Masahiro Kajikawa

Cloud droplet size dependence of the concentrations of various ions in cloud water at a mountain ridge in northern Japan

Acid precipitation is one of the global environmental problems affecting terrestrial and aquatic ecosystems. Our research group has recently studied the acid precipitation in Hyogo and Akita Prefectures in Japan, combining chemical analysis of ions with analysis of meteorological conditions, and has analyzed the source of pollutants by Ž . factor analysis Ozeki et al., 1995, 1997; Ogawa et al., 1998a,b . It is known that fogrcloud water is significantly more acidic and has higher concentrations of chemical Ž . components than rain water e.g., Waldman et al., 1982; Hosono et al., 1994 . The mechanism of uptake of ion components into cloud droplets, especially for the difference between ions, is not completely understood. Cloud water and rain water samples were collected at the Hachimantai mountain range in Akita Prefecture in northern Japan to obtain information on the mechanism of uptake of ion components into cloud droplets. The chemical composition of the cloud water was analyzed and compared with that of the rain water. The relationship among ion concentrations in the cloud water and droplet size was examined Ž X X Cloud water samples were collected along the mountainside 39856 N, 140851 E, . Ž . 1465 m, a.s.l. of Mt. Mokkodake 1578 m, a.s.l. , a mountain ridge in the Hachimantai Ž . Ž range. A passive fog sampler Okita, 1961 with a cylindrical Teflon wire screen Model . FWP-500, Usui Kogyo Kenkyusho was exposed during the period from August to Ž . September 1997. Rain water samples were collected at Akita City Akita University

Wintertime precipitation behavior in the western Canadian Arctic region

To investigate the precipitation formation process in the two major types of weather systems (“Pacific origin” and “storm track” types) in the western Canadian Arctic region, an X-band vertical pointing Doppler radar, microwave radiometer were installed at Inuvik, Northwest Territories, Canada, during the midwinter of 1995/1996. Precise precipitation observations specially for ice crystals with replicator, microscope, and close-up photos were also conducted at the same place. Precipitation formation mechanisms were quite different between these two major weather systems. For the Pacific-origin-type disturbance, warm and moist air was advected from the Pacific Ocean between 1.5 and 3.5 km msl. Convective echo patterns appeared by radar, and a large amount of precipitable water vapor and liquid water path were estimated by a microwave radiometer. As the air temperature was below the freezing point, the liquid water was identified as being in the supercooled state. Densely rimed dendrites and graupel particles were observed predominantly on the ground. Collision and coalescence processes of supercooled cloud droplets were dominant. On the contrary, for the storm track disturbance the moisture came from the Arctic Ocean, and strong winds were observed on the ground. The air mass was colder than −20°C throughout the layer. Stratiform echo patterns were observed by radar, a smaller amount of precipitable water vapor, and only a small liquid water path were observed by a microwave radiometer. It was suggested that the condensation growth was predominant. Snow crystal shapes of plates, columns, and bullet rosettes were observed predominantly on the ground.

Evaluation of ionic pollutants in cloud droplets at a mountain ridge in northern Japan using constrained oblique rotational factor analysis

The scavenging of aerosol particles by precipitation and fogrcloud plays an important role in the distribution and concentration of pollutants in the atmosphere. Our research group has recently studied the acid precipitation in Hyogo and Akita Prefectures in Japan, combining chemical analysis of ions and analysis of meteorological Ž . Ž conditions, and has analyzed the ionic pollutants salts by factor analysis Ogawa et al., . 1998a,b, 1999a,b; Ozeki et al., 1995, 1997 . In general, it is known that fogrcloud water is significantly more acidic and has higher concentrations of chemical components than Ž . rain water e.g., Waldman et al., 1982, Hosono et al., 1994, Ogawa et al., 1999a,b . But the mechanism of uptake of ion components into cloud droplets, especially for the Ž difference between ions, is not completely understood. In our previous works Ogawa et . al., 1999a,b , cloud water and rain water samples were collected at the Hachimantai mountain range in Akita Prefecture in northern Japan to obtain information on the mechanism of uptake of ion components into cloud droplets. We obtained the information about relationship among ion concentrations in the cloud water and droplet size Ž . Ogawa et al., 1999a,b . In this work, we tried to analyze the seasonal change of ionic pollutants in cloud water due to a variation of mesoscale precipitation system and their dependence upon the cloud droplet size using constrained oblique rotational factor analysis, which has

Chemical Characterization of Acid Fog and Rain in Northern Japan Using Back Trajectory and Oblique Rotational Factor Analysis

Fog/cloud and rain water were collected at the mountainside of Hachimantai range in northern Japan and rain water was also collected at Akita City in order to investigate the air pollutant scavenging mechanism. The concentrations of various ions in these samples were analyzed, and the fog drop size and the wind direction were measured at each fog event. The fog at Hachimantai range had a very high total ion concentration, and was considerably acidified by non sea salt (nss-) SO42− and NO3−, compared with the rain at Akita and all sites in Hachimantai range. Using the oblique rotational factor analysis, three factors were extracted as the air pollutants; A: (NH4)2SO4+H2SO4, B: sea salts+HNO3+H2SO4, C: NH4NO3+OH−. These salts are well-known as the cloud condensation nuclei (CCN). Combining the factor analysis with the 72h back trajectory at 850hPa level, the contribution of Factor A was closely connected to the long-range transportation of anthropogenic or natural aerosol in air masses of continental origin.

Supercooled drizzle formed by condensation-coalescence in the mid-winter season of the Canadian Arctic

Abstract Supercooled drizzle (freezing drizzle) was observed at Inuvik, N.W.T., Canada (68°22′N, 133°42′W) on December 20, 21 and 27, 1995. Meteorological conditions in which the supercooled drizzle could form under low temperatures (colder than −20°C) in the mid-winter season of the Canadian Arctic were examined from the sounding data and data measured by a passive microwave radiometer at ground level. The following results were obtained. (1) Supercooled drizzle fell to the ground with ice pellets and frozen drops on snow crystals. (2) The maximum size of supercooled drizzle particles increased as the depth of cloud layer saturated with respect to water increased. (3) Because a layer of air temperature higher than 0°C was not detected from the sounding data at Inuvik, melting of snow particles was impossible. It was concluded, therefore, that supercooled drizzle was formed by the condensation–coalescence process below freezing temperature.

Aggregation of needle snow crystals

Abstract For the purpose of studying the early process of snowflake growth, characteristics of the aggregation (collision–adhesion process) of needle snow crystals were investigated by examining photomicrographs of snowflakes composed of two crystals. The adhesion type of the snowflakes was classified into crossed adhesion and point adhesion types. When the sizes of the two crystals were similar, which is indicative of nearly equal fall velocity, there was an increased number of the crossed adhesion type, whereas the point adhesion type was predominant when there was a large difference in size, thus fall velocity. In the case of the crossed adhesion type, the angle between the c -axes of the two crystals was usually greater than 70°, whereas the angle in the case of the point adhesion type showed no such distinct feature. Our findings suggest that the crossed adhesion type snowflakes are formed mainly through the interaction of the flow fields around two crystals (the collision due to relative horizontal motions) and the point adhesion snowflakes were formed through the inertial collision between smaller crystals and larger ones (the collision due to the velocity difference).

Relationships between chemical compositions and meteorological conditions for fog and rain at Hachimantai range, and rain at Akita city in Japan.

Acid fog and rain samples were collected at Mountain range of Hachimantai and at Akita City in Japan. Various ion concentration of these sample were analyzed using an ion chromatography and pH meter. The NO3- concentration of rain at Akita increased gradually year to year. The fog water had a high concentration of various ions compared with the rain. The highest concentration was observed in the weather chart of high pressure on Japan Island. The fog water had a low concentration for various ions in autumn compared with those in spring, so that this result agreed with the fact that the autumn sky is clear and clear in Japan.

The relation between prevailing precipitation-particle type and radar echo structure around the Dewa Hills

Abstract Snow clouds influenced by topography were observed on 13–19 February 1992, and were analyzed using the data of Doppler radars, surface observations and rawinsondes. The analysis period was divided into two stages (stages I and II) based on the radar echo pattern and the rawinsonde data. The radar echo intensified over the Dewa Hills in both stages. Each stage represented the different type of snow cloud. The cloud type was clearly related to the prevailing precipitation-particle type. The cold outbreak was weak and widespread echoes appeared in stage I. Snowflakes were dominated among the observed precipitation-particles, and weak orographic lifting was expected. It is suggested that deposition growth prevailed over the Dewa Hills in stage I. The cold outbreak was strong and many echo cells were observed in stage II. Graupels dominated among the observed precipitation-particles. The low-level wind favored the strong orographic lifting. It is inferred that riming growth prevailed over the Dewa Hills in stage II. The contribution of graupel to the precipitation intensity was larger when the observation site was closer to the center of an echo cell.