It is well known that the sea return echo contains contributions from at least two scattering mechanisms. In addition to the resonant Bragg scattering, the specular point scattering plays an important role as the inci...It is well known that the sea return echo contains contributions from at least two scattering mechanisms. In addition to the resonant Bragg scattering, the specular point scattering plays an important role as the incidence angle becomes smaller （≥ 20°）. Here, in combination with the Kirchhoff integral equation of scattering field and the stationary phase approximation, analytical expressions for Doppler shift and spectral bandwidth of specular point scattering, which are insensitive to the polarization state, are derived theoretically. For comparison, the simulated results related to the two-scale method （TSM） and the method of moment （MOM） are also presented. It is found that the Doppler shift and the spectral bandwidth given by TSM are insufficient at small incidence angles. However, a comparison between the analytical results and the numerical simulations by MOM in the backscatter configuration shows that our proposed formulas are valid for the specular point scattering case. In this work, the dependences of the predicted results on incidence angle, radar frequency, and wind speed are also discussed. The obtained conclusions seem promising for a better understanding of the Doppler spectra of the specular point scattering fields from time-varying sea surfaces.展开更多
"Wide Sargasso Sea"is one of Jean Rhys' novella which appealed enormous research. Although many studies touched on different meanings from its narrative perspective, most of them illustrated from the asp..."Wide Sargasso Sea"is one of Jean Rhys' novella which appealed enormous research. Although many studies touched on different meanings from its narrative perspective, most of them illustrated from the aspect which mixed narrator and point of view. This study researched this novella from the perspective of point of view suggested by Prof. Shen Dan to decode author's method of telling a"plausible story".展开更多
Sea ice concentration is an important parameter for polar sea ice monitoring. Based on 89 GHz AMSR-E （Advanced Microwave Scanning Radiometer for Earth Observing System） data, a gridded high-resolution passive microw...Sea ice concentration is an important parameter for polar sea ice monitoring. Based on 89 GHz AMSR-E （Advanced Microwave Scanning Radiometer for Earth Observing System） data, a gridded high-resolution passive microwave sea ice concentration product can be obtained using the ASI （the Arctic Radiation And Turbulence Interaction Study （ARTIST） Sea Ice） retrieval algorithm. Instead of using fixed-point values, we developed ASi algorithm based on daily changed tie points, called as the dynamic tie point ASI algorithm in this study. Here the tie points are expressed as the brightness temperature polarization difference of open water and 100% sea ice. In 2010, the yearly-averaged tie points of open water and sea ice in Arctic are estimated to be 50.8 K and 7.8 K, respectively. It is confirmed that the sea ice concentrations retrieved by the dynamic tie point ASI algorithm can increase （decrease） the sea ice concentrations in low-value （high-value） areas. This improved the sea ice concentrations by present retrieval algorithm from microwave data to some extent. Comparing with the products using fixed tie points, the sea ice concentrations retrieved from AMSR-E data by using the dynamic tie point ASI algorithm are closer to those obtained from MODIS （Moderate-resolution Imaging Spectroradiometer） data. In 40 selected cloud-free sample regions, 95% of our results have smaller mean differences and 75% of our results have lower root mean square （RMS） differences compare with those by the fixed tie points.展开更多
The wave period probability densities in non-Gaussian mixed sea states are calculated by utilizing a transformed Gaussian process method. The transformation relating the non-Gaussian process and the original Gaussian ...The wave period probability densities in non-Gaussian mixed sea states are calculated by utilizing a transformed Gaussian process method. The transformation relating the non-Gaussian process and the original Gaussian process is obtained based on the equivalence of the level up-crossing rates of the two processes. A saddle point approximation procedure is applied for calculating the level up-crossing rates in this study. The accuracy and efficiency of the transformed Gaussian process method are validated by comparing the results predicted by using the method with those predicted by the Monte Carlo simulation method.展开更多
Seasonal interaction between sea-surface temperature (SST) in the tropical eastern Pacific and ozone layer in Northern Hemisphere, ahd the layer,s teleconnection spatial structure caused by SST effeets, for January a...Seasonal interaction between sea-surface temperature (SST) in the tropical eastern Pacific and ozone layer in Northern Hemisphere, ahd the layer,s teleconnection spatial structure caused by SST effeets, for January and July, are statistically analysed. The result indicates that the areas spacially correlated between SST and ozone layer in January greatly differ from the ones in July and they show opposite tendency in the signs of correlation, so do the teleconnection pattern for the ozone lay6r due to effects of SST in different seasons. In addition, persistent' influence of SST on the ozone layer results insuperposition of seasonal SST effects on the layer and makes it characteristic of well-defined wavetrainsin responses to SST. It is concluded that SST in the tropical eastern Pacific is of great importance to thenorthern ozone layer distribution and its seasonal evolution.展开更多
Earthquakes perturb both the ocean bottom topography due to displacements of sea floor and the geoid due to mass redistribution, which induces the relative sea level(RSL) change. However, the relative global mean sea ...Earthquakes perturb both the ocean bottom topography due to displacements of sea floor and the geoid due to mass redistribution, which induces the relative sea level(RSL) change. However, the relative global mean sea level(GMSL) change is zero in that sea water mass is conserved. But the absolute GMSL change is not zero because earthquakes displace total ocean mass with respect to the Earth’s center of mass(CM) which remains unchanged after an earthquake. This displacement, i.e. the absolute GMSL change, may be detectable by altimetry since the satellites are orbiting around CM. In this paper, we proposed a method to estimate co-seismic absolute GMSL change caused by earthquakes based on the point dislocation theory for a spherically symmetric, non-rotating, elastic and isotropic(SNREI) Earth.This change can be directly connected to the perturbation of ocean bottom topography. We first computed co-seismic displacements as well as the change in geo-potential and solved the sea level equation to validate the insignificance of the oceans’ feedback, i.e. the loading effect due to RSL change, to co-seismic displacements. The results imply that the loading effect due to RSL change is negligible on displacements while is considerable on geoid. We then computed the absolute GMSL change caused by co-seismic vertical and horizontal displacements by making use of the integrated Green’s function method. The numerical results show that a large earthquake may raise the absolute GMSL by magnitude of sub-millimeter and the recent three large events cause GMSL to rise about one millimeter, in which the contribution from horizontal displacement is non-negligible.展开更多
The ESMD method can be seen as a new alternate of the well-known Hilbert-Huang transform (HHT) for non-steady data processing. It is good at finding the optimal adaptive global mean fitting curve, which is superior to...The ESMD method can be seen as a new alternate of the well-known Hilbert-Huang transform (HHT) for non-steady data processing. It is good at finding the optimal adaptive global mean fitting curve, which is superior to the common least-square method and running-mean approach. Take the air-sea momentum flux investigation as an example, only when the non-turbulent wind components is well extracted, can the remainder signal be seen as actual oscillations caused by turbulence. With the aid of —5/3 power law for the turbulence, a mode-filtering approach based on ESMD decomposition is developed here. The test on observational data indicates that this approach is very feasible and it may greatly reduce the error caused by the non-turbulent components.展开更多
基金Project supported by the Young Scientists Fund of the National Natural Science Foundation of China(Grant No.40906088)the Specialized Research Fund for the Doctoral Program of Higher Education,China(Grant No.200804231021)
文摘It is well known that the sea return echo contains contributions from at least two scattering mechanisms. In addition to the resonant Bragg scattering, the specular point scattering plays an important role as the incidence angle becomes smaller （≥ 20°）. Here, in combination with the Kirchhoff integral equation of scattering field and the stationary phase approximation, analytical expressions for Doppler shift and spectral bandwidth of specular point scattering, which are insensitive to the polarization state, are derived theoretically. For comparison, the simulated results related to the two-scale method （TSM） and the method of moment （MOM） are also presented. It is found that the Doppler shift and the spectral bandwidth given by TSM are insufficient at small incidence angles. However, a comparison between the analytical results and the numerical simulations by MOM in the backscatter configuration shows that our proposed formulas are valid for the specular point scattering case. In this work, the dependences of the predicted results on incidence angle, radar frequency, and wind speed are also discussed. The obtained conclusions seem promising for a better understanding of the Doppler spectra of the specular point scattering fields from time-varying sea surfaces.
文摘"Wide Sargasso Sea"is one of Jean Rhys' novella which appealed enormous research. Although many studies touched on different meanings from its narrative perspective, most of them illustrated from the aspect which mixed narrator and point of view. This study researched this novella from the perspective of point of view suggested by Prof. Shen Dan to decode author's method of telling a"plausible story".
基金The Global Change Research Program of China under contract No.2015CB953901the National Natural Science Foundation of China under contract Nos 41330960 and 41276193
文摘Sea ice concentration is an important parameter for polar sea ice monitoring. Based on 89 GHz AMSR-E （Advanced Microwave Scanning Radiometer for Earth Observing System） data, a gridded high-resolution passive microwave sea ice concentration product can be obtained using the ASI （the Arctic Radiation And Turbulence Interaction Study （ARTIST） Sea Ice） retrieval algorithm. Instead of using fixed-point values, we developed ASi algorithm based on daily changed tie points, called as the dynamic tie point ASI algorithm in this study. Here the tie points are expressed as the brightness temperature polarization difference of open water and 100% sea ice. In 2010, the yearly-averaged tie points of open water and sea ice in Arctic are estimated to be 50.8 K and 7.8 K, respectively. It is confirmed that the sea ice concentrations retrieved by the dynamic tie point ASI algorithm can increase （decrease） the sea ice concentrations in low-value （high-value） areas. This improved the sea ice concentrations by present retrieval algorithm from microwave data to some extent. Comparing with the products using fixed tie points, the sea ice concentrations retrieved from AMSR-E data by using the dynamic tie point ASI algorithm are closer to those obtained from MODIS （Moderate-resolution Imaging Spectroradiometer） data. In 40 selected cloud-free sample regions, 95% of our results have smaller mean differences and 75% of our results have lower root mean square （RMS） differences compare with those by the fixed tie points.
文摘The wave period probability densities in non-Gaussian mixed sea states are calculated by utilizing a transformed Gaussian process method. The transformation relating the non-Gaussian process and the original Gaussian process is obtained based on the equivalence of the level up-crossing rates of the two processes. A saddle point approximation procedure is applied for calculating the level up-crossing rates in this study. The accuracy and efficiency of the transformed Gaussian process method are validated by comparing the results predicted by using the method with those predicted by the Monte Carlo simulation method.
文摘Seasonal interaction between sea-surface temperature (SST) in the tropical eastern Pacific and ozone layer in Northern Hemisphere, ahd the layer,s teleconnection spatial structure caused by SST effeets, for January and July, are statistically analysed. The result indicates that the areas spacially correlated between SST and ozone layer in January greatly differ from the ones in July and they show opposite tendency in the signs of correlation, so do the teleconnection pattern for the ozone lay6r due to effects of SST in different seasons. In addition, persistent' influence of SST on the ozone layer results insuperposition of seasonal SST effects on the layer and makes it characteristic of well-defined wavetrainsin responses to SST. It is concluded that SST in the tropical eastern Pacific is of great importance to thenorthern ozone layer distribution and its seasonal evolution.
基金financially supported by the "973" project of China (Grant No. 2014CB845902)the NSFC projects(Grant Nos. 41874026, 41374025 and 41621091)
文摘Earthquakes perturb both the ocean bottom topography due to displacements of sea floor and the geoid due to mass redistribution, which induces the relative sea level(RSL) change. However, the relative global mean sea level(GMSL) change is zero in that sea water mass is conserved. But the absolute GMSL change is not zero because earthquakes displace total ocean mass with respect to the Earth’s center of mass(CM) which remains unchanged after an earthquake. This displacement, i.e. the absolute GMSL change, may be detectable by altimetry since the satellites are orbiting around CM. In this paper, we proposed a method to estimate co-seismic absolute GMSL change caused by earthquakes based on the point dislocation theory for a spherically symmetric, non-rotating, elastic and isotropic(SNREI) Earth.This change can be directly connected to the perturbation of ocean bottom topography. We first computed co-seismic displacements as well as the change in geo-potential and solved the sea level equation to validate the insignificance of the oceans’ feedback, i.e. the loading effect due to RSL change, to co-seismic displacements. The results imply that the loading effect due to RSL change is negligible on displacements while is considerable on geoid. We then computed the absolute GMSL change caused by co-seismic vertical and horizontal displacements by making use of the integrated Green’s function method. The numerical results show that a large earthquake may raise the absolute GMSL by magnitude of sub-millimeter and the recent three large events cause GMSL to rise about one millimeter, in which the contribution from horizontal displacement is non-negligible.
文摘The ESMD method can be seen as a new alternate of the well-known Hilbert-Huang transform (HHT) for non-steady data processing. It is good at finding the optimal adaptive global mean fitting curve, which is superior to the common least-square method and running-mean approach. Take the air-sea momentum flux investigation as an example, only when the non-turbulent wind components is well extracted, can the remainder signal be seen as actual oscillations caused by turbulence. With the aid of —5/3 power law for the turbulence, a mode-filtering approach based on ESMD decomposition is developed here. The test on observational data indicates that this approach is very feasible and it may greatly reduce the error caused by the non-turbulent components.
