Interaction of Dust Radiative Forcing and the Asian Summer Monsoon

沙尘辐射强迫与亚洲夏季风的相互作用

• 批准号: 0620066
• 负责人: Ron Miller
• 金额: $ 34.14万
• 依托单位: Columbia University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2006
• 资助国家: 美国
• 起止时间: 2006-10-01 至 2009-09-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0620066&HistoricalAwards=false
• 关键词: Interaction; Dust; Radiative; Forcing; Asian

Wind-blown dust is ubiquitous over the Arabian Sea during the Asian summer monsoon. Absorption of solar radiation within the layer acts as an elevated heat source, which can induce ascent and precipitation. Whether the monsoon circulation is strengthened by aerosols depends upon the response of the Indian Ocean. If surface radiative forcing by aerosols is compensated over the Arabian Sea by a reduction in evaporation, then atmospheric latent heating will decrease and oppose radiative heating within the aerosol layer. In contrast, if the surface forcing is balanced by a reduction in ocean heat export, then evaporation need not decrease and radiative heating within the aerosol layer can strengthen the monsoon without opposition. Consideration of the ocean response resolves an apparent contradiction among previous numerical simulations whereby the monsoon either strengthens or weakens in response to aerosol radiative forcing. When sea surface temperature (SST) is prescribed, a surface energy constraint is absent, and aerosol radiative forcing at the surface is implicitly balanced by a reduction in ocean heat export, allowing a strengthened monsoon. Conversely, the monsoon weakens in most models where SST is calculated and evaporation rather than ocean heat export decreases to balance the reduction of incident sunlight beneath the aerosol layer. To represent the full range of feedbacks between the monsoon, the Indian Ocean, and dust radiative forcing, the Principal Investigators (PIs) will perform experiments with an atmospheric general circulation model (AGCM) coupled to fully interactive models of the ocean circulation and dust aerosol cycle. Unlike other absorbing aerosols, dust concentration is a sensitive function of the climate through the surface wind speed. A previous calculation found that the dust load was increased by strengthened monsoonal winds driven by dust radiative forcing. The simulated relationship will be compared to observations of key variables such as dust amount, wind speed, evaporation, and precipitation over the Arabian Sea, on both daily and seasonal time scales. The daily response to dust is of interest because dust outbreaks are episodic, in contrast to the slow seasonal variations of absorbing aerosols created by pollution. The research will join relatively few previous studies about the interaction of the monsoon and aerosol radiative forcing, and help to understand contrasting results about the effect of aerosols upon the monsoon strength (that result from the effect of prescribed versus calculated SST, for example). Studies considering the particular effect of dust aerosols have so far not considered the effect of ocean heat transport. Calculation of the climate response to dust is necessary to distinguish the global and regional response to anthropogenic forcing by greenhouse gases and other aerosols.Results from the study will be used to improve a publicly available AGCM, including a model of the dust cycle, and will be incorporated into teaching and presentations to general audiences by the PI. By the end of the project, a doctoral student will complete her dissertation under the supervision of the PI.

亚洲夏季季风期间，阿拉伯海上空随风飘扬的沙尘无处不在。该层内太阳辐射的吸收充当升高的热源，可以引起上升和降水。气溶胶是否加强季风环流取决于印度洋的反应。如果通过减少蒸发来补偿阿拉伯海上空气溶胶的表面辐射强迫，那么大气潜热将减少并与气溶胶层内的辐射加热相反。相反，如果表面强迫通过海洋热量输出的减少来平衡，那么蒸发就不需要减少，并且气溶胶层内的辐射加热可以在没有对抗的情况下加强季风。对海洋响应的考虑解决了先前数值模拟中的一个明显矛盾，即季风响应气溶胶辐射强迫而增强或减弱。当规定海面温度（SST）时，不存在表面能量约束，并且表面的气溶胶辐射强迫通过海洋热量输出的减少而隐式平衡，从而使季风增强。相反，在大多数计算海表温度的模型中，季风减弱，并且蒸发而不是海洋热量输出减少，以平衡气溶胶层下方入射阳光的减少。为了代表季风、印度洋和尘埃辐射强迫之间的全方位反馈，首席研究员 (PI) 将使用大气环流模型 (AGCM) 与海洋环流和尘埃气溶胶循环的完全交互模型相结合进行实验。与其他吸收性气溶胶不同，粉尘浓度是气候通过表面风速的敏感函数。先前的计算发现，沙尘辐射强迫驱动的季风增强导致沙尘负荷增加。模拟关系将与阿拉伯海沙尘量、风速、蒸发和降水等关键变量在每日和季节时间尺度上的观测结果进行比较。对灰尘的日常反应很有趣，因为灰尘的爆发是偶发的，而污染产生的吸收气溶胶的季节性变化却很缓慢。这项研究将加入之前相对较少的关于季风和气溶胶辐射强迫相互作用的研究，并有助于了解气溶胶对季风强度影响的对比结果（例如，由规定的海表温度与计算的海表温度的影响产生的结果）。迄今为止，考虑尘埃气溶胶特殊影响的研究尚未考虑海洋热传输的影响。计算对沙尘的气候响应对于区分全球和区域对温室气体和其他气溶胶人为强迫的响应是必要的。研究结果将用于改进公开的 AGCM，包括沙尘循环模型，并将纳入 PI 向普通观众的教学和演示中。项目结束时，博士生将在 PI 的监督下完成论文。