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It is well known that sea-salt aerosols in particulate matter (PM) react with acids such as H 2 SO 4 and HNO 3 during transportation and thereby lose chloride ions (Cl-loss). The PM and fog were sampled concurrently at different altitudes in the Hachimantai mountain range, northern Japan. The PM and fog sampled at different altitudes had nearly identical properties for the ion components. However, the PM was in a Cl-depleted state (more than 80% of all samples), but the fog water was not in so Cl-depleted state (less than 29%). As a result, it could be explained that this phenomenon caused because the fog droplets took up the gaseous state HCl other than sea-salt PM. After all Cl - in the fog water recovered and was rather rich compared with the sea-salt or the PM by the uptake of the gaseous state HCl. Moreover, it was found that for PM coarse (2.5

二重防風ネット内で堆積した乾き新積雪の密度に対する平均気温および平均降水強度の影響に加えて,降雪粒子の卓越結晶形,水平粒度分布,霰寄与率(質量フラックスに占める霰の割合),雪面への運動エネルギーフラックスおよび粒子投映像の円形度との関係を解析した.その結果,新積雪密度への影響として,卓越結晶と平均降水強度の他に,雲粒付樹枝では運動エネルギーフラックスとの相関が大きかった.また,雲粒付立体樹枝では水平粒度分布,円形度,霰寄与率および運動エネルギーフラックスの影響も比較的顕著にみられた.さらに,卓越結晶形の霰(霰寄与率≧70%)では,水平粒度分布の影響が他の因子より大きかった.

Water samples from radiation and upslope types of fog were collected at Takanosu Basin and Hachimantai mountain range of Akita Prefecture in northern Japan, respectively. The effect of the long-range transport of pollutants from the Asian Continent to the basin and the mountain range on the chemical characteristics of two types of fog was studied using chemical analysis data for the water samples as well as the back-trajectories of the air mass. In particular, non-sea-salt (nss)-SO 4 2 - of radiation fog provided a much higher concentration than that of upslope fog, which suggests that nss-SO 4 2 - might be transported mainly from the Asian Continent. The transport and uptake mechanism of pollutants in the radiation fog water were explained based on their accumulation in the basin due to anticyclonic subsidence and by the long-lasting fog behavior.

の結果をみると，ほぼ日本全国にわたって平均pH 4 台の雨水が観測されている．現在の被害は樹木の立ち枯れ（これも直接原因かどうか分からない）等以外には顕著ではないが，近い将来，他の生態系への影響が懸念されている．その中で農業県秋田では，農作物などに対する影響が心配されているが，酸性雨水の系統的な研究は少なく，著者らの研究グループ以外にはほとんど見られない．特に，1 雨水又は1 日ごとのサンプリングの結果はほとんど報告されていなかった．そこで著者らの研究グループでは1993 年冬季から秋田県の雨水を1 日ごとにサンプリングし，その化学組成を分析し，雨水の酸性化の原因や汚染起源を特定するために化学的，統計的，気象学的な解析を行ってきた

Fog water samples were collected at the Akita Hachimantai mountain range in northern Japan from August to September 1997 and from June to September 1988 to 2000 to investigate the pollution mechanism of fog. Ionic components and insoluble substances in fog water were analyzed using ion chromatography and particle induced X-ray emission (PIXE) analysis, respectively. Combining a 72 h back trajectory and principal component analysis (PCA) to chemical analysis data elucidated the effect of the transport course of an air mass on samples insoluble substances and ionic components. When the air mass was transported from northern China to the Hachimantai range, the nss- SO 42- was greater than in other cases. That fog contained "Kosa" as an insoluble substance from northern China. Our PCA analysis revealed that the score of PC1 (which was about –0.5) was a measure of containing "Kosa".

In mid-winter ice pellets were observed at Inuvik, Canada and Kiruna, Sweden in the Arctic region. The size distribution, morphology and crystalline nature were examined from the photomicrographs. Moreover, meteorological conditions in which the ice pellets could form were examined from the sounding data at Inuvik. The following results were obtained. (1) The sizes of ice pellets in the Arctic regions were considerably smaller than those in temperate regions. (2) The ice pellets simultaneously fell with the snow crystals with frozen small raindrops. (3) The morphology of ice pellets with a bulge or a spike was qualitatively similar to the results of laboratory experiments. (4) The rate of shattering was smaller than the results of laboratory experiments. (5) Single crystalline ice pellets were abundant in the size < 200μm. (6) Ice pellets in the Arctic are formed through the freezing of supercooled drizzle drops, which are formed by condensation-coalescence process below the freezing temperature.

雪片の構成因子(構成雪結晶の数,形,粒径など)を明らかにするため,雪片を個々の結晶にほぐす方法(分離法)による観測を行い,以下の結果を得た.構成結晶数が同じ場合,雪片の粒径は結晶の平均粒径が大きいほど大きくなること,樹枝状結晶は放射状結晶よりも平均粒径が大きいため,大きい雪片を形成することが確認された.雪片の粒径は構成結晶の平均粒径をパラメータとして結晶数のべき関数で表され,この関係は構成結晶数10個未満とそれ以上とで異なった.雪片の形状を仮定した簡単なモデルによる考察から,前者の関係は外形が平板状に近い付着の仕方を反映していること,後者は球状雪片に対応していることが示唆された.

A new approach is described for calculating the mass (m) and terminal velocity (Vt) of ice particles from airborne and balloon-borne imaging probe data as well as its applications for remote sensing and modeling studies. Unlike past studies that derived these parameters from the maximum (projected) dimension (D) and habit alone, the ‘‘two-parameter approach’’ uses D and the particle’s projected cross-sectional area ( A). Expressions were developed that relate the area ratio ( Ar; the projected area of an ice particle normalized by the area of a circle with diameter D) to its effective density ( re) and to Vt. Habit-dependent, power-law relationships between re and Ar were developed using analytic representations of the geometry of various types of planar and spatial ice crystals. Relationships were also derived from new or reanalyzed data for single ice particles and aggregates observed in clouds and at the ground. The mass relationships were evaluated by comparing calculations to direct measurements of ice water content (IWC). The calculations were from Particle Measuring Systems (PMS) 2D-C and 2D-P probes of particle size distributions in ice cloud layers on 3 days during an Atmospheric Radiation Measurement (ARM) field campaign in Oklahoma; the direct measurements were from counterflow virtual impactor (CVI) observations in ice cloud layers during the field campaign. Agreement was generally to within 20%, whereas using previous mass‐ dimension relationship approaches usually produced larger differences. Comparison of ground-based measurements of radar reflectivity with calculations from collocated balloon-borne ice crystal measurements also showed that the new method accurately captured the vertical reflectivity structure. Improvements in the accuracy of the estimates from the earlier mass‐dimension relationships were achieved by converting them to the new form. A new, more accurate mass‐dimension relationship for spatial, cirrus-type crystals was deduced from the comparison. The relationship between Vt and Ar was derived from a combination of theory and observations. A new expression accounting for the drag coefficients of large aggregates was developed from observational data. Explicit relationships for calculating Vt as a function of D for aggregates with a variety of component crystals were developed.

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-) SO4 2− 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.

Fog water was collected at the mountainside of Hachimantai range in Northern Japan from June to September in 1998 and 1999. The various ion concentrations in these samples were analyzed, and the fog droplet sizes were measured for each fog event. As the fog droplet size increased, the ion concentration decreased, and the slope of log-log plots of the concentration versus the droplet size was different each other. In order to characterize the air pollutant, moreover, these data were quantitatively analyzed by an oblique rotational factor analysis. We found that three factors were extracted as the air pollutant source; A: (NH4) 2SO4, B: acids (HNO3+H2SO4), C: sea-salt. Combining the factor analysis with the 72 h back trajectory at 850 hPa level, we found that the contribution of each factor varies with the back trajectory. In 1998, the contribution of factor A tends to increase at the trajectories from Northeastern China, while factor C increases at the trajectories through the East China Sea and the Sea of 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.

In order to investigate the acidification and pollution of fog, fog water samples were collected in the Akita Hachimantai mountain range at the northern Japan from August to September, 1997 and June to September, 1998 and 1999. The ionic components and the insoluble substances in fog water were analyzed using ion chromatography and Particle Induced X-ray Emission (PIXE) analysis, respectively. Combining a 72h back trajectory to the chemical analysis, the effect of the transportation course of an air mass on the insoluble substances and ionic components in the samples was discussed. When the air mass was transported from the northeastern China to the Hachimantai range, the acidity of fog water was highest in all cases. This acidification was mainly caused by nss-SO42- and NO3-. It was found that the fog water in this case would contain “Kosa” as the insoluble substances from the northeastern China.

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).

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.

An ion thruster emits a high density plasma plume and the electromagnetic noise radiated from the plasma current may affect the spacecraft instrument. An electromagnetic particle simulation code has been developed to investigate the effects of the electromagnetic interference induced from the ion thruster plume. The electromagnetic waves are excited due to plasma instability caused by strong polarization field inside imperfectly neutralized plume. The strength and frequencies of electromagnetic noise radiated by ion thruster plume depend on the distribution of charged particles inside the plume, static magnetic field strength and its orientation.

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.

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

Fog/cloud and rain water was collected at the mountainside of Hachiman tai range and rain water was also collected at Akita City. The various ion concentrations (H+, Cl-, SO42-, NO3-, Na+, NH4+, K+, Ca2+, Mg2+) of these sam ples were analyzed, and the droplet size and the wind direction were measured for each fog sample. The fog at Hachimantai range had a very high total ion concentration, and was considerably acidified by nss (non sea-salt)-SO42- and NO3-, in comparison with the rain at Akita and Onuma (Hachimantai range). There were some fog and rain samples whose chemical components in insoluble substance, which were analyzed by PIXE analysis, were similar to that of Kosa from China. As the fog droplet size increased, the ion concentration decreased, and the slope of plots of the concentration versus the droplet size was different from each other. From the negative slope of the plots, we can conclude that the fog samples in this work were in the size interval I (unactivated or freshly-activated) for the droplet growth.

Observations of cloud liquid water path, columnar water vapor amount, and downward flux of infrared radiation in the Arctic region Inuvik, Canada and Kiruna, Sweden, during winter were carried out with a microwave radiometer and a pyrgeometer. The algorithm used in this study for the retrieval of liquid water path and columnar water vapor amount from measured intensity of microwave radiation requires the atmospheric temperature profile and the cloud temperature, which were obtained from radiosonde measurements. It was shown from microwave radiometer measurements that the columnar water vapor amount changed between 1-13kgm^ during about a month in both observation points, and supercooled liquid water existed on several days. At Inuvik liquid water path reached about 0.25kgm^ at most; this is comparable to a typical value of summer clouds in mid-latitude. It was also shown that the downward flux of infrared radiation on the ground surface changed between 130 Wm^2&acd;300Wm^. Finally, the downward flux of infrared radiation was calculated using the liquid water path retrieved from the microwave radiometer and water vapor and temperature profiles obtained from radiosonde observations. A comparison between the calculated and the measured values shows that both are in good agreement and the downward flux of infrared radiation in the Arctic region is primarily dependent on the water vapor amounts and temperature profile.

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.

To investigate the characteristics of chemical composition of precipitation, especially, of snowfall, samples were collected on a daily basis in Akita City(39°43'N, 140°08'E, 10m a.s.l)from April 1993 to March 1994 and in Yuzawa City(39°09'N, 140°30'E, 96 m a.s.l.)from January to March 1994. Ions such as H+(as pH), Na+, NH4+, K+, Ca2+, Mg2+, Cl-, NO3- and SO42- were analyzed for 185 samples collected at Akita and for 59 samples at Yuzawa. The pH values at Akita in the winter were lower than those of other seasons, this tendency was the same at other coastal cities of the Japan Sea. It was concluded that the source of acid in the snowfall was non-sea-salt (nss)-SO42-.It is well-known that the sea-salt concentration in the precipitation decreases exponentially with the distance from the coast; however, the sea-salt concentration in the winter precipitation at Yuzawa, which is located about 50 km to the east of the coast, occasionally did not show marked decrease in comparison with the case at Akita which is 6.5 km from the coast. It was likely that when the surface wind direction was nearly NW, Na+ and nss-SO42- were transported from Akita to Yuzawa; high Na+ concentrations at Yuzawa were mainly affected by the surface pressure pattern and the surface wind direction during snowfalls.

日本は海に囲まれており,降水中には海塩起源と考えられるイオンが多量に含まれる.そこで,降水中でも海水中のイオン組成比が保持されると仮定し,Na+又はCl-イオン濃度を基準に,降水中の汚染物質を海塩起源(ss)と非海塩起源(nss)に区分することが一般的になされてきた.しかし,汚染物質を含んだ雨雲や乾性浮遊物が移動する途中にガス状酸性物質とイオン交換する可能性などがあり,必ずしもss/nssという区分は正しくないという意見もあつた.そこで,1993年4月から1995年3月までの期間,秋田市と湯沢市で1日ごとの降水を採取し,そのイオン組成を化学分析し,それらのデータに,著者らが開発した制限斜交回転因子分析法を適用し, 降水中の汚染起源を抽出し解析した.その結果,海水中の塩組成に非常に近い海塩由来の汚染起源が抽出された.しかし,Na+及びCl-イオンを含む海塩成分の一部が降水を酸性にする硫酸酸性の汚染起源の中にも含まれていることが分かつた.この因子は,冬季と冬季以外,又海に近い秋田と内陸の湯沢で組成の違いを示した.このことは,海塩由来の汚染物質が採水地点に到達するまでに,組成の変質を受けていることを強く示している.

A statistical method developed by our group, "the constrained oblique rotational factor analysis" enables feature reduction and grouping of the pollutant sources in precipitations from their chemical compositions. A study applied to the precipitations has indicated the necessity of the numerical evaluation of contributions of the extracted sources. In this paper, a procedure for the numerical evaluation is demonstrated; and, as one application, the precipitations collected in Hyogo prefecture are compared with those in Akita prefecture. The analysis has proposed that an ion-balance check of the extracted pollutant source gives a simple criterion about how many pollutant sources should be extracted. As a result, the causes of lowering of the pH of the precipitation of these two areas are explained by two sources: 1) an acidic source with sulfuric acid predominant brought over the Sea of Japan from China by winter monsoons; and 2) another acidic source with sulfuric acid and nitric acid predominant emitted domestically. The seasonal changes of acidity of the precipitation of Japan depend upon the amounts of these two contributions.

Radar is a powerful instrument in meteorology not only for research but for operational use. For quantitative measurements of precipitation, however, further studies need to be done for reducing measurement errors. Satellite microwave radiometer begins to be used for estimation of precipitation not only over sea but over land by using scattering models. To improve the accuracy of estimation, information vertical profile of size distribution of rain and snow derived from radar process should be combined data observed by passive microwave sensors. This study shows the possibility of snowfall observation with the combination of the radar and the microwave radiometer.

落下中の雪片のストロボ写真を解析して,落下速度におよぼす構成結晶形の影響を調べた.主な結果は以下の通りである.1)雪片の落下速度は,サイズまたは質量および地上気温に加えて,卓越結晶形(最も数の多い構成結晶形)に強く依存する.2)雪片の落下速度を表す場合に,融解直径のべき乗の関係式が適切であるとは必ずしもいえない.3)雪片の抵抗係数は,多くの種類でレイノルズ数の増加と共に小さくなる傾向がある.雪片の構成結晶形の差異に着目して,落下速度の測定結果を解析した.雪片の落下速度は,サイズまたは質量および気温に,卓越結晶形(雪片の構成結晶形のうち,最も多数を占める結晶形)を組み合わせて表すのが実用的である.落下速度を雪片の融解直径またはサイズの関数として.表す場合,べき乗関係が必ずしも相関が高いとは限らない.また,雪片の抵抗係数はレイノルズ数め増加と共に,ほとんどの種類で小さくなる傾向にある.

紡錘状霰の落下姿勢の安定性に及ぼす内部密度の不均一さの影響を検証するために,8ケースの降雪について頂点部と底面部の密度を測定した.この測定に加えて,頂角と宙返り運動との関係を自由落下姿勢の観測データを用いて再解析した.バルク密度が約0.3g・cm-3以下の範囲では,頂点部と底面部の密度差は小さいので,宙返りに対しては頂角θの効果が顕著となり,θ>θ*では完全宙返り(頂点が真下の位置を含む姿勢),θ θ*の領域でも不完全宙返りの割合が増加する.これらの結果は,紡錘状霰がその形を保ったまま成長し続けて,サイズが1cm近くになったり,紡錘状の雹になったりする可能性を示唆している.

雪片成長の初期過程を探るため,針状雪結晶の集合特性(衝突・付着過程の特性)を結晶2個から成る雪片の顕微鏡写真により調べた.両結晶の付着型は,交差付着型と点付着型に分類された.交差付着型は,両結晶のサイズが類似し,したがって落下速度差が小さい場合に多くみられた.一方,点付着型の割合は,両結晶のサイズの差が大きく,落下速度差が大きい場合に増加した.両結晶のc―軸のなす角度は,交差付着型で直角に近いものが多数を占めたが,点付着型ではその頻度分布に目立った特徴はみられなかった.これらの結果は,交差付着型と点付着型の雪片が,各々両結晶まわりの流れの相互作用と小さい結晶の大きい結晶への慣性衝突に主に起因することを示唆している.

A field experiment for snowfall at the coastal area in northern Japan was performed, and chemical components in snow were analyzed. When the synoptic weather pattern is a high pressure in the west and a low pressure in the east of Japan (WH&EL), it is influenced that the sea-salt concentration in the snow was in proportion to the squares of the wind speed at the sampling site. This relationship offers that the amount of sea-salt aerosol supplied from sea surface to air mass and finally to the snow depends strongly on the squares of the friction speed on the sea surface and of the wind speed at the snowfall site.

新積雪の圧縮粘性係数に及ぼす降雪粒子の結晶形の影響を調べるために, 秋田県鹿角市八幡平でかわき新雪の密度変化を6時間毎に観測した.主な結果は次の通りである.1) 三次元的な外形を持つ立体樹枝から成る新雪の圧縮粘性係数は, 同じ密度で比較すると, 二次元的な外形を持つ樹枝の場合より約5倍大きい.2) 新雪とこしまり雪との圧縮粘性係数の比較によると, 立体樹枝を主とする雪層では密度が0.1g・cm3以下で, 樹枝や角板を主とする雪層ではそれ以上の密度でこしまり雪へ変化すると考えられる.この事は, 結晶形により圧密過程が異なることを示唆している.3) 立体樹枝, 雲粒付立体樹枝, 角板および樹枝を主とする各々の新雪について, 圧縮粘性係数を密度および雪温の関数として表わす実験式が導かれた.

Fog droplets in the atmosphere are first produced by the activation of cloud condensation nuclei (CCN), which are originally some ionic compound. Subsequently, the nuclei grow by vapor diffusion. Fog droplets are polluted through the activation process and successive diffusion growth and residence (post activation). We cannot distinguish the effects of the two pollution processes of natural fog water samples. We found that fog droplets can be produced artificially without CCN using an ultrasonic humidifier. Because the artificial fog droplets are not polluted by CCN, the movement of the fog droplets in natural air will take up some pollutants in the air. Consequently, the two pollution processes of fog (the activation of CCN and the post activation process) can be discriminated using data from field experiments. This sampling analytical method is extremely important for further research regarding fog, clouds and environmental chemistry.

Fog and rain water samples were collected at the same time in the Akita Hachimantai mountain range in northern Japan from June to September in 1998 and 1999. The various ion concentrations in these samples were analyzed, and the fog droplet sizes were measured for each fog event. As the fog droplet size increased, the ion concentration decreased. The slope of log-log plots of the concentration versus the droplet size differed with the kind of ion. In order to characterize the air pollutant, moreover, these data were quantitatively analyzed by an oblique rotational factor analysis. We found that three factors were extracted as the air pollutant source: (NH4)2SO4, acids (HNO3 + H2SO4) and sea-salt. Combining the factor analysis with the 72 h back-trajectory at 850 hPa level, we found that the contribution of each factor varied with the transport pattern of air masses.

Supercooled 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 in the mid-winter season of Arctic Canada 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℃ 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 collision-coalescence process below freezing temperature.

The WANTS (Water vapor, Aerosol and Nuclei Transportation and Snow crystals) Arctic Experiment was carried out in Inuvik, NWT, Arctic Canada during the mid-winter of 1995/96. Many organizations participated in this research program. A vertical pointing Doppler radar, and microwave radiometer were set up on the roof of the Inuvik Science Research Center, and precipitation and aerosol particle observations by microscope, replica method and filter method were also conducted on the ground surface. Valuable and successive data over 40 days were obtained in the Arctic mid-winter. Two different major vapor routes were classified by synoptic weather analysis. One route was from the Gulf of Alaska across the mountainous region near the west coast of the North American Continent. The other was from the Arctic Ocean or Northern Alaska directly. Precipitation features between them were quite different. In the former the warm air mass was intruded aloft, a convective radar echo was observed and a high amount of liquid water was observed by microwave radiometer. Densely rimed dendrites, small graupel particles, needles and supercooled liquid water droplets were observed on the ground surface. The precipitation intensity was strong, however, the precipitation period was short. The latter was a windy and cold air mass, the radar echo was stratiform and the liquid water path was very small as observed by microwave radiometer. The crystal shapes of combination of bullets, columns and crossed plates type were observed. The precipitation intensity was characterized by weak intensity and long period.