Winds of Change: Exploring the Meteorological Drivers of Global Dust

University Of California-San Diego Scripps Inst Of Oceanography, La Jolla CA

Investigators

Abstract

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.