Analysis of Lhù’ààn Mân’ (Kluane Lake) dust plumes using passive and active ground-based remote sensing supported by physical surface measurements
Abstract. There is growing recognition that high latitude dust (HLD), originating from local, drainage-basin flows, is the dominant source for certain important phenomena such as particle deposition on snow / ice. The analysis of such local plumes (including a better exploitation of remote sensing data) has been targeted as a key aerosol issue by the HLD community. The sub-Arctic Lhù’ààn Mân’ (Kluane Lake) region in the Canadian Yukon is subject to regular drainage, wind-induced dust plumes. This dust emission site is one of many current and potential proglacial dust sources in the Canadian North. In situ ground-based measurements are, due to constraints in accessing these types of regions, rare. Ground- and satellite-based remote sensing accordingly play an important role in helping characterize local dust sources in the Arctic and sub-Arctic.
We compared ground-based, passive and active remote sensing springtime (May 2019) retrievals with microphysical surface-based measurements in the Lhù’ààn Mân’ region in order to better understand the potential for ground- and satellite-based remote sensing of HLD plumes. This included correlation analyzes between ground-based coarse mode (CM) aerosol optical depth (AOD) retrievals from AERONET AOD spectra, CM AODs derived from co-located Doppler lidar profiles and OPS (Optical Particle Sizer) surface measurements of CM particle-volume concentration (vc (0)). An automated dust classification scheme was developed to objectively identify local dust events. The classification process helped distinguish lidar-derived CM AODs which co-varied with vdust (0) (during recognized dust events) and those that varied at the same columnar scale as AERONET-derived CM AOD (and thus could be remotely sensed). False positive cloud events for which dust-induced, high frequency variations in lidar-derived CM AODs in cloudless atmospheres indicated that the AERONET cloud-screening process was rejecting CM dust AODs. The persistence of a positive lidar ratio bias in comparing the CIMEL/lidar-derived value with a prescribed value obtained from OPS-derived particle sizes coupled with dust-speciation-derived refractive indices led to the suggestion that the prescribed value could be increased to optically-derived values of 20 sr by the presence of optically significant dust particles at an effective radius of 11–12 µm. Bimodal CM PSDs from full-fledged AERONET inversions (the combination of AOD spectra and almucantar radiances) also showed CM peaks at ~ 1.3 µm and 5–6.6 µm radius: this, we argued, was associated with springtime Asian dust and Lhù’ààn Mân’ dust, respectively. Correlations between the CIMEL-derived fine mode (FM) AOD and FM OPS-derived particle-volume concentration suggest that remote sensing techniques can be employed to monitor FM dust (which is arguably a better indicator of the long-distance transport of HLD).
