Journal of the Meteorological Society of Japan. Ser. II
Online ISSN : 2186-9057
Print ISSN : 0026-1165
ISSN-L : 0026-1165
Volume 32 , Issue 7-8
Showing 1-7 articles out of 7 articles from the selected issue
  • I. Imai
    1954 Volume 32 Issue 7-8 Pages 183-191
    Published: August 25, 1954
    Released: February 05, 2009
    JOURNALS FREE ACCESS
    Recently, it is frequently observed that the ascensional rate of a balloon for aerological observation gradually diminishes with increasing altitude. However, the cause of this effect is not clear as yet. From data of double theodolite observations made by Dines, Horiguti, Oishi, and Ishimaru, the number of ascents being some 1, 800 in total, the author computed the drag coefficient CD and the corresponding Reynolds' number Re by means of the following equations:
    Here ρ=density of the surrounding air; μ=viscosity of air; α=1-σ/ρ;σ=density of inner gas (hydrogen); υ=ascensional rate; L=free lift; Q=total lift; and g=acceleration of gravity.
    Because the available data of v from the referred materials were the average values for the layer of 0_??_3km altogether, the values of ρ and μ for the height of 1.5km were employed in this computation. The results are plotted in Fig. 1, in which CD gradually decreases with increasing Re, and no indication of steep change in CD can be seen for Reynolds' numbers up to 6×105. The obtained drag curve seems to join rather smoothly with that by Bacon and Reid (1922), who made experiments dropping various spheres from an airplane.
    When a balloon ascends, the Reynolds' number decreases with increasing altitude, so the drag coefficient increases. Whether the ascensional rate increases or decreases with height depends on the relation between CD and Re. Differentiating (1) and (2), and replacing μ∝T5/6, we obtain: where g/R=autoconvection gradient, and γ=-dT/dh.
    If we put n=dlnCD/dlnRe, and eliminate Re and CD in (3) and (4), we have:
    This means that the rate of increase of v with height is determined by the slope of CD curve on double log-paper, n, and the temperature lapse rate γ. The loci of 1/v dv/dh in % per km as a function of n and γ are shown in Fig. 2, where T=300°K is assumed. The area surrounded by hatched border indicates the region of decreasing ascensional rate. It is shown by this figure that in usual conditions the decrease of ascensional rate is rather small. Observed large values of decrease appear to be due to other causes, say, the effect of radiation on balloons, the excess pressure in balloons, the vertical currents in the atmosphere, etc.
    It is also shown theoretically, that the steep part of CD curve where n<-2 can not be realized in free ascension or fall of a sphere, because any point on such a part of CD curve is unstable, when the resistance of the sphere should be kept constant.
    Download PDF (491K)
  • Ichiro Imai
    1954 Volume 32 Issue 7-8 Pages 192-214
    Published: August 25, 1954
    Released: February 05, 2009
    JOURNALS FREE ACCESS
    Observations of precipitation elements were made with actual-size photography and microphotography during two winter seasons at Wajima, situated on the northern coast of the Noto peninsula which juts out into the Japan Sea, and the relation to the meteorological conditions was studied. Obtained results may be summarized as follows:
    (1) The typical precipitation under winter monsoon conditions at Wajima is of the showery type of short duration. Continuous precipitation with nearly uniform intensity occurs only when a depression approaches or a local discontinuity exists in the vicinity.
    (2) At the beginning of a showery precipitation, a fall of temperature, _??_ rise of barometer, gusts, and a cyclonic shift of wind direction are observed usually, in like manner as in an air mass thunderstorm. A shower cloud may be regarded as a small scale thundercloud.
    (3) The showery precipitation by winter monsoon is nothing else than an instability shower, which is characteristic of cold air that travels over a warm sea surface. The occurrence of showers is found to be the more frequent, the lower the temperature at 700 mb level (Fig. 14).
    (4) At the beginning of a shower, large grains of graupel fall first usually, which last some 5 to 10 minutes but gradually decrease their sizes, and are f_??_ally replaced by large snowflakes. The total duration of a shower amounts generally from 20 to 30 minutes. In some cases, only graupel falls from beginning to end; in other cases, thickly rimed. crystals fall at the beginning which are gradually replaced by bare crystals. Frequently somewhat smaller graupel pellets or snowflakes precede the larger ones.
    (5) Most crystals which fall in a shower are of the stellar or the spatial-dendritic: form. These crystals are considered to be fallen after sufficient growth in relatively short time because of their large growth rate.
    (6) Soft hail is nothing but soft rime which is formed in the free atmosphere. Its external form may be classified into 4 types: conical, hexagonal, granular, and rime-like Each of these 4 types may, however, approach to conical (or truncated-conical) form after sufficient development, so the cone-type may be the fundamental form of soft hail. The crystalline appendages, frequently observed at the top of a cone or on the upper surface of a truncated cone, are inferred to be formed while falling through water-saturated atmosphere. The density of soft hail is found to be about 0.40, nearly agreeing with that of soft rime already known to be 0.20_??_0.60.
    (7) Small hail is precipitation corresponding to hard rime. Its external form is conical, similar to soft hail, but the internal structure is hard and semi-transparent. It falls usually intermingled with rain accompanying the passage of a strong cold front with vigorous convective activity. Such small hail as is defined in most textbooks never fell under winter monsoon conditions at Wajima.
    (8) For a few examples of continuous snowfall, the correspondence between crystal forms and the upper air conditions was investigated.
    (9) A rise of temperature is frequently observed at the cold-front passage in the nighttime. This is considered to be caused by the destruction of a ground inversion layer (masked front of H. v. Ficker). The same cause may account for the temperature rise occurring with showery precipitation in night.
    In order to confirm the above conclusions, it is desirable to make further observations concerning the horizontal distribution of monsoon showers and its variation with time, with radar or a dense surface network, and to make more detailed observations relating to their precipitation elements.
    Download PDF (4409K)
  • K. Mohri
    1954 Volume 32 Issue 7-8 Pages 215-224
    Published: August 25, 1954
    Released: February 05, 2009
    JOURNALS FREE ACCESS
    First, main characteristics of mean conditions of the upper troposphere during June 1953 are as follows:
    1) Mean jet of 140°E meridian is situated at 37°N near 12km (50m sec-1). On 12km level chart the mean jet passes through the northern part of Korean Strait and 37°N 140°E.
    2) Along 140°E meridian, just under the mean jet, mean horizontal temperature gradient is relatively strong between 500 mb and 300 mb.
    3) On 500 mb chart, northern part of the mean jet axis (of 12km) is dry (relative humidity 50%) and southern part is wet (60_??_70%).
    Second, main characteristics of the meridional cross sections through Japan during 6_??_7 June, 1953 are as follows:
    4) Polar front (Baiu-front) is rather shallow over Honshu and increases its inclinatiom over Hokkaido. Polar-front jet is situated at 45°N near 250 mb.
    5) Subtropical jet is situated at 40°N near 150_??_200 mb. Under this jet there exists a frontal zone between temperate air and tropical air. This frontal zone might be called as a subtropical front.
    6) Distinct polar-front tropopause (in Palmén's sense) is observed associated with the polar-front jet and the subtropical jet.
    7) Tropical cyclone Judy (5302) has its maximum wind speed at 450 mb level, at 12 Japanese Standard Time, 7 June.
    Download PDF (604K)
  • R. Otsuka, K. Shimada
    1954 Volume 32 Issue 7-8 Pages 225-239
    Published: August 25, 1954
    Released: February 05, 2009
    JOURNALS FREE ACCESS
    Weather situations in low latitudes of the northwestern Pacific at the beginning of March 1954, when an H-bomb experiment was performed at Bikini, are analyzed. Some of the results are as follows:
    (1) Broadscale pattern in pressure field shows an unstable condition in the vicinity of Bikini.
    (2) Streamline patterns at lower, middle and upper levels in the troposphere are different, and the maximum of wind speed exists near the level of the tropopause.
    (3) Rather strong easterlies have prevailed in the stratosphere throughout this period.
    (4) There are divergence and convergence areas to the west of Eniwetok and to the south of Kwajelein respectively.
    (5) The upper currents over Bikini are as follows: 0-2km 3-17km >18km easterlies westerlies easterlies
    (6) Height of the tropopause in low latitudes during this period is about 16km, with the maximum at about 12-13°N.
    (7) Time-cross sections of upper currents for some station show that easterlies are prevailing in the lower layer below 3km, westerlies are prevailing in the layer between 3km and the height of tropopause, and easterlies are prevailing again in the higher level above 21km. The maximum wind speed in the higher easterlies is 65 mph which is observed at the level of 25km over Guam.
    The maximum in the westerlies is 115 mph which is observed at the level of 14km over Wake.
    Download PDF (739K)
  • H. Arakawa
    1954 Volume 32 Issue 7-8 Pages 240-242
    Published: August 25, 1954
    Released: February 05, 2009
    JOURNALS FREE ACCESS
    Download PDF (255K)
  • [in Japanese], [in Japanese]
    1954 Volume 32 Issue 7-8 Pages 242-248
    Published: August 25, 1954
    Released: February 05, 2009
    JOURNALS FREE ACCESS
    Download PDF (4215K)
  • [in Japanese]
    1954 Volume 32 Issue 7-8 Pages 248-249
    Published: August 25, 1954
    Released: February 05, 2009
    JOURNALS FREE ACCESS
    Download PDF (79K)
feedback
Top