Mountain Wind Mechanisms Driving High-Latitude Dust Emissions in the Yukon Territories, Canada.

Abstract:

Following a period of rapid geomorphological upheaval, induced by glacial retreat, the Ä’äy Chù (Slims River) valley has demonstrated an increase in the frequency and magnitude of dust emission beyond historical activity, marking this site as ideal to explore the dynamics of aeolian erosion from a high-latitude, inland dust source. The propensity and number of high-latitude dust sources are under-estimated at only ~5% of the global, resulting from remote locations with persistent cloud cover, small emission source regions, and mesoscale flow mechanisms. Two seasonal fieldwork campaigns have currently been undertaken in this location, deploying sonic anemometry alongside fast-response optical particle counters (0.28 – 10 µm), supported by additional meteorological, ground-based lidar and sun/moon photometer monitoring. Investigation of the influence of synoptic-scale flows on surface winds during May 2019 emission events through in situ and ERA5 reanalysis data show poor temporal correlation, indicating that dust activity is strongly driven by mesoscale flows through the valley. Down-valley thermal winds dominate the surface wind record almost entirely, with the valley exhibiting a characteristic diurnal variation in wind speed, peaking in the early evening. Incidences of up-valley emissions are infrequent but of comparable magnitude and are likely driven by mesoscale contributions from surrounding valley systems. Event-based analysis revealed peak 10-minute averaged PM10 concentrations on the order of 10⁴ µg m^-3 and particle concentrations of over 900,000 cm^-3 min^-1. This preliminary analysis of the flow mechanisms that characterize this source region identifies surface wind systems driven by mesoscale processes poorly related to synoptic-level systems. The current under-estimation of dust emissions from high-latitude sources is supported by these results, which indicate that a mesoscale level analysis of potential high-latitude sources is needed to better constrain the likely larger and increasing, in a warming world, importance that these sources will contribute to the global aerosol loading.