Date of Award

5-2008

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Atmospheric Studies

Abstract

Asian dust events occur frequently during the northern hemisphere spring season. Some of these events can transport dust downwind to North America within 7 days’ time and turn a regional impact into one of a much larger scale. To further quantify the transpacific transport and evolution of Asian dust to North America and assess the impact on regional climate, NASA led a field experiment called the Intercontinental Chemical Transport Experiment - Phase B (INTEX-B) during April-May 2006 over the eastern Pacific Ocean. This study documents the physical and optical properties of Asian dust, as well as its strength and evolution from its source near the Gobi desert to its sink in North America, during INTEX-B using surface, satellite and DC-8 aircraft measurements.

A total of 11 dust events have been identified and summarized. Two dust events, originating from the Gobi desert on 7 and 17 April 2006, have been extensively analyzed, and their trajectories, strength and evolution have been tracked. For the strong Asian dust episode on 17 April 2006, the observed total downwelling shortwave (SW) flux over Xianghe, a site near Beijing, is only 46% of the clear-sky value with almost no direct transmission, and nearly double the diffuse SW clear-sky value. The surface averaged aerosol optical depth (AOD) increased from 0.17 (clear-sky) to 4.0, and the Angstrom exponent (AE) dropped from 1.26 (clear-sky) to below 0.1. This event was also captured by satellite and the UND/NASA DC-8 over the eastern Pacific Ocean from 23-24 April 2006. By this time, its strength degraded due to dispersion and larger particles settling out. The DC-8 observed this dust plume with higher averaged aerosol scattering ratios of 10.5 at 1064 nm and 2.0 at 588 nm and a depolarization of 25%. The DC-8 nephelometer also observed this dust event in-situ and confirmed that the highest scattering coefficient ranged from 80-100 mm'1. When this dust transported to North America, its AOD values decreased from a mean of 2.0 over the source region to 0.2 over North America.

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