2019 Vol. 41, No. 7
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2019, 41(7): .
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2019, 41(7): .
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2019, 41(7): 1-14.
doi: 10.3969/j.issn.0253-4193.2019.07.001
Abstract:
Simple Ocean Data Assimilation reanalysis and other data were used to explore seasonal variation characteristics of freshwater transport between the Arabian Sea (AS) and the Equatorial Western Indian Ocean (EWIO), and the Gulf of Oman (GOO). Freshwater budget in the AS is characterized by a basic balance and its seasonal variation is also present. Our results indicate that the amount of input freshwater from the EWIO and river discharge is roughly equal to the amount of freshwater output to GOO and lost caused by the evaporation overwhelming the precipitation (P–E). The lost freshwater via air-sea exchange (i.e. P–E) is compensated by freshwater flux from the EWIO and the Bay of Bengal (BOB), which plays a key role in maintaining the basic balance of salinity over the AS. Net freshwater flux in the AS is negative (i.e. lost freshwater) from January to June together with December, and positive (i.e. receive freshwater) during July and November with a maximum positive value in September. The seasonal variation characteristics of net freshwater flux in the AS shows a single remarkable peak. Along the 9°N section, freshwater exchange between the EWIO and the AS primarily occurs from the surface to 200 m depth, with a multi-year averaged net flux into the AS of about 0.1×106 m3/s. From October to next March, the BOB low-salinity water extends into the AS at above 60 m depth through the southwest of the Indian peninsula. In summer and autumn, the transport associated with the Great Whirl located at the east of Somali Peninsula, is characterized by low (high) salinity water in the west (east) of the whirl transported northward (southward) into the AS (equatorial Indian Ocean). This transport during these two seasons is largest in a year with its influence can extend downward to about 300 m depth, which forms in June, then peaks in August and September, and finally decays rapidly in November. Water exchange between the AS and the GOO is relatively weak, and has a sandwich-like three-layer structure in vertical direction: high salinity water intrudes from GOO into the AS in the upper 10 m layer and in the bottom layer between 175 m and 400 m depth; whereas in the middle layer (i.e. 15 m to 170 m depth) low salinity water is transported from the AS to the GOO. On multi-year average, a net freshwater transport of about 0.39×104 m3/s is further estimated into the GOO from the AS across the section along the GOO mouth.
Simple Ocean Data Assimilation reanalysis and other data were used to explore seasonal variation characteristics of freshwater transport between the Arabian Sea (AS) and the Equatorial Western Indian Ocean (EWIO), and the Gulf of Oman (GOO). Freshwater budget in the AS is characterized by a basic balance and its seasonal variation is also present. Our results indicate that the amount of input freshwater from the EWIO and river discharge is roughly equal to the amount of freshwater output to GOO and lost caused by the evaporation overwhelming the precipitation (P–E). The lost freshwater via air-sea exchange (i.e. P–E) is compensated by freshwater flux from the EWIO and the Bay of Bengal (BOB), which plays a key role in maintaining the basic balance of salinity over the AS. Net freshwater flux in the AS is negative (i.e. lost freshwater) from January to June together with December, and positive (i.e. receive freshwater) during July and November with a maximum positive value in September. The seasonal variation characteristics of net freshwater flux in the AS shows a single remarkable peak. Along the 9°N section, freshwater exchange between the EWIO and the AS primarily occurs from the surface to 200 m depth, with a multi-year averaged net flux into the AS of about 0.1×106 m3/s. From October to next March, the BOB low-salinity water extends into the AS at above 60 m depth through the southwest of the Indian peninsula. In summer and autumn, the transport associated with the Great Whirl located at the east of Somali Peninsula, is characterized by low (high) salinity water in the west (east) of the whirl transported northward (southward) into the AS (equatorial Indian Ocean). This transport during these two seasons is largest in a year with its influence can extend downward to about 300 m depth, which forms in June, then peaks in August and September, and finally decays rapidly in November. Water exchange between the AS and the GOO is relatively weak, and has a sandwich-like three-layer structure in vertical direction: high salinity water intrudes from GOO into the AS in the upper 10 m layer and in the bottom layer between 175 m and 400 m depth; whereas in the middle layer (i.e. 15 m to 170 m depth) low salinity water is transported from the AS to the GOO. On multi-year average, a net freshwater transport of about 0.39×104 m3/s is further estimated into the GOO from the AS across the section along the GOO mouth.
The velocity characteristics of internal solitary waves in the Andaman Sea by optical remote sensing
2019, 41(7): 15-21.
doi: 10.3969/j.issn.0253-4193.2019.07.002
Abstract:
Internal solitary waves (ISWs) are widely distributed and have a large scale in the Andaman Sea. The velocity of ISWs is an important dynamic parameter. In this paper, approaches are proposed and demonstrated for calculating the propagation velocity of ISWs by optical remote sensing. The optical remote sensing data of MODIS in the Andaman Sea are collected and two methods are adopted to aquire velocity. One is to track the same ISWs based on two remote sensing satellites. The other is to find two or more packets of ISWs from the same generation in a single image. The overview of velocity distribution in the whole Andaman Sea is obtained by combining two methods. The results show that the propagation velocity of the Andaman Sea internal solitary wave ranges from 0.5 m/s to 2.7 m/s. The direction of the velocity is mainly influenced by the bottom topography, and the velocity decreases with the depth of water. In addition, different seasons correspond to different velocities in the deep water areas.
Internal solitary waves (ISWs) are widely distributed and have a large scale in the Andaman Sea. The velocity of ISWs is an important dynamic parameter. In this paper, approaches are proposed and demonstrated for calculating the propagation velocity of ISWs by optical remote sensing. The optical remote sensing data of MODIS in the Andaman Sea are collected and two methods are adopted to aquire velocity. One is to track the same ISWs based on two remote sensing satellites. The other is to find two or more packets of ISWs from the same generation in a single image. The overview of velocity distribution in the whole Andaman Sea is obtained by combining two methods. The results show that the propagation velocity of the Andaman Sea internal solitary wave ranges from 0.5 m/s to 2.7 m/s. The direction of the velocity is mainly influenced by the bottom topography, and the velocity decreases with the depth of water. In addition, different seasons correspond to different velocities in the deep water areas.
2019, 41(7): 22-35.
doi: 10.3969/j.issn.0253-4193.2019.07.003
Abstract:
Based on the in-situ data from mooring deployed in the northwest South China Sea, we investigate the dynamical and thermal dynamical response of upper ocean to Typhoon Doksuri. In the aspect of dynamic response, as the Typhoon passing, the currents in upper layer enhanced strikingly, the zonal currents in the mixed layer reaches 1.20 m/s. After the passage of Typhoon Doksuri, the currents in the upper layer are dominated by near-inertial oscillation, which rotate clockwise with a period between 36–40 hours. The kinetic energy of near-inertial wave shows two high energetic cores in vertical, which locates at the mixed layer and the thermocline layer, respectively. The estimated e-folding time-scale of near-inertial energy decay is about 3.7 d, and we believe that the downward propagation of energy is the major reason for the decay. The power spectra analysis of currents reveals that power density at inertial frequency, during the period of Typhoon Doksuri, increases about 29.4 times larger than that before the Typhoon arriving. Nevertheless, power density both at diurnal (K1) and semidiurnal (M2) frequency decreases during Typhoon period. Additionally, a blue shift at inertial frequency is identified. We find that the averaged near-internal frequency in upper 400 m is 1.167 f0 for zonal near-inertial currents and 1.170 f0 for meridional near-inertial currents (where f0 is the local inertial frequency). This blue shift is connected with the downward propagation of near-inertial waves and input of positive relative vorticity. In the aspect of thermodynamic response, the temperature rises in the upper layer between 40–250 m depth, due to the stirring induced by strong wind, and the maximum increased temperature amplitude is about 1℃. In addition, the decrease of salinity above 70 m may be related to the precipitation caused by the Typhoon. While the upwelling induced by Ekman pumping may have significant contribution to the increase of salinity at the depth of 70–100 m.
Based on the in-situ data from mooring deployed in the northwest South China Sea, we investigate the dynamical and thermal dynamical response of upper ocean to Typhoon Doksuri. In the aspect of dynamic response, as the Typhoon passing, the currents in upper layer enhanced strikingly, the zonal currents in the mixed layer reaches 1.20 m/s. After the passage of Typhoon Doksuri, the currents in the upper layer are dominated by near-inertial oscillation, which rotate clockwise with a period between 36–40 hours. The kinetic energy of near-inertial wave shows two high energetic cores in vertical, which locates at the mixed layer and the thermocline layer, respectively. The estimated e-folding time-scale of near-inertial energy decay is about 3.7 d, and we believe that the downward propagation of energy is the major reason for the decay. The power spectra analysis of currents reveals that power density at inertial frequency, during the period of Typhoon Doksuri, increases about 29.4 times larger than that before the Typhoon arriving. Nevertheless, power density both at diurnal (K1) and semidiurnal (M2) frequency decreases during Typhoon period. Additionally, a blue shift at inertial frequency is identified. We find that the averaged near-internal frequency in upper 400 m is 1.167 f0 for zonal near-inertial currents and 1.170 f0 for meridional near-inertial currents (where f0 is the local inertial frequency). This blue shift is connected with the downward propagation of near-inertial waves and input of positive relative vorticity. In the aspect of thermodynamic response, the temperature rises in the upper layer between 40–250 m depth, due to the stirring induced by strong wind, and the maximum increased temperature amplitude is about 1℃. In addition, the decrease of salinity above 70 m may be related to the precipitation caused by the Typhoon. While the upwelling induced by Ekman pumping may have significant contribution to the increase of salinity at the depth of 70–100 m.
2019, 41(7): 36-51.
doi: 10.3969/j.issn.0253-4193.2019.07.004
Abstract:
Based on the daily reanalysis from 1982 to 2017, this paper focuses on the analysis of the extreme characteristics, historical evolution, spatial pattern and possible impactions of sea surface temperature (SST) in coastal China seas (CCS), and discusses the correlation with global change and regional climate variability. The SST in the CCS overall increased significantly in recent more than 30 years, especially in the spring near the Changjiang River Estuary and offshore areas south of it with the warming rate up to 0.2℃/(10 a). Nevertheless the response of nearshore waters to the global warming hiatus is likely to be more pronounced. The extreme high (low) temperature intensity is mainly enhanced (weakened), especially in spring (summer). The increase of extreme temperature difference in the nearshore area in spring can easily lead to frequent ecological disasters such as biological migration and red tide. The consecutive days of extreme events in the northern sea areas are longer than in the south. The consecutive days of extreme high temperature in the Yellow Sea and East China Sea increased significantly, which may have a potential impact on fishery resources. Mostly due to the global warming hiatus, the consecutive days of extreme low temperature is also increased significantly. The cumulative frequency of extreme high temperature near the Changjiang River Estuary, the Taiwan Strait and the northern part of the South China Sea (SCS) increased significantly. In the future, extreme marine heat waves are likely increase continuously, which will have a greater impact on the coral reefs in the SCS and so on. The cumulative frequency of extreme low temperature is mainly reduced. The extreme low temperature along the Changjiang River Estuary and the southern nearshore sea areas increased obviously in winter and spring, which may have some influence on mangrove. During the warm phase of the Pacific decadal oscillation (PDO), the ENSO warm event is enhanced, which is likely to cause the frequent occurrence of extreme low temperature in the CCS. In addition, as the Arctic oscillation (AO) is in positive phase, the cold air in the polar region is restricted to expand southward, and the frequency of extreme high temperature in the CCS surface tends to increase, which enhances the disaster risk.
Based on the daily reanalysis from 1982 to 2017, this paper focuses on the analysis of the extreme characteristics, historical evolution, spatial pattern and possible impactions of sea surface temperature (SST) in coastal China seas (CCS), and discusses the correlation with global change and regional climate variability. The SST in the CCS overall increased significantly in recent more than 30 years, especially in the spring near the Changjiang River Estuary and offshore areas south of it with the warming rate up to 0.2℃/(10 a). Nevertheless the response of nearshore waters to the global warming hiatus is likely to be more pronounced. The extreme high (low) temperature intensity is mainly enhanced (weakened), especially in spring (summer). The increase of extreme temperature difference in the nearshore area in spring can easily lead to frequent ecological disasters such as biological migration and red tide. The consecutive days of extreme events in the northern sea areas are longer than in the south. The consecutive days of extreme high temperature in the Yellow Sea and East China Sea increased significantly, which may have a potential impact on fishery resources. Mostly due to the global warming hiatus, the consecutive days of extreme low temperature is also increased significantly. The cumulative frequency of extreme high temperature near the Changjiang River Estuary, the Taiwan Strait and the northern part of the South China Sea (SCS) increased significantly. In the future, extreme marine heat waves are likely increase continuously, which will have a greater impact on the coral reefs in the SCS and so on. The cumulative frequency of extreme low temperature is mainly reduced. The extreme low temperature along the Changjiang River Estuary and the southern nearshore sea areas increased obviously in winter and spring, which may have some influence on mangrove. During the warm phase of the Pacific decadal oscillation (PDO), the ENSO warm event is enhanced, which is likely to cause the frequent occurrence of extreme low temperature in the CCS. In addition, as the Arctic oscillation (AO) is in positive phase, the cold air in the polar region is restricted to expand southward, and the frequency of extreme high temperature in the CCS surface tends to increase, which enhances the disaster risk.
2019, 41(7): 52-64.
doi: 10.3969/j.issn.0253-4193.2019.07.005
Abstract:
The shipboard ADCP (Acoustic Doppler Current Profilers) backscatter intensity data in the Eighth Arctic Science Expedition are analyzed for the temporal and spatial characteristics of the sound scattering layer (SSL), by combining the solar altitude, the sea ice concentration and the in-situ data of the water environment parameters. The results show that the higher the latitude is, the shorter the time of the SSL is on the sea surface. Even during the period of polar day and all covered by sea ice, the migration amplitude and backscattering intensity of the SSL are weakened, but they are still affected by the change of the solar elevation, and there is a strong temporal correlation between them and solar altitude angle. In the middle section of the Arctic, the migration of the SSL is weak, and there is no obvious SSL observed, the reason may be that the concentration of zooplanktons and fishes are relatively lower and the migration is weak, which is beyond the accuracy range of ADCP used in this paper. ADCP data in the back and forth from the Okhotsk Sea to the southwest of the Bering Sea, show that there are two SSLs, the shallower depth and the greater backscatter intensity, but their vertical migration time is synchronized, and the spacing between them is gradually reduced and combined as the latitude increases, it may be caused by marine organisms with different life habit.
The shipboard ADCP (Acoustic Doppler Current Profilers) backscatter intensity data in the Eighth Arctic Science Expedition are analyzed for the temporal and spatial characteristics of the sound scattering layer (SSL), by combining the solar altitude, the sea ice concentration and the in-situ data of the water environment parameters. The results show that the higher the latitude is, the shorter the time of the SSL is on the sea surface. Even during the period of polar day and all covered by sea ice, the migration amplitude and backscattering intensity of the SSL are weakened, but they are still affected by the change of the solar elevation, and there is a strong temporal correlation between them and solar altitude angle. In the middle section of the Arctic, the migration of the SSL is weak, and there is no obvious SSL observed, the reason may be that the concentration of zooplanktons and fishes are relatively lower and the migration is weak, which is beyond the accuracy range of ADCP used in this paper. ADCP data in the back and forth from the Okhotsk Sea to the southwest of the Bering Sea, show that there are two SSLs, the shallower depth and the greater backscatter intensity, but their vertical migration time is synchronized, and the spacing between them is gradually reduced and combined as the latitude increases, it may be caused by marine organisms with different life habit.
2019, 41(7): 65-76.
doi: 10.3969/j.issn.0253-4193.2019.07.006
Abstract:
The composition of clinopyroxene in pyroclastic rocks at the bottom of the Xisha Islands was determined in detail by electron microprobe analysis. The results show that the clinopyroxenes are mostly rich in calcium and have a zonal structure. Ca, Fe and Ti concentrations increased from the core to the outer layers, reflecting the normal sequence of magmatic crystallization. The chemical characteristics of the pyroxene, including low Si, high Al (SiO2=41.40%–48.44%, Al2O3=5.54%–10.20%) and even higher AlIV concentrations, coincide with those of basic magma. The main element data of the clinopyroxene show that the concentration of monoclinic Ca is high. The Ca/(Ca+Mg+Fe) ratio is between 46.1% and 51.4%. The large amount of high-calcium clinopyroxene may be attributed to the high concentration of Ca in magma. Combining this with the earthquake and tectonic data of the Xisha sea area, we speculate that the basement of the coral reefs of Chenhang Island is a flat-topped seamount composed of basaltic volcanic clastic rocks. Further, we infer that its formation involved the passing of magma through the lithospheric layer of the fault and its eruption in the seabed of the Xisha Islands. The volcanic clastic material is thus formed by accumulation and consolidation, and the original rock of the volcanic clastic rock is an intraplate alkaline basalt.
The composition of clinopyroxene in pyroclastic rocks at the bottom of the Xisha Islands was determined in detail by electron microprobe analysis. The results show that the clinopyroxenes are mostly rich in calcium and have a zonal structure. Ca, Fe and Ti concentrations increased from the core to the outer layers, reflecting the normal sequence of magmatic crystallization. The chemical characteristics of the pyroxene, including low Si, high Al (SiO2=41.40%–48.44%, Al2O3=5.54%–10.20%) and even higher AlIV concentrations, coincide with those of basic magma. The main element data of the clinopyroxene show that the concentration of monoclinic Ca is high. The Ca/(Ca+Mg+Fe) ratio is between 46.1% and 51.4%. The large amount of high-calcium clinopyroxene may be attributed to the high concentration of Ca in magma. Combining this with the earthquake and tectonic data of the Xisha sea area, we speculate that the basement of the coral reefs of Chenhang Island is a flat-topped seamount composed of basaltic volcanic clastic rocks. Further, we infer that its formation involved the passing of magma through the lithospheric layer of the fault and its eruption in the seabed of the Xisha Islands. The volcanic clastic material is thus formed by accumulation and consolidation, and the original rock of the volcanic clastic rock is an intraplate alkaline basalt.
2019, 41(7): 77-91.
doi: 10.3969/j.issn.0253-4193.2019.07.007
Abstract:
Rare earth element (REE) in the surface sediments from Pahang River (28 samples) and Kelantan River (22 samples) in the eastern portion of Malay Peninsula are analyzed to decipher the characteristics of REE composition and distribution, to discern the controlling factors of REE composition, and to illustrate the significances of provenance tracing of REE. The results show that the total REE ranges from 24.88 μg/g to 304.29 μg/g, with an average of 165.22 μg/g, for the Pahang River; and 126.02 μg/g to 281.40 μg/g, with an average of 181.15 μg/g, for the Kelantan River, respectively. The UCC standardization of REE indicates that Pahang River sediments enrich with heavy rare earth elements, in relative to light rare earth elements. However, there is no significant difference between light and heavy rare earth elements in the Kelantan River. The composition of source rocks and minerals plays a controlling role in the REE composition of the two rivers. The influence of chemical weathering in the Pahang River is greater than Kelantan River, and the difference of grain size among the Pahang River sediments leads to larger REE variations. δEuUCC-(Gd/Yb)UCC discrimination diagram demonstrates that it can be used as an effective index to qualitatively seperate the sediment source of two rivers. It can further be used to trace and identify the source of sediments quantitatively on the continental shelf of Malay Peninsula.
Rare earth element (REE) in the surface sediments from Pahang River (28 samples) and Kelantan River (22 samples) in the eastern portion of Malay Peninsula are analyzed to decipher the characteristics of REE composition and distribution, to discern the controlling factors of REE composition, and to illustrate the significances of provenance tracing of REE. The results show that the total REE ranges from 24.88 μg/g to 304.29 μg/g, with an average of 165.22 μg/g, for the Pahang River; and 126.02 μg/g to 281.40 μg/g, with an average of 181.15 μg/g, for the Kelantan River, respectively. The UCC standardization of REE indicates that Pahang River sediments enrich with heavy rare earth elements, in relative to light rare earth elements. However, there is no significant difference between light and heavy rare earth elements in the Kelantan River. The composition of source rocks and minerals plays a controlling role in the REE composition of the two rivers. The influence of chemical weathering in the Pahang River is greater than Kelantan River, and the difference of grain size among the Pahang River sediments leads to larger REE variations. δEuUCC-(Gd/Yb)UCC discrimination diagram demonstrates that it can be used as an effective index to qualitatively seperate the sediment source of two rivers. It can further be used to trace and identify the source of sediments quantitatively on the continental shelf of Malay Peninsula.
2019, 41(7): 92-102.
doi: 10.3969/j.issn.0253-4193.2019.07.008
Abstract:
The Weixi’nan Sag is the important research area of exploration and development integration. This study takes the Weizhou Formation of the No.2 Fracture Zone as the research object. By analyzing the geometry, kinematics, and dynamics characteristics of fracture, the "slope-flat" fault system in the middle section and the "shovel-type" fault system on both sides are divided into the level 3 en-echelon main fracture zone, the level 4 branch fracture zone, and the level 5 branch fracture zone. The "slope-flat" fault system in the middle section is subjected to higher in-situ stress, and the main and branch faults are more developed. The vast majority of oil and gas are distributed in the "slope-flat" fault system. A comprehensive analysis of the relationship between the internal fracture system of the differential fault system in the No.2 Fracture Zone and the oil-gas distribution law is made, and obtains the corresponding regular of 3 aspects of fracture reservoir controlling mechanism and 8 types of fracture reservoir controlling patterns. Under the regular of fracture reservoir controlling mechanism and patterns, the search and evaluation of targets are carried out around the inner or surrounding oil fields of the No.2 Fracture Zone, and good results are obtained. Based on the field production, the potential targets of North 1, North 3 and North 4 in the middle part of the No.2 Fracture Zone are searched and optimized. The three blocks have been successfully drilled, and the purpose of the geological reservoir has been achieved. The regular of fracture reservoir controlling mechanism and patterns which have been applied to the potential zone of the No.2 Fracture Zone in the southwest depression play very good effect.
The Weixi’nan Sag is the important research area of exploration and development integration. This study takes the Weizhou Formation of the No.2 Fracture Zone as the research object. By analyzing the geometry, kinematics, and dynamics characteristics of fracture, the "slope-flat" fault system in the middle section and the "shovel-type" fault system on both sides are divided into the level 3 en-echelon main fracture zone, the level 4 branch fracture zone, and the level 5 branch fracture zone. The "slope-flat" fault system in the middle section is subjected to higher in-situ stress, and the main and branch faults are more developed. The vast majority of oil and gas are distributed in the "slope-flat" fault system. A comprehensive analysis of the relationship between the internal fracture system of the differential fault system in the No.2 Fracture Zone and the oil-gas distribution law is made, and obtains the corresponding regular of 3 aspects of fracture reservoir controlling mechanism and 8 types of fracture reservoir controlling patterns. Under the regular of fracture reservoir controlling mechanism and patterns, the search and evaluation of targets are carried out around the inner or surrounding oil fields of the No.2 Fracture Zone, and good results are obtained. Based on the field production, the potential targets of North 1, North 3 and North 4 in the middle part of the No.2 Fracture Zone are searched and optimized. The three blocks have been successfully drilled, and the purpose of the geological reservoir has been achieved. The regular of fracture reservoir controlling mechanism and patterns which have been applied to the potential zone of the No.2 Fracture Zone in the southwest depression play very good effect.
2019, 41(7): 103-115.
doi: 10.3969/j.issn.0253-4193.2019.07.009
Abstract:
By monitoring the typical profiles of the artificial cobble and sandy beach on Xiamen Tianquan Bay and Huizhan before and after the super Typhoon No.1614 Meranti, combined with the observation and numerical simulation of hydrodynamic factors, we calculate the wave field together with the total water level during the typhoon process, and analyze the morphology and the average variation of the profile. Results show that the characteristics of response to typhoon between artificial cobble and sandy beach on macro-tidal coast are significantly different. The majority of cobbles transported onshore, the beach face eroded while the beach berm accumulated to form a higher beach berm, and the slope of the artificial cobble beach is obviously steepened. In contract, the artificial sandy beach shows obvious sediment transport offshore, the upper beach face eroded and the lower beach face deposited, the slope of the beach face obviously become gentler, moreover the top of the beach berm become flattened due to the strong onshore wind after the typhoon landing, and the height of the beach berm almost remain unchanged. Whether the beach berm eroded during typhoon process is closely related to the total water level including astronomical tide, storm surge and wave run-up. During the process of typhoon, the artificial cobble beach characterized with higher wave energy and steeper beach slope showed less profile variation comparing to that of the artificial sandy beach. The artificial cobble beach performed a small degree of response to typhoon. Taken together, it is an effective approach of slowing sandy beach erosion by using gravels and other coarse-grained sediments for beach nourishment on strong eroded high-energy macro-tidal coasts.
By monitoring the typical profiles of the artificial cobble and sandy beach on Xiamen Tianquan Bay and Huizhan before and after the super Typhoon No.1614 Meranti, combined with the observation and numerical simulation of hydrodynamic factors, we calculate the wave field together with the total water level during the typhoon process, and analyze the morphology and the average variation of the profile. Results show that the characteristics of response to typhoon between artificial cobble and sandy beach on macro-tidal coast are significantly different. The majority of cobbles transported onshore, the beach face eroded while the beach berm accumulated to form a higher beach berm, and the slope of the artificial cobble beach is obviously steepened. In contract, the artificial sandy beach shows obvious sediment transport offshore, the upper beach face eroded and the lower beach face deposited, the slope of the beach face obviously become gentler, moreover the top of the beach berm become flattened due to the strong onshore wind after the typhoon landing, and the height of the beach berm almost remain unchanged. Whether the beach berm eroded during typhoon process is closely related to the total water level including astronomical tide, storm surge and wave run-up. During the process of typhoon, the artificial cobble beach characterized with higher wave energy and steeper beach slope showed less profile variation comparing to that of the artificial sandy beach. The artificial cobble beach performed a small degree of response to typhoon. Taken together, it is an effective approach of slowing sandy beach erosion by using gravels and other coarse-grained sediments for beach nourishment on strong eroded high-energy macro-tidal coasts.
2019, 41(7): 116-122.
doi: 10.3969/j.issn.0253-4193.2019.07.010
Abstract:
Variation of pore pressure between soil particles, which caused by the cyclic loading from waves to seabed, is the main reason for soil liquefaction. By using a self-designed pore pressure monitoring equipment, we monitored pore pressure with a long-period, high-precision way in the easy-liquefied zone in Chengdao sea area of Yellow River Estuary. The monitoring results show that the maximum wave-affected depth is between 0.5 m to 1.5 m and no obvious pore pressure response in the deeper sediment during this period. Pore pressure variation in soil is mainly determined by tide level and wave height. Tide level changes can result in smooth change in pore pressure but can not cause the emergence of excess pore pressure while wave height changes can result in severe oscillation in pore pressure and lead to the appearance of excess pore pressure.
Variation of pore pressure between soil particles, which caused by the cyclic loading from waves to seabed, is the main reason for soil liquefaction. By using a self-designed pore pressure monitoring equipment, we monitored pore pressure with a long-period, high-precision way in the easy-liquefied zone in Chengdao sea area of Yellow River Estuary. The monitoring results show that the maximum wave-affected depth is between 0.5 m to 1.5 m and no obvious pore pressure response in the deeper sediment during this period. Pore pressure variation in soil is mainly determined by tide level and wave height. Tide level changes can result in smooth change in pore pressure but can not cause the emergence of excess pore pressure while wave height changes can result in severe oscillation in pore pressure and lead to the appearance of excess pore pressure.
2019, 41(7): 123-135.
doi: 10.3969/j.issn.0253-4193.2019.07.011
Abstract:
Comparison with Geophysical Model Function (GMF) developed by methods of empirical statistics, ocean microwave scattering model works well at all microwave frequency. Composite radar backscattering model is comprised of Bragg scattering model and geometrical optics model. We calculated the normalized radar cross sections (NRCSs) from the composite scattering model by using the sea surface wind speeds and directions measured by buoys moored in the northern of South China Sea in the whole year of 2014, and then compared them with SAR on board RADARSAT-2 at C-band, microwave scatterometer on board HY-2A satellite (HSCAT) at Ku-band, respectively. The biases of comparison are (–0.22±1.88) dB ( for SAR), (0.33±2.71) dB (for HSCAT in VV polarization) and (–1.35±2.88) dB (for HSCAT in HH polarization), respectively. We also calculated the NRCSs from the model by using the sea surface wind speeds and directions measured by NDBC buoys in the time period from October 1, 2011 to September 30, 2014, and then compared them with radar altimeter on board Jason-2 and HY-2A both at Ku-band with the bias of (1.01±1.15) dB and (1.12±1.29) dB, respectively. Although the biases of NRCSs between space-borne sensors and composite scattering model in medium and normal incidence are different each other, the accuracies of their sea surface wind speed products are the same(i.e. the root mean square errors are all less than 1.71 m/s). The results show that we can simulate the sea surface radar NRCSs of satellite-borne SAR, microwave scatterometer, and altimeter by using the composite radar backscattering model, and the simulations are consistent with that of CMOD5, NSCAT-2 and the GMF of operational wind retrieval for altimeter. It also indicates that the composite radar backscattering model could be used in calibration and validation of microwave sensors and simulation of radar backscatter from sea surface.
Comparison with Geophysical Model Function (GMF) developed by methods of empirical statistics, ocean microwave scattering model works well at all microwave frequency. Composite radar backscattering model is comprised of Bragg scattering model and geometrical optics model. We calculated the normalized radar cross sections (NRCSs) from the composite scattering model by using the sea surface wind speeds and directions measured by buoys moored in the northern of South China Sea in the whole year of 2014, and then compared them with SAR on board RADARSAT-2 at C-band, microwave scatterometer on board HY-2A satellite (HSCAT) at Ku-band, respectively. The biases of comparison are (–0.22±1.88) dB ( for SAR), (0.33±2.71) dB (for HSCAT in VV polarization) and (–1.35±2.88) dB (for HSCAT in HH polarization), respectively. We also calculated the NRCSs from the model by using the sea surface wind speeds and directions measured by NDBC buoys in the time period from October 1, 2011 to September 30, 2014, and then compared them with radar altimeter on board Jason-2 and HY-2A both at Ku-band with the bias of (1.01±1.15) dB and (1.12±1.29) dB, respectively. Although the biases of NRCSs between space-borne sensors and composite scattering model in medium and normal incidence are different each other, the accuracies of their sea surface wind speed products are the same(i.e. the root mean square errors are all less than 1.71 m/s). The results show that we can simulate the sea surface radar NRCSs of satellite-borne SAR, microwave scatterometer, and altimeter by using the composite radar backscattering model, and the simulations are consistent with that of CMOD5, NSCAT-2 and the GMF of operational wind retrieval for altimeter. It also indicates that the composite radar backscattering model could be used in calibration and validation of microwave sensors and simulation of radar backscatter from sea surface.
2019, 41(7): 136-142.
doi: 10.3969/j.issn.0253-4193.2019.07.012
Abstract:
The tide gauge data provide an effective way to evaluate the accuracy of satellite altimeter data. The HY-2A data are filtered based on the data edited criterion and the model of real-time atmospheric pressure provided by NCEP are used to solve the problem caused by the unavailable dry tropospheric correction and inverse barometer correction in the later stage of the HY-2A exact repeat mission (ERM). By matching the HY-2A altimeter data and the tide gauges data in temporal and spatial, the correlation coefficient and standard deviation between the two kinds of altimeter data are calculated in the nine selected tide gauges area. According to the analysis results, the average correlation coefficient is about 0.676 9, the optimum is up to 0.898 7, and the average standard deviation is 0.089 5 m. The results show that the quality of HY-2A satellite altimetry data meet the design target and achieve the expected level. It provides a new reliable data source for the application research of the marine gravity field inversion.
The tide gauge data provide an effective way to evaluate the accuracy of satellite altimeter data. The HY-2A data are filtered based on the data edited criterion and the model of real-time atmospheric pressure provided by NCEP are used to solve the problem caused by the unavailable dry tropospheric correction and inverse barometer correction in the later stage of the HY-2A exact repeat mission (ERM). By matching the HY-2A altimeter data and the tide gauges data in temporal and spatial, the correlation coefficient and standard deviation between the two kinds of altimeter data are calculated in the nine selected tide gauges area. According to the analysis results, the average correlation coefficient is about 0.676 9, the optimum is up to 0.898 7, and the average standard deviation is 0.089 5 m. The results show that the quality of HY-2A satellite altimetry data meet the design target and achieve the expected level. It provides a new reliable data source for the application research of the marine gravity field inversion.
2019, 41(7): 143-148.
doi: 10.3969/j.issn.0253-4193.2019.07.013
Abstract:
Based on the ionospheric correction data of Global Ionospheric Map (GIM) and dual-frequency, extracting the Pacific Ocean dataset from the Jason-2 Altimeter’s Geophysical Data Set (GDR) including 38-period in 2015. The dataset is divided into small twelve cell according to the features of ionosphere over seasons and in latitude. The result shows that there is a significant difference between the GIM and the dual-frequency correction value, and the GIM correction value is generally higher than the dual-frequency correction value, indicating that GIM overestimates the ionosphere path delay, also, the difference between the GIM and the dual-frequency is related to the season and latitude. Applying the modified equation to the 2016 Jason-2 annual data, the corrected GIM value is very close to the dual-frequency correction value, and the applicability of the modified equation remains the same over time. In the case where the single-frequency altimeter cannot use the ionospheric dual-frequency correction algorithm, the GIM value of the altimeter of the same height can be corrected by using the correction equations of different quarters and different latitude regions to achieve the accuracy level of the dual-frequency correction value.
Based on the ionospheric correction data of Global Ionospheric Map (GIM) and dual-frequency, extracting the Pacific Ocean dataset from the Jason-2 Altimeter’s Geophysical Data Set (GDR) including 38-period in 2015. The dataset is divided into small twelve cell according to the features of ionosphere over seasons and in latitude. The result shows that there is a significant difference between the GIM and the dual-frequency correction value, and the GIM correction value is generally higher than the dual-frequency correction value, indicating that GIM overestimates the ionosphere path delay, also, the difference between the GIM and the dual-frequency is related to the season and latitude. Applying the modified equation to the 2016 Jason-2 annual data, the corrected GIM value is very close to the dual-frequency correction value, and the applicability of the modified equation remains the same over time. In the case where the single-frequency altimeter cannot use the ionospheric dual-frequency correction algorithm, the GIM value of the altimeter of the same height can be corrected by using the correction equations of different quarters and different latitude regions to achieve the accuracy level of the dual-frequency correction value.
2019, 41(7): 149-158.
doi: 10.3969/j.issn.0253-4193.2019.07.014
Abstract:
The spectral width of the electromagnetic scattering from sea surface is closely related to the SWH (significant wave height), and thus the spectral width can be used to retrieve the SWH. In this paper, the linear filtering method is employed to simulate the radial velocity of the orbit velocity of the each scattering element on sea surface. Based on the radial velocity, we establish a spectral width model, and analyze the influences of spatial resolution, time sampling length and SWH on spectral width. At the same time, we also discuss how to select the parameters such as time sampling length and the azimuth angle during the actual observation. Here, the theoretical results are compared with the estimated results based on the measured data required by the CSIR-X band radar. The comparisons demonstrate that the spectral width obtained by the estimation method based on Gaussian distribution standard deviation agree well with the theoretical results after eliminating the effects of radar noise and frequency leakage, which proves the reliability of the theoretical results. The results obtained in this paper have certain reference value for the retrieval of the SWH.
The spectral width of the electromagnetic scattering from sea surface is closely related to the SWH (significant wave height), and thus the spectral width can be used to retrieve the SWH. In this paper, the linear filtering method is employed to simulate the radial velocity of the orbit velocity of the each scattering element on sea surface. Based on the radial velocity, we establish a spectral width model, and analyze the influences of spatial resolution, time sampling length and SWH on spectral width. At the same time, we also discuss how to select the parameters such as time sampling length and the azimuth angle during the actual observation. Here, the theoretical results are compared with the estimated results based on the measured data required by the CSIR-X band radar. The comparisons demonstrate that the spectral width obtained by the estimation method based on Gaussian distribution standard deviation agree well with the theoretical results after eliminating the effects of radar noise and frequency leakage, which proves the reliability of the theoretical results. The results obtained in this paper have certain reference value for the retrieval of the SWH.
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