Remote sensing of a high-Arctic, local dust event over Hazen (, , )

Keyvan Ranjbar, Norm T. O'Neill, Liviu Ivanescu, James King, Patrick L. Hayes

Invited presentation, HLD workshop, Reykjavik, Iceland, Feb 11, 2021 Dust aerosols in the high Arctic

 Examples

Dust event over the golf of Alaska

Dust Activity occurs anywhere along a ~1,000 miles coastline.

Icelandic Dust

Dust is an important contributor to the radiation budget in the Arctic

Dust activity in Iceland

2 Study site:

Lake Hazen:

The Arctic's largest lake, by volume (51.4 km3)

Located on Ellesmere Island

About 300 km northeast of our PEARL* observatory at Eureka

* Polar Environment Atmospheric Research Lab 3 4 Drainage Winds over Lake Hazen

 We used a 12-year (1988–1999) Lake Hazen climate data set

 Predominance of calm winds most of the time with distinct high wind events: those events likely associated with topographically induced drainage.

 The ensemble wind velocity results shows that during the month of May, daily wind speeds greater than 4 and 7 m/s occur 6.5 and 4.0% of the time, respectively.

5 Identification of the dust plume

 MISR different angle view  MISR employs nine discrete cameras pointed at fixed angles  The position of the plume from the forward to the aft camera moves progressively from the top to the bottom of the image  We can literally see the plume moving!

6 Identification of the dust plume

Brightness Temperature (BT) Differences:

 BTD11-12 blinking with MODIS true colour image  A clear (negative) minimum in the neighborhood of the thickest portion of the RGB plume can be observed.

 Negative BTD11-12 is a robust indicator of a dust plume.

7 Dust plume height retrieval

 Aerosol plume retrieval heights based on MISR stereoscopy

 The maximum dust plume height was around 1.4 km

 The purple dashed line shows the orbit line of the CALIOP profile

MISR true-colour image 8 Dust plume height retrieval

 Zero-wind heights (red points)

 Wind-corrected heights (blue rectangles)

 Terrain height (green line)

 High total attenuated backscatter and intermediate depolarization ratio (~ 0.3) helped* to confirm the existence of the dust plume

* in conjunction with MODIS and MISR imagery evidence

9 Characterization of dust properties  The MODIS, CALIOP, CALIOP/ CloudSat and DARDAR retrieval process failed to classify the dust nature of the plume  We estimated the dust optical depth (DOD)

and effective particle radius (reff) of the upper plume particles  We employed the DARDAR retrievals as a baseline from which uncertainties could be calculated  This yielded:  A 532 nm DOD of ~ 0.5 ± 0.2

 reff ~ 15 - 25 mm (“giant” dust particles)

10  We compared the MODIS imagery (19

May 2014) with the Woo et al’s

AVHRR-derived map of snow-melt

zones on the Fosheim Pennisula

(AVHRR 1 km resolution imagery, 17

May 1990).

 The MODIS imagery blinking with

Woo et al’s AVHRR-derived map shows

remarkable spatial correlation with their

“dark spots” taken 24 years earlier Conclusions

 Successful application of diverse RS techniques to detect a low-altitude dust plume using a diverse array of passive and active, satellite-based RS techniques.

 We exploited MISR multi-angle imaging capabilities and multi-spectral imaging capabilities (MODIS) as well as the particle size dependant profiling capabilities of the CALIOP lidar and the CloudSat radar to identify, localize and characterize the key physical and optical properties of the dust.

 This process was accomplished in spite of the fact that the remote sensing products of all these sensors were not adapted to Arctic conditions.

12 Conclusions

 We are not aware of any published RS investigations of local Arctic dust: RS measuring conditions over a complex surface of snow, ice and deposited dust are marginal at best.

 We succeeded in characterizing the upper plume thickness in terms of a 532 nm DOD (~ 0.5 ± 0.2 ) and a

reff typical of “large” dust particles (between 15 and 25 mm radius).

 We produced MODIS-derived imagery over Lake Hazen and Ellesmere Island that demonstrated the browning (albedo reducing) effects that were likely due to drainage-flow dust events;

 The impact of absorbing dust on snow and ice melt at high-latitudes has been recognized as a potentially important positive feedback effect

13 Thanks!

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