je nach Ausdehnung und Höhe des zirkumpolaren Tiefs und nach Ausdehnung und Höhe des Hochdruckgebietes in mittleren oder niedrigen Breiten werden 8 Wintertypen festgestellt. Nach der absoluten Höhe der Antizyklone in der östlichen Hemisphäre und ihrer Breitenerstreckung werden 5 Sommertypen charakterisiert. Auf Grund dieser Klassifikationskriterien wird eine Chronologie aufgestellt und die normale Jahresschwankung der Typen aufgezeigt. Schließlich werden die Beziehungen zwischen den Typen der 100mb-Fläche und den 500mb-, 50mb- und 10mb-Flächen diskutiert. Es zeigt sich, daß einige Wintertypen der 100mb-Fläche eine enge Beziehung zu zonalen oder meridionalen Zirkulationstypen der 500mb-Fläche haben Für die Lage der Zentren des zirkumpolaren Tiefs wurde eine Beziehung zwischen dem 50mb- und dem 100mb-Niveau gefunden. Die durchgeführten Analysen der Beziehungen zeigen, daß mit einigen Ausnahmen die typischen Formen der Topographie der 100mb-Fläche den Zirkulationstypen im 10mb-Niveau vorausgehen.