Winds of Change: Exploring the Meteorological Drivers of Global Dust

从旱地扬起的矿物粉尘占空气中颗粒物的很大一部分，据一些人估计，这一比例高达全球颗粒物气溶胶负荷的三分之二。大气多尘的一个原因是，自工业革命以来，大气粉尘浓度急剧增加，这可能是由于开垦、耕作的农田扩大所致。尘埃作为一种大气气溶胶的重要性及其随时间的急剧增加推动了对其气候影响的研究，其中包括通过将阳光反射回太空来降温，通过捕获发出的红外辐射来变暖，以及由于尘埃对云层的影响而产生的间接影响。但这类研究的复杂性在于，当大风吹过干燥的土壤时，矿物粉尘会进入大气，因此零星发生的小范围极端风事件可能会对全球负担做出过大的贡献。小规模极端事件的突出对理解沙尘在气候系统中的作用的努力提出了挑战，特别是依赖于对全球气候模型的长期模拟的努力，而全球气候模式缺乏捕捉小规模风暴所需的分辨率和动力学复杂性。该奖项下的研究考虑了两种类型的风事件在全球沙尘排放中的作用：山区的下坡风暴和大风，以及由坍塌雷暴的下击引起的强直线风事件。这两类风事件都与强烈的尘埃排放有关，都是由当前全球气候模型没有捕捉到的小尺度动力驱动的。该项目利用了跨尺度预测模式(MPAS)的40天模拟，该模式具有精细的分辨率(3.75公里网格间距)和更复杂的动力学，需要用于下坡风暴和飓风。来自MPAS模拟的地面风被作为离线尘埃排放模式的输入，以确定这些事件所排放的尘埃量。第二项研究调整了最先进的气候模型--共同体地球系统模型版本(CESM)，以复制离线尘埃排放实验中产生的尘埃。CESM模拟是为了与观测到的大气环流相一致，以便将尘埃气溶胶浓度及其对气候的影响与真实世界的测量结果进行比较。考虑到空气中扬尘的潜在气候影响、这些影响的巨大不确定性以及人类活动可能导致尘埃浓度大幅变化的程度，这项工作具有社会和科学意义。大气中的灰尘还有其他影响，例如，它降低了空气质量，但它也为海洋生态系统提供了铁和其他营养物质的来源。该项目还包括与圣地亚哥县教育办公室合作，为加州高中科学教师开展教学活动。此外，该项目为研究生和博士后提供支持和培训，从而为这一研究领域的未来劳动力提供支持。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Mineral dust kicked up from dry land accounts for a remarkably large portion of the particulate matter in the air, by some estimates as much as two thirds of the global particulate aerosol burden. One reason for the dustiness of the atmosphere is that atmospheric dust concentration has increased dramatically since the Industrial Revolution, possibly due to the expansion of cleared, tilled, agricultural land. The prominence of dust as an atmospheric aerosol and its dramatic increase over time motivate research on its climatic effects, among them cooling by reflecting sunlight back to space, warming by trapping outgoing infrared radiation, and indirect effects due to the influence of dust on clouds. But such research is complicated by the fact that mineral dust enters the atmosphere when strong winds blow over dry soil, thus extreme wind events occurring sporadically and over small areas can make an outsized contribution to the global burden. The prominence of small-scale extreme events challenges efforts to understand the role of dust in the climate system, especially efforts that rely on long simulations of global climate models which lack the resolution and dynamical sophistication needed to capture small-scale windstorms.Research under this award considers the role of two types of wind events in global dust emissions: downslope windstorms in mountainous regions and haboobs, strong straight-line wind events caused by the downbursts of collapsing thunderstorms. Both types of wind events are associated with strong dust emissions and both are driven by small-scale dynamics that are not captured by current global climate models. The project takes advantage of 40-day simulations of the Model for Predication Across Scales (MPAS), which has the fine-scale resolution (3.75km grid spacing) and more sophisticated dynamics needed for downslope windstorms and haboobs. The surface winds from the MPAS simulations are taken as inputs to an offline dust emission model to determine the amount of dust emitted by these events. A second line of research adjusts a state-of-the-art climate model, the Community Earth System Model version (CESM), to replicate the dust generated in the offline dust emission experiments. The CESM simulations are "nudged" to conform to observed atmospheric circulation so that the dust aerosol concentration and its climate effects can be compared against real-world measurements.The work is of societal as well as scientific interest given the potential climatic effects of airborne dust, the large uncertainty as to those effects, and the extent to which human activity could cause large changes in dust concentration. The dustiness of the atmosphere has other effects, for instance it reduces air quality but it also provides a source of iron and other nutrients for marine ecosystems. The project also includes a collaboration with the San Diego County Office of Education to develop teaching activities for California high school science teachers. In addition, the project provides support and training to a graduate student and a postdoc, thereby providing for the future workforce in this research area.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.