Transport of Asian Desert Aerosol to the Hawaiian Islands

Abstract

A cloud of aerosol with optical thickness τ ≈ 0.18 (500 nm wavelength), passed over the Hawaiian Islands from late April to early May 1979. Vertical profiles, taken by evaluating the optical extinction coefficient by sun photometry, showed that 80?90% of the aerosol was confined to a 1 km thick layer centered at 3.5?4km altitude. Trajectory analysis at the 500 mb pressure level (?5 km) indicated that the aerosol probably had its origin in sandstorms in the eastern deserts of Asia nine days before the event. The dust cloud was first observed passing over Japan where sand particles fell out at Nagasaki on 21 April. By the time dust from the sandstone reached Hawaii, it has spread out to ?1500 km and contained an estimated 1011 g of sand material, mainly in the 0.5 < r < 5.0 ?m size range. This episode clearly indicates that substantial quantities of primary aerosol are being transported on global distance scales. The episode is used to obtain a desert aerosol surface particle flux which agrees to an order of magnitude with that suggested by Junge.