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Dust Load (dust + load)

Distribution by Scientific Domains
Earth and Environmental Science100%

Selected Abstracts

Airborne dust deposition in the Okavango Delta, Botswana, and its impact on landforms

EARTH SURFACE PROCESSES AND LANDFORMS, Issue 5 2004
M. Krah
Abstract This study investigated the local-scale generation and movement of dust in the seasonal swamps of the Okavango Delta, Botswana, with a view to examining possible transfer of material between ,ood plains and islands. It was found that most of the dust load was carried in the lowest 3 m of the air column, and consisted mainly of amorphous silica, indicating that dust was generated largely on the ,ood plains. Dust loads were found to be highest above the ,ood plains and lowest over the interiors of islands, probably due to the baf,ing effect of the island trees on wind velocity. The contrast in dust loads between islands and ,ood plains suggests that there is a net transfer of dust from ,ood plains to islands, but it was not possible to quantify this transfer. It is evident, however, that ,ood plains experience net erosion and islands net aggradation. A strong seasonality in dust loads was observed, with the maximum dust loads coinciding with maximum wind velocity in October. This also coincides with peak seasonal ,ooding in the delta, and only non-inundated ,ood plains are capable of generating dust. Years of low ,ood therefore appear to be more dusty. There may also be transfer of material from higher-lying to lower-lying ,ood plains, which may reduce the topographic contrast on the ,ood plains. Copyright © 2004 John Wiley & Sons, Ltd. [source]

Effects of CO2 and dust on present-day solar radiation and climate on Mars

THE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 611 2005
Hannu Savijärvi
Abstract A comprehensive spectrum-resolving radiative transfer model (SRM) was used to simulate the average, present-day, solar radiation field on Mars. A CO2 -only 6 hPa Martian atmosphere absorbs about 1% of zenith solar radiation, producing a modest heating rate of 4,5 K day,1 in the lowest 10 km. The trace gases have an insignificant effect but airborne dust reduces the downwelling solar flux effectively, and the reflected flux somewhat less. This produces an anti-greenhouse trend (cooling at the surface, warming within the atmosphere, reflection at the top), which increases strongly with the dust load. For instance, with dust visible optical depth of unity and sun in zenith, the surface solar irradiation is attenuated by 26% and the solar heating rate increases to about 70 K day,1 in the lowest 25 km. The numbers are however strongly dependent on the optical properties of the dust, which are not known very well. Several fast two-stream methods for dust were compared with the SRM results. Their common systematic errors were reduced by a simple, physically-based correction. The global albedo of Mars was then studied as a function of dust load, dust optics and surface albedo. The crossover from added airborne dust tending to make the whole planet look whiter or darker occurred at surface albedo of about 35%, nearly independently of the dust load. We demonstrate, however, that this value is sensitive to the optical properties of the assumed dust. Copyright © 2005 Royal Meteorological Society [source]

Airborne dust deposition in the Okavango Delta, Botswana, and its impact on landforms

EARTH SURFACE PROCESSES AND LANDFORMS, Issue 5 2004
M. Krah
Abstract This study investigated the local-scale generation and movement of dust in the seasonal swamps of the Okavango Delta, Botswana, with a view to examining possible transfer of material between ,ood plains and islands. It was found that most of the dust load was carried in the lowest 3 m of the air column, and consisted mainly of amorphous silica, indicating that dust was generated largely on the ,ood plains. Dust loads were found to be highest above the ,ood plains and lowest over the interiors of islands, probably due to the baf,ing effect of the island trees on wind velocity. The contrast in dust loads between islands and ,ood plains suggests that there is a net transfer of dust from ,ood plains to islands, but it was not possible to quantify this transfer. It is evident, however, that ,ood plains experience net erosion and islands net aggradation. A strong seasonality in dust loads was observed, with the maximum dust loads coinciding with maximum wind velocity in October. This also coincides with peak seasonal ,ooding in the delta, and only non-inundated ,ood plains are capable of generating dust. Years of low ,ood therefore appear to be more dusty. There may also be transfer of material from higher-lying to lower-lying ,ood plains, which may reduce the topographic contrast on the ,ood plains. Copyright © 2004 John Wiley & Sons, Ltd. [source]