北极地区是全球气候系统的关键组成部分，在近几十年的气候变化研究中占有重要地位，而云在调节北极的地表辐射能量平衡和物质平衡中发挥着至关重要的作用。北极夏季海冰减少意味着开放水域面积的增加，为发展北极航运路线提供了有利条件；北极格陵兰冰盖(Greenland Ice Sheet, GrIS)的融化也对全球海平面上升有着重要影响。研究北极环境变化，尤其是北极海冰和GrIS上空云的变化，对于理解地球气候系统变化和制定相关应对策略具有重大意义。

本论文通过使用卫星遥感数据和再分析气象资料，系统研究了夏季北极海冰区域及GrIS区域海冰与云的时空分布特性及其年际变化趋势，并探讨了海冰、云与特定大气环流模式之间的关系。此外，本论文还分析了夏季GrIS区域不同相态云在地表/大气层顶(Top of Atmosphere, TOA)的辐射效应，发现了云在高反照率表面上的短波增暖效应。本论文的主要结论如下：

（1）北极云频率在波佛特海和楚科奇海区域(3-4.5%/10年)有明显的增加，导致了云辐射效应(Cloud Radiative Effect, CRE)的相应变化。虽然云辐射强迫同时具有短波冷却效应与长波增暖效应，但其在北极地区的变化趋势为冷却效应增强。自1979年来，北极海冰的融化开始日期提前，而冻结开始日期推迟，表明北极海冰正在快速衰退。北极9月份海冰的密度和厚度显示出了显著的下降趋势，尤其是在北冰洋的太平洋扇区。因此，北极夏季云频率的增加在一定程度上可以降低全球变暖背景下北极海冰的衰退趋势。

（2）通过个例研究和合成分析，本论文研究了夏季CRE对海冰快速变化的反馈作用，并分析了它们与北极偶极子(Dipole Anomaly, DA)异常的关系。本论文将北极海冰在1979-2021年期间的衰退分为三个阶段：小幅振荡期(1979-1989)、大幅振荡期(1990-1999)和振荡衰退期(2000-2021)，并通过研究振荡衰退期的三个典型案例，发现了海冰衰退与DA异常之间的关联。DA异常期间，大气环流场的变化影响了云频率和CRE的变化，继而对9月海冰厚度的衰退起到了减缓作用。本论文通过分析DA正事件与负事件之间的差异，发现夏季CRE对波佛特海海冰厚度有+12.9 cm的影响，而9月波佛特海海冰厚度总变化为−58.8 cm；在楚科奇海为+1.9 cm(­总变化为−36.6 cm)；东西伯利亚海为+22.6 cm(总变化为−48.5 cm)；格陵兰海为−27.3 cm(总变化为+42.4 cm)。

（3）通过综合多源云数据产品，本研究分析了GrIS夏季云的时空分布特征和变化规律，并探索了不同相态云在GrIS上空的空间分布、地表辐射强迫，以及在北大西洋涛动(North Atlantic Oscillation, NAO)正负位相间的差异。与NAO负相位相比，NAO正相位期间西风在GrIS中西部地区增强，导致冰云和液态云频率上升，地表CRE增加+2.07 W/m²；中央区域温度下降，冰云比例上升，液态云频率下降，导致净辐射强迫为−2.05 W/m²；中东部地区出现下沉气流，冰云和液态云频率都有所减少，地表净CRE为−1.34 W/m²。GrIS上空不同相态的云变化与NAO密切相关，NAO期间云对大气环流场变化的响应在GrIS的不同区域表现出差异。

（4）发现GrIS高反照率下垫面上空云短波辐射强迫的增温效应，与传统认知的云短波辐射冷却效应相反。本论文通过分析2000-2022年夏季GrIS区域的TOA云短波辐射效应空间分布发现，单层云的TOA短波辐射强迫可以在GrIS边缘区域造成+20-50 W/m²的TOA净辐射强迫。进一步研究发现，当表面反照率与TOA反射率之比(定义为R_S/T值)超过1.42时，TOA短波CRE为正值。因此，不仅仅对GrIS，对全球具有足够高地表反照率的地方(例如南极大陆、青藏高原，以及“雪球地球”时期地球上绝大部分区域)，或云光学厚度较薄(TOA反射率较低)时，TOA处短波CRE将有可能高于0，对整个地-气系统产生短波增暖效应。

The Arctic region is a crucial component of the global climate system and has been a focus region for climate change studies during recent decades. Clouds play a vital role in regulating the surface radiation balance and material balance over the Arctic. Associated with the reduction of summer Arctic sea ice, the increase of open water areas provides favorable conditions for the development of Arctic shipping routes; the melting of the Greenland Ice Sheet (GrIS) also has a significant impact on global sea-level rise. Investigating the spation-temporal characteristics of Arctic environment, particularly the variations of Arctic sea ice and clouds over particular regions such as the GrIS, is of great significance for understanding the Earth's climate system and policy making related to climate change.

This study systematically investigates the spatiotemporal distribution characteristics and interannual variation trends of sea ice and clouds over the Arctic sea ice region and the Greenland ice sheet area using satellite remote sensing data and reanalysis data products. It also explores the relationships between sea ice, clouds, and specific atmospheric circulation patterns. Additionally, this study examines the surface/top-of-atmosphere (TOA) radiative effects of different cloud phases over the GrIS area and identifies the shortwave warming effect of clouds on high albedo surfaces. The main conclusions of this study are as follows:

(1) There has been a noticeable increase in cloud frequency in the Beaufort and Chukchi Sea regions (3-4.5% per decade), leading to corresponding changes in the Cloud Radiative Effect (CRE). Although cloud radiative forcing has both shortwave cooling and longwave warming effects, the trend in the Arctic region is towards an enhanced cooling effect. Since 1979, the onset of Arctic sea ice melt has advanced, while the freeze-up start date has been delayed, indicating a rapid decline in Arctic sea ice. The density and thickness of Arctic sea ice in September have shown a significant decreasing trend, especially in the Pacific sector of the Arctic Ocean. Therefore, the increase in cloud frequency during the Arctic summer can, to some extent, mitigate the declining trend of Arctic sea ice under the backdrop of global warming.

(2) Through case study analysis and composite analysis, this study investigates the feedback effects of summer Cloud Radiative Effect (CRE) on rapid sea ice changes and analyzes their relationship with the Arctic Dipole Anomaly (DA). The study categorizes the decline of Arctic sea ice from 1979 to 2021 into three stages: a period of minor oscillations (1979-1989), a period of major oscillations (1990-1999), and a period of oscillatory decline (2000-2021). By examining three typical cases during the oscillatory decline period, a link between sea ice decline and DA anomalies was identified. During DA anomaly periods, changes in atmospheric circulation fields affected cloud frequency and CRE, subsequently mitigating the decline of sea ice thickness in September. The study reveals that summer CRE has a +12.9 cm impact on Beaufort Sea ice thickness, with the total change in September being −58.8 cm; in the Chukchi Sea, the impact is +1.9 cm (with a total change of −36.6 cm); in the East Siberian Sea, +22.6 cm (with a total change of −48.5 cm); and in the Greenland Sea, −27.3 cm (with a total change of +42.4 cm) by analyzing the differences between positive and negative DA events.

(3) By integrating multi-source cloud data products, this study analyzes the spatiotemporal distribution characteristics and variation patterns of summer clouds and explores the spatial distribution of clouds in different phases over GrIS, surface radiative forcing, as well as the differences between positive and negative phases of the North Atlantic Oscillation (NAO). Compared to the negative phase of the NAO, during the positive phase, westerly winds in the central-western region of GrIS intensify, leading to an increase in the frequency of ice and liquid-bearing clouds, and an increase in surface Cloud Radiative Effect (CRE) by +2.07 W/m²; the central region experiences a temperature drop, an increase in the proportion of ice clouds, a decrease in the frequency of liquid-bearing clouds, resulting in a net radiative forcing of −2.05 W/m²; in the central-eastern region, subsidence airflows occur, reducing the frequency of both ice and liquid-bearing clouds, with a net surface CRE of −1.34 W/m². The cloud changes over GrIS in different phases are closely related to the NAO, and the cloud response to changes in the atmospheric circulation field during the NAO exhibits regional differences over GrIS.

(4) A warming effect of shortwave radiative forcing by clouds over the high albedo surfaces of the GrIS was identified, contrary to the traditionally understood shortwave radiative cooling effect of clouds. This study, by analyzing the spatial distribution of TOA cloud shortwave radiative effects oved GrIS during the summers of 2000-2022, found that single-layer cloud TOA shortwave radiative forcing can cause a TOA net radiative forcing of +20-50 W/m² in the peripheral areas of GrIS. Further research revealed that when the ratio of surface albedo to TOA reflectance (defined as R_S/T) exceeds 1.42, the TOA shortwave Cloud Radiative Effect (CRE) is positive. Therefore, not only over GrIS, but in any region globally with sufficiently high surface albedo (such as the Antarctic continent, the Tibetan Plateau, and most areas of the Earth during the "Snowball Earth" periods), or when cloud optical thickness is thin (TOA reflectance is low), the TOA shortwave CRE could exceed 0, producing a shortwave warming effect on the entire Earth-atmosphere system.