Data assimilation is the process by which measurements and model predictions are combined to obtain an accurate representation of the state of the modeled system. We implemented a data assimilation scheme called LETKF...Data assimilation is the process by which measurements and model predictions are combined to obtain an accurate representation of the state of the modeled system. We implemented a data assimilation scheme called LETKF (local ensemble transform Kalman filter) with FSUGSM (Florida State University Global Spectral Model) and made an experiment to evaluate the initial condition generated to numerical weather prediction to FSUGSM model. The LETKF analysis carries out independently at each grid point with the use of "local" observations. An ensemble of estimates in state space represents uncertainty. The FSUGSM is a multilevel (27 vertical levels) spectral primitive equation model, where the variables are expanded horizontally in a truncated series of spherical harmonic functions (at resolution T63) and a transform technique is applied to calculate the physical processes in real space The assimilation cycle runs on the period 01/01/2001 to 31/01/2001 at (00, 06, 12 and 18 GMT) for each day. We examined the atmospheric fields during the period and the OMF (observation-minus-forecast) and the OMA (observation-minus-analysis) statistics to verify the analysis quality comparing with forecasts and observations. The analyses present stability and show suitable to initiate the weather predictions.展开更多
Today's math education basic syllabus gives an ever increasing emphasis to Geometry and Patterns. Curricula also advocate an approach that allows student to understand the concepts involved supported by dynamical com...Today's math education basic syllabus gives an ever increasing emphasis to Geometry and Patterns. Curricula also advocate an approach that allows student to understand the concepts involved supported by dynamical computer tools. However, there is not much research work joining these paradigms. Therefore, a case study was developed, with 9th grade students (14-15 years old), to evaluate the impact of a creative approach to isometries and symmetries-friezes, rosaceas (rosettes) and wallpapers-centered in patterns (reproduction, continuation, completion, description and creation) and using Geometer's Sketchpad software to solve, mainly in pairs, and discuss, with the whole class, the challenging tasks proposed, involving the formulation of hypothesis, argumentation and justification of the reasoning. The statistical analysis of the quantifiable data and content analysis of the qualitative data, collecting trough enquiry, direct observation and documental analysis (involving questionnaires, field notes, logbook, pre-tests and post-test, other works of the students including those computer related, and internal documents of the school) enable to conclude positively regarding the main research question underlying the study. In fact, it led to the conclusion that the teaching strategy implemented has contributed to deepen the student's knowledge and skills on geometry, mathematical communication and autonomy as well as to develop a closer relation with the field of geometry itself. This article focuses on one of the cases studied. The pair was selected due to be representative of most students and due to their communication skills.展开更多
Decadal prediction experiments of Beijing Climate Center climate system model version 1.1 (BCC- CSM1.1) participated in Coupled Model Intercomparison Project Phase 5 (CMIPS) had poor skill in extratropics of the N...Decadal prediction experiments of Beijing Climate Center climate system model version 1.1 (BCC- CSM1.1) participated in Coupled Model Intercomparison Project Phase 5 (CMIPS) had poor skill in extratropics of the North Atlantic, the initialization of which was done by relaxing modeled ocean temperature to the Simple Ocean Data Assimilation (SODA) reanalysis data. This study aims to improve the prediction skill of this model by using the assimilation technique in the initialization. New ocean data are firstly generated by assimilating the sea surface temperature (SST) of the Hadley Centre Sea Ice and Sea Surface Temperature (HadlSST) dataset to the ocean model of BCC-CSM1.1 via Ensemble Optimum Interpolation (EnOI). Then a suite of decadal reforecasts launched annually over the period 1961- 2005 is carried out with simulated ocean temperature restored to the assimilated ocean data. Comparisons between the re-forecasts and previous CMIP5 forecasts show that the re-forecasts are more skillful in mid-to-high latitude SST of the North Atlantic. Improved prediction skill is also found for the Atlantic multi-decadal oscillation (AMO), which is consistent with the better skill of Atlantic meridional overturning circulation (AMOC) predicted by the re-forecasts. We conclude that the EnOl assimilation generates better ocean data than the SODA reanalysis for initializing decadal climate prediction of BCC-CSM1.1 model.展开更多
文摘Data assimilation is the process by which measurements and model predictions are combined to obtain an accurate representation of the state of the modeled system. We implemented a data assimilation scheme called LETKF (local ensemble transform Kalman filter) with FSUGSM (Florida State University Global Spectral Model) and made an experiment to evaluate the initial condition generated to numerical weather prediction to FSUGSM model. The LETKF analysis carries out independently at each grid point with the use of "local" observations. An ensemble of estimates in state space represents uncertainty. The FSUGSM is a multilevel (27 vertical levels) spectral primitive equation model, where the variables are expanded horizontally in a truncated series of spherical harmonic functions (at resolution T63) and a transform technique is applied to calculate the physical processes in real space The assimilation cycle runs on the period 01/01/2001 to 31/01/2001 at (00, 06, 12 and 18 GMT) for each day. We examined the atmospheric fields during the period and the OMF (observation-minus-forecast) and the OMA (observation-minus-analysis) statistics to verify the analysis quality comparing with forecasts and observations. The analyses present stability and show suitable to initiate the weather predictions.
文摘Today's math education basic syllabus gives an ever increasing emphasis to Geometry and Patterns. Curricula also advocate an approach that allows student to understand the concepts involved supported by dynamical computer tools. However, there is not much research work joining these paradigms. Therefore, a case study was developed, with 9th grade students (14-15 years old), to evaluate the impact of a creative approach to isometries and symmetries-friezes, rosaceas (rosettes) and wallpapers-centered in patterns (reproduction, continuation, completion, description and creation) and using Geometer's Sketchpad software to solve, mainly in pairs, and discuss, with the whole class, the challenging tasks proposed, involving the formulation of hypothesis, argumentation and justification of the reasoning. The statistical analysis of the quantifiable data and content analysis of the qualitative data, collecting trough enquiry, direct observation and documental analysis (involving questionnaires, field notes, logbook, pre-tests and post-test, other works of the students including those computer related, and internal documents of the school) enable to conclude positively regarding the main research question underlying the study. In fact, it led to the conclusion that the teaching strategy implemented has contributed to deepen the student's knowledge and skills on geometry, mathematical communication and autonomy as well as to develop a closer relation with the field of geometry itself. This article focuses on one of the cases studied. The pair was selected due to be representative of most students and due to their communication skills.
基金supported by the National Program on Key Basic Research Project of China(2012CB955203,2016YFA0602100,2013CB430202,2016YFA0602200 and 2016YFE0102404)Tsinghua University Initiative Scientific Research Program(20131089357)
文摘Decadal prediction experiments of Beijing Climate Center climate system model version 1.1 (BCC- CSM1.1) participated in Coupled Model Intercomparison Project Phase 5 (CMIPS) had poor skill in extratropics of the North Atlantic, the initialization of which was done by relaxing modeled ocean temperature to the Simple Ocean Data Assimilation (SODA) reanalysis data. This study aims to improve the prediction skill of this model by using the assimilation technique in the initialization. New ocean data are firstly generated by assimilating the sea surface temperature (SST) of the Hadley Centre Sea Ice and Sea Surface Temperature (HadlSST) dataset to the ocean model of BCC-CSM1.1 via Ensemble Optimum Interpolation (EnOI). Then a suite of decadal reforecasts launched annually over the period 1961- 2005 is carried out with simulated ocean temperature restored to the assimilated ocean data. Comparisons between the re-forecasts and previous CMIP5 forecasts show that the re-forecasts are more skillful in mid-to-high latitude SST of the North Atlantic. Improved prediction skill is also found for the Atlantic multi-decadal oscillation (AMO), which is consistent with the better skill of Atlantic meridional overturning circulation (AMOC) predicted by the re-forecasts. We conclude that the EnOl assimilation generates better ocean data than the SODA reanalysis for initializing decadal climate prediction of BCC-CSM1.1 model.