Asian Dust Over the Pacific Ocean
22-24 April 1998

GOES-9 visible -- 22 April 1998

GOES-9 visible
22 April 1998

(850 hPa streamlines)

GOES-9 visible -- 23 April 1998

GOES-9 visible
23 April 1998

(850 hPa streamlines)

GOES-9 visible -- 24 April 1998

GOES-9 visible
24 April 1998

(850 hPa streamlines)

A major dust storm affected parts of the Xinjiang region of northwestern China on 18-19 April 1998. Several days later, large areas of airborne dust were evident on GOES-9 visible imagery (above) over the central North Pacific Ocean (between Japan and Hawaii). The hazy appearance of the dust is enhanced by forward scattering late in the day over this particular region. As the parent storm system moved from eastern Asia toward the Bering Sea, dust was transported 7000-8000 km (4000-5000 miles) from its source region by the strong flow of cyclonically-curved westerly winds within the southern quadrant of the cyclone. CIMSS low-level visible cloud drift winds (22 April | 23 April | 24 April) show wind speeds as high as 50-65 knots within the 600-700 hPa layer in the region of the advancing dust cloud.

The Asian dust is also apparent on GOES-9 "split window" InfraRed (IR) difference images (below). This difference product is created by subtracting the 12.0 micron IR brightness temperatures from the 10.7 micron IR brightness temperatures -- darker shades represent a negative difference. A negative difference (warmer 12.0 micron brightness temperature) results from absorption (and subsequent emission) of outgoing 12.0 micron thermal radiation by the silicate aerosols which compose the dust cloud. A high silicate concentration implies a sandy aerosol source region, which in this case was likely the Gobi Desert region of China.

The areal coverage of dust appears larger in the visible imagery than that indicated by the IR difference product imagery. It can be implied that the darkest areas on the IR difference images represent the highest concentrations of suspended dust particulate (maximum dust optical depth) within the more widespread dust cloud. DMSP SSM/I water vapor composites for 22 April, 23 April and 24 April show that the dust-laden air mass was relatively dry (daily average of 20 kg/m2 or less of total precipitable water vapor); therefore, the variability in the dust signatures is not likely due to "contamination" from 12.0 micron absorption by gradients in the low-level water vapor.

Long-range transport of Asian dust across the North Pacific Ocean is common during the Northern Hemisphere winter and spring seasons. A similar phenomenon occurs with Saharan dust over the Atlantic Ocean. The use of GOES imagery to monitor the transport of dust can be helpful to advise aviation interests of potential visibility hazards; this imagery is also of value to atmospheric chemistry and climate studies.

GOES-9 split window IR -- 22 April 1998

GOES-9 split window IR
22 April 1998

(IR / visible comparison)

GOES-9 split window IR -- 23 April 1998

GOES-9 split window IR
23 April 1998

(IR / visible comparison)

GOES-9 split window IR -- 24 April 1998

GOES-9 split window IR
24 April 1998

(IR / visible comparison)


Update: Parts of this dust plume reached the western United States as early as 25-26 April (following a week of transport across the Pacific). Air Stagnation Advisories were issued for eastern Washington State on 30 April as light winds allowed the dust layer and low-level pollutants to reduce air quality over that region. The Center for Air Pollution Impact and Trend Analysis has NASA SeaWiFS and GOES-10 imagery showing the entire history of this dust transport event. NASA Goddard Space Flight Center has an animation of TOMS Aerosol Index from 13-30 April over the North Pacific Basin.

Large-scale GOES-9 visible images showing the dust over the eastern North Pacific:

23 April | 24 April | 25 April | 26 April | 27 April | 28 April

(Java animation)


Java animations of GOES-9 cloud tracked winds:
Visible | 10.7um IR | 6.7um IR (water vapor)

Address any questions or comments to Scott.Bachmeier@ssec.wisc.edu

Back to the CIMSS GOES Gallery