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Volume 67 (1989)
- Issue 6 Pages 949-
- Issue 5 Pages 691-
- Issue 4 Pages 495-
- Issue 3 Pages 313-
- Issue 2 Pages 177-
- Issue 1 Pages 1-
Volume 67, Issue 6
Displaying 1-11 of 11 articles from this issue
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Yoshihisa Matsuda, Hajime Takayamal1989 Volume 67 Issue 6 Pages 949-966
Published: 1989
Released on J-STAGE: October 19, 2007
JOURNAL FREE ACCESSIn order to examine the applicability of the concept, "geostrophic adjustment" on an _??_-plane to the atmosphere on the sphere, we study systematically the evolution of localized non-geostrophic disturbances in mid- and tropical latitudes. We solve numerically the linearized shallow water equations as an initial value problem for various initial conditions. For this calculation we use eigenfunctions of the shallow water equations on the sphere (Hough functions).
For an initial disturbance given in mid-latitudes, when ε={(rotational velocity of the planet)/(velocity of gravity wave)}2 is large (i.e., the deformation radius is smaller than the spa- tial scale of the disturbance which is comparable with the earth's radius), the inertia-gravity waves emitted from the disturbance in a process of geostrophic adjustment propagate equatorward and dis- perse over the tropical region. When ε is small (i.e., the deformation radius is larger than the spatial scale of the disturbance), the excited gravity waves oscillate between the location of the disturbance and its antipodean point without dispersion.
When an initial disturbance is given in the tropics and ε is large, the evolution of the disturbance can be understood as that of equatorial waves; if the initial disturbance is symmetric about the equator, then the disturbance splits out into Kelvin and Rossby waves. When a is small, the evolution of tropical disturbance is similar to that in mid-latitudes, i.e., a geostrophic adjustment is made in a usual sense.
The evolution of each disturbance after an establishment of the geostrophic relation is also discussed.View full abstractDownload PDF (2978K) -
Classification with the Fuzzy c-means MethodFumiaki Fujibe1989 Volume 67 Issue 6 Pages 967-983
Published: 1989
Released on J-STAGE: October 19, 2007
JOURNAL FREE ACCESSSpatial patterns of short-term precipitation in central Honshu were classified by using the fuzzy c-means method (FCM). This is similar to cluster analysis except that each data element is allocated to all clusters with variable weight. The original algorithm was modified into a form suitable for classifying precipitation patterns and applied to 403 cases selected from data for nine years.
The classification of highest resolution consists of thirteen clusters, while most cases of intense cyclones belong to the six major ones. A composite analysis on synoptic fields reveals that thesesix clusters include three types of pressure patterns. Orographic effects on precipitation are most conspicuous in the cluster which corresponds to the warm sector and cold fronts. In this cluster, a rain shadow exists to the east of the Central Mountain Region under strong southwesterly winds. On the other hand, clusters which correspond to the northern portion of cyclones show only a slight increase in precipitation to the south-southeast of mountain regions.View full abstractDownload PDF (2685K) -
Kazuhisa Tsuboki, Yasushi Fujiyoshi, Gorow Wakahama1989 Volume 67 Issue 6 Pages 985-999
Published: 1989
Released on J-STAGE: October 19, 2007
JOURNAL FREE ACCESSA convergence band cloud moved southwestward through the Ishikari Plain on 20 January, 1986. In this study, we mainly used a single Doppler radar to examine the kinematic and radar echo structures of a convergence band cloud of the cold frontal type. The band cloud, approximately 40km in width, shifted southwestward and accompanied an advancing land-breeze front. The front was geometrically and dynamically similar to that of a gravity current found in laboratory experiments. Kelvin-Helmholtz instability waves with wavelength of 1-2km were observed along the interface of the land breeze and the northwesterly monsoon wind. Two small (-6km) vertical circulations similar to those seen in the warm frontal type were embedded in the mesoscale (-15km) vertical circulation. A low-level convergence and a resultant updraft which were stronger than that of the warm frontal type were located ahead of the front. A distinct subsidence, which is not found in the warm frontal type, followed the front. The updraft caused strong convective echoes ahead of the front, while, owing to the subsidence, the echoes behind the front rapidly weakened. The height of maximum updraft coincided with that of the potential instability layer. The updraft and the potential instability may be respon- sible for the formation of the convergence band cloud. Based on our observations, we constructed a conceptual model of the formation of the convergence band cloud.View full abstractDownload PDF (2992K) -
Akio Kitoh1989 Volume 67 Issue 6 Pages 1001-1013
Published: 1989
Released on J-STAGE: October 19, 2007
JOURNAL FREE ACCESSPersistence of the extratropical planetary-scale circulations is examined by the use of pattern correlations between daily 500mb height anomalies. The dataset consists of the observation for the period from 1980 to 1987 and a 12-year simulation of the Meteorological Research Institute general circulation model (MRI.GCM) with climatological sea surface temperatures. Using 5-day lag correlations, a comparison is made between the Northern and the Southern Hemispheres, between the Pacific and the Atlantic sectors and between the observation and the simulation.
The observed anomalies in the Northern Hemisphere are more persistent than those in the Southern Hemisphere. There is no obvious distinction of the persistence between the Pacific and the Atlantic sectors in the Northern Hemisphere. However the distinction is evident between the two sectors in the Southern Hemisphere; the persistence in the Pacific sector is higher than that in the Atlantic. A contrast between the Northern and the Southern Hemispheres is small in the Pacific sector, while it islarge in the Atlantic. Seasonal variation of the persistence in the Southern Hemisphere is parallel with that in the Northern Hemisphere; both are high in late boreal winter and low in late boreal summer. This parallelism is distinct in the Atlantic sector. Year-to-year variation of the yearly mean 5-day lag correlations shows a tendency that when the Northern Hemisphere persistence is high, the Southern Hemisphere persistence is also high. This relationship is higher in boreal summer.
The simulated persistence is generally smaller and its standard deviation is larger than the observation. Less persistence in the GCM is distinct in the Pacific sector. Model's systematic errors such as stronger westerlies and less variance of height fields should have affected the difference of persistence between the GCM and the observation. However, the effects of the interannual variation of sea surface temperatures in regulating the atmospheric persistence should also be investigated.View full abstractDownload PDF (1992K) -
Akira Watanabe1989 Volume 67 Issue 6 Pages 1015-1021
Published: 1989
Released on J-STAGE: October 19, 2007
JOURNAL FREE ACCESSBased on two case studies, the process of large-scale transport of a polluted air mass northward of Tokyo is described. Comparison of oxidant concentrations with meteorological data reveals that the polluted air mass produced along the coastal area of Tokyo is transported about 200km by a low-level jet whose core is located around the 950mb level. The stable layer formed between the 800mb and 900mb levels also plays an important role in this process.View full abstractDownload PDF (980K) -
Aerosols: II. Estimation of Aerosol Optical PropertiesShoji Asano1989 Volume 67 Issue 6 Pages 1023-1034
Published: 1989
Released on J-STAGE: October 19, 2007
JOURNAL FREE ACCESSThe size distribution and the complex refractive index of tropospheric aerosols have been retrieved from the simultaneous observations of solar radiation and aerosols described in Part I of this study (Asano and Shiobara, 1989). Three sets of observations over the Tsukuba area have been analyzed, for which the aerosol optical thicknesses were available from ground-based spectral attenuation measurements of direct solar radiation.
The bimodal size distribution for tropospheric aerosols was approximated by a composite powerlaw distribution function. The parameters of the distribution function were determined by fitting the function to the columnar size distributions inverted from photometrically measured spectral optical thicknesses. Estimation was made of wavelength-mean effective values of the complex refractive index m*=mr-mii which optimally simulate the observed solar fluxes and heating rates for the total solar spectral region. In the simulated calculations, the observed profiles of aerosols and water vapor were considered. The single scattering properties were computed from Mie theory for the determined size distribution and for a reasonably assumed real part of the index of refraction of mr=1.52. The optimal value of mi=0.03×0.02 was estimated for the imaginary part of the index of refraction of the tropospheric aerosols.View full abstractDownload PDF (1848K) -
Ruby Krishnamurti, T.N. Krishnamurti, H.S. Bedi1989 Volume 67 Issue 6 Pages 1035-1045
Published: 1989
Released on J-STAGE: October 19, 2007
JOURNAL FREE ACCESSLaboratory experiments on Rayleigh-Benard convection with no imposed mean flow have shown that at sufficiently high Rayleigh numbers a mean horizontal flow u(z) is spontaneously generated. This flow is maintained against viscous dissipation by the countergradient momentum transport of the Reynolds stress uw associated with the tilted plumes. The shear of the mean flow ∂u/∂z at mid-depth may be of either sign, depending upon initial conditions. However, for either sign, the tilt of the plumes is always such that horizontal momentum is transported up the mean gradient in the interior. In similar experiments, but with an externally imposed shear flow, it is found that for a sufficiently large shear and sufficiently large Rayleigh number, the tilt of the plumes is determined by the imposed shear. For either sign of shear the plumes tilt in such a way as to transport momentum up the mean gradient. Sufficient data now exists to express the momentum flux as a function of the Rayleigh number and the imposed shear.
In the atmosphere measurements of vertical transport of horizontal momentum, counter to the mean gradient, include those in the sub-cloud layer under fair weather cumulus, and in deep cumulonimbus convection in several squall lines observed during GATE.
Although the parameterization of heat and moisture flux by cumulus convection has been successfully incorporated into numerical weather prediction models, momentum flux has generally not been so included. We attempt to include such a parameterization of the vertical momentum flux by convection, using laboratory measurements as a guide. In this application the conventional Rayleigh number is replaced by an atmospheric parameter which is proportional to the vertical gradient of the equivalent potential temperature. The momentum flux by the convective clouds is then parameterized as a function of the modified Rayleigh and Reynolds numbers.
The results from a control experiment without the inclusion of this parameterization are compared with an experiment where it is included. Of specific interest to the study are the errors in the trade winds of the Atlantic and Pacific Oceans and the low level monsoon circulation over the Indian Ocean. This formulation is shown to reduce the systematic errors of the low level winds over the central Pacific Ocean quite dramatically by over 10 ms-1. However the reduction of errors over tropical land areas, especially around regions of elevation exceeding 500mb, are smaller.View full abstractDownload PDF (2044K) -
Kiyotaka Shibata1989 Volume 67 Issue 6 Pages 1047-1055
Published: 1989
Released on J-STAGE: October 19, 2007
JOURNAL FREE ACCESSA computationally fast scheme has been developed which accurately evaluates the vertical integral of the transmission function for longwave radiative transfer, incorporating with the multi-parameter random model. In this scheme transmittances are calculated only between the half-levels of the vertical coordinate, while the Planck fluxes are evaluated at both the half- and full-levels. The vertical integral in one layer can be represented with two terms; one is for a temperature profile with no inversion and the other for a profile with inversion.
The validity of this scheme has been investigated by calculating temperature profiles in radiative and radiative-convective equilibria. It has been found that this scheme can accurately evaluate the cooling rates at levels with extreme temperatures near the tropopause and stratopause, and that the temperature profiles contain no fluctuation due to two-grid noise.View full abstractDownload PDF (1309K) -
Akira Noda, Tatsushi Tokioka1989 Volume 67 Issue 6 Pages 1057-1069
Published: 1989
Released on J-STAGE: October 19, 2007
JOURNAL FREE ACCESSDownload PDF (1641K) -
Yoshinobu Wakata, Toshio Yamagata1989 Volume 67 Issue 6 Pages 1071-1079
Published: 1989
Released on J-STAGE: October 19, 2007
JOURNAL FREE ACCESSDownload PDF (1392K) -
Hajime Komuro1989 Volume 67 Issue 6 Pages 1081-1082
Published: 1989
Released on J-STAGE: October 19, 2007
JOURNAL FREE ACCESSDownload PDF (305K)
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