According to ship observation data over the NW Pacific Ocean during 1950 - 1995. taking 5°×5° grid, the characteristics and variation rule of wind, wave and swell are analyzed. This area is typical mons...According to ship observation data over the NW Pacific Ocean during 1950 - 1995. taking 5°×5° grid, the characteristics and variation rule of wind, wave and swell are analyzed. This area is typical monsoon area. In the period of monsoon, the directions of wind, sea wave and swell are roughly consistent. Sea wave of northeasterly is always prevailing in equatorial zone. The monsoon in winter is stronger than in summer, correspondingly, average wave height is higher, and the frequencies of high sea and heavy swell are also bigger. Both of North Indian Ocean and adjacent sea area is also monsoon area, but characteristic is opposite. This paper provides specific data of wind field and wave field and variaton for ship navigation, operation and scientific experiment in the NW Pacific Ocean.展开更多
To improve retrieval accuracy, this paper studies wave effects on retrieved wind field from a scatterometer. First, the advanced scatterometer （ASCAT） data and buoy data of the National Data Buoy Center （NDBC） are...To improve retrieval accuracy, this paper studies wave effects on retrieved wind field from a scatterometer. First, the advanced scatterometer （ASCAT） data and buoy data of the National Data Buoy Center （NDBC） are collocated. Buoy wind speed is converted into neutral wind at 10 m height. Then, ASCAT data are com- pared with the buoy data for the wind speed and direction. Subsequently, the errors between the ASCAT and the buoy wind as a function of each wave parameter are used to analyze the wave effects. Wave param- eters include dominant wave period （dpd）, significant wave height （swh）, average wave period （apd） and the angle between the dominant wave direction （dwd） and the wind direction. Collocated data are divided into sub-datasets according to the different intervals of each wave parameter. A root mean square error （RMSE） for the wind speed and a mean absolute error （MAE） for the wind direction are calculated from the sub-datasets, which are considered as the function of wave parameters. Finally, optimal wave conditions on wind retrieved from the ASCAT are determined based on the error analyses. The results show the ocean wave parameters have correlative relationships with the RMSE of the retrieved wind speed and the MAE of the retrieved wind direction. The optimal wave conditions are presented in terms of dpd, swh, apd and angle.展开更多
On the basis of the wave energy balance equation, the response model of mean directions of locally wind-generated waves in slowly turning wind fields has been derived. The results show that in a homogeneous field, the...On the basis of the wave energy balance equation, the response model of mean directions of locally wind-generated waves in slowly turning wind fields has been derived. The results show that in a homogeneous field, the time scale of the response is not only related to the rate of wave growth, but also to the directional energy distribution and the angle between the wind direction and the mean wave direction. Furthermore, the law of change in the mean wave direction has been derived. The numerical computations show that the response of wave directions to slowly turning wind directions can be treated as the superposition of the responses of wave directions to a series of sudden small-angle changes of wind directions and the turning rate of the mean wave direction depends on the turning rate and the total turning angles of the wind direction. The response of wave directions is in agreement with the response for a sudden change of wind directions if the change in wind directions is very fast. Based on the normalized rates of wave growth under local winds presented by Wen et al. (1989), a quantitative estimate of the time scale of the response shows that the relationships between the dimensionless time scale and both the dimensionless total wave energy and the dimensionless peak frequency agree fairly well with the observations in comparison with other models.展开更多
将Holland风场与ERA5风场相结合,通过引入一个随风速半径变化的权重系数,构建了混合风场,进而利用MIKE21 SW建立了浙江海域台风浪模型。使用Holland风场、ERA5风场、混合风场作为输入风场模拟1918号台风“米娜”期间的风速和有效波高,...将Holland风场与ERA5风场相结合,通过引入一个随风速半径变化的权重系数,构建了混合风场,进而利用MIKE21 SW建立了浙江海域台风浪模型。使用Holland风场、ERA5风场、混合风场作为输入风场模拟1918号台风“米娜”期间的风速和有效波高,验证结果说明Holland风场和ERA5风场均无法准确反映真实风场和有效波高,而本文构建的混合风场弥补了两种风场的不足。为验证混合风场在浙江海域是否具有普适性,选取近5年影响浙江海域最为严重的5个典型台风进行台风浪数值模拟实验,并开展误差统计分析。结果表明:Holland风场在台风中心周围的风速模拟表现较好,最大风速的平均相对误差为8.62%~10.19%,但10 m s以下风速的平均相对误差较大,为29.76%~44.29%;ERA5风场在台风中心周围的风速偏小,最大风速的平均相对误差为17.64%~25.77%,但10 m s以下风速的平均相对误差比Holland风场小,为19.64%~32.00%。对5个台风的模拟中,由Holland风场、ERA5风场和混合风场驱动得到的台风浪有效波高平均相对误差的平均值分别为29.92%、25.62%和22.82%,均方根误差的平均值分别为0.46 m、0.42 m和0.39 m,一致性指数分别为0.94、0.95和0.96。上述结果说明本文构建的混合风场在浙江海域具有普适性,能够提高台风浪的模拟准确度。展开更多
The spectral form of wind waves is investigated based on the ocean wave data observed at three nearshore stations of Taiwan. In this study, the generalized forms of Pierson-Moskowitz spectrum and JONSWAP spectrum are ...The spectral form of wind waves is investigated based on the ocean wave data observed at three nearshore stations of Taiwan. In this study, the generalized forms of Pierson-Moskowitz spectrum and JONSWAP spectrum are used to describe the local wave spectrum by selecting suitable spectral form parameters. It is shown that, at a specific site, the similarity of wave spectral form exists. Thus it is possible to use a representative spectral form for a given nearshore region to describe the wave spectrum at this nearshore. On the other hand, the effects of relative water depth on spectral form are examined. The feasibility of two spectral models in finite water depth is evaluated by using the same field wave data.展开更多
In Earth's high-latitude ionosphere, the poleward motion of east–west elongated auroral arcs has been attributed to standing hydromagnetic waves, especially when the auroral arcs appear quasi-periodically with a ...In Earth's high-latitude ionosphere, the poleward motion of east–west elongated auroral arcs has been attributed to standing hydromagnetic waves, especially when the auroral arcs appear quasi-periodically with a recurrence time of a few minutes. The validation of this scenario requires spacecraft observations of ultra-low-frequency hydromagnetic waves in the magnetosphere and simultaneous observations of poleward-moving auroral arcs near the spacecraft footprints. Here we present the first observational evidence from the multi-spacecraft THEMIS (Time History of Events and Macroscale Interactions during Substorms) mission and the conjugated all-sky imager to support the scenario that standing hydromagnetic waves can generate the quasi-periodic appearance of poleward-moving auroral arcs. In this specific event, the observed waves were toroidal branches of the standing hydromagnetic waves, which were excited by a pulse in the solar wind dynamic pressure. Multi-spacecraft measurements from THEMIS also suggest higher wave frequencies at lower L shells (consistent with the distribution of magnetic field line eigenfrequencies), which indicates that the phase difference across latitudes would increase with time. As time proceeds, the enlarged phase difference corresponds to a lower propagation speed of the auroral arcs, which agrees very well with the ground-based optical data.展开更多
文摘According to ship observation data over the NW Pacific Ocean during 1950 - 1995. taking 5°×5° grid, the characteristics and variation rule of wind, wave and swell are analyzed. This area is typical monsoon area. In the period of monsoon, the directions of wind, sea wave and swell are roughly consistent. Sea wave of northeasterly is always prevailing in equatorial zone. The monsoon in winter is stronger than in summer, correspondingly, average wave height is higher, and the frequencies of high sea and heavy swell are also bigger. Both of North Indian Ocean and adjacent sea area is also monsoon area, but characteristic is opposite. This paper provides specific data of wind field and wave field and variaton for ship navigation, operation and scientific experiment in the NW Pacific Ocean.
基金The National Natural Science Youth Foundation of China under contract Nos 41306191 and 41306192the National High Tech-nology Development Program(863 Program) of China under contract No.2013AA09A505the Scientific Research Fund of the Second Institute of Oceanography,State Oceanic Administration of China under contract No.JG1317
文摘To improve retrieval accuracy, this paper studies wave effects on retrieved wind field from a scatterometer. First, the advanced scatterometer （ASCAT） data and buoy data of the National Data Buoy Center （NDBC） are collocated. Buoy wind speed is converted into neutral wind at 10 m height. Then, ASCAT data are com- pared with the buoy data for the wind speed and direction. Subsequently, the errors between the ASCAT and the buoy wind as a function of each wave parameter are used to analyze the wave effects. Wave param- eters include dominant wave period （dpd）, significant wave height （swh）, average wave period （apd） and the angle between the dominant wave direction （dwd） and the wind direction. Collocated data are divided into sub-datasets according to the different intervals of each wave parameter. A root mean square error （RMSE） for the wind speed and a mean absolute error （MAE） for the wind direction are calculated from the sub-datasets, which are considered as the function of wave parameters. Finally, optimal wave conditions on wind retrieved from the ASCAT are determined based on the error analyses. The results show the ocean wave parameters have correlative relationships with the RMSE of the retrieved wind speed and the MAE of the retrieved wind direction. The optimal wave conditions are presented in terms of dpd, swh, apd and angle.
文摘On the basis of the wave energy balance equation, the response model of mean directions of locally wind-generated waves in slowly turning wind fields has been derived. The results show that in a homogeneous field, the time scale of the response is not only related to the rate of wave growth, but also to the directional energy distribution and the angle between the wind direction and the mean wave direction. Furthermore, the law of change in the mean wave direction has been derived. The numerical computations show that the response of wave directions to slowly turning wind directions can be treated as the superposition of the responses of wave directions to a series of sudden small-angle changes of wind directions and the turning rate of the mean wave direction depends on the turning rate and the total turning angles of the wind direction. The response of wave directions is in agreement with the response for a sudden change of wind directions if the change in wind directions is very fast. Based on the normalized rates of wave growth under local winds presented by Wen et al. (1989), a quantitative estimate of the time scale of the response shows that the relationships between the dimensionless time scale and both the dimensionless total wave energy and the dimensionless peak frequency agree fairly well with the observations in comparison with other models.
文摘将Holland风场与ERA5风场相结合,通过引入一个随风速半径变化的权重系数,构建了混合风场,进而利用MIKE21 SW建立了浙江海域台风浪模型。使用Holland风场、ERA5风场、混合风场作为输入风场模拟1918号台风“米娜”期间的风速和有效波高,验证结果说明Holland风场和ERA5风场均无法准确反映真实风场和有效波高,而本文构建的混合风场弥补了两种风场的不足。为验证混合风场在浙江海域是否具有普适性,选取近5年影响浙江海域最为严重的5个典型台风进行台风浪数值模拟实验,并开展误差统计分析。结果表明:Holland风场在台风中心周围的风速模拟表现较好,最大风速的平均相对误差为8.62%~10.19%,但10 m s以下风速的平均相对误差较大,为29.76%~44.29%;ERA5风场在台风中心周围的风速偏小,最大风速的平均相对误差为17.64%~25.77%,但10 m s以下风速的平均相对误差比Holland风场小,为19.64%~32.00%。对5个台风的模拟中,由Holland风场、ERA5风场和混合风场驱动得到的台风浪有效波高平均相对误差的平均值分别为29.92%、25.62%和22.82%,均方根误差的平均值分别为0.46 m、0.42 m和0.39 m,一致性指数分别为0.94、0.95和0.96。上述结果说明本文构建的混合风场在浙江海域具有普适性,能够提高台风浪的模拟准确度。
文摘The spectral form of wind waves is investigated based on the ocean wave data observed at three nearshore stations of Taiwan. In this study, the generalized forms of Pierson-Moskowitz spectrum and JONSWAP spectrum are used to describe the local wave spectrum by selecting suitable spectral form parameters. It is shown that, at a specific site, the similarity of wave spectral form exists. Thus it is possible to use a representative spectral form for a given nearshore region to describe the wave spectrum at this nearshore. On the other hand, the effects of relative water depth on spectral form are examined. The feasibility of two spectral models in finite water depth is evaluated by using the same field wave data.
基金supported by the National Natural Science Foundation of China (grant numbers 41774168 and 41421003)
文摘In Earth's high-latitude ionosphere, the poleward motion of east–west elongated auroral arcs has been attributed to standing hydromagnetic waves, especially when the auroral arcs appear quasi-periodically with a recurrence time of a few minutes. The validation of this scenario requires spacecraft observations of ultra-low-frequency hydromagnetic waves in the magnetosphere and simultaneous observations of poleward-moving auroral arcs near the spacecraft footprints. Here we present the first observational evidence from the multi-spacecraft THEMIS (Time History of Events and Macroscale Interactions during Substorms) mission and the conjugated all-sky imager to support the scenario that standing hydromagnetic waves can generate the quasi-periodic appearance of poleward-moving auroral arcs. In this specific event, the observed waves were toroidal branches of the standing hydromagnetic waves, which were excited by a pulse in the solar wind dynamic pressure. Multi-spacecraft measurements from THEMIS also suggest higher wave frequencies at lower L shells (consistent with the distribution of magnetic field line eigenfrequencies), which indicates that the phase difference across latitudes would increase with time. As time proceeds, the enlarged phase difference corresponds to a lower propagation speed of the auroral arcs, which agrees very well with the ground-based optical data.
