Several observational studies indicate enhancement of the Asian subtropical front (Baiu front) in the vicinity of the Japan Islands due to the thermodynamic influence of cumulus ensemble. In the present real data forecast experiments, we demonstrate the influence through comparisons among predictions by a coarse-mesh primitive equation model without condensation (NO CND model), a model with large-scale condensation (LG CND model) and a model including both large-scale condensation and convective adjustment (AJS model), for two typical cases of Baiu front. The Baiu front is remarkably enhanced in AJS model as compared with the front in NO CND and LG CND model. An important fact found by the experiment is that the generation of thermal instability due to large-scale advection process is restricted within the zone along the northern periphery of the tropical marine air mass. The release of instability and the concomitant enhancement of Baiu front are consequently restricted in the aforementioned periphery zone.
Gridded fields of horizontal and vertical winds, temperature and height are objectively calculated for regions encompassing a major wintertime storm which developed during the Air-Mass Transformation Experiment (AMTEX) 1975. The objective analysis, the Pattern Conserving Technique (PCT), used to obtain the gridded fields was developed within the framework of the calculus of variations. PCT, through the application of several variational constraints such as proposed by Sasaki (1970) and implemented by Baxter (1975), simulates the thought processes and subjective analysis techniques of the human analyst. The analyses fields are further refined by including physical constraints which minimize inertial instability, satisfy hydrostatic balance and insure for mass continuity. From the resulting horizontal wind analyses, vertical motion fields are computed using the kinematic method and are verified for representativeness by subjectively comparing them with synoptic features such as fronts, precipitation reports, cloud analyses, and satellite photographs obtained from the U.S. Air Force Global Weather Central (AFGWC). The vertical motion fields are also compared with those derived from the quasi-geostrophic omega equation as solved by the Japanese Meteorological Agency (JMA), and the AFGWC, and with vertical motions kinematically computed from subjectively analyzed horizontal winds. The results of the comparison show that the vertical motion fields obtained from PCT exhibit a marked improvement in representing the synoptic situation and related weather features.
Evolutions of a laminar jet produced by an axial body force in a rotating fluid, which is inviscid, homogeneous and incompressible, are investigated by means of a linear theory. The body force is assumed to be axisymmetric and confined to a certain limited region. The forcing is suddenly initiated. As for the subsequent behavior of the forcing with time, the following are considered: 1) Continuous forcing. 2) Forcing of a finite duration. For continuous forcing the flow fields become uniform in the axial direction as time passes with the exception of the azimuthal velocity and pressure fields within the forcing region, where the Taylor-Proudman theorem can not be applied. In the forcing region an axial pressure-gradient is gradually built up which acts to oppose the forcing. It is found that the pressure-gradient becomes nearly steady after t*=10.90/f, where t* is the ellapsed time from the initiation of the forcing and f is the Coriolis parameter. The resulting pres- sure-gradient force balances the forcing in the axial direction, and the Coriolis force in the radial direction (geostrophic balance). For forcing of a finite duration it is found that the response of the fluid in the forcing region when the forcing ceases does not depend on the duration of the forcing T* if T* is larger than 10.90/f. For such a large value of T*, a reverse flow appears in the forcing region between t*'=3.4/f and 6.5/f after the forcing is stopped. Here, t*'=t*-T*. This phenomenon is caused by the reverse pressure-gradient force which has been maintaining a balance with the forcing. After the reverse flow weakens, continuous damped oscillations remain near the forcing region. The period of the oscillations is about 2π/f. The present model is considered to be a refined form of a linear theory (Niino, 1978), which was developed to explain the reverse flow found in the laboratory experiment on turbulent jets in a rotating fluid.
Freezing experiments on supercooled hemispheric water drops of an approximate 1mm in diameter were carried out from a point of view of the formation mechanisms of the origin of polycrystallization of frozen cloud droplets. Hemispheric water drops were seeded with a basal plane and a prism plane of single crystalline ice of needle type in the temperature ranges of -17 to -20°C, -20 to -23°C and -23 to -26°C, respectively. Notable polycrystallization occurred when hemispheric water drops were seeded with basal planes of single crystalline ice of needle type. The axial angle between the c-axis of a seeding crystal and that of a frozen hemispheric water drop had a prominent peak around 70° at all temperatures from -17 to -26°C. The axial angle between the c-axes of neighbouring two crystals making up a frozen hemispheric water drop had peaks around 70° 55°C and 40°C. Based upon these angles in this experiment, a possible arrangement of the c-axes of crystals making up a frozen water droplet was proposed.
Flash photography was used to examine the impact of water drops with flat, solid surfaces in order to determine the influence of drop size R and surface roughness parameter Ra upon the critical impact velocity VT above which splashing occurs. The existence of a critical impact velocity may be inferred from the literature but has not been proven prior to these experiments. It is shown that for a given surface roughness the product ST=RVT1.69 remains constant for the range R=0.70-2.25mm, suggesting that the condition for splashing is determined uniquely by the Reynolds Number and the Weber Number. The critical impact velocity VT is a decreasing function of Ra (the mean absolute deviation of surface contour from the mean surface level) and the variation of VT with Ra is of the order 3ms-1μm-1 for Ra<1μm; for surfaces of Ra<1μm, the corresponding variation is of the order 0.05ms-1μm-1. The data obtained here suggest that the number of drops produced per collision N may be predicted by the relationship N=k[R3V2-R182ST1.18] where k is an experimentally determined constant and V is the actual impact velocity of the drop. The relationship is superior to that proposed by Stow and Stainer (1977) in that it provides the correct functional relationship between R and VT, and correctly predicts values of N observed by Stow and Stainer. For drops impacting at their terminal velocity, the effect of the roughness of the target is believed to be crucial in predicting the occurrence of a splash only if drops possess radii in the range 0.5-0.8mm; for smaller drops no splash is likely, even on a very rough surface, and larger drops will splash on a perfectly smooth surface. Although of, perhaps, secondary importance, it was also noted that VT is higher for the more prolate drops of any given mass; the effect of drop eccentricity on the splash process has not been previously documented. These data may facilitate computations of those microphysical processes within clouds which involve collisions between ice particles and water drops and which may lead to the production of secondary drops.
This paper presents a discussion of the effective complex refractive index of aerosols composed of particles having large and small absorption coefficients in the visible region. Based on Mie theory, the effective complex refractive indices at the wavelength of 0.55μm which give correct values of both the extinction coefficient and the single-scattering albedo were calculated for the following two kinds of aerosol models: one is composed of carbon soot and ammonium sulfate particles and the other is composed of hematite and ammonium sulfate particles in varied proportion. The power law was assumed for the size distribution of the particles, with the exponent being varied from 2.5 to 3.5. The phase functions and the volume backscattering coefficients were also calculated in order to check the validity of using the effective refractive indices. The imaginary part of the effective refractive index increases with increase of carbon soot or hematite content and it also depends on the size distribution of these substances. The imaginary part of the refractive index obtained for a possible range of the soot content is consistent with that so far reported for atmospheric aerosols by several authors. It rarely exceeds 0.05 in this study. Based on these results, the possible effect of aerosol on the heat balance of the earth-atmosphere system is briefly discussed.
The size distributions of Submicron aerosols were measured at Minamitorishima Is. (Marcus Is., 24°N, 154°E) and the Ogasawara islands (Bonin Is., 27°N, 142°E) during two weeks in the autumns of 1975 and 1976 respectively. The purpose of these measurements was to get information about the concentrations and size distributions of aerosols in the North Pacific maritime atmosphere. To get the continuous records of the size distribution of natural aerosols, we employed the diffusion decay technique and an improved Pollak type condensation nucleus counter. From the set of decay rates of concentration of aerosols passing through the diffusion batteries, the size distribution of aerosol particles with radii between 0.002 and 0.2μm was determined by use of a response matrix method. The most important finding in the present work is that there is a notable difference in the size distributions and total concentrations of aerosols depending upon the origin of the air mass. In an air mass which has come from the main island of Japan, the total number concentration of aerosols is of the order of 1, 000 to 2, 000cm-3 and their size distribution tends to have a narrow range with a main peak between 0.02 and 0.07μm in radius. On the other hand in an air mass of mid-latitude maritime origin, the total number concentration of aerosols is of the order of 250cm-3, which is comparable to the background concentra- tion in these oceanic regions. The size distribution of aerosols in such an air mass tends to have a rather broad range with a main peak at around 0.02μm and a second peak, though not always detected, at around 0.004μm in radius. Present results suggest the possibility of the aerosols transported from land affecting the background concentration of the cloud condensation nuclei in the clean oceanic atmosphere.