Analysis of the sea-level variability along the Chinese coast and estimation of the impact of a CO2-perturbed atmospheric circulation

Abstract

The relationship between monthly sea-level data measured at stations located along the Chinesecoast and concurrent large-scale atmospheric forcing in the period 1960–1990 is examined. Itis found that sea-level varies quite coherently along the whole coast, despite the geographicalextension of the station set. A canonical correlation analysis between sea-level and sea-levelpressure (SLP) indicates that a great part of the sea-level variability can be explained by theaction of the wind stress on the ocean surface. The relationship between sea-level and sea-levelpressure is analyzed separately for the summer and winter half-years. In winter, one factoraffecting sea-level variability at all stations is the SLP contrast between the continent and thePacific Ocean, hence the intensity of the winter Monsoon circulation. Another factor that affectscoherently all stations is the intensity of the zonal circulation at mid-latitudes. In the summerhalf year, on the other hand, the influence of SLP on sea-level is spatially less coherent: thestations in the Yellow Sea are affected by a more localized circulation anomaly pattern, whereasthe rest of the stations is more directly connected to the intensity of the zonal circulation. Basedon this analysis, statistical models (different for summer and winter) to hindcast coastal sealevelanomalies from the large-scale SLP field are formulated. These models have been testedby fitting their internal parameters in a test period and reproducing reasonably the sea-levelevolution in an independent period. These statistical models are also used to estimate thecontribution of the changes of the atmospheric circulation on sea-level along the Chinese coastin an altered climate. For this purpose the ouput of 150 year-long experiment with the coupled ocean-atmosphere model ECHAM1-LSG has been analyzed, in which the atmospheric concentrationof greenhouse gases was continuously increased from 1940 until 2090, according to theScenario A projection of the Intergovermental Panel on Climate Change. In this experimentthe meridional (zonal) circulation relevant for sea-level tends to become weaker (stronger) inthe winter half year and stronger (weaker) in summer. The estimated contribution of thisatmospheric circulation changes to coastal sea-level is of the order of a few centimeters at theend of the integration, being in winter negative in the Yellow Sea and positive in the China Seawith opposite signs in the summer half-year.