Dust Layer Height Research Articles

The Influence of Synoptic-scale Air Flow and Local Circulation on the Dust Layer Height in the North of the Taklimakan Desert

The present study investigates the influences of synoptic-scale air flows and local wind circulations on the dust layer height (DLH) in the Taklimakan Desert, based on lidar observations performed in the north of the desert in March 2003. The DLH fluctuates approximately every three days between 2500 m (above sea level) and 5000 m, including diurnal variations. Meteorological analyses and numerical simulations show that the three-day fluctuation of DLH corresponds with variations in synoptic-scale air flows over the Taklimakan Desert, and the diurnal variations are linked to downdrafts and updrafts that are formed over the north of the desert as part of local circulations. When strong northerly winds prevail in the upper troposphere and a developed valley wind blows toward the Tienshan Mountains in the lower troposphere, the downdrafts strengthen in the middle troposphere over the north of the desert, lowering the DLH to about 2500 m. In contrast, the DLH rises to about 5000 m when the updrafts develop between strong southerly winds in the upper troposphere and a developed mountain wind blowing from the Tienshan Mountains. Simulations for the local circulation behavior without the presence of the Tienshan Mountains demonstrate that the valley and mountain winds on the southern slope of the Tienshan Mountains control the intensity of the downdrafts and updrafts, thereby influencing the DLH over the north of the Taklimakan Desert.

Determination of radiative forcing of Saharan dust using combined TOMS and ERBE data

We determine the direct radiative forcing of Saharan dust aerosols by combining aerosol information derived from Nimbus‐7 TOMS with radiation measurements observed at the top of atmosphere (TOA) by NOAA‐9 ERBE made during February‐July 1985. Cloud parameters and precipitable water derived from NOAA‐9 HIRS2 were used to aid in screening for clouds and water vapor in the analyses. Our results indicate that under “cloud‐free” and “dry” conditions there is a good correlation between the ERBE TOA outgoing longwave fluxes and the TOMS aerosol index measurements over both land and ocean in areas under the influence of airborne Saharan dust. The ERBE TOA outgoing shortwave fluxes were also found to correlate well with the dust loading derived from TOMS over ocean. However, the calculated shortwave forcing of Saharan dust aerosols is very weak and noisy over land for the range of solar zenith angle viewed by the NOAA‐9 ERBE in 1985. Sensitivity factors of the TOA outgoing fluxes to changes in aerosol index were estimated using a linear regression fit to the ERBE and TOMS measurements. The ratio of the shortwave‐to‐longwave response to changes in dust loading over the ocean is found to be roughly 2 to 3 but opposite in sign. The monthly averaged “clear‐sky” TOA direct forcing of airborne Saharan dust was also calculated by multiplying these sensitivity factors by the TOMS monthly averaged “clear‐sky” aerosol index. Both the observational and theoretical analyses indicate that the underlying surface properties, dust layer height, ambient moisture content, and the presence of cloud all play important roles in determining the TOA direct radiative forcing due to mineral aerosols.

Transport and deposition of desert dust in the Kafirnigan River Valley (Tadzhikistan) from Shaartuz to Esanbay: Measurements and a simple model

Abstract A model of deposition and transport was constructed for the Kafirnigan Valley, in Soviet Central Asia. Data, consisting of deposition measurements at Shaartuz, atmospheric columnar mass, aerosol concentrations, wind speed, optical scattering, and movement of soil, were collected for the dust storms of 16 and 20 September 1989. Results from the model were compared with measurements of total atmospheric columnar mass loading for the dust storm of 16 September. Although sensitivity of the model to dust layer height does not recommend the model for general use, the model has some merit in predicting transport and deposition for dust contained in a river valley.