Passage Of Typhoon Research Articles

Satellite observation of chlorophyll and nutrients increase induced by Typhoon Megi in the Japan/East Sea

Remotely‐sensed sea surface temperature (SST) and chlorophyll data were used to assess the biological response to the Typhoon Megi in the Japan/East Sea (JES). Mean SST from in situ measurements and satellite data decreased by about 2–4°C in the JES after Typhoon Megi. Mean concentration of MODIS chlorophyll in the post–typhoon period increased by about 70% along the typhoon passage. The cold, nutrient‐rich waters entrained into the surface layer lead to an enhancement of phytoplankton growth. Typhoon‐induced variability of nitrate, phosphate, and silicate at the sea surface of the JES were derived from the MODIS SST using a nutrient‐temperature relationship based on in situ measurements. After the passage of the typhoon, there were increases in NO3, PO4, and SiO2 by about 90%, 40%, and 35%, respectively. The nutrient flux brought into the surface water by the storm‐induced mixing has the potential to support new production.

Fishing perturbations and beached corals in the Cape d’Aguilar Marine Reserve, Hong Kong (2000–2002) and a summary of data obtained from January 1996 to March 2003

Every month for four years (1996–1999) and every three months for three years thereafter (2000–2003) stranded corals were collected from Telecom Bay Beach in the Cape d’Aguilar Marine Reserve, Hong Kong. Over time, the numbers of coral pieces and heads recovered declined progressively. Exceptions to this at first occurred after the passage of tropical depressions and typhoons over Hong Kong when the numbers of coral heads rose sharply. This was particularly obvious from 1996 to 1999. During this period, however, fishing was banned in the marine reserve and in 2000 and 2001 only a few corals were beached despite the passage of a series of typhoons over Hong Kong in both years. It is argued that gill net and purse seine fishermen had stopped snagging their nets on the shallow corals of Telecom Bay and they were thus no longer being dislodged and subsequently deposited on the beach by typhoon surges and waves. In 2002, therefore, few corals were collected. This situation changed in September 2002, however, when Severe Tropical Storm Hagiput deposited numerous large living coral heads on the beach. A seabed inspection showed there to be three active ghost nets in the reserve. Natural perturbations such as, for example, coral bleaching in the El Nino year of 1997–1998 also affected community composition at Cape d’Aguilar through selective, low salinity-induced mortality.

Application of Real-time Monitoring Buoy Systems for Physical and Biogeochemical Parameters in the Coastal Ocean around the Korean Peninsula

We introduce technological achievements while developing real-time ocean monitoring buoy systems in the key coastal regions around the Korean peninsula, and highlight their potential contribution to oceanographic studies in the region. Major achievements are an integration of physical and biogeochemical sensors, real-time and two-way communication, sustainable maintenance with stable power supply and mooring design, and the two-way control of sensor and sampling strategies with high sampling rates (as often as every minute). The time-series data from two buoy systems deployed in the key coastal regions are given as examples to show their potential use in studying oceanographic issues, such as major current variations along the east coast of Korea, wind-driven episodic events including typhoon passages, and frequent changes due to internal wave passages. The real-time and high-frequency monitoring of biogeochemical properties of seawater together with physical parameters could be used for numerous oceanographic studies in the coastal region, i.e., air-sea gas exchange, harmful dinoflagellate bloom, interaction between physical and biogeochemical processes.

High resolution analyses of temporal variations of airborne radionuclides

Temporal variations of 210Pb, 21 2Pb and 7Be were measured at 1–2 h of intervals simultaneously at Tatsunokuchi, Shishiku Highland (640 m above sea level) and Hegura Island located 50 km from Noto Peninsula. It was recognized that variations of these nuclides occured in a short time depending on meteorological circumstances such as the passage of typhoon, snow fall and even in calm conditions.

Typhoons in the Philippine Islands, 1901-1934

A chronology of typhoons and storms in the Western North Pacific is presented, based on the previous work of Miguel Selga, a former director of the Manila Observatory. It includes data about 863 typhoons, storms and depressions over the western Pacific area between 1901 and 1934. The chronology provides information covering a wide area, from Guam to the Gulf of Tonkin and from the equator to Japan. The resulting typhoon series has been included in a database, which is freely accessible, and annual typhoon occurrence and trajectories are also shown. A comparison of the typhoon passage frequency over the Philippine area with a previously available chronology was made to assure the validity of Selga's observations, showing good agreement.

Observed sediment fluxes in the southwesternmost Okinawa Trough enhanced by episodic events: flood runoff from Taiwan rivers and large earthquakes

The sediment fluxes to the southwesternmost Okinawa Trough (SOT) off northeast Taiwan have been measured with four sets of sediment traps. The sediment fluxes observed were much higher than those in many marginal seas and showed great variations in time and space. The fluxes exhibited a drastic seaward decline from northeastern Taiwan to the central trough and an increase with depth. Temporal variability of fluxes was in a wide range from three times to one order of magnitude for certain traps. The observed sediment fluxes had a positive correlation with river runoff from the Lanyang Hsi, a river in northeastern Taiwan. Usually, the highest fluxes could be attributed to episodic events, for example, typhoon passages, which always cause ample rainfall leading to high runoff and sediment discharge, and sediment fluxes that were observed during typhoon passages accounted for more than 50% of the long-term flux. Large earthquakes are suggested to be responsible for some sediment flux anomalies observed on the nearby steep slope because of a good match in time between sediment collection and earthquake occurrence. A conceptual model is proposed to illustrate the sources and transport of the SOT sediment. The study highlights the greater contribution of Taiwan fluvial sediments to the SOT compared to that of the Changjiang, and it provides evidence demonstrating the combined effects of river runoff and large earthquakes on the sediment fluxes observed in such a deep marginal sea.

Interdecadal Changes in Summertime Typhoon Tracks

Abstract The present work examines interdecadal variations of typhoon tracks in the western North Pacific (WNP) during the boreal summer (June–September) for the period 1951–2001. Typhoon tracks are expressed as percentage values of the total number of typhoon passages into a 5° × 5° latitude–longitude grid box with respect to the total number of typhoons formed in the WNP. The analysis period is divided into two interdecadal periods: ID1 (1951–79) and ID2 (1980–2001). From ID1 to ID2, typhoon passage frequency decreased significantly in the East China Sea and Philippine Sea, but increased slightly in the South China Sea. The time series of typhoon passage frequency over the East China Sea and South China Sea further reveal a regime shift in the late 1970s, while those over the Philippine Sea indicate a continuous downward trend of −9% decade−1. The interdecadal changes in typhoon tracks are associated with the westward expansion of the subtropical northwestern Pacific high (SNPH) in the late 1970s. The e...

태풍통과시 동해에서의 해수면 냉각현상

Sea surface cooling (SSC) with the passage of typhoons is examined in the East Sea using the Japan Meteorological Agency buoy data <TEX>$(37^{\circ}45'N,\;134^{\circ}23'E)$</TEX> during 1983-2000 and a three-dimensional primitive equation model (the Princeton Ocean Model). Forty typhoons in this period induced the SST decrease ranging from about <TEX>$-0.5^{\circ}C\;to\;-4.3^{\circ}C.$</TEX> Intense SSC <TEX>$(<-2^{\circ}C)$</TEX> occurs with typhoons that passed mainly through the left-hand side of the buoy station. The model is implemented to examine a physical process of SSC with a typical-track typhoon in the northwestern Pacific <TEX>$(24^{\circ}N\;to\;52^{\circ}N).$</TEX> The model well reproduces prominent features in the observation and addresses how it happens; SSC is induced mainly by momentum mixing effect stirred with the typhoon rather than upwelling.

Horizontal variability of near‐inertial oscillations associated with the passage of a typhoon

Surface currents to the east of Okinawa Island were observed by using HF (high‐frequency) ocean radars in August–September 1995. During that period, a typhoon passed near the observation area, and the horizontal variability of near‐inertial oscillations associated with the typhoon passage was estimated. In addition, the near‐inertial amplitudes and horizontal wave number vectors were estimated. These estimations showed that the near‐inertial amplitude was large in the offshore area and small near the coast. The maximum near‐inertial wavelength was estimated to be in the order of 1000 km, and the near‐inertial wave direction was southward and changed to northwestward on 23 August in 1995. A slab model, incorporating low‐frequency currents, was used to calculate near‐inertial currents. It was found that the amplitude of calculated near‐inertial oscillations was also large in the offshore area. Moreover, the phase‐propagation direction of the near‐inertial waves was southward and changed to northwestward or westward on 22 August. The growth rate obtained from the dispersion relation was large in the offshore area, where the near‐inertial amplitude was large.

태풍에 의해 발생하는 한국근해 해황이상변동

Abnormal oceanic conditions associated with the passage of typhoons are examined using hydrographic and satellite data 1990-2002. During the passage period of typhoons in the Korean waters, an abrupt decrease of sea surface temperature (SST) in range of 5 to <TEX>$8^{\circ}C$</TEX> was observed. The areas of SST decrease were an order of 100-200 km, and the low SST lasted about 15-25 days after passage of typhoon. After passage of typhoon, the water temperatures in the surface mixed layer of 30 m show negative anomalies for quite a long period. In addition, stratification parameters were substantially decreased and chlorophyll a density was rapidly increased.

Field measurements of wind effects on the tallest building in Hong Kong

AbstractCentral Plaza has a height of approximately 374 m and is 78‐storeys tall. It is the tallest structure in Hong Kong and was the highest reinforced‐concrete building in the world when it was built several years ago. This paper describes some results obtained from the full‐scale measurements of wind effects on Central Plaza. The field data such as wind speed, wind direction and acceleration responses have been measured during the close passage of several typhoons in recent years. Detailed analysis of the field data is conducted to investigate wind effects on the tall building. The full‐scale measurements are compared with the wind tunnel results. The amplitude‐dependent characteristics of damping that were obtained by using the random decrement technique are investigated on the basis of the field measurements. Copyright © 2003 John Wiley &amp; Sons, Ltd.

The Processes of SST Cooling by Typhoon Passage and Case Study of Typhoon Rex with a Mixed layer Ocean Model.

The mechanisms by which sea surface temperatures (SSTs) decrease by passage of typhoons under various initial oceanic conditions and the atmospheric boundary conditions were investigated. A stronger wind stress, slower typhoon translation, excessive heat flux from the sea to the atmosphere, a thinner initial mixed layer, and a greater vertical gradient of the sea temperature in the thermocline layer, all have an effect on mixed layer temperature (MLT) cooling. MLT cooling occurs through intermingled processes by enhanced entrainment and upwelling. In contrast, horizontal advection produced by near-inertial oscillation has a slight effect on determining the distributions of MLTs. The depth in the mixed layer near the area along the typhoon track is determined by the magnitudes of the wind stresses and the translation speeds irrespective of the initial thickness of the mixed layer. In addition, under different wind stresses, translation speeds, and vertical profiles of sea temperatures, the MLT cooling is closely related to the ratio of maximum variation of depth by upwelling to the maximum thickness of the mixed layer. The ratio of maximum variation of depth by upwelling to the maximum thickness of the mixed layer under conditions of excessive heat fluxes, is the same as that under conditions of no heat flux. However, MLT cooling under conditions in which the maximum heat flux reaches 800W/m2 is 0.7°C greater than those in no heat flux. In this case, seawater cooling at the transition layer caused by entrainment influences MLT cooling. Numerical simulations were conducted to elucidate the 3°C SST cooling by Typhoon Rex that was observed by R/V Keifu Maru of the Japan Meteorological Agency (JMA). The SST variation obtained by numerical simulation captures the aspects of observational SSTs reported by R/V Keifu Maru, in that the SST rapidly decreases and the maximum SST cooling reaches about 3°C. This rapid SST cooling is mainly caused by the stronger wind stresses and slower translation speeds of Typhoon Rex. The ocean heat contents, based on the model-computed sea temperature, are closely related to the intensities of Typhoon Rex.

A study of the characteristic structures of strong wind

Characteristics of the wind field during a typhoon passage were studied. Both spectral and statistical analyses were carried out. The turbulent fluctuating components of the velocity, as well as that of the temperature, were fitted with two statistical models. Auto- and cross-spectra of the fluctuating components were also calculated. During the passage of the typhoon, the high frequency tails of the spectra for the velocity components were found to have slopes that are flatter than the Kolmogorov −5/3 law prescribes. While the spectra of the temperature fluctuations usually have features that are characteristic for white noise, they become steeper just before the passage of the strongest wind. In general, the Gaussian model can be used to describe the distributions of all the three velocity components, although the Gram–Charlier series expansion would yield better fits.

Sea surface height variations in the Yellow and East China Seas: 1. Linear response to local wind stress

The sea surface height (SSH) variations observed by the TOPEX/POSEIDON satellite in the Yellow and East China Seas are examined over the 3 years from 1993 through 1995 assuming a linear response to wind stress across the region. The transfer function relating wind stress to SSH is modeled by a series of increasingly complex functions that gradually allow wind stress over successively broader regions and time periods to influence the SSH solution at a particular point. The SSH response to instantaneous wind stress at the same point in space implies an Ekman transport, but the response explains only a small fraction of the SSH variability. Relating SSH to wind stress averaged over two subregions and including both instantaneous and 12‐hour lagged wind stress indicates that a significant portion of SSH variability responds to winds that are remote in both space and time. An optimal estimation of the transfer function by minimizing the error variance leads to an extended empirical orthogonal function (EEOF) analysis of the wind stress field. The SSH response to each wind mode is determined. The analysis shows the principle variations in the wind stress to consist of northerly wind bursts during winter, which produce large SSH drops in the Bohai Bay and northern Yellow Sea region. The principal wind mode also is significantly related to variations along the shelf break near the Kuroshio Current. The third and fourth wind stress modes indicate the passage of typhoons.

Statistical Analysis of the Characteristics of Severe Typhoons Hitting the Japanese Main Islands

Abstract Characteristics of 51 severe typhoons hitting the Japanese main islands with central pressure equal to or less than 980 hPa during the period 1955–94 were analyzed by an objective method using hourly station observation during typhoon passages. Position of a typhoon center, central pressure depth Δp, and radius of the maximum wind rm, were obtained at hourly intervals after landfall on the main islands of Japan. The pressure profile of severe typhoons used in this analysis was chosen from formulas presented in previous papers, namely the same as one used by the U.S. Army Corps of Engineers for hurricanes hitting Florida. Coastlines of the main islands were divided into three sections: areas A, B, and C extending from west to east. Statistical analyses of parameters were made for each area. At time of landfall, the maximum value of Δp was 83.2 hPa for area A, 85.2 hPa for area B, and 47.8 hPa for area C. The differences in return period of Δp among areas are considered to be caused by the SST dist...

Seasonal variability of intrusion of the Kuroshio water across the continental shelf northeast of Taiwan

The currents over the East China Sea continental slope northeast of Taiwan were monitored from mid-July to early December, 1992 and again from late March to early August, 1993, covering the two transition periods of monsoon seasons. In 1992, we found massive Kuroshio intrusion (onshore velocity reaching 25 cm/s or more) occurred at mid-October, a lag of one month after the wind pattern changed from southerly to northeasterly. By comparing the surface meteorological with observed cross-slope velocity, we suggest that cooling rather than direct wind forcing, i.e., mid-October cold air outbreaks associated with the Siberia highs moving across the East China Sea, may be the major cause for triggering the observed winter intrusion event. The intrusion continued until the end of the 1992 data in early December and again in late March and early April of 1993 when the data became available. In mid-April, 1993, the intrusion suddenly halted when the lows replaced the highs and the wind reversed with warm air from south. In addition, we found that short-period intrusions appeared in August and early September, 1992 and in late July, 1993. All of these summer intrusions coincide with the occurrence of typhoon passages over or further offshore of the area northeast of Taiwan.

Small-Scale Wind Disturbances Observed by the MU Radar during the Passage of Typhoon Kelly

This paper describes small-scale wind disturbances associated with Typhoon Kelly (October 1987) that were observed by the MU radar, one of the MST (mesosphere, stratosphere, and troposphere) radars, continuously for about 60 hours with fine time and height resolution. First, in order to elucidate the background of small-scale disturbances, synoptic-scale variation in atmospheric stability related to the typhoon structure during the observation is examined. When the typhoon passed near the MU radar site, the structure was no longer axisymmetric. There is deep convection only in the front (north-northeast) side of the typhoon while convection behind it is suppressed by a synoptic-scale cold air mass moving eastward to the west of the typhoon. A drastic change in atmospheric stability over the radar site as indicated by echo power profiles is likely due to the passage of the sharp transition zone of convection. Strong small-scale wind disturbances were observed around the typhoon passage. It is shown that the statistical characteristics are significantly different before (BT) and after (AT) the typhoon passage, especially in frequency spectra of vertical wind fluctuations. The spectra for BT are unique compared with earlier studies of vertical winds observed by VHF radars. Another difference is dominance of a horizontal wind component with a vertical wavelength of about 3 km, which is observed only in AT. Further analyses are made of detailed characteristics and vertical momentum fluxes for dominant disturbances. It is found that some of the disturbances are generated so as to remove the momentum of cyclonic wind rotation of the typhoon. Deep convection, topographic effects in strong winds, and strong vertical shear of horizontal winds around an inversion layer are possible sources of the dominant disturbances. Moreover, two monochromatic disturbances lasting for more than 10 h in the lower stratosphere observed in BT and AT, respectively, are identified as inertio-gravity waves, by obtaining wave parameters consistent with all observed quantities. Both of the inertio-gravity waves propagate energy away from the typhoon.

A Typhoon Observed with the MU Radar

Abstract During the passage of Typhoon 8719 a 60-h continuous observation was made of the troposphere and the lower stratosphere with the MU (middle and upper atmosphere) radar. Height profiles of the wind velocity vector were measured every 2.5 min with a height resolution of 150 m. The typhoon struck Japan's main island on 17 October 1987, and passed within 100 km of the MU radar. A clear turning of the wind velocity associated with the typhoon was observed up to a height of around 18 km, while short-period wind fluctuations showed strong effects associated with the typhoon up to 24 km. Prominent waves with vertical wavelength of 2–4 km and apparent period of ∼10 h were found throughout the observation period. The vertical hodograph analysis revealed that these waves propagate both upward and downward from around the layer of a temperature inversion, suggesting the generation of these waves from that layer.

International Experiments to Study Tropical Cyclones in the Western North Pacific

Four separate (but coincident in time) field experiments to study tropical cyclones in the western North Pacific area will be carried out during August/September 1990 by the United States, the Economic and Social Commission for Asia and the Pacific/World Meteorological Organization (ESCAP/WMO) Typhoon Committee, the USSR, and by Taiwanese scientists. The objective of the U.S. experiment is to improve basic understanding of tropical cyclone motion. The focus of the ESCAP/WMO Typhoon Committee experiment is to improve operational track prediction. A multi-ship and aircraft expedition is planned by the USSR to understand the effects of the ocean inhomogeneities on tropical cyclones, and the response of the ocean to typhoon passage. Researchers in Taiwan will organize special observations of typhoons approaching Taiwan to understand the wind and precipitation distributions. The combined observations from these experiments should result in a comprehensive dataset for the study of western Pacific tropical cyclones.

On the wave dependence of sea-surface wind stress

Analysis is made of wind and wave data, which were obtained during the passage of Typhoon 8013 at an Ocean Data Buoy Station south of Honshu operated by the Japan Meteorological Agency, in order to investigate the wave dependence of sea-surface roughness parameter in the situation where wind waves are dominant with less significant swells. The data fit better the wave-dependent expression of the wind stress,z 0 σ p/u*=γ, than to Charnock's formula,gz 0/u*2=β, wherez 0 is the roughness length,σ p the angular frequency of the spectral peak of wind waves,u* the friction velocity of air,g the acceleration of gravity,γ andβ are non-dimensional constants. The results are very similar to those of our previous study using data from an oil producing platform in the Bass Strait, Australia, although the type of observation system and the synoptic situation of the winds and wind waves were totally different.