Gaseous hydrogen peroxide (H2O2) concentrations were measured in the city of Nagoya during the period from January 1993 to August 1994. The results show both diurnal and seasonal variations together with a special event. They reached the maximum concentrations in the afternoon mainly due to photochemical reactions in the polluted atmosphere, and the minimum concentrations were observed at mid-night. Daytime H2O2 concentrations were principally correlated with the solar radiation, whereas night-time H2O2 concentrations were well correlated with wind speed as a, n indication of boundary layer instability. Seasonally, the maximum concentrations appeared in summer and the concentrations were very low in winter. The monthly mean value reached the maximum in May in 1993, but in August in 1994. This shows that there was a depletion of solar radiation during July and August in 1993. Judging from SO2 concentrations measured in the city of Nagoya, there is a severe shortage of the reactive oxidant to SO2 in winter. A dramatic phenomenon that the ground level H2O2 concentrations in night-time abruptly increased in association with the passage of a cyclone was observed. This is likely due to direct downward transport of H2O2 from the free atmosphere where H2O2 concentration is usually higher.
Using the climatic signal-noise ratio, as well as other tests, dates have been detected around which important changes in Northeasterly and Westerly circulation have been observed in mid-latitude South America. These changes in zonal circulation intensity which occur, on average, in periods of 10 years or more, have been generally coincident with those registered in the Northern Hemisphere, in the last century. The Westerly intensities series show climatic jumps along six months of the calendar year. Information on those registered in July of 1939, 1949, 1967 and 1977 and January 1974 is included. Climatic jumps were observed in Northeasterly intensities in the monthly and seasonal scales, respectively, with no effect upon the annual values. An important change in average conditions of the North-easterlies detected at the beginning of the 1950s, and fluctuations of low frequency, might be the cause of outstanding precipitation jumps in the Argentina's subtropical area, where abundant (scanty) precipitation was associated with strong (weak) Northeasterlies.
A narrow cloud band developed over Kanto Plain on 22 April 1992 in association with the passage of an extratropical cyclone. Its unique features include the rapid formation and appearance of an arc-shaped solid cloud wall, rather than a line of a number of isolated convective cells. It evolved along the southern edge of a much broader weak rain area in a manner similar to the embedded areal type as identified by Bluestein and Jain (1985). A mesoscale analysis of conventional observation data reveals that a local cold air mass propagated southeastward from the northwestern part of Kanto Plain. It was driven by the horizontal pressure gradient force associated with the eastward-propagating cyclone. The cloud band was found to be forced to form when and where the cold surge collided with the synoptic-scale southwesterly flow which was prevailing over the southern part of Kanto Plain. It is further revealed that the cold surge was a leading part of a low-level mesoscale air mass which was termed as the "forerunner". It was so named since it existed in front of the synoptic-scale northwesterly flow and beneath the southwesterly flow ahead of the upper-level trough.
Continuous sampling of deposition and determination of chemical species in it were performed at two small, less populated and less industrialized islands in the Pacific Ocean, southern part of the Japanese islands, in order to evaluate the deposition amount over the Pacific. The chemical characteristics of the deposition on both islands were mostly maritime in nature, with some non-seasalt sulfate (nss-sulfate), non-seasalt calcium (nss-calcium), ammonium and a small amount of nitrate. At Amami O-shima (Naze), the ratio of nss-calcium to total calcium was found to be higher than that of Hachijo-jima, indicating some influence of crustal materials. The seasonal trend of the deposition amount of nss-sulfate was found to be similar at both islands, i. e., high during winter to spring and lower during summer to autumn. The net deposition amount of nss-sulfate was a little lower at Naze than at Hachijo-jima, depending upon the net precipitation amounts of both sites. Considering meteorological conditions, it was suggested that significant parts of the deposition amounts of nss-sulfate and nss-calcium at both islands were under the influence of the Asian Continent, though in the case of Hachijo-jima, some of the pollution might be due to the western part of Japan.
The trend in the zonally averaged temperature, 1964-1993, was positive in most of the extratropical troposphere. It was negative in the annual mean in the stratosphere. In January a positive trend appeared in the middle stratosphere in the arctic which progressed downward through the winter. This is reflected in a reversal of the trends in the geopotential heights at 30 hPa and 10 hPa in late winter. The trends in the annual mean geopotential heights in both troposphere and stratosphere were positive south of about 60°N and negative to the north. The zonally averaged geostrophic westerly wind between middle and high latitudes therefore increased during the period.
Number concentrations of aerosols in 5 radius ranges (0. 15-0. 25 μm, 0. 25-0. 5 μm, 0. 5-1. 5 μm, 1. 5-2. 5 μm, 2. 5-5. 0 μm) were observed at Zhangye in northwestern China during the period from March 1991 to October 1992 by using an optical particle counter. The averaged number concentration of coarse particles (radius γ&ge ; 1. 5 μm) showed a seasonal variation that had a large maximum in spring and a large minimum in summer. In addition, a small maximum in late fall and a small minimum in winter were also observed. Fine particle (γ < 1. 5 μm) concentration shows a maximum in winter and a minimum in summer. The correlation between coarse particles (γ &ge ; 2. 5 μm) concentration and wind speed based on daily averaged data was not so high. However, the seasonal variation of coarse particles could be explained mainly by the variation of average wind speed. Almost no relation was found between aerosol concentration and wind direction. The concentration of aerosols was also influenced by precipitation. Dust-storm events were recorded in all seasons except mid-winter, and the appearance frequency of dust storm was highest in spring. During the dust-storm events, the concentration of coarse particles (γ &ge ; 1. 5 μm) increased by approximately one order of magnitude as compared with that before the event, along with a small decrease in fine particle (γ < 0. 5 μm) concentration.
Desert in Xin-jiang, China, since 1991 to investigate the desertification processes of arid lands. For this purpose, an automatic weather station was installed over gobi desert at the southern edge of the Taklimakan Desert. Observed data for about one year were analyzed and compared with the data over grass on the outskirts of the oasis. The monthly mean of soil surface temperature is higher than that of air temperature in every month. This means that the monthly mean sensible heat flux is upward all the year round. Daytime increase of specific humidity is evident in the summer season and is probably caused by the water vapor advection from the relatively wet oasis area located upwind. Two prevailing wind directions were found : a strong (&ge ; 7.0 ms<-1>) westerly wind from April to June, and a southsoutheasterly wind during nighttime. The southsoutheasterly wind is accompanied by the diurnal clockwise wind course which is found throughout the year. Diurnal variations of wind direction at gobi and grass within oasis, 11 km away from gobi, show same characteristics. An identical wind course can be recognized in the vertical profile at Hotan, 100 km west of the gobi site, from the surface to 160 m in height. It is strongly suggested that this diurnal wind course is induced by the local circulation between Kunlun Mountains and the desert area.
In this study, interannual variations of summertime precipitation over arid and semi-arid regions in China and Mongolia are investigated. To clarify the regionality of the interannual variability in summer precipitation, an analysis technique of rotated empirical orthogonal functions is applied for a recent 40-year (1951-1990) period of summer precipitation. As a result of the REOF, five regions have been determined : I) Taklimakan Desert, II) Loess Plateau, III) North China to central and the southeastern part of Mongolia, IV) the north of Tianshan Mountains, and V) the northern part of Mongolia. Summertime precipitation over Region III) shows a significant decreasing trend after 1955. Next, to examine how the variations in precipitation in these regions are influenced by the Asian (Indian)summer monsoon activity in the mid-latitudes, correlations with all-India monthly and seasonal rainfall (IMR) are investigated. Further, the change of atmospheric circulation patterns with the interannual variation of summer precipitation of Regions I and II are also examined. The results are summarized as follows : 1) The interannual variation of summer precipitation of Region I (Taklimakan Desert) is mainly related to the windward mid-latitude circulation and eastward (westward) shift of the Tibetan High in a wet (dry)year. This region shows a clear negative correlation with IMR in June and July, and the relationships are caused by a rather local circulation change with IMR variation over Central Asia. 2) In Region II (Loess Plateau, the middle reaches of Yellow River), interannual variation of summer precipitation shows a positive correlation with IMR through the summer monsoon season. It shows a clear 2-3 year periodic oscillation, and seems to be closely related to the atmosphere/ocean interaction in the equatorial Pacific.
Seasonal variations of surface energy budget and evapotranspiration in an oasis were reported based on in-situ measurements of radiation and turbulent fluxes as one of the basic stations of HEIFE (HEIhe river Field Experiment). The oasis is characterized as a moist area surrounded by dry desert, and the observed data were compared with those of the desert. It is found that significant differences were observed in upward shortwave/longwave radiation between oasis and desert. This is ascribed to the difference of the surface vegetation and leads to a larger net radiation flux at the oasis. A smaller Bowen ratio (nearly 0.2) is also an important charactersitic of the oasis when compared with that of the desert (more than 1), except in winter. The surface energy budget was examined and it was found that some residuals were left even when the soil heat flux was included. This issue was left for future studies of horizontal advection. Based on the eddy correlation water vapor flux measurements, the daily mean evapotranspiration were estimeted as 3.4 mm (Aug.), 1.7 mm (Oct.), 0.2 mm (Dec.), 2.8 mm (May.) and 3.9 mm (Jun.), respectively during the Intensive Observation Periods (IOP). Evapotranspiration was also estimeted from continuous tower profile data and the result is almost consistent with that from eddy fluxes. Based on the profile-derived continuous water vapor flux, annual evapotranspiration was estimated as 535 mm, which is about 1/4 of the evaporation pan data at the Zhangye meteorological office.
Most methods of measuring soil-surface evaporation originate from those of measuring water-surface evaporation, and hence they are not necessarily suitable for making measurements of evaporation from dry land surfaces. The major reason is that, as observation shows, when the dry surface layer (DSL) forms on the soil, the constant-flux layer of water vapor is barely developed in the surface air layer. However, during most of the day, the upward water vapor flux in the DSL is nearly constant with depth. The principle of the DSL method is to estimate this upward near-constant flux in the DSL from the depth profiles of temperature and soil water content in the layer. The DSL method was applied to measurements of evaporation from a sand surface at the HEIFE desert station and they were compared to the decreases in soil moisture in the top 1 m of sand, from which the following results were obtained. (a) Estimates of daily evaporation about a week after rainfall of 15 mm or so, which were made on the basis of seven measurements taken by the DSL method during the day, were in good agreement with the daily decreases in soil moisture in the top 30 cm of sand. (b) Daily evaporation from dry soil can be approximately estimated from one measurement of evaporation rate made by the DSL method in the afternoon and the time lapsed since the last rainfall.
1990 at Zhangye and its surrounding areas in northwestern China and analyzed with an electron microscope equipped with an energy-dispersive X-ray (EDX) analyzer. The weight percentages of elements with atomic numbers larger than 11 (sodium) in individual particles were obtained using EDX spectra. Three samples collected in spring and one sample in summer were analyzed and particle type classifications were given. In spring, mineral particles were present in high number fractions (97-98 %) of particles in the radius range of 0. 1-6 μm. Particles mainly composed of aluminosilicate comprised 60-70 % of mineral particles. The samples were characterized by the presence of "Ca-rich" particles. The "Ca-rich" particles were present in number proportions (10-20 %) of mineral particles and often contained S, suggesting the presence of CaSO4. 2H2O (gypsum). However, most of the mineral particles had the weight ratios of S/Ca less than 0. 1. The analysis showed that "Ca-dominant" particles, which would be mainly composed of CaCO3 (calcite), were present mainly in the sub-micrometer radius range. In summer, particles were collected under the atmospheric condition of strong wind (8 ms-1). The sample also showed that mineral particles were dominant (98 % by number) in particles of 0.1-5μm radius. This result suggests the importance of mineral particles, even in the summertime atmosphere.
Simultaneous measurements of water vapor, sensible heat, carbon dioxide and momentum fluxes were made above and within plant canopies of a wheat field at Zhangye oasis in June, 1992, using the eddy correlation method. The diurnal variations of energy and carbon dioxide budget components and related meteorological parameters were obtained. Vertical fluxes of water vapor, sensible heat and carbon dioxide above plant canopies were predominant, compared with the fluxes at the middle layer of the plant canopy. This implies that, in the daytime, the upper part of dense plant canopies (LAI = 5) was an active source region of water vapor as well as an active sink region of carbon dioxide. A moderate and steady wind from the surrounding warmer desert and Gobi areas increased an upward water vapor flux and caused a significant downward sensible heat flux above plant canopies ; these phenomena are the so-called oasis effects peculiar to the arid region. The diurnal variations of turbulent fluxes and related quantities observed in a wheat field were compared with the results of Goudriaan's simulation model. The model simulates well some primary characteristics of wheat crop micrometeorology ; large loss of latent heat in upper parts of plant canopies, and a significant downward sensible heat flux under moderate wind speed conditions.
The annual evaporation from the HEIFE Linze Desert Station in the Hexi Corridor, Gansu, China was estimated by the energy balance method, using observed net radiation, sensible heat flux estimated by the bulk method, with transfer coefficients obtained during short IOP's in the four seasons and heat flux into the ground estimated from the soil temperature profile for every 10 days, to be about 120 mm/year in 1991 and 1992. This method was used because turbulent characteristics of water vapor showed unexpected characteristics from existing knowledge over the dry and hot desert surface air layer. The value of annual evaporation is larger than annual precipitation of l00 mm/year in the bottom part of Hexi Corridor or HEIFE area by about 20 %.