Journal of the Meteorological Society of Japan. Ser. II
Online ISSN : 2186-9057
Print ISSN : 0026-1165
ISSN-L : 0026-1165
Volume 26 , Issue 9-12
Showing 1-6 articles out of 6 articles from the selected issue
  • Y. Yazawa
    1948 Volume 26 Issue 9-12 Pages 227-232
    Published: 1948
    Released: February 05, 2009
    It has been often observed that the pressure curve of one station trends symmetrically to each other towards the both sides of a point on it, and this character had been used to predict the pressure trend. If the pressure values were predicted with considerable accuracy for several days ingeneral, the trends of pressure fields should be also predicted for several days. This work is very important to long-range forecasting.
    To examine whether there may be symmetry characters on the pressure curves or not, the symmetry points were usually looked for at first by the harmonic analysis of the original curves. But this method is not always effective because the original curves are usually very complicated to analyse them easily to some elementary waves. It is natural that the pressure trend correlates very closely to each other on the both sides of symmetry point. So if the points were found, with which the original curve has the above mentioned characters, that points may be considered as symmetry points.
    The author examined at first the pressure curve in the period Oct. 1928 to March 1929 in Tokyo, according to the symmetry index of each day in this period (by the Stumpf's method), and he found that the point which has considerable high symmetry index (for example. 90⟨, ⟨.10 or. 80⟨, .20⟩) for some period (for example 12, 18, 24 days etc.) may be considered also as the symmetry point for longer period (for example for a period several days longer than original period), and he could predict the pressure trend with considerable accuracy for several days according to this method.
    By the way it is also important to correct the prediction according to the differences between the real trend and the predicted trend from the symmetry point to now.
    The author applied this method to many points on the Eurasian continent in the period from Jan. to April 1940 and predicted the pressure trend on each of them, and ne could get considerable good results. So this method may be considered as effective for long rang forecasting if there are symmetry points on the perssure curves.
    Fig. 1 An example of symmetry point and symmetry phenomena on the pressure curve in Tokyo.
    Fig. 2 An example of the trend of symmetry index.
    Fig. 3 Comparison between the real and predicted trend of the pressure field.
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  • S. Ogiwara
    1948 Volume 26 Issue 9-12 Pages 232-234
    Published: 1948
    Released: February 05, 2009
    Formerly the author investigated this problem using the Blasius' result on the velocity distribution in the boundary layer. The velocity distribution in the boundary layer has been calculated by Pohlhausen from the momentum equation of boundary layer and in the present paper the same method was applied to the diffusion equation of water vapour to obtain a formula expressing the rate of evaporation of water. The result was given as where M is the rate of evaporation of water from a vessel of which breadth and length are i and L respectively; C0, C∞ concentration of water vapour on the surface of water and outside the boundary layer; h the diffusion codf. of water vapour through the air; U_??_ the velocity of the air; V the kinematic viscosity of the air. Comparing this with the result formerly obtained in which the coef. of evaporation was 0.555 both results may be considered to be fairily in agreement.
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  • H. Arakawa
    1948 Volume 26 Issue 9-12 Pages 234-236
    Published: 1948
    Released: February 05, 2009
    During the recurvature typhoons increase in strength and their progressive movement slackens. After the recurvature they travel to the eastward, and decrease in strength, travelling at a great rate In this stage, the tropical revolving storms become gradually oblong and decre se in strength.
    According to the Norwegian School, the warm-sector cyclones deepen with an unaccelerated celerity as the occlusion process proceeds regularly, and from the time when the cyclone is occluded there is a very slow and gradual change from the deepening to filing. But the final stage of tropical cyclones differs much from that theory. In this stage, corresponding to the cyclolysis-frontogenssis, tropical cyclones deform from symmetric to asymmetric with appreciable filling.
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  • S. Takahashi
    1948 Volume 26 Issue 9-12 Pages 236-242
    Published: 1948
    Released: February 05, 2009
    1) Definition of winter an summer air temperature
    The author calculated the consecutive means of 6 pentads temperature in winter and summer, whose min. and max. are defined as the winter and the summer air temperature.
    2) Conclusions
    There exist some symmetrical variations in the secular variation of the winter and the summer temperature at Miyako, as shown in the attached Table.
    (a) The symmetrical variations occur successively, namely, when one march of symmetrical variation ends, then the next march begin.
    (b) The year of symmetry (point of symmetry) appears alternately in the manner such that, when a year of symmetry exists in the march of winter temperature variation, the next year of symmetry is found in the march of summer temperature variation.
    The above result can be applied to all the years investigated (65 years) at Miyako without exception, and will also be applicable to the other localities in Tohoku District, northern part of Japan Proper.
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  • S. Homma
    1948 Volume 26 Issue 9-12 Pages 243-254
    Published: 1948
    Released: February 05, 2009
    §. 1 Introduction. In the present paper, it is proved that the maximum amplitudes of a dispersive wave, the individual waves of which have maximum and minimum group velocities, are propagated with those group velocities. According to the late Professor K. Sezawa and Dr. K. Kanai(1), the maximum amplitude should always be propagated with the group velocity of the individua_wave of infinite wave length, being inconsistent with our conclusion. It is revealed that the examples treated by them are not suitable to examine the present problem, because such dispersion laws as discussed by them have no maximum or minimum group velocities except those corresponding to infinite wave length.
    §. 2 Fundamental Equations.
    Notations. V: Amplitude, C: Phase velocity, xπ/f: Wave length, t: Time, x: Space coordinate measured in the direction of propagation.
    The solution being responsible for the initial conditions, V=V0(x)and _??_ when t=0
    The relation between c and f is assumen to be given as where U is the group velocity. (Fig. 1). Then (2.4) may be reduced to and V0, V1 and V2 are certain constants.
    From physical point of view, the valucs of V2(±) when t is large will be most interesting; thus we will confine our attention only to the evaluation of V2(±).
    §. 3 Evaluation of V for a moderate valus of t under a Special Assumption of the Initial Conditions. (Omitted)
    §. 4 Evaluation of V for a Large Value of t under General Initial Conditions.
    To evaluate the right side of (2.10) for a large value of t, we must at first consider the integral under the condition _??_ To apply the method of steepest descent, let us suppose that f is, in general, a complex variable and put
    It may be concluded, after some detailed examinations, that the positions of saddle points and the steepest paths in the (X, Y) plane are given as shown in Fig. 5. (In this figure, _??_, _??_ and _??_ indicate the terminal point of integral, the sadde point and triple point _??_espectively. A saddle point coincides with a terminal point at _??_.)
    Fig. 6 shows the relation between P/mg and x.
    The integrals near the terminal points (f=a and _??_) and the saddle points are carried out. Finally, comparing these values of integrals with each other, we may come to the conclusion that the most important terms are the integrals V2(+) älong the paths through the triple points, where P/mg=U1/β-x/βt=±1, and they are given by. where V1=A+(U0-U1)α+β/mcos(_??_) and A is an integral constant.
    The above values are O(g-1/3), Whereas the integrals through the other saddle points or the terminal points are O(g-1/2) or O(g-1) respectively and the largest values of V2(-) obtained are O(g-1/2) Thus, for a large value of t (viz_??_ -g_??_1), the maximum amplitudes in the wave train are found to appear at the points x=(U1±β)t, in which U1+β and U1-β mean the maximum and minimum group velocities respectively.
    §. 5 Some Notes on the Results obtained. (4.19) and (4.20) show that in general cases the amplitude of the wave group when U has its maximum value are greater than that when U has its minimum value. It agrees with the observational fact for Rayleigh waves of higer degrees along a surface of stratified ground as already discussed by Dr. K. Kanai(1) or the present author(2).
    If the extremum value of U corresponds to f=∞, V2(+) will not have such large magnitude of order as (4.19) or (4.20), because in this case _??_(f) and _??_(f) may be small quantities of O(f-1), as will be easily shown by Riemann-Lebesque's Lemma.
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  • K. Sakata
    1948 Volume 26 Issue 9-12 Pages 254-258
    Published: 1948
    Released: February 05, 2009
    There are many methods to gradate a series of irregular values obtained by experiments or observations though most of tem are compound in process, the author's method developed here is very much simpler and more usable.
    Let A_??_(X_??_) be a series of observed values and be expressed as continuous broken lines in a diagram in which the ordinate is A and the abscissa X. Further, let the middle Points of _??_, _??_, _??_, _??_ etc, B_??_, _??_, C_??_ etc, and _??_, _??_ be the coordinates of n, the middle 'point thus obtained then we have
    _??_=1/2n{nC0y0+nC1y1+nC2y2+… +nCryr+…+nCnyn}
    nCr=_??_ r=0.1.2.…n
    _??_ may be considered as a weighted mean, the weights of which are given by the coefficients of binomial theorem.
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