Episodic Dust Events of Utah’s Wasatch Front and Adjoining Region

Jeffrey D. Massey, W. J. SteenburghDepartment of Atmospheric Sciences, University of Utah, Salt Lake City, Utah

Thomas H. PainterJet Propulsion Laboratory, Pasadena, California

Introduction• Recent studies from

Colorado’s San Juan Mountains suggest dust on snow reduces the annual runoff in the upper Colorado River Basin (Painter et al. 2010)

• Dust loading increases the snowpack’s absorption of solar radiation leading to an earlier meltout by several weeks (Painter et al. 2007)

• Utah’s Wasatch Mountains experience episodic dust events with considerable interannual variability

ALTA

IntroductionObjectives

1.Establish a long term climatology of dust events for Salt Lake City (KSLC)2.Identify the meteorological mechanisms responsible for dust generation and transport3.Identify dust source regions over the Intermountain West

• Alpine lake sediments from North America show dramatically larger dust deposition rates after the mid-nineteenth century (Neff et al. 2008 and Reynolds et al. 2010)

• Farming, grazing, and recreation break the biological and physical crusts over desert surfaces

Long term Climatology

• Hourly weather observations were taken from Salt Lake City International Airport (KSLC) from 1930 – 2010

• A dust event had at least one observer comment of blowing dust, dust in suspension, or dust storm with a visibility < 10 km during the day.

• Dust concentrations are not quantified making the identification and classification of dust subjective

• Considerable inter-annual variability

• Bimodal monthly distribution

• Afternoon peak

Wind Direction

• Bimodal dust event wind directions with peaks at southerly and north-northwesterly.• Possibly representing pre and post frontal

conditions

• Intermountain cold front frequency is highly correlated to dust event frequency

Monthly frequency of strong cold frontal passages (Schafer and Steenburgh, 2008)

Dust Event Classification (2001-2010)

Dust Event Synoptic Conditions

1.Cold front or baroclinic trough (48%)2.Airmass convection (33%)3.Stationary or slowly moving fronts or baroclinic troughs (12%)4.Other synoptic conditions (6%)

Recent dust events were classified subjectively using radar, NARR reanalysis, observer comments, and GOES imagery

Dust detection algorithmModified MODIS algorithm (Zhoa et al, 2010)

1. Albedo threshold screens for clouds2. Infrared brightness temperature differences detect dust

Limitations:

1.4km resolution

2.Cannot detect shallow dust

3.Cannot detect through clouds

4.Cannot detect during low sun angles

SLC

Baroclinic Trough or Cold Front Event

5/10/2004

Surface Conditions 3/30/2010

Plume Identification• Plumes had to be persistent for more than one frame and have

a cloud free origin• For vast majority, southwestern most dust pixel taken as origin• Line approximates trajectory

Dust Source Regions:1. Milford Valley2. Sevier Desert3. Escalente Desert4. Carson Sink

Low elevation late Pleistocene to Holocene alluvial environments in southern and western Utah and southern and western Nevada

Conclusions

• Dust events at KSLC occur with considerable inter-annual variability and have a bimodal distribution, with a peak in Apr and a secondary peak in Sep

• Baroclinic troughs and cold fronts are the most common dust emitters for this region

• Emission sources are concentrated in low elevation Late Pleistocene to Holocene alluvial environments in southern and western Utah and southern and western Nevada