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Lanzhou University (2022)

Precipitation Change and Its Related Mechanism in Semi-arid Region of Middle Latitude in Northern Hemisphere

朱开玮

Titre : Precipitation Change and Its Related Mechanism in Semi-arid Region of Middle Latitude in Northern Hemisphere

Auteur : 朱开玮

Grade : Master 2022

Université : Lanzhou University

Résumé partiel
The semi-arid region is one of the regions with the largest contribution to global warming,the fastest expanding,and the most ecologically fragile.As one of the key variables in semi-arid regions,the changes of precipitation has been widely concerned and many research achievements have been obtained.However,due to the unique of the climate in semi-arid regions,precipitation in semi-arid regions is crucial for regional ecological recovery and economic development.We studied the four typical semi-arid regions in the Northern Hemisphere separately,and analyzed the characteristics of precipitation changes in each semi-arid region,explained the dynamic mechanism of precipitation changes in each semi-arid region one by one.The future precipitation changes in some semi-arid regions are predicted by some conclusions derived from our study combined with CMIP6 model,and the main points show that :(1)In the past 30 years,Atlantic Multidecadal Oscillation(AMO)has changed from negative phase to positive phase,which led to a decrease of precipitation in the regions with annual precipitation below 400 mm and an increase of precipitation in the regions with annual precipitation above 400 mm in the semi-arid regions of the Northern Hemisphere.Therefore,AMO can have an important impact on decadal precipitation variability in most semi-arid regions of the Northern Hemisphere.Precipitation in most of the semi-arid regions of the Northern Hemisphere showed the same variability characteristics during two different AMO cycles,1901-1963 and 1964-2016.This indicates that AMO maintains a long-term and stable relationship with precipitation in these parts of the semi-arid regions.Besides,the closer to the North Atlantic Ocean,the faster the response of precipitation and the stronger the relationship between precipitation and AMO.(2)The influence of AMO on precipitation in semi-arid regions is through atmospheric circulation system.In summer,during the positive phases of AMO,the northerly winds from the western part of the North Atlantic cyclonic circulation anomaly meet the southerly winds from the eastern part of the North American continental cyclonic circulation anomaly,causing anomalous low-level divergence and making the precipitation in the semi-arid region of North America decrease.Meanwhile,the decrease of sea level pressure in the North Atlantic extends to the African continent,which will enhance the Saharan thermal low pressure,thus enhancing the North African summer monsoon and causing the precipitation in the semi-arid region of North Africa to increase.In contrast,a roughly opposite flow field occurs during the negative phases of the AMO,leading to opposite changes in precipitation in the semi-arid regions of North America and North Africa.It is predicted by the E3SM-1-1 model that the AMO will be in negative phase in the next decade,and the precipitation in the southern part of semi-arid region in North America will increase by more than 20 mm,and the precipitation in the whole semi-arid region of North Africa will decrease by more than20 mm

Mots clés : precipitation variation ;semi-arid region ;mechanism;atmospheric circulation ;CMIP6 model ;

Présentation (CNKI)

Page publiée le 24 octobre 2022