Journal of the Meteorological Society of Japan. Ser. II
Online ISSN : 2186-9057
Print ISSN : 0026-1165
ISSN-L : 0026-1165
Volume 77 , Issue 2
Showing 1-16 articles out of 16 articles from the selected issue
  • Tetsuya Takemi
    1999 Volume 77 Issue 2 Pages 387-397
    Published: April 25, 1999
    Released: September 15, 2009
    JOURNALS FREE ACCESS
    The evaporation of rain falling through a dry subcloud layer was investigated by using a one-dimensional, time-dependent model only including sedimentation and evaporation. The model assumed a stratiform-type; weak rain under a condition of a dry, deep atmospheric boundary layer typical of the northwest China desert region in summer. Two kinds of experiments were conducted. In the first experiment, the air was assumed to be at rest. With a medium rain intensity (9.5mmh-1) surface rain occurred at about 1h after rain started at the model top, whereas with a light rain intensity (0.97mmh-1) surface rainfall occurred at about 11.5h. The amount of rain depleted by evaporation varied widely according to the fall distance from the top and rain intensity. With a constant amount of total rain provided at the top, the amount of evaporated rain increased with rain intensity. In the second experiment, constant downward vertical velocity was prescribed to examine the effect of subsidence warming on the rain evaporation. Only a descent of a few tens of cms-1 significantly enhanced the rain depletion. Compared with the surface observations in the desert, it was suggested from the model results that evaporation of rain is a dominant cause of the observed changes typical of a desert rain event.
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  • Part I: Chaotic Wandering
    Hisanori Itoh, Masahide Kimoto, Hiromatsu Aoki
    1999 Volume 77 Issue 2 Pages 399-412
    Published: April 25, 1999
    Released: September 15, 2009
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    An alternate variation between single and double jet structures in the Southern Hemisphere (SH) troposphere is investigated observationally and numerically.
    First, data analyses are made for 17 winters from 1979 to 1995 using the NCEP reanalysis dataset. Empirical orthogonal functions (EOFs) of the zonal-mean flow are calculated, and a probability density function (PDF) is constructed by the two leading EOF modes. Maxima of the PDF coincide with the two regimes, i. e., the single and double jet regimes, although the latter has relatively large variations in flow patterns. A statistical test indicates marginal significance for the bimodality. Transitions between the two show no marked periodicity.
    A low-resolution numerical model based on the primitive equation system is constructed, and is found capable of simulating the observed alternation in the single and double jet structures. The dynamical basis of this phenomenon is sought by examining the model's behavior with respect to changes in the magnitude of the horizontal diffusion coefficient. Simulated maxima in PDFs are not so significant for the lower and more realistic values of the diffusion, but become more significant for higher values. Furthermore, it is found that the model has only one attractor corresponding to the single jet regime for sufficiently large diffusivity that makes the system more stable. Near the critical value of the diffusion parameter, the system resides for a very long time in each one of the two flow regimes, and transits irregularly between them. Therefore, it is suggested that the observed variability in the SH jet structure can be understood as chaotic wandering between two distinct flow regimes, whose existence would be clearer if the system were less turbulent.
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  • Shin-Ya Ogino, Manabu D. Yamanaka, Shoichiro Fukao
    1999 Volume 77 Issue 2 Pages 413-429
    Published: April 25, 1999
    Released: September 15, 2009
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    Interannual and day-to-day variations of gravity wave activities in the lower stratosphere were examined using operational rawinsonde data over eastern part of Japan (27°N-45°N, roughly aolng∼140°E) during 1989-95. The gravity-wave activities were quantified by variances of temperature and zonal wind fluctuations with vertical scales of 2-6km.
    Active gravity waves were confirmed to appear around the 20km altitude level over Akita (∼40°N) every winter throughout the seven year period. It was found that the gravity wave activities observed in this region have remarkable interannual and day-to-day variations. The interannual variation of temperature variance at about the 20km level over Akita in winter shows ∼1.5 times increase from 1990/91 to 1994/95 together with the increase in the background zonal wind. On the other hand, a clear relationship was not observed between the temperature variance and the background Väisälä-Brunt number.
    The day-to-day variation of the gravity wave activity in the same region (around the 20km level over Akita in winter) is characterized by intermittent appearance with a periodicity of several days. Cross-correlation analyses between the temperature variance and the background zonal wind velocity at each altitude level, showed clearly that gravity wave activity around the 20km level was intensified when zonal wind near the surface is strong. The similar features were also found at other stations over the northeastern and northern part of Japan. The results suggest that the fluctuations that appear around 20km over northeastern and northern Japan every winter, are due to mountain waves excited by strong zonal wind flowing over north-south running mountain ranges.
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  • Shigeo Yoden, Takashi Yamaga, Steven Pawson, Ulrike Langematz
    1999 Volume 77 Issue 2 Pages 431-445
    Published: April 25, 1999
    Released: September 15, 2009
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    A 7, 200-day dataset from a perpetual January integration of the Berlin Troposphere-Stratosphere-Mesosphere General Circulation Model is analyzed to clarify the basic nature of the dynamical linkage between the stratosphere and the troposphere. Much attention is paid to the stratospheric sudden warming events; sixty-four events are detected in this dataset, with no clear periodicity.
    The 64 sudden warming events are divided into two groups according to the relative strength of planetary waves of zonal wavenumber 1 and 2 in the stratosphere, although each event has its own dynamical characteristics. Composites for each group show some general features of the stratospheric sudden warmings, including the “preconditioned” zonal mean states in the lower stratosphere and the upward propagation of the enhancement of planetary-scale waves from the troposphere to the stratosphere. In the preconditioned states the zonal mean temperature is lower than normal in the polar region, and the zonal mean zonal wind is stronger in the middle and high latitudes.
    Each group shows some different dynamical behavior, not only in the stratosphere but also in the troposphere before, during and after the sudden warming events. In the group in which the wavenumber 1 component dominates, the preconditioned states are more evident and confined to lower altitudes. Such states continue even after sudden warming events near the tropopause. In the other group of wavenumber 2 dominance, signals of sudden warming descend to the upper troposphere after the events.
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  • Yoshinori Yamada, Michel Chong
    1999 Volume 77 Issue 2 Pages 447-457
    Published: April 25, 1999
    Released: September 15, 2009
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    Doppler velocity dealiasing based on the continuity between adjacent gates in the azimuthal and/or radial directions cannot completely remove the ambiguity because the folding character of the initial value used to start the process is not always known. A method to determine the Nyquist interval number (n) that could affect this reference value, and hence the continuity-checked data ensemble, is proposed on the basis of the Velocity Azimuth Display analysis. It is shown that the associated zeroth-order Fourier coefficient (a0) is a measure of an eventual global shift, which can be defined so that (a0+2nVa) fall within [-Va, +Va], Va being the Nyquist velocity of Doppler radar. This is the case for a full 360° distribution of Doppler velocity, but for partial-azimuthal data samplings the Fourier modeling is strongly dependent both on the azimuthal extent of continuity-checked data and on the quality of data. Numerical and experimental data are used to investigate the reliability of the VAD-based determination of Nyquist interval number for various azimuth intervals. It is found that such methods could properly work for sampling intervals higher than 160°, and probably also for reduced intervals (130°) if non-linear wind components are negligible. A great advantage of the present method lies in performance without environmental wind information.
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  • Kazumasa Mori, Syuji Ishigaki, Takao Maehira, Masakatsu Ohya, Hitoshi ...
    1999 Volume 77 Issue 2 Pages 459-482
    Published: April 25, 1999
    Released: September 15, 2009
    JOURNALS FREE ACCESS
    Typhoon Yancy (T9313), which was in the early gradual developing stage and moved westward over the northwestern Pacific near (19N, 129E), was observed by the Japan Meteorological Agency research vessel Keifu Maru, during 30 August to 1 September 1993. During that period, the circulation center of Yancy approached as close as 80km to the north of the Keifu Maru. Convection in the major part of Yancy was analyzed using the radar, maritime weather and upper air observation data obtained on the ship and recently available satellite data. Cell echo tracking winds (CET winds) were estimated and utilized to supplement low level wind data around Yancy.
    During the early developing stage, an in-concentric structure of Yancy in which a cloud system existed in a southwest quadrant of a lower-level cyclonic circulation (LLCC) of 1500km scale was transformed to a concentric one through a formation of a central dense overcast (‘CDO’) in the cloud system. After the establishment of the concentric structure, Yancy began rapid development.
    Various mesoscale (100-500km) precipitation features (MPFs) were organized and evolved successively within Yancy. The configurations of the MPFs were changed as the early developing process progressed through four sub-stages. In the initial sub-stage, a large (400km) echo system (LES) was organized in the southwest quadrant of the LLCC, over which a round cloud system appeared. In the second sub-stage, a long lasting mesoscale intense convective area (MICA) was formed around the northwestern edge of the LES, which was a mesoscale precipitation entity of the ‘CDO’ in the round cloud system. LLCC appeared to be intensified on a 500km scale after the formation of MICA. In the third sub-stage, LES and the cloud system evolved into a comma-shaped spiral band with length over 500km in the intense cyclonic circulation. In the final sub-stage, curvature of the spiral band was increased and an inner near-circular spiral band emerged in the further intensified LLCC. The northern head of the comma-shaped cloud system was encircling the LLCC center. Line systems transversal and longitudinal to lower-level circulation were formed around MICA in the first sub-stage, and in the second sub-stage, respectively.
    LES and MICA constructed a kernel structure of Yancy on the early developing process. The MICA possessed a three dimensionally well organized structure for long lasting intense convection whose echo top attained 16km in height. The MICA and 500km scale LLCC appeared to mutually reinforce each other. Several aspects of the MPFs were summarized, which appear to correspond well to those numerically simulated mesoscale convection within developing tropical cyclone in Yamasaki (1983, 1986).
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  • Hitoshi Mukougawa, Hitoshi Sato
    1999 Volume 77 Issue 2 Pages 483-494
    Published: April 25, 1999
    Released: September 15, 2009
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    Summertime weather regimes are examined over the North Atlantic sector based on a 44-year series of daily 700hPa height anomalies for the period 1951-1994 in order to deepen our understandings of weather regime dynamics in the real atmosphere. Weather regimes are identified by examining the probability density function (PDF) in three-dimensional phase space, which is spanned by the three leading empirical orthogonal functions (EOFs) of the anomaly fields.
    Five weather regimes are obtained. Each weather regime corresponds to a distinct region with statistically significant large PDF values compared with multivariate Gaussianity. These include two extreme phases of the North Atlantic Oscillation (NAO), and flow patterns with intensified jet streams over the North Atlantic.
    The characteristics of weather regimes in summer are described in comparison with those in winter. The similarity in the circulation pattern of weather regimes in both seasons suggests the robustness of summertime weather regimes against the seasonal cycle. We discuss the persistence and transition of summertime weather regimes in connection with the bifurcation property of weather regimes elucidated in simple atmospheric models. The interannual variation of the occurrence frequency of weather regimes is also discussed.
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  • Yasuaki Ohhashi, Koji Yamazaki
    1999 Volume 77 Issue 2 Pages 495-511
    Published: April 25, 1999
    Released: September 15, 2009
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    In this study, recent variability of the Eurasian (EU) pattern during 1978-94 and its association with wave activity flux are investigated. The sign of the wintertime EU index abruptly reversed from positive to negative in winter 1988/89, concurrent with the intensified polar vortex. To investigate the mechanism of the EU pattern in detail, we computed the wave activity flux. When the EU index is positive, the Rossby wave propagation appears from North Europe to East Asia directly. When the EU index is negative the wave activity flux is directed more southeastward to the Middle East.
    An empirical orthogonal function (EOF) analysis is performed for the wave activity flux to clarify the variations of the Rossby wave propagation over Eurasia. Two dominant modes associated with the EU pattern were detected. The first mode is closely linked with the height anomaly over arctic regions and contributes to a shift in the 1988/89 winter atmosphere. The second mode is related to the other principal teleconnection patterns: the North Atlantic Oscillation (NAO), and Pacific/North American (PNA) patterns.
    The appearance of the modes are interpreted in terms of wave forcing to the zonal wind, and the meridional wave propagation of Rossby waves. The Rossby wave with wavenumber three, plays an important role in the zonal wind changes of the first mode. The meridional profile of the zonal wind is consistent with the structure of wave activity flux. The positive feedback between the wave activity and the zonal wind is responsible for the dominance of the first EU mode.
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  • I. Observation System and Results of Frontal Cirrostratus Clouds on June 22 and 30, 1989
    A. Uchiyama, S. Asano, M. Shiobara, M. Fukabori
    1999 Volume 77 Issue 2 Pages 513-532
    Published: April 25, 1999
    Released: September 15, 2009
    JOURNALS FREE ACCESS
    A ground-based observation system of high-level ice clouds has been developed at the Meteorological Research Institute (MRI) of the Japan Meteorological Agency (JMA) for simultaneous measurements of cloud microphysical, and radiative properties. The observation system has been designed by integrating the MRI hydrometeor-video-sondes (HYVIS), a lidar, and various radiometers to obtain simultaneous data both of the cloud microphysical properties and solar and atmospheric radiation measured at the surface. In this paper, the ground-based observation system is described and the cloud physical structures and radiative properties have been analyzed for thick cirrostratus clouds associated with the stationary Bai-u fronts, on June 22 and 30, 1989.
    The size distribution of ice-crystals measured by HYVIS was approximated by a power-law function with an exponent of 3.2 averaged over the entire cloud layers. Evident temperature dependence was not found in the size distribution functions. The broadband solar transmittances derived from the solar irradiance measurements were related to the coincident visible optical thicknesses derived from the sunphotometer measurement, and compared with theoretically simulated transmittances. The comparison revealed that the single scattering asymmetry factor for ice-crystals should be smaller than that of spherical counterparts. The downward effective emissivity was estimated from the 10.5μm radiances measured by the radiation-thermometer. Further, spectral distribution of the downward effective emissivity in the wavenumber region from 800 to 1200cm-1 was also estimated from the spectral zenith radiance measurement by the FTIR radiometer. The observed cirrostratus clouds were optically thick with visible optical thicknesses larger than 1.0, and effective emissivities greater than 0.4.
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  • II. Spectral Properties of Cirrostratus Clouds in the 8-12μm
    A. Uchiyama, M. Fukabori
    1999 Volume 77 Issue 2 Pages 533-552
    Published: April 25, 1999
    Released: September 15, 2009
    JOURNALS FREE ACCESS
    A ground-based observation system has been developed at the Meteorological Research Institute (MRI) for simultaneous measurements of cloud structure and radiative properties of high-level ice clouds. In this observation system, the cloud microphysical quantities and spectral radiances in the region of the 10μm window could be simultaneously observed by a Hydrometeor Video Sonde (HYVIS) and a Fourier Transform Infrared (FTIR) spectro-radiometer. On the basis of the results measured by HYVIS, the size distribution of ice particles was approximated by the power law distribution, and the simulation calculations of observed radiances were made for the some combination of the lower limit of power law distribution (γ1) and the optical thickness at 10.5μm(τ10.5). Using these data, the minimum error point is searched in the error map. By this method, we retrieve optical thickness and particle size information.
    The optically thin, medium and thick cases were analyzed in order to investigate the characteristic of our retrieval method. It is found that the optical thickness determined the magnitude of observed radiance, and size distributions determined the slope of the spectrum in the 860 to 980cm-1 region. The simulated and observed radiances agree within ±2mW/(m2 sr cm-1), except the 9.6μm ozone band and the root mean squares error 1.2mW/(m2 sr cm-1). The error analysis showed that though 5% systematic error is permitted to optical thickness retrieval in some cases, 1% systematic error causes large errors in the size information retrieval, and that a ±500m height error corresponds to 1 to 3% radiance error. Furthermore, the values estimated from the radiance in the region of wavenumber 860 to 980cm-1 were almost the same as those from radiance in the whole region, and the optical thickness may be determined from data in the region 1080 to 1200cm-1 without being affected by the size distribution. We also retrieved τ10.5 and effective radius (γeff) using the log-normal size distribution within the same degree of error as obtained by the power law model.
    Furthermore, we investigated the relationship between the parameters retrieved. The ratio of the visible optical thickness at 0.5μm(τ0.5) to the infrared one at 10.5μm(τ10.5) on June 22 is 0.4 to 1.0, and that on June 30 is 1.0 to 1.8. There is a tendency that the ratio of τ10.5 to τ0.5 becomes large as the effective radius increases. We also investigated the relation between τ10.5 and the effective radius (γeff) of log-normal size distribution. The relation between them changes case by case. There is a negative correlation between them in the case of June 22. In the case of June 30, the effective radius is scattered between 20 and 85μm.
    Concurrent NOAA-11 satellite data over the Tsukuba area were also analyzed. The results show that observation from the satellite is consistent with the ground based observation, and that the large difference of the brightness temperature observed by the different window channels is closely related to the existence of small ice particles of order 10μm.
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  • Song-You Hong, Hann-Ming Henry Juang, Dong-Kyou Lee
    1999 Volume 77 Issue 2 Pages 553-572
    Published: April 25, 1999
    Released: September 15, 2009
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    This study examines the National Centers for Environmental Prediction Regional Spectral Model (NCEP RSM)'s capability as a tool for providing regional climate details over East Asia during the summertime. Toward this end, perfect boundary condition experiments driven by analysis data are performed. The NCEP-National Center for Atmospheric Research (NCAR) re-analysis is used to provide large-scale forcings for the RSM configured with an approximately 25-km grid over East Asia centered on the Korean peninsula. Month-long simulations are conducted for July, which is the major monsoon precipitation period for Korea. The selected years are 1987 and 1988, which correspond to an El Niño and La Niña year, respectively.
    Overall, the model results are satisfactory in terms of the simulated large-scale features for the different years. Deviation of the simulated large-scale features from the analysis generally remains small. Domainaveraged error of the simulated temperature shows a maximum of 0.8K at 300hPa, and relative humidity less than 2% within the entire troposphere. A discernible bias is found in the simulated climate, including a warming in the northern part and a cooling in the southern part of the domain in the lower troposphere. Cooling is dominant in the middle and upper troposphere, with values less than 1K in much of the domain. This deviation commonly appears for both years, indicating that the anomaly forecasts relative to a RSM climatology can alleviate uncertainties related to a RSM systematic error. The monthly accumulated precipitation simulated by the RSM compares well with the observations in terms of anomalous precipitation patterns for the two different summers. Regional features, including a local maximum and minimum, are not reproduced well in the RSM. However, the amount of the domain-averaged precipitation for a month is nearly the same as that recorded by observations. The skill of providing the daily variation of simulated precipitation over Korea is relatively poor. Evolution of the daily precipitation in the simulations generally compares with the observations qualitatively, but the amount and onset of precipitation events are not well reproduced. The two severe weather events causing disastrous rainfall over Korea, a tropical cyclone and a mesoscale convective system, are evaluated in detail.
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  • Shang-Ping Xie, Hideyuki Noguchi, Shinji Matsumura
    1999 Volume 77 Issue 2 Pages 573-582
    Published: April 25, 1999
    Released: September 15, 2009
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    Pronounced quasi-decadal oscillation in surface air temperature over northern Japan is linked to the North Atlantic Oscillation (NAO). A NAO-based regression analysis reveals a hemispheric-scale decadal temperature anomaly pattern that features a seesaw between eastern Canada/Greenland and northern Eurasia at high latitudes, with additional centers of action in the eastern United States and North Africa/Middle East. Advection of climatological mean temperature gradient by anomalous winds seems to be a mechanism for these temperature anomalies. Particularly, positive temperature anomalies over Siberia at NAO's positive phase are associated with anomalous southwesterly winds on the upstream side. The advection by mean westerlies is also important over Eurasia, bringing large decadal variability to northern Japan. This quasi-decadal oscillation can be traced farther eastward to the North Pacific, in the Aleutian low and in sea surface temperature on the subarctic front. A possible inter-oceanic link between the North Atlantic and Pacific is discussed.
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  • Shin Miyazaki, Tetsuzo Yasunari, Tsohiogiin Adyasuren
    1999 Volume 77 Issue 2 Pages 583-593
    Published: April 25, 1999
    Released: September 15, 2009
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    Continuous observations of surface meteorological elements have been carried out since September 30, 1993, to study the roles of land surface processes in seasonal climate variation. The observations were taken by the AANDERA Automatic Weather Station (AWS) at Baruunkharaa (48°55′N, 106°4′E) in northern Mongolia. This location is the center of the source region of the Siberian high, which is a major center of action for the winter climate and atmospheric circulation over the Eurasian Continent.
    Abrupt changes of air temperature and specific humidity were detected during the course of seasonal change from October 1993 to September 1994. The annual cycle was divided into four seasons, based on the timing of these abrupt changes: i. e., winter (mid-November to early March), spring (mid-March to early June), summer (mid-June to later August) and autumn (early September to early November). Over several days in mid-November the air temperature decreased about 20°C, concurrent with an increase in the albedo from 0.5 to 0.9. A coreless winter was characterized by a near constant air temperature of about -15°C or less, along with a high albedo of more than 0.5: i. e., continuous snow cover except for the period from mid-February to early March. Winter ended with a sudden increase of air temperature of about 20°C during several days in mid-March. Spring was characterized by the development of the daytime mixed layer, as suggested from the afternoon decrease of specific humidity. An abrupt increase of specific humidity of about 5gkg-1 -which occurred in mid-June- coincided with the onset of the summer season. During summer, the daytime increase of specific humidity attained its annual maximum, this is likely due to strong evaporation from the surface. In early September, the specific humidity dropped by about 5gkg-1 over a period of several days. The characteristics of the autumn onset were nearly the same as spring, except for the absence of afternoon decrease in specific humidity, which implied that the diurnal growth of the mixed layer was not strong enough to create a strong entrainment.
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  • Teruo Aoki, Tadao Aoki, Masashi Fukabori, Akihiro Uchiyama
    1999 Volume 77 Issue 2 Pages 595-614
    Published: April 25, 1999
    Released: September 15, 2009
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    The atmospheric effects on the spectral and spectrally integrated snow albedos at the snow surface and top of the atmosphere (TOA) are investigated. A multiple scattering radiative transfer model based on the “doubling and adding” method, combined with the Mie theory is applied to estimate the effects of absorption and scattering by atmospheric molecules, absorptive gases, aerosols and clouds.
    It is shown that the spectral surface albedo is reduced by the atmospheric absorptive gases at large solar zenith angles. The solar zenith angle dependence is weakened in the wavelength region shorter than 0.5μm by the Rayleigh scattering, and at almost all wavelengths by the atmospheric aerosols and cloud cover. H2O rich atmosphere decreases the spectral surface albedo at large solar zenith angles in the H2O bands, while the additional reduction of downward solar flux in the near infrared region by H2O absorption causes the spectrally integrated surface albedo to increase by several percent. Aerosols increase the spectrally integrated surface albedo at small solar zenith angles and reduce it at large solar zenith angles, however they reduce the spectrally integrated planetary albedo, except at large solar zenith angles. Optically-thick cloud cover increases both the spectrally integrated surface and planetary albedos at any solar zenith angle.
    In the visible region at small solar zenith angles, the downward solar flux on the snow surface under cloudy sky can exceed that for the clear case, and both further exceed the extraterrestrial solar flux, resulting from the multiple reflection between snow surface and the atmosphere (cloud cover). The global solar radiation on the snow surface under cloudy sky, however, never exceeds that for the clear case and that at TOA.
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  • Yukio Misumi
    1999 Volume 77 Issue 2 Pages 615-635
    Published: April 25, 1999
    Released: September 15, 2009
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    Diurnal variations of precipitation from 1988 to 1993 are investigated using the radar echo composite chart covering the Japanese archipelago and adjacent seas at intervals of one or three hours. We focus on studying expansive areas on land and sea connected by eighteen digitized radars, and determining variations of precipitation due to the following cloud categories based on a horizontal scale and maximum precipitation intensity: large-scale precipitation clouds originating in quasi-horizontal circulation and cumulus-scale precipitation clouds originating in convection.
    The cumulus-scale precipitation cloud, defined as small precipitation clouds with strong intensity, pre-dominates in afternoon peaks over four major islands of Japan excluding some points, the south Korean Peninsula, and Okinawa at about 26N. This is attributed to boundary layer heating by solar radiation during the daytime. Other precipitation clouds mainly composed of the large-scale precipitation cloud exhibit a diurnal cycle peaking in the morning, regardless of land-sea circulation.
    Westerly wind fields over Japan have two effects on diurnal variations. Westerly winds over northeastern Japan maximize the cumulus-scale precipitation cloud over the east; and cause an evening peak over the eastern inshore by driving clouds east. Large-scale precipitation cloud driven by westerly wind often pass through the Nansei Islands from the northwest in the afternoon between May and July, and are responsible for afternoon peak precipitation in these islands.
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  • 1999 Volume 77 Issue 2 Pages 638
    Published: 1999
    Released: September 15, 2009
    JOURNALS FREE ACCESS
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