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Volume 75, Issue 6
Displaying 1-16 of 16 articles from this issue
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George Tai-Jen Chen, Ying-Shao Hsu1997 Volume 75 Issue 6 Pages 1003-1018
Published: December 25, 1997
Released on J-STAGE: September 15, 2009
JOURNAL FREE ACCESSThree cases of southwesterly low-level jet (LLJ) were selected during the 1987 TAMEX field phase (May-June) to reveal the structure and evolution of the LLJ. To suppress minor differences among different cases of LLJs, a composite technique was employed to obtain all the meteorological parameters with respect to the 700hPa jet axis.
Results showed that the LLJ formed and intensified in association with a non-quasigeostrophic trough intensification process. It had a highly supergeostrophic nature. Warm advection prevailed over the jet region and moisture flux convergence occurred over the region downstream from the jet core. The distribution of divergence and vertical velocity was mainly characterized by an antisymmetrical pattern upstream and downstream with upward motion caused by the along-jet ageostrophic wind speed convergence over the exit region. It also showed an antisymmetrical pattern to a lesser degree on both the left and right sides. The characteristics of secondary circulations across the jet axis were quite different from those of the upper-level jet. A thermally indirect circulation across the jet axis was observed in the entrance and the jet core regions and a thermally direct circulation existed over the exit region.View full abstractDownload PDF (3181K) -
Akio Kitoh, Seiji Yukimoto, Akira Noda, Tatsuo Motoi1997 Volume 75 Issue 6 Pages 1019-1031
Published: December 25, 1997
Released on J-STAGE: September 15, 2009
JOURNAL FREE ACCESSPossible changes in the Asian summer monsoon due to increased atmospheric CO2 are investigated by an MRI global coupled atmosphere-ocean general circulation model. The summer (June-August) monsoon rainfall in India increases significantly with global warming. On the other hand, the monsoon wind shear index, defined as the difference between 850hPa and 200hPa zonal winds over the northern Indian Ocean, decreases. At 850hPa, the westerly wind shifts northward and intensifies from the Sahel to northwest of India, but the monsoon westerly over the Arabian Sea weakens. It is found that increased moisture content in the warmer air leads to larger moisture flux convergence, contributing to the increased rainfall. Therefore, the monsoon wind shear index is not a good indicator for identifying any change of monsoon accompanying global warming. In contrast to the increased rainfall in India, change in rainfall is little over China where soil moisture becomes drier at times of increased CO2. It is also noted that the northern Eurasian continent becomes wetter in the increased-CO2 climate.
The magnitude of the interannual variability of the Asian summer monsoon rainfall becomes larger in the CO2 experiment than in the control experiment, particularly in the later stage of the experiment after CO2 doubling. However it should be noted that the interdecadal variation of this interannual variability is also large both in the control and the CO2 experiments.View full abstractDownload PDF (2879K) -
Narihiro Orikasa, Masataka Murakami1997 Volume 75 Issue 6 Pages 1033-1039
Published: December 25, 1997
Released on J-STAGE: September 15, 2009
JOURNAL FREE ACCESSA new version of hydrometeor videosonde (HYVIS) has been developed to measure the vertical distribution of hydrometeors in cirrus clouds with low ice crystal concentrations. This sonde has two small video cameras that take pictures of particles from 7μm to 5mm in size, and transmits particle images by 1.6GHz microwave to a ground station. The original HYVIS did not have enough sampling volume to evaluate the size distribution of hydrometeors in clouds with low number concentrations. To increase sampling volume, a small suction fan was added. From laboratory experiments, we have estimated the variation in sampling volume with changes of ambient air pressure and ascent velocity of the sonde. Theoretical calculation showed that the collection efficiency of the new HYVIS should be unity for all ice crystals larger than 10μm.
Some examples of cirrus cloud observations have demonstrated that the new HYVIS enabled us to determine reliable size distributions of ice crystals larger than 10μm at 250m intervals. The results of the new HYVIS measurements provide us with useful information about mechanisms for the formation and maintenance of cirrus clouds.View full abstractDownload PDF (2346K) -
Fumiaki Fujibe1997 Volume 75 Issue 6 Pages 1041-1051
Published: December 25, 1997
Released on J-STAGE: September 15, 2009
JOURNAL FREE ACCESSLong-term changes of urban temperature was examined by using hourly or four-hourly data at 42 stations in Japan. The magnitude of temperature change (T') was defined by the difference between averages for two periods: one from 1891 to 1928 and the other from 1977 to 1994. At many stations, T' values are larger at nighttime than in the daytime, and are nearly constant between a few hours after sunset and sunrise. Moreover, nighttime T' values are nearly equal to the change of daily minimum temperature (T'min). However, some stations in the northern part of Japan show larger values of T'min than T' at each fixed time, with a difference of 1°C or more at stations in inland of Hokkaido. This indicates a decrease in nocturnal temperature fluctuation, and is likely to be explained by a weakening of the surface inversion due to urban growth.View full abstractDownload PDF (1869K) -
Hiromitsu Kanno1997 Volume 75 Issue 6 Pages 1053-1071
Published: December 25, 1997
Released on J-STAGE: September 15, 2009
JOURNAL FREE ACCESSThe Yamase wind -a cold northeasterly wind which produces cool weather in summer over northeastern Japan- was classified by using upper-air meteorological data. A cluster analysis was performed of the vertical structures of the Yamase air masses, which were divided into seven clusters. The mean features of the Yamase air mass in each cluster are investigated. The surface low temperature area is in proportion to the Yamase air mass height but the air mass height does not always correspond to the height of the easterly wind. In the case of the Yamase air mass and easterly wind being both high (over about 800hPa), the surface easterly wind blows over northeastern Japan and an extremely low temperature area spreads over the Pacific side (Clusters 2 and 6). In the case of the easterly wind being high (over about 800hPa) but the Yamase air mass being low (below about 800hPa), the surface easterly wind blows over northeastern Japan but the surface temperature is not extremely low, and the cold air is effectively blocked by the mountain range (Clusters 3 and 5). In the case of the easterly wind and Yamase air mass heights being both low, the surface easterly wind and low temperature area are restricted to the Pacific side (Clusters 1, 4 and 7). The Yamase wind appearances in each cluster show a seasonal dependence; the Yamase wind included in Clusters 6 and 7 blows only in June, that in Clusters 2 and 4 appears mainly in the Baiu season, in Clusters 1 and 3 it blows from late Baiu to summer, and in Cluster 5 blows in the summer season. Also the surface pressure pattern, front distribution, and the mean 500hPa geopotential height field have the unique characteristics in each cluster. The Yamase-wind appearances in each year indicate that the severe cool summer years (1980, 1988, 1993) are induced by the Yamase winds classified in Clusters 2, 3, and 4; however, the Yamase wind in Cluster 2 having a thick and cold air mass plays an especially important role in causing a cool summer.View full abstractDownload PDF (3037K) -
Melinda S. Peng, Simon W. Chang1997 Volume 75 Issue 6 Pages 1073-1089
Published: December 25, 1997
Released on J-STAGE: September 15, 2009
JOURNAL FREE ACCESSAssimilation of SSM/I-retrieved rainrate has been shown to be beneficial in the numerical prediction of tropical cyclones with a limited-area model (Peng and Chang, 1996). However, due to the near sun-synchronous orbits and the narrow swath, SSM/I coverage of the tropics is not complete. There are many instances that one or more tropical cyclones are not covered by SSM/I swaths; therefore, rainrates cannot be retrieved for assimilation into the prediction models. In this study, the effect of the assimilation of rainrate inferred from cloud top brightness temperature (BT) is assessed. The algorithm inferring rainrates from infrared (IR) cloud top brightness temperature based on concurrent retrieval of the Special Sensor Microwave/Imager (SSM/I) rainfall of Manobianco et al. (1994) was applied in a numerical prediction experiment for Typhoon Flo of 1990. It was found that assimilating IR rainfall rates produced a positive impact on both track and intensity forecasts of Typhoon Flo, qualitatively similar to those in Peng and Chang using the SSM/I-retrieved rainrates. The analytic algorithm relating the IR rainrates to the SSM/I rainrates became less accurate when concurrent IR and SSM/I brightness temperatures were not available. The accuracy of the IR rainrates and improvements in forecast skill both decreased in a sensitivity experiment where IR rainrates were obtained by an obsolete relationship of IR brightness temperature and rainfall rates.View full abstractDownload PDF (2041K) -
an Index for the Asian Monsoon and ENSO SystemTomoaki Ose, Yukuan Song, Akio Kitoh1997 Volume 75 Issue 6 Pages 1091-1107
Published: December 25, 1997
Released on J-STAGE: September 15, 2009
JOURNAL FREE ACCESSInterannual variability of the sea surface temperature anomalies (SSTA) over the South China Sea (SCS) is recognized as an index for the Asian monsoon and ENSO system because of its special geographical location for that system.
The following results are obtained by the statistical analysis of the observational data.
(1) In the northern winter, the SCS SSTA are quite sensitive to the longitudinal shift of global wind anomalies associated with the equatorial Pacific SSTA. This fact is related to that the SCS SSTA and the neighbor SSTA have strong biennial oscillation.
(2) When the global wind anomalies are shifted eastward in the winter (BO-type years), the tropical eastern Pacific SSTA tend to change in the following spring. On the other hand, when those wind anomalies are shifted westward (LF-type years), the eastern Pacific SSTA tend to be maintained through the year. The associated differences between the BO and LF-type years are found in the seasonal change of the low-level tropical wind anomalies from the preceding summer through winter.
(3) The northern summer SCS SSTA seem to be controlled by in-situ low-level wind anomalies. Furthermore, easterly anomalies over South Asia and the tropical western Pacific and westerly anomalies over East Asia are found in the lower atmosphere for the positive SCS SSTA. It is also shown that the summer SCS SSTA have a statistical relationship with the equatorial central Pacific SSTA in the preceding winter. This fact suggests a relationship between the summer Asian monsoon and the winter phase of ENSO.View full abstractDownload PDF (3216K) -
Minoru Tanaka1997 Volume 75 Issue 6 Pages 1109-1123
Published: December 25, 1997
Released on J-STAGE: September 15, 2009
JOURNAL FREE ACCESSInterannual and interdecadal variations of the Western North Pacific Monsoon (WNPM) and the East Asian Baiu rainfall are analyzed using 30-year (1963-1992) daily sea-level pressure, 30-year monthly and daily rainfall data for the East Asia, and 15-year (April 1978-December 1992) 5-day mean 1-degree latitude-longitude gridded GMS high-cloud-amount data. The relationship to the El Niño-La Niña cycles are investigated by using monthly sea surface temperatures (SST) data over a region defined by 4°N-4°S, 150°W-90°W in the equatorial Eastern Pacific (NINO3 SST) for a 30-year period from 1963 to 1992.
An analysis of Interannual variations in intensity of the WNPM in late July shows high negative correlations with the NINO3 SST during a recent 15-year period from 1978 to 1992. In the La Niña (El Niño) years, strong (weak) WNPM are observed. For the Baiu rainfall, high positive correlations with the NINO3 SST are observed in July during this period. In the La Niña (El Niño) years, light (heavy) Baiu rainfall is observed. These correlations are the results of a delay of about 20 days in the onset dates of the WNPM and the peak dates of the Baiu rainfall between the La Niña and El Niño years. In the La Niña years, the early onset of the WNPM and early peak of the Baiu rainfall are observed. In the El Niño years, the late onset of the WNPM and late peak of the Baiu rainfall are observed.
The Baiu rainfall also shows a high positive correlation with the NINO3 SST during the early 15-year period from 1963 to 1977. However, difference in the dates of peak of the Baiu rainfall between the La Niña and El Niño years are smaller.
An analysis of the lag-correlations among the WNPM, the Baiu rainfall and the NINO3 SST shows that the SST leads the WNPM by 1 to 2 months. On the other hand, the Baiu rainfall leads (lags) the SST by 3 (2) months during a recent (early) 15-year period from 1978 to 1992 (1963 to 1977).
An autocorrelation analysis of the NINO3 SST shows that the biennial oscillation mode was pronounced during a 15-year period from 1963 to 1977. In a recent 15-year period, the low-frequency mode was dominant. These changes in the periods of the SST oscillations may be related to the recent increase in the correlations among the NINO3 SST and the WNPM and Baiu rainfall.View full abstractDownload PDF (2149K) -
Y. Hayashi, D. G. Golder, P. W. Jones1997 Volume 75 Issue 6 Pages 1125-1139
Published: December 25, 1997
Released on J-STAGE: September 15, 2009
JOURNAL FREE ACCESSTropical gravity waves and superclusters simulated by 40-level GFDL SKYHI general circulation model experiments with higher horizontal resolutions (0.6° longitude×0.72° latitude) and (1.0°×1.2°) are compared with those simulated by a lower-resolution (3.0°×3.6°) experiment.
Results indicated that simulated precipitational heating appears to excite tropical gravity waves. At higher resolutions, precipitation is more confined in space and time, resulting in a broader wavenumber-frequency spectral distribution. Grid-scale precipitation, which is thought to mimic the precipitation associated with cloud clusters, is organized into larger-scale superclusters. The westward propagation of cloud clusters and eastward propagation of superclusters can be more clearly seen in the high-resolution experiments.
The high-resolution (0.6°×0.72°) model indicates that the lower-stratospheric gravity-wave momentum flux is dominated by high-frequency components having periods shorter than one day. This flux doubles as the resolution is increased from (3.0°×3.6°) to (0.6°×0.72°). It is speculated that a further increase in both the horizontal and vertical resolutions could substantially enhance the gravity-wave momentum flux convergence, thus forcing a stronger quasi-biennial oscillation.View full abstractDownload PDF (2873K) -
Xindong Peng, Kazuhisa Tsuboki1997 Volume 75 Issue 6 Pages 1141-1154
Published: December 25, 1997
Released on J-STAGE: September 15, 2009
JOURNAL FREE ACCESSFour cumulus parameterizations, including the moist connective adjustment (MA), Kuo-Anthes (KA), Kain-Fritsch (KF) and Arakawa-Schubert (AS) schemes, were coupled into the Japan Spectral Model (JSM) and tested in the case of successively developed cloud clusters along the Baiu front during the period from 16 to 17 July 1993 in western Japan. All four experiments with these four parameterizations simulated synoptic features well: locations of lows and the front. The mesoscale precipitation associated with the Baiu front was, in contrast, sensitive to the convective parameterization. Intense precipitation in the Kyushu district was caused by the successive development of cloud clusters. This characteristic feature was simulated by the experiment with the AS scheme. The other three schemes were, however, not so effective in describing the mesoscale precipitation system in the Baiu front. Three sensitivity tests in which the number of types of clouds was reduced to two from six in the AS scheme were also performed to examine the importance of cloud interaction. None of the three simulated the characteristics of the Baiu frontal precipitation. The results suggest that a sophisticated parameterization of convection is necessary to simulate mesoscale precipitation associated with the Baiu front, which is characterized by weakly baroclinic forcing and significant convective instability. An additional experiment for the latent heating in the AS scheme was also performed. The result showed that precipitation in the Baiu frontal zone was greatly affected by the diabatic heating.View full abstractDownload PDF (3406K) -
Kenji Kai, Zhe-Gong Huang, Masataka Shiobara, Zibao Shen, Yasushi Mits ...1997 Volume 75 Issue 6 Pages 1155-1163
Published: December 25, 1997
Released on J-STAGE: September 15, 2009
JOURNAL FREE ACCESSAtmospheric turbidity data from multi-wavelength sunphotometers at both oasis and desert sites in the Hexi Corridor of northwest China, from January 1991 to September 1992, have been analyzed. The aerosol optical thickness revealed a seasonal cycle with a spring maximum due to the frequent occurrence of duststorms in the Gobi Desert and its surrounding areas. The ratio of the aerosol optical thickness at 675nm to that at 500nm suggested a seasonal variation of the aerosol size distribution.
Although the observation sites are located near the Gobi Desert, which is one of the major sources of dust aerosols, the aerosol optical thickness under background conditions was not high. The mean values of aerosol optical thickness at 500nm were 0.254 over the oasis and 0.327 over the desert. The aerosol optical thickness over the desert was 1.28 times larger than that over the oasis.View full abstractDownload PDF (1250K) -
Hirotada Kanehisa1997 Volume 75 Issue 6 Pages 1165-1170
Published: December 25, 1997
Released on J-STAGE: September 15, 2009
JOURNAL FREE ACCESSA steady-flow system on an f-plane whose velocity is uniform in one horizontal direction, say y direction, is considered. The velocity far upstream in the other horizontal direction, say minus x direction, is assumed to be horizontal and dependent only on the vertical coordinate, say z. The potential temperature, Bernoulli function or potential vorticity is not necessarily conserved along the stream lines projected onto the 2-dimensional (z, x) vertical plane, although they are conserved along the true stream lines in the 3-dimensional (z, x, y) space. In this note, a temperature-like quantity Θ, an energy-like quantity B and a vorticity-like quantity Q, which are conserved along the projected stream lines on the (z, x) vertical plane, are constructed. They become functions of the 2-dimensional stream function ψ=ψ(z, x). As in the case of the true Bernoulli function and potential vorticity, Q=Q[ψ] is the derivative of B=B[ψ], i. e., Q[ψ]=dB[ψ]/dψ.
As an application of the conservation laws, a problem of hydrostatic neutral flow with a horizontal rigid lid over a mountain is exactly solved. In particular, both the z and x components of velocity are shown not to be affected by the rotation.View full abstractDownload PDF (761K) -
Kenji Kai, Mayumi Matsuda, Ritsuko Sato1997 Volume 75 Issue 6 Pages 1171-1178
Published: December 25, 1997
Released on J-STAGE: September 15, 2009
JOURNAL FREE ACCESSThe surface energy balance at the Zhangye Oasis during June 1991 was calculated from the fundamental observation period (FOP) data of the Heihe River Basin Field Experiment (HEIFE). Typical phenomena induced by the oasis effect were observed during the afternoons on fair weather days in June. An inversion layer over the oasis developed from the surface to 8m height in the afternoon when the wind speed was strong. The temperature difference between 1-8m heights was about 2°C. The specific humidity exhibited a steep vertical gradient over the oasis. The latent heat flux was the dominant term in the surface energy balance. The sensible heat flux was small and upward during the morning hours, but was directed downward in the afternoon due to large evaporative heat loss.
On the contrary, the sensible heat flux was the dominant term at the desert station. The net radiation in the daytime was small and only 63% of that at the oasis.
A model of the observed oasis effect is proposed in the present note.View full abstractDownload PDF (1625K) -
Tetsu Sakai, Takashi Shibata, Yasunobu Iwasaka1997 Volume 75 Issue 6 Pages 1179-1185
Published: December 25, 1997
Released on J-STAGE: September 15, 2009
JOURNAL FREE ACCESSSimultaneous observation of the vertical profiles of tropospheric water vapor and the density and nonsphericity of aerosol particles was made with a Raman lidar at Nagoya (35°N, 137°E). The data from observations made on April 17, 1994 showed the following features of the water vapor and aerosol particles. Temporal and systematic variations of the parameters were observed at the lower altitude range of 1.0-2.2km, where the mixing ratio of aerosol particles (backscattering ratio) increased and the nonsphericity of the particles (depolarization ratio) decreased with increasing humidity. There was a positive correlation between the vertical profiles of backscattering ratio and the water vapor mixing ratio. The depolarization ratio was positively correlated with the water vapor mixing ratio above 2.2km and negatively correlated below this level. The altitudes where the discontinuities of the water vapor and aerosol parameters were found and that where the correlation between the depolarization ratio and the water vapor mixing ratio changed showed the correspondences with the temperature inversion or wind shears observed at Hamamatsu (35°N, 138°E).View full abstractDownload PDF (973K) -
Hirotada Kanehisa1997 Volume 75 Issue 6 Pages 1187-1192
Published: December 25, 1997
Released on J-STAGE: September 15, 2009
JOURNAL FREE ACCESSThe effect of a diabatic forcing on downslope windstorms is analytically investigated in a 2-dimensional steady hydrostatic system. The environmental flow is assumed to have a uniform horizontal velocity with a constant buoyancy frequency. A diabatic forcing is considered in which the material derivative of potential temperature is proportional to vertical velocity in each region of positive or negative vertical velocity. The proportionality constant for negative vertical velocity is not greater than for positive vertical velocity, and may be zero. The result shows that the downslope wind speed is diminished by the diabatic forcing. The downslope wind speed is smaller than the adiabatic counterpart, and greater than that in the reversible case (i. e., the case of the same proportionality constant for the negative vertical velocity as for the positive vertical velocity).View full abstractDownload PDF (806K) -
1997 Volume 75 Issue 6 Pages 1193
Published: 1997
Released on J-STAGE: September 15, 2009
JOURNAL FREE ACCESSDownload PDF (85K)
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