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 • • • • • • 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Ecological Applications, v15, n1 Metals in Lake Sediments – San Juan Mountains, CO 150 years BP J. Neff and others, unpublished data Colorado Plateau Winslow San Juan Mountains 5-21-2004 Photo courtesy JPL (Ian McCubbin) San Juan Mountains 5-19-2004 Photo courtesy CSAS (Chris Landry)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 • • • • • • • • • 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 • • • • • • 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.