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D. A. Gillette, R. N. Clayton, T. K. Mayeda, M. L. Jackson, and K. Sridhar

Abstract

Tropospheric aerosols from major dust storms (visibility <11 km) originating in cultivated areas of the High Plains in west central Texas and adjacent areas of New Mexico, Oklahoma and Colorado, were sampled by ground-based airturbine samplers with stacks 1 to 6 m high, by membrane filters, by airplane-borne dust samplers and by a static ground-level sampler. The particle size distributions of the aerosol dust obtained by airplane sampling fell mainly between 1 and 30 μm diameter. A bimodal size distribution occurred for the dust from ground samplers, with large concentrations in the 40 to 80 μm range as well as in the 1 to 30 μm range. The concentration of dust 2 to 5 km above the ground, measured by both the filtering and impactor methods, ranged from 0.1 to 0.4 mg m−3 for four intense dust storms in Texas during April of 1972 and 1973. The vertical flux for dust storms over the four-year period ranged from 0.25 × 10−7 to 2.2 × 10−8 g cm−2 s−1.

Oxygen isotopic ratio values of 1 to 10 μm quartz isolated from 17 dusts collected by ground-based samplers ranged from 16.4 to 19.5‰ (mean, 18.35 ± 0.77‰); three dusts from the airplane samplers averaged 18.2 ± 1.1‰. The Texas dusts arose largely from 13 wind-eroding soil mapping units and erodibility classes of sandy to clayey texture in the four states; the δ 18O values of the 1 to 10 μm quartz of these soils averaged 19.55 ± 0.28‰ (reported elsewhere). Abrasion by wind-induced inter-particle impact may have introduced a small amount of coarser quartz into the 1 to 10 μm aerosol fraction. Quartz from the coarser fractions of the dusts had δ 18O values ranging from 16.9 to 13.9‰ with the lower values applying to the preponderantly sand sizes (>53 μm). The fine silt from eroding sandy soils, derived not only from weathering but also possibly from eolian deposition, serves as a reservoir for long-range aerosol minerals, in addition to that from shales.

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R. A. Ferrare, E. V. Browell, S. Ismail, S. A. Kooi, L. H. Brasseur, V. G. Brackett, M. B. Clayton, J. D. W. Barrick, G. S. Diskin, J. E. M. Goldsmith, B. M. Lesht, J. R. Podolske, G. W. Sachse, F. J. Schmidlin, D. D. Turner, D. N. Whiteman, D. Tobin, L. M. Miloshevich, H. E. Revercomb, B. B. Demoz, and P. Di Girolamo

Abstract

Water vapor mass mixing ratio profiles from NASA's Lidar Atmospheric Sensing Experiment (LASE) system acquired during the Atmospheric Radiation Measurement (ARM)–First International Satellite Cloud Climatology Project (ISCCP) Regional Experiment (FIRE) Water Vapor Experiment (AFWEX) are used as a reference to characterize upper-troposphere water vapor (UTWV) measured by ground-based Raman lidars, radiosondes, and in situ aircraft sensors over the Department of Energy (DOE) ARM Southern Great Plains (SGP) site in northern Oklahoma. LASE was deployed from the NASA DC-8 aircraft and measured water vapor over the ARM SGP Central Facility (CF) site during seven flights between 27 November and 10 December 2000. Initially, the DOE ARM SGP Cloud and Radiation Testbed (CART) Raman lidar (CARL) UTWV profiles were about 5%–7% wetter than LASE in the upper troposphere, and the Vaisala RS80-H radiosonde profiles were about 10% drier than LASE between 8 and 12 km. Scaling the Vaisala water vapor profiles to match the precipitable water vapor (PWV) measured by the ARM SGP microwave radiometer (MWR) did not change these results significantly. By accounting for an overlap correction of the CARL water vapor profiles and by employing schemes designed to correct the Vaisala RS80-H calibration method and account for the time response of the Vaisala RS80-H water vapor sensor, the average differences between the CARL and Vaisala radiosonde upper-troposphere water vapor profiles are reduced to about 5%, which is within the ARM goal of mean differences of less than 10%. The LASE and DC-8 in situ diode laser hygrometer (DLH) UTWV measurements generally agreed to within about 3%–4%. The DC-8 in situ frost point cryogenic hygrometer and Snow White chilled-mirror measurements were drier than the LASE, Raman lidars, and corrected Vaisala RS80H measurements by about 10%–25% and 10%–15%, respectively. Sippican (formerly VIZ Manufacturing) carbon hygristor radiosondes exhibited large variabilities and poor agreement with the other measurements. PWV derived from the LASE profiles agreed to within about 3% on average with PWV derived from the ARM SGP microwave radiometer. The agreement between the LASE and MWR PWV and the LASE and CARL UTWV measurements supports the hypotheses that MWR measurements of the 22-GHz water vapor line can accurately constrain the total water vapor amount and that the CART Raman lidar, when calibrated using the MWR PWV, can provide an accurate, stable reference for characterizing upper-troposphere water vapor.

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