What Processes Drive Southern Ocean Sea Ice Variability and Trends? Insights from the Energy Budget of the Coupled Cryosphere-ocean-atmosphere System

该项目将利用观测和耦合气候模式模拟来研究海冰变化的原因。在观测记录中，南大洋的海冰面积有所增加，但研究人员尚未就其原因达成一致。研究人员认为，地表风的变化、上层海洋的清新或海洋/大气内部的变化可能是海冰面积增加的主要驱动因素。这个项目将确定每年海冰面积的变化有多少是由于海洋、大气和辐射过程造成的。将基于观测的认识与海冰变率的模式表示相协调，将提高对南大洋海冰未来变化预估的信心。这项提议的目标是提高我们对推动南大洋海冰逐年变化和长期趋势的过程的理解。这些知识将使我们深入了解过去南大洋海冰如何对温室气体和臭氧强迫作出反应，以及它将如何在未来作出反应。冰冻圈/海洋/大气耦合气候系统的能量收支将作为一个框架来解开海冰损失事件的驱动因素和响应。该技术包括：(1)计算每月时间尺度上气候系统的耦合能量平衡；(2)在观测到的卫星辐射记录中将海冰变率的辐射影响与云变率的辐射影响分离出来；(3)分析大气能量输送的垂直结构，以确定进入大气的能量输送的垂直剖面。这一框架将使研究人员能够区分冰损失事件是由海洋过程、大气动力学还是辐射过程引发的。初步结果表明，在耦合气候模式中，多种机制可以驱动南大洋海冰变率，而观测到的海冰变率似乎主要受大气动力学的支配。在平均状态和特定过程中对模式和观测之间偏差的探索，将对南大洋海冰的未来产生更准确的预测。

This project will use observations and coupled climate model simulations to examine the causes of sea ice variability. Sea ice in the Southern Ocean has increased in area over the observational record but researchers have yet to agree on the cause. Researchers suggests that changes in surface winds, upper-ocean freshening, or internal ocean/atmosphere variability could be the main driver for the increase in sea ice area. This project will determine how much of the change in sea ice area from year to year is due to oceanic, atmospheric, and radiative processes. Reconciling the observation-based understanding with model representations of sea ice variability will improve confidence in projections of future changes in Southern Ocean sea ice.The goal of this proposal is to improve our understanding of the processes that drive Southern Ocean sea ice year-to-year variability and long term trends. This knowledge will provide insight into how Southern Ocean sea ice responded to greenhouse gas and ozone forcing in the past and how it will respond in the future. The energy budget of the coupled cryosphere/ocean/atmosphere climate system will be used as a framework to disentangle drivers and responses during sea ice loss events. The technique consists of: (i) calculating the coupled energy budget of the climate system at the monthly timescale, (ii) isolating the radiative impact of sea ice variability from the radiative impact of cloud variability in the observed satellite radiation record and (iii) analyzing the vertical structure of atmospheric energy transport to determine the vertical profile of energy transport into the atmospheric column. This framework will allow the investigators to distinguish whether ice loss events are triggered by oceanic processes, atmospheric dynamics, or radiative processes. Preliminary results show that a diversity of mechanisms can drive Southern Ocean sea ice variability in coupled climate models whereas observed sea ice variability appears to be dominated by atmospheric dynamics. The exploration of biases between models and observations in both the mean state and in specific processes will yield more accurate projections of the future of sea ice in the Southern Ocean.