A multi-scale high-order recursive filter approach for the sea ice concentration analysis

With the development and deployment of observation systems in the ocean,more precise passive and active microwave data are becoming available for the weather forecasting and the climate monitoring.Due to the complicated variability of the sea ice concentration(SIC)in the marginal ice zone and the scarcity of high-precision sea ice data,how to use less data to accurately reconstruct the sea ice field has become an urgent problem to be solved.A reconstruction method for gridding observations using the variational optimization technique,called the multi-scale high-order recursive filter(MHRF),which is a combination of Van Vliet fourth-order recursive filter and the three-dimensional variational(3D-VAR)analysis,has been designed in this study to reproduce the refined structure of sea ice field.Compared with the existing spatial multi-scale first-order recursive filter(SMRF)in which left and right filter iterative processes are executed many times,the MHRF scheme only executes the same filter process once to reduce the analysis errors caused by multiple filters and improve the filter precision.Furthermore,the series connected transfer function in the high-order recursive filter is equivalently replaced by the paralleled one,which can carry out the independent filter process in every direction in order to improve the filter efficiency.Experimental results demonstrate that this method possesses a good potential in extracting the observation information to successfully reconstruct the SIC field in computational efficiency.

China Ocean ReAnalysis(CORA)version 1.0 products and validation for 2009-18

China Ocean ReAnalysis(CORA) version 1.0 products for the period 2009-18 have been developed and validated.The model configuration and assimilation algorithm have both been updated compared to those of the 51-year(1958-2008) products.The assimilated observations include temperature and salinity field data,satellite remote sensing sea surface temperature,and merged sea surface height(SSH) anomaly data.The validation includes the following three aspects:(1) Temperature,salinity,and SSH anomaly root-mean-square errors(RMSEs) are computed as a primary evaluation of the reanalysis quality.The 0-2000 m domain-averaged RMSEs of temperature and salinity are 0.61℃ and 0.08 psu,respectively.The SSH anomaly RMSE is less than 0.2 m in most regions.(2) The 35°N temperature section is used to evaluate the ability to reproduce the thermocline,mixing layer,and Yellow Sea cold water mass.In summer,the thermocline is reinforced,with the gradient changing from 3℃ in May to 10℃ in August.The mixing-layer depth reproduced by CORA is consistent with that computed from the observed climatology.The Yellow Sea cold water mass forms at a depth of 50 m.(3) The reanalysis current is examined against the tracks of some drifting buoys.The results show that the reanalysis current can capture the mesoscale eddies near the Kuroshio,which are similar to those described by the drifting buoys.Overall,the 2009-18 CORA reanalysis products are capable of reproducing major oceanic phenomena and processes in the coastal waters of China and adjacent seas.

Climate change and China's coastal zones and seas:Impacts,risks,and adaptation

This article provides an assessment of the changes in marine climate drivers(hazards),associated impacts,risks,and adaptation to the coastal China zones and seas since the mid 20th century.The results show that:①Marine climate drivers,such as ocean warming,sea level rise,typhoon,storm surges and marine heat waves(MHWs),have increased significantly in strength,frequency and range over the past decades.②Ocean warming has caused substantial changes in marine phenology,species composition,geographical distribution,and frequent occurrences of ecological disasters such as red tides,green tides,and macro-jellyfish outbreaks,while MHWs have induced degradation in tropical coral reefs and major losses in the marine aquaculture industry in the coastal China seas.③Sea level rise threatens the typical habitats of coastal wetlands such as mangrove and estuaries,and exacerbates coastal erosion,seawater intrusion and the impacts of typhoon,storm surges on the coastal flood disasters.④Human activities,such as large-scale reclamation,pollutant discharge,and overfishing,have increased the exposure and vulnerability of China's marine and coastal ecosystems,leading to the low-aging and miniaturization of fishery types,decline of offshore fishery resources,reduction of coastal wetland areas,and degradation of biodiversity and ecosystem stability.⑤Under different climate scenarios such as low and high greenhouse gases emission scenario(RCP 2.6 and 8.5),as the warming and sea level rise in the coastal China seas continue,extreme sea level(ESL)events will occur more frequently,e.g.,by the end of this century,the current once per century ESL events will become annually or even annually less(RCP 8.5)in many coastal areas,such as at Lvsi and Xiamen tidal gauge stations;and the ESL events could pose serious risks on the coastal areas.Finally,the article further discusses the adaptation measures and related uncertain issues to address climate change in the coastal China zones and seas,and puts forward relevant countermeasures and suggestions in order to reduce its negative impacts on the sustainable development of human community.

A new presentation of the Indian Ocean shallow overturning circulation from a vertical perspective

The calculation of the meridional overturning streamfunction in the southern Indian Ocean is biased by the Indonesian Throughflow.Therefore,this study applies the vertical overturning streamfunction to diagnose the shallow overturning circulation in the Indian Ocean.Using the Ocean General Circulation Model for the Earth simulator output,improvements with the vertical overturning streamfunction compared with the meridional overturning streamfunction are explored.The results show that the vertical overturning streamfunction smoothly connects the shallow overturning circulations of the northern Indian Ocean and the southern Indian Ocean with the whole cycle of the subtropical cell and the cross-equatorial cell.The vertical overturning streamfunction shows a much cleaner shallow overturning circulation,which is underestimated by the meridional overturning streamfunction.It shows that the shallow overturning circulation has a magnitude of~13 Sv(1 Sv≡106 m 3 s−1),of which the subtropical cell accounts for~8 Sv.In addition,the vertical overturning streamfunction captures a clockwise overturning cell in the upper 600 m layer between 30°S and 34°S.This cell has a magnitude of about−5 Sv and probably corresponds to the wind-forced subtropical gyre.Therefore,the vertical overturning streamfunction provides a new approach for estimating the shallow overturning circulation in the Indian Ocean.