No abstract

No abstract

[1] A synergistic process was developed to study the vertical distributions of aerosol optical properties and their effects on solar heating using data retrieved from ground-based radiation measurements and radiative transfer simulations. Continuous MPLNET and AERONET observations were made at a rural site in northern Taiwan from 2005 to 2007. The aerosol vertical extinction profiles retrieved from ground-based lidar measurements were categorized into near-surface, mixed, and two-layer transport types, representing 76% of all cases. Fine-mode (Ångström exponent, a, ∼1.4) and moderately absorbing aerosols (columnar single-scattering albedo ∼0.93, asymmetry factor ∼0.73 at 440 nm wavelength) dominated in this region. The column-integrated aerosol optical thickness at 500 nm (t 500nm ) ranges from 0.1 to 0.6 for the near-surface transport type but can be doubled in the presence of upper layer aerosol transport. We utilize aerosol radiative efficiency (ARE, the impact on solar radiation per unit change of t 500nm ) to quantify the radiative effects due to different vertical distributions of aerosols. Our results show that the ARE at the top of atmosphere (−23 W m −2 ) is weakly sensitive to aerosol vertical distributions confined in the lower troposphere. On the other hand, values of the ARE at the surface are −44.3, −40.6, and −39.7 W m −2 for near-surface, mixed, and two-layer transport types, respectively. Further analyses show that the impact of aerosols on the vertical profile of solar heating is larger for the near-surface transport type than for the two-layer transport type. The impacts of aerosol on the surface radiation and the solar heating profiles have implications for the stability and convection in the lower troposphere.

[1] Cirrus clouds, particularly subvisual high thin cirrus with low optical thickness, are difficult to screen in operational aerosol retrieval algorithms. Collocated aerosol and cirrus observations from ground measurements, such as the Aerosol Robotic Network (AERONET) and the Micro-Pulse Lidar Network (MPLNET), provide us with an unprecedented opportunity to systematically examine the susceptibility of operational aerosol products to cirrus contamination. Quality assured aerosol optical thickness (AOT) measurements were also tested against the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) vertical feature mask (VFM) and the Moderate Resolution Imaging Spectroradiometer (MODIS) thin cirrus screening parameters for the purpose of evaluating cirrus contamination. Key results of this study include: (1) quantitative evaluations of data uncertainties in AERONET AOT retrievals are conducted; although AERONET cirrus screening schemes are successful in removing most cirrus contamination, strong residuals displaying strong spatial and seasonal variability still exist, particularly over thin cirrus prevalent regions during cirrus peak seasons; (2) challenges in matching up different data for analysis are highlighted and corresponding solutions proposed; and (3) estimates of the relative contributions from cirrus contamination to aerosol retrievals are discussed. The results are valuable for better understanding and further improving ground aerosol measurements that are critical for aerosol-related climate research.

For decades, the satellite images acquired in visible and infrared bands have been used for environmental monitoring. In this purpose, the normal ized difference vegetation index (NDVI) is the commonly used vegetation index model for canopy monitoring and biomass assessment. However, due to the fact that the NDVI index is susceptible to various outside influencesmost notably the atmospheric disturbance and currently more bands are provided by satellite platforms-additional indexes have been developed to counter these effects. This paper explores two such indexes-the Aerosol Free Vegetation Index (AFRI) and the Atmospherically Resistant Vegeta tion Index (ARVI). Comparisons were made with the NDVI index to see if they indeed performed better. The relationship of the different outcomes exhibited• between the indexes with the aerosol optical depth (AOD) was analyzed and exploited to see if this scattering effect was more reduced than with NDVI. In general, the results showed that the AFRI and ARVI (with gamma= 1) indeed did perform better than their NDVI counterpart study with the related channels were employed.