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1.
Numerical study of 1998 late summer flood in East Asia 总被引：1，自引：0，他引：1
Wen-Yih Sun Ki-Hong Min Jiun-Dar Chern 《Asia-Pacific Journal of Atmospheric Sciences》2011,47(2):123-135
The Purdue Regional Model (PRM) is applied to study the evolution of regional climate and weather systems during the heavy precipitation over Korea and China between 30 July and 18 August 1998. The results show that heavy rainfall along the Mei-yu and Changma front was due to the combination of: (1) an anomalous 850 hPa subtropical high, (2) a stronger baroclinicity around 40°N over eastern Asia and a low pressure located to the north of the front, and (3) an excessive evaporation from abnormal wet, warm land. The precipitation ended by 18 August when the subtropical high had retreated and the low pressure in Mongolia moved away from Asia continent. The model reproduced in great detail the observed baroclinic waves to the north, subtropical high and low-level jet to the south, and the front with heavy precipitation extending from southern China, and the Korean peninsula to Japan. High correlations are found for mass, momentum, and moisture fields between model simulation and the European Center for Medium Range Weather Forecast (ECMWF) reanalysis for the 20-day means. 相似文献
2.
Numerical study of upper ocean response to a typhoon moving zonally across the Luzon Strait 总被引：1，自引：0，他引：1
The Luzon Strait (LS) is a wide channel between Taiwan and the Luzon islands. Eastward of the LS, the Kuroshio Current (KC)
flows northward along the eastern coasts of Luzon and Taiwan. A typhoon is a strong and localized low-pressure weather system
that occurs frequently in the vicinity of the Taiwan area. One typical typhoon track, passing through the seas surrounding
Taiwan, is a zonal path across the LS. The satellite measured SST, corresponding to typhoons Pabuk (5 Aug. 2007–12 Aug. 2007)
and Dujuan (29 Aug. 2003–5 Sep. 2003), which both moved along this path, demonstrated that a classic right bias cooling occurs
to the north of the storm track, during the typhoon forced period. However, some cold anomaly water also present toward left
(south) of the storm track east of the LS in the relaxation period. This paper adopted a three-dimensional hydrostatic primitive
equation model to study the possible causes of this southward transport of cold waters. Both model results and the observed
SST anomaly revealed that the strength of the upper ocean cooling depends on whether a resonant regime between the typhoon
winds and the near-inertial currents can be excited. To the east of the LS, the convergence between the warm Kuroshio water
and the cold wakes in the poststorm period will enhance the southward spreading of cold anomaly water. The enhanced vertical
mixing, induced by the southward propagation of nearly inertial waves associated with the cold wakes, can also produce some
cold anomaly to the south of a storm track in the poststorm period. Both mechanisms can contribute to the occurrence of some
cold anomaly water to the south of the storm track east of the KC. To the west of the LS, the convergence between the warm
Kuroshio water and the cold upwelling water from the northern South China Sea can further strengthen the Kuroshio front in
the LS. 相似文献
3.
Transition of Tidal Waves from the East to South China Seas over the Taiwan Strait: Influence of the Abrupt Step in the Topography 总被引：7，自引：0，他引：7
Observations of tidal waves between the East and South China Seas (ECS and SCS) over the Taiwan Strait (TS) suggest that the
diurnal tides simply appear as one southward-propagating wave from the ECS to the SCS through the TS. The semidiurnal tides,
however, behave differently in that they appear as a southward-propagating Kelvin wave in the western TS and a nearly standing
wave in the eastern TS, and then diminish rapidly over the shallow shoal in the southern TS. A smaller-domain model, with
sea-level boundary conditions derived from a larger-domain tidal model, was first used to simulate tides in the TS to an overall
percentage of accuracy of about 90%. Subsequent numerical experiments and theoretical analysis revealed that the southward-propagating
semidiurnal tides to be impeded and then reflected as they arrive at an abrupt, deepened step in the topography of the southern
TS. This reflection enhances the amplitudes of the incident semidiurnal tides and contributes to the formation of a nearly
standing wave in the eastern TS. The southward-propagating diurnal tides in the TS are connected by the diurnal tides in the
northern SCS when the amplitudes of the two tide systems are comparable and their phases nearly equal at the step.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
4.
Upper-layer circulation in the South China Sea has been investigated using a three-dimensional primitive equation eddy-resolving
model. The model domain covers the region from 99° to 122°E and from 3° to 23°N. The model is forced by the monthly averaged
European Centre for Medium-Range Weather Forecasts (ECMWF) model winds and the climatological monthly sea surface temperature
data from National Oceanographic Data Center (NODC). Inflow and outflow through the Taiwan Strait and the Sunda shelf are
prescribed monthly from the Wyrtki estimates. Inflow of the Kuroshio branch current in the Luzon Strait is assumed to have
a constant volume transport of 12 Sv (1 Sv = 106 m3/s), and the outflow from the open boundary to the east of Taiwan is adjusted to ensure the net volume transport through all
open boundaries is zero at any instant. The model reveals that a cyclonic circulation exists all year round in the northern
South China Sea. During the winter time this cyclonic eddy is located off the northwest of Luzon, coinciding with the region
of positive wind stress curl in this season. This cyclonic eddy moves northward in spring due to the weakening of the northeast
winds. The cyclonic circulation becomes weak and stays in the continental slope region in the northern South China Sea in
the summer period. The southwest wind can raise the water level along the west coast of Luzon, but there is no anticyclonic
circulation in the northern South China Sea. After the onset of the northeast monsoon winds in fall, the cyclonic eddy moves
back to the region off the west coast of Luzon. In the southern South China Sea and off the Vietnam coast, the model predicts
a similar flow structure as in the previous related studies.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
5.
The South China Sea,a <Emphasis Type="Italic">cul-de-sac</Emphasis> of North Pacific Intermediate Water 总被引：1，自引：0，他引：1
Yuzhu?YouEmail author Ching-Sheng?Chern Yih?Yang Cho-Teng?Liu Kon-Kee?Liu Su-Cheng?Pai 《Journal of Oceanography》2005,61(3):509-527
This study discusses branching of the Kuroshio Current including North Pacific Intermediate Water (NPIW) into the South China Sea (SCS). The spreading path of the subtropical salinity minimum of NPIW is southwestward pointing to the Luzon Strait between Taiwan and Luzon islands. Using a large collection of updated hydrography, results show that the SCS is a cul-de-sac for the subtropical NPIW because even the NPIW’s upper boundary neutral density surface σ N = 26.5 is completely blocked by the Palawan sill and partly blocked by the southern Mindoro Strait. In autumn, NPIW is driven out of the Luzon Strait by the preceding anticyclonic summer monsoon due to an intraseasonal variation and seasonal phase lag response to the weaker summer monsoon. Stronger inflow under winter monsoon than outflow under summer monsoon results in a net annual transport of NPIW of about 1.1 ± 0.2 Sv (1 Sv = 106 m3s−1) into the SCS. This net transport accounts for the anomaly in NPIW transport across the World Ocean Circulation Experiment section P8 (130° E). An earlier study estimated a large westward NPIW transport of about 3.9 ± 0.2 Sv, resulting in a difference of 1.2 ± 0.2 Sv from the basin-wide mean of 2.7 ± 0.2 Sv. Observations are generally in agreement with numerical results although the intraseasonal signal seems to cause a slight bias and remains to be simulated by future model experiments. 相似文献
6.
Experimental and analytical studies of base isolation by free rolling rods under basement are described in this paper. The tests of the system, a one-storey, 326-kg structure mounted on a set of free rolling rods, is carried out on a 3m × 3m shaking-table. The dynamic behaviour of the isolated structure is studied and used to verify the analytical results. In the isolation system, the coefficient of kinetic rolling friction, measured at different angular velocities, ranges from 0·0007 to 0·0016. The coefficients are reduced by decreasing the angular velocities. Two earthquakes, a short-period and a long-period motion in Taiwan, are utilized as the input signals. The accelerations experienced by the superstructure are decreased by factors of 56 and 60 in comparison with the fixed-base condition for the two input earthquakes. Also, for each test, the peak relative-to-ground displacement of the basement is nearly equal to the peak ground displacement, and the permanent displacement of the basement is present after the end of the earthquake. Finally, tests of the system with a recentring-force device is undertaken, where a soft spring added to the basement reduces efficiently the permanent displacement. Comparisons show a good agreement between experimental and theoretical results. 相似文献
7.
Previous investigations have suggested that wind stress curl, the balance of influx- and outflux-induced upwelling, as well
as a positive vorticity source fed from the left flank of the Kuroshio are all possible mechanisms that contribute to a persistent
cyclonic gyre in the South China Sea (SCS). Studies have also suggested that the loop current that forms from the Kuroshio
intrusion in the Luzon Strait, similar to the Loop Current in the Gulf of Mexico (GOM), has rarely been observed in the northern
SCS. In this research, an idealized numerical model driven by annual mean wind stress was adopted to investigate the relative
importance of dynamic processes that control the mean flow pattern of Kuroshio in the Luzon Strait and regulate circulation
in the SCS. An analysis of results drawn from numerical experiments suggests that the three mechanisms are of approximately
equal importance in the formation of the persistent cyclonic gyre in the northern SCS. Unlike the Gulf Stream which enters
the Gulf of Mexico through the Yucatan Channel, the two topographic ridges that align nearly meridionally in the Luzon Strait
keep the Kuroshio flowing roughly northward without distinct intrusion into the SCS. Unsurprisingly, an anticyclonic loop
current similar to the Gulf Stream pathway in the GOM was barely observed in the northern SCS. 相似文献
8.
The hydrographic surveys in an area immediately northeast of Taiwan showed that the Kuroshio surface water intruded onto the shelf in the spring and there was a thick mixed layer and weak vertical stratification in the Kuroshio at the time. During the summer season, a strong thermocline was developed in the Kuroshio and the flow shifted offshore from Taiwan in front of the continental shelf break of the East China Sea. A numerical model is used to examine the effect of this seasonal thermocline on the flow pattern of the survey area. We find that the surface strength of the disturbance above the Su-Ao ridge is closely related to the occurrence of the on-shelf intrusion of Kuroshio. The presence of a seasonal thermocline in the Kuroshio can greatly diminish this disturbance in the surface level. 相似文献
9.
A one-dimensional land surface model, based on conservations of heat and water substance inside the soil and snow, is presented. To validate the model, a stand-alone experiment is carried out with five years of meteorological and hydrological observations collected from the NOAA-ARS Cooperative Snow Research Project (1966–1974) at the Sleepers River watershed in Danville, Vermont, U.S.A. The numerical results show that the model is capable of reproducing the observed soil temperature at different depths during the winter as well as a rapid increase of soil temperature after snow melts in the spring. The model also simulates the density, temperature, thickness, and equivalent water depth of snow reasonably well. The numerical results are sensitive to the fresh snow density and the soil properties used in the model, which affect the heat exchange between the snowpack and the soil. 相似文献
10.
Typhoons can cause substantial sea surface cooling (typically 2–4 °C), which is usually biased to the right side of the storm track. Under influence of the complex bathymetry of the southern Taiwan Strait (TS), two types of sea surface temperature (SST) response, cooling and warming, each associated with a different type of typhoon track were identified using satellite and mooring observations. When a typhoon moved westward (or northwestward) and passed through the TS (track A), the SST cooling in the TS was biased toward the left of the storm track. Numerical model results indicated that in track A, strong wind stress accelerates the flow east of the Taiwan Banks and drove the bottom flow to uplift due to the topography. Moreover, both wind stress and wind stress curl enhanced the Luzon loop. After the typhoon passed, the mean circulation was modified around strong cooling in the southern TS, causing more South China Sea surface water to be distributed to the Kuroshio region. However, when a typhoon moved westward (or northwestward) and passed south of the TS, SST warming was induced in the southern TS (track B). The model results indicated that when the typhoon passed to the south of the TS, the typhoon-induced horizontal divergent flow travelled to the north, where it encountered the shallower shelf of the TS that was confined to the water, causing warm water transported into this area to accumulate and downwelling to occur. This can be regarded as redistributing the heat content in the shelf area. After the typhoon, the thickened mixed layer resulting from downwelling prevented the formation of near-inertial waves and reduced the vertical mixing. 相似文献