Tuesday, March 27, 2018

Saharan Dust Creates "Snirty" Eurasian Snow

Some remarkable photos and videos of extreme dust storms in the Mediterranean Basin and the mountains of Eurasia have gone viral on Twitter.  To begin, here's how things looked on March 22nd on Crete and March 23rd in Santorini, Greece.

In addition to bad air quality, such storms lead to dust deposition in the mountains of Eurasia, leading to "snirty" snow (a take on part snow part dirt).  The photos below are from the Caucasus Mountains near Sochi, Russia.

Although the most recent event has caught widespread attention, it is the most recent of a series of major dust storms that have impacted the region over the past few weeks. Note, for example, the dust layering in this snow pit from the mountains of Greece, indicative of a series of dust storms.
The loop below is based on daily images collected by the MODIS sensor on NASA's Terra satellite and covers the period from March 1 through March 28th.  You can see a series of dust storms originating over the Sahara with transport across the Mediterranean into southern Europe and in some cases beyond.


Favoring these frequent dust storms has been an anomalously deep upper-level trough centered over western Europe.  This has resulted in frequent cyclogenesis over the Mediterranean basin and associated strong flow over the northern Sahara.



Long range transport of this dust is evident in the MODIS images below for 25, 26, and 27 March.  Note in particular how dust is transported across the Mediterranean from multiple origins and eventually moves downstream over the Black Sea.




These events are of course lousy for skiing, which I sometimes describe as "Snirty Dancing." However, they also play an important role in mountain hydrology.  Dust is dark, and it absorbs more solar radiation than clean snow.  This leads to an earlier and faster snowmelt in areas where dust has been deposited in and on the snowpack.  Even if covered by a layer of fresh snow, as the snow melts, it percolates through the snowpack, withe the dust eventually emerging at the top of the snowpack to affect the solar radiation absorption.

Dust storms also occur frequently in the western United States and play an important role in our snow-driven hydroclimate.  For some discussion of this topic, see our previous post Dusty Snow: The Monster in the Basement.
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2 comments:

  1. AnonymousMarch 28, 2018 at 1:22 PM

    Interesting post regarding dusty snow in Sochi. Thank you. :)

    Do we sometimes get that with blowing dust, early and late season?

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    1. Jim SMarch 28, 2018 at 1:23 PM

      I'm not sure what is meant by "we" but if you mean Utah, we can and do get dust storms. They are most intense and frequent in the spring, but can happen any time of year under the right conditions.

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