Measurement of aerosol particles was performed over the North Pacific Ocean and the North Atlantic Ocean during two expeditions of the R/V Hakuho-Maru to investigate the modification of individual sea-salt particles. The analyzed results of individual particles with a scanning electron microscope and an energy dispersive X-ray spectrometer are as follows: (1) The Cl/Na mass ratios of square-shaped particles are nearly equal to the value of seawater (1.8), regardless of the particle size. (2) The Cl/Na ratios decrease with increasing the mass fraction of non sea-salt (excess) S in association with the change in shape on the collecting surface from square to circular or irregular. (3) From the relative mass ratios of Na, S and Cl, it is evident that the modified sea-salt particles contain not only Na2SO4 but also other compounds, for example NaNO3, as suggested by previous researchers. (4) The degree of modification over the sea is not dependent on the distance from the shore but on the transport time period, implying that the modification of sea-salt particles collected over the open seas is affected by the transport of the continental air mass. (5) It is found that the modification of the sea-salt particles is closely related to the concentration level of Aitken particles. There is no modification where the concentration of Aitken particles is less than about 400/cm3.
A description is given of two striking examples of diurnal variation in the movement of surface cold fronts in central Honshu associated with slowly moving synoptic-scale frontal systems in the warm season. In these cases, the surface cold front was intensified along the coast due to the daytime heating over the land and moved inland during the afternoon on two successive days, displaying a recurrent or oscillatory movement for more than one diurnal cycle. As a result, part of the region experienced two frontal passages repeated at an interval of about 24 hours. A number of similar examples can be found for this type of diurnal variation, indicating that it is not a rare event.
Analytic solutions are derived for simple models of equatorial wave-CISK with conditional (positiveonly) heating. Conditional heating favors an unstable mode having a single wet region of infinitesimal width. This result helps explain model simulations of tropical superclusters and intraseasonal oscillations. Mechanisms of scale selection and propagation are discussed, and the model is generalized to include evaporation-wind feedback, multiple vertical-mode CISK, and scale-dependent damping. The first two mechanisms cause zonal propagation, without scale selection. Scale-dependent damping breaks the inviscid continuum (wherein modes exist as a continuous function of wet region width) into discrete modes with unique horizontal structure and phase speed. Results are contrasted with the hierarchy of scales in observed intraseasonal oscillations.
Evidence of large temporal and spatial variability in the eddy fluxes of sensible heat in the lower troposphere (100-50 kPa layer) in January, from 1946 to 1987, is presented. The January climatological (1946-87) spatial distribution of the meridional standing eddy heat flux is characterized by four main features, or "centers of action": (1) a region north of Korea (extreme eastern Siberia), (2) northeastern Atlantic Ocean, (3) the Gulf of Alaska, and (4) a region over midwestern Canada. Even though the center just north of Korea is the most intense, much of the interannual variability of the meridional January standing eddy sensible heat transport is associated with the two centers over the northeastern Atlantic and the Gulf of Alaska. Spatial and temporal variability of these centers are correlated with the intensities of the Icelandic Low and the Aleutian Low, respectively. The standing eddy heat transport in the Greenland Sea is well correlated with the ice margin there during years of large abnormal heat transport by the standing eddy component. The long term variability of the heat transport over the period 1946-87 shows a clear interdecadal signal in the Gulf of Alaska. Over the North Atlantic, the variability is instead dominated by a large perturbation in the early 1970's. The January climatological spatial distribution of the meridional transient eddy heat flux is dominated by a center over the Aleutian Peninsula, and an elongated cell stretching from eastern United States to North Sea, with a center off Newfoundland and another over Iceland. The spatial pattern follows closely the climatological tracks of baroclinic disturbances, i. e., synoptic storms. The geographical distribution of the spatial and temporal variability of the January meridional transient eddy heat flux is less organized than the pattern associated with the standing eddy heat flux. Much of the variability is confined to the western hemisphere, from the mid-North Atlantic Ocean, across North America, to the eastern half of the North Pacific. The centers of variability are located at (1) Gulf of Alaska, (2) western and eastern Canada, and (3) southeastern United States.
The effect of excessive snow mass over the Eurasian continent on the spring and summer climate is investigated by using the MRI⋅GCM. The ensemble mean of the four runs (SNOW runs) with the excessive snow mass of 5 cm (water equivalent) at the beginning of March over the snow cover area of the continent is compared with that of the control runs, to deduce the effect of the snow mass on the climatic parameters in the later seasons. The main results are summarized as follows: (1) In spring, the albedo effect is dominated in the lower latitudes particularly over the Tibetan Plateau. The reduced net radiation by the anomalous snow cover balances the reduced surface sensible and latent heat fluxes, which account for the significant decrease of surface temperature, cloudiness and total diabatic heating over there in the SNOW runs. (2) In summer, in contrast, the snow-hydrological effect is significant, particularly in the mid-latitudes. The increase of ground wetness in the SNOW runs causes anomalous cooling and higher pressure near the surface. A moderate signal of the weakened Asian summer monsoon is also obtained. However, the increase of evaporation activates cumulus convection, which partly compensates for the decrease of total diabatic heating by the cooling near the surface. This evaporation/convection feedback seems to work, on the other hand, to sustain the increased ground wetness throughout the summer. (3) The atmospheric teleconnection patterns induced by the anomalous snow cover over the Tibetan Plateau and east Asia significantly appear over the north Pacific and the North American continent in spring through late summer. These anomalous circulations cause the considerable decrease of surface temperature over the northeastern part of North America. (4) The implication of these results for the Ice Age issue is also briefly discussed.
A very dense network of recording rain-gauges spaced at intervals of about one kilometre extended from the west coast at sea level to an altitude of 400 m and 13 km inland. Catches at each site were compared under conditions when rain was generally widespread both for prevailing offshore and on-shore winds. Rainfall was evaluated in terms of total catch per rain period, the distribution of rainfall intensities within each rain period, and correlations of intensities between individual gauges. Consistent with seeder-feeder theories, the catch was found to increase with distance from the coast. However, short-term rainfall intensities at pairs of sites were highly correlated and not subject to the non-linear dependence on the absolute value of the rainfall intensity noted by previous workers studying total catches. Catch ratios of up to 3:1 were measured for offshore winds.