2022 Vol. 44, No. 3
Display Method:
2022, 44(3): 1-14.
doi: 10.12284/hyxb2022023
Abstract:
Eddies in the Southern Ocean play a critical role in transporting material and heat across fronts. Scotia Sea is located downstream of the Drake Passage and is an important economic fishery area, hence study on the distribution and role of eddies in this region is of urgent importance. Based on satellite remote sensing data from 2005 to 2019, the characteristics of eddies are statistically calculated, including radius, propagation distance, and lifespan. Their spatial distribution, cross-front movement, and movement characteristics are also analyzed. Meanwhile, the internal hydrographic characteristics of eddies are analyzed based on profile data. Results show that about 92% of eddies have a lifespan shorter than 30 d, with an average radius between 10 km and 30 km. The generating location of eddies are mainly near Polar Front (PF), Southern ACC Front (SACCF), and Sub-antarctic Front (SAF), corresponding to the bottom depth ranging 3 000 m to 5 000 m. Large values of eddy kinetic energy (EKE) concentrate between PF and SAF due to the obstruction of the submarine ridges, and EKE reaches a significant positive anomaly after 2016. The number of equator-ward eddies is dominant in the eddies across PF and SACCF, with most being cyclonic eddies. Anticyclonic eddies are dominant in poleward eddies. The internal hydrographic structures of eddies show that temperature and salinity are relatively low in the subsurface layer of the cold eddies, consistent with the characteristics of water masses at high latitudes. While they are relatively high in the subsurface layer of the warm eddies. It suggests that cold eddies may carry water from high latitudes to low latitudes and warm eddies may carry seawater from low latitudes to high latitudes. This study provides a basis for further understanding of the characteristics of eddies in the Scotia Sea and their effects on the distribution of biological populations and material and energy transport.
Eddies in the Southern Ocean play a critical role in transporting material and heat across fronts. Scotia Sea is located downstream of the Drake Passage and is an important economic fishery area, hence study on the distribution and role of eddies in this region is of urgent importance. Based on satellite remote sensing data from 2005 to 2019, the characteristics of eddies are statistically calculated, including radius, propagation distance, and lifespan. Their spatial distribution, cross-front movement, and movement characteristics are also analyzed. Meanwhile, the internal hydrographic characteristics of eddies are analyzed based on profile data. Results show that about 92% of eddies have a lifespan shorter than 30 d, with an average radius between 10 km and 30 km. The generating location of eddies are mainly near Polar Front (PF), Southern ACC Front (SACCF), and Sub-antarctic Front (SAF), corresponding to the bottom depth ranging 3 000 m to 5 000 m. Large values of eddy kinetic energy (EKE) concentrate between PF and SAF due to the obstruction of the submarine ridges, and EKE reaches a significant positive anomaly after 2016. The number of equator-ward eddies is dominant in the eddies across PF and SACCF, with most being cyclonic eddies. Anticyclonic eddies are dominant in poleward eddies. The internal hydrographic structures of eddies show that temperature and salinity are relatively low in the subsurface layer of the cold eddies, consistent with the characteristics of water masses at high latitudes. While they are relatively high in the subsurface layer of the warm eddies. It suggests that cold eddies may carry water from high latitudes to low latitudes and warm eddies may carry seawater from low latitudes to high latitudes. This study provides a basis for further understanding of the characteristics of eddies in the Scotia Sea and their effects on the distribution of biological populations and material and energy transport.
2022, 44(3): 15-24.
doi: 10.12284/hyxb2022013
Abstract:
In this paper, using the equatorial beta-plane approximation of the linear barotropic perturbation equations and introducing the reduced gravitational acceleration, we obtain the analytical solutions of anomalous equatorial ocean stationary wave and give the calculation results of the solutions. Then we compare the results with the modes of complex EOF analysis about abnormal circulation of the real tropical Pacific Ocean and Indian Ocean. The main conclusions are: in the first mode of anomalous equatorial ocean stationary wave, the current disturbance throughout the whole ocean is the half wave, which appears as the consistent zonal flow. The maximum disturbance appears at the middle of the tropical ocean and decays rapidly from equator to north and south, which is restricted in about 2 degree range on both sides of the equator. In the second mode, the current disturbance throughout the whole ocean is the full wave and has the opposite flow direction at east and west of the ocean. The degree of the attenuation of the current disturbance from equator to north and south is as that of the first mode. Anomalous equatorial ocean stationary wave meets the boundary conditions of the east and west coast directing along the longitude. The coefficient is inversely proportional to the square root of the product of the reduced gravity acceleration and the upper water standard depth, which determines the decay rate of anomalous equatorial ocean stationary wave on both sides of the equator. If the square root values take the same, the decay rates are the same. The oscillation frequency of anomalous stationary wave is proportional to the modal number and the square root values, which is inversely proportional to the width of tropical ocean. The modal number is lower and the width is larger, the frequency is lower and the corresponding oscillation period is longer; the first mode of the oscillation period is the longest. Taking every parameters as the typical values and the modal number as one, then taking the width of the equatorial Pacific Ocean and Indian Ocean respectively, the calculation results show that the spatial distribution and interannual variability of the first mode are the same as the corresponding mode of the real abnormal circulation obtaining from the complex EOF analysis; this means that the nature of the first mode above is the anomalous equatorial ocean stationary wave and the anomalous stationary wave is one of the generating mechanism of ENSO and IOD.
In this paper, using the equatorial beta-plane approximation of the linear barotropic perturbation equations and introducing the reduced gravitational acceleration, we obtain the analytical solutions of anomalous equatorial ocean stationary wave and give the calculation results of the solutions. Then we compare the results with the modes of complex EOF analysis about abnormal circulation of the real tropical Pacific Ocean and Indian Ocean. The main conclusions are: in the first mode of anomalous equatorial ocean stationary wave, the current disturbance throughout the whole ocean is the half wave, which appears as the consistent zonal flow. The maximum disturbance appears at the middle of the tropical ocean and decays rapidly from equator to north and south, which is restricted in about 2 degree range on both sides of the equator. In the second mode, the current disturbance throughout the whole ocean is the full wave and has the opposite flow direction at east and west of the ocean. The degree of the attenuation of the current disturbance from equator to north and south is as that of the first mode. Anomalous equatorial ocean stationary wave meets the boundary conditions of the east and west coast directing along the longitude. The coefficient is inversely proportional to the square root of the product of the reduced gravity acceleration and the upper water standard depth, which determines the decay rate of anomalous equatorial ocean stationary wave on both sides of the equator. If the square root values take the same, the decay rates are the same. The oscillation frequency of anomalous stationary wave is proportional to the modal number and the square root values, which is inversely proportional to the width of tropical ocean. The modal number is lower and the width is larger, the frequency is lower and the corresponding oscillation period is longer; the first mode of the oscillation period is the longest. Taking every parameters as the typical values and the modal number as one, then taking the width of the equatorial Pacific Ocean and Indian Ocean respectively, the calculation results show that the spatial distribution and interannual variability of the first mode are the same as the corresponding mode of the real abnormal circulation obtaining from the complex EOF analysis; this means that the nature of the first mode above is the anomalous equatorial ocean stationary wave and the anomalous stationary wave is one of the generating mechanism of ENSO and IOD.
2022, 44(3): 25-39.
doi: 10.12284/hyxb2022027
Abstract:
Three monthly altimeter datasets of the Arctic Ocean are compared in this paper. The datasets provided by the Centre for Polar Observation and Modelling (CPOM) and Technical University of Denmark (DTU) are found to be consistent with each other and due to their high spapce coverage, are more suitable for the study of the sea level variation in the Arctic Ocean, the former is better in terms of spatial resolution, smoothness, and consistency with the tide gauge observation. Based on the data of both altimeter and tide gauge, the temporal and spatial characteristics of sea level in the Arctic Ocean are analyzed and the results show that the climatological sea level in the Arctic Ocean is represented by the striking contrast between the high values in the Canadian Basin and low values in the Eurasian basin. The variation of sea level in the Arctic Ocean is dominated by the seasonal variability and low-frequency variability associated with the Arctic Oscillation, large amplitudes of both the seasonal and inter-annual sea level variability are found in the Canadian Basin, and large seasonal variability occurs along the coast of Russia. During the period 2003−2014, the mean sea level of the Arctic Ocean is rising with the largest rising rate is found in the Canadian Basin, while the sea level in the Russian coastal area is declining slightly. It is also found that large uncertainty exists in the altimetry products of the Canadian Basin and the coast of Russia, as the difference both between altimetry products and between altimeter and tide gauge data cannot be ignored, data in these areas should be used with caution.
Three monthly altimeter datasets of the Arctic Ocean are compared in this paper. The datasets provided by the Centre for Polar Observation and Modelling (CPOM) and Technical University of Denmark (DTU) are found to be consistent with each other and due to their high spapce coverage, are more suitable for the study of the sea level variation in the Arctic Ocean, the former is better in terms of spatial resolution, smoothness, and consistency with the tide gauge observation. Based on the data of both altimeter and tide gauge, the temporal and spatial characteristics of sea level in the Arctic Ocean are analyzed and the results show that the climatological sea level in the Arctic Ocean is represented by the striking contrast between the high values in the Canadian Basin and low values in the Eurasian basin. The variation of sea level in the Arctic Ocean is dominated by the seasonal variability and low-frequency variability associated with the Arctic Oscillation, large amplitudes of both the seasonal and inter-annual sea level variability are found in the Canadian Basin, and large seasonal variability occurs along the coast of Russia. During the period 2003−2014, the mean sea level of the Arctic Ocean is rising with the largest rising rate is found in the Canadian Basin, while the sea level in the Russian coastal area is declining slightly. It is also found that large uncertainty exists in the altimetry products of the Canadian Basin and the coast of Russia, as the difference both between altimetry products and between altimeter and tide gauge data cannot be ignored, data in these areas should be used with caution.
2022, 44(3): 40-52.
doi: 10.12284/hyxb2022087
Abstract:
Based on the Typhoon Hato in 2017, the Himawari-8 AHI infrared radiance data are assimilated under the clear-sky condition in WRFDA system to investigate its impact on the typhoon forecast. The structure, strength, as well as the track forecasts are also studied for the Typhoon Hato. The results show that the clear-sky assimilation of Himawari-8 infrared radiance data provides obvious increment of cyclonic winds in the typhoon core and an obvious increase of typhoon in background field. Compared with the control experiment without assimilating Himawari-8 AHI infrared radiance data, the experiment that assimilates Himawari-8 AHI data strengthens the wind field of Typhoon Hato, 500 hPa pressure field analysis, and typhoon cyclonic circulation. In addition, the AHI radiance assimilation further improves the forecast of track, minimum sea level pressure, and the maximum wind speed of the Typhoon Hato. The average track error, the precipitation distribution, the root mean square error against the conventional data are also improved.
Based on the Typhoon Hato in 2017, the Himawari-8 AHI infrared radiance data are assimilated under the clear-sky condition in WRFDA system to investigate its impact on the typhoon forecast. The structure, strength, as well as the track forecasts are also studied for the Typhoon Hato. The results show that the clear-sky assimilation of Himawari-8 infrared radiance data provides obvious increment of cyclonic winds in the typhoon core and an obvious increase of typhoon in background field. Compared with the control experiment without assimilating Himawari-8 AHI infrared radiance data, the experiment that assimilates Himawari-8 AHI data strengthens the wind field of Typhoon Hato, 500 hPa pressure field analysis, and typhoon cyclonic circulation. In addition, the AHI radiance assimilation further improves the forecast of track, minimum sea level pressure, and the maximum wind speed of the Typhoon Hato. The average track error, the precipitation distribution, the root mean square error against the conventional data are also improved.
2022, 44(3): 53-60.
doi: 10.12284/hyxb2022017
Abstract:
Based on the data of Philippine shallow strata profile, combined with the sample data and borehole data in this area, this paper has a preliminary understanding of the shallow sediment characteristics of Kyushu-Palau Ridge and the West Philippine Basin and Parisi Vera Basin adjacent to the ridge. There are generally three wave impedance interfaces below the seabed, and the reflection characteristics of the shallow stratum profile are divided into four basic types. The causes of the profile characteristics are preliminarily discussed. It is believed that the sediment supply, tectonic activities, topography and hydrodynamic conditions play an important role in the deep-water sedimentation during the sedimentation process. Besides being influenced by the main control factors, most of them are also superimposed with the transformation effects of various factors in the later period. In this paper, the sedimentary characteristics and controlling factors of shallow strata in Philippine Sea are analyzed, which can provide useful reference for further study of deep shallow sediments in Philippine Sea.
Based on the data of Philippine shallow strata profile, combined with the sample data and borehole data in this area, this paper has a preliminary understanding of the shallow sediment characteristics of Kyushu-Palau Ridge and the West Philippine Basin and Parisi Vera Basin adjacent to the ridge. There are generally three wave impedance interfaces below the seabed, and the reflection characteristics of the shallow stratum profile are divided into four basic types. The causes of the profile characteristics are preliminarily discussed. It is believed that the sediment supply, tectonic activities, topography and hydrodynamic conditions play an important role in the deep-water sedimentation during the sedimentation process. Besides being influenced by the main control factors, most of them are also superimposed with the transformation effects of various factors in the later period. In this paper, the sedimentary characteristics and controlling factors of shallow strata in Philippine Sea are analyzed, which can provide useful reference for further study of deep shallow sediments in Philippine Sea.
2022, 44(3): 61-69.
doi: 10.12284/hyxb2022025
Abstract:
Morphodynamic relationships between fringing reefs and back-reef beach play key roles in understanding the evolution of coral coasts. The fringing reef coasts of Leizhou Peninsula, in Xiluo Port, Xuwen, are taken as the research object in this paper. RTK-GPS and unmanned-surface-vessel are used to measure and analyze the topography of the beach profile and reef as well as the sediment sampling in beach. FUNWAVE-TVD is used to simulate and analyze the hydrodynamic process of short wave and infragravity wave cross the different reef. The results show that the reef topography in the study area has significant effects on the morphology of back-reef beach. Whether the nearshore wave energy dominated by the short wave band or the infragravity band is controlled by the topography. In the narrow reef, there is a predominance of infragravity energy near the back-reef beach. The dominated wave band in the nearshore wave energy is the main factor shape the back-reef beach equilibrium profile. However, the beach equilibrium profile model of coral coast proposed by Muñóz-Pérez did not take this factor into account, it need to further research.
Morphodynamic relationships between fringing reefs and back-reef beach play key roles in understanding the evolution of coral coasts. The fringing reef coasts of Leizhou Peninsula, in Xiluo Port, Xuwen, are taken as the research object in this paper. RTK-GPS and unmanned-surface-vessel are used to measure and analyze the topography of the beach profile and reef as well as the sediment sampling in beach. FUNWAVE-TVD is used to simulate and analyze the hydrodynamic process of short wave and infragravity wave cross the different reef. The results show that the reef topography in the study area has significant effects on the morphology of back-reef beach. Whether the nearshore wave energy dominated by the short wave band or the infragravity band is controlled by the topography. In the narrow reef, there is a predominance of infragravity energy near the back-reef beach. The dominated wave band in the nearshore wave energy is the main factor shape the back-reef beach equilibrium profile. However, the beach equilibrium profile model of coral coast proposed by Muñóz-Pérez did not take this factor into account, it need to further research.
2022, 44(3): 70-80.
doi: 10.12284/hyxb2022009
Abstract:
We presented an optimized and purification procedure as well as an analytical method for Cu and Zn isotopes measurement in marine sediments. We reported Cu and Zn isotope of 5 samples in a sediment cores and 20 surface sediment samples in the northern and southern Okinawa Trough. Anion exchange resin (AG MP-1M) was applied to separate matrix elements of sediment samples from Cu, Fe and Zn using 8.2 mol/L HCl+0.01% HF+0.001% H2O2, 2 mol/L HCl+0.001% H2O2 and 0.5 mol/L HNO3 as eluents. The recoveries of Cu and Zn were both close to 100%. Cu and Zn isotopes were measured on a Nu Plasma multi-collector inductively coupled plasma mass spectrometer (MC-ICP-MS). Instrumental mass bias was corrected using a combination of sample-standard bracketing and internal spiking. The long-term reproducibilities were 0.11‰ (2SD) for Cu isotopes and 0.09‰ (2SD) for Zn isotopes. The δ66Zn of surface sediments varies from 0.07‰ to 0.67‰, with an average of 0.31‰ ± 0.32‰ (2SD); the δ65Cu of surface sediments ranges from −2.26‰ to −0.52‰, with an average of −1.21‰ ± 0.55‰ (2SD). The results show that Cu and Zn isotopes of surface sediments in the Okinawa Trough varies widely, meanwhile, Cu and Zn isotopes in sediment core varies with depth.
We presented an optimized and purification procedure as well as an analytical method for Cu and Zn isotopes measurement in marine sediments. We reported Cu and Zn isotope of 5 samples in a sediment cores and 20 surface sediment samples in the northern and southern Okinawa Trough. Anion exchange resin (AG MP-1M) was applied to separate matrix elements of sediment samples from Cu, Fe and Zn using 8.2 mol/L HCl+0.01% HF+0.001% H2O2, 2 mol/L HCl+0.001% H2O2 and 0.5 mol/L HNO3 as eluents. The recoveries of Cu and Zn were both close to 100%. Cu and Zn isotopes were measured on a Nu Plasma multi-collector inductively coupled plasma mass spectrometer (MC-ICP-MS). Instrumental mass bias was corrected using a combination of sample-standard bracketing and internal spiking. The long-term reproducibilities were 0.11‰ (2SD) for Cu isotopes and 0.09‰ (2SD) for Zn isotopes. The δ66Zn of surface sediments varies from 0.07‰ to 0.67‰, with an average of 0.31‰ ± 0.32‰ (2SD); the δ65Cu of surface sediments ranges from −2.26‰ to −0.52‰, with an average of −1.21‰ ± 0.55‰ (2SD). The results show that Cu and Zn isotopes of surface sediments in the Okinawa Trough varies widely, meanwhile, Cu and Zn isotopes in sediment core varies with depth.
2022, 44(3): 81-97.
doi: 10.12284/hyxb2022015
Abstract:
With the rapid economic development and increasing anthropogenic activities, the groundwater in the coastal area has been excessively exploited. The resulting seawater intrusion has become a widely distributed environmental geological problem. Taken the coastal area of Laizhou Bay as a research area, the dynamics of groundwater level (GWL) and electrical conductivity (EC) were analyzed with the continuous monitoring data. Based on the rainfall, evaporation, tide and agricultural irrigation and drainage electricity consumption that affect the groundwater variation, the hybrid model of wavelet analysis (WA) and NARX neural network was introduced to predict the dynamics of GWL and EC. The root mean square error (RMSE) and goodness of fit (R2) were used to measure the prediction accuracy. The results showed that the annual variation of GWL was characterized by a type of rainfall infiltration-exploitation. A significant correlation at the frequency of 0.5 d was observed between groundwater level and tide, and the influence of tide on EC was weaker than that on GWL. For the dynamics prediction with WA-NARX method, the RMSE was less than 0.03 and R2 was greater than 0.98 in both the training and testing stages. The results indicated the hybrid model had a good performance and could effectively predict the dynamics of GWL and EC. The effects of different influencing factors as model input parameters on the prediction results were further compared. The results showed that rainfall and tide parameters were the main variables affecting the GWL and EC variations in the coastal zone. The pumping information reflected by the evaporation and agricultural drainage and irrigation power consumption also affected the groundwater dynamics. The degree of influence was related to the observation frequency. The research results can provide theoretical and technical support for real-time monitoring, prediction and early warning of seawater intrusion in coastal zone.
With the rapid economic development and increasing anthropogenic activities, the groundwater in the coastal area has been excessively exploited. The resulting seawater intrusion has become a widely distributed environmental geological problem. Taken the coastal area of Laizhou Bay as a research area, the dynamics of groundwater level (GWL) and electrical conductivity (EC) were analyzed with the continuous monitoring data. Based on the rainfall, evaporation, tide and agricultural irrigation and drainage electricity consumption that affect the groundwater variation, the hybrid model of wavelet analysis (WA) and NARX neural network was introduced to predict the dynamics of GWL and EC. The root mean square error (RMSE) and goodness of fit (R2) were used to measure the prediction accuracy. The results showed that the annual variation of GWL was characterized by a type of rainfall infiltration-exploitation. A significant correlation at the frequency of 0.5 d was observed between groundwater level and tide, and the influence of tide on EC was weaker than that on GWL. For the dynamics prediction with WA-NARX method, the RMSE was less than 0.03 and R2 was greater than 0.98 in both the training and testing stages. The results indicated the hybrid model had a good performance and could effectively predict the dynamics of GWL and EC. The effects of different influencing factors as model input parameters on the prediction results were further compared. The results showed that rainfall and tide parameters were the main variables affecting the GWL and EC variations in the coastal zone. The pumping information reflected by the evaporation and agricultural drainage and irrigation power consumption also affected the groundwater dynamics. The degree of influence was related to the observation frequency. The research results can provide theoretical and technical support for real-time monitoring, prediction and early warning of seawater intrusion in coastal zone.
2022, 44(3): 137-146.
doi: 10.12284/hyxb2022001
Abstract:
In recent years, artificial islands have been widely constructed in coastal areas to quickly obtain high-quality land resources. However, the construction of artificial islands may exert substantial effects on the distribution patterns and transport processes of offshore seabed sediments. To understand the changes and transport characteristics of sediments after the construction of artificial islands, this article focuses on the impact of Nanhaimingzhu (NHMZ) artificial island on the properties and distribution of offshore seabed sediments in the Haikou Bay. With surface sediments sampled respectively in the offshore of the Haikou Bay before and after the construction of NHMZ artificial island, the changes in sediment characteristics were analyzed. The impact of NHMZ artificial island on the surface sediments properties and transport trend in the Haikou Bay was discussed with sedimentary dynamic and grain size trends analysis. The results showed that the surface sediment properties changed significantly after the construction of NHMZ artificial island, with the fine-grained sediment composition increased, grain size decreased and the sorting worsen. It was found that the weakening of sedimentary dynamic conditions in the Haikou Bay caused by NHMZ artificial island was an important factor for the changes in seabed surface sediments grain size and the trend of sediment transport.
In recent years, artificial islands have been widely constructed in coastal areas to quickly obtain high-quality land resources. However, the construction of artificial islands may exert substantial effects on the distribution patterns and transport processes of offshore seabed sediments. To understand the changes and transport characteristics of sediments after the construction of artificial islands, this article focuses on the impact of Nanhaimingzhu (NHMZ) artificial island on the properties and distribution of offshore seabed sediments in the Haikou Bay. With surface sediments sampled respectively in the offshore of the Haikou Bay before and after the construction of NHMZ artificial island, the changes in sediment characteristics were analyzed. The impact of NHMZ artificial island on the surface sediments properties and transport trend in the Haikou Bay was discussed with sedimentary dynamic and grain size trends analysis. The results showed that the surface sediment properties changed significantly after the construction of NHMZ artificial island, with the fine-grained sediment composition increased, grain size decreased and the sorting worsen. It was found that the weakening of sedimentary dynamic conditions in the Haikou Bay caused by NHMZ artificial island was an important factor for the changes in seabed surface sediments grain size and the trend of sediment transport.
2022, 44(3): 98-108.
doi: 10.12284/hyxb2022005
Abstract:
In view of the prominent partial wind effect on islands, the wind profiles of idealized islands topography with three slopes are fitted by means of boundary layer wind tunnel test and numerical simulation. The difference factor is defined to describe the variation of wind profile, the distribution of maximum acceleration ratio and difference factor on the windward side of islands is studied by numerical simulation, and the effects of island slope and height on maximum acceleration ratio and difference factor are discussed comprehensively. Moreover, based on the wind tunnel data, the along-wind, cross-wind and vertical turbulence intensity and gust factor of the windward and leeward sides are studied. The results show that the numerical simulation is basically consistent with the wind tunnel test results and the wind profile exponent (α) is smaller on the windward side of islands. It also shows acceleration effect near the top of the island is particularly obvious and its maximum acceleration ratio is between 0.4 and 1.0. Moreover, the difference factor at the hillside is lower, and with the increase of the angle of the island ridge, the position where the difference factor is 0 tends to approach the slope toe. As the island slope increases to 25°, the maximum acceleration ratio and difference factor on the 0° island ridge are large. The distribution of three-dimensional turbulence intensity on the windward side is relatively regular, while that on the leeward side is disordered especially in the range of 100 m away from the island’s surface. It is worth noting that the trends of gust factor and turbulence intensity are highly consistent.
In view of the prominent partial wind effect on islands, the wind profiles of idealized islands topography with three slopes are fitted by means of boundary layer wind tunnel test and numerical simulation. The difference factor is defined to describe the variation of wind profile, the distribution of maximum acceleration ratio and difference factor on the windward side of islands is studied by numerical simulation, and the effects of island slope and height on maximum acceleration ratio and difference factor are discussed comprehensively. Moreover, based on the wind tunnel data, the along-wind, cross-wind and vertical turbulence intensity and gust factor of the windward and leeward sides are studied. The results show that the numerical simulation is basically consistent with the wind tunnel test results and the wind profile exponent (α) is smaller on the windward side of islands. It also shows acceleration effect near the top of the island is particularly obvious and its maximum acceleration ratio is between 0.4 and 1.0. Moreover, the difference factor at the hillside is lower, and with the increase of the angle of the island ridge, the position where the difference factor is 0 tends to approach the slope toe. As the island slope increases to 25°, the maximum acceleration ratio and difference factor on the 0° island ridge are large. The distribution of three-dimensional turbulence intensity on the windward side is relatively regular, while that on the leeward side is disordered especially in the range of 100 m away from the island’s surface. It is worth noting that the trends of gust factor and turbulence intensity are highly consistent.
2022, 44(3): 109-117.
doi: 10.12284/hyxb2022007
Abstract:
To overcome the difficulty of removing the wind field contribution in the SAR Doppler centroid anomaly method when retrieving the ocean surface current, in this paper, a secant downhill method based on the M4S model is proposed. The contribution of the wind field is removed by iteratively calculating the sea surface current field in a local area and subsequently estimating the wind contribution factor to the Doppler velocity of the whole SAR map. Our method is used to retrieve the radial velocity of sea surface from Radarsat-2 data. Its retrieval accuracy is verified by matching measured data. The results show that the proposed method not only can possess well convergence and high convergent speed, but also the deviation of the radial velocity of the surface is 0.04 m/s and 0.15 m/s respectively for two scene SAR data used in this paper.
To overcome the difficulty of removing the wind field contribution in the SAR Doppler centroid anomaly method when retrieving the ocean surface current, in this paper, a secant downhill method based on the M4S model is proposed. The contribution of the wind field is removed by iteratively calculating the sea surface current field in a local area and subsequently estimating the wind contribution factor to the Doppler velocity of the whole SAR map. Our method is used to retrieve the radial velocity of sea surface from Radarsat-2 data. Its retrieval accuracy is verified by matching measured data. The results show that the proposed method not only can possess well convergence and high convergent speed, but also the deviation of the radial velocity of the surface is 0.04 m/s and 0.15 m/s respectively for two scene SAR data used in this paper.
2022, 44(3): 118-127.
doi: 10.12284/hyxb2022003
Abstract:
Based on mesoscale eddy dataset from February 1993 to January 2016, the distribution characteristics and evolution processes of mesoscale eddies in the Indo-Pacific Warm Pool (15º S~15º N, 60º E~170º W), and its seasonal variation and relationship with ENSO are statistically analyzed in this paper. It shows that most mesoscale eddies in the Indo-Pacific Warm Pool are short-lived and nonlinear, and propagate westward. The study also finds that the distribution characteristics of cyclonic eddies and anticyclone eddies are similar, and so do their variation trends over the eddy lifecycle. The seasonal numbers of mesoscale eddies vary insignificantly in the whole domain and are affected by ENSO in the meanwhile.
Based on mesoscale eddy dataset from February 1993 to January 2016, the distribution characteristics and evolution processes of mesoscale eddies in the Indo-Pacific Warm Pool (15º S~15º N, 60º E~170º W), and its seasonal variation and relationship with ENSO are statistically analyzed in this paper. It shows that most mesoscale eddies in the Indo-Pacific Warm Pool are short-lived and nonlinear, and propagate westward. The study also finds that the distribution characteristics of cyclonic eddies and anticyclone eddies are similar, and so do their variation trends over the eddy lifecycle. The seasonal numbers of mesoscale eddies vary insignificantly in the whole domain and are affected by ENSO in the meanwhile.
2022, 44(3): 128-136.
doi: 10.12284/hyxb2022019
Abstract:
Water transparency (Zsd) is an important optical parameter for evaluating water quality. This paper tuned a remote sensing model for estimating Zsd from MODIS (moderate resolution imaging spectroradiometer) data in the South Yellow Sea. This model was then used to analyze the spatial and temporal variations of Zsd in the South Yellow Sea based long-term MODIS data in the past 20 years (2002–2020), and their driving factors were examined. The results show that the Zsd estimation model has good accuracy with R2, root mean square error and mean absolute percent error values of 0.91, 1.69 m and 25.1%, respectively. The Zsd levels are generally high in the offshore but low in the coastal area. Meanwhile, Zsd indicates high values in summer but low values in winter. In the past 20 years, Zsd in the central South Yellow Sea, the southern South Yellow Sea and the Changjiang River Estuary showed slowly increase trends, while Zsd in the Jiangsu coast was decreasing slowly. In general, the Zsd is negatively driven by the concentration of suspended particulate matter, of which the influence is the greatest. In addition, sea surface temperature and solar radiation have positive driving effects on Zsd, while wind speed has negative driving effect.
Water transparency (Zsd) is an important optical parameter for evaluating water quality. This paper tuned a remote sensing model for estimating Zsd from MODIS (moderate resolution imaging spectroradiometer) data in the South Yellow Sea. This model was then used to analyze the spatial and temporal variations of Zsd in the South Yellow Sea based long-term MODIS data in the past 20 years (2002–2020), and their driving factors were examined. The results show that the Zsd estimation model has good accuracy with R2, root mean square error and mean absolute percent error values of 0.91, 1.69 m and 25.1%, respectively. The Zsd levels are generally high in the offshore but low in the coastal area. Meanwhile, Zsd indicates high values in summer but low values in winter. In the past 20 years, Zsd in the central South Yellow Sea, the southern South Yellow Sea and the Changjiang River Estuary showed slowly increase trends, while Zsd in the Jiangsu coast was decreasing slowly. In general, the Zsd is negatively driven by the concentration of suspended particulate matter, of which the influence is the greatest. In addition, sea surface temperature and solar radiation have positive driving effects on Zsd, while wind speed has negative driving effect.
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