Radiative and hydrologic forcings of
desert dust in mountain snow cover
Thomas H. Painter
National Snow and Ice Data Center, CU-Boulder, CO
Acknowledgements
• Jay Fein (NSF Atmospheric Sciences) and Thomas
Baerwald (NSF Geography) ATM-0432327
• Collaborators Chris Landry (CSAS), Andrew Barrett
(NSIDC), Jason Neff (CU-Boulder)
• Jeffrey Deems (CSU), Corey Lawrence (CU-Boulder),
Maureen Cassidy (NSIDC), Tania Painter (CU-Boulder),
Kathleen Thatcher (NAU), Ashley Ballantyne (Duke), Ian
McCubbin (DRI- formerly JPL)
• Mountain Studies Institute, Silverton, CO
Brad Udall does PowerPoint
Performing mountain biogeography in the Pyrenees
Observations
H.A. Jones (1913), Effect of dust on the melting of snow, Monthly
Weather Reviews, April, p.599. Wagon Wheel Gap, Colorado.
During the night of March 18-19, 1913, there was a fall of 0.6 inch of snow
at this station. At the end of the storm the dust layer was about 6 inches
beneath the surface. This dust blanket very effectively intercepted
insolation, which spends itself not at the surface but pierces into the
snow, decreasing in intensity with the increase of depth. Within two or
three days after the storm, the upper layers of snow had melted and the
dust blanket was exposed at the surface, and all fresh snow that fell
since melted quickly into the lower layers and kept the dust persistently
at the surface.
No effect was felt on our streams from surface run-off, as automatically
recorded in our experimental work, until near the end of the month. The
melting had had the effect mainly of increasing the density of the lower
layers of snow. At the close of the month, however, it was evident that
the melting season was nearly a month in advance of the normal,
despite the fact that the mean temperatures were below the seasonal
average.
Outline
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Past, Present, and Future of Dust in Snow
Radiative Effects of Dust in Snow
Surface Shortwave Radiative Forcing
Radiative Forcing Results
Point Hydrologic Results
Conclusions
Canyonlands NP
Emission monitoring
J F M A M J J A S O N D
Neff et al. 2005, Ecological Applications,
v15, n1
Metals in Lake Sediments – San Juan Mountains, CO
150 years BP
J. Neff and others, unpublished data
Colorado Plateau
Winslow
San Juan Mountains 5-21-2004
Photo courtesy JPL (Ian McCubbin)
San Juan Mountains 5-19-2004
Photo courtesy CSAS (Chris Landry)
1999
2003
Mid-May snowpits, San Juan Mountains, CO
2004
2005
Mid-May snowpits, San Juan Mountains, CO
Deposition Events - Senator Beck Basin
Winslow, AZ precipitation
June-May (annum)
1 2006 71.88
2 2004 76.71
3 1974 97.03
4 2003 111.25
5 1900 118.87
6 1970 119.38
7 1971 120.14
8 1938 124.71
9 1989 125.98
10 2002 129.03
11 1943 139.45
12 1945 139.95
13 1990 140.97
14 1969 142.24
15 1950 143.26
March-May
1 2006 2.11
2 1999 2.29
3 2000 4.57
4 1921 7.11
5 1930 7.11
6 1947 7.62
7 1953 8.38
8 1967 9.40
9 1971 11.43
10 1955 12.19
11 1964 12.19
12 1900 12.70
13 1959 13.46
14 1951 13.97
15 1994 14.73
Temperature
Precipitation
Dust Provenance
87/86
Sr
143/144
Nd
εNd
Bedrock
0.707397
(0.000013)
0.512216
-8.23
Mar 23, 05
0.720471
(0.000013)
0.512089
-10.71
April 4, 05
0.716402
(0.000012)
0.512084
-10.81
April 8, 05
0.714878
(0.000009)
0.512104
-10.42
May 9, 05
0.713525
(0.000007)
0.512103
-10.44
Dust
Provenance
GOES-West Infrared Band 1-Band 2
Stochastic Time-Inverted Lagrangian
Transport model, Lin et al. (2003), JGR.
GOES Courtesy Max Bleiweiss, NMTU
Backtrajectories for Dust Events
Radiative Effects of Dust in Snow
As per Hansen and Nazarenko (2004, PNAS)
• Direct effect
Absorption in visible and near-infrared (for large
concentrations)
• First indirect effect
Enhanced grain growth that further decreases albedo
• Second indirect effect
Earlier exposure of darker substrate (snow-albedo
feedback)
Stratigraphy
α = 0.72
α = 0.43
Surface Shortwave Radiative Forcing
Here, we define surface shortwave radiative forcing as:
The perturbation of net shortwave radiation at the surface due
to the deposition of dust to snow cover (W m-2) – as such it
is an instantaneous surface forcing.
Fdust = (Edir α Sdustfree _ dir + Ediff α Sdustfree _ diff )
− (Edirα Sdust _ dir + Ediff α Sdust _ diff )
λ =3.0 µm
Fdust =
∫ Eµ λ (α λ
,tot
, dustfree
− α λ ,dust )dλ
λ = 0.28 m
Fdust = Fdust ,direct + Fdust ,indirect1 + Fdust ,indirect2
Operated by Center for Snow and
Avalanche Studies, Silverton, CO
Alpine Site
Sub-alpine Site
Instrumentation
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Solar irradiance (K&Z CM21) (285-4000 nm)
Diffuse solar irradiance (CM21)
Reflected solar flux (CM21) (285-4000 nm)
Filtered solar irradiance and reflected flux (CM21)
(695-4000 nm)
Longwave irradiance (CG4)
RH, Tair, wind speed and direction (2 heights)
Pressure
Surface slope and aspect for albedo correction
Atmospheric column properties (CIMEL sunphotometer)
Measurements
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Snowpits (weekly)
Gravimetrics for dust concentration (weekly)
Dust event collection (per event)
Optical grain size stratigraphy (monthly)
Snow depth spatial distribution (monthly)
Density and liquid water content profiles
(monthly)
Albedo
Time Series
Inference of Dust Effect
Fdust = Fdust ,direct + Fdust ,indirect1 + Fdust ,indirect 2
minimum
maximum
Fdust ,direct min = EVIS ,total (0.92 − αVIS )
Fdust ,directmax +indirect1 = EVIS ,total (0.92 − αVIS )

 1
+ E NIR ,totalα NIR 
− 1
 AR 
where
AR = 1.0 − 1.689(∆αVIS );
AR = 0.67;
{∆αVIS ∈ [0,0.17]}
{∆αVIS > 0.17}
Snowmelt Implications
SNOBAL (Marks et al., 1998)
Alpine Tower, Senator Beck Basin
Measured meteorological fields
Measured snow profiles
Dust removed = perturbation of
radiation to remove mean
direct+indirect effect
∆ SAG = 20 days
2005
Spring mean Fdust
42- 60 W m-2
Spring mean
Fdust 16-34 W m-2
Mean daily Fdust MarJune
Alpine: 24 W m-2
Subalpine: 34 W m-2
2006
Cumulative forcing (MJ m-2)
Fcumulative = ∫ Fdust dt
t
Second Indirect Effect
Mean Fdust during period:
144 W m-2
Summary
• Increased dust deposition to mountain snow
cover with drying and land use change
• Surface shortwave radiative and hydrologic
forcing:
– March through June daily averaged surface shortwave radiative
forcing was 16-34 W m-2 in 2005 and increased significantly to
42- 60 W m-2 in 2006.
– Snow cover duration was reduced by 17-29 days in 2005 and
22-31 days in 2006 due to dust radiative forcing, despite ~20%
less snow accumulation in 2006.
– These reductions in snow cover duration contributed to mean
daily second indirect radiative forcing of 128-147 W m-2 in 2005
and 144-151 W m-2 in 2006.
Summary
• WY 2006 may represent an analogue for future
desert-mountain interactions under global
warming scenarios
• WY 2006 exhibited nearly double the surface
shortwave radiative forcing that did WY2005.
• Snow albedo is poorly understood and
measured. In the western US there are 5
measurements and the MODIS snow albedo
product is presently bug-ridden.