Mechanism Of The Multi-scale Variations Of The Spring Ross Ice Shelf Polynya

In the context of global warming,there is a growing interest in polar regions,especially in Antarctica where sea ice exhibits significant regional and seasonal variations.As one of the most typical area where sea ice is increasing,the Ross Sea has recently attracted much attention.Here one common meso-scale phenome in sea ice is polynya.The Ross Ice Shelf Polynya(RISP)is the largest coastal polynya in the Antarctic.It has been discussed in previous study as a major source region of Antarctic bottom water(AABW).During the austral spring and summer,the RISP makes a great contribution to the local high primary production and is regarded as the habitat for krill,whales and penguins.Influenced by synoptic weather and climate modes,the spring RISP shows significant multi-scale variations.However,the related research is still insufficient.Based on satellite observations and reanalysis data,this thesis discusses the multi-scale connection between the spring RISP and atmospheric forcing from 1980 to 2019.The main conclusions are following:(1)The spring RISP area time series depict synoptic scale variations.It shows significant fluctuations and the extreme difference can reach 1×10~5km~2.Influenced by storms or high pressure systems,the variation of the spring RISP growth changes from day to day.When the location or intensity of storms or high pressure systems varies,the related modulation on local dynamical and thermal processes will change.Our results show that the RISP expansion is modulated by the pressure pattern that the low pressure system is located in the southeastern Ross Sea while the high pressure system in the northwestern Ross Sea.This pressure pattern can cause the southwesterly anomaly near the edge of the Ross Ice Shelf,enhancing the northeastward transport of sea ice and resulting a faster expansion of the spring RISP.Usually the intensity of pressure system shows positive relationship with the effects.(2)The spring RISP is featured with the interannual variation in zonal position.We obtained the principal spatial patterns of the spring RISP by using the empirical orthogonal function(EOF)analysis.The leading EOF(EOF1)reflects the zonal variation of the RISP,explaining 48.1%of the variance.The EOF2 depicts the meridional variation with an explained variance of 27.4%.There is also a strong positive correlation between the spring RISP area and the first principal component time series(PC1).And the southwesterly in the east is favorable to the eastward expansion of the RISP.Besides,we discovered the lagged relationship between the spring RISP and the Amundsen Sea Low(ASL).A deeper and more eastward ASL in November often coincides with a larger and more eastward RISP in December.Our results suggest that the preconditioning of sea ice in November provides the key link between the November ASL and the spring RISP.In conclusion,there are different mechanisms between multi-scale variations of the spring RISP and atmospheric forcing.On synoptic scale,the spring RISP has a rapid response to the dynamical forcing,while on interannual scale there is a significant lagged relationship between them.The RISP in November contributes to this result.