Remote sensing products are significant in the data assimilation of an ocean model. Considering the resolution and space coverage of different remote sensing data, two types of sea surface height（SSH） product are em...Remote sensing products are significant in the data assimilation of an ocean model. Considering the resolution and space coverage of different remote sensing data, two types of sea surface height（SSH） product are employed in the assimilation, including the gridded products from AVISO and the original along-track observations used in the generation. To explore their impact on the assimilation results, an experiment focus on the South China Sea（SCS） is conducted based on the Regional Ocean Modeling System（ROMS） and the four-dimensional variational data assimilation（4 DVAR） technology. The comparison with EN4 data set and Argo profile indicates that, the along-track SSH assimilation result presents to be more accurate than the gridded SSH assimilation, because some noises may have been introduced in the merging process. Moreover, the mesoscale eddy detection capability of the assimilation results is analyzed by a vector geometry–based algorithm. It is verified that, the assimilation of the gridded SSH shows superiority in describing the eddy＇s characteristics, since the complete structure of the ocean surface has been reconstructed by the original data merging.展开更多
In this paper, we first analyzed cloud drift wind(CDW) data distribution in the vertical direction, and then reassigned the height of every CDW in the research domain in terms of background information, and finally, c...In this paper, we first analyzed cloud drift wind(CDW) data distribution in the vertical direction, and then reassigned the height of every CDW in the research domain in terms of background information, and finally, conducted contrast numerical experiments of assimilating the CDW data before and after reassignment to examine the impacts on the forecast of the track of Typhoon Chanthu(1003) from 00:00(Coordinated Universal Time) 21 July to 00:00 UTC23 July, 2010. The analysis results of the CDW data indicate that the number of CDWs is mainly distributed in the midand upper-troposphere above 500 h Pa, with the maximum number at about 300 h Pa. The height reassigning method mentioned in this work may update the height effectively, and the CDW data are distributed reasonably and no obvious contradiction occurs in the horizontal direction after height reassignment. After assimilating the height-reassigned CDW data, especially the water vapor CDW data, the initial wind field around Typhoon Chanthu(1003) became more reasonable, and then the steering current leading the typhoon to move to the correct location became stronger. As a result, the numerical track predictions are improved.展开更多
Satellite altimetry has been widely used in measuring ocean topography from space. The conventional altimeter system is the nadir radar altimeter system which has the limitations of one-dimensional measurement and is ...Satellite altimetry has been widely used in measuring ocean topography from space. The conventional altimeter system is the nadir radar altimeter system which has the limitations of one-dimensional measurement and is unable to get both high temporal and spatial resolution. The InSAR altimetry system using InSAR altimeter instead of nadir radar altimeter is an improvement which can get both high cross-track and along-track resolution and wide swath. However, the conventional SAR interferometry only can achieve meter level height accuracy. This paper focuses on a method of radar echo-tracking for InSAR altimeter system in order to correct the slant range measurements and finally to improve the height measurement accuracy to several centimeters＇ level. Radar slant range （from observed pixels to radar antenna） estimation error affects the height measurement accuracy badly, nevertheless not considered in the conventional SAR interferometry. The proposed method is ameliorated based on the traditional echo-model used in nadir radar altimeter system, focusing on the echo signals from observed pixels with different incident angles. Simulations of sea surface height measurements are performed in the last part of this paper, and the conclusions are drawn that, with corrected slant range, the accuracy of InSAR altimetry can be much better than the conventional SAR interferometry.展开更多
Combining with the exigent demand of the development of satellite gravimetry system in China, aiming at the determination of technical indexes of gravity satellite orbit parameters, on the basis of the numerical exper...Combining with the exigent demand of the development of satellite gravimetry system in China, aiming at the determination of technical indexes of gravity satellite orbit parameters, on the basis of the numerical experiments and results analysis, the design indexes of gravity satellite orbit height, inter-satellite range and the orbit inclination are analyzed and calculated, and the issues towards twin gravity satellites such as coherence requirement of the orbit semi-major axes, control requirement of the pitch angle and time interval requirement to keep twin satellites formation in mobility are diseussed. Results show that the satellite orbit height is 400 km to 500 km, the inter-satellite range is about 220 km, the satellite orbit inclination is between polar orbit and sun-synchronous orbit, the semi-major axes difference of twin satellites orbit is within ± 70. 146 m, the pitch angle of twin satellites is about 0.9 degree, and the time interval to keep twin satellites formation in mobility is 7 days to 15 days.展开更多
The characteristics of 200 hPa divergent wind and velocity potential have been analysed for four kinds of tropical cyclone tracks having impact on the SOuth China Sea. It is found that the difference of monsoon circul...The characteristics of 200 hPa divergent wind and velocity potential have been analysed for four kinds of tropical cyclone tracks having impact on the SOuth China Sea. It is found that the difference of monsoon circulation in 200 hPa divergence wind field may affect the medium-range movement characteristics of tropical cyclone tracks. Corresponding to the west Pacific subtropical high,the orientation of 200 hPa secondary convergence line and its extension to the west may indicate the variability of track types.The direction of tropical cyclone movement is 2 longitudes west of and parallel to the 200 hPa secondary divergence line.展开更多
基金The National Key Research and Development Program of China under contract No.2016YFC1401800the National Natural Science Foundation of China under contract Nos 41576176 and 11401140the Key Project of Science and Technology of Harbin Institute of Technology at Weihai of China under contract No.2014 DXGJ14
文摘Remote sensing products are significant in the data assimilation of an ocean model. Considering the resolution and space coverage of different remote sensing data, two types of sea surface height（SSH） product are employed in the assimilation, including the gridded products from AVISO and the original along-track observations used in the generation. To explore their impact on the assimilation results, an experiment focus on the South China Sea（SCS） is conducted based on the Regional Ocean Modeling System（ROMS） and the four-dimensional variational data assimilation（4 DVAR） technology. The comparison with EN4 data set and Argo profile indicates that, the along-track SSH assimilation result presents to be more accurate than the gridded SSH assimilation, because some noises may have been introduced in the merging process. Moreover, the mesoscale eddy detection capability of the assimilation results is analyzed by a vector geometry–based algorithm. It is verified that, the assimilation of the gridded SSH shows superiority in describing the eddy＇s characteristics, since the complete structure of the ocean surface has been reconstructed by the original data merging.
基金Specialized Science Project for Public Welfare Industries(Metrological Sector)(GYHY201206010,GYHY201406009)Science and Technology Planning Project for Guangdong Province(2012A061400012)+3 种基金Program for the 12th Five-Year Economic Development(2012BAC22B00)Natural Science Foundation of China(41075083)Program for Integration and Application of Key Meteorological Techniques from CMA(CMAGJ2012M36)Project from Guangdong Meteorological Bureau(2013A04)
文摘In this paper, we first analyzed cloud drift wind(CDW) data distribution in the vertical direction, and then reassigned the height of every CDW in the research domain in terms of background information, and finally, conducted contrast numerical experiments of assimilating the CDW data before and after reassignment to examine the impacts on the forecast of the track of Typhoon Chanthu(1003) from 00:00(Coordinated Universal Time) 21 July to 00:00 UTC23 July, 2010. The analysis results of the CDW data indicate that the number of CDWs is mainly distributed in the midand upper-troposphere above 500 h Pa, with the maximum number at about 300 h Pa. The height reassigning method mentioned in this work may update the height effectively, and the CDW data are distributed reasonably and no obvious contradiction occurs in the horizontal direction after height reassignment. After assimilating the height-reassigned CDW data, especially the water vapor CDW data, the initial wind field around Typhoon Chanthu(1003) became more reasonable, and then the steering current leading the typhoon to move to the correct location became stronger. As a result, the numerical track predictions are improved.
基金funded by the National Nature Science Foundations of China(41404019,41674026)the open fund of Key Laboratory of Space Utilization,Chinese Academy of Sciences(CSUWX-A-KJ-2016-044)
文摘Satellite altimetry has been widely used in measuring ocean topography from space. The conventional altimeter system is the nadir radar altimeter system which has the limitations of one-dimensional measurement and is unable to get both high temporal and spatial resolution. The InSAR altimetry system using InSAR altimeter instead of nadir radar altimeter is an improvement which can get both high cross-track and along-track resolution and wide swath. However, the conventional SAR interferometry only can achieve meter level height accuracy. This paper focuses on a method of radar echo-tracking for InSAR altimeter system in order to correct the slant range measurements and finally to improve the height measurement accuracy to several centimeters＇ level. Radar slant range （from observed pixels to radar antenna） estimation error affects the height measurement accuracy badly, nevertheless not considered in the conventional SAR interferometry. The proposed method is ameliorated based on the traditional echo-model used in nadir radar altimeter system, focusing on the echo signals from observed pixels with different incident angles. Simulations of sea surface height measurements are performed in the last part of this paper, and the conclusions are drawn that, with corrected slant range, the accuracy of InSAR altimetry can be much better than the conventional SAR interferometry.
基金supported by the National Natural Science Foundation of China(41174026,41104047,41174017)the Key laboratory Foundation of Geo-space Environment and Geodesy of Ministry of Education(11-01-03)
文摘Combining with the exigent demand of the development of satellite gravimetry system in China, aiming at the determination of technical indexes of gravity satellite orbit parameters, on the basis of the numerical experiments and results analysis, the design indexes of gravity satellite orbit height, inter-satellite range and the orbit inclination are analyzed and calculated, and the issues towards twin gravity satellites such as coherence requirement of the orbit semi-major axes, control requirement of the pitch angle and time interval requirement to keep twin satellites formation in mobility are diseussed. Results show that the satellite orbit height is 400 km to 500 km, the inter-satellite range is about 220 km, the satellite orbit inclination is between polar orbit and sun-synchronous orbit, the semi-major axes difference of twin satellites orbit is within ± 70. 146 m, the pitch angle of twin satellites is about 0.9 degree, and the time interval to keep twin satellites formation in mobility is 7 days to 15 days.
文摘The characteristics of 200 hPa divergent wind and velocity potential have been analysed for four kinds of tropical cyclone tracks having impact on the SOuth China Sea. It is found that the difference of monsoon circulation in 200 hPa divergence wind field may affect the medium-range movement characteristics of tropical cyclone tracks. Corresponding to the west Pacific subtropical high,the orientation of 200 hPa secondary convergence line and its extension to the west may indicate the variability of track types.The direction of tropical cyclone movement is 2 longitudes west of and parallel to the 200 hPa secondary divergence line.
