Showing papers in "Journal of the Meteorological Society of Japan in 1989"

Dynamics of super cloud clusters, westerly wind bursts, 30-60 day oscillations and ENSO - An unified view

Abstract: Results are presented on numerical experiments that were carried out to investigate the mechanisms of the observed variabilities in wind and convection associated with supercloud clusters (SCCs), westerly wind bursts, and 30-60 day oscillations in the western Pacific region. It is shown that the generation of a 30-60 day eastward propagating precipitation pattern in the Lau and Peng (1987) model, which can be identified as SCC, is accompanied by convective clusters coming in opposite direction to that of the SCC itself. The results suggest that the westward propagating cloud clusters are produced at the initial stage of the 30-60 day disturbance due to mutual adjustment of the large-scale flow and heating.

Composite analyses of wintertime wind stress vector fields with respect to SST anomalies in the western north Pacific and the ENSO events Part II. ENSO composite

Abstract: Long-term wind stress vector (WSV) fields in winter over the North Pacific, which were calculated by Kutsuwada and Teramoto (1987), are analyzed by means of the composite method with respect to SST anomalies in the mid-latitudes of western North Pacific (SST composite). According to SST anomalies, two categorized winters, i.e., warm and cold winters are selected during 24 years from 1961 to 1984. The numbers of warm and cold winters are six and five, respectively. In order to examine whether or not the composite WSV fields are well-ordered and/or rigid ones, maps of stability of WSV anomalies are constructed, and the new parameter, Degree of similarity of WSV anomaly field of each winter to the composited WSV anomaly field is introduced and discussed. Both parameters show that the extracted patterns for two categorized winters are well-ordered. In warm (cold) winter, mid-latitudes westerly weakens (strengthens) and shifts northward (southward). As a result, the East Asian Winter Monsoon (Kisetsuhu) over Japan weakens (strengthens). It is also seen that in the equatorial region, in warm winter the region with SST higher than 28* extends to the central to eastern part and its anomaly fields are very similar to those in ENSO year winter. Actually, winters selected as warm (cold) winter include the ENSO (ENSO+1) year winters, i.e., winters during ENSO events, but not the ENSO+I (ENSO) year winters. Time series of Degree of similarity for westerly region to warm-winter composited WSV anomaly fields are well in agreement with those of \"Far East zonal index\", which is used by the Japan Meteorological Agency. From the composite map for sea level pressures, it is shown that shifts of westerly axis correspond to north (warm winter)-south (cold winter) shifts of the Aleutian Low.

Chemical and Physical Properties of Stratospheric Aerosol Particles in the Vicinity of Tropopause Folding

Abstract: The chemical composition and physical state of individual aerosol particles were examined for the aerosol collected on board an aircraft. The collection of aerosol particles was carried out at altitudes between 2.0 and 7.6km including the vicinity of tropopause folding and above tropopause over the Japan Sea on 14 February, 1984. The molecular state of sulfate particles was determined by vapordeposited calcium thin-film method (pre-coating) in order to avoid the possible chemical modification of samples by ammonia after collection. Nitrate and sulfate in particles were detected by use of the vapor-deposited nitron thin-film method and barium chloride thin-film method, respectively. Whether stratospheric aerosol particles are frozen or supercooled was examined by comparing the morphology of collected particles with that of frozen sulfuric acid particles produced in the laboratory. Sulfuric acid particles were predominant in the stratosphere without any serious ammoniation. These sulfuric acid particles are much larger than those in the lower troposphere. No nitrate-containing particles and few particles of tropospheric origin were found in the stratosphere. The fact that nitrate can not be detected in the particles suggests that most of the nitric acid is not dissolved in particles but exists in the gas phase in the stratosphere. Stratospheric sulfuric acid particles were not frozen, but supercooled even at -48*. Stratospheric aerosols were constituted of sulfuric acid particles, of which the chemical composition was much more uniform in space than that of tropospheric aerosols. We can safely state that supercooled sulfuric acid particles are predominant in the mid-latitude stratosphere. On the other hand, aerosols of several different origins coexisted in the troposphere. Sulfuric acid particles were mostly predominant in the middle and upper troposphere, although their ammoniated particles also existed. Acidity of the sulfate-containing particles increased with increasing altitude between 2.0 and 5.5km. It was observed that stratospheric sulfuric acid particles coexisted with particles of lower tropospheric origin (probably ammonium sulfate particles) in the tropopause folding. The observation was carried out during the period when there was a slight possibility that the effect of volcanic eruption of E1 chichon in 1982 on the stratospheric aerosol layer still remained. However, it is not possible to determine the degree of any volcanic effect from the present study.