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Li J.,Nanjing University of Information Science and Technology | Yin Y.,Nanjing University of Information Science and Technology | Li P.,Weather Modification Office of Shanxi Province | Li Z.,Beijing Normal University | And 10 more authors.
Atmospheric Research | Year: 2015

For the first time, comprehensive aircraft measurements of atmospheric aerosols and cloud condensation nuclei (CCN) were made over the Loess Plateau in Shanxi, China. Data from six flights in July and August 2013 were analyzed. Fine aerosols were predominant over the region. On the one hazy day, the fraction of fine particles in the total aerosol load was the greatest. Aerosol number concentration decreased exponentially with altitude. Inversion layers caused low-level aerosol accumulation zones. The mean aerosol particle size increased with altitude, and the larger particles were mainly found above 2km. Aerosol number size distributions at different height ranges showed two or three peaks. The aerosol number size distribution from 0.01μm to 20μm can be fitted with three log-normal distribution functions. The number concentration of CCN (NCCN) decreased with altitude. NCCN was linearly related to the CN concentration (NCN). The fraction of CCN to CN (fCCN/CN) at 0.3% SS was half of that at 0.4% SS. The fCCN/CN on the hazy day was lower than on the clear days. Vertical profiles of fCCN/CN and the effective diameter (ED) were similar, although the fCCN/CN increased with altitude. © 2014 Elsevier B.V.


Zhu Y.,Meteorological Institute of Shaanxi Province | Rosenfeld D.,Hebrew University of Jerusalem | Yu X.,Meteorological Institute of Shaanxi Province | Li Z.,Beijing Normal University | Li Z.,The Interdisciplinary Center
Journal of Geophysical Research D: Atmospheres | Year: 2015

The high resolution (375 m) of the Visible Infrared Imaging Radiometer Suite on board the Suomi National Polar-Orbiting Partnership satellite allows retrieving relatively accurately the vertical evolution of convective cloud drop effective radius (re) with height or temperature. A tight relationship is found over SE Asia and the adjacent seas during summer between the cloud-free aerosol optical depth (AOD) and the cloud thickness required for the initiation of warm rain, as represented by the satellite-retrieved cloud droplet re of 14 μm, for a subset of conditions that minimize measurement artifacts. This cloud depth (ΔT14) is parameterized as the difference between the cloud base temperature and the temperature at the height where re exceeds 14 μm (T14). For a unit increase of AOD, the height of rain initiation is increased by about 5.5 km. The concern of data artifacts due to the increase in AOD near clouds was mitigated by selecting only scenes with cloud fraction (CF) < 0.1. For CF > 0.1 and ΔT14 > ∼20°C, the increase of ΔT14 gradually levels off with further increase of AOD, possibly because the AOD is enhanced by aerosol upward transport and detrainment through the clouds below the T14 isotherm. The bias in the retrieved re due to the different geometries of solar illumination was also quantified. It was shown that the retrievals are valid only for backscatter views or when avoiding scenes with significant amount of cloud self-shadowing. These artifacts might have contributed to past reported relationships between cloud properties and AOD. © 2015. American Geophysical Union. All Rights Reserved.


Rosenfeld D.,Hebrew University of Jerusalem | Yu X.,Meteorological Institute of Shaanxi Province | Liu G.,Meteorological Institute of Shaanxi Province | Xu X.,Meteorological Institute of Shaanxi Province | And 6 more authors.
Geophysical Research Letters | Year: 2011

Heavy aerosol loads have been observed to suppress warm rain by reducing cloud drop size and slowing drop coalescence. The ice forming nuclei (IFN) activity of the same aerosols glaciate the clouds and create ice precipitation instead of the suppressed warm rain. Satellite observations show that desert dust and heavy air pollution over East Asia have similar ability to glaciate the tops of growing convective clouds at glaciation temperature of Tg < ∼-20°C, whereas similarly heavy smoke from forest fires in Siberia without dust or industrial pollution glaciated clouds at Tg ≤-33°C. The observation that both smoke and air pollution have same effect on reducing cloud drop size implies that the difference in Tg is due to the IFN activity. This dependence of Tg on aerosol types appears only for clouds with re-5 < 12 μm (re-5 is the cloud drop effective radius at the-5°C isotherm, above which ice rarely forms in cloud tops). For the rest of the clouds the glaciation temperature increases strongly with re-5 with little relation to the aerosol types, reaching Tg> ∼-15°C for the largest re-5, which are typical to marine clouds in pristine atmosphere. Copyright 2011 by the American Geophysical Union.


Rosenfeld D.,Hebrew University of Jerusalem | Liu G.,Meteorological Institute of Shaanxi Province | Yu X.,Meteorological Institute of Shaanxi Province | Zhu Y.,Meteorological Institute of Shaanxi Province | And 2 more authors.
Atmospheric Chemistry and Physics | Year: 2014

VIIRS (Visible Infrared Imaging Radiometer Suite), onboard the Suomi NPP (National Polar-orbiting Partnership) satellite, has an improved resolution of 750 m with respect to the 1000 m of the Moderate Resolution Imaging Spectroradiometer for the channels that allow retrieving cloud microphysical parameters such as cloud drop effective radius (re). VIIRS also has an imager with five channels of double resolution of 375 m, which was not designed for retrieving cloud products. A methodology for a high-resolution retrieval of and microphysical presentation of the cloud field based on the VIIRS imager was developed and evaluated with respect to MODIS in this study. The tripled microphysical resolution with respect to MODIS allows obtaining new insights for cloud-aerosol interactions, especially at the smallest cloud scales, because the VIIRS imager can resolve the small convective elements that are sub-pixel for MODIS cloud products. Examples are given for new insights into ship tracks in marine stratocumulus, pollution tracks from point and diffused sources in stratocumulus and cumulus clouds over land, deep tropical convection in pristine air mass over ocean and land, tropical clouds that develop in smoke from forest fires and in heavy pollution haze over densely populated regions in southeastern Asia, and for pyro-cumulonimbus clouds.
It is found that the VIIRS imager provides more robust physical interpretation and refined information for cloud and aerosol microphysics as compared to MODIS, especially in the initial stage of cloud formation. VIIRS is found to identify significantly more fully cloudy pixels when small boundary layer convective elements are present. This, in turn, allows for a better quantification of cloud-aerosol interactions and impacts on precipitation-forming processes. © 2014 Author (s).


Zhu Y.,Meteorological Institute of Shaanxi Province | Rosenfeld D.,Hebrew University of Jerusalem | Yu X.,Meteorological Institute of Shaanxi Province | Liu G.,Meteorological Institute of Shaanxi Province | And 2 more authors.
Geophysical Research Letters | Year: 2014

The advent of the Visible Infrared Imaging Radiometer Suite (VIIRS) onboard the Suomi National Polar-Orbiting Partnership (NPP) satellite provided a quantum jump in the satellite capabilities of retrieving cloud properties, because it nearly tripled the resolution in the thermal channels (375 m). This allowed us to develop a methodology for retrieving convective cloud base temperature (Tb) and validate it over the Atmospheric System Research Southern Great Plains site for the satellite early afternoon overpass time. The standard error of the Tb retrieval was only 1.1°C. The knowledge of Tb allows the calculation of cloud base height and the depth of the boundary layer, as well as the boundary layer water vapor mixing ratio with an accuracy of about 10%. The feasibility of retrieving cloud base temperature and height is an essential component that is required for retrieving cloud condensation nuclei (CCN) from satellites by using convective clouds as natural CCN chambers. Key Points Convective cloud base temperature was retrieved from satellite with 1°C accuracy Boundary layer vapor mixing ratio was retrieved with 10% accuracy This became possible by using the 375 m resolution of the NPP/VIIRS Imager ©2014. American Geophysical Union. All Rights Reserved.

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